Dynamic Analysis of Aquaculture Fish Cages in Irregular Waves

Abstract

The aquaculture fish cage encounters random waves in the open sea. Understandings of their dynamic behaviors are important for design of the deepwater fish cages. In this paper, the hydrodynamic responses of a gravity-typed fish cage in irregular waves are studied based on FEM and Morison equations. The floating collar and the bottom ring are modeled by beam elements. Net lines are modeled by truss elements. Hydrodynamic forces are calculated by a modified Morison equation taking the relative motion between the fluid and structure members into account. The displacement responses characters (time history and spectrum) of the fish cage floating collar in random waves are investigated. The response results show some similarities between fish cage in regular waves and irregular waves. Both rigid body motions and flexible structural deformations can be seen of the floating collar and the whole fish cage. The net volume changes with time in irregular wave and also high frequency responses caused by the structural deformation are observed.