A STUDY ON NUMERICAL ACCURACY FOR THE PREDICTION OF MOTION RESPONSES AND DRIFT FORCES OF MULTIPLE FLOATING BODIES

Wave drift forces play an important role when a vessel is floating in the vicinity of another vessel or, floating structure. The numerical accuracy in the computation of the wave exciting forces and the hydrodynamic forces of multiple floating bodies influences the motion response that eventually affects the second order wave drift forces of each floating body. The present study is based on the far-field method where the velocity potential is calculated by 3D sink-source technique. In order to justify the validity of the present calculations, some comparisons are made for simple multi-body floating systems like multiple floating cylinders and cylindrical body with box shaped body. The numerical calculations have been investigated for a parallel arrangement of FPSO and an LNG carrier. The computations of motion responses and drift forces are carried out for a number of different wave heading angles and for different separation distances between the FPSO and LNG carrier. The numerical results are compared with the experimental ones as well as with previous computations to illustrate the improved numerical accuracy of the present computations. It has been observed that due to the lack of accuracy in the numerical scheme adopted for the computer code, the computed results of drift forces sometimes shows completely opposite trend than that of the experimental ones.