Short-term Distribution and the Variability of Fish Cage Responses under Irregular Waves

The present study proposes an approach to investigate the short-term distribution and variability of fish cage responses under irregular wave conditions. The finite element method-based software package AquaSim is used to simulate the hydroelastic response of a gravity-type fish cage. A set of irregular wave series is generated by the Pierson–Moskowitz wave spectrum, and the response cycle samples are extracted using a level up-crossing technique. Four candidate probabilistic distribution models were examined and statistically tested for their goodness-of-fit to the response samples, and the variability of the maximum response under given stationary sea states was quantitatively analyzed. The target responses determined by two types of equivalent wave design methods were also compared and evaluated against the short-term maximum response values under different design safety levels. The results indicate that the generalized extreme value distribution is suitable for fitting most mooring force response samples, while the Weibull distribution is better for describing the stress response and vertical displacement response of the floating collar in most cases. Compared to the design method based on regular waves, the maximum response of fish cages under irregular waves exhibits significant uncertainty, highlighting the need to consider short-term variability. These findings provide helpful references for the structural strength and safety design of fish cages.