机器鱼跨介质游动的运动学和动力学研究

论文总字数：35907字

摘 要

首先，通过三维建模软件建立标准金枪鱼三维模型，通过前处理软件Gambit对生成模型进行详细的网格划分，同时建立计算区域并定义初始的边界条件。利用Microsoft Visual C 编写程序模拟给定鱼体域的自身运动学变形，求解流体域的控制方程得到流体作用力，并将该作用力传递于鱼体域，进而求解鱼体域的控制方程得到游动运动参数，控制鱼体域运动，通过FLUENT仿真，实现了鱼体游动。

其次，通过Fluent的VOF（volume of fluid）模型功能建立气液两相自由液面计算域，研究并确定在二相流问题中Fluent所适用的求解器及相关参数设定。将鱼体置于不同的液面高度，通过改变鱼体在气液两相中所占比例，分别进行游动仿真，得到仿生机器鱼在两相介质共同作用下的稳态游速及功率性能，研究结果表明：①鱼体的推进力全部来自于液相介质的反作用力。随着鱼体在水中百分比的增加，从静止加速至稳态的过程越趋于平缓，且需要更长的加速时间。最终稳态游速Ux随之增大，速度上升趋势在30%至40%和60%至70%处幅度较大，在40%至60%处上升较为平缓，尤其在70%至100%区间内稳态游速基本无变化。②鱼体游动时的游向功率及侧向功率以及推进效率均随着鱼体浸入水中百分比的增加而增加。

再次，详细论述了VOF模型求解器及科朗系数，更好模拟鱼体出水过程。以飞鱼为运动模型，通过变换坐标系与自由液面的设置，模拟出金枪鱼类在水中垂直加速上升直至冲出水面的过程。通过分析鱼体速度曲线与功率曲线，表明鱼体加速出水基本依靠尾鳍的击水作用，且功率随时间上升。

最后，在前章垂直出水的基础上，通过坐标计算域的转换进一步探究仿生机器鱼不同角度及摆动频率的加速出水过程，发现随着鱼体出水角度的增大，虽然在竖直方向上拥有更大的推进分力，但由于水的阻力及胸鳍产生的额外升力，在本文研究范围内最佳出水角度在约为。

关键词：仿生机器鱼，数值模拟， VOF模型 ，摆动加速 ，跨介质出水

Kinematics and dynamics research of cross-medium fishlike robot of thuniniform

02009420 Hongzhi Li

Supervised by Dan Xia

Abstract: Ocean is a huge treasure trove of resources. In recent years, many countries have developed their own ocean detectors. The research on fluid machinery, especially in deep-ocean high pressure conditions, has become a main trend. Different from the traditional propeller propulsion, fish rely on swing to create propulsion which has excellent dynamic performance and is an ideal future underwater propulsion mode. This project will conduct a systematic study which focuses on cross-media for fish swimming to further demonstrate its dynamics characteristics.

Firstly, a standard tuna model is built in the three-dimensional modeling software. Meshes of the generated model are elaborately divided by using the preprocess software Gambit. At the same time, the computational area is established and the initial boundary condition is defined. With programs in Microsoft Visual C , the kinetic transformation of the given fish body area is simulated. Fluid working force is acquired by solving the control equations in fluid fields. Then the force is transmitted to the fish body area and the control equation of the fish body area can be solved to obtain swimming parameters. With these parameters, the motion of the fish body area can be controlled by means of simulation in FLUENT and the fish swimming action is achieved.

Secondly, gas-fluid two-phase computational area is established by using the function of model VOF in FLUENT. Plus, the solver and its relative parameter setting applicable in FLUENT should be studied and defined. Then the fish is set at different heights of liquid level. By changing the proportion of gas and fluid phase in which the fish occupies, the swimming simulation is carried out to obtain the stable swimming velocity and power performance of the fish-like robot effected in two phases. By plotting and analysis, I arrived at conclusions as follows:

The propulsion force of a fish body all comes from the counterforce of liquid medium. With the increase in proportion of the fish body occupying in water, the process of accelerating from static to steady state tends to be placid and the accelerating time is longer. Eventually, the steady swimming velocity Ux increases as well. The rising extent is relatively large both in 30-40% and 60-70%, little in 40-60%, and almost unchangeable in 70-100%.

The power of swimming direction and side direction as well as the propulsion efficiency gain with the increase in the proportion of water the fish occupies. The studies have shown that:fish accelerated mainly depends on the caudal fin.

Thirdly, in order to better simulate the process of fish leaving water, VOF model solver and the Courant coefficient is involved. With the kinetic model of flying fish, by transforming the setting of coordinate and free fluid level, the process from tuna’s accelerating vertically in water to coming outside water is initially simulated. By analyzing the velocity curves and the power curves, we can tentatively studying the kinetic mechanism of the fish-like robot accelerating to leave water.

Eventually, on the basis of the pre-chapters, which discuss the vertically leaving-water process, by transforming the coordinate computational area, this article will further study the different accelerating leaving-water processes of fish-like robots with different angles and swinging frequencies. With the increase in the fish bodies leaving-water angles, although the propulsion forces are bigger in the vertical direction, the optimal leaving-water angle concluded in the study range of this article is about , due to the drag forces from water and the extra elevating forces from pectoral fin.

Key words: fish-like robot, numerical simulation, model VOF, swinging acceleration, cross medium

目 录

1、绪 论 - 1 -

1.1 背景及意义 - 1 -

1.2 鱼类推进模式分类及仿生推进器的特点 - 2 -

1.2.1 BCF模式 - 3 -

1.2.2 MPF模式 - 4 -

1.3仿生推进机理的研究现状 - 4 -

1.3.1仿生推进机理的理论研究 - 4 -

1.3.2仿生推进机理的实验研究 - 6 -

1.3.3仿生推进机理的数值研究 - 7 -

1.4仿生机器鱼研究现状综述 - 7 -

1.4.1 BCF模式仿生机器鱼 - 8 -

1.4.2 MPF模式仿生机器鱼 - 9 -

1.5 本文的研究目的和主要研究内容 - 10 -

2、鲔科鱼类的仿生学及运动学模型 - 12 -

2.1 鲔科运动学模型 - 12 -

2.1.1 柔性身体运动学 - 13 -

2.1.2 刚性尾鳍运动学 - 14 -

2.2 尾科仿生鱼动力学 - 15 -

2.3 力学参数计算公式 - 16 -

2.4 数值求解方法与仿真过程 - 18 -

2.4.1 建模与仿真前处理 - 19 -

2.4.2 FLUENT与仿真过程 - 20 -

2.5 动网格技术（Dynamic Mesh） - 21 -

2.6 多相流及两相VOF模型 - 22 -

2.6.1 VOF求解器设置 - 23 -

2.6.2 气液自由液面拟合 - 24 -

3、仿生鱼气液两相直线游动机理 - 26 -

3.1 引言 - 26 -

3.2 直线游动的运动学 - 26 -

3.3 跨介质游动建模及前处理 - 27 -

3.4 仿生鱼气液两相直线游动的数值模拟 - 28 -

3.5 本章小结 - 32 -

4、仿生鱼垂直出水游动 - 34 -

4.1 引言 - 34 -

4.2 出水游动建模及前处理 - 35 -

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