| 1. |
- Ayob, Mohd Nasir, et al.
(författare)
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Small-Scale Renewable Energy Converters for Battery Charging
- 2018
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Ingår i: Journal of Marine Science and Engineering. - : MDPI. - 2077-1312. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- 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. |
- Engström, Jens, et al.
(författare)
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Buoy geometry and its influence on survivability for apoint absorbing wave energy converter : Scaleexperiment and CFD simulations
- 2017
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Giassi, Marianna, et al.
(författare)
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Layout design of wave energy parks by a genetic algorithm
- 2018
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 154, s. 252-261
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Tidskriftsartikel (refereegranskat)abstract
- If wave energy systems are to become a viable option competitive with more mature renewable energy sources, the systems must be optimized with respect to maximal electricity production and minimized costs. The number of parameters involved in large-scale wave energy systems is typically too large for traditional optimization methods to be feasible, and the solution space may contain many local minima. Here, an optimization tool for application in wave energy design based on a genetic algorithm is presented. The internal parameters of single point-absorbing wave energy converters (buoy radius, draft and generator damping) are optimized and the results validated against parameters sweep optimization. Further, since the individual devices in a park affect each other by scattered and radiated waves propagating in all directions, the tool is used to find the optimal spatial layout of parks. Arrays with different number of devices are studied and similar optimal layouts appear in all cases, which allows extrapolation of the results to even larger parks. The results show that the tool is effective in finding layouts that avoid destructive interactions and get a q-factor slightly above 1.
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| 5. |
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| 6. |
- Giassi, Marianna
(författare)
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Optimization of Point Absorber Wave Energy Parks
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Renewable energies are believed to play the key role in assuring a future of sustainable energy supply and low carbon emissions. Particularly, this thesis focus on wave energy, which is created by extracting the power stored in the waves of the oceans. In order for wave energy to become a commercialized form of energy, modular deployment of many wave energy converters (WECs) together will be required in the upcoming future. This design will thus allow to benefit, among others, from the modular construction, the shared electrical cables connections and moorings, the reduction in the power fluctuations and reduction of deployment and maintenance costs. When it comes to arrays, the complexity of the design process increase enormously compared with the single WEC, given the mutual influence of most of the design parameters (i.e. hydrodynamic and electrical interactions, dimensions, geometrical layout, wave climate etc.). Uppsala University has developed and tested WECs since 2001, with the first offshore deployment held in 2006. The device is classified as a point absorber and consists in a linear electric generator located on the seabed, driven in the vertical direction by the motion of a floating buoy at the surface. Nowadays, one of the difficulties of the sector is that the cost of electricity is still too high and not competitive, due to high capital and operational costs and low survivability. Therefore, one step to try to reduce these costs is the development of reliable and fast optimization tools for parks of many units. In this thesis, a first attempt of systematic optimization for arrays of the Uppsala University WEC has been proposed. A genetic algorithm (GA) has been used to optimize the geometry of the floater and the damping coefficient of the generator of a single device. Afterwards, the optimal layout of parks up to 14 devices has been studied using two different codes, a continuous and a discrete variables real coded GA. Moreover, the method has been extended to study arrays with devices of different dimensions. A deterministic evaluation of small array layouts in real wave climate has also been carried out. Finally, a physical scale test has been initiated which will allow the validation of the results. A multi--parameter optimization of wave power arrays of the Uppsala University WEC has been shown to be possible and represents a tool that could help to reduce the total cost of electricity, enhance the performance of wave power plants and improve the reliability.
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| 7. |
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| 8. |
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| 9. |
- Göteman, Malin, 1980-, et al.
(författare)
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Arrays of Point-Absorbing Wave Energy Converters in Short-Crested Irregular Waves
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 10. |
- Göteman, Malin, 1980-, et al.
(författare)
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Fast modeling of large wave energy farms using interaction distance cut-off
- 2015
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 8:12, s. 13741-13757
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 11. |
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| 12. |
- Göteman, Malin, 1980-, et al.
(författare)
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Optimizing wave energy parks with over 1000 interacting point-absorbers using an approximate analytical method
- 2015
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Ingår i: International Journal of Marine Energy. - : Elsevier BV. - 2214-1669. ; 10, s. 113-126
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 13. |
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| 14. |
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| 15. |
- Göteman, Malin, 1980-
(författare)
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Wave energy parks with point-absorbers of different dimensions
- 2017
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 0889-9746 .- 1095-8622. ; 74, s. 142-157
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Tidskriftsartikel (refereegranskat)abstract
- An analytical model for point-absorbing wave energy converters connected to floats of different geometries and topologies is presented. The floats can be truncated cylinder or cylinder with moonpool buoys and have different outer radius, inner radius, draft, mass and can be connected to linear generators of different power take-off constants. The model is implemented into a numerical code where the input is measured time-series of irregular waves. After validation against benchmark software, the model is used to study optimal configurations of wave energy arrays consisting of different wave energy devices. It is shown that the total power absorption can be improved if the wave energy array consists of devices of different dimensions, and that a higher power-to-mass ratio can be achieved.
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| 16. |
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| 17. |
- Hai, Ling, et al.
(författare)
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A Methodology of Modelling a Wave Power System via an Equivalent RLC Circuit
- 2016
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Ingår i: IEEE Transactions on Sustainable Energy. - 1949-3029 .- 1949-3037. ; 7:4, s. 1362-1370
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Tidskriftsartikel (refereegranskat)abstract
- The equivalent circuit method can be an effective modelling technique for system studies of point absorbing wave energy converters (WECs). For the continuously evolving design and study of WEC systems, an instruction on how to draw the corresponding equivalent RLC circuit model is needed. It is not only vital to make sure the model is correct, but to allow the model to be easily adapted for different cases and implemented by different researchers. This paper presents a force analysis oriented methodology based on a typical WEC unit composed of a heaving buoy and a linear generator. Three cases are studied in order to demonstrate the procedures: the generator with a retracting spring, the connection line with a rubber damper, and buoy motion in both heave and surge directions. The presented methodology serves as a guide to produce non-linear circuit models that give a reliable description of the dynamics of real wave energy systems.
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| 18. |
- Isberg, Jan, 1964-, et al.
(författare)
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Control of rapid phase oscillations in the modelling of large wave energy arrays
- 2015
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Ingår i: International Journal of Marine Energy. - : Elsevier. - 2214-1669. ; 11, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Jin, Peng, et al.
(författare)
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Performance optimization of a coaxial-cylinder wave energy converter
- 2019
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 174, s. 450-459
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Tidskriftsartikel (refereegranskat)abstract
- To achieve a wider frequency range where the device has a larger capture width ratio, the performance of a heaving coaxial-cylinder wave energy converter is optimized through actively controlled generator damping and stiffness using a linear frequency domain model. The generator power take-off system is modeled as a damping-spring system, and the numerical model is validated against published results. The coupled dynamics of a two-body model is analyzed to search for the optimal generator damping and stiffness leading to maximal capture width ratio. The optimization process, which can be decoupled into two independent steps, leads to an improved performance of the device, with increased frequency bandwidth and better capture width ratio. The effects of water depth, mooring stiffness, and the dimensions of the WEC on the capture width ratio are also studied, and parameter values are identified which correspond to optimal performance of the device.
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| 20. |
- Ning, Dezhi, et al.
(författare)
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Hydrodynamic performance of a pile-restrained WEC-type floating breakwater : An experimental study
- 2016
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 95, s. 531-541
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a system which integrates an oscillating buoy type wave energy converter with a vertical pile-restrained floating breakwater is introduced. A preliminary experimental study on the hydrodynamic performance of the system is carried out in a wave flume under the action of regular waves. A current controller-magnetic powder brake system is used to simulate the power generation system. The design is verified against published results. The power-take off damping characteristics are investigated, and the current controller-magnetic powder brake system can simulate the (approximate) Coulomb damping force very well. The effects of various parameters, including wave period and wave height, dimensions of the system and excitation current, on the hydrodynamic performance are investigated. Results indicate that the power take-off damping force, draft and relative width between the floating breakwater and the wavelength have a significant influence on the hydrodynamic performance of the system. A range can be observed for which the capture width ratio of the system can achieve approximately 24% while transmission coefficient was kept lower than 0.50 with the proper adjustment of power take-off damping force, and the floating breakwater performs in an effective manner. The new concept provides a promising way to utilize wave energy cost-effectively.
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| 21. |
- Ning, Dezhi, et al.
(författare)
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Hydrodynamic performance of an oscillating wave surge converter in regular and irregular waves : an experimental study
- 2017
-
Ingår i: Journal of Marine Science and Technology. - 0948-4280 .- 1437-8213. ; 25:5, s. 520-530
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Tidskriftsartikel (refereegranskat)abstract
- A series of physical experiments are carried out to investigate the hydrodynamic performance of a bottom-hinged flap-type oscillating wave surge converter (OWSC). The power take-off (PTO) system in the OWSC is achieved with the magnetic powder brake. Both regular and irregular wave conditions are considered. It is observed that the capture width ratio (CWR) of the proposed OWSC is strongly affected by the PTO damping torque, incident wave amplitude, inertia of the structure and wave spectrum etc.
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| 22. |
- Parwal, Arvind, et al.
(författare)
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Energy management for a grid-connected wave energy park through a hybrid energy storage system
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 231, s. 399-411
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Tidskriftsartikel (refereegranskat)abstract
- The concern for climate change and energy consumption has increased the demand for renewable energy production considerably. Marine energy sources attract attention because of their high energy density. Wave energy is an attractive renewable energy source with large potential. Due to the nature of the ocean waves, a linear wave energy converter generates intermittent power. It is therefore crucial to regularize the power before connecting to the grid. Energy storage systems present effective ways to minimize the power fluctuations and deliver a steady power to the grid. In this paper, we present an energy management control system with a dynamic rate limiter. The method is applied to control a hybrid energy storage system, combining battery and supercapacitor, with a fully active topology controlled by the power converters. The results show that the method is able to control the charging and discharging states of the battery and the supercapacitor, and minimize the power fluctuation to the grid. The algorithm ensures low losses by shifting the required power and the stored power smoothly over the energy storage system.
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| 23. |
- Parwal, Arvind, et al.
(författare)
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Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden : A Status Update
- 2015
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Konferensbidrag (refereegranskat)abstract
- This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.
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| 24. |
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| 25. |
- Sjökvist, Linnea, et al.
(författare)
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Calculating Buoy Response for a Wave Energy Converter - a Comparsion Between Two Computational Methods and Experimental Results
- 2017
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Ingår i: Theoretical and Applied Mechanics Letters. - : Elsevier BV. - 2095-0349. ; 7:3, s. 164-168
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Tidskriftsartikel (refereegranskat)abstract
- When designing a wave power plant, reliable and fast simulation tools are required. Computational fluid dynamics (CFD) software provides high accuracy but with a very high computational cost, and in operational, moderate sea states, linear potential flow theories may be sufficient to model the hydrodynamics. In this paper, a model is built in COMSOL Multiphysics to solve for the hydrodynamic parameters of a point-absorbing wave energy device. The results are compared with a linear model where the hydrodynamical parameters are computed using WAMIT, and to experimental results from the Lysekil research site. The agreement with experimental data is good for both numerical models.
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| 26. |
- Sjökvist, Linnea, et al.
(författare)
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Numerical models for the motion and forces of point-absorbing wave energy converters in extreme waves
- 2017
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 145, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Reliable simulation tools are necessary to study the performance and survivability of wave energy devices, since experiments are both expensive and difficult to implement. In particular, survivability in nonlinear, high waves is one of the largest challenges for wave energy, and since the wave loads and dynamics are largely model dependent, each device must be studied separately with validated tools. In this paper, two numerical methods based on fully nonlinear computational fluid dynamics (CFD) are presented and compared with a simpler linear method. All three methods are compared and validated against experimental data for a point-absorbing wave energy converter in nonlinear, high waves. The wave energy converter consists of a floating buoy attached to a linear generator situated on the seabed. The line forces and motion of the buoy are studied, and computational cost and accuracy are compared and discussed. Whereas the simpler linear method is very fast, its accuracy is not sufficient in high and extreme waves, where instead the computationally costly CFD methods are required. The OpenFOAM model showed the highest accuracy, but also a higher computational cost than the ANSYS Fluent model.
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| 27. |
- Sjökvist, Linnea, et al.
(författare)
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Peak forces on a point absorbing wave energy converter impacted by tsunami waves
- 2019
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 133, s. 1024-1033
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Tidskriftsartikel (refereegranskat)abstract
- Although a tsunami wave in deep sea can be simulated using linear shallow water theory, the wave dynamics of a tsunami running up a continental shelf is very complex, and different phenomena may occur, depending on the width and profile of the shelf, the topography of the coast, incident angle of the tsunami and other factors. How to simulate tsunami waves at an intermediate depth is studied in this paper by using three different simulation approaches for tsunamis, a soliton, a simulated high incident current and a dam-break approach. The surface wave profiles as well as the velocity- and pressure profiles for the undisturbed waves are compared. A regular Stokes 5th wave of the same amplitude is simulated for comparison. A wave energy converter model, previously validated with wave tank experiment, is then used to study the survivability of the Uppsala University wave energy device for the different waves. The force in the mooring line is studied together with the resulting force on a bottom mounted column, corresponding to the linear generator on the seabed.
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| 28. |
- Sjökvist, Linnea, et al.
(författare)
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Peak Forces on Wave Energy Linear Generators in Tsunami and Extreme Waves
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:9
-
Tidskriftsartikel (refereegranskat)abstract
- The focus of this paper is the survivability of wave energy converters (WECs) in extreme waves and tsunamis, using realistic WEC parameters. The impact of a generator damping factor has been studied, and the peak forces plotted as a function of wave height. The paper shows that an increased damping decreases the force in the endstop hit, which is in agreement with earlier studies. However, when analyzing this in more detail, we can show that friction damping and velocity dependent generator damping affect the performance of the device differently, and that friction can have a latching effect on devices in tsunami waves, leading to higher peak forces. In addition, we study the impact of different line lengths, and find that longer line lengths reduce the endstop forces in extreme regular waves, but on the contrary increase the forces in tsunami waves due to the different fluid velocity fields.
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| 29. |
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| 30. |
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| 31. |
- Sjökvist, Linnea
(författare)
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Wave Loads and Peak Forces on Moored Wave Energy Devices in Tsunamis and Extreme Waves
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface gravity waves carry enormous amounts of energy over our oceans, and if their energy could be harvested to generate electricity, it could make a significant contribution to the worlds power demand. But the survivability of wave energy devices in harsh operating conditions has proven challenging, and for wave energy to be a possibility, peak forces during storms and extreme waves must be studied and the devices behaviour understood. Although the wave power industry has benefited from research and development in traditional offshore industries, there are important differences. Traditional offshore structures are designed to minimize power absorption and to have small motion response, while wave power devices are designed to maximize power absorption and to have a high motion response. This increase the difficulty of the already challenging survivability issue. Further, nonlinear effects such as turbulence and overtopping can not be neglected in harsh operating conditions. In contrast to traditional offshore structures, it is also important to correctly account for the power take off system in a wave energy converter (WEC), as it is strongly coupled to the devices behaviour.The focus in this thesis is the wave loads and the peak forces that occur when a WEC with a limited stroke length is operated in waves higher than the maximum stroke length. The studied WEC is developed at Uppsala University, Sweden, and consists of a linear generator at the seabed that is directly driven by a surface buoy. A fully nonlinear CFD model is developed in the finite volume software OpenFOAM, and validated with physical wave tank experiments. It is then used to study the motion and the forces on the WEC in extreme waves; high regular waves and during tsunami events, and how the WECs behaviour is influenced by different generator parameters, such as generator damping, friction and the length of the connection line. Further, physical experiments are performed on full scale linear generators, measuring the total speed dependent damping force that can be expected for different loads. The OpenFOAM model is used to study how the measured generator behaviour affects the force in the connection line.
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| 32. |
- Thomas, Simon, et al.
(författare)
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A model free control based on machine learning for energy converters in an array
- 2018
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Ingår i: Big Data and Cognitive Computing. - : MDPI. - 2504-2289. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a model-free, "on-the-fly" learning control strategy for arrays of energy converters with adjustable generator damping. The devices are arranged so that they are affected simultaneously by the energy medium. Each device uses a different control strategy, of which at least one has to be the machine learning approach presented in this paper. During operation all energy converters record the absorbed power and control output; the machine learning device gets the data from the converter with the highest power absorption and so learns the best performing control strategy for each state. Consequently, the overall network has a better overall performance than each individual strategy. This concept is evaluated for wave energy converter (WEC) with numerical simulations and experiments with physical scale models in a wave tank. In the first of two numerical simulations, the learnable WEC works in an array with four WECs applying a constant damping factor. In the second simulation, two learnable WECs were learning with each other. It showed that in the first test the WEC was able to absorb as much as the best constant damping WEC, while in the second run it could absorb even slightly more. During the physical model test, the ANN showed its ability to select the better of two possible damping coefficients based on real world input data.
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| 33. |
- Thomas, Simon, et al.
(författare)
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Experimental and numerical collaborative latching control of wave energy converter arrays
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:11
-
Tidskriftsartikel (refereegranskat)abstract
- A challenge while applying latching control on a wave energy converter (WEC) is to find a reliable and robust control strategy working in irregular waves and handling the non-ideal behavior of real WECs. In this paper, a robust and model-free collaborative learning approach for latchable WECs in an array is presented. A machine learning algorithm with a shallow artificial neural network (ANN) is used to find optimal latching times. The applied strategy is compared to a latching time that is linearly correlated with the mean wave period: It is remarkable that the ANN-based WEC achieved a similar power absorption as the WEC applying a linear latching time, by applying only two different latching times. The strategy was tested in a numerical simulation, where for some sea states it absorbed more than twice the power compared to the uncontrolled WEC and over 30% more power than a WEC with constant latching. In wave tank tests with a 1:10 physical scale model the advantage decreased to +3% compared to the best tested constant latching WEC, which is explained by the lower advantage of the latching strategy caused by the non-ideal latching of the physical power take-off model.
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| 34. |
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| 35. |
- Thomas, Simon, et al.
(författare)
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Performance of a Direct-Driven Wave Energy Point Absorber with High Inertia Rotatory Power Take-off
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- An alternating rotatory generator using an eddy current break is developed as a physicalscale model of a direct-driven floating point absorber power take-off (PTO) for wave tank tests. It isshown that this design is a simple and cost-effective way to get an accurate linear damping PTO. Thedevice shows some beneficial characteristics, making it an interesting option for full scale devices:For similar weights the inertia can be significantly higher than for linear generators, allowing it tooperate with natural frequencies close to typical wave frequencies. The influence of the higher inertiaon the power absorption is tested using both a numerical simulation and physical wave tank tests.With the increased inertia the PTO is able to absorb more than double the energy of a comparabledirect-driven linear generator in some sea states. Moreover, the alternating rotatory generator allowsthe absorption characteristic to be tuned by changing the inertia and the generator damping.
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| 36. |
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| 37. |
- Ulvgård, Liselotte, 1988-, et al.
(författare)
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Line Force and Damping at Full and Partial Stator Overlap in a Linear Generator for Wave Power
- 2016
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 4:4
-
Tidskriftsartikel (refereegranskat)abstract
- A full scale linear generator for wave power has been experimentally evaluated bymeasuring the line force and translator position throughout the full translator stroke. The measuredline force, in relation to translator speed, generator damping and stator overlap, has been studied bycomparing the line force and the damping coefficient, γ, for multiple load cases along the translatorstroke length. The study also compares the generator ’s behavior during upward and downwardmotion, studies oscillations and determines the no load losses at two different speeds. The generatordamping factor, γ, was determined for five different load cases during both upward and downwardmotion. The γ value was found to be constant for full stator overlap and to decrease linearly witha decreasing overlap, as the translator moved towards the endstops. The decline varied with theexternal load case, as previously suggested but not shown. In addition, during partial stator overlap,a higher γ value was noted as the translator was leaving the stator, compared to when it was enteringthe stator. Finally, new insights were gained regarding how translator weight and generator dampingwill affect the translator downward motion during offshore operation. This is important for powerproduction and for avoiding damaging forces acting on the wave energy converter during operation.
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| 38. |
- Wang, Liguo, et al.
(författare)
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Constrained optimal control of a point absorber wave energy converter with linear generator
- 2015
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Ingår i: Journal of Renewable and Sustainable Energy. - : AIP Publishing. - 1941-7012. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates a method for optimal control of a point absorbing wave energy converter by considering the constraints on motions and forces in the time domain. The problem is converted to an optimization problem with the cost function being convex quadratic and the constraints being nonlinear. The influence of the constraints on the converter is studied, and the results are compared with uncontrolled cases and established theoretical bounds. Since this method is based on the knowledge of the future sea state or the excitation force, the influence of the prediction horizon is indicated. The resulting performance of the wave energy converter under different regular waves shows that this method leads to a substantial increase in conversion efficiency.
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| 39. |
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| 40. |
- Wu, Jinming, et al.
(författare)
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Latching and Declutching Control of the Solo Duck Wave-Energy Converter with Different Load Types
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- The solo duck wave-energy converter (WEC) captures power in a point absorber manner, hence it exhibits high power-capture efficiency within only a narrow bandwidth. Passive control is characterized by a unidirectional power flow, and thus its engineering implementation can be simplified. In this paper, two typical passive control strategies, latching and declutching control, are applied to the solo duck WEC to improve its power-capture performance at wave periods larger and smaller than the natural period of the WEC, respectively. Special attention is paid to the peak value of instantaneous WEC performance parameters, including the peak motion excursion, the peak power take-off (PTO) moment, and the peak-to-average power ratio, when the captured power is maximized. Performance differences between the linear and coulomb loads are also investigated. Results show that both latching and declutching control can effectively improve captured power, but also incidentally increase the peak motion excursion and peak-to-average power ratio. When under latching and declutching control, the coulomb load leads to the same maximum relative capture width and peak motion excursion as the linear load, but presents smaller peak PTO moment and peak-to-average power ratio than the linear load, hence making the coulomb load the better choice for the solo duck WEC.
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| 41. |
- Wu, Jinming, et al.
(författare)
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Numerical and Experimental Study of the Solo Duck Wave Energy Converter
- 2019
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- The Edinburgh Duck is one of the highly-efficient wave energy converters (WECs). Compared to the spine-connected Duck configuration, the solo Duck will be able to use the point absorber effect to enhance its power capture performance. In this paper, a 3D computational fluid dynamic (CFD) model is developed to predict the hydrodynamic performance of the solo Duck WEC in regular waveswithin a wide range ofwave steepness until the Duck capsizes. A set of experiments was designed to validate the accuracy of the CFD model. Boundary element method (BEM) simulations are also performed for comparison. CFD results agree well with experimental results and the main difference comes from the friction in the mechanical transmission system. CFD results also agree well with BEM results and differences appear at large wave steepness as a result of two hydrodynamic nonlinear factors: the nonlinear waveform and the vortex generation process. The influence of both two nonlinear factors iscombined to be quantitatively represented by the drag torque coefficient.The vortex generation process is found to cause a rapid drop of the pressure force due to the vortexes taking away the kinetic energy from the fluid.
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| 42. |
- Wu, Jinming, et al.
(författare)
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Optimizing the Performance of Solo Duck Wave Energy Converter in Tide
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- The high efficiency performance of the Edinburgh Duck wave energy converter (WEC) in 2D regular wave tests makes it a promising wave energy conversion scheme. A solo Duck WEC will be able to apply the point absorber effect to further enhance its performance. Since released degree of freedom will decrease the efficiency, a Duck WEC with fixed pitching axis will be a better option. However, for fixed supported WECs, tide is a non-ignorable consideration. In this paper, a movable mass method is utilized in the whole tidal range to not only balance the Duck to appropriate beak angles, but also follow the variation of hydrodynamic coefficients to keep cancelling the reactance of the system impedance so that complex conjugate control can be realized to optimize the power capture performance of the Duck WEC in tide. Results show that the beak angle should be adjusted to as large a value as possible so that the response amplitude of the Duck at maximum relative capture width will be reasonable small, and the lowest weight of the movable mass is found when its designed position locates at the center of the Duck profile.
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| 43. |
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| 44. |
- Wu, Jinming, et al.
(författare)
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Performance analysis of solo Duck wave energy converter arrays under motion constraints
- 2017
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 139, s. 155-169
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the power capture performance of solo Duck wave energy converter (WEC) arrays. The barrier function method combined with a quasi-Newton BFGS optimization algorithm is applied to find the maximum captured power of the array when the Ducks are under motion constraints. Based on this optimized maximum captured power, the effects of separation distance, wave period, incident wave direction and Duck width on the array performance are investigated. For the two Ducks array, results show that the alternative constructive and destructive interaction stripes in the contour plot of the q-factor variation with non-dimensional separation distance are resulted from the diffracted wave pattern from each Duck, and the hydrodynamic interaction strength is reduced when constraints affect the performance. For the three Ducks array, the middle Duck shows larger variability of captured power than the side Ducks due to experiencing double in phase diffracted wave from the side ones. The captured power of the solo Duck WEC array is sensitive to incident wave direction, and arrays with Ducks of smaller width are found to have better performance in power capture efficiency.
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| 45. |
- Wu, Jinming, et al.
(författare)
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Real-time latching control strategies for the solo Duck wave energy converter in irregular waves
- 2018
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 222, s. 717-728
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Tidskriftsartikel (refereegranskat)abstract
- As a point absorber, the solo Duck wave energy converter (WEC) shows high power capture efficiency within a narrow bandwidth around the natural period. In this paper, real-time latching control is applied to the solo Duck WEC in irregular waves to improve its performance in sea states away from the natural period. Two predictive latching control strategies, in which one is close-to-optimal and the other is sub-optimal, and one non-predictive strategy are considered. The improvement of the WEC performance due to latching control is studied. Compared to the performance under simple resistive control, the three latching control strategies show almost equivalent control effect, leading to an average increase of the maximum relative capture width by around 70% and an average decrease of the optimal power take-off (PTO) damping coefficient by around 60%. Since the non-predictive strategy requires no prediction of future excitation force and WEC motion, it can be identified as the best choice for the solo Duck WEC under latching control. Although latching control leads to significant increase of fatigue load on the WEC hull like other advanced controls, it does not cause additional fatigue damage to the PTO.
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| 46. |
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| 47. |
- Zhao, Xuan-lie, et al.
(författare)
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Effect of the PTO damping force on the wave pressures on a 2-D wave energy converter
- 2017
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Ingår i: Journal of Hydrodynamics. - 1001-6058 .- 1000-4874. ; 29:5, s. 863-870
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Tidskriftsartikel (refereegranskat)abstract
- The information of the wave loads on a wave energy device in operational waves is required for designing an efficient wave energy system with high survivability. It is also required as a reference for numerical modeling. In this paper, a novel system, which integrates an oscillating wave energy converter with a pile-restrained floating breakwater, is experimentally investigated in a 2-D wave flume. The measurements of the wave pressure on the wet-surface of the device are made as the function of the power take-off (PTO) damping force. It is shown that the wave pressure is significantly affected by the PTO system, in particular, at the edges, and the wave pressure varies under different wave conditions. From the results, conclusions can be drawn on how the PTO damping force and wave conditions affect the loads on the device, which is of engineering concern for constructing safe and reliable devices.
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