Effect of body motion on the wave loads computed with CFD on the INO-WINDMOOR floater

CFD simulations were carried out on the 1:40 model of the INO WINDMOOR floater in regular waves to extract hydrodynamic loads, both on the structure, the single columns and sections from each column. Three different approaches for the platform motion were used, (i) fixed, i.e., restrained from motion, (ii) prescribed, i.e., forcing the floater to follow the motion recorded during model tests and (iii) 6 DOF, i.e., allowing the floater to move according to external forces from waves and anchor lines. The obtained results show the effect of the free surface on the local drag forces at sections with different submergences, which are important to include when modelling the motion with simplified methods based on pre-computed force coefficients. A comparison of the surge force shows that the amplitudes of the loads obtained with moving platform are reduced compared to the corresponding fixed case. The mean total surge force computed on the single columns and the whole platform show small quantitative differences between the different methods. The motion responses of the platform for surge and heave obtained with CFD are in fair agreement with the experiments.