Numerical Modeling and Analysis of a Semi-submersible Fish-cage

Abstract

The concept of rigid fish-farm was raised to overcome the space limitation of traditional fish-farm. To ensure that the structure has the ability to withstand the harsh sea environment, this report investigates a rigid semi-submersible fish-farm.

The study object is Ocean Farm 1. FEM model of Ocean Farm 1 has been built in GeniE. Considering the dimension difference of structure components, larger parts, like pontoons and main columns were built with panel elements, while slender beams were modeled by Morison elements. A mass model has been built to provide a more precise mass distribution and correct position of center of gravity. Total number of elements of FEM model was up to 14380. Hydrodynamic calculations were accomplished in HydroD with all FEM model input. Mass matrix, damping matrix and RAOs were calculated in frequency, range from 0-2 rad/s.

Hydrodynamic results were saved in G1 file and input to SIMA for time domain response calculation. Morison elements in previous FEM model were rebuilt as slender elements to take drag force into consideration. Furthermore, wave force on net was also included, which was carried out by an external communicative file. Environment condition was determined by sea states in Frohavet sea. Current velocity was taken as 0.75 m/s and results were verified with previous research. Twelve wave states wre also studied. Comparisons were made between model with and without net force, as well as responses under different wave condition.