To analyze the dynamic response of mooring line, it is necessary to take into account the non-linear phenomena such as large deflection (geometrical stiffeness), contact problem at the bottom of the sea and drag force. The time domain analysis is used to treat such non-linear phenomena, but it takes much time in computation. In this paper, the modal method in the frequency domain analysis has been studied, by using finite element model of mooring line and equivalent linealization method of drag force. Further, the method to reduce the error caused by neglecting the higher modes has been also investigated. The calculation results by this method are compared with those by the non-linear time domain analysis, there by a good agreement of both has been confirmed. It is shown that this method has good accuracy and takes less time in computation.
