大网目底拖网在稳定流场中的数值模拟

通过有限单元法构建大网目底拖网渔具的数学模型,以计算在定常流条件下底拖网渔具的受力情况、网口扩张和渔具的形态变化。为了提高计算效率,提出了适用于拖网的网目群化方法。群化后的拖网模型为单元数6513的model-1模型和单元数1787的model-2模型两种规格,分别进行数值计算,并与水槽物理模型试验结果进行比较。结果表明,model-1模型和model-2模型在相同流速条件下的形态变化趋势基本一致;model-1的阻力计算结果相较于model-2更接近于物理模型试验结果,model-2的计算结果存在16%~26%的相对误差;两种数值模型的网口垂直扩张和水平扩张的计算结果与物理模型试验结果相近,最大相对误差仅5%~10%。数值模拟较好地呈现了大网目底拖网在稳定流场中的状态,可以在一定程度上代替传统的水槽模型试验,为拖网渔具设计和优化提供一种可供选择的数值分析方法。

Numerical simulation of bottom trawl with large-size mesh in steady flow field

The physical model experiment and numerical model calculation of bottom trawl gear with large-size mesh were carried out for verifying the application of numerical method in bottom trawl,which provides an alternative numerical analysis method for the design and optimization of bottom trawl gear.The mathematical models of bottom trawl gear with large-size mesh were constructed by using the finite element method to calculate the resistance,the expansion of net mouth and changes of fishing gear shape under steady flow conditions.In order to improve the computational efficiency of numerical trawl model,a new kind of mesh group method was proposed in this paper,and results of two different models of different computational units were compared to find a better group number of large trawl.The physical model was designed according to the Tani similarity criterion,which was tested in the static flume,and the large scale ratio was 1∶35.After mesh grouping in numerical calculation,two specifications of model-1 with 6513 virtual elements and model-2 with 1787 virtual elements were established,which were respectively calculated and compared with the experimental results of physical model in water tank.Results showed that the morphological variation trend of model-1 and model-2 was basically consistent under the same flow velocity.The resistance calculation results of model-1 was closer to that of the physical model test than those of model-2,and there was a relative error of 16%-26%between the calculation results of model-2 and the physical model.The calculated results of vertical and horizontal expansion of the two numerical models were close to those of physical model test,and the maximum relative error was only 5%-10%.The state of bottom trawl with large-size mesh was presented in the steady flow field successfully through numerical simulation,which should be able to replace the traditional flume model experiment to some extent.