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  • 1.
    Ayob, Mohd Nasir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Control Strategy for a Tidal Compensation System for Wave Energy Converter Device2018Conference paper (Refereed)
  • 2.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thermal Rating of a Submerged Substation for Wave Power2016In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 1, p. 436-445Article in journal (Refereed)
    Abstract [en]

    The costs of offshore maintenance operations put high reliability-requirements on offshore equipment for ocean energy, especially on submerged ones. Thermal management is thus essential in the design of the prototypes of a marine substation, developed at Uppsala University, for grid interface of wave power parks. The cooling system itself should be efficient as well as reliable. Therefore, the feasibility of a completely passive cooling strategy was evaluated. The studied substation includes various power components, which dissipate heat and are installed in one pressurized vessel. Thermal cross-coupling was investigated with 3-D submodels and a thermal network model. An electric circuit was coupled to determine the rated power of the substation. The results depend mainly on the dc-voltage, the seawater temperature, and the thermal contact between the components and the hull.

  • 3.
    Björkman, Elin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Osäkerhet vid översvämningskartering av vattendrag: En kunskapsöversikt och tillämpning på MIKE 112014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Due to uncertainty in data, parameters and model structure, there may be large uncertainties in flood inundation models. Despite of this, uncertainty analysis is still rarely used by practitioners when creating flood maps. A reason why uncertainty analysis has not yet become customary in flood inundation modeling may be due to a lack of knowledge. Low availability of data can sometimes also make it more difficult to do an uncertainty analysis. Moreover, no examples exist of how uncertainties can be analyzed in MIKE 11, which is one of the most common models used in flood mapping at consultant agencies.

    The aim of this study was twofold. Firstly, to provide a general overview of current research on uncertainty and uncertainty analysis for flood inundation modeling. This in order to increase knowledge among consultants and decision makers. Secondly, to give an example of how uncertainties can be estimated in a flood inundation model created in MIKE 11 when there is limited access to data.

    The research overview showed that there is often considerable uncertainty in the discharge calculations and geometrical description in hydraulic models, and that there are many different ways to analyze the uncertainties. Some methods that are often used are Monte Carlo simulations, fuzzy sets, scenario analysis, Bayesian calibration and Generalized Likelihood Uncertainty Estimation, GLUE.

    A case study was performed in which a hydraulic model was built for the River Kungsbackaån in MIKE 11. A scenario analysis was carried out to show the uncertainties in the hydraulic model. Overall, 36 different model runs were made in which the calibration discharge, Manning's number and design flow were varied. Scenario analysis cannot provide a precise estimate of the uncertainty, it can only give a subjective estimate. The results of the scenario analysis showed that when the sea level in Kungsbackafjorden was 0,92 m the simulated water levels differed at most by 1,3 m for the 100-year discharge and by 0,41 m for the calculated maximum flow. Also, the flood extent of the two discharges were investigated. The greatest uncertainty in the extent was found in the flat areas even though the uncertainty in water levels was smaller there.

  • 4.
    Bozzi, S.
    et al.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Bizzozero, F.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Gruosso, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Passoni, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analysis of Interaction of Point Absorbers' Arrays for Seawave Electrical Energy Generation in Italian Seas2016In: 2016 International Symposium On Power Electronics, Electrical Drives, Automation And Motion (SPEEDAM), 2016, p. 1369-1374Conference paper (Refereed)
    Abstract [en]

    This work focuses on interactions between wave energy converters (WEC) in array configuration. The arrays are simulated in the time domain by a coupled hydrodynamic electromagnetic model. The hydrodynamic parameters of the model are estimated by boundary element code while the electrical ones are obtained by finite element code. Wave parks of two and four devices are simulated considering different layouts. The ultimate goal of the work is to identify the optimal array design at four Italian locations. The results show that: (i) it is possible to find an array configuration which performs better than four isolated devices, at each study sites, (ii) the highest energy production is obtained with the linear layout at all the locations, (ii) optimum WEC distance varies between ten and twenty diameters, depending on the deployment site and (iv) the difference in energy production between the best and worst array configuration (i.e. over all the possible combinations of geometrical layout, spatial orientation and WEC distance) ranges from 3% to 7%, depending on the deployment site..

  • 5.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Resource Assessment: Measurements and Characterization2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites.

    A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin.

    A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake.

    An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique.

    List of papers
    1. Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    Open this publication in new window or tab >>Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

    Keywords
    Acoustic Doppler Current Profiler (ADCP), tidal energy resource
    National Category
    Marine Engineering Ocean and River Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-230659 (URN)000363498500053 ()978-0-7918-4550-9 (ISBN)
    Conference
    33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), San Francisco, California, USA, June 8-13, 2014
    Available from: 2014-08-27 Created: 2014-08-27 Last updated: 2017-04-04Bibliographically approved
    2. Tidal resource characterization in the Folda Fjord, Norway
    Open this publication in new window or tab >>Tidal resource characterization in the Folda Fjord, Norway
    2016 (English)In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, p. 27-44Article in journal (Refereed) Published
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

    Keywords
    Tidal resource assessment, ADCP, Characterizing metrics
    National Category
    Engineering and Technology Ocean and River Engineering Oceanography, Hydrology and Water Resources
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-266674 (URN)10.1016/j.ijome.2016.01.001 (DOI)000381687600003 ()
    Funder
    StandUpCarl Tryggers foundation
    Available from: 2015-11-10 Created: 2015-11-10 Last updated: 2018-01-10Bibliographically approved
    3. The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Open this publication in new window or tab >>The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    The Division of Electricity at Uppsala University recently deployed an experimental hydrokinetic power station for in-stream experiments at a site in a river. This paper briefly describes the deployment process and reports some initial results from measurements made at the test site.

    Keywords
    Marine Current Power, Renewable energy, Söderfors, Strömkraft, Förnybar energi, Söderfors
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-209220 (URN)
    Conference
    10th European Wave and Tidal Energy Conference (EWTEC), 2-5 september, 2013, Aalborg, Denmark
    Projects
    Marine Current Power
    Funder
    StandUpSwedish Research Council, 621-2009-4946
    Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2019-01-22Bibliographically approved
    4. Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    Open this publication in new window or tab >>Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    2015 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Wake characteristics of marine current turbines are of significant importance to the development of the marine current power source. Turbine wake recovery determines spacing of turbines in arrays, and environmental impact on e.g. the seabed is heavily influenced by wake behaviour. The majority of previous studies on wakes has been performed on flow-aligned (horizontal) axis turbines and mainly carried out as scale model experiments or numerical simulations.

    This paper describes the performance of wake measurements at the Söderfors test site, where an experimental marine current power station is operated in a river. The turbine is of the cross-flow (vertical) axis type, and the measurements are performed using an Acoustic Doppler Current Profiler (ADCP) towed on the surface by a boat. Positioning data is taken from a high-accuracy Global Navigation Satellite System. The paper discusses various aspects of the methodology employed and provides examples of taken measurements.

    National Category
    Energy Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-265358 (URN)
    Conference
    11th European Wave and Tidal Energy Conference, EWTEC15, 6-11 September 2015, Nantes, France
    Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2017-04-04Bibliographically approved
    5. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Show others...
    2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, p. 356-375Article in journal (Refereed) Published
    National Category
    Energy Engineering Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
    Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2018-08-01
  • 6.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Potentialbedömning av marin strömkraft i Finnhamn: Fältmätningar och resultat2015Report (Other academic)
    Abstract [sv]

    På uppdrag av Skärgårdsstiftelsen utfördes mätningar av vattenhastigheten utanför Finnhamn i syfte att undersöka potentialen för att installera och driva ett marint strömkraftverk på platsen. Denna rapport presenterar resultaten från den undersökningen som genomförts med tvärsnittsmätningar och långtidsmätningar av vattenhastigheterna. Resultaten visar på låga vattenhastigheter under mätperioden. Slutsatsen är att platsen inte har tillräckligt stor energipotential för att vara av intresse för utbyggnad av strömkraftverk utifrån den teknik som finns idag.

  • 7.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Resource characterization and variability studies for marine current power2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.

    In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.

    Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.

    The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.

    List of papers
    1. Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    Open this publication in new window or tab >>Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper, Oral presentation only (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

    Keywords
    Acoustic Doppler Current Profiler (ADCP), tidal energy resource
    National Category
    Marine Engineering Ocean and River Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-230659 (URN)000363498500053 ()978-0-7918-4550-9 (ISBN)
    Conference
    33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), San Francisco, California, USA, June 8-13, 2014
    Available from: 2014-08-27 Created: 2014-08-27 Last updated: 2017-04-04Bibliographically approved
    2. Tidal resource characterization in the Folda Fjord, Norway
    Open this publication in new window or tab >>Tidal resource characterization in the Folda Fjord, Norway
    2016 (English)In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, p. 27-44Article in journal (Refereed) Published
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

    Keywords
    Tidal resource assessment, ADCP, Characterizing metrics
    National Category
    Engineering and Technology Ocean and River Engineering Oceanography, Hydrology and Water Resources
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-266674 (URN)10.1016/j.ijome.2016.01.001 (DOI)000381687600003 ()
    Funder
    StandUpCarl Tryggers foundation
    Available from: 2015-11-10 Created: 2015-11-10 Last updated: 2018-01-10Bibliographically approved
    3. The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Open this publication in new window or tab >>The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    The Division of Electricity at Uppsala University recently deployed an experimental hydrokinetic power station for in-stream experiments at a site in a river. This paper briefly describes the deployment process and reports some initial results from measurements made at the test site.

    Keywords
    Marine Current Power, Renewable energy, Söderfors, Strömkraft, Förnybar energi, Söderfors
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-209220 (URN)
    Conference
    10th European Wave and Tidal Energy Conference (EWTEC), 2-5 september, 2013, Aalborg, Denmark
    Projects
    Marine Current Power
    Funder
    StandUpSwedish Research Council, 621-2009-4946
    Available from: 2013-10-15 Created: 2013-10-15 Last updated: 2019-01-22Bibliographically approved
    4. Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    Open this publication in new window or tab >>Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    2015 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Wake characteristics of marine current turbines are of significant importance to the development of the marine current power source. Turbine wake recovery determines spacing of turbines in arrays, and environmental impact on e.g. the seabed is heavily influenced by wake behaviour. The majority of previous studies on wakes has been performed on flow-aligned (horizontal) axis turbines and mainly carried out as scale model experiments or numerical simulations.

    This paper describes the performance of wake measurements at the Söderfors test site, where an experimental marine current power station is operated in a river. The turbine is of the cross-flow (vertical) axis type, and the measurements are performed using an Acoustic Doppler Current Profiler (ADCP) towed on the surface by a boat. Positioning data is taken from a high-accuracy Global Navigation Satellite System. The paper discusses various aspects of the methodology employed and provides examples of taken measurements.

    National Category
    Energy Engineering Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-265358 (URN)
    Conference
    11th European Wave and Tidal Energy Conference, EWTEC15, 6-11 September 2015, Nantes, France
    Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2017-04-04Bibliographically approved
    5. Observation of cavitating flow using multibeam and dual-beam sonar systems: A comparison of wake strength caused by propeller vs waterjet thrusted vessels. In a marine renewable energy perspective (Part-a)
    Open this publication in new window or tab >>Observation of cavitating flow using multibeam and dual-beam sonar systems: A comparison of wake strength caused by propeller vs waterjet thrusted vessels. In a marine renewable energy perspective (Part-a)
    (English)In: Article in journal (Refereed) Submitted
    Abstract
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-307239 (URN)
    Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2017-04-04
    6. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Show others...
    2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, p. 356-375Article in journal (Refereed) Published
    National Category
    Energy Engineering Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
    Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2018-08-01
    7. Net load variability in Nordic countries with a highly or fully renewable power system
    Open this publication in new window or tab >>Net load variability in Nordic countries with a highly or fully renewable power system
    Show others...
    2016 (English)In: Nature Energy, ISSN 2058-7546, Vol. 1, p. 1-8, article id 16175Article in journal (Refereed) Published
    Abstract [en]

    Increasing the share of intermittent renewable energy (IRE) resources such as solar, wind, wave and tidal energy in a power system poses a challenge in terms of increased net load variability. Fully renewable power systems have previously been analysed, but more systematic analyses are needed that explore the effect of different IRE mixes on system-wide variability across different timescales and the optimal combinations of IRE for reducing variability on a given timescale. Here we investigate these questions for the Nordic power system. We show that the optimal mix of IRE is dependent on the frequency band considered. Long-term (>4 months) and short-term (<2 days) fluctuations can be similar to today’s, even for a fully renewable system. However, fluctuations with periods in between will inevitably increase significantly. This study indicates that, from a variability point of view, a fossil- and nuclear-free Nordic power system is feasible if properly balanced by hydropower.

    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-302836 (URN)10.1038/NENERGY.2016.175 (DOI)000394793000001 ()
    Funder
    StandUpStandUp for Wind
    Available from: 2016-09-11 Created: 2016-09-11 Last updated: 2019-04-05
    8. Tidal current phasing along the coast of Norway
    Open this publication in new window or tab >>Tidal current phasing along the coast of Norway
    2016 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    Tidal currents provide an intermittent source of renewable energy. A high degree of intermittency is unfavorable in the existing power system. However, by aggregating tidal power from sites with variable tidal phase a more firm power outpu tmay be achieved. In this paper, the tidal current phasing between 114 potential tidal energy sites along the Norwegian coast is investigated. Time series of tidal currents are generated with a model that considers the variation in current strength due to the variability in the semi-diurnal tidal cycle (spring to neap, flood to ebb, first to second daily tide etc.). From these, available kinetic energy in the natural flow is calculated. A constant conversion rate is then applied to give the power output at each site. Three scenarios, with varying number of sites and energy extraction, are investigated. The variability in each scenario is quantified on different time scales by filtering the aggregated power and calculate standard deviation and step change. It is found that the variability can be lowered by choosing sites with an advantageous time lag and limit the power output from the most energetic sites. As expected, smoothing is most distinct on short time scales.

    Keywords
    Tidal energy, tidal phasing, variability optimization, significant impact factor, model scenarios
    National Category
    Ocean and River Engineering Marine Engineering Oceanography, Hydrology and Water Resources
    Identifiers
    urn:nbn:se:uu:diva-307495 (URN)
    Conference
    3rd International Asian Wave and Tidal Energy Conference (AWTEC), Singapore 24-28 oct, 2016
    Funder
    StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development), 16-196
    Available from: 2016-12-14 Created: 2016-11-16 Last updated: 2018-01-13
  • 8.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

  • 9.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tidal current phasing along the coast of Norway2016Conference paper (Refereed)
    Abstract [en]

    Tidal currents provide an intermittent source of renewable energy. A high degree of intermittency is unfavorable in the existing power system. However, by aggregating tidal power from sites with variable tidal phase a more firm power outpu tmay be achieved. In this paper, the tidal current phasing between 114 potential tidal energy sites along the Norwegian coast is investigated. Time series of tidal currents are generated with a model that considers the variation in current strength due to the variability in the semi-diurnal tidal cycle (spring to neap, flood to ebb, first to second daily tide etc.). From these, available kinetic energy in the natural flow is calculated. A constant conversion rate is then applied to give the power output at each site. Three scenarios, with varying number of sites and energy extraction, are investigated. The variability in each scenario is quantified on different time scales by filtering the aggregated power and calculate standard deviation and step change. It is found that the variability can be lowered by choosing sites with an advantageous time lag and limit the power output from the most energetic sites. As expected, smoothing is most distinct on short time scales.

  • 10.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tidal resource characterization in the Folda Fjord, Norway2016In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, p. 27-44Article in journal (Refereed)
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

  • 11. Castellucci, Valeria
    Tidal Effect Compensation System for Wave Energy Converters2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 12.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Impact of Tidal Level Variations on the Wave Energy Absorption at Wave Hub2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 10, article id 843Article in journal (Refereed)
    Abstract [en]

    The energy absorption of the wave energy converters (WEC) characterized by a limited stroke length - like the point absorbers developed at Uppsala University-depends on the sea level variation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy production of the generators is not optimal. The study presented in this paper quantifies the effects of the changing sea level at the Wave Hub test site, located at the south-west coast of England. This area is strongly affected by tides: the tidal height calculated as the difference between the Mean High Water Spring and the Mean Low Water Spring in 2014 was about 6.6 m. The results are obtained from a hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking into account the sea state occurrence scatter diagram and the tidal time series at the site. It turns out that the impact of the tide decreases the energy absorption by 53%. For this reason, the need for a tidal compensation system to be included in the design of the WEC becomes compelling. The economic advantages are evaluated for different scenarios: the economic analysis proposed within the paper allows an educated guess to be made on the profits. The alternative of extending the stroke length of the WEC is investigated, and the gain in energy absorption is estimated.

  • 13.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Conference paper (Refereed)
    Abstract [en]

    Within the year 2013, four linear generators with point absorber buoy systems were deployed in the Lysekil test site. Until now, deployments of these point absorbing wave energy converters have been expensive, time consuming, complicated and raised safety issues. In the present paper, we focus on the analysis and optimization of the offshore deployment process of wave energy converters with a linear generator power take-off which has been constructed by Uppsala University. To address the crucial issues regarding the deployment difficulties, case study of previous offshore deployments at the Lysekil test site are presented regarding such parameters as safety, cost and time efficiency. It was discovered that the deployment process can be improved significantly, mainly by using new technologies, e.g., new specialized deployment vessels, underwater robots for inspections and for connecting cables and an automatized pressurizing process. Addressing the main deployment difficulties and constrains leads us to discovery of methods that makes offshore deployments more cost-efficient and faster, in a safety context.

  • 14.
    Chatzigiannakou, Maria Angeliki
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Efficiency evaluation of the offshore deployments of wave energy converters and marine substations2017Licentiate thesis, comprehensive summary (Other academic)
  • 15.
    Francisco, Francisco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Use of Multibeam and Dual-Beam Sonar Systems to Observe Cavitating Flow Produced by Ferryboats: In a Marine Renewable Energy Perspective2017In: Journal of Marine Science and Engineering, Vol. 5, no 30, p. 1-14Article in journal (Refereed)
    Abstract [en]

    With the prospect to deploy hydrokinetic energy converters in areas with heavy boat traffic, a study was conducted to observe and assess the depth range of cavitating flow produced by ferryboats in narrow channels. This study was conducted in the vicinity of Finnhamn Island in Stockholm Archipelago. The objectives of the survey were to assess whether the sonar systems were able to observe and measure the depth of what can be cavitating flow (in a form of convected cloud cavitation) produced by one specific type of ferryboats frequently operating in that route, as well as investigate if the cavitating flow within the wake would propagate deep enough to disturb the water column underneath the surface. A multibeam and a dual-beam sonar systems were used as measurement instruments. The hypothesis was that strong and deep wake can disturb the optimal operation of a hydrokinetic energy converter, therefore causing damages to its rotors and hydrofoils. The results showed that both sonar system could detect cavitating flows including its strength, part of the geometrical shape and propagation depth. Moreover, the boat with a propeller thruster produced cavitating flow with an intense core reaching 4 m of depth while lasting approximately 90 s. The ferry with waterjet thruster produced a less intense cavitating flow; the core reached depths of approximately 6 m, and lasted about 90 s. From this study, it was concluded that multibeam and dual-beam sonar systems with operating frequencies higher than 200 kHz were able to detect cavitating flows in real conditions, as long as they are properly deployed and the data properly analyzed.

  • 16.
    Francisco, Francisco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Power as Solution for Off-Grid Water Desalination Systems: Resource Characterization for Kilifi-Kenya2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 4, article id 4Article in journal (Refereed)
    Abstract [en]

    Freshwater scarcity is one of humanity's reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly in the form of a reliable electricity supply, which in many cases is supplied by diesel generators. The objective of this work is to analyze the wave power resource availability in Kilifi-Kenya and evaluate the possible use of wave power converter (WEC) to power desalination plants. A particular focus is given use of WECs developed by Uppsala University (UU-WEC). The results here presented were achieved using reanalysis-wave data revealed that the local wave climate has an approximate annual mean of 7 kW/m and mode of 5 kW/m. Significant wave height and wave mean period are within 0.8-2 m and 7-8 s respectively, with a predominant wave mean direction from southeast. The seasonal cycle appeared to be the most relevant for energy conversion, having the highest difference of 6 kW/m, in which April is the lowest (3.8 kW/m) and August is the peak (10.5 kW/m). In such mild wave climates, the UU-WEC and similar devices can be suitable for ocean energy harvesting for water desalination systems. Technically, with a capacity factor of 30% and energy consumption of 3 kWh/m(3), a coastal community of about five thousand inhabitants can be provided of freshwater by only ten WECs with installed capacity of 20 kW.

  • 17.
    Garcia Teran, Jessica
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Positional Analysis of Wave Power: Applied at the Pacific Ocean in Mexico.2013Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The energy transition has started. The key is to find an alternative to uneconomical and unsustainable energy production. In this sense it is a challenge to develop renewable energy technologies suitable for the present and proper for the future. Uppsala University is driving the Lysekil project at its Division of Electricity. The aim is to design an environmentally friendly energy system with wave energy converters (WECs) that are simple and strong in design. However, little has been done to know more about its economically feasibility and the social impact of its benefits. Therefore, this research focuses on a positional analysis of a 3 MW Wave Power Park to understand the relevant aspects of implementing this kind of technology. The target area will be at Rosarito, Baja California at the Pacific Ocean in the Northeast of Mexico, a region experiencing increasing energy demand. This thesis combines technical, economical and social aspects. The technical part describes how the device works. The analysis is complemented by describing the current energy situation in Mexico and the social benefits of sustainable energy. Finally, the economical analysis is presented, it is focused on the perspective of the Merchant Power Plant. The review shows that wave power could be economically viable due to its high degree of utilisation. Energy diversification and security, economic and sustainable development, and clean energy are some of the advantages of wave power. Therefore, wave power is an interesting alternative for generating electricity in Mexico. However, the energy sector is highly subsidised, making it difficult for new technologies to enter the market without government participation. Another finding is that in the long run if the equipment cost decreases or subsidies are applied, the technology might be successfully implemented. Environmental consequences are described briefly, concluding that little is known and more research is needed.

    The environmental constraints, economic implications and uncertainties of a high energy future are disturbing. In that sense, renewable energy appears to be unequivocally better than rely to a greater extent on fossil fuels, in the sense that they offer a sustainable development and less environmental damage. 

  • 18.
    Guerrero, José-Luis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Westerberg, Ida
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Halldin, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lundin, Lars-Christer
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Xu, Cong-Yu
    Exploring the hydrological robustness of model-parameter values with alpha shapes2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 10, p. 6700-6715Article in journal (Refereed)
    Abstract [en]

    Estimation of parameter values in hydrological models has gradually moved from subjective, trial-and-error methods into objective estimation methods. Translation of nature's complexity to bit operations is an uncertain process as a result of data errors, epistemic gaps, computational deficiencies, and other limitations, and relies on calibration to fit model output to observed data. The robustness of the calibrated parameter values to these types of uncertainties is therefore an important concern. In this study, we investigated how the hydrological robustness of the model-parameter values varied within the geometric structure of the behavioral (well-performing) parameter space with a depth function based on α shapes and an in-depth posterior performance analysis of the simulations in relation to the observed discharge uncertainty. The α shape depth is a nonconvex measure that may provide an accurate and tight delimitation of the geometric structure of the behavioral space for both unimodal and multimodal parameter-value distributions. WASMOD, a parsimonious rainfall-runoff model, was applied to six Honduran and one UK catchment, with differing data quality and hydrological characteristics. Model evaluation was done with two performance measures, the Nash-Sutcliffe efficiency and one based on flow-duration curves. Deep parameter vectors were in general found to be more hydrologically robust than shallow ones in the analyses we performed; model-performance values increased with depth, deviations to the observed data for the high-flow aspects of the hydrograph generally decreased with increasing depth, deep parameter vectors generally transferred in time with maintained high performance values, and the model had a low sensitivity to small changes in the parameter values. The tight delimitation of the behavioral space provided by the α shapes depth function showed a potential to improve the efficiency of calibration techniques that require further exploration. For computational reasons only a three-parameter model could be used, which limited the applicability of this depth measure and the conclusions drawn in this paper, especially concerning hydrological robustness at low flows.

  • 19.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave energy parks with point-absorbers of different dimensions2017In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 74, p. 142-157Article in journal (Refereed)
    Abstract [en]

    An analytical model for point-absorbing wave energy converters connected to floats of different geometries and topologies is presented. The floats can be truncated cylinder or cylinder with moonpool buoys and have different outer radius, inner radius, draft, mass and can be connected to linear generators of different power take-off constants. The model is implemented into a numerical code where the input is measured time-series of irregular waves. After validation against benchmark software, the model is used to study optimal configurations of wave energy arrays consisting of different wave energy devices. It is shown that the total power absorption can be improved if the wave energy array consists of devices of different dimensions, and that a higher power-to-mass ratio can be achieved.

  • 20.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Jens, Engström
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mikael, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hann, Martyn
    Plymouth University.
    Ransley, Edward
    Plymouth University.
    Greaves, Deborah
    Plymouth University.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave loads on a point-absorbing wave energy device in extreme waves2015Conference paper (Refereed)
  • 21.
    Hai, Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Force in the connection line for a wave energy converter: simulation and experimental setup2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, San Francisco, USA, 2014Conference paper (Refereed)
    Abstract [en]

    In order to capture ocean wave energy and transform it into electric energy, Uppsala University has developed a point absorber wave energy converter (AVEC) for electricity production. For a better understanding of a torus shaped buoy's performance, this paper conducts a force analysis under linear conditions, to investigate the hydrodynamic characteristic and line force differences between the torus buoy that is going to be deployed, and two similar cylindrical buoys. The result reveals the line force fromthis torus buoy is roughly 5% larger than from cylindrical buoys for the most energy dense wave climate in Lysekil test site, and negative added mass phenomena won't have a significant impact for the line force. To measure the line force, a force measurement system has been designed. A detailed description is given on the design of the 500 kN force measurement system, and the major differences compared with former force measurement systems. Onshore test result has also been presented. With the force measurement experiment, hydrodynamic analysis for torus buoy can be validated when the system performs linearly, and extreme force for storm weather can be monitored to provide information for future WEC structure's mechanical design.

  • 22.
    Hai, Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Southampton, Energy & Climate Change Div, Fac Engn & Environm, Southampton, Hants, England.
    Modelling a point absorbing wave energy converter by the equivalent electric circuit theory: A feasibility study2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, article id 164901Article in journal (Refereed)
    Abstract [en]

    There is a need to have a reliable tool to quickly assess wave energy converters (WECs). This paper explores whether it is possible to apply the equivalent electric circuit theory as an evaluation tool for point absorbing WEC system modelling. The circuits were developed starting from the force analysis, in which the hydrodynamic, mechanical, and electrical parameters were expressed by electrical components. A methodology on how to determine the parameters for electrical components has been explained. It is found that by using a multimeter, forces in the connection line and the absorbed electric power can be simulated and read directly from the electric circuit model. Finally, the circuit model has been validated against the full scale offshore experiment. The results indicated that the captured power could be predicted rather accurately and the line force could be estimated accurately near the designed working condition of the WEC.

  • 23.
    Hong, Yue
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear generator-based wave energy converter model with experimental verification and three loading strategies2016In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 3, p. 349-359Article in journal (Refereed)
    Abstract [en]

    Within the Lysekil wave energy research project at the Swedish west coast, more than ten Wave Energy Converters (WECs) prototypes have been developed and installed in an ocean based test site. Since 2006 various experiments have been conducted and the generated electricity was delivered to shore at a nearby island. While experiments are essential for the development of wave energy converters, theoretical studies and simulations are an important complement – not only in the search for advanced designs with higher efficiency, but also for improving the economic viability of the studied concepts. In this paper a WEC model is presented. The model consists of three subsystems: i) the hydrodynamic source, ii) the linear generator model, and iii) the electrical conversion system. After the validation with the experimental results at the research site, the generator model is connected to three passive load strategies – linear resistive load, passive rectification and resonance circuit. The paper focuses on analysing the operation of the model coupled with three load cases. The results prove that the WEC model correctly simulates the linear generator developed in the Lysekil Project. Moreover, the comparison among different load cases is made and discussed. The results gives an indication of the efficiency of energy production as well as the force ripples and resulting mechanical loads on the wave energy converters.

  • 24.
    Lejerskog, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea2016In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 8, p. 1204-1210Article in journal (Refereed)
    Abstract [en]

    To experimentally study how a wave energy converter (WEC) behaves when parameters such as weight on the translator and buoy volume are changing is of significant importance when trying to optimise the WEC system. This study presents results from a WEC deployed at the Baltic Sea near the island of Åland. Compared with earlier experiments, the weight on the translator has been significantly increased to suit the buoy volume. Experimental results show that the power output between the upward and the downward motions are comparable up to the maximum speed for the downward motion of the translator. To study the speed of the translator in downward direction a model has been derived. The model has also been used to study the impact of having a changing active area. Moreover, finite element (FE) simulations done on the generator have been compared with experimental data and show a good agreement, but at high speeds of the translator the FE simulations start to deviate from the experiments.

  • 25.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chen, Wenchuang
    Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bivariate joint distribution modeling of wave climate data using a copula method2016In: International Journal of Energy and Statistics, ISSN 2335-6812, Vol. 4, no 3, article id UNSP 1650015Article in journal (Refereed)
    Abstract [en]

    The bivariate joint distribution of the significant wave height and the wave period is of great importance in characterizing the wave climate at a wave energy converter test site. In this paper, we investigate bivariate joint distribution modeling of the wave climate at the Lysekil wave energy converter test site off the Swedish west coast. This study is based on 9 years of wave observations at the test site from 2005 to 2013. Archimedean Copulas are used for the bivariate joint distribution modeling of the significant wave height and the wave period. Measured wave data is compared with simulated wave climate data for the Lysekil test site using three Archimedean Copula models, the Clayton, Frank and Gumbel copulas. The R-squared statistical test yields a better goodness of fit for the Gumbel copula compared to the other two copulas. In addition, the Archimedean Copula method is applied to the measured wave climate data from two other sites to illustrate the general applicability. It shows that the Archimedean Copulas exhibits stable performance with good accuracy in characterizing the wave climate and they can be employed for forecasting the wave energy resource and assessing the survivability of wave energy converters.

  • 26.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 6, article id 396Article in journal (Refereed)
    Abstract [en]

    The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005-2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site. The mixed-distribution model is also applied to measured wave data from four other sites and it provides an illustration of the general applicability of the proposed model. The methodologies used in this paper can be applied to general wave climate analysis of wave energy test sites to estimate extreme waves for the survivability assessment of wave energy converters and characterize the long wave climate to forecast the wave energy resource of the test sites and the energy production of the wave energy converters.

  • 27.
    Lindblad, Liselotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Southampton, Engn & Environm, Energy & Climate Change, Southampton, Hants, England..
    Measurement System For Wave Energy Converter - Design And Implementation2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, AMER SOC MECHANICAL ENGINEERS , 2014Conference paper (Refereed)
    Abstract [en]

    A Wave Energy Converter (WEC) measurement system has been constructed and installed with the purpose to measure, log and evaluate the WEC's performance during operation at sea. The WEC is to be deployed at Uppsala University's wave power research site in Lysekil on the west coast of Sweden. In designing such a system the key research objectives has been (1) to study the risk of overheating due to high currents in the stator windings, (2) to evaluate how the WEC's outer structure withstands drag and bending forces from the buoy line and (3) to construct a detection system which indicates if water leaks into the generator. The measurement system was designed to collect data essential to study these key objectives. Transducers were used to measure: buoy line force, translator position, phase currents, bending and tensile strain on the generator hull, water level inside generator and the temperature at multiple places inside the generator. The measurement system has been installed and calibrated in the WEC. Furthermore, the design has been evaluated in lab experiments in order to verify the function and accuracy of the different measurements. This paper presents the underlying research objectives for developing the WEC generator measurement system, together with a description of the technical implementation.

  • 28.
    Lindroth [formerly Tyrberg], Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed.

    This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values.

    The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly.

    The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong.

    As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

    List of papers
    1. Wave Energy from the North Sea: Experiences from the Lysekil Research Site
    Open this publication in new window or tab >>Wave Energy from the North Sea: Experiences from the Lysekil Research Site
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    2008 (English)In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed) Published
    Abstract [en]

    This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

    Keywords
    Wave power, Renewable energy, Sea trial, Linear generator, Point absorber, Environmental impact
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-107215 (URN)10.1007/s10712-008-9047-x (DOI)000260967900002 ()
    Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2017-12-13Bibliographically approved
    2. The Lysekil Wave Power Project: Status Update
    Open this publication in new window or tab >>The Lysekil Wave Power Project: Status Update
    Show others...
    2008 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97846 (URN)
    Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2014-04-29Bibliographically approved
    3. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Show others...
    2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
    Abstract [en]

    The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
    4. Tracking a Wave Power Buoy Using a Network Camera: System Analysis and First Results
    Open this publication in new window or tab >>Tracking a Wave Power Buoy Using a Network Camera: System Analysis and First Results
    2009 (English)In: Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, Honolulu, Hawaii, 2009, p. 799-807Conference paper, Published paper (Refereed)
    Abstract [en]

    Anobservation system has been set up on a small isleton the Swedish west coast. The purpose of the systemis to monitor the wave buoys in The Lysekil Project.The project is an attempt to harvest wave energy usinglinear generators and point absorbing buoys. The observation system isself-sufficient and uses a network camera to follow the buoymotions. The first results from the camera, which has beenoperating since July 2008, have been analyzed to examine themotion tracking capabilities of the system. The motion tracking wouldwork as a complement to the other measurements that arebeing done on the buoy. The method for extracting motiondata from the two-dimensional pictures is presented. The results aregraphs of translative buoy motion in two dimensions, and rotationalmotion about two different axes. The vertical buoy motion forthe studied sequence is in the range of ±0.5 m.

    Place, publisher, year, edition, pages
    Honolulu, Hawaii: , 2009
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113302 (URN)10.1115/OMAE2009-79121 (DOI)
    Conference
    ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2009) May 31–June 5, 2009 , Honolulu, Hawaii, USA
    Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2014-04-29Bibliographically approved
    5. Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment
    Open this publication in new window or tab >>Wave Power Absorption as a Function of Water Level and Wave Height: Theory and Experiment
    2010 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 35, no 3, p. 558-564Article in journal (Refereed) Published
    Abstract [en]

    This paper investigates the sensitivity of a wave power system to variations in still water levels and significant wave heights. The system consists of a floating point absorber connected to a linear generator on the seabed. Changing still water levels are expected to affect the power absorption, since they will displace the equilibrium position for the generator translator. Similarly, changing significant wave heights will affect the rate at which the translator leaves the stator. Both these effects will in some cases result in a smaller active area of the stator. A theoretical expression to describe this effect is derived, and compared to measured experimental values for the wave energy converter at the Lysekil research site. During the time of measurements, the still water levels at the site were in the range of [-0.70 m, +0.46 m], and the significant wave heights in the range of [0 m, 2.7 m]. The experimental values exhibit characteristics similar to those of the theoretical expression, especially with changing significant wave heights.

    Keywords
    Energy capture, experimental results, linear generator, power absorption, wave power
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97852 (URN)10.1109/JOE.2010.2052692 (DOI)000283226500008 ()
    Available from: 2012-01-09 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved
    6. Experimental Results From an Offshore Wave Energy Converter
    Open this publication in new window or tab >>Experimental Results From an Offshore Wave Energy Converter
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    2010 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 132, no 4, p. 041103-Article in journal (Refereed) Published
    Abstract [en]

    An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.

    Keywords
    ocean wave power, linear generators, conversion systems, experimental results
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-133599 (URN)10.1115/1.4001443 (DOI)000283325300003 ()
    Available from: 2010-11-15 Created: 2010-11-11 Last updated: 2017-12-12Bibliographically approved
    7. Wave Buoy and Translator Motions - On-Site Measurements and Simulations
    Open this publication in new window or tab >>Wave Buoy and Translator Motions - On-Site Measurements and Simulations
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    2011 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 36, no 3, p. 377-385Article in journal (Refereed) Published
    Abstract [en]

    For a complete understanding of a wave energy conversion device, it is important to know how the proposed device moves in the water, how this motion can be measured, and to what extent the motion can be predicted or simulated. The magnitude and character of the motion has impacts on engineering issues and optimization of control parameters, as well as the theoretical understanding of the system. This paper presents real sea measurements of buoy motion and translator motion fora wave energy system using a linear generator. Buoy motion has been measured using two different systems: a land-based optical system and a buoy-based accelerometer system. The data have been compared to simulations from a Simulink model for the entire system. The two real sea measurements of buoy motion have been found to correlate well in the vertical direction, where the measured range of motion and the standard deviation of the position distributions differed with 3 and 4 cm, respectively. The difference in the horizontal direction ismore substantial. The main reason for this is that the buoy rotation about its axis of symmetry was not measured. However, used together the two systems give a good understanding of buoy motion. In a first comparison, the simulations show good agreement with the measured motion for both translator and buoy.

    Keywords
    Accelerometers, energy conversion, experimental results, image motion analysis, oceanic engineering, marine technology, wave power
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160072 (URN)10.1109/JOE.2011.2136970 (DOI)
    Available from: 2012-01-09 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
    8. Lysekil Research Site, Sweden: A status update
    Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
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    2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160039 (URN)
    Conference
    9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
    9. Offshore wave power measurements: a review
    Open this publication in new window or tab >>Offshore wave power measurements: a review
    2011 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 15, no 9, p. 4274-4285Article in journal (Refereed) Published
    Abstract [en]

    The first wave power patent was filed in 1799. Since then, hundreds of ideas for extraction of energy from ocean waves have surfaced. In the process of developing a concept, it is important to learn from previous successes and failures, and this is not least important when moving into the ocean. In this paper, a review has been made with the purpose of finding wave power projects that have made ocean trials, and that also have reported what has been measured during the trials, and how it has been measured.

    In relation to how many projects have done work on wave power, surprisingly few have reported on such measurements. There can be many reasons for this, but one is likely the great difficulties in working with experiments in an ocean environment. Many of the projects have reported on sensor failures, unforeseen events, and other general problems in making measurements at sea.

    The most common site measurement found in this review was wave height. Such measurements was almost universal, although the technologies used differed somewhat. The most common device measurements were electric voltages and/or currents and system pressures (air and water). Device motion and mooring forces were also commonly measured. The motion measurements differed the most between the projects, and many varying methods were used, such as accelerometers, wire sensors, GPS systems, optical systems and echo sounders.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Wave power, Measurement system, Offshore
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160081 (URN)10.1016/j.rser.2011.07.123 (DOI)000298764400006 ()
    Available from: 2012-01-09 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
    10. Spectral Parameters and Wave Energy Converter Performance
    Open this publication in new window or tab >>Spectral Parameters and Wave Energy Converter Performance
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Wave energy converter performance is typically specified for given values of significant wave height Hm0 and energy period T-10, in a matrix. For such a representation to be valid, it must be assumed that two parameters determine the performance of the wave energy converter satisfactorily. However, studying performance data for the wave energy converter L1 at the Lysekil research site, it can be seen that for measurements with similar values of Hm0 and T-10, there are values of relative absorption that range from 5 % to 25 %. It therefore seems probable that the properties of the sea state that are not captured using Hm0 and T-10 have an effect on how a WEC performs. It has been proposed in the literature that the width of the wave spectrum is one such property. In this paper, six parameters that describe spectral width have been tested against performance data to look for correlations. In addition to this, the performance data was tested against peak period and standard deviation of peak frequency, as found through wavelet analysis. Out of the parameters tested, κ and ε1 displayed the strongest correlation with relative absorption. Even this correlation was not very strong however, and did only exhibit an r2-value of 0.39 in a linear fit for L1 connected to a 4.9 Ω load. It was also found that the lowest absorption values were connected to the lowest and highest values for peak period.

    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160084 (URN)
    Available from: 2011-10-14 Created: 2011-10-14 Last updated: 2012-01-04
  • 29.
    Lundin, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Forslund, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yuen, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental demonstration of performance of a vertical axis marine current turbine in a river2016In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 8, no 6, article id 064501Article in journal (Refereed)
    Abstract [en]

    An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents.

  • 30.
    Morén, Ida
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Andersson, Elin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Comparing water capacity and water usage in the Gorom-Lampsar river system, Senegal2014Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
  • 31.
    Ning, Dezhi
    et al.
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Zhao, Xuanlie
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kang, Haigui
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Hydrodynamic performance of a pile-restrained WEC-type floating breakwater: An experimental study2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 95, p. 531-541Article in journal (Refereed)
    Abstract [en]

    In this paper, a system which integrates an oscillating buoy type wave energy converter with a vertical pile-restrained floating breakwater is introduced. A preliminary experimental study on the hydrodynamic performance of the system is carried out in a wave flume under the action of regular waves. A current controller-magnetic powder brake system is used to simulate the power generation system. The design is verified against published results. The power-take off damping characteristics are investigated, and the current controller-magnetic powder brake system can simulate the (approximate) Coulomb damping force very well. The effects of various parameters, including wave period and wave height, dimensions of the system and excitation current, on the hydrodynamic performance are investigated. Results indicate that the power take-off damping force, draft and relative width between the floating breakwater and the wavelength have a significant influence on the hydrodynamic performance of the system. A range can be observed for which the capture width ratio of the system can achieve approximately 24% while transmission coefficient was kept lower than 0.50 with the proper adjustment of power take-off damping force, and the floating breakwater performs in an effective manner. The new concept provides a promising way to utilize wave energy cost-effectively.

  • 32.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Remouit, Flore
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hong, Yue
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Francisco, Francisco
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castelucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ulvgård, Liselotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nasir, M
    Chatzigiannakou, Maria Angiliki
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, C.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update2015Conference paper (Refereed)
    Abstract [en]

    This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

  • 33.
    Remouit, Flore
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Automation of underwater operations on wave energy converters using remotely operated vehicles2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last fifteen years, the Division of Electricity at Uppsala University has been developing a wave energy converter (WEC) concept. The concept is based on a point-absorbing buoy with a directly driven linear generator placed on the seabed. Several units are connected to a marine substation, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.

    A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations.

    Existing ROVs need additional modules and equipment in order to carry out operations with the required force and precision. Typical missions are inspection, shackles or slings removal, valve closing, and cable connection. The latter demands especially high precision in the positioning: 5 mm in distance and 5◦ in heading angle. In addition, this operation involves forces up to 200 N. This combination power-precision is not reached by existing ROVs. This PhD thesis presents a positioning system for underwater robot to enable autonomous positioning of the vehicle before cable connection.

    The positioning system is composed of two green lasers and a monocular camera, and is based on image processing. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas the heading is minimized to 2◦. The computational time for the image processing is 13.6 ms per image, meaning the possibility of a 30 Hz measurement system. Used together with a closed-loop path-following unit, this positioning system can support autonomous docking. This PhD thesis presents the model of an autopilot and results from docking simulations, showing the performance of the positioning system used in closed-loop.

    List of papers
    1. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Show others...
    2015 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

    Keywords
    Wave energy, point absorber, experiments, arrays, generators, ROVs
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
    Identifiers
    urn:nbn:se:uu:diva-265218 (URN)
    Conference
    Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
    Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2019-08-19Bibliographically approved
    2. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Open this publication in new window or tab >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
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    2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, p. 356-375Article in journal (Refereed) Published
    National Category
    Energy Engineering Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
    Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2018-08-01
    3. Automation of subsea connections for clusters of wave energy converters
    Open this publication in new window or tab >>Automation of subsea connections for clusters of wave energy converters
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    2015 (English)In: The Proceedings of the Twenty-fifth (2015) International Ocean and Polar Engineering Conference, 2015Conference paper, Published paper (Refereed)
    Abstract [en]

    To make wave power a viable energy source, large clusters of wave energy converters should be deployed. For most of the farms the output power of the WECs should be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater cable connection operations is one of the main issues in offshore operations. Underwater connections can be conducted with wet- or dry-mateable connectors, performed by divers or ROVs. Although there are existing solutions used by the oil and gas industry that could be employed, the capital expenditure needed is not compatible with the offshore renewable energy industry.

     

    The objective of this research is to decrease costs and minimize working hazards associated with sub-sea work when performing these underwater electrical connections. This article presents a solution using small ROV’s instead of divers to execute the task. The main idea is to perform the connection underwater, but using dry-mateable connectors. A solution to make this possible is to install air pockets at the substation enclosing the connectors. These boxes are meant to be filled with air and hence create a dry environment in which to perform the connections. This is achieved with help of two tools. First a docking system allows the operator to fix the ROV at the substation before doing the connection. Then a gripper tool added to the ROV grasps the cable and connects it to the substation in the air pocket. The procedure and design of this low-cost solution are described, and the different prototypes that have been tested for offshore operation are also shown.

    Keywords
    Wave energy, ROV, subsea connection, gripper, substation
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-259835 (URN)978-1-880653-89-0 (ISBN)
    Conference
    The Twenty-fifth International Ocean and Polar Engineering Conference, June 21-26, Kona, Hawaii, USA
    Projects
    Lysekil project
    Available from: 2015-08-12 Created: 2015-08-12 Last updated: 2018-08-01Bibliographically approved
    4. Review of Electrical Connectors for Underwater Applications
    Open this publication in new window or tab >>Review of Electrical Connectors for Underwater Applications
    2018 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 43, no 4, p. 1037-1047Article in journal (Refereed) Published
    Abstract [en]

    The history of underwater electrical connectors is relativelynew: In 1858, the first transatlantic communication cable was created. Sincethen, the need for subsea electrical connectors has been growing very fastin the offshore industry. Today numerous companies offer a large choiceof underwater connectors and assemblies, and it can be intricate to distinguish the different technologies employed for each of them. However theuse, deployment, maintenance, and lifetime of any subsea equipment, froma simple sonar to a wave energy converter, relies on its connectors. Hencethe design of an underwater electrical connector is to be carefully lookedat, and especially for tailor-made applications that have more specific requirements. To produce a good connector, it is necessary to account for thermal, electrical, and mechanical properties, as well as to determine thebest materials that should be used for the application. Finally, connector issues go hand in hand with the deployment and operation of any electrical equipment, and it is of interest to review the different techniques for cable connection, as well as the challenges related to cable layout. Those challenges can be of different nature, but they should all be taken into account for any subsea connection.

    Keywords
    Cable, connector, electrical, review, subsea, underwater
    National Category
    Engineering and Technology Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-334294 (URN)10.1109/JOE.2017.2745598 (DOI)000448542200017 ()
    Funder
    EU, FP7, Seventh Framework Programme, 607656
    Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2019-01-24Bibliographically approved
    5. Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
    Open this publication in new window or tab >>Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
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    2018 (English)In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, no 2, article id 39Article in journal (Refereed) Published
    Abstract [en]

    Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles during the installation and monitoring phase of wave energy converters. Methods and results are based on the wave energy converter system developed by Uppsala University, and our experience in offshore deployments obtained during the past eleven years. The complexity of underwater operations, carried out by either divers or remotely-operated vehicles, is emphasized. Three methods for the deployment of wave energy converters are economically and technically analyzed and compared: one using divers alone, a fully-automated approach using remotely-operated vehicles, and an intermediate approach, involving both divers and underwater vehicles. The monitoring of wave energy converters by robots is also studied, both in terms of costs and technical challenges. The results show that choosing an autonomous deployment method is more advantageous than a diver-assisted method in terms of operational time, but that numerous factors prevent the wide application of robotized operations. Technical solutions are presented to enable the use of remotely-operated vehicles instead of divers in ocean renewable technology operations. Economically, it is more efficient to use divers than autonomous vehicles for the deployment of six or fewer wave energy converters. From seven devices, remotely-operated vehicles become advantageous.

    National Category
    Marine Engineering
    Identifiers
    urn:nbn:se:uu:diva-348816 (URN)10.3390/jmse6020039 (DOI)000436558500011 ()
    Funder
    StandUpEU, FP7, Seventh Framework Programme, 607656Swedish Energy Agency
    Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-04-01Bibliographically approved
    6. Optical System for Underwater Positioning of Observation Class Remotely Operated Vehicle
    Open this publication in new window or tab >>Optical System for Underwater Positioning of Observation Class Remotely Operated Vehicle
    2016 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    To make wave power a viable energy source, large clusters of wave energy converters (WECs) will be deployed into large farms. For most of these farms, the output power of the WECs will be aggregated in a marine substation and then transmitted to the grid. The need for cost effective underwater connection operations is one of the main challenges with this kind of offshore installation. Our research is related to underwater connection with help of Observation Class Remotely Operated Vehicles (OC ROVs). The main idea is to use a docking system in order for the small and light ROV to perform the connection, using the reaction force from its docking point instead of the motors propulsion, the latter being too little. This docking operation has to be very accurate and needs both an autopilot and a good positioning tool. In this paper we present an optical positioning system made of green lasers that together with the ROV’s camera measure the distances to the docking point. This is obtained by tracking the laser beams on the images captured from the camera and using triangulation of the points extracted. The tool has been implemented into an OCROV and tested in a tank.

    Keywords
    ROV, positioning, underwater connections, wave energy converters
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-302641 (URN)
    External cooperation:
    Conference
    3rd Asian Wave and Tidal Energy Conference, AWTEC, Singapore
    Available from: 2016-09-07 Created: 2016-09-07 Last updated: 2018-08-01Bibliographically approved
    7. Laser-based relative positioning system for underwater remotely operated vehicle
    Open this publication in new window or tab >>Laser-based relative positioning system for underwater remotely operated vehicle
    (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Refereed) Submitted
    Abstract [en]

    This paper addresses the development, testing and verification of a relative positioning system for underwater vehicles. The position and orientation of the vehicle relative to a plane based target is estimated through a laser-based optical system. The sensor package consists of two green line-lasers and a camera. The image processing algorithm is built on the probabilistic Hough transform and a light but robust filtering method. This decreases the computational time to 13.6 ms per image. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas in heading is 2°.

    Keywords
    Optical positioning, Green lasers, Image processing, Relative positioning, Remotely operated vehicle
    National Category
    Robotics
    Identifiers
    urn:nbn:se:uu:diva-356535 (URN)
    Available from: 2018-07-31 Created: 2018-07-31 Last updated: 2018-08-07
    8. Autonomous docking based on optical positioning system for remotely operated vehicle
    Open this publication in new window or tab >>Autonomous docking based on optical positioning system for remotely operated vehicle
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Underwater docking is of high interest as it could be used to chargeunderwater robots while on a mission, thus extending their range of ac-tion, or to upload data without retrieving the vehicle, thus increasing itsmemory capacity. In this paper, the purpose of the docking system is toperform cable connections using remotely operated vehicles. The modelof an autopilot for autonomous docking is presented and the performancesof its components are analysed. This autopilot is based on measurementsfrom an optical positioning system which localizes the vehicle based onfeature detection from image processing. It shows that this positioning system could be integrated to the modelled autopilot and used in closed-loop for autonomous docking.

    Keywords
    Optical positioning; closed-loop; Image processing; Remotely operated vehicle; Autonomous docking.
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-356562 (URN)
    Available from: 2018-08-01 Created: 2018-08-01 Last updated: 2018-08-01
  • 34.
    Sigfridson, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Skyddsinfiltrationens influensområde för en fallstudie: - modellering och osäkerheter2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To evaluate the area of influence due to artificial infiltration several analytical models are available. Some of the parameters taken into account by these models are the hydraulic conductivity and storage coefficient, but with these models some assumptions, which in reality cannot be fulfilled, are made. An alternative approach to evaluate the area of influence is therefore with numerical models, which in a greater extent account for the site-specific conditions. Due to this, numerical models are more time consuming and require more input data.

    This project aims to investigate the most effective approaches to evaluate the area of influence due to artificial infiltration for a case study in Bromsten, located 15 kilometers northwest of Stockholm. Two numerical models, with different background data due to the extent of site knowledge, were developed to represent the site's geological settings and groundwater properties to simulate the groundwaterlevels with and without infiltration. Moreover the area of influence were calculated with four analytical models. All of the models were then applied on four different scenarios, in which the data resolution and the site knowledge increased. Site-specific data was added as a result of geological surveys and hydrogeological tests. The study also aims to answer which data is most important in order to determine the area of influence with analytical and numerical models and what differences there are between the analytical solutions compared with the numerical solutions.

    Among the methods investigated, constructing a more complex model with data from scenario 4, the scenario with the greatest data supply, resulted in the most reliable results and was therefore the best method and the method to choose for this case-study. Other results indicated that the numerical models first of all are sensitive to the conductivity and that the more simpel numerical model is sensitive to the storage coefficient as well. The last result shows that this model does not reach the steady state conditions as observed in field, which highlights the importance of goetechnical investigation for the numerical models. Moreover none of the numerical models were sensitive to the specific yield. Among the analytical models the storage coefficient was the most important followed by the conductivity. For one of the analytical models (Sichardts formula) the conductivity was the most sensitive parameter. The thickness of the aquifer had no significant impact on the analytical models.

  • 35.
    Skoglund, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Skotte, Maja
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Fors, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Jeppsson Stahl, Fanny
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Löf, Harald
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Renberg, Johanna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Avsaltning av brackvatten som lösning för Ålands framtida vattenförsörjning2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Målet med detta projekt var att jämföra nuvarande dricksvattenproduktion på Åland med ett eventuellt kompletterande avsaltningsverk, samt undersöka om det är rimligt att uppföra ett sådant. Detta genomfördes genom informationsinsamling i en litteraturstudie och jämförelse mellan nuvarande vattenverk och ett eventuellt avsaltningsverk i en beslutsmatris. Kategorier som ansågs relevanta för jämförelsen identifierades och sedan utvecklades dessa genom att identifiera parametrar som byggde upp kategorierna. Den insamlade informationen användes sedan för att klassa de olika parametrarna inom kategorierna och en samlad bedömning gjordes. De kategorier som undersöktes var: dricksvattenkvalitet, miljökonsekvenser, energiförbrukning och kostnader samt tillräcklig och säker dricksvattentillgång. Det eventuella kompletterande avsaltningsverket ansågs kunna konkurrera med nuvarande vattenproduktion med avseende på alla dessa fyra kategorier och metoden bedömdes vara en bra grund för jämförelsen. För att utveckla projektet i framtiden rekommenderades modellering och en pilotstudie.

  • 36.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Submerged Transmission in Wave Energy Converters: Full Scale In-Situ Experimental Measurements2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Different wave power technologies are in development around the world in different stages of prototype testing. So far only a few devices have been deployed offshore at full scale for extended periods of time. Little data is published about how these different devices perform.

    This thesis presents results from experiments with the full-scale offshore wave energy converters at the Lysekil research site on the Swedish west coast. The theories, experiments, measurements, performance evaluations and developments of the submerged transmission in the direct driven permanent magnet linear generator are in focus. The reciprocating submerged transmission fulfills the purpose of transmitting the absorbed mechanical wave energy through the capsule wall into the generator, while preventing the seawater from entering the capsule and reducing the life time of the converter.

    A measuring system with seven laser triangulation sensors has been developed to measure small relative displacements between piston rod and seal housing in the submerged transmission with excellent accuracy for the purpose of evaluating both functional behavior and successive wear in-situ. A method for calculating relative tilt angles, azimuth angles, differential tilt angles, and successive wear in the submerged transmission has been developed. Additional sensors systems have been installed in the converter enabling correlation and a thorough investigation into the operating conditions of the transmission and the converter. The thesis presents unique results from the measurements. A data acquisition system transmits the signals from the converter on the seabed to an onshore measuring station. Results are presented in time-, frequency- and the time-frequency domain.

    The results have given important information for further development of the submerged transmission, which is important to the survivability of the system. The thesis describes the status of research, and is a step that may influence future designs of wave energy devices for reaching survivability and a cost-effective renewable energy system.

    List of papers
    1. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Show others...
    2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
    Abstract [en]

    The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
    2. Wave Energy from the North Sea: Experiences from the Lysekil Research Site
    Open this publication in new window or tab >>Wave Energy from the North Sea: Experiences from the Lysekil Research Site
    Show others...
    2008 (English)In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 29, no 3, p. 221-240Article, review/survey (Refereed) Published
    Abstract [en]

    This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider™ buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.

    Keywords
    Wave power, Renewable energy, Sea trial, Linear generator, Point absorber, Environmental impact
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-107215 (URN)10.1007/s10712-008-9047-x (DOI)000260967900002 ()
    Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2017-12-13Bibliographically approved
    3. Experimental results from sea trials of an offshore wave energy system
    Open this publication in new window or tab >>Experimental results from sea trials of an offshore wave energy system
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    2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 3, p. 034105-Article in journal (Refereed) Published
    Abstract [en]

    A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.

    Keywords
    High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-95683 (URN)10.1063/1.2432168 (DOI)000243582400105 ()
    Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
    4. Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
    Open this publication in new window or tab >>Ocean wave energy absorption in response to wave period and amplitude: offshore experiments on a wave energy converter
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    2011 (English)In: IET Renewable Power Generation, ISSN 1752-1416, Vol. 5, no 6, p. 465-469Article in journal (Refereed) Published
    Abstract [en]

    The ability of a wave energy converter to capture the energy of ocean waves has been studied in offshore experiments. This study covers 50 days during which the converter was subjected to ocean waves over a wide range of frequencies and amplitudes as well as three different electrical loads. The results present the wave energy converter??s energy absorption as a function of significant wave height, energy period and electrical load. It is shown that the power generated overall continues to increase with wave amplitude, whereas the relative absorption decreases towards the highest periods and amplitudes. The absorption reached a maximum of approximately 24% with the used combination of buoy, generator and electrical load. Absorption to cover for iron and mechanical losses has not been included. A brief study of the nature of the electromagnetic damping force has also been included in the study. The wave energy converter is of the technology that is being researched at Uppsala University and experimented on off the Swedish west coast at the Lysekil wave energy research site.

    Place, publisher, year, edition, pages
    IEEE Press, 2011
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-165034 (URN)10.1049/iet-rpg.2010.0124 (DOI)000303376900007 ()
    Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2013-05-17Bibliographically approved
    5. Study of aWave Energy Converter Connected to a Nonlinear Load
    Open this publication in new window or tab >>Study of aWave Energy Converter Connected to a Nonlinear Load
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    2009 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 2, p. 123-127Article in journal (Refereed) Published
    Abstract [en]

    This paper presents experimental results from a wave energy converter (WEC) that is based on a linear generator connected to a rectifier and filter components. The converter-filter system is installed onshore, while the linear wave generator operates offshore a few kilometers from the Swedish west coast. The power from the generator has been rectified with a diode bridge and then filtered using a capacitive filter. Performance of the whole conversion system was studied using resistive loads connected across the filter. The aim was to investigate the operational characteristics of the generator while supplying a nonlinear load. By changing the value of the resistive component of the load, the speed of the translator can be changed and so also the damping of the generator. The power absorbed by the generator was studied at different sea states as well. The observations presented in this paper could be beneficial for the design of efficient wave energy conversion systems.

    Keywords
    ocean waves
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112947 (URN)10.1109/JOE.2009.2015021 (DOI)000266245600004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-12-12Bibliographically approved
    6. Sensors and Measurements Inside the Second and Third Wave Energy Converter at the Lysekil Research Site.
    Open this publication in new window or tab >>Sensors and Measurements Inside the Second and Third Wave Energy Converter at the Lysekil Research Site.
    2011 (English)Conference paper, Published paper (Refereed)
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-162252 (URN)
    Conference
    Conference
    Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2016-04-19
    7. A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor
    Open this publication in new window or tab >>A Set-Up of 7 Laser Triangulation Sensors and a Draw-Wire Sensor for Measuring Relative Displacement of a Piston Rod Mechanical Lead-Through Transmission in an Offshore Wave Energy Converter on the Ocean Floor
    2012 (English)In: ISRN Renewable Energy, ISSN 2090-746X, Vol. 2012, p. 746865-Article in journal (Refereed) Published
    Abstract [en]

    A concept for offshore wave energy conversion is being developed at the Swedish Centre for Renewable Electric Energy Conversion at Uppsala University in Sweden. The wave energy converter (WEC) in focus contains a piston rod mechanical lead-through transmission for transmitting the absorbed mechanical wave energy through the generator capsule wall while preventing seawater from entering the capsule. A set-up of 7 laser triangulation sensors has been installed inside the WEC to measure relative displacement of the piston rod and its corresponding seal housing. A draw-wire sensor has also been set up to measure translator position and the axial displacement of the piston rod. The paper gives a brief introduction to the Lysekil research site, the WEC concept, and the direct drive of WEC prototype L2. A model of operation for the piston rod mechanical lead-through transmission is given. The paper presents sensor choice, configuration, adaptation, mounting, and measurement system calibration along with a description of the data acquisition system. Results from 60 s measurements of nominal operation two months apart with centered moving averages are presented. Uncertainty and error estimations with statistical analyses and signal-to-noise ratios are presented. Conclusions are drawn on the relative motions of the piston rod and the seal housing under normal operating conditions, and an assessment of the applicability of the measurement system is made.

    Place, publisher, year, edition, pages
    New York: Hindawi Publishing Corporation, 2012
    Keywords
    Wave energy, Laser, Sensor, Triangulation, Draw-wire, Piston rod, Transmission, Submerged, Offshore, Measurements, Mechanical lead-through.
    National Category
    Applied Mechanics Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179099 (URN)10.5402/2012/746865 (DOI)
    Projects
    The Lysekil Wave Power Project
    Available from: 2012-08-07 Created: 2012-08-07 Last updated: 2012-09-20Bibliographically approved
    8. Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
    Open this publication in new window or tab >>Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
    (English)In: Energy and Power Engineering, ISSN 1949-243XArticle in journal (Other academic) Submitted
    Abstract [en]

    The second wave energy converter (WEC) prototype launched at the Lysekil research site on the Swedish west coast in March 2009 contained a number of sensor systems for measuring the mechanical performance of the WEC and mechanical subsystems within the WEC. Measurements were carried out during the first experimental period starting from May 15th and ending on September 23rd. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Two measurement periods separated by 2.5 month are presented to be able to draw conclusion on what happens with time. Comparisons and correlations are made between different sensors measuring simultaneously, especially for the laser triangulation sensor measurements. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period in August. Vibrations frequencies due to wear is possible from comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.

    Keywords
    wave energy converter, linear generator, sensor measurements, spectral analysis, cogging, filtering, laser triangulation sensor, draw-wire sensor, force transducer, strain gauges, search coils, power generation
    National Category
    Ocean and River Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179733 (URN)
    Projects
    The Lysekil Wave Power Project
    Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2012-09-07Bibliographically approved
    9. Measurements of Relative Displacement and Tilting of a Piston Rod Transmission in a Submerged Linear Wave Energy Converter Operating with End Stop Impact
    Open this publication in new window or tab >>Measurements of Relative Displacement and Tilting of a Piston Rod Transmission in a Submerged Linear Wave Energy Converter Operating with End Stop Impact
    (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896XArticle in journal (Other academic) Submitted
    Abstract [en]

    A type of piston rod mechanical-lead through transmission has been designed and implemented inside the two first wave energy converter (WEC) prototypes at the Lysekil wave energy research site on the Swedish west cost. The transmission constitutes a direct drive which transfers the mechanical force, absorbed from the waves by a heaving surface-floating buoy, through an encapsulation and into a permanent magnet linear generator bolted to a foundation on the seabed, while sealing off the corrosive seawater. A set-up of 7 laser triangulation sensors have been installed in the second wave energy converter prototype to measure the relative displacement of the piston rod and seal housing in the mechanical lead-through in-situ. This paper presents measurements from full scale operation in two different sea states with end stop impact. Since wear is a successive process stretched out over time measurements have been performed for both sea states with 2.5 month separation. The experimental set-up and sensors are described. Equations for calculating tilt angles and azimuth angles for the piston rod are presented. Results from structure mechanical FEM simulations performed on the wave energy converter structure at end stop impact is also presented. The laser sensor measurements of the relative sideway displacements are correlated with measurements of the translator position and piston rod stroke length performed with a draw wire sensor. A force transducer is used for measuring the force in the buoy line to better understand the variations in motion due to changes in the buoy line axial force. Tilt angles and azimuth angles are presented for a wave period in each measurement period. The results are discussed and conclusions drawn with specific emphasis on the effects of the end stop impacts and wear on the funnel. The successive wear in the buoy line guiding system results in a 6 fold increase in relative tilt angle of the piston rod over a period of 2.5 months. A corresponding increase in motion is also seen for the seal housing, but to a lesser extent, indicating wear on the dynamic sealing system housed inside. The measurements of the relative displacement of the piston rod and seal housing are intended for further research.

    Keywords
    wave energy converter, linear generator, direct drive, submerged transmission, piston rod, laser triangulation sensor, draw-wire sensor, force transducer, FEM simulation, relative displacement measurement, end stop impact
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179735 (URN)
    Projects
    The Lysekil Wave Power Project
    Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2017-12-07Bibliographically approved
    10. In-Situ Measurements of Relative Displacement between Piston Rod and Seal Housing with Estimations of Wear on a Sealing System in a Submerged Transmission of an Offshore Underwater Wave Energy Converter
    Open this publication in new window or tab >>In-Situ Measurements of Relative Displacement between Piston Rod and Seal Housing with Estimations of Wear on a Sealing System in a Submerged Transmission of an Offshore Underwater Wave Energy Converter
    (English)In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012Article in journal (Other academic) Submitted
    Abstract [en]

    A type of submerged piston rod mechanical lead-through transmission has been designed and implemented inside the two first full scale wave energy converter (WEC) prototypes at the Lysekil wave energy research site on the Swedish west cost. The transmission constitutes a direct drive which transfers the mechanical force, absorbed from the waves by a heaving surface-floating buoy, through an encapsulation and into a permanent magnet linear generator bolted to a foundation on the seabed, while sealing off the corrosive seawater. A set-up of 7 laser triangulation sensors has been installed in the second wave energy converter prototype to measure the relative displacement of the piston rod and the seal housing in-situ. This paper focus on investigating the relative tilt angles of both objects, the differential tilt angle between the piston rod and the seal housing and how they move in the time and space as they tilt with the ocean waves. Estimations on wear of the sealing components in the dynamic sealing system are made. The measurements are performed for two sea states with 2.5 month separation. The paper describes the experimental set-up and the sensor measuring systems. Equations for calculating the relative differential tilt angle between piston rod and seal housing are presented. The calculated differential tilt angle is correlated with measurements of the piston stroke length and translator position performed with the draw-wire sensor. Tilt angles, azimuth angles and differential tilt angles are presented for one wave period in each measurement period. The wear is estimated by calculating the relative change in traversed clearance gap by the piston rod across the interface inside the seal housing. Results show the expected differential tilt angle early in the experiment. A substantial increase in differential tilt angle developed over 3 months time as a consequence of large wear between buoy line and guiding funnel causing a large tilt angle on the piston rod and unintentionally large normal forces between piston rod and the dynamic sealing system inside the seal housing. The results indicate the need of a more flexible mechanical lead-through design, which is presented at the end of the paper. The results are discussed and conclusions are drawn with specific emphasis on improving the sealing system with stronger guide elements and the patented mechanical lead-through design.

    Keywords
    wave energy converter; linear generator; direct drive; piston rod; seal housing; mechanical lead-through; submerged transmission; relative displacement measurement; laser triangulation sensor; tilting; tilt angle; azimuth angle; estimation of wear; sealing component.
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179737 (URN)
    Projects
    The Lysekil Wave Power Project
    Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2012-09-07Bibliographically approved
    11. Temperature measurements in a linear generator and marine substation for wave power
    Open this publication in new window or tab >>Temperature measurements in a linear generator and marine substation for wave power
    Show others...
    2012 (English)In: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme, ISSN 0892-7219, E-ISSN 1528-896X, Vol. 134, no 2, p. 021901-Article in journal (Refereed) Published
    Abstract [en]

    This paper analyzes temperature measurements acquired in the offshore operation of a wave energy converter array. The three directly driven wave energy converters have linear generators and are connected to a marine substation placed on the seabed. The highly irregular individual linear generator voltages are rectified and added on a common dc-link and inverted to 50 Hz to facilitate future grid-connection. The electrical power is transmitted to shore and converted to heat in a measuring station. The first results of temperature measurements on substation components and on the stator of one of the linear generators are presented based on operation in linear and in nonlinear damping. The results indicate that there might be some convective heat transfer in the substation vessel. If high power levels are extracted from the waves, this has to be considered when placing components in the substation vessel in order to avoid heating from neighboring components. The results also indicate that the temperature increase in the linear generator stator is very small. Failure due to excessive heating of the stator winding polyvinyl chloride cable insulation is unlikely to occur even in very energetic sea states. Should this conclusion be incorrect, the thermal conductivity between the stator and the hull of the wave energy converter could be enhanced. Another suggested alteration is to lower the resistive losses by reducing the linear generator current density.

    Keywords
    convection, linear machines, machine insulation, machine windings, offshore installations, power convertors, stators, substations, temperature measurement, wave power generation
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-140113 (URN)10.1115/1.4004629 (DOI)000308596500021 ()
    Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2017-12-11Bibliographically approved
    12. Wave Buoy and Translator Motions - On-Site Measurements and Simulations
    Open this publication in new window or tab >>Wave Buoy and Translator Motions - On-Site Measurements and Simulations
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    2011 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 36, no 3, p. 377-385Article in journal (Refereed) Published
    Abstract [en]

    For a complete understanding of a wave energy conversion device, it is important to know how the proposed device moves in the water, how this motion can be measured, and to what extent the motion can be predicted or simulated. The magnitude and character of the motion has impacts on engineering issues and optimization of control parameters, as well as the theoretical understanding of the system. This paper presents real sea measurements of buoy motion and translator motion fora wave energy system using a linear generator. Buoy motion has been measured using two different systems: a land-based optical system and a buoy-based accelerometer system. The data have been compared to simulations from a Simulink model for the entire system. The two real sea measurements of buoy motion have been found to correlate well in the vertical direction, where the measured range of motion and the standard deviation of the position distributions differed with 3 and 4 cm, respectively. The difference in the horizontal direction ismore substantial. The main reason for this is that the buoy rotation about its axis of symmetry was not measured. However, used together the two systems give a good understanding of buoy motion. In a first comparison, the simulations show good agreement with the measured motion for both translator and buoy.

    Keywords
    Accelerometers, energy conversion, experimental results, image motion analysis, oceanic engineering, marine technology, wave power
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160072 (URN)10.1109/JOE.2011.2136970 (DOI)
    Available from: 2012-01-09 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
    13. Description of a torus shaped buoy for wave energy point absorber
    Open this publication in new window or tab >>Description of a torus shaped buoy for wave energy point absorber
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    2010 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-142504 (URN)
    Conference
    Renewable Energy 2010, 27 June - 2 July, Pacifico Yokohama, Japan
    Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2015-01-07Bibliographically approved
    14. Lysekil Research Site, Sweden: A status update
    Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
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    2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160039 (URN)
    Conference
    9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
    15. A wave power unit
    Open this publication in new window or tab >>A wave power unit
    2010 (English)Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention relates to a wave-power unit for the production of electric power. It comprises a floating body arranged for floating on the sea and an electric linear generator having a stator and a translator reciprocating along a center axis. The stator is arranged to be anchored in the bed of the sea and the translator is connected tothe floating body by connection means. According to the invention the generator is enclosed in a watertight encapsulation having an upper end wall with an opening through which the connection means extends. The opening has a seal that seals against the connection means. The seal is flexibly mounted. The invention also relates to the use of the wave-power unit and to a method for producing electric power.

    Keywords
    wave power, submerged, transmission, flexible unit, compensator, seal housing, piston rod
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179738 (URN)
    Patent
    World Intellectual Property Organization WO2010/024740 A1 (2010-03-04)
    Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2012-08-31Bibliographically approved
    16. A wave power unit, a buoy, use of a wave power unit and a method for producing electric energy
    Open this publication in new window or tab >>A wave power unit, a buoy, use of a wave power unit and a method for producing electric energy
    2008 (English)Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention relates to a wave power unit with a buoy, adapted to float on a water surface. An electric generator is connected to the buoy through connection means. According to the invention the buoy when floating on a water surface and when seen in a direction perpendicular to the water surface has the shape of a closed loop enclosing an inner opening. The invention also relates to a buoy for a wave power unit, which buoy has the corresponding features as above. Further, the invention relates to the use of the invented wave power unit and to a method for producing electric energy with the invented wave power unit.    

    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-179739 (URN)
    Patent
    World Intellectual Property Organization WO2008/130295 A1 (2008-10-30)
    Available from: 2012-08-21 Created: 2012-08-21 Last updated: 2012-09-07Bibliographically approved
  • 37.
    Strömstedt, Erland
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator TechnologyIn: Energy and Power Engineering, ISSN 1949-243XArticle in journal (Other academic)
    Abstract [en]

    The second wave energy converter (WEC) prototype launched at the Lysekil research site on the Swedish west coast in March 2009 contained a number of sensor systems for measuring the mechanical performance of the WEC and mechanical subsystems within the WEC. Measurements were carried out during the first experimental period starting from May 15th and ending on September 23rd. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Two measurement periods separated by 2.5 month are presented to be able to draw conclusion on what happens with time. Comparisons and correlations are made between different sensors measuring simultaneously, especially for the laser triangulation sensor measurements. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period in August. Vibrations frequencies due to wear is possible from comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.

  • 38.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental results from the Lysekil Wave Power Research Site2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.

    The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.

    The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.

    Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.

    The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.

    Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.