Chun-Wei Bi

NUMERICAL SIMULATION OF INTERACTION BETWEEN WAVES AND NET PANEL USING POROUS MEDIA MODEL

Abstract Based on the finite volume method, adopting the movement border as a wave generator, a two-dimensional numerical wave flume is established. The volume of fluid (VOF) method is used to track the wave surface. After comparison of the numerical results with the theoretical results, the accuracy of the numerical wave flume is verified. In the numerical simulation, the net panel is simplified as porous media entirely. The coefficients of the porous media are determined by the least squares method. In this way, the porous media model will have the same pressure drop as the net panel. In order to validate the numerical model, the numerical results were compared with the data obtained from corresponding physical model tests, and the numerical results and the corresponding experimental data show reasonably good agreement. Using the proposed numerical approach, this paper presents wave propagation through a net panel with different net solidities, different attack angles as well as two nets with different spacing distances. The impacts of the wave height and wavelength on the wave propagation through the net panel are also discussed.

Deformation and stress distribution of floating collar of net cage in steady current

ABSTRACT A numerical model is developed to investigate the deformations and stress distribution of floating pipes of fish cage subjected to the flow. The modelling approach is based on the combination of the finite element method using the shell element to simulate the floating pipes and the hydrodynamic model improved from the Morisons equation and lumped-mass method. The hydrodynamic response of the fish cage and forces on the floating pipes can be obtained by the hydrodynamic model. The stress and deformation of the floating pipes can be calculated based on the finite element method. Employing an appropriate iterative scheme, the stress distribution and maximum stress of the floating pipes in high currents can be obtained using the proposed model. To validate the numerical model, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results agree well with the experimental data. On that basis, the simulations of fish cage in currents were performed to investigate the maximum deformation and the stress distribution of the floating collars. Simulations of the fish cage in different flow velocity are performed to analyse the effect of the net and flow velocity on the deformations and stress of the floating pipes. The simulation results show that the stress and deformations drastically increase with the increase of flow velocity and the net has great influence on the stress distribution. Comparing results of floating pipes with different mooring line arrangements indicates that increasing mooring lines can efficiently lower the stress of the floating pipes. The simulations of the single-point mooring cage system with multiple net cages in current are performed and the results show that the middle cage is most dangerous for the tripartite-cage system.

The Numerical Simulation of Hydrodynamics of Fishing Net Cage

The aquaculture industry is playing an increasingly important role in the fish production industry as the demand for seafood increases. At present, the net cage is widely used in aquaculture industry all over the world. Because of environmental impact concerns and limited near-shore locations, more and more net cages for aquaculture will be located offshore and exposed to more waves and currents. Thus, knowledge of their hydrodynamic behavior of net cage under the action of waves and current is of great importance to the design of gravity cages in the open sea.

Development of a Coupled Fluid-Structure Model with Application to a Fishing Net in Current

Aquaculture is expanding all over the world, and the net cage is becoming prevalent in the aquaculture industry. Good knowledge of the hydrodynamic characteristics of the net cage has important significance to the design of the net cage and the welfare of the fish. An important component of a net cage is the fishing net, where the fish are kept and grown. The fishing net is completely submerged and infinitely flexible. When exposed to current, the fishing net changes its shape to reduce the hydrodynamic force acting on it, and the deformed net in turn affects the flow field around the fishing net. In this way, the flow field and the deformation of the fishing net interact and mutually influence each other. Therefore, it is very necessary to consider the fluid-structure interaction between flow and the fishing net when calculating the hydrodynamic characteristics of the net cage.

A Numerical Study on Wave Propagating Through In-Line Net Cages

A three-dimensional numerical model is established to simulate the interaction between waves and net cages. The porous-media fluid model is introduced to model the net cage in waves. An oscillating-boundary method is used to generate waves at one end of a tank partially filled with water. The flow motion of an incompressible, viscous fluid is described by Navier-Stokes equations and the free surface is tracked by volume of fluid (VOF) method. Validation of the numerical model is conducted by comparing the numerical results with the corresponding physical-model measurements of a net-cage model. In order to visualize the wave field around in-line net cages, numerical results of both wave elevation and water-particle-velocity distribution on a vertical plane of a transient field are presented. Compared with the undisturbed wave field, the effects of the net cages on both the wave elevation and the water-particle-velocity distribution around the net cages are noticeable. The study will contribute to understanding of the damping effect of a large fish farm on wave propagation.Copyright

Numerical Investigation of the Influences of Fishing Net on Waves

A two-dimensional numerical wave flume is established based on the finite-volume method. The movement border method is adopted as a wave generator at one end of the flume. The volume of fluid (VOF) method is used to track the wave surface. In the numerical simulation, the plane net is simplified as porous-media model. The coefficients of the porous media are determined by the least squares method. In this way, the porous-media model will has the same pressure drop with the fishing net. To validate the numerical model, the numerical results are compared with the data obtained from corresponding physical model tests. It is found that the numerical results are in good agreement with the corresponding experimental data. Using the proposed numerical model, wave propagation through a plane net with different net solidities, different attack angles as well as two nets with different spacing distances are investigated. The impacts of the wave height and wavelength on the wave propagation through the plane net are also discussed.Copyright