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  • 1.
    Ayob, Mohd Nasir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Malaysia Perlis, Sch Mechatron Engn, Arau 02600, Perlis, Malaysia.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Small-Scale Renewable Energy Converters for Battery Charging2018In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 6, no 1, article id 26Article in journal (Refereed)
    Abstract [en]

    This paper presents two wave energy concepts for small-scale electricity generation. In the presented case, these concepts are installed on the buoy of a heaving, point-absorbing wave energy converter (WEC) for large scale electricity production. In the studied WEC, developed by Uppsala University, small-scale electricity generation in the buoy is needed to power a tidal compensating system designed to increase the performance of the WEC in areas with high tides. The two considered and modeled concepts are an oscillating water column (OWC) and a heaving point absorber. The results indicate that the OWC is too small for the task and does not produce enough energy. On the other hand, the results show that a hybrid system composed of a small heaving point absorber combined with a solar energy system would be able to provide a requested minimum power of around 37.7W on average year around. The WEC and solar panel complement each other, as the WEC produces enough energy by itself during wintertime (but not in the summer), while the solar panel produces enough energy in the summer (but not in the winter).

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  • 2.
    Boström, Cecilia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Björklöf, Daniel
    Johansson, Tobias
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design proposal of electrical system for linear generator wave power plants2009In: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS, IEEE , 2009, p. 4180-4185Conference paper (Refereed)
    Abstract [en]

    This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed.

    The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.

  • 3.
    Crespo, Alejandro J.
    et al.
    Universidade de Vigo, Spain.
    Tagliafierro, Bonaventura
    Universidade de Vigo & UPC, Spain.
    Martınez-Estevez, Ivan
    Universidade de Vigo, Spain.
    Domınguez, Jose M.
    Universidade de Vigo, Spain.
    deCastro, Maite
    Universidade de Vigo, Spain.
    Gómez-Gesteira, Moncho
    Altomare, Corrado
    Brito, Moises
    Bernardo, Francisco
    Ferreira, Rui M.
    Capasso, Salvatore
    Viccione, Giacomo
    Quartier, Nicolas
    Stratigaki, Vasiliki
    Troch, Peter
    Simonetti, Irene
    Cappietti, Lorenzo
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Clemente, Daniel
    Rosa-Santos, Paulo
    Taveira-Pinto, Francisco
    Bacelli, Giorgio
    Coe, Ryan
    Fourtakas, Georgios
    Rogers, Benedict
    The University of Manchester, UK.
    Stansby, Peter
    The University of Manchester, UK.
    On the state-of-the-art of CFD simulations for wave energy converters within the open-source numerical framework of DualSPHysics2023In: Proceedings of the 15th European Wave and Tidal Energy Conference, Bilbao, 3-7 September 2023, European Wave and Tidal Energy Conference , 2023Conference paper (Refereed)
    Abstract [en]

    There are currently several types of devices capable of harnessing wave energy, exploiting a broad variety of physical transformation processes. These devices – known as Wave Energy Converters (WECs) – are developed to maximize their power output. However, there are still uncertainties about their response and survivability to loads induced by adverse environmental conditions, with a consequent increase of the Levelized Cost of Energy (LCOE), which prevents in fact their commercial diffusion. As evidenced by a large body of research, marine renewable energy devices need to have more robust design practices. To address this issue, we propose the CFD-based DualSPHysics toolbox as a support in the design stages. DualSPHysics is high-fidelity software inherently suited to numerically address most challenges posed by multiphysics simulations, which are required to reliably predict WEC response in situations well beyond operational conditions. It should be noted that WECs, generally, may be connected to the seabed and comprise mechanical systems named Power Take-Offs (PTO) used to convert the energy from waves into electricity or other usable energies. To reproduce these features, DualSPHysics benefits from coupling with the multiphysics library Project Chrono and the dynamic mooring model Moordyn+. In this work, the augmented DualSPHysics framework is utilised to simulate a range of very different types of WECs with a variety of elements, such as catenary connections, taut mooring lines, or linear and nonlinear PTO actuators. Version 5.2 of the open-source licensed code was recently released, making the numerical framework publicly available as one unit. This work aims to provide a numerical review of past applications, and to demonstrate how the same open-source code is able to simulate very different technologies.

    Specifically, this paper proposes routine modeling and validation procedures using the SPH-based solver DualSPHysics applied to five different WEC types: i) a moored point absorber (PA); ii) an oscillating wave surge converter (OWSC); iii) a floating OWSC (so called FOSWEC); iv) a wave energy hyperbaric converter (WEHC); and v) a multi-body attenuator (so called Multi-float M4). For each device listed above, we provide validation proof against physical model data for various components of the floater(s) and PTO related quantities, performed under specific sea conditions that aim to challenge their survivability. Within the scope of this research, we present the WEC response with respect to the degrees of freedom that really matter for each of the floatings due to hydrodynamic interactions (i.e., heave, surge, and pitch), along with quantities more intimately connected to the anchoring systems (e.g., line tension) or the mechanical apparatus (e.g., end-stopper force). The quality of the results, the discussion built upon them and the demonstrated solver exploitability to a wide range of WECs show that one software model can run all cases using the exact same methodology, which is of great value for the marine energy R&D community. Finally, we discuss future research objectives, which include the implementation of automation to apply open control systems and possible applications to subsets of WEC farm arrays and other floating energy harnessing devices.

  • 4.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hydrodynamic Modeling of the Energy Conversion from Ocean Waves to Electricity2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Research within wave energy conversion has seen a large increase during the last years. Several concepts are now taking the final steps towards commercialization. Conversion from wave energy for grid connection is a multi disciplinary task involving many challenges; one being the fact that the device has to be dimensioned for a nominal power and still be able to withstand the extreme powers in some of the harshest conditions on earth. The research and development of a concept based on a point absorber converting wave energy to a direct driven linear generator were initiated in 2002 at Uppsala University. Theoretical simulations have now been compared to offshore full scale experiments at the research test site. This thesis focuses on the hydrodynamic wave/device interaction for a Wave Energy Converter subjected to Swedish west coast wave climate. First conclusions on the Wave Energy Converters dynamics and energy absorption have been drawn based on earlier results. A thorough study of the sea state of Skagerrak and Kattegat has been made to asses the potential and get design parameters for the Wave Energy Converter. Based on that, a Wave Energy Converter model using potential linear wave theory and with the generator as a linear damper, has been developed to simulate the dynamics and power capture ratio. The model has also been used to simulate how biomass accumulated on the buoy will affect the dynamics. As a next step, the model has been further developed to simulate a two component system having optimum amplitude response at frequencies coinciding with Swedish west coast conditions. Results are presented for time series of real ocean wave data collected at the research test site as well as for empirical spectra. An enhanced amplitude response for the two component system is achieved by adding supplementary inertia by use of the added mass from a submerged body. Simulations show that the increased velocity in the two component system gives an increased power capture ratio by a factor of two compared to the regular system of a point absorber. The increased velocity also leads to a decrease in optimal damping for energy absorption with 60 %. The main weakness of the hydrodynamical modeling is thought to be the neglected viscosity that might lead to unpredicted energy losses, pointing out the direction for improvement and future work.

  • 5.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface.

    The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions.

    Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

    List of papers
    1. Offshore experiments on a direct-driven Wave Energy Converter
    Open this publication in new window or tab >>Offshore experiments on a direct-driven Wave Energy Converter
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    2007 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-14172 (URN)
    Conference
    Proceedings of the 7th European Wave and Tidal Energy Conference, 11-13 September 2007, Porto, Portugal.
    Available from: 2008-04-25 Created: 2008-04-25 Last updated: 2022-01-28
    2. Wave Climate off the Swedish West Coast
    Open this publication in new window or tab >>Wave Climate off the Swedish West Coast
    2009 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 34, no 6, p. 1600-1606Article in journal (Refereed) Published
    Abstract [en]

    This paper presents and discusses the wave climate off the Swedish west coast It is based on 8 years (1997-2004) of wave data from 13 sites, nearshore and offshore, in the Skagerrak and Kattegat. The data is a product of the WAM and SWAN wave models calibrated at one site by a wave measurement buoy. It is found that the average energy flux is approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the nearshore Skagerrak, and 2.4 kW/m in the Kattegat. One of the studied sites, i.e. site 9, is the location of a wave energy research site run by the Centre for Renewable Electric Energy Conversion at Uppsala University. This site has had a wave power plant installed since the spring of 2006, and another seven are planned to be installed during 2008. Wave energy as a renewable energy source was the driving interest that led to this study and the results are briefly discussed from this perspective.

    Keywords
    Wave climate, Wave power, Sea state, Extreme waves, Skagerrak, Kattegat
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97856 (URN)10.1016/j.renene.2008.11.016 (DOI)000264306500024 ()
    Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2017-12-14Bibliographically approved
    3. The Lysekil Wave Power Project: Status Update
    Open this publication in new window or tab >>The Lysekil Wave Power Project: Status Update
    Show others...
    2008 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97846 (URN)
    Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2022-01-28Bibliographically approved
    4. Artificial reef effect and fouling impacts on offshore wave power foundations and buoys: a pilot study
    Open this publication in new window or tab >>Artificial reef effect and fouling impacts on offshore wave power foundations and buoys: a pilot study
    2009 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 82, no 3, p. 426-432Article in journal (Refereed) Published
    Abstract [en]

    Little is known about the effects of offshore energy installations on the marine environment, and further research could assist in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. While biofouling on marine energy conversion devices on one hand has the potential to be an engineering concern, these structures can also affect biodiversity by functioning as artificial reefs. The Lysekil Project is a test park for wave power located at the Swedish west coast. Here, buoys acting as point absorbers on the surface are connected to generators anchored on concrete foundations on the seabed. In this study we investigated the colonisation of foundations by invertebrates and fish, as well as fouling assemblages on buoys. We examined the influence of surface orientation of the wave power foundations on epibenthic colonisation, and made observations of habitat use by fish and crustaceans during three years of submergence. We also examined fouling assemblages on buoys and calculated the effects of biofouling on the energy absorption of the wave power buoys. On foundations we demonstrated a succession in colonisation over time with a higher degree of coverage on vertical surfaces. Buoys were dominated by the blue mussel Mytilus edulis. Calculations indicated that biofouling have no significant effect in the energy absorption on a buoy working as a point absorber. This study is the first structured investigation on marine organisms associated with wave power devices

    Keywords
    biodiversity, benthos, fish, shellfish, renewable energy, wave power, Sweden
    National Category
    Biological Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-107217 (URN)10.1016/j.ecss.2009.02.009 (DOI)000265573400007 ()
    Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2022-01-28Bibliographically approved
    5. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Show others...
    2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
    Abstract [en]

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

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
    6. Wave energy converter with enhanced amplitude response at frequencies coinciding with Swedish west coast sea states by use of a supplementary submerged body
    Open this publication in new window or tab >>Wave energy converter with enhanced amplitude response at frequencies coinciding with Swedish west coast sea states by use of a supplementary submerged body
    2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 6, article id 064512Article in journal (Refereed) Published
    Abstract [en]

    The full-scale direct-driven wave energy converter developed at Uppsala University has been in offshore operation at the Swedish west coast since 2006. Earlier simulations have now been validated by full-scale experiment with good agreement. Based on that, a theoretical model for a passive system having optimum amplitude response at frequencies coinciding with Swedish west coast conditions has been developed. The amplitude response is increased by adding supplementary inertia by use of the additional mass from a submerged body. A sphere with neutral buoyancy is chosen as the submerged body and modeled as being below the motion of the waves. The model is based on potential linear wave theory and the power capture ratio is studied for real ocean wave data collected at the research test site. It is found that the power capture ratio for the two body system can be increased from 30% to 60% compared to a single body system. Increased velocity in the system also decreases the value for optimal load damping from the generator, opening up the possibility to design smaller units.

    Place, publisher, year, edition, pages
    USA: American Institute of Physics, 2009
    Keywords
    data acquisition, ocean waves
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113142 (URN)10.1063/1.3233656 (DOI)000270378100147 ()0021-8979 (ISBN)
    Note

    10907471 Wave Energy Converter enhanced amplitude response Swedish west coast sea states supplementary submerged body Uppsala University offshore operation passive system optimum amplitude response neutral buoyancy waves motion potential linear wave theory power capture ratio ocean wave data collection research test site Two Body System single body system

    Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
    7. Depth variation of energy transport in fluid gravity waves
    Open this publication in new window or tab >>Depth variation of energy transport in fluid gravity waves
    2010 (English)In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 2, no 2, p. 023104-Article in journal (Refereed) Published
    Abstract [en]

    We calculate the distribution of energy flux as a function of the distance below the surface for propagating polychromatic gravity fluid surface waves. Linear theory has been used to derive closed-form expressions for the energy flux as a function of depth. In this context we discuss the power distribution for real ocean waves measured off the west coast of Sweden and compare this to the energy flux distribution for waves with Pierson-Moskowitz and Bretschneider spectral distributions. This is done in order to get an improved understanding of how to improve the power absorption in wave energy converters, and this is also discussed in this paper.

    Keywords
    gravity waves, hydroelectric power, ocean waves, surface waves (fluid)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-140346 (URN)10.1063/1.3424711 (DOI)000287922200005 ()
    Note

    11431539 energy flux distribution polychromatic gravity fluid surface waves energy transport linear theory closed-form expressions power distribution ocean waves Sweden Pierson-Moskowitz distribution Bretschneider spectral distributions power absorption wave energy converters

    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2024-01-17Bibliographically approved
    8. Wave Buoy and Translator Motions - On-Site Measurements and Simulations
    Open this publication in new window or tab >>Wave Buoy and Translator Motions - On-Site Measurements and Simulations
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    2011 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 36, no 3, p. 377-385Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Accelerometers, energy conversion, experimental results, image motion analysis, oceanic engineering, marine technology, wave power
    National Category
    Energy Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160072 (URN)10.1109/JOE.2011.2136970 (DOI)
    Available from: 2012-01-09 Created: 2011-10-14 Last updated: 2017-12-08Bibliographically approved
    9. Optimization of the Dimensions of a Gravity-based Wave Energy Converter Foundation Based on Heave and Surge Forces
    Open this publication in new window or tab >>Optimization of the Dimensions of a Gravity-based Wave Energy Converter Foundation Based on Heave and Surge Forces
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    2011 (English)In: 9th European Wave and Tidak Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160035 (URN)
    Conference
    9th European Wave and Tidak Energy Conference, Southampton, UK, 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
    10. Lysekil Research Site, Sweden: A status update
    Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
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    2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160039 (URN)
    Conference
    9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
    11. Total instantaneous energy transport in polychromatic fluid gravity waves at finite depth
    Open this publication in new window or tab >>Total instantaneous energy transport in polychromatic fluid gravity waves at finite depth
    2012 (English)In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 4, no 3, p. 033108-1-033108-8Article in journal (Refereed) Published
    Abstract [en]

    The total instantaneous energy transport can be found for polychromatic waves when using the deep water approximation. Expanding this theory to waves in waters of finite depth, we derive an expression for the total instantaneous energy transport for polychromatic fluid gravity waves based on potential theory with linearized free surface boundary conditions. We present the results for time series of wave elevation measured at the Uppsala University wave energy research test site. We show that a significant proportion of the total instantaneous energy transport is not accounted for when using the deep water theory. This is important since many wave energy conversion devices under development will operate in waters that do not fulfil the deep water criteria.

    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160028 (URN)10.1063/1.4719678 (DOI)000305882200019 ()
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2024-01-17
    12. Properties of the energy transport for plane-parallel polychromatic surface gravity waves in waters of arbitrary depth
    Open this publication in new window or tab >>Properties of the energy transport for plane-parallel polychromatic surface gravity waves in waters of arbitrary depth
    (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Other academic) Submitted
    National Category
    Fluid Mechanics and Acoustics Oceanography, Hydrology and Water Resources
    Identifiers
    urn:nbn:se:uu:diva-160026 (URN)
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2018-01-12Bibliographically approved
    13. Modelling and Simulation of Linear Wave Energy Converter
    Open this publication in new window or tab >>Modelling and Simulation of Linear Wave Energy Converter
    Show others...
    (English)In: IET Renewable Power GenerationArticle in journal (Other academic) Submitted
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-160304 (URN)
    Available from: 2011-10-20 Created: 2011-10-20 Last updated: 2011-11-23Bibliographically approved
    14. A resonant Two Body System for a point absorbing Wave Energy Converter with direct-driven linear generator
    Open this publication in new window or tab >>A resonant Two Body System for a point absorbing Wave Energy Converter with direct-driven linear generator
    2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 12, p. 124904-Article in journal (Refereed) Published
    Abstract [en]

    Based on an earlier conceptual model of a two body system point absorbing wave energy converter tuned to resonance in Swedish west coast sea states, an extended coupled hydrodynamic, mechanic, and electromagnetic model has been developed. The hydrodynamic characteristics of the two body system are studied in the frequency and time domain, while its response to real Swedish west coast sea states are studied in the time domain, by using a wave energy converter model with two independently moving bodies connected to a direct driven linear generator with non-linear damping. The two body system wave energy converter gives nearly 80% power capture ratio in irregular waves. The resonant behaviour is shown to be sensitive to the shape of the spectrum, and the distance between the two bodies is shown to have a large effect on the power absorption.

    Keywords
    direct energy conversion, linear machines, resonant power convertors, wave power generation
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-160032 (URN)10.1063/1.3664855 (DOI)000298639800142 ()
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-12-08
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  • 6.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance of large arrays of point absorbing direct-driven wave energy converters2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 20, p. 204502-Article in journal (Refereed)
    Abstract [en]

    Future commercial installation of wave energy plants using point absorber technology will require clusters of tens up to several hundred devices, in order to reach a viable electricity production. Interconnected devices also serve the purpose of power smoothing, which is especially important for devices using direct-driven power take off. The scope of this paper is to evaluate a method to optimize wave energy farms in terms of power production, economic viability and resources. In particular, the paper deals with the power variation in a large array of point-absorbing direct-driven wave energy converters, and the smoothing effect due to the number of devices and their hydrodynamic interactions. A few array geometries are compared and 34 sea states measured at the Lysekil research site at the Swedish west coast are used in the simulations. Potential linear flow theory are used with full hydrodynamic interactions between the buoys. It is shown that the variance in power production depends crucially on the geometry of the array and the number of interacting devices, but not significantly on the energy period of the waves.

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    Performance of large arrays of point absorbing direct-driven wave energy converters
  • 7.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave energy converter with enhanced amplitude response at frequencies coinciding with Swedish west coast sea states by use of a supplementary submerged body2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 6, article id 064512Article in journal (Refereed)
    Abstract [en]

    The full-scale direct-driven wave energy converter developed at Uppsala University has been in offshore operation at the Swedish west coast since 2006. Earlier simulations have now been validated by full-scale experiment with good agreement. Based on that, a theoretical model for a passive system having optimum amplitude response at frequencies coinciding with Swedish west coast conditions has been developed. The amplitude response is increased by adding supplementary inertia by use of the additional mass from a submerged body. A sphere with neutral buoyancy is chosen as the submerged body and modeled as being below the motion of the waves. The model is based on potential linear wave theory and the power capture ratio is studied for real ocean wave data collected at the research test site. It is found that the power capture ratio for the two body system can be increased from 30% to 60% compared to a single body system. Increased velocity in the system also decreases the value for optimal load damping from the generator, opening up the possibility to design smaller units.

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  • 8.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Nilsson, Erik O.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Energy absorption from parks of point-absorbing wave energy converters in the Swedish exclusive economic zone2020In: Energy Science & Engineering, ISSN 2050-0505, Vol. 8, no 1, p. 38-49Article in journal (Refereed)
    Abstract [en]

    In a future energy system based on renewable energy sources, wave energy will most likely play a role due to its high energy potential and low intermittency. The power production from parks of wave energy converters of point absorber type has been extensively studied. This is also the case for the wave energy resource at many coastal areas around the globe. Wave energy has not yet reached a commercial level, and a large variety of technologies exist; therefore, an established method to calculate the technical potential for wave energy has still not been established. To estimate the technical potential of wave energy conversion, some approximations inevitably need to be taken due to the systems high complexity. In this study, a detailed mapping of the wave climate and simulation of large arrays of hydrodynamically cross‐coupled wave energy converters are combined to calculate the technical potential for wave energy conversion in the Swedish exclusive economic zone. A 16‐year wave data set distributed in a 1.1 km × 1.1 km grid is used to calculate the absorbed energy from a park of 200 generic point absorbers. The areas with best potential have an average annual energy absorption of 16 GWh for the selected wave energy park adapted to 1 km2 when using a constant damping, while the theoretical upper bound is 63 GWh for the same area.

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  • 9.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Properties of the Energy Transport for Plane-Parallel Polychromatic Surface Gravity Waves in Waters of Arbitrary Depth2015In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 40, no 2, p. 408-416Article in journal (Refereed)
    Abstract [en]

    It is well known that the energy transport of ocean waves propagates with the group velocity and that the energy decreases exponentially with depth. Expanding this theory, we will derive expressions for the energy transport as a function of depth and the total instantaneous transport's development over time for waves in waters of finite depth. Solutions to the Laplace equation are found for plane-parallel polychromatic waves with linearized boundary conditions. A time series of wave elevation collected at Uppsala University's wave energy research test site is chosen to present the results. Solutions for waters of both infinite and arbitrary depths are presented and compared. The solutions are convolution-type integrals with the wave elevation where we have found efficient ways to calculate the kernels. The difference in group velocity between finite depth and infinite depth and its impact on the energy transport is clearly seen in the results. The use of the deep-water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. We further show that the total instantaneous energy transport can actually have a direction that is opposite to the direction of the waves as observed from a reference frame fixed to the seabed.

  • 10.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Seabased Industry AB, Uppsala.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Total instantaneous energy transport in polychromatic fluid gravity waves at finite depth2012In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 4, no 3, p. 033108-1-033108-8Article in journal (Refereed)
    Abstract [en]

    The total instantaneous energy transport can be found for polychromatic waves when using the deep water approximation. Expanding this theory to waves in waters of finite depth, we derive an expression for the total instantaneous energy transport for polychromatic fluid gravity waves based on potential theory with linearized free surface boundary conditions. We present the results for time series of wave elevation measured at the Uppsala University wave energy research test site. We show that a significant proportion of the total instantaneous energy transport is not accounted for when using the deep water theory. This is important since many wave energy conversion devices under development will operate in waters that do not fulfil the deep water criteria.

  • 11.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kurupath, Venugopalan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A resonant Two Body System for a point absorbing Wave Energy Converter with direct-driven linear generator2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 12, p. 124904-Article in journal (Refereed)
    Abstract [en]

    Based on an earlier conceptual model of a two body system point absorbing wave energy converter tuned to resonance in Swedish west coast sea states, an extended coupled hydrodynamic, mechanic, and electromagnetic model has been developed. The hydrodynamic characteristics of the two body system are studied in the frequency and time domain, while its response to real Swedish west coast sea states are studied in the time domain, by using a wave energy converter model with two independently moving bodies connected to a direct driven linear generator with non-linear damping. The two body system wave energy converter gives nearly 80% power capture ratio in irregular waves. The resonant behaviour is shown to be sensitive to the shape of the spectrum, and the distance between the two bodies is shown to have a large effect on the power absorption.

  • 12.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Katsidoniotaki, Eirini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Stavropoulou, Charitini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Department of Applied Mechanics.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Offshore Measurements and Numerical Validation of the Mooring Forces on a 1:5 Scale Buoy2023In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 11, no 1, article id 231Article in journal (Refereed)
    Abstract [en]

    Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We present here results from two weeks of measurement with a force measurement buoy deployed at Uppsala University’s test site for wave energy research at the west coast of Sweden. The collected data have been used to investigate the reliability for two typical numerical wave energy converter models: one low fidelity model based on linear wave theory and one high fidelity Reynolds-Averaged Navier–Stokes model. The line force data is also analysed by extreme value theory using the peak-over-threshold method to study the statistical distribution of extreme forces and to predict the return period. The high fidelity model shows rather good agreement for the smaller waves, but overestimates the forces for larger waves, which can be attributed to uncertainties related to field measurements and numerical modelling uncertainties. The peak-over-threshold method gives a rather satisfying result for this data set. A significant deviation is observed in the measured force for sea states with the same significant wave height. This indicates that it will be difficult to calculate the force based on the significant wave height only, which points out the importance of more offshore experiments.

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  • 13.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Sjökvist, Linnea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Hann, Martyn
    Plymouth University.
    Ransley, Edward
    Plymouth University.
    Greaves, Deborah
    Plymouth University.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Buoy geometry and its influence on survivability for apoint absorbing wave energy converter: Scaleexperiment and CFD simulations2017Conference paper (Refereed)
    Abstract [en]

    For wave energy to be an economically viable energysource, the technology has to withstand power levelsduring storms that can be close to 50 times higher thanduring normal operating conditions, and withstandmany years of wear. The impact of high wave loads isstudied not only within the field of wave energy, buthas long been a subject of study for ships, platformsand other offshore structures.To model the force on the device under extreme and/orovertopping waves is a difficult task. Experiments areexpensive and difficult to implement, and numerical meth-ods are either very computationally demanding CFD-methods, or less accurate approximative methods. Inaddition, the performance and experienced forces during extreme waves are model dependent, and differentoffshore structures must be studied independently.Here, a 1:20 scale model of the Uppsala Universitypoint-absorber type wave energy converter (WEC) has been tested in extreme wave conditions at the COASTLaboratory Ocean Basin at Plymouth University. The WEC consists of a linear generator connected to a buoyat the sea surface, and performance of two differentbuoys is studied: a cylinder and cylinder with moon-pool. Two types of wave sets have been used: focusedwaves embedded into regular waves, and irregular waves. The focus of this paperis on comparing the performance of the two buoys, and on analysing the experimental data using a numerical model. A fully non-linear computational fluid dynamics(CFD) model based on OpenFOAM is presented and validated.

  • 14.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stålberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Henfridsson, U
    Bergman, K
    Asmussen, J
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore experiments on a direct-driven Wave Energy Converter2007Conference paper (Refereed)
  • 15.
    Francisco, Francisco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Jennifer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Power as Solution for Off-Grid Water Desalination Systems: Resource Characterization for Kilifi-Kenya2018In: Energies, E-ISSN 1996-1073, Vol. 11, no 4, article id 4Article in journal (Refereed)
    Abstract [en]

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

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  • 16.
    Giannini, Gianmaria
    et al.
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Temiz, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Rosa-Santos, Paulo
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Ramos, Victor
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Day, Sandy
    Univ Strathclyde, Dept Naval Architecture Ocean & Marine Engn, Glasgow G4 0LZ, Lanark, Scotland..
    Taveira-Pinto, Francisco
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Wave Energy Converter Power Take-Off System Scaling and Physical Modelling2020In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, no 9, article id 632Article in journal (Refereed)
    Abstract [en]

    Absorbing wave power from oceans for producing a usable form of energy represents an attractive challenge, which for the most part concerns the development and integration, in a wave energy device, of a reliable, efficient and cost-effective power take-off mechanism. During the various stages of progress, for assessing a wave energy device, it is convenient to carry out experimental testing that, opportunely, takes into account the realistic behaviour of the power take-off mechanism at a small scale. To successfully replicate and assess the power take-off, good practices need to be implemented aiming to correctly scale and evaluate the power take-off mechanism and its behaviour. The present paper aims to explore and propose solutions that can be applied for reproducing and assessing the power take-off element during experimental studies, namely experimental set-ups enhancements, calibration practices, and error estimation methods. A series of recommendations on how to practically organize and carry out experiments were identified and three case studies are briefly covered. It was found that, despite specific options that can be strictly technology-dependent, various recommendations could be universally applicable.

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  • 17.
    Giassi, Marianna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    An economical cost function for the optimization of wave energy converter arrays2019In: The 29th International Ocean and Polar Engineering Conference, 2019Conference paper (Refereed)
  • 18.
    Giassi, Marianna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Comparison of wave energy park layouts by experimental and numerical methods2020In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, no 10, article id 750Article in journal (Refereed)
    Abstract [en]

    An experimental campaign of arrays with direct-driven wave energy converters of point-absorbing type is presented. The arrays consist of six identical floats, moving in six degrees of freedom, and six rotating power take-off systems, based on the design developed at Uppsala University. The goals of the work were to study and compare the performances of three different array layouts under several regular and irregular long-crested waves, and in addition, to determine whether the numerical predictions of the best performing array layouts were confirmed by experimental data. The simulations were executed with a frequency domain model restricted to heave, which is a computationally fast approach that was merged into a genetic algorithm optimization routine and used to find optimal array configurations. The results show that good agreement between experiments and simulations is achieved when the test conditions do not induce phenomena of parametric resonance, slack line and wave breaking. Specific non-linear dynamics or extensive sway motion are not captured by the used model, and in such cases the simulation predictions are not accurate, but can nevertheless be used to get an estimate of the power output.

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  • 19.
    Giassi, Marianna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Multi-parameter optimization of hybrid arrays of point absorber Wave Energy Converters2017In: Proceedings of the 12th European Wave and Tidal Energy Conference, 2017Conference paper (Refereed)
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    12EWTECGiassi
  • 20.
    Giassi, Marianna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tosdevin, Tom
    Hann, Martyn
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Preliminary results from a scaled test of arrays of point-absorbers with 6 DOF2019In: Proceedings of the 13th European Wave and Tidal Energy Conference, 2019Conference paper (Refereed)
  • 21.
    Giassi, Marianna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Thomas, Simon
    Maynooth University.
    Tosdevin, Tom
    Plymouth University.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Hann, Martyn
    Plymouth University.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Capturing the experimental behaviour of a point-absorber WEC by simplified numerical models2020In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 99, article id 103143Article in journal (Refereed)
    Abstract [en]

    The paper presents a wave basin experiment of a direct-driven point-absorber wave energy converter moving in six degrees of freedom. The goal of the work is to study the dynamics and energy absorption of the wave energy converter, and to verify under which conditions numerical models restricted to heave can capture the behaviour of a point-absorber moving in six degrees of freedom. Several regular and irregular long-crested waves and different damping values of the power take-off system have been tested. We collected data in terms of power output, device motion in six degrees of freedom and wave elevation at different points of the wave basin. A single-body numerical model in the frequency domain and a two-body model in the time domain are used in the study. Motion instabilities due to parametric resonance observed during the experiments are discussed and analysis of the buoy motion in terms of the Mathieu instability is also presented. Our results show that the simplified models can reproduce the body dynamics of the studied converter as long as the transverse non-linear instabilities are not excited, which typically is the case in irregular waves. The performance of the more complex time domain model is able to reproduce both the buoy and PTO dynamics, while the simpler frequency domain model can only reproduce the PTO dynamics for specific cases. Finally, we show that the two-body dynamics of the studied wave energy converter affects the power absorption significantly, and that common assumptions in the numerical models, such as stiff mooring line or that the float moves only in heave, may lead to incorrect predictions for certain sea states.

  • 22.
    Gravråkmo, Halvar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Description of a torus shaped buoy for wave energy point absorber2010Conference paper (Refereed)
  • 23.
    Gravråkmo, Halvar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Engström, Jens
    Svensson, Olle
    Leijon, Mats
    Toroidal Buoy for Point Absorver WEC with Focus on Added Mass and OverloadsIn: Article in journal (Refereed)
    Abstract [en]

    In order for a wave energy converter (WEC) to produce electricity at competitive prices, the generator must not be over dimensioned in order to save money on production, transport and installation, but the WEC, in this case a point absorber, must also be dimensioned to withstand harsh sea states. High added mass will in some cases create severe inertia forces on the generator and might shorten the service life of the system. The magnitude of the overload forces can be reduced by choosing a buoy geometry with small added mass. Measurements of snap loads produced by a toroidal buoy and calculations of buoy intertia forces causing overloads on a generator with a toroidal buoy and an equal generator with a cylindrical buoy are investigated in order to compare the two shapes numerically. A toroidal buoy was found to have less added mass than a vertical cylindrical buoy with similar excitation force, which caused reduced overloads at short wave periods, thus reducing the overloads on the generator. Snap loads were found to not cause much greater loads than other forces found during operation.

  • 24.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hann, Martyn
    Ransley, Edward
    Greaves, Deborah
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave loads on a point-absorbing wave energy device in extreme waves2015In: Journal of Ocean and Wind Energy, E-ISSN 2310-3604, Vol. 2, no 3, p. 176-181Article in journal (Refereed)
    Download full text (pdf)
    Paper8
  • 25.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fast modeling of large wave energy farms using interaction distance cut-off2015In: Energies, E-ISSN 1996-1073, Vol. 8, no 12, p. 13741-13757Article in journal (Refereed)
    Abstract [en]

    In many wave energy concepts, power output in the MW range requires the simultaneous operation of many wave energy converters. In particular, this is true for small point-absorbers, where a wave energy farm may contain several hundred devices. The total performance of the farm is affected by the hydrodynamic interactions between the individual devices, and reliable tools that can model full farms are needed to study power output and find optimal design parameters. This paper presents a novel method to model the hydrodynamic interactions and power output of very large wave energy farms. The method is based on analytical multiple scattering theory and uses time series of irregular wave amplitudes to compute the instantaneous power of each device. An interaction distance cut-off is introduced to improve the computational cost with acceptable accuracy. As an application of the method, wave energy farms with over 100 devices are studied in the MW range using one month of wave data measured at an off-shore site.

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  • 26.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Interaction distance for scattered and radiated waves in large wave energy parks2015Conference paper (Refereed)
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    IWWWFB2015
  • 27. Göteman, Malin
    et al.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical and semi-analytical methods for optimizing wave energy parks2014Conference paper (Refereed)
  • 28.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimizing wave energy parks with over 1000 interacting point-absorbers using an approximate analytical method2015In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 10, p. 113-126Article in journal (Refereed)
    Abstract [en]

    Large arrays of wave energy converters of point-absorber type are studied using an approximate analytical model. The model is validated against a numerical method that takes into account full hydrodynamic interactions based on linear potential flow theory. The low computational cost of the analytical model enables parameter studies of parks in the MW range and includes up to over 1000 interacting devices. The model is actuated by irregular wave data obtained at the Swedish west coast. In particular, focus is on comparing park geometries and improving park configurations to minimize the power fluctuations.

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  • 29. Göteman, Malin
    et al.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical and numerical approaches to optimizing fluid-structure interactions in wave energy parks2014Conference paper (Refereed)
  • 30.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Methods of reducing power fluctuations in wave energy parks2014In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 6, p. 043103-Article in journal (Refereed)
    Abstract [en]

    One of the major challenges in constructing effective and economically viable wave energy parks is to reduce the large fluctuations in power output. In this paper, we study different methods of reducing the fluctuations and improve the output power quality. The parameters studied include the number of devices, the separating distance between units, the global and local geometries of the array, sea state and incoming wave direction, and the impact of including buoys of different radii in an array. Our results show that, e. g., the fluctuations as well as power per device decrease strictly with the number of interacting units, when the separating distance is kept constant. However, including more devices in a park with fixed area will not necessarily result in lowered power fluctuations. We also show that varying the distance between units affects the power fluctuations to a much larger extent than it affects the magnitude of the absorbed power. The fluctuations are slightly lower in more realistic, randomized geometries where the buoys tend to drift slightly off their mean positions, and significantly lower in semi-circular geometries as opposed to rectangular geometries. 

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  • 31.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Advances and Challenges in Wave Energy Park Optimization: A Review2020In: Frontiers in Energy Research, E-ISSN 2296-598X, Vol. 8, article id 26Article, review/survey (Refereed)
    Abstract [en]

    A commercial wave energy system will typically consist of many interacting wave energy converters installed in a park. The performance of the park depends on many parameters such as array layout and number of devices, and may be evaluated based on different measures such as energy absorption, electricity quality, or cost of the produced electricity. As wave energy is currently at the stage where several large-scale installations are being planned, optimizing the park performance is an active research area, with many important contributions in the past few years. Here, this research is reviewed, with a focus on identifying the current state of the art, analyzing how realistic, reliable, and relevant the methods and the results are, and outlining directions for future research.

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  • 32.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Jens, Engström
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mikael, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hann, Martyn
    Plymouth University.
    Ransley, Edward
    Plymouth University.
    Greaves, Deborah
    Plymouth University.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave loads on a point-absorbing wave energy device in extreme waves2015Conference paper (Refereed)
  • 33.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mathew, Jude
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave energy farm performance and availability as functions of weather windows2018Conference paper (Refereed)
  • 34.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    McNatt, Cameron
    Mocean Energy, Edinburgh EH9 3BF, Midlothian, Scotland.
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arrays of Point-Absorbing Wave Energy Converters in Short-Crested Irregular Waves2018In: Energies, E-ISSN 1996-1073, Vol. 11, no 4, article id 964Article in journal (Refereed)
    Abstract [en]

    For most wave energy technology concepts, large-scale electricity production and cost-efficiency require that the devices are installed together in parks. The hydrodynamical interactions between the devices will affect the total performance of the park, and the optimization of the park layout and other park design parameters is a topic of active research. Most studies have considered wave energy parks in long-crested, unidirectional waves. However, real ocean waves can be short-crested, with waves propagating simultaneously in several directions, and some studies have indicated that the wave energy park performance might change in short-crested waves. Here, theory for short-crested waves is integrated in an analytical multiple scattering method, and used to evaluate wave energy park performance in irregular, short-crested waves with different number of wave directions and directional spreading parameters. The results show that the energy absorption is comparable to the situation in long-crested waves, but that the power fluctuations are significantly lower.

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  • 35.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Stavropoulou, Charitini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Katsidoniotaki, Eirini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Resilience of wave energy farms using metocean dependent failure rates and repair operations2023In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 280, article id 114678Article in journal (Refereed)
    Abstract [en]

    Emerging offshore renewable energy technologies are expected to become an important part of the futureenergy system, and reliability for these new technologies in different metocean scenarios must be guaranteed.This poses a challenge in extreme weather scenarios like storms, in particular for less mature technologiessuch as wave energy. Not only the offshore survivability must be controlled; the restoration after disruptiveevents and failures should be addressed and optimized. Offshore operations are costly and cannot be carriedout if the weather is too harsh, and the resulting downtime after failures may be financially devastating forprojects. In this paper, the resilience of large wave energy systems is studied with respect to wave conditions,metocean dependent failure rates, and weather windows available for offshore repair operations. A metocean-and time-dependent failure rate is derived based on a Weibull distribution, which is a novelty of the paper.The performance of the farm is assessed using the varying failure rates and metocean data at different offshoresites. Critical metocean thresholds for different offshore vessels are considered, and the resilience is quantifiedusing relevant measures such as unavailability and expected energy not supplied. The resilience analysis iscoupled to an economic assessment of the wave farm and different repair strategies. Our results show thatthe commonly used assumption of constant failure rates is seen to overestimate the annual energy productionthan when a more realistic varying failure rate is used. Two offshore sites are compared, and the availabilityis found to be higher at the calmer site. Most of the evaluated repair strategies cannot be considered to beeconomically justified, when compared to the cost of the energy not supplied.

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  • 36.
    Hong, Yue
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Review on electrical control strategies for wave energy converting systems2014In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 31, p. 329-342Article, review/survey (Refereed)
    Abstract [en]

    Renewable energy techniques are now gaining more and more attention as the years pass by, not only because of the threat of climate change but also, e.g. due to serious pollution problems in some countries and because the renewable energy technologies have matured and can be depended upon an increasing degree. The energy from ocean waves bares tremendous potential as a source of renewable energy, and the related technologies have continually been improved during the last decades. In this paper, different types of wave energy converters are classified by their mechanical structure and how they absorb energy from ocean waves. The paper presents a review of strategies for electrical control of wave energy converters as well as energy storage techniques. Strategies of electrical control are used to achieve a higher energy absorption, and they are also of interest because of the large variety among different strategies. Furthermore, the control strategies strongly affect the complexity of both the mechanical and the electrical system, thus not only impacting energy absorption but also robustness, survivability, maintenance requirements and thus in the end the cost of electricity from ocean waves.

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  • 37.
    Isberg, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Control of rapid phase oscillations in the modelling of large wave energy arrays2015In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 11, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Several recently developed concepts for economically viable conversion of ocean wave energy are based on large arrays of point absorbers. Simulations of the hydrodynamic interactions between devices in wave energy parks provide guidelines for optimal configurations with regard to maximizing produced electricity while minimizing fluctuations and costs. Parameters that influence the performance include the geometrical lay-out of the park, the number of wave energy converters and their dimensions and separating distance, as well as the wave climate and the incoming wave spectral characteristics. However, the complexity of the simulations increases rapidly with growing number of interacting units, and simulations become a severe challenge that calls for new methods. Here we address the problem of rapid phase oscillations appearing in the simulation of large arrays of point absorbers using potential theory for the structure–fluid interaction. We do this by analytically integrating out the factors that are causing the oscillations. Our group has successfully utilized this method to model parks with up to 1000 point absorbers.

  • 38.
    Isberg, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Depth variation of energy transport in fluid gravity waves2010In: Journal of Renewable and Sustainable Energy, E-ISSN 1941-7012, Vol. 2, no 2, p. 023104-Article in journal (Refereed)
    Abstract [en]

    We calculate the distribution of energy flux as a function of the distance below the surface for propagating polychromatic gravity fluid surface waves. Linear theory has been used to derive closed-form expressions for the energy flux as a function of depth. In this context we discuss the power distribution for real ocean waves measured off the west coast of Sweden and compare this to the energy flux distribution for waves with Pierson-Moskowitz and Bretschneider spectral distributions. This is done in order to get an improved understanding of how to improve the power absorption in wave energy converters, and this is also discussed in this paper.

  • 39.
    Katsidoniotaki, Eirini
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Nilsson, Erik O.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Centre of Natural Hazards and Disaster Science, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Centre of Natural Hazards and Disaster Science, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Response of Point-Absorbing Wave Energy Conversion System in 50-Years Return Period Extreme Focused Waves2021In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 9, no 3, article id 345Article in journal (Refereed)
    Abstract [en]

    This work evaluates the survivability of a point-absorbing wave energy converter at sea states along and inside the 50-year environmental contour for a selected-site in North Sea, by utilizing CFD simulations. Focused wave groups based on NewWave theory are used to model the extreme waves. The numerical breaking waves have been previously predicted by the analytical breaking criterion, showing that the latter provides an accurate estimate for the breaking state. The forces on key components of the device and the system’s dynamics are studied and compared. Slamming loads are identified in the interaction with extreme waves, particularly with breaking waves, and compared with the analytical formulas for slamming estimation as suggested by industrial standards. Considering the extreme wave characteristics, the accompanied phenomena and the resulting WEC’s response, this work contributes to the identification of the design-waves given the environmental contour of the selected site. The top-left side of the contour is identified as the more critical area as it consists of steep and high waves inducing significant nonlinear phenomena, resulting in high loads.

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  • 40.
    Katsidoniotaki, Eirini
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eskilsson, Claes
    Palm, Johannes
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Validation of a CFD model for wave energy system dynamics in extreme waves2023In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 268, article id 113320Article in journal (Refereed)
    Abstract [en]

    The design of wave energy converters should rely on numerical models that are able to estimate accurately the dynamics and loads in extreme wave conditions. A high-fidelity CFD model of a 1:30 scale point-absorber is developed and validated on experimental data. This work constitutes beyond the state-of-the-art validation study as the system is subjected to 50-year return period waves. Additionally, a new methodology that addresses the well-known challenge in CFD codes of mesh deformation is successfully applied and validated. The CFD model is evaluated in different conditions: wave-only, free decay, and wave–structure interaction. The results show that the extreme waves and the experimental setup of the wave energy converter are simulated within an accuracy of 2%. The developed high-fidelity model is able to capture the motion of the system and the force in the mooring line under extreme waves with satisfactory accuracy. The deviation between the numerical and corresponding experimental RAOs is lower than 7% for waves with smaller steepness. In higher waves, the deviation increases up to 10% due to the inevitable wave reflections and complex dynamics. The pitch motion presents a larger deviation, however, the pitch is of secondary importance for a point-absorber wave energy converter.

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  • 41.
    Langhamer, Olivia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wilhelmsson, D
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Development of Invertebrate Assemblages and Fish on Offshore Wave Power2009Conference paper (Refereed)
  • 42.
    Langhamer, Olivia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Wilhelmsson, Dan
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Artificial reef effect and fouling impacts on offshore wave power foundations and buoys: a pilot study2009In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 82, no 3, p. 426-432Article in journal (Refereed)
    Abstract [en]

    Little is known about the effects of offshore energy installations on the marine environment, and further research could assist in minimizing environmental risks as well as in enhancing potential positive effects on the marine environment. While biofouling on marine energy conversion devices on one hand has the potential to be an engineering concern, these structures can also affect biodiversity by functioning as artificial reefs. The Lysekil Project is a test park for wave power located at the Swedish west coast. Here, buoys acting as point absorbers on the surface are connected to generators anchored on concrete foundations on the seabed. In this study we investigated the colonisation of foundations by invertebrates and fish, as well as fouling assemblages on buoys. We examined the influence of surface orientation of the wave power foundations on epibenthic colonisation, and made observations of habitat use by fish and crustaceans during three years of submergence. We also examined fouling assemblages on buoys and calculated the effects of biofouling on the energy absorption of the wave power buoys. On foundations we demonstrated a succession in colonisation over time with a higher degree of coverage on vertical surfaces. Buoys were dominated by the blue mussel Mytilus edulis. Calculations indicated that biofouling have no significant effect in the energy absorption on a buoy working as a point absorber. This study is the first structured investigation on marine organisms associated with wave power devices

  • 43.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Anttila, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Frost, Anna E.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Renewable Energy Sources for Desalination, Generating Freshwater and Lithium2019Conference paper (Refereed)
  • 44.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Anttila, Sara
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Frost, Anna E.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Lindahl, Olof
    Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Business Studies.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Freshwater and Lithium from Desalination Powered by Marine Energy Sources2020In: International Journal of Offshore and Polar Engineering, ISSN 1053-5381, Vol. 30, no 3, p. 283-285Article in journal (Refereed)
    Abstract [en]

    To our knowledge, this paper represents an initial study of a novel concept in freshwater and lithium extraction from desalination powered off-grid by marine renewable energy sources. The project's background is interest in the local supply of lithium for the growing numbers of electric vehicles. The desalination technologies investigated are reverse osmosis and electrodialysis. The collocation of the marine resources, possibly available and future technical solutions, and demands for freshwater and lithium suggest that the proposed system could be interesting to study further.

  • 45.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Desalination and wave power for freshwater supply on Gotland2024In: Energy Strategy Reviews, ISSN 2211-467X, E-ISSN 2211-4688, Vol. 53, p. 101404-101404, article id 101404Article in journal (Refereed)
  • 46.
    Leijon, Jennifer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Salar, Dana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Chalmers Univ Technol, Dept Elect Engn, Gothenburg, Sweden.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Variable renewable energy sources for powering reverse osmosis desalination, with a case study of wave powered desalination for Kilifi, Kenya2020In: Desalination, ISSN 0011-9164, E-ISSN 1873-4464, Vol. 494, no 114669Article in journal (Refereed)
    Abstract [en]

    An analysis of reverse osmosis powered by ocean wave power is provided. A commercially available desalination system is connected via a DC/AC converter to a variable DC source and the input voltage is altered to emulate the response of a renewable energy system. Specifically, wave data from Kilifi in Kenya during 2015 is used. The wave resource variations provide variations in estimated power output from a wave energy converter, as well as in estimated freshwater production from a wave powered desalination system. Up to three wave energy converters for desalination are investigated for Kilifi. Also, a hybrid system including solar and wave power is proposed. The experiments show that reverse osmosis desalination systems can function at power levels below the rated values, but with lower freshwater flowrates. It is concluded that wave power, or wave power combined with PV systems, may be considered as power sources for desalination, with or without battery storage.

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  • 47.
    Leijon, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Danielsson, Oskar
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bolund, Björn
    Gustafsson, Stefan
    Thorburn, Karin
    Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach2009In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed)
    Abstract [en]

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

  • 48.
    Lejerskog, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andreij
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Krishna, Remya
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekergård, Boel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kurupath, Venugopalan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lysekil Research Site, Sweden: A status update2011In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper (Refereed)
  • 49.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bontemps, Stephanie
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimization of the Dimensions of a Gravity-based Wave Energy Converter Foundation Based on Heave and Surge Forces2011In: 9th European Wave and Tidak Energy Conference, Southampton, UK, 2011, 2011Conference paper (Refereed)
  • 50.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bontemps, Stephanie
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimization of the Dimensions of a Gravity-based Wave Energy Converter Foundation Based on Heave and Surge Forces2011In: 9th European Wave and Tidak Energy Conference, Southampton, UK, 2011, 2011Conference paper (Refereed)
12 1 - 50 of 91
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