Applicability of numerical water tank for the dynamic response analysis of the barge-type floating platform

Abstract

A fully nonlinear Navier-Stokes/VOF numerical water tank is developed for barge-type floaters with coupling to the dynamic mooring line model. Wave excitation forces, free decay responses, and dynamic responses in regular waves predicted by numerical water tank show good agreement with experimental results. Then, hydrodynamic force models used in engineering models are improved by applying the numerical water tank results. It is clarified that the cause of the overestimation of normalized wave excitation force at water tank test relative to that predicted by potential theory is the underestimation of the input wave height due to the interference of the reflected wave from the floater. The new drag coefficient model is proposed based on numerical forced oscillation simulations at the surge natural period. The wave drift QTF is evaluated using the numerical water tank and the prediction accuracy of the mean floater displacement in the surge direction is improved, compared to the conventional Newman's approximation model. The surge-pitch coupling terms of drag force and its mechanism are investigated by forced oscillation simulations. The correction method of surge-pitch coupling terms of drag force is proposed and the prediction accuracy of the floater displacement in the surge direction is improved.