| Since lack of profound scientific understanding to development and utilization of marine resources in the last century, marine fishery resources has been overfishing and global marine resources is clearly in recession. Furthermore, fishing was out of control In our coastal waters, which led to fish density decrease, Catch decline in the quality and economic species precocity miniaturization. With the reduction of fishery resources, to adjust to the trend, composition of fishing vessels also changed. The large-scale fishing vessels gradually reduced, and the number of small vessels increased. It is reported that the number of small vessels in2009increased13401than2008, growth rate was3.86%. For the composition of fishing vessels, the vessels whose engine power<44.1kW accounted for83.7%of the total amount. For the length of motor vessels, fishing vessels whose length<12m increased7.7%than last year, and its growth rate is the fastest. So the small vessels played an important role in composition of fishing vessels in China, and they provided the necessary protection of production operations for fishermen. The most fishing method of small vessels is trawl. It is different from fishing gear made on the large-scale trawl vessels.Otter board as the important accessory of trawl, and hydrodynamic performance of otter board have an impact on the operability and catch efficiency of the trawl. Although there were researches on the otter board in recent years, most focused on energy efficiency of the trawl. In the1970s, there were some researches on otter board hydrodynamic, but most for large trawl otter board. There was little research on otter board used on small motor power vessel. With the rapid development of computer technology, computational fluid dynamics (CFD) has been a wide range of applications over the past decade, especially promotion of the CFD commercial software to promote the scope of application of numerical simulation. And CFD overcomes the shortcomings of the theoretical calculations and the model test. Only on the computer it will be able to ’test’, in terms of fishing gear hydrodynamic simulation there were new ideas and methods. Abroad has appeared on the numerical simulation of net hydrodynamic study, but the domestic research is lagging behind.This article is composed of six chapters, Chapter1is researches at home and abroad on the otter board hydrodynamic performance and numerical simulation. Chapter2and3introduce the hydrodynamic performance of the otter board, the basics and related theoretical studies of fishing gear model test and computational fluid dynamics. Chapter4Chapter5is the results of model tests and Fluent software simulation of the otter board, and compares the results. Chapter6is the summary of the full text and further research. In this paper, it carries out hydrodynamic experiment and numerical simulation on Qingdao inshore small coastal trawl otter board. The model test conducted in aquaculture engineering hydrodynamic laboratory circulating channel in the Ocean University of China, and flow velocity is set at0.2m/s to0.7m/s, and the angle of attack measured from0°to50°. The paper obtain specific hydrodynamic coefficients (lift coefficient, the maximum lift-drag ratio, best operating angle of attack) on this type of otter board, providing a scientific basis for the use of the otter board. Numerical simulation by FLUENT software on the otter board under the specific angle of attack, obtained at20°ngle of attack flow field pressure and velocity distribution around otter board, as well as otter board force under the different flow rates. The experimental results show that the Reynolds number at3.14×105～4.50×105range, the lift coefficient and drag coefficient of the otter board remained stable. The Reynolds number of3.14×105～4.50×105, corresponding to the actual operation rate0.69to0.99m/s is in automatic model area. It is similar to the actual maximum drag speed2nm/h, meeting the conditions of model test. The results show that the otter board drag coefficient, lift coefficient, and the critical angle of attack of to reach maximum lift-drag ratio near15～25°,which is about1.86. Numerical simulation of the network board in the20°angle of attack, drawn stencil pressure distribution and velocity distribution, we can see the back of the otter board large eddy. Eddy size is different at different flow rates. Drag force and lift force results the relative error of the model test results were13.8%and15.6%. That numerical results can be used as a study reference. Consideration can be given on the otter board to make improvements and further validate the use of CFD simulation method. |
