Comparison between physical model testing and numerical simulation using two-way fluid-structure interaction approach of new trawl design for coastal bottom trawl net

In this work, the hydrodynamic performance of a scaled bottom trawl model in current was investigated by using numerical simulations based on the fluid structure interaction (FSI) method in two-way coupling and the flume tank test based on modified Tauti's law. In this numerical model, a finite volume approach was used for solving the Navier-Stokes equations combined with a k-omega shear stress turbulent (SST) model for describing the flow. A finite element approach was used for solving the large deformation nonlinear structural dynamic equation to describe the trawl net configuration and the nodal displacement. A series of flume tank tests was conducted on three scaled bottom trawl models with different twine diameters, twine materials, and mesh sizes. In addition, three-dimensional (3D) Acoustic Doppler Velocimeter (ADV) measurements were performed to experimentally investigate the effect of turbulent flow on the bottom trawl net performance. The comparisons showed that the numerical results were in good agreement with the experimental data. Both the numerical and experimental results indicated that the increase in mesh size using Dyneema multifilament and the decrease in twine diameter using nylon monofilament led to decrease in the drag force by about 2.1 times and 2.2 times, respectively (p < 0.002 ANCOVA test). It was found that there was spatial development of turbulent boundary layer flow around the trawl net and the vortex shedding in the trawl wake. In addition, the equivalent stress, elastic strain, and total deformation increased with the increase in flow velocity and, mesh size, and the decrease in twine diameter.