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. ... Read more

The hydrodynamic coefficients are evaluated by fully nonlinear Navier-Stokes forced oscillation simulations using the volume of fluid method. Richardson extrapolation is employed to obtain the grid-independent solution. The predicted hydrodynamic coefficients are validated by the water tank tests. The applicability of the drag coefficient models as the function of Keulegan-Carpenter numbers in the surge and heave directions are investigated for the barge-type floater by comparing with the numerically predicted drag coefficients. The dynamic response analyses are then conducted using the engineering model with the validated drag coefficient models. The predicted mean values of surge and mooring tension without considering drag forces underestimate the measurements in the high wave height condition, where those with considering drag forces show good agreement, which is analytically explained by the mean drag force being inversely proportional to the square of wave period and proportional to the cube of wave height. Dynamic responses of floater predicted without considering drag forces caused overestimation at the natural frequencies in the heave and pitch directions, while those considering drag forces show good agreement with the measurements. ... Read more