![]() ![]() show that the hydrodynamic efficiency of a fixed oscillating water column (OWC) attains a maximum value at a critical wave slope and decreases when the wave nonlinearity becomes either stronger or weaker. Additionally, the wave nonlinearity affects the hydrodynamic efficiency of a WEC. ![]() The difference in loads calculated including the wave nonlinearity versus the loads calculated by purely linear models is important for load design and survival and is examined by Viuff et al. Wave breaking, as an extreme case, is a very nonlinear process (see review in Saincher and Banerjee ). As the relative water depth decreases and/or the relative wave height increases (relative with respect to the wave length), then the linear theory breaks down and the wave becomes nonlinear. Hydrodynamic Nonlinearities-Typesįigure 3 shows that linear theory is only valid in deep and intermediate water depths for small amplitude waves. Modeling these nonlinearities requires a more thorough treatment of the NSE, without the full range of linearing assumptions inherent to LPF, as detailed in Section 2.3. Section 2.1 discusses the types of nonlinearities which can appear during WEC operation and Section 2.2 details the factors which influence the prevalence or absence of these nonlinearities in WECs. ![]() However, in reality, this does not hold for a large portion of the simulations required for WEC design, due to nonlinear effects. Thus, if the wave height is doubled, the resulting amplitude of WEC motion also doubles. Correspondingly, this type of modeling approach leads to a linear relationship between the input wave and the output WEC motion. The traditional modeling approach treats the hydrodynamic forces linearly (see Falnes for an in-depth description), for time domain and/or frequency domain analyses of the WEC based on LPF. OutlineĪ good description of WEC hydrodynamics is given in Todalshaug, detailing the fundamental principles of wave absorption and hydrodynamic forces on bodies. In addition, a good book detailing the current state-of-the-art in WEC hydrodynamic modeling was recently published in 2016. focus on the modeling methods for WEC survival in extreme seas. Saincher and Banerjee review the influence of wave breaking on WEC hydrodynamics. review integrated approaches to numerical and experimental testing, from full-scale prototype and physical wave tank (PWT) models to RANS and LPF simulations. specifically focus on RANS modeling of WECs. Nonlinear hydrodynamic modeling of WECs is the focus of the reviews in Wolgamot and Fitzgerald and Penalba et al. reviewed hydrodynamic modeling for WEC arrays, which were again later reviewed in DeChowdhury et al. Nearly three decades later, in 2012, Li and Yu reviewed the modeling methods available for point absorber type WECs. Previous ReviewsĪ very early comparison of numerical methods in free-surface hydrodynamics can be found in Yeung from the Hydrodynamics of Ocean Wave-Energy Utilization Symposium in 1985. ![]() In this paper, we set out to review the CFD theories and related methods that are intermediate to LPF and RANS with a view to identifying promising avenues for a specialist WEC simulation tool. CFD Theories that are intermediate to LPF and RANS exist, but compared to LPF and RANS are relatively under-developed with few commercial or open-source software products available and knowledge of the properties of these approaches is often only available to the creators of research codes. We propose that a specialist WEC simulation tool based on an intermediate CFD theory is needed. It is the contention of the authors that neither of these mature approaches satisfies the requirements for an ideal WEC simulation tool, the fast methods are not accurate or robust enough and the accurate methods are not fast or affordable enough. Mature software packages, both commercial and open-source, based on the opposite extremes of the speed-fidelity spectrum are available and their properties are relatively well known. ![]()
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