Hydrodynamic response of a cage system under waves and currents using a Morison-force model

Abstract

Accurate computation of forces and deformations on cages under wave and current loads is a key element when designing mooring systems for fish farms. In this study, an analysis of a cage under combinations of current and wave loading is carried out and the numerical results are compared with experimental data. The numerical tool used in this analysis is based on a Morison-force model. For the case of single frequency tests, drag and inertia coefficients for the surface collar are selected based on Re and KC numbers. For irregular wave conditions, coefficients in Morison equation are selected based on significant wave height and peak period. Net is represented by an equivalent array of cylinders, which considers the same wet mass, projected area, and axial stiffness as the prototype net. This approach allows discretizing the net using a small number of elements. The present model predicts the loads over the floating collar as well as the drag force over the net. Overall, the study shows that current load dominates for most of wave and current conditions analyzed; yet, for large and steep waves, its effect is of similar importance as the current load.