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  • 301.
    Carpman, Nicole
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Potentialbedömning av marin strömkraft i Finnhamn: Fältmätningar och resultat2015Rapport (Annet vitenskapelig)
    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.

    Fulltekst (pdf)
    Carpman - Potentialbedömningar Finnhamn
  • 302.
    Carpman, Nicole
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Uppsala University.
    Resource characterization and variability studies for marine current power2017Doktoravhandling, med artikler (Annet vitenskapelig)
    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.

    Delarbeid
    1. Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    Åpne denne publikasjonen i ny fane eller vindu >>Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP
    2014 (engelsk)Inngår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Konferansepaper, Oral presentation only (Fagfellevurdert)
    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.

    Emneord
    Acoustic Doppler Current Profiler (ADCP), tidal energy resource
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-230659 (URN)000363498500053 ()978-0-7918-4550-9 (ISBN)
    Konferanse
    33rd International Conference on Ocean, Offshore and Arctic Engineering (OMAE2014), San Francisco, California, USA, June 8-13, 2014
    Tilgjengelig fra: 2014-08-27 Laget: 2014-08-27 Sist oppdatert: 2017-04-04bibliografisk kontrollert
    2. Tidal resource characterization in the Folda Fjord, Norway
    Åpne denne publikasjonen i ny fane eller vindu >>Tidal resource characterization in the Folda Fjord, Norway
    2016 (engelsk)Inngår i: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, s. 27-44Artikkel i tidsskrift (Fagfellevurdert) 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.

    Emneord
    Tidal resource assessment, ADCP, Characterizing metrics
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-266674 (URN)10.1016/j.ijome.2016.01.001 (DOI)000381687600003 ()
    Forskningsfinansiär
    StandUpCarl Tryggers foundation
    Tilgjengelig fra: 2015-11-10 Laget: 2015-11-10 Sist oppdatert: 2018-01-10bibliografisk kontrollert
    3. The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Åpne denne publikasjonen i ny fane eller vindu >>The Söderfors Project: Experimental Hydrokinetic Power Station Deployment and First Results
    Vise andre…
    2013 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    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.

    Emneord
    Marine Current Power, Renewable energy, Söderfors, Strömkraft, Förnybar energi, Söderfors
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-209220 (URN)
    Konferanse
    10th European Wave and Tidal Energy Conference (EWTEC), 2-5 september, 2013, Aalborg, Denmark
    Prosjekter
    Marine Current Power
    Forskningsfinansiär
    StandUpSwedish Research Council, 621-2009-4946
    Tilgjengelig fra: 2013-10-15 Laget: 2013-10-15 Sist oppdatert: 2019-01-22bibliografisk kontrollert
    4. Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    Åpne denne publikasjonen i ny fane eller vindu >>Studying the Wake of a Marine Current Turbine Using an Acoustic Doppler Current Profiler
    2015 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    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.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-265358 (URN)
    Konferanse
    11th European Wave and Tidal Energy Conference, EWTEC15, 6-11 September 2015, Nantes, France
    Tilgjengelig fra: 2015-10-27 Laget: 2015-10-27 Sist oppdatert: 2017-04-04bibliografisk kontrollert
    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)
    Åpne denne publikasjonen i ny fane eller vindu >>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)
    (engelsk)Inngår i: Artikkel i tidsskrift (Fagfellevurdert) Submitted
    Abstract
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-307239 (URN)
    Tilgjengelig fra: 2016-11-11 Laget: 2016-11-11 Sist oppdatert: 2017-04-04
    6. Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Åpne denne publikasjonen i ny fane eller vindu >>Variability Assessment and Forecasting of Renewables: A Review for Solar, Wind, Wave and Tidal Resources
    Vise andre…
    2015 (engelsk)Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 44, s. 356-375Artikkel i tidsskrift (Fagfellevurdert) Published
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära; Teknisk fysik med inriktning mot fasta tillståndets fysik
    Identifikatorer
    urn:nbn:se:uu:diva-225870 (URN)10.1016/j.rser.2014.12.019 (DOI)000351324300025 ()
    Tilgjengelig fra: 2014-06-09 Laget: 2014-06-09 Sist oppdatert: 2018-08-01
    7. Net load variability in Nordic countries with a highly or fully renewable power system
    Åpne denne publikasjonen i ny fane eller vindu >>Net load variability in Nordic countries with a highly or fully renewable power system
    Vise andre…
    2016 (engelsk)Inngår i: Nature Energy, ISSN 2058-7546, Vol. 1, s. 1-8, artikkel-id 16175Artikkel i tidsskrift (Fagfellevurdert) 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.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-302836 (URN)10.1038/NENERGY.2016.175 (DOI)000394793000001 ()
    Forskningsfinansiär
    StandUpStandUp for Wind
    Tilgjengelig fra: 2016-09-11 Laget: 2016-09-11 Sist oppdatert: 2019-04-05
    8. Tidal current phasing along the coast of Norway
    Åpne denne publikasjonen i ny fane eller vindu >>Tidal current phasing along the coast of Norway
    2016 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    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.

    Emneord
    Tidal energy, tidal phasing, variability optimization, significant impact factor, model scenarios
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-307495 (URN)
    Konferanse
    3rd International Asian Wave and Tidal Energy Conference (AWTEC), Singapore 24-28 oct, 2016
    Forskningsfinansiär
    StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development), 16-196
    Tilgjengelig fra: 2016-12-14 Laget: 2016-11-16 Sist oppdatert: 2018-01-13
    Fulltekst (pdf)
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  • 303.
    Carpman, Nicole
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP2014Inngår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Konferansepaper (Fagfellevurdert)
    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.

  • 304.
    Carpman, Nicole
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Thomas, Karin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Tidal current phasing along the coast of Norway2016Konferansepaper (Fagfellevurdert)
    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.

  • 305.
    Carpman, Nicole
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Thomas, Karin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Tidal resource characterization in the Folda Fjord, Norway2016Inngår i: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, s. 27-44Artikkel i tidsskrift (Fagfellevurdert)
    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.

    Fulltekst (pdf)
    fulltext
  • 306.
    Castellucci, Valeria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sea Level Compensation System for Wave Energy Converters2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The wave energy converter developed at Uppsala University consists of a linear generator at the seabed driven by the motion of a buoy on the water surface. The energy absorbed by the generator is negatively affected by variations of the mean sea level caused by tides, changes in barometric pressure, strong winds, and storm surges.

    The work presented in this doctoral thesis aims to investigate the losses in energy absorption for the present generation wave energy converter due to the effect of sea level variations, mainly caused by tides. This goal is achieved through the modeling of the interaction between the waves and the point absorber. An estimation of the economic cost that these losses imply is also made. Moreover, solutions on how to reduce the negative effect of sea level variations are discussed. To this end, two compensation systems which adjust the length of the connection line between the floater and the generator are designed, and the first prototype is built and tested near the Lysekil research site.

    The theoretical study assesses the energy loss at about 400 coastal points all over the world and for one generator design. The results highlight critical locations where the need for a compensation system appears compelling. The same hydro-mechanic model is applied to a specific site, the Wave Hub on the west coast of Cornwall, United Kingdom, where the energy loss is calculated to be about 53 %. The experimental work led to the construction of a buoy equipped with a screw jack together with its control, measurement and communication systems. The prototype, suitable for sea level variations of small range, is tested and its performance evaluated. A second prototype, suitable for high range variations, is also designed and is currently under construction.

    One main conclusion is that including the compensation systems in the design of the wave energy converter will increase the competitiveness of the technology from an economic point of view by decreasing its cost per kWh. The need for a cost-effective wave energy converter with increased survivability emphasizes the importance of the presented research and its future development.

    Delarbeid
    1. Influence of Sea State and Tidal Height on Wave Power Absorption
    Åpne denne publikasjonen i ny fane eller vindu >>Influence of Sea State and Tidal Height on Wave Power Absorption
    Vise andre…
    2017 (engelsk)Inngår i: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 42, nr 3, s. 566-573Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The wave energy converter developed at Uppsala University (Uppsala, Sweden) consists of a linear generator placed on the seabed and driven by the motion of a buoy on the water surface. The buoy is connected to the moving part of the linear generator, the translator, which is made of ferrite magnets. The translator moves vertically inducing voltage in the windings of a fixed component, the so-called stator. The energy conversion of the linear generator is affected by the sea state and by variations of mean sea level. The sea state influences the speed and the stroke length of the translator, while the variation of tidal level shifts the average position of the translator with respect to the center of the stator. The aim of this study is to evaluate the energy absorption of the wave energy converter at different locations around the world. This goal is achieved by developing a hydromechanic model which analyses the optimum generator damping factor for different wave climates and the power absorbed by the generator, given a fixed geometry of the buoy and a fixed stroke length of the translator. Economic considerations regarding the optimization of the damping factor are included within the paper. The results suggest a nominal damping factor and show the power absorption losses at various locations, each of them characterized by a different wave climate and tidal range. The power losses reach up to 67% and in many locations a tidal compensation system, included in the design of the wave energy converter, is strongly motivated.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-295597 (URN)10.1109/JOE.2016.2598480 (DOI)000405673800007 ()
    Forskningsfinansiär
    Swedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)Carl Tryggers foundation
    Tilgjengelig fra: 2016-06-08 Laget: 2016-06-08 Sist oppdatert: 2017-10-24bibliografisk kontrollert
    2. Impact of Tidal Level Variations on the Wave Energy Absorption at Wave Hub
    Åpne denne publikasjonen i ny fane eller vindu >>Impact of Tidal Level Variations on the Wave Energy Absorption at Wave Hub
    2016 (engelsk)Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, nr 10, artikkel-id 843Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    Emneord
    wave energy converter (WEC), tides, Wave Hub, energy absorption, economic analysis
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-295599 (URN)10.3390/en9100843 (DOI)000388578800084 ()
    Forskningsfinansiär
    Swedish Research CouncilÅForsk (Ångpanneföreningen's Foundation for Research and Development)Carl Tryggers foundation
    Tilgjengelig fra: 2016-06-08 Laget: 2016-06-08 Sist oppdatert: 2017-11-30bibliografisk kontrollert
    3. Tidal effect compensation system for point absorbing wave energy converters
    Åpne denne publikasjonen i ny fane eller vindu >>Tidal effect compensation system for point absorbing wave energy converters
    2013 (engelsk)Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 51, s. 247-254Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Recent studies show that there is a correlation between water level and energy absorption values for the studied wave energy converters: the absorption decreases when the water levels deviate from average. The situation appears during tides when the water level changes significantly. The main objective of the paper is to present a first attempt to increase the energy absorption during tides by designing and realizing a small-scale model of a point absorber equipped with a device that is able to adjust the length of the rope connected to the generator. The adjustment is achieved by a screw that moves upwards in the presence of low tides and downwards in the presence of high tides. Numerical results as well as experimental tests suggest that the solution adopted to minimize the tidal effect on the power generation shows potential for further development.

    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-194181 (URN)10.1016/j.renene.2012.09.043 (DOI)000312922000032 ()
    Tilgjengelig fra: 2013-02-13 Laget: 2013-02-11 Sist oppdatert: 2017-12-06
    4. Algorithm for the Calculation of the Translator Position in Permanent Magnet Linear Generators
    Åpne denne publikasjonen i ny fane eller vindu >>Algorithm for the Calculation of the Translator Position in Permanent Magnet Linear Generators
    2014 (engelsk)Inngår i: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 6, nr 6, s. 063102-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A permanent magnet linear generator for direct drive wave energy converters is a suitable power take-off system for ocean wave energy extraction, especially when coupled with a point absorbing buoy via a connection line. The performance of the linear generator is affected by the excursion of the translator along the stator. The optimal stroke is achieved when the midpoint of the oscillations coincides with the center of the stator. However, sea level changes due to, e.g., tides will shift these oscillations. This paper proposes a model able to detect the position of the translator from the generator output voltage. The algorithm will be integrated in the control system of a mechanical device that adjusts the length of the connection line in order to center the average position of the translator with the center of the stator. Thereby, the output power from the wave energy converter increases, and the mechanical stresses on the hull of the generator decrease. The results obtained by the model show good agreement with the experimental results from two linear generators, L2 and L3, deployed in the Lysekil wave energy research site, Sweden. The theoretical results differ from the experimental results by −4 mm for L2 and 21 mm for L3 with a standard deviation of 27 mm and 31 mm, respectively.

    Emneord
    ocean waves, permanent magnet generators, stators, wave power generation, linear machines
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-237446 (URN)10.1063/1.4900553 (DOI)000347152500003 ()
    Tilgjengelig fra: 2014-12-02 Laget: 2014-12-02 Sist oppdatert: 2017-12-05
    5. Wireless System for Tidal Effect Compensation in the Lysekil Research Site
    Åpne denne publikasjonen i ny fane eller vindu >>Wireless System for Tidal Effect Compensation in the Lysekil Research Site
    Vise andre…
    2012 (engelsk)Inngår i: Proceedings of the ASME 31st International Conference on Ocean, Offshore and Arctic Engineering, vol. 7, 2012, s. 293-298Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    This paper describes, firstly, the rope adjustment device for wave energy converters (WECs) to minimize the tidal effect on the electricity production and, secondly, a wireless communication network between point absorbing WECs in the Lysekil Research Site and a computer station at the Department of Engineering Sciences at Uppsala University. The device is driven by a motor that activates when the main water level deviates from the average. The adjustment is achieved through a screw that moves upwards during low tides and downwards during high tides. For the purpose of testing the device in the research site, a wireless connection between the buoy in the sea and a computer on land will be designed. A sensor located close to the research site monitors the sea water level and, every time a significant variation is registered, it sends wirelessly a signal to the data logger that controls the power to the motor The position of the screw is observed by a second sensor and the measurements are retrieved back to Uppsala via GSM connection. The full scale device is tested in the lab and it is demonstrated to work properly, requiring less than 750 W to lift and lower different loads. Moreover, the wireless communication network is designed and once it will be built, it will allow to recall and store data, send information from one node of the system to another, monitor the proper functioning of the device and modify the control as desired.

    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-190207 (URN)10.1115/OMAE2012-83361 (DOI)000324507000036 ()978-0-7918-4494-6 (ISBN)
    Konferanse
    31st International Conference on Ocean, Offshore and Arctic Engineering, July 1-6, 2012 Rio de Janeiro, Brazil
    Tilgjengelig fra: 2013-01-07 Laget: 2013-01-07 Sist oppdatert: 2016-10-06bibliografisk kontrollert
    6. Control System for Compensator of Mean Sea Level Variations at the Lysekil Research Site
    Åpne denne publikasjonen i ny fane eller vindu >>Control System for Compensator of Mean Sea Level Variations at the Lysekil Research Site
    2014 (engelsk)Konferansepaper, Publicerat paper (Annet vitenskapelig)
    sted, utgiver, år, opplag, sider
    Japan, Tokyo: , 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-237524 (URN)
    Konferanse
    2nd Asian Wave and Tidal Energy Conference
    Tilgjengelig fra: 2014-12-03 Laget: 2014-12-03 Sist oppdatert: 2017-10-08
    7. Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
    Åpne denne publikasjonen i ny fane eller vindu >>Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
    2015 (engelsk)Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, nr 4, s. 3272-3291Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-255300 (URN)10.3390/en8043272 (DOI)000353963400045 ()
    Tilgjengelig fra: 2015-06-18 Laget: 2015-06-15 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    8. Tidal Effect Compensation System Design for High Range Sea Level Variations
    Åpne denne publikasjonen i ny fane eller vindu >>Tidal Effect Compensation System Design for High Range Sea Level Variations
    2015 (engelsk)Konferansepaper, Poster (with or without abstract) (Fagfellevurdert)
    Abstract [en]

    The working principle of the wave energy converter (WEC) from Uppsala University is a heaving point absorber with directly driven linear generator placed on the seabed. The heave motion of the buoy is transmitted to the generator via a steel cable. When tides occur, the sea level changes, and thus making the WEC works below optimal condition. This system is designed so that the WEC is able to work at sea level variation up to 8 meters. A compensation system is designed to continuously make the WEC work in its optimal condition even at different sea levels. We present a mechanical system and its control algorithm that monitor and control the length of the connecting line. The connecting line is consist of a steel wire and a steel chain connected together. The mechanical part of the system is the winch that retracts or releases the steel chain that connects the translator and the buoy at the water surface. The rotation of the winch is controlled by a motor with the help of microcontrollers and several sensors for accuracy and feedback. The result from simulation showed that the system works fine. The approach of compensating the wire length connecting the buoy and the translator allow more flexibility to WEC to work in the area with high sea level variation.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-286598 (URN)
    Konferanse
    Proceedings of the 11th European Wave and Tidal Energy Conference 6-11th Sept 2015, Nantes, France
    Tilgjengelig fra: 2016-04-21 Laget: 2016-04-21 Sist oppdatert: 2019-04-05
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  • 307.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Abrahamsson, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Kamf, Tobias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters2015Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, nr 4, s. 3272-3291Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.

    Fulltekst (pdf)
    fulltext
  • 308.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Abrahamsson, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Svensson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Algorithm for the Calculation of the Translator Position in Permanent Magnet Linear Generators2014Inngår i: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 6, nr 6, s. 063102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A permanent magnet linear generator for direct drive wave energy converters is a suitable power take-off system for ocean wave energy extraction, especially when coupled with a point absorbing buoy via a connection line. The performance of the linear generator is affected by the excursion of the translator along the stator. The optimal stroke is achieved when the midpoint of the oscillations coincides with the center of the stator. However, sea level changes due to, e.g., tides will shift these oscillations. This paper proposes a model able to detect the position of the translator from the generator output voltage. The algorithm will be integrated in the control system of a mechanical device that adjusts the length of the connection line in order to center the average position of the translator with the center of the stator. Thereby, the output power from the wave energy converter increases, and the mechanical stresses on the hull of the generator decrease. The results obtained by the model show good agreement with the experimental results from two linear generators, L2 and L3, deployed in the Lysekil wave energy research site, Sweden. The theoretical results differ from the experimental results by −4 mm for L2 and 21 mm for L3 with a standard deviation of 27 mm and 31 mm, respectively.

  • 309.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Eriksson, Markus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Apelfröjd, Senad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Wireless System for Tidal Effect Compensation in the Lysekil Research Site2012Inngår i: Proceedings of the ASME 31st International Conference on Ocean, Offshore and Arctic Engineering, vol. 7, 2012, s. 293-298Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper describes, firstly, the rope adjustment device for wave energy converters (WECs) to minimize the tidal effect on the electricity production and, secondly, a wireless communication network between point absorbing WECs in the Lysekil Research Site and a computer station at the Department of Engineering Sciences at Uppsala University. The device is driven by a motor that activates when the main water level deviates from the average. The adjustment is achieved through a screw that moves upwards during low tides and downwards during high tides. For the purpose of testing the device in the research site, a wireless connection between the buoy in the sea and a computer on land will be designed. A sensor located close to the research site monitors the sea water level and, every time a significant variation is registered, it sends wirelessly a signal to the data logger that controls the power to the motor The position of the screw is observed by a second sensor and the measurements are retrieved back to Uppsala via GSM connection. The full scale device is tested in the lab and it is demonstrated to work properly, requiring less than 750 W to lift and lower different loads. Moreover, the wireless communication network is designed and once it will be built, it will allow to recall and store data, send information from one node of the system to another, monitor the proper functioning of the device and modify the control as desired.

  • 310.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Eriksson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Impact of Tidal Level Variations on the Wave Energy Absorption at Wave Hub2016Inngår i: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, nr 10, artikkel-id 843Artikkel i tidsskrift (Fagfellevurdert)
    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.

    Fulltekst (pdf)
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  • 311.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    García-Terán, Jessica
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Eriksson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Padman, Laurence
    Earth & Space Res, Corvallis, OR 97333 USA.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Influence of Sea State and Tidal Height on Wave Power Absorption2017Inngår i: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 42, nr 3, s. 566-573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wave energy converter developed at Uppsala University (Uppsala, Sweden) consists of a linear generator placed on the seabed and driven by the motion of a buoy on the water surface. The buoy is connected to the moving part of the linear generator, the translator, which is made of ferrite magnets. The translator moves vertically inducing voltage in the windings of a fixed component, the so-called stator. The energy conversion of the linear generator is affected by the sea state and by variations of mean sea level. The sea state influences the speed and the stroke length of the translator, while the variation of tidal level shifts the average position of the translator with respect to the center of the stator. The aim of this study is to evaluate the energy absorption of the wave energy converter at different locations around the world. This goal is achieved by developing a hydromechanic model which analyses the optimum generator damping factor for different wave climates and the power absorbed by the generator, given a fixed geometry of the buoy and a fixed stroke length of the translator. Economic considerations regarding the optimization of the damping factor are included within the paper. The results suggest a nominal damping factor and show the power absorption losses at various locations, each of them characterized by a different wave climate and tidal range. The power losses reach up to 67% and in many locations a tidal compensation system, included in the design of the wave energy converter, is strongly motivated.

  • 312.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Kamf, Tobias
    Hai, Ling
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Control System for Compensator of Mean Sea Level Variations at the Lysekil Research Site2014Konferansepaper (Annet vitenskapelig)
  • 313.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Strömstedt, Erland
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sea level variability in the Swedish Exclusive Economic Zone and adjacent seawaters: influence on a point absorbing wave energy converter2019Inngår i: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 15, s. 1517-1529Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Low-frequency sea level variability can be a critical factor for several wave energy converter (WEC) systems, for instance, linear systems with a limited stroke length. Consequently, when investigating suitable areas for deployment of those WEC systems, sea level variability should be taken into account. In order to facilitate wave energy developers finding the most suitable areas for wave energy park installations, this paper describes a study that gives them additional information by exploring the annual and monthly variability of the sea level in the Baltic Sea and adjacent seawaters, with a focus on the Swedish Exclusive Economic Zone. Overall, 10 years of reanalysis data from the Copernicus project have been used to conduct this investigation. The results are presented by means of maps showing the maximum range and the standard deviation of the sea level with a horizontal spatial resolution of about 1 km. A case study illustrates how the results can be used by the WEC developers to limit the energy absorption loss of their devices due to sea level variation. Depending on the WEC technology one wants to examine, the results lead to different conclusions. For the Uppsala point absorber L12 and the sea state considered in the case study, the most suitable sites where to deploy WEC parks from a sea level variation viewpoint are found in the Gotland basins and in the Bothnian Sea, where the energy loss due to sea level variations is negligible.

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  • 314.
    Castellucci, Valeria
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Waters, Rafael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Eriksson, Markus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Tidal effect compensation system for point absorbing wave energy converters2013Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 51, s. 247-254Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent studies show that there is a correlation between water level and energy absorption values for the studied wave energy converters: the absorption decreases when the water levels deviate from average. The situation appears during tides when the water level changes significantly. The main objective of the paper is to present a first attempt to increase the energy absorption during tides by designing and realizing a small-scale model of a point absorber equipped with a device that is able to adjust the length of the rope connected to the generator. The adjustment is achieved by a screw that moves upwards in the presence of low tides and downwards in the presence of high tides. Numerical results as well as experimental tests suggest that the solution adopted to minimize the tidal effect on the power generation shows potential for further development.

  • 315.
    Catarina, Sparre
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Scenarier för framtida effektbalans i elområde tre2019Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
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  • 316.
    Cederholm, Simon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Verification of the program PowerGrid and establishment of reference grid for calculations2015Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Fortum Distribution AB uses a program called PowerGrid (PG) in its daily work. PG is a combined Network information system and grid calculation program. The development of this program is an ongoing process, so Fortum desired a reference program be set up as a means of controlling the continued accuracy of PG’s calculation results. Fortum is aware that PG has had difficulties in calculating some grid designs. An important goal, therefore, is to verify if these problems still exist so that Fortum if so can put increased pressure on their program developer to resolve them.

    This thesis includes work on 9 different grid set-ups that were known or thought to cause problems in PG. They are drawn up and calculated in PG and then modeled in Matlab where e.g. power flow and short-circuit calculations are carried out. Results are compared, the goal being to discover problems and deviations in PG and to understand more about how PG works.

    In short, a number of problems are discovered with PG’s calculations, and most grid set-ups that were suspected to be problematic are confirmed to be so. The largest problems occur when alternatives to the single 2-winded main-transformer set-up are tested. Otherwise, it is in the transitions between voltage levels that most of the problems arise. A related observation is that having more than one medium-voltage level or more than one low-voltage level is difficult for PG to handle.

    Finally, an Excel macro is introduced – a macro that can be used to compare results from different PG calculation engines and highlight any found differences. In short, it can be used as a quick-check before more thorough investigations are launched.

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  • 317. Chandimal, APL
    et al.
    Hettiarachchi, Pasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Nanayakkara, Sankha
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Rahman, Mahbubur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Fernando, M.
    Special attention to impedance of conductivity enhancing backfill materials2016Konferansepaper (Fagfellevurdert)
  • 318. Chandimal, Lasantha
    et al.
    Hettiarachchi, Pasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Nanayakkara, Sankha
    Sapumanage, Nilantha
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Rahman, Mahbubur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Impedance behaviour of earth enhancing compound under lightning transient conditions2018Konferansepaper (Fagfellevurdert)
  • 319.
    Chatzigiannakou, Maria A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ekergård, Boel
    Högskolan Väst.
    Temiz, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Numerical analysis of an Uppsala University WEC deployment by a barge for different sea states2020Inngår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, artikkel-id 107287Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wave energy converters (WECs) have been deployed onshore, nearshore, and offshore to convert ocean wave movement into electricity. The exploitation of renewable energy sources has restrictions; in the case of wave energy, high installation, maintenance, and decommissioning costs have limited their commercial use. Moreover, these offshore operations can be compromised by safety issues. This paper draws attention to offshore operation safety of a WEC developed by Uppsala University. Specifically, this paper investigates what sea states are suitable for the safe deployment of a WEC from a barge. This study follows recommendations in DNV-RP-H103 for analysis of offshore operations, namely lifting through the wave zone. ANSYS Aqwa is used to find hydrodynamic forces acting on a typical barge, using frequency domain analysis. Based on these hydrodynamic simulation results and methodology given in DNV-RP-H103, tables are created to show the sea states that would allow for the safe installation of a WEC using a typical barge. Considered sea states have significant wave heights varying between 0 m and 3 m and the wave zero crossing periods varying between 3 s and 13 s. The WEC submersions are considered between 0 m and 7 m, i.e. when the WEC is in the air until it is fully submerged.

  • 320.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Dolguntseva, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ekström, Rickard
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Offshore Deployment of Marine Substation in the Lysekil Research Site2015Konferansepaper (Fagfellevurdert)
  • 321.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Dolguntseva, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site2014Inngår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Konferansepaper (Fagfellevurdert)
    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.

  • 322.
    Chatzigiannakou, Maria Angeliki
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Efficiency evaluation of the offshore deployments of wave energy converters and marine substations2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    fulltext
  • 323.
    Chatzigiannakou, Maria Angeliki
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Offshore deployments of marine energy converters2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The depletion warning of non-renewable resources, such as gas, coal and oil, and the imminent effects of climate change turned the attention to clean and fossil fuel-free generated electricity. University research groups worldwide are studying solar, wind, geothermal, biomass and ocean energy harvesting. The focus of this thesis is the wave and marine current energy researched at the division of Electricity at Uppsala University (UU). 

    The main drawbacks that hinder the commercialization of marine energy converter devices is a high installation, operation, maintenance and decommissioning cost. Furthermore, these processes are highly weather dependent and thus, can be time consuming beyond planning. In this thesis, an evaluation of the cost, time and safety efficiency of the devices’ offshore deployment (both wave and marine current), and a comparative evaluation regarding the safety in the use of divers and remotely operated vehicles (ROVs) are conducted. Moreover, a risk analysis study for a common deployment barge while installing an UU wave energy converter (WEC) is presented with the aim to investigate the failure of the crane hoisting system.

    The UU wave energy project have been initiated in 2001, and since then 14 WECs of various designs have been developed and deployed offshore, at the Lysekil research site (LRS), on the Swedish west coast and in Åland, Finland. The UU device is a point absorber with a linear generator power take off. It is secured on the seabed by a concrete gravity foundation. The absorbed wave energy is transmitted to shore through the marine substation (MS) where all the generators are interconnected. In 2008 an UU spin-off company, Seabased AB (SAB), was established and so far has developed and installed several WECs and two MSs, after the UU devices main principle. SAB deployments were conducted in Sotenäs, Sweden, at the Maren test site (MTS) in Norway; and in Ada Foah, Ghana. The active participation and the thorough study of the above deployments led to a cost, time and safety evaluation of the methods followed. Four main methods were identified and the most suitable one can be chosen depending on the deployment type, for example, for single or mass device deployment.

    The first UU full scale marine current energy converter (MCEC) was constructed in 2007 at the Ångström Laboratory and deployed at Söderfors, in the river Dalälven in March 2013. The UU turbine is of a vertical axis type and is connected to a directly driven permanent magnet synchronous generator of a low-speed. With this deployment as an example, four MCEC installation methods were proposed and evaluated in terms of cost and time efficiency.

    A comparative study on the use of divers and ROVs for the deployment and maintenance of WECs at the LRS has been carried out, showing the potential time and costs saved when using ROVs instead of divers in underwater operations. The main restrictions when using divers and ROVs were presented. Most importantly, the modelling introduced is generalized for most types of wave energy technologies, since it does not depend on the structure size or type.

    Finally, a table of safe launch operation of a WEC is presented. In this table the safe, restrictive and prohibitive sea states are found for a single WEC deployment, using a barge and a crane placed on it. The table can be utilized as a guidance for offshore operations safety and can be extended for a variety of device types and vessels.

    Delarbeid
    1. Offshore Deployments of Wave Energy Converters by Seabased Industry AB
    Åpne denne publikasjonen i ny fane eller vindu >>Offshore Deployments of Wave Energy Converters by Seabased Industry AB
    2017 (engelsk)Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, nr 2, artikkel-id 15Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Since 2008, Seabased Industry AB (SIAB) has manufactured and deployed several units of wave energy converters (WECs) of different design. The WECs are linear generators with point absorber buoy systems that are placed on the seabed, mounted on a gravitation concrete foundation. These deployments have taken place in different areas, using different deployment vessels. Offshore deployments of WECs and underwater substations have so far been complicated procedures, that were both expensive and time-consuming. The focus of this paper is to discuss these deployments in terms of economy and time efficiency, as well as safety. Because seven vessels have been used to facilitate the deployments, an evaluation on the above basis is carried out for them. The main conclusions and certain solutions are presented for the various problems encountered during these deployments and the vessel choice is discussed. It is found that the offshore deployment process can be optimized in terms of cost, time efficiency and safety with a careful vessel choice, use of the latest available technologies and detailed planning and organizing.

    Emneord
    offshore deployment; wave energy converter; specialized vessel; underwater substation
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-318633 (URN)10.3390/jmse5020015 (DOI)000423689700001 ()
    Tilgjengelig fra: 2017-03-27 Laget: 2017-03-27 Sist oppdatert: 2019-04-01bibliografisk kontrollert
    2. Offshore Deployments of Wave Energy Converters by Uppsala University
    Åpne denne publikasjonen i ny fane eller vindu >>Offshore Deployments of Wave Energy Converters by Uppsala University
    2017 (engelsk)Inngår i: Artikkel i tidsskrift (Fagfellevurdert) Submitted
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-329835 (URN)
    Tilgjengelig fra: 2017-09-21 Laget: 2017-09-21 Sist oppdatert: 2019-04-01
    3. Marine Current Energy Converters deployments modelling
    Åpne denne publikasjonen i ny fane eller vindu >>Marine Current Energy Converters deployments modelling
    (engelsk)Inngår i: Artikkel i tidsskrift (Annet vitenskapelig) Submitted
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-380858 (URN)
    Tilgjengelig fra: 2019-04-01 Laget: 2019-04-01 Sist oppdatert: 2019-04-01
    4. Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
    Åpne denne publikasjonen i ny fane eller vindu >>Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
    Vise andre…
    2018 (engelsk)Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, nr 2, artikkel-id 39Artikkel i tidsskrift (Fagfellevurdert) 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.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-348816 (URN)10.3390/jmse6020039 (DOI)000436558500011 ()
    Forskningsfinansiär
    StandUpEU, FP7, Seventh Framework Programme, 607656Swedish Energy Agency
    Tilgjengelig fra: 2018-04-17 Laget: 2018-04-17 Sist oppdatert: 2019-04-01bibliografisk kontrollert
    5. Risk assessment of deployment of an Uppsala University wave energy converter from a barge in different sea states.
    Åpne denne publikasjonen i ny fane eller vindu >>Risk assessment of deployment of an Uppsala University wave energy converter from a barge in different sea states.
    (engelsk)Inngår i: Artikkel i tidsskrift (Annet vitenskapelig) Submitted
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-380859 (URN)
    Tilgjengelig fra: 2019-04-01 Laget: 2019-04-01 Sist oppdatert: 2019-04-01
    6. Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site
    Åpne denne publikasjonen i ny fane eller vindu >>Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site
    2014 (engelsk)Inngår i: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Konferansepaper, Publicerat paper (Fagfellevurdert)
    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.

    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-222445 (URN)10.1115/OMAE2014-23396 (DOI)000363499000023 ()978-0-7918-4553-0 (ISBN)
    Konferanse
    Proceedings of the 33rd International Conference on Ocean, Offshore and Arctic Engineering, ASME 2014
    Tilgjengelig fra: 2014-04-11 Laget: 2014-04-10 Sist oppdatert: 2019-04-01bibliografisk kontrollert
    7. Offshore Deployment of Marine Substation in the Lysekil Research Site
    Åpne denne publikasjonen i ny fane eller vindu >>Offshore Deployment of Marine Substation in the Lysekil Research Site
    2015 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    Emneord
    energy conversion; marine substation; offshore deployment; offshore deployment optimization; renewable energy.
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-248539 (URN)
    Konferanse
    25th International Ocean and Polar Engineering Conference, ISOPE 2015, June 21-26, 2015, Kona, Big Island, Hawaii
    Tilgjengelig fra: 2015-03-31 Laget: 2015-03-31 Sist oppdatert: 2019-04-01
    8. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Åpne denne publikasjonen i ny fane eller vindu >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
    Vise andre…
    2015 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    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.

    Emneord
    Wave energy, point absorber, experiments, arrays, generators, ROVs
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-265218 (URN)
    Konferanse
    Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
    Tilgjengelig fra: 2015-10-26 Laget: 2015-10-26 Sist oppdatert: 2019-08-19bibliografisk kontrollert
    9. Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
    Åpne denne publikasjonen i ny fane eller vindu >>Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
    Vise andre…
    2018 (engelsk)Inngår i: 2018 5th International Conference on Electric Power and Energy Conversion Systems (EPECS), 2018Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    This paper provides an overview of electric power conversion system installed at the Lysekil research site, located at the west coast of Sweden. The electric power conversion system consists of rectifiers, rectifying the power from the wave energy converters, a DC-link and a grid-tied inverter. The paper focuses on the performance of the inverter and the filter and presents experimental results obtained during the grid integration.

    Serie
    International Conference on Electric Power and Energy Conversion Systems, ISSN 2325-2677
    Emneord
    wave energy converter (WEC), wave energy havesting, grid integration, LCL filter response
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-373349 (URN)10.1109/EPECS.2018.8443488 (DOI)000450072100010 ()978-1-5386-6457-5 (ISBN)
    Konferanse
    5th International Conference on Electric Power and Energy Conversion Systems (EPECS), Kitakyushu, April 23-25, 2018
    Forskningsfinansiär
    Swedish Research Council, 2015-03126Swedish Energy AgencyStandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development)
    Tilgjengelig fra: 2019-01-15 Laget: 2019-01-15 Sist oppdatert: 2020-05-15bibliografisk kontrollert
    10. Grid Integration and a Power Quality Assessment of a Wave Energy Park.
    Åpne denne publikasjonen i ny fane eller vindu >>Grid Integration and a Power Quality Assessment of a Wave Energy Park.
    Vise andre…
    (engelsk)Inngår i: Artikkel i tidsskrift (Annet vitenskapelig) Submitted
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-380860 (URN)
    Tilgjengelig fra: 2019-04-01 Laget: 2019-04-01 Sist oppdatert: 2019-04-01
    Fulltekst (pdf)
    fulltext
    Download (jpg)
    presentationsbild
  • 324.
    Chatzigiannakou, Maria Angeliki
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ulvgård, Liselotte
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Dolguntseva, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Offshore Deployments of Wave Energy Converters by Uppsala University2017Inngår i: Artikkel i tidsskrift (Fagfellevurdert)
  • 325.
    Chatzigiannakou, Maria Angiliki
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Dolguntseva, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Offshore Deployments of Wave Energy Converters by Seabased Industry AB2017Inngår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, nr 2, artikkel-id 15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since 2008, Seabased Industry AB (SIAB) has manufactured and deployed several units of wave energy converters (WECs) of different design. The WECs are linear generators with point absorber buoy systems that are placed on the seabed, mounted on a gravitation concrete foundation. These deployments have taken place in different areas, using different deployment vessels. Offshore deployments of WECs and underwater substations have so far been complicated procedures, that were both expensive and time-consuming. The focus of this paper is to discuss these deployments in terms of economy and time efficiency, as well as safety. Because seven vessels have been used to facilitate the deployments, an evaluation on the above basis is carried out for them. The main conclusions and certain solutions are presented for the various problems encountered during these deployments and the vessel choice is discussed. It is found that the offshore deployment process can be optimized in terms of cost, time efficiency and safety with a careful vessel choice, use of the latest available technologies and detailed planning and organizing.

    Fulltekst (pdf)
    fulltext
  • 326.
    Chen, WenChuang
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China..
    Dolguntseva, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Savin, Andrej
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Zhang, YongLiang
    Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China..
    Li, Wei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Svensson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves2017Inngår i: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 63, s. 90-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.

  • 327. Chernitskiy, S. V.
    et al.
    Gann, V. V.
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Static Neutronic Calculation of a Fusion Neutron Source2014Inngår i: Problems of Atomic Science and Technology, ISSN 1562-6016, nr 6, s. 12-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX numerical code has been used to model a fusion neutron source based on a combined stellarator-mirror trap. Calculation results for the neutron flux and spectrum inside the first wall are presented. Heat load and irradiation damage on the first wall are calculated.

  • 328. Chernitskiy, S. V.
    et al.
    Moiseenko, V. E.
    Noack, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Neutronic Model of a Stellarator-Mirror Fusion-Fission Hybrid2013Inngår i: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 63, nr 1T, s. 322-324Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX numerical code has been used to model the neutron transport in a mirror based fusion-fission reactor. The purpose is to find a principal design of the fission mantle which fits to the neutron source and to calculate the leakage of neutrons through the mantle surface of the fission reactor. The fission reactor part has a cylindrical shape with an outer radius 1.66 m and a 4 m length. The fuel has the isotopic composition of the spent nuclear fuel from PWR after uranium-238 removal. Inside the fission reactor core is a vacuum chamber with a radius 0.5 m containing a 4 m long hot plasma producing fusion neutrons. To sustain the hot ion plasma which is responsible for the fusion neutron production, neutral beam injection is considered. Calculation results for the radial leakage of neutrons through the mantle surface of the fission reactor are presented. These calculations predict that the power released with neutrons from the reactor to outer space would be small and will not exceed the value of 6 kW while the reactor thermal power is 1 GWth.

  • 329. Chernitskiy, S. V.
    et al.
    Moiseenko, V. E.
    Noack, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Abdullayev, A.
    Neutronic Model of a Stellarator-Mirror Fusion-Fission Hybrid2012Inngår i: PROBL ATOM SCI TECH, ISSN 1562-6016, nr 6, s. 58-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX numerical code has been used to model a compact concept for a fusion-fission reactor based on a combined stellarator-mirror trap. Calculation results for the radial leakage of neutrons through the mantle surface of the fission reactor are presented.

  • 330. Chernitskiy, S. V.
    et al.
    Moiseenko, V. E.
    Noack, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Abdullayev, A.
    Static neutronic calculation of a subcritical transmutation stellarator-mirror fusion-fission hybrid2014Inngår i: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 72, s. 413-420Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX Monte-Carlo code has been used to model the neutron transport in a sub-critical fast fission reactor driven by a fusion neutron source. A stellarator-mirror device is considered as the fusion neutron source. The principal composition for a fission blanket of a mirror fusion-fission hybrid is devised from the calculations. Heat load on the first wall, the distribution of the neutron fields in the reactor, the neutron spectrum and the distribution of energy release in the blanket are calculated. The possibility of tritium breeding inside the installation in quantities that meet the needs of the fusion neutron source is analyzed. The portion of the plasma column generates fusion neutrons that mainly do not reach the fission reactor core is proposed to be surrounded by a vessel filled with borated water to absorb the flying out neutrons. The flux of the neutrons escaping from the device to surrounding space is also calculated.

  • 331.
    Chernitskiy, S. V.
    et al.
    NSC KIPT, Nucl Fuel Cycle Sci & Technol Estab, Kharkov, Ukraine..
    Moiseenko, V. E.
    NSC KIPT, Inst Plasma Phys, Kharkov, Ukraine..
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Noack, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A fuel cycle for minor actinides burning in a stellarator-mirror fusion-fission hybrid2017Inngår i: PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, ISSN 1562-6016, nr 1, s. 36-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX Monte-Carlo code has been used to model a concept of a fusion-fission stellarator-mirror hybrid aimed for transmutation transuranic content from the spent nuclear fuel. A fuel cycle for the subcritical fusion-fission hybrid is investigated and discussed.

  • 332. Chernitskiy, S. V.
    et al.
    Moiseenko, V. E.
    Ågren, Olov
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Noack, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Abdullayev, A.
    Neutronic Model Of A Fusion Neutron Source2013Inngår i: Problems of Atomic Science and Technology, ISSN 1562-6016, nr 1, s. 61-63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The MCNPX numerical code has been used to model a fusion neutron source based on a combined stellarator-mirror trap. Calculation results for the neutron spectrum near the inner wall and radial leakage of neutrons through the mantle surface of the fusion neutron source are presented.

  • 333. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Application of electromagnetic fields of an accelerating charge to obtain the electromagnetic fields of a propagating current pulse2012Inngår i: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, s. 55-65Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    It was recently demonstrated that electromagnetic fields from accelerating charges can be utilized to evaluate the electromagnetic fields from lightning return strokes. It was documented in detail how to utilize the equations to calculate electromagnetic fields of various engineering return stroke models, both current propagation and current generation types.It was also demonstrated how the equations can be utilized to calculate radiation fields generated by currents propagating along transmission lines in the presence of bends. The basics of this technique are summarized in this chapter by applying it to evaluate the electromagnetic fields of a propagating current pulse.

  • 334. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Could Some Ball Lightning Observations be Optical Hallucinations Caused by Epileptic Seizures?2008Inngår i: The Open Atmospheric Science Journal, ISSN 1874-2823, Vol. 2, s. 101-105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The great difficulty of encompassing all observed features of ball lightning into a single theory makes it highly probable that many observations and experiences which have no connection to ball lightning are also categorized as ball lightning experiences. In this note we compare the eyewitness reports of ball lightning and the symptoms of epileptic seizures of the occipital lobe as described in the medical literature and show that a person experiencing such a seizure for the first time may believe that he has witnessed a ball lightning event. Since many of the ball lightning reports are associated with nearby lightning strikes, the possibility that the rapidly changing magnetic field of a close lightning strike could trigger an epileptic seizure is analyzed. The results show that the time derivative of the magnetic field in the vicinity of an intense lightning flash is strong enough to stimulate neurons in the brain. This strengthens the possibility of inducing seizures in the occipital lobe of a person located in the vicinity of lightning strikes.

  • 335. Cooray, Gerald
    et al.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Electromagnetic fields of a short electric dipole in free space - revisited2012Inngår i: PROG ELECTROMAGN RES, ISSN 1559-8985, Vol. 131, s. 357-373Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Maxwell's equations specify that electromagnetic radiation fields are generated by accelerating charges. However, the electromagnetic radiation fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r >> l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r(2), while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r(2) and 1/r(3).

  • 336.
    Cooray, V
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    On the concepts used in return stroke models applied in engineering practice2003Inngår i: Transactions IEEE (EMC), Vol. 45, s. 101-108Artikkel i tidsskrift (Fagfellevurdert)
  • 337.
    Cooray, V
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Some considerations on the Cooray-Rubinstein Formulation Used in Deriving the Horizontal Electric Field of Lightning Return Strokes Over Finitely Conducting Ground2002Inngår i: IEEE Transactions on Electromagnetic Compatibility, Vol. 44, nr 4, s. 560-566Artikkel i tidsskrift (Fagfellevurdert)
  • 338.
    Cooray, V
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Fernando, M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Gomes, C
    Sorensen, T
    The Fine Structure of Positive Return Stroke Radiation Fields2004Inngår i: IEEE Transactions on EMC, Vol. 46, s. 87-95Artikkel i tidsskrift (Fagfellevurdert)
  • 339.
    Cooray, V
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Montano, R
    Theethayi, N
    Zitnik, M
    Manyahi, M
    Scuka, V
    A channel base current model to represent both negative and positive first return strokes with connecting leaders2002Inngår i: Proceedings of the 26th International Conference on Lightning Protection, Cracow, Poland, 2002, s. 36-41Konferansepaper (Annet vitenskapelig)
  • 340.
    Cooray, V
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Zitnik, M
    Manyahi, M
    Montano, R
    Rahman, M
    Liu, Y
    Physical model of surge-current characteristics of buried vertical rods in the presence of soil ionisation2002Inngår i: Proceedings of the 26th International Conference on Lightning Protection, Cracow, Poland, 2002, s. 357-362Konferansepaper (Annet vitenskapelig)
  • 341.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A novel procedure to represent lightning return strokes: current dissipation return stroke models2009Inngår i: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, nr 3, s. 748-755Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Engineering return stroke models available in the literature can be divided into two categories, namely, current propagation models and current generation models. Based on the theory of pulse propagation along transmission lines in the presence of corona, a third procedure to describe return strokes, which, in fact, is the inverse of current generation models, is introduced. Models based on the new concept are called current dissipation models. In the current generation models, the corona currents generated by the neutralization of the corona sheath travel downward and the cumulative effects of these corona currents generate the return stroke current. In current dissipation models, the return stroke is initiated by a current pulse injected into the core of the leader channel at ground level. This injected current pulse travels upward with speed vc . If the return stroke channel is treated as a transmission line, then this speed is equal to the speed of light. The propagation of this pulse along the central core initiates the neutralization of the corona sheath leading to the release of corona currents into the central core. In contrast to current generation models in which corona currents travel downward, these corona currents travel upward along the core. The speed of propagation of the corona pulses upward along the core is also equal to vc. The corona currents, being of opposite polarity, lead to the dissipation of the injected current pulse. As in the case of current generation models, a current dissipation model can be described completely by any three of the following four parameters. They are: 1) channel base current; 2) spatial variation of the return stroke velocity; 3) spatial variation of the corona decay time constant; and 4) the spatial variation of the positive charge deposited by the return stroke on the leader channel. It is also shown that current propagation models available in the literature are special cases of current dissipation models.

  • 342.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A novel procedure to represent lightning strokes – current dissipation return stroke models2008Konferansepaper (Fagfellevurdert)
  • 343.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A return stroke model based purely on the current dissipation concept2015Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, nr Part A, s. 61-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A return stroke model based purely on the current dissipation concept is introduced. With three model parameters the model is capable of generating electric and magnetic fields that are in reasonable agreement with experimentally observed electromagnetic fields.

  • 344.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A review of simulation procedures utilized to study the attachment of lightning flashes to grounded structures2011Inngår i: CIGRE ELECTRA, Vol. 257Artikkel i tidsskrift (Fagfellevurdert)
  • 345.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Attachment of lightning flashes to grounded structures2012Inngår i: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, s. 765-787Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    A grounded structure can interact with a lightning flash in two different ways. It can interact with either a downward or an upward lightning flash. The initiation of a downward lightning flash takes place in the cloud, whereas in the case of upward lightning flash, the point of initiation is usually at the tip of a tall structure. In other words, upward lightning flashes are created by the grounded structure itself. In this chapter, a brief description of various models used to study the lightning attachment is given together with some of their predictions.

  • 346.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Authora reply to comments on On the concepts used in return stroke models applied in engineering practice2003Inngår i: IEEE Transactions on EMC, Vol. 45Artikkel i tidsskrift (Fagfellevurdert)
  • 347.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Basic discharge processes in the atmosphere2012Inngår i: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, s. 65-85Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The main constituents of air in the Earth's atmosphere are nitrogen (78%), oxygen (20%), noble gases (1%), water vapour (0.03%), carbon dioxide (0.97%) and other trace gas species. In general, air is a good insulator and it can maintain its insulating properties until the applied electric field exceeds about 2.8 x 104 V/cm at standard atmospheric conditions (i.e. T= 293 K and P =1 atm). When the background electric field exceeds this critical value, the free electrons in air generated mainly by the high energetic radiation of cosmic rays and radio active gases generated from the Earth start accelerating in this electric field and gain enough energy between collisions with atoms and molecules to ionize other atoms. This cumulative ionization leads to an increase in the number of electrons initiating the electrical breakdown of air. The threshold electric field necessary for electrical breakdown of air is a function of atmospheric density. When the leaders reach an electrode of opposite polarity or a region of opposite charge density, a rapid neutralization of the charge on the leader takes place. This neutralization process is called a return stroke. The exact mechanism of the return stroke is not yet known, but different types of models have been developed to describe them. These models are described in several chapters of this book. Here, we will concentrate on the four discharge processes mentioned above. Some parts of this chapter are adopted and summarized from Reference 1 where an extensive description of basic physics of discharges is given.

  • 348.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Blixten - så fungerar naturens fyrverkeri2003Bok (Annet vitenskapelig)
  • 349.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Electric field of the return stroke channel2012Inngår i: 31st International Conference on Lightning Protection ICLP 2012, 2012, s. 6344241-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Return stroke models specify the temporal and spatial variation of the return stroke current along the channel. This information is sufficient to evaluate the temporal development of the electric field along the channel of the return stroke. In this paper the mathematical procedure necessary to do this is introduced. The derived equations can be combined with any return stroke model to calculate the power and energy dissipation during the return stroke.

  • 350.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Horizontal electric field above and under ground produced by lightning flashes2009Konferansepaper (Fagfellevurdert)
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