Fast real-time prediction of wave exciting force for a point absorber based on impulse response functions

Abstract

Fast real-time prediction of wave exciting forces is necessary for the optimal control of Point Absorbers (PAs) in wave energy conversion. However, the non-causality of the impulse response function (IRF) of wave exciting force is a crucial issue for the prediction. To address this problem, this study employs deterministic wave prediction using upstream measured wave data. By integrating the IRFs of water waves and wave exciting forces, a real-time prediction method of wave exciting force is developed. Once the wave exciting force can be estimated, body motion, outgoing waves, and energy absorption efficiency are easily determined. For the verification of the proposed method, regular wave analysis is carried out, and numerical results are compared with those obtained from the frequency domain analysis using the two-dimensional boundary element method (2D-BEM). The results are also verified by the energy conservation principles. Through these verifications, it is shown that the proposed results strongly agree with the 2D-BEM results. Additionally, the real-time applicability is evaluated using the real-time factor (RTF). It is shown that the method achieves RTFs less than $10^{-2}$; computational efficiency and practical feasibility are demonstrated.