Hydrodynamic behaviors of a spring-mounted fishing net in wave-current combined flows

Abstract

The flexible fishing nets used in the deep-sea aquaculture cages are usually very large and they are tied tightly on the steel frames of the cages. Under the action of currents and waves, the fishing nets are easily broken at the connections. In this paper, a large fishing net mounted on a steel frame with linear and nonlinear springs is modelled theoretically and its hydrodynamic behaviors in the wave-current combined flows are analysed. The wave-current combined flows are described with the potential flow theory. The flexible fishing net is simulated with the lumped-mass method. The viscous drag forces caused by the fluid flows are calculated with the screen model. The simulation results demonstrate that when the fishing net is mounted with linear or nonlinear springs which have larger stiffnesses, the vibration displacements of the fishing net will become smaller while the dynamic tensions of the net twines will become larger.