Viscous damping forces for slow drift oscillation of the floating structure acting on the hull and mooring lines

An experimental study on the viscous drag forces acting on the model of a semi-submersible oscillating in waves is carried out. The dynamic tensions of mooring lines are also measured. The experimental studies are carried out with the view of studying damping forces for the slow drift oscillation. The Morison equation extended to the Relative motion concept is applied in the analyses of the viscous drag force acting on the model oscillating with the large amplitude and long period in waves. Experiments show that the drag coefficients depend on the reduced velocity defined by the maximum velocity of the slow oscillation, period of incident wave and diameter of the column. The results are compared with those obtained by applying the Independent flow field concept.