毕业论文移动版

摘要：超声导波广泛用于管材和杆件的无损检测，通过导波传播特性的变化检测结构中的损伤以及材料的特性。本课题利用有限元模拟以及平台实验研究超声导波在埋入多孔介质中的棒的传播。分析了多孔介质特性对导波传播特性的影响。根据波在棒中的波动运动方程以及棒的边界条件，推导棒中导波的特征方程，并得到棒中导波的频散曲线。由于埋入多孔介质中的棒的边界条件发生了变化，进而影响了导波的传播特性。在利用有限元软件模拟棒中导波传播时，选取150kHz的纵向L(0,1)模态的导波在直径10mm，长1m的嵌入土壤的棒中传播，分析研究导波传播时声速以及衰减等传播特性，以及分析土壤特性的变化对传播特性的影响；另外，通过实验在金属棒中激励相应导波，并测试其传播特性，并与数值模拟结果比较。结果表明，随着土壤密度的增加，导波的衰减也随之增大。由此，利用密度与导波衰减的对应关系，达到用导波检测土壤密度的目的。

关键词：有限元模拟；导波；多孔介质；土壤性质；传播特性

Abstract：Ultrasonic guided wave is widely used to non-destructively test the structures of pipe and bar. The defects in structure can be detected and material properties can be measured by the variations of propagating characteristics of guided wave. In this paper, the guided wave propagating in bar which is embedded in porous media was studied by simulation of finite element method and experimental measurement. The influence of soil properties on the propagation characteristics of guided waves was analyzed. Based on the wave equation of motion and the boundary condition of the bar, the characteristic equation of the guided wave in the bar is deduced, and the dispersion curve of the guided wave in the bar is obtained. When the bar buried in the ground, it’s the boundary conditions of guided wave were changed, thus affected the propagating characteristics of guided wave. When the finite element software was used to simulate the guided wave propagating in the bar, the longitudinal mode L (0, 1) with frequency of 150 kHz was selected to propagate in the metal bar with diameter of 10mm and length of 1m. The propagation characteristics of guided wave, such as velocity and attenuation was studied and the influence of soil properties surrounding the bar on propagation characteristics were analyzed. Furthermore, the guided wave was experimentally excited, the propagation characteristics were measured which were compared with the numerical simulation results. The results show that the attenuation of the guided wave increases with the density of soil. Thus, the relationship between the attenuation of guided wave and soil properties provides a convenient way to measure soil properties.

Keywords: finite element simulation; guided wave; porous media; soil properties; propagation characteristics

目 录

第一章绪论1

1.1项目研究的意义1

1.2项目的研究现状2

1.3主要研究内容3

第二章棒中导波传播的相关理论-5

2.1金属棒中导波传播的相关理论5

2.1.1波在无限长棒中的传播5

2.1.2波在圆柱体中的三种振动形式6

2.2多孔介质对金属棒中导波传播波的影响相关理论9

2.2.1特征方程9

2.2.2埋于土中金属棒中L（0，m）模态导波衰减12

2.2.3导波模态和频率的选择-14

第三章金属棒中导波传播的有限元模拟15

3.1有限元数值模拟介绍-15

3.1.1有限元基本介绍-15

3.1.2项目软件（ABAQUS）介绍-15

3.1.3ABAQUS软件分析的基本过程-17

3.2金属棒中导波传播的有限元模拟-18

3.2.1模型的创建及参数分配-18 (责任编辑：qin)