The influence of flow field bottom effect and sand cloud effect on the hydrodynamic performance and stability of bottom trawling otter board under tilted attitudes

Abstract

To explore how bottom and sand cloud effects influence the hydrodynamic performance and stability of bottom trawling otter board under tilted attitudes, this study combines numerical simulations by oval cambered otter board and flume tank experiments verification. By assessing drag and lift coefficients (CD,CL), center-of-pressure coefficients (Cpc, Cpb) and longitudinal moment (My) in different heel angles, the study evaluates the impact under the two effects on hydrodynamics and stability. Findings reveal that inward and outward tilting increases CD maximally under sand cloud effect, while minimizing it under broad-field only water conditions; CL is maximal under bottom effect and minimal under broad-field only water conditions. For forward and backward tilting, CD under sand cloud effect is greater than that under bottom effect, with minimal values in broad-field only water conditions; CL is maximal under bottom effect and minimal under broad-field only water conditions. Additionally, stability varies across different flow field conditions, deteriorating along the x-axis due to bottom and sand cloud effects, while maintaining relative stability along the y-axis and z-axis. This study demonstrates that the bottom effect and sand cloud effect alter the otter board's proximity to the seabed and the fluid viscosity, leading to differences in hydrodynamic performance and stability under inclined attitudes. The findings aim to provide insights for the use and design of bottom trawling otter boards, ensuring stability and safety under various operating conditions and attitudes.