Study On Hydrodynamic Behavior Of The Bat-wing Otter Board

The vast ocean contains abundant marine life resources,especially fish resources,not only can meet people’s demand for protein and alleviate the food shortage caused by population growth,but also is an important part of our national economy.China have the highest marine fishing production in the world,marine fishing is still at the top of marine fishery production.As a result of the overfishing of marine fishery resources in the last century,the global fish resources declined obviously,especially in offshore areas,which caused the decrease of large fishing vessels with double drag.The single ship trawl is the most important working methods in China’s current pelagic fishery because of its high efficiency,active and flexible fishing characteristics.The otter board is an important accessory in the single ship trawl system,which is used to provide horizontal tension to expand the trawl,and its hydrodynamic performance will directly affect the fishing efficiency and economic benefit of trawl operation.The otter board in the process will also produce resistance,accounting for the entire trawl system resistance of 30%.The resistance not only will increase the fuel consumption of fishing boats and improve the cost of trawl operations,but also produce greenhouse gases such as carbon dioxide.Therefore,it is of great significance to study the hydrodynamic characteristics of the otter board,and to develop the high efficiency,low energy consumption and environment-friendly network board for marine fishing and environmental protection.In this paper,two types of otter board are studied.One is the vertical cambered otter board,the hydrodynamic coefficient of the otter board is studied by CFD numerical simulation,and the influence of the aspect ratio on the hydrodynamic characteristics of the vertical cambered otter board is discussed.The second one is a new type of "bat-wing" otter board.By means of physical model test and numerical simulation,the hydrodynamic performance of the otter board at different AOAs is studied,and the influence of the mast rake on the hydrodynamic characteristics is discussed.The flow field around the otter board is visualized by the post processing software,which could provide suggestion for the improvement and optimization of the otter boards.This article contains five chapters.The first chapter mainly introduces the research background of the subject,the introduction of the otter board,the research situation of domestic and foreign scholars and the main research content of this article.The second chapter introduces the basic theory of CFD numerical model,including governing equation,turbulence model and numerical calculation method.In the third chapter,the establishment of the numerical model of the vertical cambered otter board is introduced,and the simulation results of the hydrodynamic coefficients are compared with those of the experimental results.The results show that the larger the aspect ratio,the smaller the stall angle and the maximum lift coefficient of the mesh plate,the greater the lift-drag ratio and the worse the stability.The fourth chapter introduces the method of physical model test and analyzed the test results,it is found that the stall angle decreases with the increase of the angle of the mast,and the corresponding lift-drag ratio becomes larger.Then it introduces the establishment and verification of the numerical model of the "bat-wing" otter board.The hydrodynamic characteristics of the otter board are analyzed,and the flow field around the otter board is visualized.The result shows that with the increase of the AOA,the flow separation phenomenon will appear on the back surface of the otter board,and the vortex around wing-tip can restrain the separation of the flow.Finally,the main achievements of this paper are summarized and prospects of further research are given.