Effect on hydrodynamics of unit net of a column-type net enclosureaquaculture engineering in current by fixations

The column-type net enclosure aquaculture (NEA) is a new ecological ocean aquaculture mode. It is mainly composed of piles and net panels. More and more attention has been paid to NEA, because it is a new aquaculture mode which has big aquaculture area, large space for fishes,more natural environment, and more ecological high quality of food. NEA is still in its developing stage, many kinds of technical problems still need to be solved.The net system is regarded as the key component which controls the safety of the whole NEA system. In this paper, based on lumped mass point and clustering mesh method, the mechanical properties of unit net of a column-type NEA engineering in current were studied using computer numerical simulation. The distribution characters of tension force in twines, the offset characters of net nodes and the load characters at fixing points were investigated. The effect of net width and fixing mode on the net hydrodynamics was discussed as well. The results showed that the maximum tension force of unit net of the pile-column type net enclosure in current mainly occurred at the both sides of the top and bottom belly lines of net panel, and was proportional to the net width.The maximum offset of the net panel mainly appeared at the upper and lower positions, and was proportional to the net width as well. Regarding the force on fixing points, the largest forces on the top and bottom fixing points of net panel were observed in this study and they were much higher than that of the middle fixing points.The research found that the forces at the fixing points decreased with the increasing of the number of fixing points, and the maximum tension force in twine and the maximum offset of net nodes declined rapidly too. When the number of fixing points exceeds a certain number, the maximum tension force and offset will no longer drop significantly. Thus, there was a critical number of fixing points, which was found to be 4 or 5 in this paper. The results achieved in this paper pointed out the potential dangerous positions of the net panel and showed the rules of influence on the force and deformation of net panel. The results may give guidance to the design and installation of the column-type NEA engineering.