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基于小波分析的超声导波法管道损伤检测研究

更新时间 2009-11-28 23:36:17 点击数:

基于小波分析的超声导波法管道损伤检测研究
Study on Wavelet-Based Damage Detection in Pipes Using Ultrasonic Longitudinal Guided Wave
【摘要】 本文利用LS-DYNA 970有限元软件对考虑横应变下的空圆管纵向超声导波损伤检测进行了数值研究;并利用ALE算法及单元共节点法,实现了充液圆管道超声导波损伤检测的仿真计算。对管道中导波在不同的激发频率下的频散现象进行了理论和数值分析,研究了缺陷反射信号强度变化的相关规律以及超声导波对缺陷的敏感度。利用适当尺度和小波基函数下的小波变换,实现了对微弱且无法直接观测的缺陷检测信号的识别。同时,通过时频分析研究了噪声信号在检测信号中的分布规律,运用小波包分解和重构算法将信噪分离,实现高噪条件下管道微缺陷的损伤识别。通过比较充液管道与空管检测中纵向超声导波信号和频散曲线之间的差异,定量分析了充液管道检测信号幅值衰减与群速度降低程度,得到充液管道所特有的纵向干扰模态及其频率相关性。分析结果表明,通过合理选择的激励信号可以有效调节并抑制充液管道中传播的特有的纵向干扰模态对损伤检测的干扰。对比不同损伤程度下空管与充液管问缺陷反射信号幅值特征差异,得到充液管缺陷反射信号的能量耗散程度随缺陷反射信号本身能量的非线性定量关系,数值分析结果与相关实验结果基本一致。

【Abstract】 A study on defects detection of the hollow and liquid-filled pipes was carried out by comparison of their detection signals and dispersion curves. A defect identification method in pipes using ultrasonic longitudinal guided-wave is studied. The numerical data of damage detection signals of the pipe based on finite element method are derived by LS-DYNA, involving the reduced stiffness and thickness of elements on the defect location. Furthermore, wavelet transform is proposed to identify the imperceptibility defect. By means of reflection signal peak intensity, the sensitivity of the proposed approach versus the change of local stiffness in pipe wall is evaluated. The effect of noise on the identified results is also discussed. Defect identification in the low signal-noise ratio is realized based on the algorithm of wavelet decomposition and reconstruction. The specific disturbance mode in liquid-filled pipes, as well as its frequency dependence, is analyzed. The results show that the disturbance mode can be adjusted and restrained remarkably by choosing some appropriate exciting signs. Furthermore, the difference of the defect reflecting signals with variable damage levels in the hollow and liquid-filled pipes indicates that there is a nonlinear relationship between the extent of the energy dissipation and the damage extent in the liquid-filled pipes. The present numerical analysis proves a good agreement with the corresponding experiment results. 

【关键词】 管道; 损伤检测; 噪声; 小波变换; 小波分解和重构; 流-固耦合
【Key words】 pipe; damage detection; wavelet transform; noise; wavelet decomposition and reconstruction; fluid-solid coupling
  基于小波分析的超声导波法管道损伤检测研究

摘要 4-5
ABSTRACT 5
第一章 绪论 10-18
    1.1 无损检测技术概述 10
    1.2 管道损伤检测的超声波法与超声导波法 10-13
    1.3 研究历史及现状 13-15
    1.4 本课题组研究概况及进展 15-16
    1.5 本文的主要工作 16-18
第二章 理论基础及数值计算 18-40
    2.1 导波信号选择 18-20
    2.2 空管导波频散曲线计算 20-27
    2.3 充液管道频散曲线 27-31
    2.4 损伤类型及其等效 31-33
    2.5 小波变换及小波包分析 33-35
    2.6 数值模拟 35-40
        2.6.1 空管的超声导波损伤检测的数值模拟 36-37
        2.6.2 充液管道的超声导波损伤检测的数值模拟 37-40
第三章 主要结果分析及与实验比较 40-59
    3.1 小波变换法识别微弱损伤信号 40-44
    3.2 含噪检测信号的小波包提纯和识别 44-49
    3.3 导波对损伤敏感度分析及其阈值关系 49-51
    3.4 充液管道导波特性及模态转换现象 51-59
第四章 结论 59-61
    4.1 主要创新点 59
    4.2 结论 59-61
参考文献 61-67
在学期间发表论文 67-68
致谢 68

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