Dynamic Analysis of Mooring Line for OTEC Plant

Abstract

The dynamic behavior of mooring lines has not been regarded as an important factor of the practical design. But, it has gained increasing interest recently, and a large number of papers have been written about methods for analyzing the dynamic response of mooring lines. In this paper, dynamic behaviors of mooring lines are analyzed in order to investigate the strength of mooring lines of the 10MWe OTEC Plant. An analytical procedure is developed for time domain analysis so as to simulate the nonlinear behavior exactly, and a computer simulation program is developed to estimate the dynamic tension of mooring line excited by the motion of platform due to wave. Firstly, the dynamic analysis of the above mooring line is carried out and the effect of the nonlinear behavior on the dynamic tension force is studied. Secondly, for estimating the maximum tension force of mooring line in 100 year storm, the static analysis to compute the dynamic neutral position of platform and mooring lines, motion analysis of platform, and time domain analysis of mooring lines are carried out. Considering the displacement of the connecting point of the platform and mooring line to be the forced displacement, the mooring line is oscillated at the upper end by that displacement. The maximum tension force occurs at the upper end of the mooring line, and it is found to be smaller than the breaking force. Thirdly, the procedure to evaluate the fatigue strength of mooring line is presented by using the results of frequency domain analysis or time domain analysis. An example of the 20-year's fatigue damage calculation of the above mentioned mooring line is shown, by using the results of frequency domain analysis. In this case, the accumulated damage by the fatigue is pretty smaller than 1.0.