南极磷虾拖网的性能优化分析

针对一顶中国目前正在使用的南极磷虾(Euphausia superba)拖网进行网具优化试验,设计了调整参数为浮沉比、上下手纲(等长)和叉纲的三因子L9(34)正交实验,并在3组L/S(水平扩张比)和5级拖速下完成了135次拖曳试验。结果表明:(1)随着拖速和L/S的增加,网具阻力增加,网口高度降低;(2)流速为3 kn情况下,L/S=0.45时,对阻力(Fs)和网具功率消耗(Ps)影响的主次顺序均为沉力(A)>叉纲(C)>手纲(B),对网口高度(Hs)影响的主次顺序为A>B>C,对能耗系数(Ce)影响的主次顺序为C>A>B,水动力性能的最优组合为A3B3C1;L/S=0.5时,对Fs、Hs和Ps影响的主次顺序均为C>A>B,对Ce影响的主次顺序为B>C>A,最优组合为A2B3C3;L/S=0.55时,对Fs和Ps影响的主次顺序均为C>A>B,对Hs影响的主次顺序为B>A>C,对Ce影响的主次顺序为B>C>A,最优组合为A2B3C3;(3)当L/S极低为0.2时,网口的水平扩张约为23 m,虽然此时网口高度有一定的提高,但网具的综合性能却显著下降,能耗系数增加;(4)增加沉力,适当放长手纲和叉纲可以有效提高已定型网具的性能。为确保在低拖速下达到网具的高扩张性能,应考虑改进网板性能,建议采用低拖速高扩张性网板。

Performance optimization of a trawl for Antarctic krill

An optimization analysis test was carried out,based on a trawl currently in use for Antarctic krill(Euphausia superba).The buoyancy/sinking force ratio,and types of bridles and straps were chosen as factors in an orthogonal array test L9(34).From 135 towing trials using 3 expansion ratios(L/S) and 5 trawl speeds,the fol-lowing conclusions were drawn.(1) At higher trawl speeds and higher values of L/S,the drag resistance of the trawl was higher and the width of the net mouth was greater.(2) At a towing speed of 3 knots and L/S = 0.45,these factors influenced resistance(Fs) and power consumption(Ps) in the following order: gravity(A) > cross rope(C) > bridle(B).The order of their influence on the net mouth height(Hs) was A>B>C,and on energy dissipation(Ce) was C>A>B.The optimal combination for hydrodynamic performance was A3B3C1.At L/S = 0.5,the order of influence on Fs,Hs and Ps was C>A>B,the order of their influence on Ce was B>C>A,and the optimal combina-tion for hydrodynamic performance was A2B3C3.At L/S = 0.55,the order of influence on Fs and Ps was C>A>B,their influence on Hs was B>A>C,their influence on Ce was B>C>A,and the optimal combination for hydrody-namic performance was A2B3C3.(3) When L/S was extremely low(0.2),the horizontal expansion of the net mouth was approximately 23 m.Although the width of the net mouth was greatly increased,the trawl was ineffi-cient overall and there was a significant increase in the coefficient of energy dissipation.(4) The main method of adjustment to improve the overall performance of the trawl is to increase the effect of gravity by appropriately lengthening the bridle and the cross rope.Based on this study,to achieve a high expansion of the trawl at low towing speeds,we recommend the use of highly expandable otter doors.