调整作业参数对小网目南极磷虾拖网水动力性能的影响

摘要

小网目南极磷虾拖网有规格小、操作方便、起放网省时的特点.针对规格为 185.4 m ×97.5 m (41.8 m)的小网目南极磷虾拖网的水平扩张、浮力、重锤重量、沉力、空纲长度5 个作业参数,分别进行3 ~6次调整试验,测试阻力和网口高度,并比较能耗系数.结果表明:在下纲端部间距分别为16.65、18.75、20.85 m3种水平扩张下,扩大水平扩张可引起网口高度下降,但阻力上升的幅度不大,能耗系数变化不明显;随着浮力的增加,网具阻力、网口高度均呈上升趋势,低拖速下增加浮力对网口高度的提升效果更明显,浮力增加可使网具的能耗系数下降,但在浮力达到19.6 kN后,再增加浮力能耗系数反而有所升高;增加重锤重量和在下中纲处增加沉力对网具阻力的影响效果相近,均呈上升趋势,增加重锤重量对网口高度的提升表现在低拖速时,随着拖速的上升网口高度的提升作用下降;增加沉力可提升网口高度,但在沉力达到14.36 kN后,再增加沉力对网口高度的提升效果不明显,能耗系数反而上升;空纲长度从66 m增加到84 m可明显提高网口高度,而网具阻力上升不明显,能耗系数呈下降趋势.%Antarctic krill trawl with small mesh has the features of small specification,convenient operation and is timesaving in picking and placing net.In this paper,trawl modeling tests were conducted with 185.4 m ×97.5 m(41.8 m)Antarctic krill trawl as the prototype,and five operation parameters (horizontal expansion, buoyancy,gravity,hammer weight and bridle length)were chosen to carry out adjustment tests for three to six times respectively.Resistance and height of net mouth were obtained,and coefficient of energy consumption was calculated and compared.Results showed that:at the distance of the end of groundline of 16.65m, 18.75m and 20.85m,expanding the horizontal distance can reduce the height of trawl mouth,while the increasing extent of resistance was small.In the adjustment test of buoyancy,both drag and height of net increased with the increasing buoyancy.At low speed,increasing the buoyancy had more apparent effects on the promotion of the height of net mouth,and reduced the energy consumption coefficient of nets,however, after the buoyancy reached 19.6 kN, additional buoyancy could improve the coefficient of energy consumption.Adding the weight of hammer or increasing gravity at the middle part of groundline had the same impact on the resistance of the trawl.Increasing the weight of hammer made the coefficient of energy consumption down,and improved the height of net mouth only at low velocity,and the impact of improving the height decreased.Adding the gravity could increase the height of trawl mouth,but more gravity had no apparent influence on the height and the coefficient of energy consumption was lowered after the gravity reached 14.36 kN.When the length of bridle increased from 66 m to 84 m,the height of net mouth was improved apparently,resistance of net had no apparent increasing,and the coefficient of energy consumption trended down.