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  • 1.
    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.

  • 2.
    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.
    Layout design of wave energy parks by a genetic algorithm2018In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 154, p. 252-261Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    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.
    Parameter optimization in wave energy design by a genetic algorithm2017In: Proceeings 32nd International Workshop on Water Waves and Floating Bodies, 2017Conference paper (Refereed)
  • 4.
    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)
  • 5.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    N=(4,4) supersymmetry and T-duality2012In: Symmetry, ISSN 2073-8994, Vol. 4, no 4, p. 603-625Article in journal (Refereed)
  • 6.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    The Complex World of Superstrings: On Semichiral Sigma Models and N=(4,4) Supersymmetry2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Non-linear sigma models with extended supersymmetry have constrained target space geometries, and can serve as effective tools for investigating and constructing new geometries. Analyzing the geometrical and topological properties of sigma models is necessary to understand the underlying structures of string theory.

    The most general two-dimensional sigma model with manifest N=(2,2) supersymmetry can be parametrized by chiral, twisted chiral and semichiral superfields. In the research presented in this thesis, N=(4,4) (twisted) supersymmetry is constructed for a semichiral sigma model. It is found that the model can only have additional supersymmetry off-shell if the target space has a dimension larger than four. For four-dimensional target manifolds, supersymmetry can be introduced on-shell, leading to a hyperkähler manifold, or pseudo-supersymmetry can be imposed off-shell, implying a target space which is neutral hyperkähler.

    Different sigma models and corresponding geometries can be related to each other by T-duality, obtained by gauging isometries of the Lagrangian. The semichiral vector multiplet and the large vector multiplet are needed for gauging isometries mixing semichiral superfields, and chiral and twisted chiral superfields, respectively. We find transformations that close off-shell to a N=(4,4) supersymmetry on the field strengths and gauge potentials of the semichiral vector multiplet, and show that this is not possible for the large vector multiplet.

    A sigma model parametrized by chiral and twisted chiral superfields can be related to a semichiral sigma model by T-duality. The N=(4,4) supersymmetry transformations of the former model are linear and close off-shell, whereas those of the latter are non-linear and close only on-shell. We show that this discrepancy can be understood from T-duality, and find the origin of the non-linear terms in the transformations.

    List of papers
    1. Pseudo-Hyperkähler Geometry and Generalized Kähler Geometry
    Open this publication in new window or tab >>Pseudo-Hyperkähler Geometry and Generalized Kähler Geometry
    2011 (English)In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 95, no 3, p. 211-222Article in journal (Refereed) Published
    Abstract [en]

    We discuss the conditions for additional supersymmetry and twisted super-symmetry in N = (2, 2) supersymmetric nonlinear sigma models described by one left and one right semi-chiral superfield and carrying a pair of non-commuting complex structures. Focus is on linear non-manifest transformations of these fields that have an algebra that closes off-shell. We find that additional linear supersymmetry has no interesting solution, whereas additional linear twisted supersymmetry has solutions with interesting geometrical properties. We solve the conditions for invariance of the action and show that these solutions correspond to a bi-hermitian metric of signature (2, 2) and a pseudo-hyperkahler geometry of the target space.

    Keywords
    supersymmetry, semi-chiral fields, sigma models, pseudo-hyperkahler geometry
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-149587 (URN)10.1007/s11005-010-0456-7 (DOI)000287856800001 ()
    Available from: 2012-10-26 Created: 2011-03-21 Last updated: 2017-12-11Bibliographically approved
    2. Sigma models with off-shell N = (4,4) supersymmetry and non-commuting complex structures
    Open this publication in new window or tab >>Sigma models with off-shell N = (4,4) supersymmetry and non-commuting complex structures
    2010 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, p. 055-Article in journal (Refereed) Published
    Abstract [en]

    We describe the conditions for extra supersymmetry in N = (2, 2) supersymmetric nonlinear sigma models written in terms of semichiral superfields. We find that some of these models have additional off-shell supersymmetry. The (4, 4) supersymmetry introduces geometrical structures on the target-space which are conveniently described in terms of Yano f-structures and Magri-Morosi concomitants. On-shell, we relate the new structures to the known bi-hypercomplex structures.

    Keywords
    Extended Supersymmetry, Sigma Models, Differential and Algebraic Geometry
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-135092 (URN)10.1007/JHEP09(2010)055 (DOI)000282370900002 ()
    Available from: 2010-12-06 Created: 2010-12-03 Last updated: 2017-12-11Bibliographically approved
    3. Off-shell N = (4,4) supersymmetry for new (2,2) vector multiplets
    Open this publication in new window or tab >>Off-shell N = (4,4) supersymmetry for new (2,2) vector multiplets
    2011 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 3, p. 088-Article in journal (Refereed) Published
    Abstract [en]

    We discuss the conditions for extra supersymmetry of the N = (2, 2) super-symmetric vector multiplets described in arXiv:0705.3201 [hep-th] and in arXiv:0808.1535 [hep-th]. We find (4, 4) supersymmetry for the semichiral vector multiplet but not for the Large Vector Multiplet.

    Keywords
    Supersymmetry and Duality, Superspaces, Differential and Algebraic Geometry
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-153951 (URN)10.1007/JHEP03(2011)088 (DOI)000289295300016 ()
    Available from: 2011-05-26 Created: 2011-05-23 Last updated: 2017-12-11Bibliographically approved
    4. Semichiral Sigma Models with 4D Hyperkähler Geometry
    Open this publication in new window or tab >>Semichiral Sigma Models with 4D Hyperkähler Geometry
    2013 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, p. 073-Article in journal (Refereed) Published
    Abstract [en]

    Semichiral sigma models with a four-dimensional target space do not support, extended N = (4, 4) supersymmetries off-shell [1, 2]. We contribute towards the understanding of the non-manifest on-shell transformations in (2,2) superspace by analyzing the extended on-shell supersymmetry of such models and find that a rather general ansatz for the additional supersymmetry (not involving central charge transformations) leads to hyperkahler geometry. We give non-trivial examples of these models.

    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:uu:diva-183358 (URN)10.1007/JHEP01(2013)073 (DOI)000315583200073 ()
    Available from: 2012-10-24 Created: 2012-10-24 Last updated: 2017-12-07Bibliographically approved
    5. N=(4,4) supersymmetry and T-duality
    Open this publication in new window or tab >>N=(4,4) supersymmetry and T-duality
    2012 (English)In: Symmetry, ISSN 2073-8994, Vol. 4, no 4, p. 603-625Article in journal (Refereed) Published
    Place, publisher, year, edition, pages
    MDPI, 2012
    Keywords
    supersymmetry, sigma models, semichiral superfields, T-duality
    National Category
    Other Physics Topics
    Research subject
    High Energy Physics; Mathematics
    Identifiers
    urn:nbn:se:uu:diva-183406 (URN)10.3390/sym4040603 (DOI)000208832800003 ()
    Available from: 2012-10-26 Created: 2012-10-25 Last updated: 2015-01-28Bibliographically approved
  • 7.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave energy parks with point-absorbers of different dimensions2017In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 74, p. 142-157Article in journal (Refereed)
    Abstract [en]

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

    The full text will be freely available from 2019-08-04 16:39
  • 8.
    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, ISSN 2310-3604, Vol. 2, no 3, p. 176-181Article in journal (Refereed)
  • 9.
    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, ISSN 1996-1073, 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.

  • 10.
    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)
  • 11. 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)
  • 12.
    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.

  • 13. 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)
  • 14.
    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, ISSN 1941-7012, 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. 

  • 15.
    Göteman, Malin
    et al.
    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.
    McNatt, Cameron
    Mocean Energy, Edinburgh, Scotland.
    Wave energy park interactions in short-crested waves2018Conference paper (Refereed)
  • 16.
    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)
  • 17.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Lindström, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Pseudo-Hyperkähler Geometry and Generalized Kähler Geometry2011In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 95, no 3, p. 211-222Article in journal (Refereed)
    Abstract [en]

    We discuss the conditions for additional supersymmetry and twisted super-symmetry in N = (2, 2) supersymmetric nonlinear sigma models described by one left and one right semi-chiral superfield and carrying a pair of non-commuting complex structures. Focus is on linear non-manifest transformations of these fields that have an algebra that closes off-shell. We find that additional linear supersymmetry has no interesting solution, whereas additional linear twisted supersymmetry has solutions with interesting geometrical properties. We solve the conditions for invariance of the action and show that these solutions correspond to a bi-hermitian metric of signature (2, 2) and a pseudo-hyperkahler geometry of the target space.

  • 18.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Lindström, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Rocek, M.
    Ryb, Itai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Sigma models with off-shell N = (4,4) supersymmetry and non-commuting complex structures2010In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 9, p. 055-Article in journal (Refereed)
    Abstract [en]

    We describe the conditions for extra supersymmetry in N = (2, 2) supersymmetric nonlinear sigma models written in terms of semichiral superfields. We find that some of these models have additional off-shell supersymmetry. The (4, 4) supersymmetry introduces geometrical structures on the target-space which are conveniently described in terms of Yano f-structures and Magri-Morosi concomitants. On-shell, we relate the new structures to the known bi-hypercomplex structures.

  • 19.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Lindström, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Rocek, Martin
    Stony Brook University, NY.
    Semichiral Sigma Models with 4D Hyperkähler Geometry2013In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 1, p. 073-Article in journal (Refereed)
    Abstract [en]

    Semichiral sigma models with a four-dimensional target space do not support, extended N = (4, 4) supersymmetries off-shell [1, 2]. We contribute towards the understanding of the non-manifest on-shell transformations in (2,2) superspace by analyzing the extended on-shell supersymmetry of such models and find that a rather general ansatz for the additional supersymmetry (not involving central charge transformations) leads to hyperkahler geometry. We give non-trivial examples of these models.

  • 20.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    McNatt, Cameron
    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, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, 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.

  • 21.
    Hai, Ling
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Methodology of Modelling a Wave Power System via an Equivalent RLC Circuit2016In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 4, p. 1362-1370Article in journal (Refereed)
    Abstract [en]

    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.

  • 22.
    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.

  • 23.
    Ning, Dezhi
    et al.
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Liu, Chengguo
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Zhang, Chongwei
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Zhao, Haitao
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Teng, Bin
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Hydrodynamic performance of an oscillating wave surge converter in regular and irregular waves: an experimental study2017In: Journal of Marine Science and Technology, ISSN 0948-4280, E-ISSN 1437-8213, Vol. 25, no 5, p. 520-530Article in journal (Refereed)
    Abstract [en]

    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.

  • 24.
    Ning, Dezhi
    et al.
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Zhao, Xuanlie
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kang, Haigui
    State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.
    Hydrodynamic performance of a pile-restrained WEC-type floating breakwater: An experimental study2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 95, p. 531-541Article in journal (Refereed)
    Abstract [en]

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

  • 25.
    Parwal, Arvind
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Remouit, Flore
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hong, Yue
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Francisco, Francisco
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castelucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hai, Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ulvgård, Liselotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nasir, M
    Chatzigiannakou, Maria Angiliki
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Haikonen, Kalle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ekström, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, C.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update2015Conference paper (Refereed)
    Abstract [en]

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

  • 26.
    Sjökvist, Linnea
    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.
    Peak Forces on Wave Energy Linear Generators in Tsunami and Extreme Waves2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 9, article id 1323Article in journal (Refereed)
    Abstract [en]

    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.

  • 27.
    Sjökvist, Linnea
    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.
    The Effect of Overtopping Waves on Peak Forceson a Point Absorbing WEC2016Conference paper (Refereed)
  • 28.
    Sjökvist, Linnea
    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.
    Rahm, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    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.
    Calculating Buoy Response for a Wave Energy Converter - a Comparsion Between Two Computational Methods and Experimental Results2017In: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 7, no 3, p. 164-168Article in journal (Refereed)
    Abstract [en]

    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.

  • 29.
    Sjökvist, Linnea
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Center for Natural Disaster Science (CNDS), Villavägen 16, SE-752 36 Uppsala, Sweden.
    Wu, Jinming
    Department of Mechanical Engineering, Harbin Institute of Technology, Harbin, China.
    Ransley, Edward
    School of Engineering, Plymouth University, UK.
    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.
    Numerical models for the motion and forces of point-absorbing wave energy converters in extreme waves2017In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 145, p. 1-14Article in journal (Refereed)
    Abstract [en]

    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.

  • 30.
    Ulvgård, Liselotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sjökvist, Linnea
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Line Force and Damping at Full and Partial Stator Overlap in a Linear Generator for Wave Power2016In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 4, no 4, article id 81Article in journal (Refereed)
    Abstract [en]

    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.

  • 31.
    Wang, Liguo
    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.
    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.
    Constrained optimal control of a point absorber wave energy converter with linear generator2015In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 7, article id 043127Article in journal (Refereed)
    Abstract [en]

    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.

  • 32.
    Wang, Liguo
    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.
    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.
    Constrained Optimal Control of Single and Arrays of Point-Absorbing Wave Energy Converters2016Conference paper (Refereed)
  • 33.
    Wu, Jinming
    et al.
    Harbin Inst Technol, Dept Mech Engn, Harbin 150001, Heilongjiang, Peoples R China..
    Yao, Yingxue
    Harbin Inst Technol, Shenzhen Grad Sch, Shenzhen 518055, Guangdong, Peoples R China..
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Zhou, Liang
    Harbin Inst Technol, Dept Mech Engn, Harbin 150001, Heilongjiang, Peoples R China..
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimizing the Performance of Solo Duck Wave Energy Converter in Tide2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 3, article id 289Article in journal (Refereed)
    Abstract [en]

    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.

  • 34.
    Wu, Jinming
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China.
    Yao, Yingxue
    Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, Guangdong, China.
    Zhou, Liang
    School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China.
    Chen, Ni
    School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China.
    Yu, Huifeng
    State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China.
    Li, Wei
    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.
    Performance analysis of solo Duck wave energy converter arrays under motion constraints2017In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 139, p. 155-169Article in journal (Refereed)
    Abstract [en]

    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.

  • 35.
    Wu, Jinming
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Harbin Inst Technol, Sch Mechatron Engn, Harbin.
    Yao, Yingxue
    Harbin Inst Technol, Shenzhen Grad Sch, Shenzhen.
    Zhou, Liang
    Harbin Inst Technol, Sch Mechatron Engn, Harbin.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Latching and Declutching Control of the Solo Duck Wave-Energy Converter with Different Load Types2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 12, article id 2070Article in journal (Refereed)
    Abstract [en]

    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.

  • 36.
    Wu, Jinming
    et al.
    School of Mechatronics Engineering, Harbin Institute of Technology, Heilongjiang, China.
    Zhao, Yingxue
    Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, Guangdong, China.
    Zhou, Liang
    School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Real-time latching control strategies for the solo Duck wave energy converter in irregular waves2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 222, p. 717-728Article in journal (Refereed)
    Abstract [en]

    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.

  • 37.
    Zhao, Xuan-lie
    et al.
    Dalian Univ Technol, State Key Lab Coastal & Offshore Engn, Dalian 116023, Peoples R China.
    Ning, De-zhi
    Dalian Univ Technol, State Key Lab Coastal & Offshore Engn, Dalian 116023, Peoples R China.; Hohai Univ, State Key Lab Hydrol Water Resources & Hydraul En, Nanjing 210098, Jiangsu, Peoples R China..
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kang, Hai-gui
    Dalian Univ Technol, State Key Lab Coastal & Offshore Engn, Dalian 116023, Peoples R China.
    Effect of the PTO damping force on the wave pressures on a 2-D wave energy converter2017In: Journal of Hydrodynamics, ISSN 1001-6058, E-ISSN 1000-4874, Vol. 29, no 5, p. 863-870Article in journal (Refereed)
    Abstract [en]

    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.

  • 38.
    Zhao, Xuanlie
    et al.
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Ning, Dezhi
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Kang, Haigui
    State Key of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effect of PTO on the dynamics of a WEC-type floating breakwater2016Conference paper (Refereed)
1 - 38 of 38
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