Hydrodynamics of the trawl codend: shape and loads calculation at different mesh orientations in fluid flow

The article presents a mathematical model for assessing the influence of mesh cell orientation relative to the fluid flow in axisymmetric mesh engineering structures under hydrodynamic backpressure conditions on the shape and loads in the structure, using the example of a trawl codend with a catch. The novelty of the approach lies in simplifying the problem by reducing the three-dimensional issue to calculations in a two-dimensional coordinate system. This significantly reduces the computational complexity, speeds up the modeling process, and allows for faster result acquisition. The authors conducted numerical simulations using a developed computer program, the results of which were compared with data from a full-scale experiment in a towing tank. The experiment showed that with the mesh shape oriented at a 90-degree angle to the flow (T90), the minimum diameter of the trawl codend increases to 29.0 mm, compared to 21.6 mm at T0. This shape change improves selectivity and enhances catch quality by minimizing damage. The consistency of the simulation results with real experiments confirms the reliability of the approach. The model accounts for key factors: hydrodynamic drag forces acting on the net; stiffness characteristics of the ropes, described by Hooke's law (elastic deformation); and the external impact of the catch, modeled as a hemisphere with a uniform pressure. This provides a realistic representation of net deformation during trawl towing, simulating real fishing conditions. The calculations use equations describing the geometry of the structure, force distribution, and volumes, which are solved using the Levenberg-Marquardt method. Applications include scientific research, educational processes, design and operation of fishing trawls, and virtual reality systems.

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