大型中层拖网结构试验

Experiments and optimization on the fore part of mid-water trawls

针对具有绳索拖网和网目结构相结合特点的中层拖网,基于L_9(3~4)正交表,设计了网身长度(变化网身第一节目数)、网袖配纲长度、侧片宽度3种因素各3种水平的正交试验,并利用方差分析对3种试验因素变化对网具阻力、网口高度、能耗系数影响的显著性进行分析,研究此种网头的最优结构型式。结果表明:网身长度增加,网具的阻力上升,网身第一节采用2目是试验的最佳水平。网袖部分配纲长度是3种试验因素中唯一对网口高度有显著影响、并对能耗系数的影响接近显著。网袖部分配纲长度每档比相邻靠近中纲位置加长5%~10%,可明显比等长配纲降低能耗系数。从试验时对网口形状观察,在试验的浮、沉力配置下,网口形状为椭圆形,侧片与背、腹片宽度相等的网头结构,在高拖速时明显冗余。低拖速(4 kn)时,侧网与上、下片的宽度比7∶8为佳,在高拖速(5 kn)时,则3∶4为试验的最佳水平。

A new structure of the fore part of mid-water trawl has the features that the rope trawls and mesh structure trawls are unified. This paper based on 1.9 （34） orthogonal array, designed thine kinds of factors of level orthogonal experiment： body length （change body＇s fist part meshes）, wing rope length and the side panel width, and used the variance analysis to three kind of experimental factors in the experimental level to test the net resistance, the net opening and the energy consumption coefficient to study the optimal fore part of net structure pattern. The results showed that the fore part of net length increases and the resistance increases, the fore part of net using 2 meshes is the best experimental level. The length of wing rope parameters only have the remarkable influences on the net opening in three kinds of experimental factors, and clearly significant influences on energy consumption coefficient. As the length of every part wing rope gradually lengthens 5 - 10%, it can obviously reduce the energy consumption coefficient more than with length equal to wing rope. The side panel uses suitably with a top and bottom panel width equal to the net structure when the net mouth shape is close to circular. During the experiment, observing the net mouth shape, under the experiments buoyancy and sinking, the net mouth shape is an ellipse, at the low towing speed of 4 kn, the experiment shows the best level when width ratio between side and top panel is 7 ： 8, and at the high towing speed of 5 kn, 3：4 is the best level in the experiment.