Computational hydrodynamics of fishing nets using a surface-based porous media model

Fishing nets are the main component of fishing gears and aquaculture cages. Modelling net panels as thin solids with porous media properties is a recent approach to study the interaction between netting and the water flow using Computational Fluid Dynamics (CFD). However, the application of this technique to complex netting geometries, like fishing trawls with selective devices, raise several difficulties related with the pre-processing and the ability to deal with large deformations. To solve these problems, we propose to model the geometry of net panels as triangulated surfaces instead of thin solids, and then automatically create regions of porous media in the CFD mesh cells that surround these surfaces. Two test cases are used to verify and assess the proposed method. Results show that it has several advantages over the thin solid approach: it greatly simplifies the pre-processing of complex netting geometries, it allows easier control over the thickness of the porous media and the number of generated porous zones, and it can deal with large deformations in net panels. It also allows an easier coupling between the solid solver and the fluid solver in fluid–structure applications, since structural models of netting can be easily mapped to triangulated surfaces.