Numerical and Experimental Modelling of a Wave Energy Converter Pitching in Close Proximity to a Fixed Structure

Abstract

Free-floating bodies are commonly modelled using Cummins' equation based on linear potential flow theory and including non-linear forces when necessary. In this paper, this methodology is applied to a body pitching around a fixed hinge (not free-floating) located close to a second bottom-fixed body. Due to the configuration of the setup, strong hydrodynamic interactions occur between the two bodies. An investigation is made into which non-linear forces need to be included in the model in order to accurately represent reality without losing computational efficiency. The non-linear forces investigated include hydrostatic restoring stiffness and different formulations of excitation forces and quadratic drag forces. Based on a numerical comparison, it is concluded that the different non-linear forces, except for the quadratic drag force, have a minor influence on the calculated motion of the pitching body. Two formulations of the quadratic drag force are shown to result in similar motions, hence the most efficient one is preferred. Comparisons to wave basin experiments show that this model is, to a large extent, representative of reality. At the wave periods where the hydrodynamic interactions between the bodies are largest, however, the amplitudes of motion measured in the wave basin are lower than those calculated numerically.

Fast nonlinear Froude–Krylov force calculation for prismatic floating platforms: a wave energy conversion application case

“…The currently widespread simulation software WEC-Sim (Lawson et al 2014) also includes a mesh-based NLFK computation feature, which has been applied to a bottom-referenced point absorber (Tosdevin et al 2019), to a self-referenced 2-body heaving point absorber (Van Rij et al 2018), and a multi-body WEC (Chandrasekaran and Sricharan 2020). Further examples of software including NLFK computation via a mesh are SIM-DYN (Somayajula and Falzarano 2015;Wang et al 2019), as well as various other in-house implementations (Guerinel et al 2013;Kim 2019, 2020). Such NLFK models are already faster than weakly-or fully-nonlinear potential flow models (Penalba et al 2017), where the potential problem is solved for each time-domain simulation at each time step on a continuously updating wetted surface (Letournel et al 2014).…”

A New Solution for Sea Wave Energy Harvesting, the Proposal of an Ironless Linear Generator

“…Oscillating wave surge converters are designed for a nearshore application. Indeed, the system is composed by a barrier, fixed on a seabed by a hinge, in order to oscillate as a pendulum, according to the wave motion in shallow water [19].…”