A Fourier Approximation Method for the Multi-Pump Multi-Piston Power Take-Off System

Abstract

In this work, a frequency-domain method for the numerical solution of the nonlinear dynamics of a wave energy converter with a pumping system is presented. To this end, a finite Fourier series is used to describe the nonlinear force components, i.e., the pumping force. The dynamics of the buoy and the piston are obtained by solving a set of linear motion equations. The numerical model is validated by comparing it with experimental results. The dynamic characteristics of the pumping system are investigated by performing a series of numerical simulations for several approximation orders under various wave conditions. The advantages and limitations of this method are also discussed in the paper. This work provides great insight into the mechanism of a WEC with a pumping unit under various sea states, which can guide the design of a multi-piston pump (MPP) system. This model will be applied to investigate the optimal configuration for the MPP system in the future.

Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study

“…It is envisioned that such a device could comprise hundreds of floating elements and pistons, thus necessitating a computationally efficient modeling method for its analysis. In [344], a single floater with pumping unit is investigated and the numerical simulations show good agreement with experimental results, able to assess the power output well but not the high-frequency responses such as slamming. Of interest is the 'sticking' phenomena in the PTO pumps, when the wave excitation force is lower than the pumping force, which can only be captured by simulations using a high number of Fourier components and for which case the computational cost increases dramatically since the Fourier series of discontinuous functions converges very slowly.…”

“…In addition to the WEC hydrodynamics, Wei et al [344,345] apply the NLFD method to the PTO system in the Ocean Grazer, comprising pistons and pumps. It is envisioned that such a device could comprise hundreds of floating elements and pistons, thus necessitating a computationally efficient modeling method for its analysis.…”