Study On Hydrodynamic Characteristics Of Square Flatfish Cage

The flatfish is one of the valuable bottom fish species. At present aquacultureproduction of flatfish mostly depends on circulating system because of their livinghabit, whereas some issues occur during the aquaculture production such as drugremnant. Recently flatfish cage aquaculture plays an increasingly important role in theflatfish production industry in China and worldwide. The configuration of flatfishcage is usually square, furthermore the surface frame of cage is made up of metal pipeand there are tight ropes in the bottom frame to hold the bottom nets. In practiceproduction the bottom component of flatfish cage will sharply incline due to highspeed ocean current and strong sea wave, moreover it results in a lot of harm to theflatfish in cage. So one of the key problem is to research the dynamic behavior of theflatfish cage under current and wave conditions for aquaculture engineering，i.e. thecage deformation should be as slight as possible to maintain balance for the flatfish incage.A series of scaled physical model tests in current and regular waves are conducted.And then the whole displacements of flatfish cage assembled support pipes in bottomframe are measured and calculated by CCD and special software. The mooring lineforces are also measured by four transducers. The APDL language provided byANSYS itself is used to develop the specific program for structural analysis of flatfishcage. And then the dynamic analysis of flatfish cage in currents and waves isconducted. Furthermore, the model test data are used to verify the validity of thesimulated results. The results show that：(1) The maximum inclination of bottom frame and the maximum values of frontmooring line force increase with increasing flow velocity in currents. And the maximum values of front mooring line force increase with increasing bottom weight.The maximum inclinations of bottom frame for cage of square mesh change lessobviously with increasing flow velocity. Moreover, the maximum values of frontmooring line force of large cage are greater than that of small cage, but the large cagehas better stability than the small cage.(2) The differences in displacement and mooring line force of flatfish cages inwaves for the three weight modes are insignificant. The maximum inclinations ofbottom frame decrease with increasing bottom weight under wave conditions. And themaximum values of front mooring line force increase with increasing bottom weight.Moreover, the maximum incline angles of bottom frame with diamond mesh arelarger than that of cage with square mesh. The tendency seems to be that thedeformation and force of flatfish cage increase with increasing wave height for thesame wave period and increase with increasing wave period for the same wave height.(3) The maximum inclination of float and bottom frame are affected by weight ofbottom frame obviously. And the heavier bottom frame is, the better stability the cagehas. The motion and load are affected by shape of mesh obviously, and the stability ofcage of square mesh is better. The motion and load are also affected by the size ofcage obviously, and the large cage is better. Then, the effect of waves and current oncage is simulated by two modes of wave-flow interaction. The results show nodifference. And the maximum inclination and front mooring line force of cagedecrease with increasing angle between wave and current.