Abstract
This paper demonstrate usage of a coupled linear hydrodynamic and structural model to assess the elastic response of closed fish cages in waves. From a design point of view it is important to avoid coupling between internal sloshing and the structure. This problem is addressed by assessing the elastic response of two closed fish cages made of an uniform elastic material. A vertical cylinder cage (bucket concept) and an ellipsoidal cage (egg concept inspired by Ovum AS design) with similar internal volume are investigated. WAMIT which is a software based on Boundary Element Method is used to compute hydrodynamic forces on rigid and elastic modes of motion. LSDYNA which is a Finite Element Method software is used to compute dry elastic mode shapes to be used as basis functions in the modal analysis. The computations were performed in frequency domain. The effective stress, i.e, Von Mises stress, is computed for the maximum responses in frequency domain to be compared with yield stress of the manufacturing material. The focus is on elastic cages for which the manufacturing material withstands bending. The effect of variation of stiffness on elastic response and its interaction with sloshing is addressed. The numerical method is explained briefly and its advantages and shortcomings are addressed. It is shown that the egg concept has a much smaller hydroelastic response than the bucket concept for the same material properties.
