On Evaluation Method of Subharmonic Motion in Sway of Moored Ship

It is hard to simulate moored ship motion because of a mooring force, especially in sway mode. When the ratio of spring constants between fender and mooring line is large, subharmonic motions occur. In previous paper, we introduced the approximate calculation method using Asymmetrical Amplification Function. In this paper, firstly we divided subharmonic motions into three wave patterns, and evaluate its influence to the ship mooring and cargo handling. We focus on the averaged value of U, the water particle velocity over wetted surface and investigate the time at which the ship collides with the fender and separate from the fender. As a conclusion, we propose a fender criterion of the subharmonic motions.