基于数值模拟的单锚张纲张网水动力性能研究

为深入开展单锚张纲张网渔具结构优化、渔获性能评价研究,使用数值计算方法对其水动力特性和形状进行模拟。根据田内准则将中国东海近海渔业生产中常用的单锚张纲张网(230 m×180 m)按大尺度比为25和小尺度比为3.95缩小,然后使用集中质量法对模型张网进行离散化处理,并对网目进行群化。建立拓扑结构,在此基础上采用有限元方法建立单锚张纲张网数学模型并进行数值模拟。结果表明:网具从初始状态到稳定状态的时间随流速的增加而减小;当流速较小时,网口水平和垂直扩张较好,随着流速的增加,网口两侧网衣垂直扩张逐渐减小,上、下纲中部高度未见明显减小,但后坠程度逐渐增大,网具纵向拉伸逐渐增大,网口的宽度明显减小,而网口高度略有下降;网具各部分网衣的缩结系数从网身到网囊逐渐减小,且随着流速的增加而减小;网具的总阻力(F)随流速的增加而增加,且与流速(v)呈F=480.1×v1.722的关系;网具上纲和下纲两端结附网线张力载荷较为集中,且随着流速的增加,集中载荷分布趋势愈加明显。研究表明,通过数值模拟分析网具的总体扩张和阻力,掌握张网网具各部分网衣和纲索的张力载荷分布,以及随流速的变化情况,分析网具的受力均匀性和结构合理性,了解各部分网衣的横向扩张情况,这对于分析网具整体选择性、滤水性和渔具的导鱼性等至关重要。

Hydrodynamic performance analysis of canvas stow net based on numerical simulation

In order to probe into the optimizing net structure and assessment of the fishing efficienc, the hydrody-namic 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 es-tablished after the stownet was discretized based on the concentrated mass method and the meshes of panels of dif-ferent 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 re-sults 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 lo-cated in different part of the stownet was decreased gradually along with from net mouth to codend direction and de-creased 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 grou-drope and such a tension distribution mode became more obvious with the increase in flow velocity.