Influence of strain-rate on the interaction between towed fishing gears and the seabed

Abstract

The ability to predict the seabed penetration and the drag force of the gear components of demersal trawlers is of significant benefit to the fisheries industry. It allows for the design of gears of reduced environmental impact and of improved fuel efficiency. This study presents a single-phase strain rate dependent soil model that can accurately predict deformation of a saturated granular soil. Elements of an otter trawl system are modelled as simplified discs which are then translated across a seabed at given speed where horizontal drag force and vertical penetration is measured. This is facilitated using an explicit Finite Element (FE) model developed in ABAQUS alongside a Coupled Eulerian-Lagrangian (CEL) mesh. Comparisons against laboratory experiments showed that the model was correctly able to capture the increase in drag force with towing speed. Further comparisons against full scale sea trials indicated the model generally compared well against test data and correctly identified the trends and magnitudes of drag force against towing speed. From these results, the influence of strain rate in the soil was studied in detail and conclusions drawn on the resultant drag force and penetration of towed fishing gears on the seabed.