Finite Element Analysis of the Effect of Currents on the Dynamics of a Moored Flexible Cylindrical Net Cage

Abstract

A numerical model associated with wave–current interactions with a moored flexible cylindrical cage was developed based on the finite element method. An analytical model was formulated under the linearised wave theory and small structural response, and a semi-analytical solution was obtained using the Fourier Bessel series solution and least squares approximation method, along with a matching technique. The numerical results from the finite element analysis of the horizontal displacements for different design parameters under a uniform current were compared with the analytical model solutions. It was seen that they had a good level of agreement with their results. The effects of different current speeds and time on the cage shapes were analysed from the finite element results. Further, the mooring forces on the flexible cage for different values of the cage height and cage radius were also presented. The comparison of the results indicated that the numerical model results could be used with confidence in the design of a flexible cylindrical net cage for applications to offshore aquacultures.

A Semi-Analytical Model for Studying Hydroelastic Behaviour of a Cylindrical Net Cage under Wave Action

“…in which Q is the axial uniform tensile force in the net, m s is the uniform mass of the net per unit length, and ρ is the water density. In [28], a comparison between the analytical model based on Equation (10) and the FEM simulation for the cylindrical net cage illustrates acceptable errors.…”

“…On the other hand, it is assumed that the cross-section of the cage maintains its circular shape under wave action if the cage is imposed a high axial tension and has a small deformation relative to its overall size. Liu et al [28] showed a deformed net cage simulated by the finite element method using truss elements, and it is observed that the cage approximately maintains a circular cross-section. Therefore, the transverse deflection of the cage is ζ = Re[η(z)e -iωt ], and the transverse vibration equation of the string to describe the complex amplitude η is given by Mandal and Sahoo [21]:…”

“…For the edge restraint condition of the net chamber, its top end is assumed to be constrained by the mooring systems according to [28], and there is no transverse traction at the bottom end, i.e.,…”

Uncertainty Assessment of the Remaining Volume of an Offshore Gravity Fish Cage

“…The results can be used to evaluate the fatigue life of the mooring ropes. Liu et al [8] described a numerical procedure to calculate the mooring forces and the cage motions for a gravity cage system.…”

Theoretical Hydrodynamic Analysis of a Surface-Piercing Porous Cylindrical Body

“…Porous cylinders are also related to fish-farm cages, the performances of which, in currents and waves, have been widely studied in the literature. Noteworthy examples of recent works in chronological order are [44][45][46][47][48][49]. In these studies a porous flexible circular cylinder is assumed, simulating the fish net.…”