不同结构网囊特性的初步研究

为了测定不同拖网网囊结构对网囊的几何形状、同目张开、网目形状和拖网阻力的影响，设计和制作了4种网囊，一种是传统的菱形同目（DM）网囊，另三种是新型网囊：方形同目（SM）网囊，菱、方形网目混合二片式（DSM2）网囊和菱、方形同目混合四片式（DSM4）网囊。于1996年9月11～12日在中山大学试验水槽进行了同模试验，结果表明：1）各网囊阻力相差不大，且随拖速和渔获的增加而增大。2）新型网囊的几何形状和同目的张开及其形状均优于传统菱形网目网囊。3）空网时，各种网囊均呈圆筒状。当网囊中有了渔获后，传统菱形同目网囊的端部变为球状，除了球状部分的网目有较大张开外，其余同目张开很小，网囊使用直径也小，而新型网囊始终保持筒状，且网目充分张开，网囊使用直径也大。4）新型例翼的几何形状及使用直径和网目的张开及形状几乎不受拖速大小、有无渔获和渔获多少的影响。

Preliminary Study on Characteristics of Different Trawl Cod-end Designs

In order to determine the effects of different trawl cod-end designs to the geometry of cod-ends, the opening and shape of its meshes and trawl resistance, we have designed and manufactured four sorts of cod-end: One traditional diamondmeshes (DM ) cod-end, and three new-type cod-ends, namely, square meshes (SM), two-panel cod-end with composite diamond and square meshes (DSM2) and four-panel cod-end diamond and square meshes (DSM4) with composite. After the experiment in the flume tank operated by Zhongshan Unversity on September 11~ 12, 1996, the results indicate that: 1 ) The non-significant resistance is increased with increase of trawl speed ; 2) geometry shape of the new cod--ends and mesh opening shape are superior to traditional diamond mesh cod-end ; 3)In case of empty net, all cod-ends will spread to a cylinder shape After catching the fish, the end of traditional diamond mesh cod-end turns into sphere shape with smaller opening and the shorter diameter, while the new cod-ends always keep its cylinder shape with fully opened meshes. 4)The geometry shape, diameter of the new type cod-end and its mesh opening shape are nearly not influenced by the trawl speed and fishing quantity.