Assessment of fatigue damage of mooring line for fish cage under wave groups

Abstract

Wave groups may have a great impact on the dynamic response of mooring line for offshore structures. Thus, it is essential to investigate the fatigue damage of mooring line for fish cage system under wave groups. Based on the wave envelope spectrum, the kinematics of wave groups for the whole wave field can be modeled and the hydrodynamic behaviors of mooring line for fish cage under wave groups are analyzed. And using the rainflow counting method and Miner's rule, the long-term fatigue damage assessment of mooring line for fish cage under wave groups is conducted. The influence of the intensity of wave groups on the mooring line tension, stress range histogram, fatigue damage plot and the short-term and long-term fatigue damage of mooring line is investigated. The results indicate that the fatigue damage of mooring line is significantly sensitive to the wave group factor of height. This demonstrates that the high wave groups will greatly affect the fatigue damage of mooring line and the fatigue life of mooring system for fish cage. Thus the analysis of the action of wave groups will help to understand the fatigue damage of mooring lines for offshore structures in the realistic seas.