【作者】 毕春伟；

【导师】 赵云鹏； 董国海；

【作者基本信息】 大连理工大学 ， 水利工程， 2012， 硕士

【摘要】 近年来,由于人口的增加,对水产品的需求增大,近海水产资源日趋枯竭。再加上过度捕捞和不合理的开发利用等因素影响,近海生态环境逐渐恶化。因此,把网箱养殖转移到外海,寻求优越的养殖环境以及高质量的养殖产品成为网箱养殖发展的必然趋势,深水养殖网箱应运而生。在深水网箱养殖过程中,箱内水体的流动与鱼类生长密切相关。在网箱水动力数值计算中,网衣的减流效应同样受到关注。因此,对网衣周围流场特性的研究有着重要意义,研究成果将对网箱养殖的生产实践起到积极的指导作用。网衣属于柔性小尺度、大变形、多孔结构,利用数值方法来实现其周围流场的模拟难度很大,目前,在网箱流场方面的研究成果大多数是采用物理模型试验和现场测量的方法,数值模拟方面的研究较少。本文采用Realizable k-ε湍流模型,结合多孔介质模型模拟网衣,建立了模拟水流作用下平面网衣周围流场的数值模型。利用最小二乘法分析作用在平面网衣上的水流力与流速和冲角的关系,得到对应的多孔介质系数,使得多孔介质区域具有与网衣相同的阻水效果。运用该数值模型对网衣及网箱周围流场特性进行数值模拟研究,获得较好效果。论文主要内容分为五章：第一章是绪论,简要介绍了课题背景和网箱流场方面的研究进展。第二章介绍了建立多孔介质模型的数值方法,主要包括控制方程、多孔介质系数、边界条件及网格划分和数值计算方法等。第三章为数值模拟及试验验证,首先采用本文提出的数学模型对平面网衣和方形网箱进行二维数值模拟,并通过模型试验进行验证。在此基础上,对不同冲角和流速条件下的平面网衣周围流场进行了三维数值模拟,并通过模型进行验证。第四章为平面网衣周围流场的数值模拟,本章对网衣倾角、高度、间距和数目等参数在一定范围内变化时,对平面网衣周围流场产生的影响进行了研究。第五章为网箱周围流场的数值模拟,在对平面网衣周围流场准确模拟的基础上,将网箱模型简化为由若干平面网衣组成,从而利用本文模型对整体网箱周围流场进行数值模拟,并对单体网箱以及组合网箱周围流场特性进行了研究。更多还原

【Abstract】 In recent years, the fishing stock is decreasing because the demand for fish production has grown substantially as the world’s population increase. On the other hand, the ecological environment of near-shore locations becomes worse and worse due to overfishing and excess exploitation. Because of the consideration of fish farming environment and high quality fish food, more and more net cages for aquaculture will be located offshore and the deep-water cage arises at the historic moment. In a deep-water cage, water flow within the net cage is closely related to the fish growth. The flow velocity reduction effect behind the fishing net is a major concern. Thus, the investigation on the flow field around the cage net has become an important subject. The research results will play a positive role in guiding the production practice of fish farming. The fishing net is a kind of small-scale flexible structure, the numerical study on flow field around the net structure is rather complex. At present, the efforts on the flow field around the net cage are mainly concentrated on physical model tests and field measurements and numerical simulation research is relatively rare.A numerical model combined the Realizable k-ε turbulence model and the porous media model is established to simulate the flow field around cage net under current. The unknown porous coefficients are determined from the experimental forces on the net and flow velocities and the angles of attack using the least square method. Therefore, the porous media act the same water-blocking effect as the net. This numerical model is applied for the simulation of the flow field around the plane net and the net cage under current and the numerical results are satisfactory.The contents are mainly composed of five chapters. The first chapter gives a general description on the background of the subject and the development of researches on flow field around net cages. The second chapter is the numerical method of the porous media model including the governing equations, porous media resistance coefficients, mesh grids and boundary conditions, numerical algorithm method. The third chapter is the experimental verifications. Firstly a two dimensional numerical model is applied for modeling the flow field around a net panel and a square cage under current and the numerical results are compared with data obtained by physical model tests. On this basis, a three dimensional numerical model is applied for modeling the flow field around a net panel at different attack angles and velocities, which is verified by physical model tests. In the fourth chapter, the flow field around a plane net with different plane net inclination angles, plane net heights, spacing distances between two plane nets and plane net numbers are presented and the effects of these parameters on the flow field around the plane net are investigated. The fifth chapter is the numerical simulation of the flow field around net cages. Based on the simulation of the flow field around plane net, the flow field inside and around a gravity cage can be simulated by dividing the net cage into many plane nets with different attack angle. Therefore, the simulation of the flow field inside and around a gravity cage is straight forward and the flow fields inside and around single gravity cage and composite-type net cages are investigated.更多还原