Prediction of non-linear wave loads on large floating structures using a 3D numerical wave tank approach

Published in: Marine Systems and Ocean Technology , December 2019 Vol No.14 Issue 4 : 129-152

Author: Shivaji Ganesan & Debabrata Sen

Date of Publication: September 2019

In the present work, non-linear wave loads acting on large floating structures are computed using a 3D numerical wave tank (NWT) approach in an approximate manner. The hydrodynamic initial boundary value problem is solved following a Rankine panel-based boundary element method in conjunction with time integration of free-surface constraints and body motion equations. To enable long-duration simulation for practical offshore configurations, total velocity potential is split into incident and perturbation part, and the latter effects are linearized. In our earlier works (Ganesan and Sen in J Ocean Eng Mar Energy 1:299–324, 2015; Ganesan and Sen in Appl Ocean Res 51:153–170, 2015), the 2nd order contributions from the linearized perturbation potential were neglected. In this work, we propose a modified formulation for the external load in which the full non-linear loads from the incident wave and up to 2nd order loads from the linear perturbation potential are considered. After presenting some results to validate the present method for steady drift force computations, non-linear loads from the modified formulation are compared with the unmodified form of the method and also with widely used 3D frequency-domain Green-function-based method. Comparative results between these three computations are presented for different geometries and the results are discussed to bring out the relative advantage of the modified formulation in predicting non-linear loads across the range of frequency and wave steepness.