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  • 1.
    Bosi, Umberto
    et al.
    INRIA Bordeaux Sud-Ouest, France.
    Engsig-Karup, Allan P.
    DTU Technical University of Denmark, Denmark.
    Eskilsson, Claes
    RISE - Research Institutes of Sweden, Safety and Transport, Safety.
    Ricchiuto, Mario
    INRIA Bordeaux Sud-Ouest, France.
    Solai, Elie
    Université de Toulon, France.
    A high-order spectral element unified Boussinesq model for floating point absorbers2018In: Coastal Engineering Proceedings, 2018Conference paper (Refereed)
    Abstract [en]

    Nonlinear wave-body problems are important in renewable energy, especially in case of wave energy converters operating in the near-shore region. In this paper we simulate nonlinear interaction between waves and truncated bodiesusing an efficient spectral/hp element depth-integrated unified Boussinesq model. The unified Boussinesq model treatsalso the fluid below the body in a depth-integrated approach. We illustrate the versatility of the model by predictingthe reflection and transmission of solitary waves passing truncated bodies. We also use the model to simulate themotion of a latched heaving box. In both cases the unified Boussinesq model show acceptable agreement with CFDresults – if applied within the underlying assumptions of dispersion and nonlinearity – but with a significant reductionin computational effort.

  • 2.
    Engsig-Karup, Allan P.
    et al.
    DTU Technical University of Denmark, Denmark.
    Eskilsson, Claes
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. Aalborg University, Denmark.
    Spectral element FNPF simulations of focused wave groups impacting a fixed FPSO2018In: Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference, The International Society of Offshore and Polar Engineering , 2018, p. 1443-1450Conference paper (Refereed)
    Abstract [en]

    For  the assessment of experimental measurements of focused wave groups impacting a surface-piecing fixed structure, we present a new Fully Nonlinear Potential Flow (FNPF) model for simulation of unsteady water waves. The FNPF model is discretized in three  spatial dimensions (3D) using high-order prismatic - possibly curvilinear - elements using a  spectral  element  method (SEM) that has support for adaptive unstructured meshes. This  SEM-FNPF model is based on an Eulerian formulation and deviates from past works in that a  direct discretization of the Laplace problem is used making it straightforward to handle  accurately floating structural bodies of arbitrary shape. Our objectives are; i) present detail of a new SEM modelling developments and ii) to consider its application to address a wave-body interaction problem for nonlinear design waves and their interaction with a model-scale fixed Floating Production, Storage and Offloading vessel (FPSO).  We first reproduce  experimental measurements for focused design waves that represent a probably extreme  wave event for a sea state represented by a wave spectrum and seek to reproduce these measurements in a numerical wave tank. The validated input signal based on measurements is then generated in a NWT setup that includes the FPSO and differences in the signal caused by nonlinear diffraction is reported.

  • 3.
    Eskilsson, Claes
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. Aalborg University, Denmark.
    Palm, Johannes
    Chalmers University of Technology, Sweden.
    Simulations of floating wave energy devices using adaptive mesh refinement2019In: Advances in Renewable Energies Offshore / [ed] C. Guedes Soares, 2019, p. 431-438Conference paper (Refereed)
    Abstract [en]

    CFD simulations of floating wave energy converters are computationally very heavy. This paper deals with a straightforward attempt to cut down on the computational effort by using adaptive mesh refinement (AMR). We investigate the use of AMR for simulations involving floating bodies inside the open-source finite volume framework OpenFOAM. A simple error indicator based on the pressure jump over cell faces is used to drive the AMR. First the use of the error indicator is illustrated for propagation of a very steep stream function wave. Then the AMR technique is applied to two cases of floating bodies: (i) a floating box and (ii) a bottom reacting point-absorber. As expected the AMR significantly reduce the number of cells in the computational meshes and subsequently lower the  computational effort.

  • 4.
    Eskilsson, Claes
    et al.
    Aalborg University, Denmark.
    Palm, Johannes
    Chalmers University of Technology, Sweden.
    Bergdahl, Lars
    Chalmers University of Technology, Sweden.
    Simulations of Moored Wave Energy Converters Using OpenFOAM: Implementation and Applications2018In: Proceedings of 6th World Maritime Technology Conference, 2018Conference paper (Refereed)
    Abstract [en]

    In this paper we present and discuss the use of CFD for coupled mooring analysis of floating wave energy converters. We use the two-phase Navier-Stokes finite volume solver in OpenFOAM and a high-order finite element model for the cable dynamics. The implementation of the coupling is described in some detail and we show validation of the scheme against laboratory data. A comparison between RANS and Euler simulations isolates effects of viscosity and geometric scale for moored point-absorbers, and parametric pitch excitation is demonstrated. The inclusion of power take-off/control follow the same blueprint as the mooring restraint and we illustrate the use of phase control.

  • 5.
    Koukounas, Dimitrios
    et al.
    Chalmers University of Technology, Sweden.
    Eskilsson, Claes
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. Aalborg University, Denmark.
    Engsig-Karup, Allan P.
    DTU Technical University of Denmark, Denmark.
    Numerical simulations of Peregrine breathers using a spectral element model2018In: Proceedings of the 37th International Conference on Ocean, Offshore and Arctic EngineeringOMAE 2018June 17-22, 2018, Madrid, Spain, 2018, Vol. 11A, article id OMAE2018-77648Conference paper (Refereed)
    Abstract [en]

    Breather solutions to the nonlinear Schrödinger equation have been put forward as a possible prototype for rouge waves and have been studied both experimentally and numerically. In the present study, we perform high resolution simulations of the evolution of Peregrine breathers in finite depth using a fully non- linear potential flow spectral element model. The spectral ele- ment model can accurately handle very steep waves as illustrated by modelling solitary waves up to limiting steepness. The an- alytic breather solution is introduced through relaxation zones. The numerical solution obtained by the spectral element model is shown to compare in large to the analytic solution as well as to CFD simulations of a Peregrine breather in finite depth pre- sented in literature. We present simulations of breathers over variable bathymetry and 3D simulations of a breather impinging on a mono-pile.

  • 6.
    Palm, Johannes
    et al.
    Chalmers University of Technology, Sweden.
    Bergdahl, Lars
    Chalmers University of Technology, Sweden.
    Eskilsson, Claes
    RISE - Research Institutes of Sweden, Safety and Transport, Safety. Aalborg University, Denmark.
    Parametric excitation of moored wave energy converters using viscous and non-viscous CFD simulations2019In: Advances in Renewable Energies Offshore / [ed] C. Guedes Soares, Taylor & Francis Group, 2019, p. 455-462Conference paper (Refereed)
    Abstract [en]

    The paper discusses the use of CFD simulations to analyse the parametric excitation of moored, full scale wave energy converters in six degrees of freedom. We present results of VOF- RANS and VOF-Euler simulations in Open FOAM® for two body shapes: (i) a truncated cylinder; and (ii) a cylinder with a smooth hemispherical bottom. Flow characteristics show large differences in smoothness of flow between the hull shapes, where the smoother shape results in a larger heave response. However the increased amplitude makes it unstable and parametric pitch excitation occurs with amplitudes up to 30°. The responses in surge, heave and pitch (including the transition to parametric motion) are found to be insensitive to the viscous effects. This is notable as the converters are working in resonance. The effect of viscous damping was visible in the roll motion, where the RANS simulations showed a smaller roll. However, the roll motion was found to be triggered not by wave-body interaction with the incident wave, but by reflections from the side walls. This highlights the importance of controlling the reflections in numerical wave tanks for simulations with WEC motion in six degrees of freedom.

1 - 6 of 6
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