Fatigue damage distribution and reliability assessment of grid mooring system for fish cage

Abstract

This paper investigates the evolution of fatigue damage distribution with the loading cycle and predicts the annual fatigue damage distribution and system reliability of the grid mooring system under fatigue limit state for fish cage, employing the generalized probability density evolution method (GPDEM). A series of the hydrodynamic analysis for the grid mooring system of fish cage are performed to obtain the fatigue damage of the grid mooring system considering the long term environmental loading. The GPDEM equation is solved to determine the evolution of probability distribution of fatigue damage in term of the loading cycles, and the probability distribution of the annual fatigue damage of mooring lines is evaluated through the combination of the GPDEM and the virtual stochastic process model. In addition, the system reliability assessment of the grid mooring system under fatigue limit state is performed by the equivalent extreme-value event method. The results indicate that the probability distribution of the fatigue damage of the mooring component becomes more asymmetrical and platykurtic with the increase of the loading cycle and the annual fatigue damage distribution of the components in the grid mooring system can be estimated by the GPDEM from a stochastic point of view without any approximations or any asymptotic distributions. And it is necessary to conduct the uncertainty quantification of the Miner's sum at failure for the system reliability prediction of the grid mooring system under fatigue limit state to ensure the safety of fish farm.