Analysis On Antarctic Krill Mid-water Trawl Performance Based On Field Measurement And Model Experiment

Antarctic krill?Euphausia superba? is currently known on the planet the largest amount of resources in a single species that belongs to crustacean zooplankton,and widely distributed in the ring south of the continental shelf waters.Its body has all the human needs of the amino-acid,with great potential for the development and utilization of the value of the world's attention.At present,the single-ship middle trawl is the main way to catch Antarctic krill in china,the use of the trawl net is also improved from the large mesh krill trawl changed small mesh krill trawl in 2009.The small mesh krill trawl in the fishing operation because of its relatively small size and no large mesh intertwined operation is more convenient and simple,is timesaving in picking and placing net else.In this paper,we focus on the current situation of the use of small mesh krill trawls at sea and the main problems of the trawl net.?1?The net position in water change relationship of towing speed and warp length is worth to be discussed;?2?Because of the vertical movement of Antarctic krill day and night,which makes the control of the net position has a certain degree of difficulty,that not only need to control the floating ratio,but also need to know how to configure the weight of heavy bob can make it stay the estimated position and What happens to performance at same time??3?How the configuration relationship between otter board resistance and trawl net resistance??4?According trawl experiment at the sea conducted by "LONGTENG" that belong China Fishery Co.,Ltd from January to May in 2016,it was found that the krill trawls has more inner net and the mesh very small,in spite of the fishing production well,but the resistance is large that probable make the energy consumption will be larger.Therefore,the impact of the twine area of inner net on the performance of the network is also worthy of study.In this paper,according the trawl catching data when the vessel production at the Antarctic sea,then combine the model test data that completed at circulation tank of Tokyo University of Marine Science and Japan Fisheries Engineering Institute in Japan.The main results of the comparative and analysis the test at sea and the model test are as follows:?1?The net?Net 1?position was mainly controlled by the length of warp,for each additional 20 m of the warp length,the net position decreased 1.9 m in average,Warp length significant effect on both the net position and net mouth height?p<0.01?,When towing speed increased from low to high speed,average rise rate of the net position reached 2.9 m/Kn,the vertical opening of net mouth account for 19.8% in average.Towing speed has significant impact on the net position and net mouth opening?p<0.05?.the net position adjustable to stable state requires an average of 3 min.?2?Complete the model test for NET 2,the research shows: the change of L/S is make the resistance change range is less,but when changed the towing speed,the resistance has a big change range.The L/S and towing speed has significant impact on the net resistance and height of net mouth?p<0.05?.At different net mouth horizontal spread,at minimum towing speed of 1.5 Kn increased to the maximum towing speed of 3.5 kn,the net resistance increased by an average of 41.19%,and as towing speed increased,the net resistance change range decreased,as net mouth horizontal increased,the change range of net resistance also increased,but the change range not large,on average of 0.925%.For the Antarctic krill trawl net,when the towing speed was 1.5 Kn,2.0Kn,2.5Kn,the Optimal shape of net mouth were at L/S=0.55.when the towing speed was 3.0Kn,3.5Kn,he Optimal shape of net mouth were both at L/S=0.55.That s to say,at high towing speed,The net mouth horizontal spread requirements do not need too much.?3?The heavy bob has significant impact on the net resistance,energy consumption coefficient and height of net mouth?p<0.05?.Changed the weight of heavy bobo is for adjustment the net position in the water,Because of the vertical movement of Antarctic krill day and night,that is need to adjust the weight of heavy bob according the krill school.The results show: Assembly of 600 kg and 300 kg heavy bob the net mouth height change is smaller,but compared to the height of the net mouth when not equipped with heavy bob,were increased by 3.08% on average.At the same time,the energy dissipation coefficient of the trawl decreases with the increase of the weight of heavy bob and the variation curve of the energy consumption coefficient when assembling 300 kg and 600 kg heavy bob is very small.It can be considered that in ensuring that the mesh can reach the preset water layer cannot need to configure the more weight of heavy bob to facilitate the operation when the network.?4?Inner net of trawl net is critical for krill as the krill individual was small.The research indicates,the twine area of inner net has significant impact on the net resistance and height of net mouth?p<0.01?.As the towing speed increased,the change of twine area of inner net caused net resistance change range could be more lager,and the energy consumption coefficient also has the same law.At the low towing speed?V?2.0 Kn?and low net mouth horizontal spread?L/S?0.45?,Ensuring that krill does not squeeze through the mesh or escape the net,may consider the twine area of inner net is optimized to 16.93%,that may be more conducive to the improvement of fishing efficiency and reduce energy consumption.?5?By comparing the results of test at sea,drag tank test and circulating water tank show that: when the towing speed less than 2.5 Kn,the net resistance was substantially equal when test at sea and drag tank.The resistance net of come from circulating tank test is 21.74% higher than that of the drag tank test,which is 31.61% higher than the average trawl resistance measured at sea.Although the test otter board spread very small at the low towing speed?V? 2.0 Kn?,but at towing speed more than 2.0 Kn the otter board could be still suitable for the krill trawl operating characteristics.Of course,in order to be able to ensure that the low speed the trawl net can also achieve better mesh effect,large expansion of the screen development is also very meaningful.Therefore,in the next trawl optimization test,we should consider the larger model of the trawl net,the main scale will be reduced,expand the stencil model is conducive to the screen is really a better understanding and test,reduce the model distortion error.The formula is optimized by the relationship between the trawl resistance and the towing speed under the three test conditions: R=135.06V^1.4706?R2=0.9099?.