A Study On Dynamic Responses Of Deep-water Gravity Cage Under Combined Wave-current Flows

In recent years,seeking better aquaculture environment and higher quality of aquaculture products become the development trend of our country and even the world. Open ocean aquaculture has to be developed in place of inshore aquaculture to settle the problems which the inshore water pollution and fish disease become more severe. Technical solution of wind wave and flow resistance are the main problems of open-ocean aquaculture. The study is aim to discuss dynamic response of gravity cage under wave opposing and following the current, which provides direction and theory for the engineering design of gravity cage and gravity cage risk assessment.In this studey, based on the principle of conservation of wave action flux and Stokes3wave theory, numerical simulation of wave deformation in current and composite wave-current flow field was developed; Based on rigid kinematic theory and lumped mass method, a numerical model of gravity-cage has been developed. The dynamic responses of the gravity-cage under different wave conditions combined current velocities were calculated. The calculated results of maximum values of mooring line force, maximum values of float collar pitch and the maximum values of displacements agree well with the experimental data. The relative error between calculated results and experimental data is1.2%～10.6%.In this paper, the model of wave-current field and gravity cage for simulating the hrdrodynamic behavior of the gravity cage in combined wave-current flow show good agreement with physical modeling tests.The numerical results show that mooring-line force is larger under wave following the current than opposing the current; the minimum value of volume holding cofficent of net cylinder is larger under wave opposing the current than following the current. These results draw a conclusion that the destruction of gravity-cage under wave following the current is more serious than opposing the current. So open ocean aquaculture of gravit cage should avoid sea area of wave following the current frequently as far as possible.