Comparison of fully nonlinear and weakly nonlinear potential flow solvers for the study of wave energy converters undergoing large amplitude motions (original) (raw)
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2010
The purpose of this work is to develop advanced numerical tools for modeling two-way fully nonlinear interactions of ocean surface waves (irregular waves in the general situation) with a submerged structure undergoing large amplitude motion. The final aim is to apply these models to simulating the behavior of a point-absorber-type Wave Energy Converter (WEC). In our modeling approach, an existing twodimensional Numerical Wave Tank (NWT), based on potential flow theory, is extended to include a submerged horizontal cylinder of arbitrary cross-section. The mathematical problem and related numerical solution are first introduced. Then we present two applications, first for the prescribed motion of a submerged body in a wave field (including the case of a fixed cylinder, such as in Chaplin's (1984) experiments), and then for a freely-moving body in waves. In the first application, we consider the forced oscillations of a circular cylinder, either in the vertical direction or in a circular motion (with comparison to the theoretical results of Wu (1993)). In the second application, dynamical equations describing the body motion are solved simultaneously with the hydrodynamic problem, which requires correctly representing the coupling forces between both mechanical and hydrodynamic problems. This is illustrated by preliminary simulations for the free motion in periodic waves of an idealized WEC; these results are favorably compared to a linear model.
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Computational modeling applied to the study of wave energy converters (WEC)
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The employment of numerical methods to solve engineering problems is a reality, as well as, the worldwide concern about the need of renewable and alternative energy sources. Thus, this work presents a computational model capable of simulating the operating principle of some Wave Energy Converters (WEC). To do so, the device is coupled in a wave tank, where the sea waves are reproduced. The Finite Volume Method (FVM) and the Volume of Fluid (VOF) model are adopted. The results showed that the converter's operating principle can be numerically reproduced, demonstrating the potential of computational modeling to study this subject.
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Volume 4: Offshore Geotechnics; Ronald W. Yeung Honoring Symposium on Offshore and Ship Hydrodynamics, 2012
To date, mathematical models for wave energy devices typically follow Cummins equation, with hydrodynamic parameters determined using boundary element methods. The resulting models are, for the vast majority of cases, linear, which has advantages for ease of computation and a basis for control design to maximise energy capture. While these linear models have attractive properties, the assumptions under which linearity is valid are restrictive. In particular, the assumption of small movements about an equilibrium point, so that higher order terms are not significant, needs some scrutiny. While this assumption is reasonable in many applications, in wave energy the main objective is to exaggerate the movement of the device through resonance, so that energy capture can be maximised. This paper examines the value of adding specific nonlinear terms to hydrodynamic models for wave energy devices, to improve the validity of such models across the full operational spectrum.
Engineering Analysis with Boundary Elements, 2012
The purpose of this work is to develop advanced numerical tools for modeling two-way fully nonlinear interactions of ocean surface waves (irregular waves in the general situation) with submerged structures undergoing large amplitude motion, that could represent Wave Energy Converters (WECs). In our modeling approach, an existing two-dimensional Numerical Wave Tank (NWT), based on potential flow theory, is extended to include a submerged horizontal cylinder of arbitrary cross-section. The mathematical problem and related numerical solution are first introduced. Then, conservation of volume and conservation of energy are checked, respectively in the case of a circular cylinder in a prescribed large amplitude motion and in the case of a circular cylinder in a free motion. Interactions between waves and a submerged circular cylinder computed by the model are then compared to mathematical solutions for two situations: a cylinder in prescribed motion and a freely moving cylinder.
Nonlinear modelling of interaction of waves with a moving submerged body
2011
The work presented herein relates to the development of an advanced simulation code allowing a description of the motion of a submerged body under the action of waves, including large oscillations. The long-term goal of this tool is to model the behaviour of certain types of submerged Wave Energy Recovery Systems (WERS). In this study a potential flow approach was adopted to describe the hydrodynamic part, limited to 2DV (i.e. in the vertical plane), corresponding to the case of a numerical wave tank. The model used to generate and propagate waves is a fully nonlinear potential flow model, based on a high-order boundary element method developed by Grilli and his colleagues over the past 20 years. This model, which has already been largely validated for a number of different oceanic and coastal applications, has been modified to take into account the presence of either a fixed or moving rigid submerged body, by including the computation of the hydrodynamic forces acting on the body. ...