Hydrodynamic performance analysis of canvas stow net based on numerical simulation
NI Zhen-yu1, ZHANG Xin-feng1,2,3, JIN Yu-feng1, ZHANG Jian1,2,3
1.College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China; 2.Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education, Shanghai 201306, China; 3.National Engineering Research Center for Oceanic Fisheries, Shanghai 201306, China
Abstract: In order to probe into the optimizing net structure and assessment of the fishing efficienc, the hydrodynamic performance and net shape of a traditional canvas stow net with single anchor (main dimension 230 m×180 m), which was used commonly in offshore of the East China Sea, were analyzed based on numerical simulation. Firstly, the stow net was scaled down to a model stow net by two scale ratios, 25 for net size and 3.95 for the mesh size, following the Tauti’s modeling law of fishing gear. Then, the topological structure of the model stownet was established after the stownet was discretized based on the concentrated mass method and the meshes of panels of different parts of stownet were grouped up to simplify the construction of stownet. After these, a numberical model of the model stownet was built by the finite element analysis method and simulated by Runge-Kutta algorithm. The results showed the duration of process from original state to stable state of the stownet was shortened with the increase in the flow velocities. The horizonal and vertical opening of the net mouth was spreaded well in relatively low flow velocity. As the flow speeds up, the vertical expansion of the side panels decreased gradually and the heights of middle part of the headline and groudrope showed no obvious decrease while the degree of fall of positions increased obviously, showing an increasement of panels extention in longitudinal direction. Moreover, the width of net mouth decreased obviously while the height slightly decreased. According to the simulation, the hanging ratios of panels located in different part of the stownet was decreased gradually along with from net mouth to codend direction and decreased with the increase in flow velocity. As for the resistance (F), it increased with the flow velocity (v), as an power relationship F=480.1×v1.722. The tension load of the bars concentrated on both sides of the headline and groudrope and such a tension distribution mode became more obvious with the increase in flow velocity.