| Antarctic krill(Euphausia superba)is a small planktonic crustacean living in Antarctic waters.Due to its enormous resources and rich nutritional value,it has attracted more and more attention from countries.China also attaches great importance to the development and utilization of Antarctic krill resources.Since China officially joined the commercial fishing of Antarctic krill in the 2009/2010 fishing season,it has introduced and developed a variety of trawl for Antarctic krill,and has made phased progress in trawling equipment and technology.However,the research on the new type of Antarctic krill truss trawl is still in its infancy.This study focuses on the two parts of the continuous pump suction beam trawl,beam and the main body of the net.The continuous pump suction beam trawl used by the "Shen Lan" fishing boat is used as a prototype to conduct the following research:1 、 Three types of beam,cylindrical,airfoil,and elliptical,are selected,and three-dimensional modeling of the three types of truss is carried out using Solidworks.Numerical simulation is conducted using the Fluent module of CFD software,and verification is conducted through tank model experiments,Compare and analyze the hydrodynamic performance of different beam structures.2、Set three different net mouth structures for nets A,B,and C,and set three different weights of 1.5t,2.0t,and3.0t on each side of each net.Among them,the A mesh is a flat net mouth without cutting,the B net mouth is a prototype net,and the side piece is cut to the end of the first section of the back net,while the C net mouth side piece is cut to the end of the second section of the back net.Exploring the effects of net mouth structure and weight on the performance of net through water tank model experiments;Select the net mouth with the best performance among A,B,and C as the prototype net,and set a total of 4 body circumference ratios of 0.65,0.60,0.55,and 0.49,respectively.Select a single 2.0t weight for the net,and explore the impact of different body circumference ratios on the performance of the net through a water tank model experiment;Based on the above research results,the net structure and operation configuration with the best performance of the net are selected as the prototype net.The pumping system assembled by the "Shen Lan" is used as the prototype,and a corresponding scale ratio model pump and hose are made using the same large-scale ratio as the model net.The water tank model test is conducted on the model net to explore the impact of the pumping system on the hydrodynamic performance of the net.The conclusions drawn from this study are as follows:(1)The results show that the resistance coefficient of the cylindrical beam is higher,the average resistance coefficient at each angle is 8.9% higher than that of the wing beam,17.0% higher than that of the elliptical beam,and the average lift coefficient at each angle is 44.8% and 40.0% lower than that of the two beam structures,respectively.Moreover,due to the influence of the lifting force of the semi-circular guide rail structure,the lift coefficient of the cylindrical beam fluctuates greatly and has poor stability.Comparing the airfoil and elliptical beam structures,the resistance coefficients of the two beam structures are basically the same at each angle of attack.At 0° angle of attack,the resistance coefficient of the airfoil beam is more specific than that of the elliptical beam,and the resistance coefficient is 87.2% larger than that of the elliptical beam.According to the visualization analysis of the flow field,the pressure at the front end of the airfoil beam is relatively large at 0°.According to the trace diagram,the boundary separation occurs at the front end of the airfoil,and two large eddies are formed at the tail.The wake deceleration zone is significantly larger than the elliptical beam.Compared with cylindrical beam structure,airfoil and elliptical beam have better hydrodynamic performance.(2)The results showed that there was no significant difference in the resistance and energy consumption coefficient of the net when the net structure was changed(P>0.05),but there was a significant difference in the height of the net(P<0.05).Under each counterweight,the net resistance B>C>A,the net opening C>B>A,and the energy consumption coefficient A>B>C.The height of the C net opening is large,the energy consumption coefficient is small,and the performance is optimal.The change of the weight of the heavy hammer has a significant impact on the resistance of the net and the height of the net opening(P<0.05),but has no significant impact on the energy consumption coefficient of the net(P>0.05).However,when the towing speed is below 3kn,the energy consumption coefficient of the net weight of1.5t and 2.0t is less than 3t.When selecting the weight of the heavy hammer,it is necessary to consider the actual operation factors such as offshore operation,which will increase the difficulty of lifting and releasing the net,and the towing speed of the beam trawl operation is generally between 2kn-3kn,so it is more appropriate to use a single side weight of about 2.0t.The change of body length ratio had a significant impact on the hydrodynamic performance of netting(P<0.05).At the towing speed of2.5kn,the net resistance increased from 175.10 KN at 0.65 to 199.25 KN at 0.49,an increase of 13.79%,the net height increased from 15.05 m to 15.82 m,an increase of5.12%,and the energy consumption coefficient increased by 8.24%.When the net body is shortened,the height of the net opening of the net increases slightly,while the net resistance and energy consumption coefficient increase significantly.The pumping system has a significant impact on the hydrodynamic performance of netting(P <0.05).At the towing speed of 2.5kn,the resistance of the net increased by 10.3%,the height of the net mouth decreased by 4.3% and the energy consumption coefficient increased by 15.3% after the pumping system was installed.This study systematically and comprehensively explored the hydrodynamic performance characteristics of each component of the Antarctic krill beam trawl,in order to provide theoretical basis for the independent design and optimization of the Antarctic krill beam trawl in China. |
PDF Full Text Request