网囊与渔获物对串行多组网囊拖网水动力学特性的影响机制研究

Serial multiple cod-ends trawl is a new type of trawl which is improved contraposing the problem of traditional trawl that catch is not fresh and energy consumption is high caused by long time haul and catch heaping up in cod-end. It connects multiple detachable cod-ends in series and removes the cod-ends duly and successively during hauling process, so as to short the hauling time of each cod-end, and achieve the aim that enhance catch quality, conserve energy and reduce emission. Thereof, mastering the influence mechanism of cod-end and catch on hydrodynamic characteristics of trawl will play a crucial role on improving trawl. Combined with the research foundation of traditional ocean engineering and fishing gear dynamics, the study make use of finite element method and lumped mass method to construct a numerical model of serial multiple coed-ends trawl in current to perform three-dimensional simulation, integrate with numerical simulation and flume experiment methods to discuss hydrodynamic characteristics changing law of trawl influenced by cod-end and catch, take advantage of dimensionless processing and multiple regression method to reveal multi-factors evaluation functional relationship of cod-end, catch and velocity factors influencing hydrodynamic characteristics of serial multiple cod-ends trawl. The study will provide theoretical method and reference basis for optimal design of trawl system, and have important academic value and practical application significance in the field of high quality fishing efficiency enhancement, safety performance improvement, energy conservation and emission reduction.

串行多组网囊拖网是针对传统拖网由于拖曳时间较长、渔获物在网囊中堆积而导致渔获物不新鲜、能耗较高等问题而改良的新型拖网。它将多个可脱卸网囊串联连接在一起，在拖曳过程中适时地依次脱落网囊，以此缩短单个网囊的拖曳时间，从而实现提高渔获物质量、节能减排的目的。其中，掌握网囊与渔获物对拖网水动力学特性的影响机制将对改良该拖网渔具起到至关重要的作用。本研究将结合传统海洋工学、渔具力学的研究基础，利用有限元和集中质量法等方法建立串行多组网囊拖网受力与形变的数学模型并进行三维仿真模拟；结合数值模拟和水槽实验的方法，探讨网囊和渔获物影响拖网水动力学特性的规律；利用无量纲处理及多元回归方法，揭示网囊、渔获物、流速等对串行多组网囊拖网水动力学特性的多因子评价函数关系。本研究为拖网系统的优化设计提供理论方法和参考依据，在增强拖网优质捕捞效率、提高拖网安全性能、节能减排等方面都具有重要的学术价值和实际应用意义。

为改良传统拖网由于拖曳时间较长、渔获物在网囊中堆积而导致渔获物不新鲜、能耗较高等问题，本研究对串行多组网囊拖网的网囊与渔获物对拖网水动力学特性的影响机制展开研究。结合传统海洋工学、渔具力学的研究基础，利用有限元和集中质量法等方法建立串行多组网囊拖网受力与形变的数学模型并进行三维仿真模拟，包括菱形网目网囊拖网数值计算模型以及方形网目网囊拖网数值计算模型，对拖网不同部位改变网囊和网目类型之后的整体网型变化以及网身目脚张力分布进行计算、分析与对比；结合水槽实验的方法，对不同长度的菱形网目网囊与方形网目网囊拖网在不同数量渔获物情况下展开水槽试验，并替换局部菱形网目网囊为方形网目网囊，对不同情况下的拖网水动力以及拖网网型展开要素进行定量比较和分析，得到各水动力学要素与流速、网囊长度、渔获物数量等各因子之间的变化规律；对不同网目尺寸末端网囊的拖网在不同数量渔获物情况下开展水槽试验，得到网目尺寸、网型变化参数及水动力之间的关系。研究结果为串行多组网囊拖网系统的优化提供了理论方法和参考依据，为丰富拖网的设计理论提供了一定的数据支撑，在开发新型优质捕捞网具、提高拖网安全性能、节能减排等方面都具有重要意义。