Numerical Simulation Research Of Hydrodynamic Performance And Structure Optimization Of Trawl Otter Board

Whether the fishery resources are taken full advantage of or not has been focused on by different countries and become a global problem.Almost all countries hope to make full use of the fishery resources effectively so that they take a lot of manpower and material resources to improve the hydrodynamic performance of trawl otter board.The otter board of high hydrodynamic performance can add to the catches benefit.The domestic and foreign scholars use many ways including flume tank experiment,tunnel experiment and numerical simulation based on computational fluid dynamics and they utilize these methods to study and analyze the diverse otter boards by changing the structure,physical dimension and weight for enhancing the hydrodynamic performance.The numerical simulation research is used in studying the otter board under the complex working condition.It is convenient method to study the hydrodynamic performance of otter board and its research result is close to the experiment result,which is highly praised by many scholars.The vertical V-type cambered slotted otter board is widely used in trawl fishing.The method of numerical simulation based on computational fluid dynamics is forwarded to apply to studying the vertical V-type cambered slotted otter board and its structure optimization under the submarine environment for improving the hydrodynamic performance and working performance of this otter board.The main parameters influencing the hydrodynamic performance of otter board includes lift coefficient,drag coefficient,lift-to-drag ratio and the working stability of otter board.And these four aspects are focused on studying on this paper.Firstly,the rectangular otter board is analyzed by the method of the numerical simulation.It is found that the critical angle of attack of the otter board whose aspect ratio is 0.252 is 45° by comparing with the hydrodynamic performance of the rectangular otter board of the different aspect ratio.The rectangular otter board has the maximum lift pressure and obtains the biggest lift coefficient through analyzing the pressure contour.And the stability of otter board is good.The otter board would lose the stability and its working efficiency would decline when the working angle of attack is over 45°.It is found that the critical angle of attack of otter board is different by analyzing the hydrodynamic performance of other otter boards of different aspect ratio.The critical angle of attack of otter boards whose aspect ratio is 0.193 and 0.318 respectively are 45°.And the critical angle of attack is 40° for otter board of its aspect ratio being 0.393.The critical angle of attack of otter boards whose aspect ratio is 0.476 and 0.566 respectively are 30°.The research results show that with the increasement of aspect ratio,the critical angle of attack goes down gradually from 45° to 30°,lift coefficient has a continuous falling trend and the value of lift-to-drag ratio goes up inch by inch through the research on the hydrodynamic performance of other otter board.A conclusion is reached that the bigger the aspect ratio is,the smaller the critical angle of attack is and the bigger the lift-to-drag ratio is.The research results show that the critical angle of attack of the rectangular otter boards whose aspect ratio is 0.476 and 0.566 are both 30°.The vortex diagrams show that the wing-tip vortex of both the otter boards is separated completely at angle of attack of 30°.And the wing-tip vortex of the otter board whose aspect ratio is 0.566 is broken down so that the working situation of otter board loses stability.The otter board with a good hydrodynamic performance has higher lift coefficient,bigger lift-drag ratio and better working stability.Therefore,0.5 is served as the optimized parameter of the aspect ratio.The full-scale vertical V-type cambered slotted otter board is studied by optimizing the structure with the optimization value of the aspect ratio.The vertical V-type cambered slotted otter board of structure optimization is studied with the method of the numerical simulation.It is found that the vertical V-type cambered slotted otter board has the same hydrodynamic performance under five velocities and the same studying conditions.The critical angle of attack of the full-scale vertical V-type cambered slotted otter board is 45°.The lift coefficient of the otter board has a rising trend when angle of attack is smaller than 45° and has a downward trend when angle of attack is bigger than 45°.And it is inferred that 45° is the best working angle of attack of the otter board.The lift-to-drag has the maximum value when angle of attack is 20°.And the researches show that the lift coefficient and lift-to-drag both obtain biggish value at angle of attack of 35°?45°.Therefore,35°?45° is suggested to be the working angle of attack of the otter board.By contrast,it is found that the hydrodynamic performance of the vertical V-type cambered slotted otter board is better than other types of otter board.And the reasons is mainly that it has bigger angle of attack and bigger range of working angle of attack than otter board of similar structure and its working stability is better.The hydrodynamic performance of the optimized vertical V-type cambered slotted otter board based on the optimization parameter of respect ratio is excellent.It shows that optimized vertical V-type cambered slotted otter board otter board has more superior working performance,which demonstrates that the numerical simulation and hydrodynamic performance research and structure optimization of the otter board are complete.