Comparative Study of Numerical Methods for Predicting Wave-Induced Motions and Loads on a Semisubmersible

Abstract

Numerical simulation tools based on potential-flow theory and/or Morison’s equation are widely used for predicting the hydrodynamic responses of floating offshore wind platforms. In general, these simplified approaches are used for the analysis under operational conditions, albeit with a carefully selected approach to account for viscous effects. Nevertheless, due to the limit hydrodynamic modelling to linear and weakly nonlinear models, these approaches severely underpredict the low-frequency nonlinear wave loads and dynamic responses of a semisubmersible. They may not capture important nonlinearities in severe sea states. For the prediction of wave-induced motions and loads on a semisubmersible, this work systematically compares a fully nonlinear viscous-flow solver and a hybrid model combining the potential-flow theory with Morison-drag loads in steep waves. Results show that when nonlinear phenomena are not dominant, the results obtained by the hybrid model and the high-fidelity method show reasonable agreement, while larger discrepancies occur for highly nonlinear regular waves. Specifically, regular waves with various steepness over different frequencies are focused in the present study, which supplements the understanding in applicability of these two groups of method.

Keywords

Potential flow / Viscous flow / Moored floating body / Steep waves / Motions and loads / CFD