Influence of bottom and sand curtain on hydrodynamic performance of otter boards

Abstract

Numerical simulation is an important method for calculating the hydrodynamic performance of otter boards used in sea floor trawling. Although such simulations have been explored in prior studies, the effects of the proximity of the otter boards to the seafloor and the plume of upward-drawn sediment during bottom trawling have largely been ignored. In this study, we assessed these factors. The results show that within the angles of attack used during normal operations, the effect of the seafloor bottom boundary of the flow field on the hydrodynamic performance of an otter board is obvious. We found that when the ratio of the distance between the bottom of an otter board and the surface boundary of the flow field to the chord length of the board exceeds 0.4, the influence of the bottom boundary of the flow field on the hydrodynamic performance of the board is negligible. For values of less than 0.4, the seafloor bottom boundary has an increasingly obvious impact on the hydrodynamic performance as this ratio decreases. We also found that the turbid plume of ocean floor sediment raised during bottom trawling has an obvious effect on the lift and resistance coefficients of an otter board at high angles of attack. At low angles, this effect on the lift-to-drag ratio is reversed and less obvious. The simulation results show that the optimal lift-to-drag ratio decreases with an increase in the sediment concentration; however, beyond a certain threshold, an increasing concentration of sediments was not found to have an obvious impact on the lift-to-drag ratio.