利用压电超声导波埋地(水下)叠合管道结构健康监测方法研究

Transportation using pipelines as a safe and efficient tool has played an important role in national economy in China. The buried or submarine pipeline structure with the laminated cross section considering the protective layer is one of the most popular lifeline systems. Once the pipeline structure gets damages or failure during the service of life, it will bring the amount of economic losses. The proposed structural health monitoring method based on ultrasonic guided waves activated by piezoelectric ceramic patches (PZT) pasted on the surface of the pipeline structure has the properties of quick response, economical and practical value which can be used in fields of petroleum and natural gas transportation as well as city water supply for nondestructive testing and longtime structural health monitoring. Based on the piezoelectric equations and the lumped mass method, the mechanical model of surface-pasted piezoelectric ceramic transducers (such as PZT) and actuating techniques for a given mode of the ultrasonic guided waves are established in the research. Based on Navier equation for the symmetrical cylindrical pipeline buried in soil or under water, the dispersion equations for the buried or submarine laminated pipeline structures with the straight or curved line are set up and numerically solved, respectively, according to the boundary conditions, and the spectrum of the dispersion curves is also drawn for a given pipeline structure. The research emphasis is put on influences of the interface performance (strong or weak connection) and the longitudinal curvature as well as the external invironmental influences on the propagation of the ultrasonic guided waves, dispersion effect, mode transferring and energy loss etc. The nonlinear finite element method (FEM) and experimental validation method for the proposed pipeline structure are applied to develop the sensitivity and applicability of the pulse-echo signal to the single or multi-damages such as the external surface corrosion, internal sediment and directional cracks aush as logitudinal or circumferential cracks. Based on the time reversal technology of the considered signal, the damage identification algorithm without reference signal which used phase deviation as the main factor is established and used for the given artificial damages. The quick imaging technology and Labview computer language are also used to set up a platform for operation and management for the future use.

管道运输在国民经济中发挥着重要作用，具有外保护层的埋地（水下）叠合截面管道结构是最普遍采用的形式之一。所提出的基于压电超声导波的埋地叠合管道结构健康监测方法具有快速、经济、实用等特点，可用于石油、天然气、城市供水等重要领域的无损检测或长期监测。利用压电方程与集总质量法，建立了粘贴式压电陶瓷（PZT）驱动（传感）器的力学模型及给定导波模态下的激励方法；采用Navier波动方程及边界条件，分别建立埋地（水下）直线或曲线叠合管道结构的频散方程并进行数值求解，绘制了频散曲线图谱；重点研究叠合界面性态（强弱结合）、纵向曲率及外部环境对导波传播特性、频散效应、模态转换、能量损失等指标的影响；分别采用非线性有限元分析和试验验证的方法，研究了脉冲-回波信号对外部腐蚀、内部沉积和方向性裂纹等单一或多点损伤的敏感性，并建立了基于时间反转技术的无需基准信号的损伤识别算法，并利用快速成像技术搭建了计算机操作平台。

本项目完成的利用压电超声导波的埋地（水下）叠合管道结构健康监测技术具有快速、经济、实用等特点，可用于石油、天然气、供暖、供水等领域重要管道结构的无损检测或长期监测，具有重要的理论意义与工程应用价值。采用理论分析、数值模拟、试验验证和工程应用的方法，实现了系统地建立利用纵向压电超声导波的埋地（水下）叠合管道结构健康监测基本理论与方法的总体研究目标。主要研究内容与成果包括：（1）建立了粘贴式压电陶瓷（PZT）换能器的力学模型及指定模态导波的激励方法。在理论和试验上均证明了利用特殊PZT列阵能够激管道结构指定模态（如L(0,2)）导波；（2）建立了超声导波在管道结构中传播的基本理论。分别建立了直线和曲线叠合管道结构的频散方程，绘制了频散曲线图谱，建立了单层管道结构的导波速度与内径、频率和壁厚的关系式；建立了激励信号的选取原则，并提出了“弱频散区域”概念，为如何选择监测信号提供理论依据；提出了叠合界面性态、纵向曲率及外部环境对导波传播特性、频散效应、模态转换、能量损失等指标的影响规律；（3）提出了一种基于时间反演技术的损伤识别算法。利用回波信号的能量值构建性能指标，并结合试验和有限元分析的结果，成功地对所提出的性能指标进行分类；利用时间反演技术，有效提高了损伤识别的灵敏度；（4）实现了复杂环境下的管道结构损伤识别与健康监测。提出了管道结构的腐蚀状态监测方法，并建立了管道中腐蚀损伤径向深度、轴向长度与波反射系数的线性关系式；提出了具有大曲率管道结构的健康监测方法，验证了弯曲管道会使超声导波产生模态转换现象；提出了管道结构法兰连接松动监测的模型，建立了松动程度与波动参数之间的关系式；（5）利用虚拟现实技术分别建立了管道结构有线、无线监测系统。建立一种考虑环境温度影响的压电陶瓷波动物理模型；将所建立的基于虚拟仪器技术和LabView语言的管道结构健康监测系统应用于实际工程，验证了所建立的理论和方法的有效性。