Abstract
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 6 513 virtual elements and model-2 with 1 787 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.
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