ON THE MOTIONS AND MOORING LINE TENSIONS OF A SEMI-SUBMERSIBLE VESSEL IN WAVES

A practical calculation method for predicting the wave-induced responses of a moored semisubmersible vessel is described. This method takes into account the effects of the drag force on the structure and also the dynamic response of the moored vessel and of the mooring lines in waves. The wave-induced responses of an Aker H-4.2 type of drilling rig, with two pontoons and eight columns, has been determined experimentally and compared with the calculated responses to demonstrate the validity of the method. It has been found that the influence of the drag force non-linearity is dominant near resonance and also that the dynamic effect on the mooring line tension is significant when the motion of the moored vessel becomes large.