Current deflection NDE for the inspection and monitoring of pipes

Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model.     

A Non‐linear Manifold Strategy for SHM Approaches

In the data‐based approach to structural health monitoring (SHM) when novelty detection is utilised as a means of diagnosis, benign operational and environmental variations of the structure can lead to false alarms and mask the presence of damage. The key element of this paper is to demonstrate a series of pattern recognition approaches which investigate complex correlations between the variables and thus potentially shed light on the variations within the data that are of interest for SHM. The non‐linear manifold learning techniques discussed here, like locally linear embedding combined with robust discordance measures like the minimum covariance determinant and regression techniques like Gaussian processes offer a strategy that includes reliable novelty detection analysis but also a method of investigating the space where structural data clusters are lying.     

光纤光栅传感网络的优化研究

光纤光栅传感网络在大型复杂结构健康监测中具有广泛的应用前景,对光纤光栅传感网络优化的研究具有重要的意义。分析了结构健康监测中光纤传感网络优化布局和可靠性的研究现状,对光纤传感网络优化中的传感器优化布局与光纤传感网络可靠性两方面进行研究。通过对结构响应特性研究,提出了对结构静力响应参数监测时,传感器布局的一般规则。将概率计算引入光纤 FBG 传感网络不同拓扑结构,给出了基于不同拓扑结构的光纤传感网络形式及其可靠性数值分析。     

Reliability assessment of cable-stayed bridges based on structural health monitoring techniques

This paper presents the reliability analysis approach of long-span cable-stayed bridges based on structural health monitoring (SHM) technology. First, the framework of structural reliability analysis is recognised based on SHM. The modelling approach of vehicle loads and environmental actions and the extreme value of responses based on SHM are proposed, and then models of vehicle and environmental actions and the extreme value of inner force are statistically obtained using the monitored data of a cable-stayed bridge. For the components without FBG strain sensors, the effects and models (extreme values) of dead load, unit temperature load, and wind load of the bridge can be calculated by the updated finite element model and monitored load models. The bearing capacity of a deteriorated structure can be obtained by the updated finite element model or durability analysis. The reliability index of the bridge's critical components (stiffening girder in this study) can be estimated by using a reliability analysis method, e.g. first order reliability method (FORM) based on the models of extreme value of response and ultimate capacity of the structure. Finally, the proposed approach is validated by a practical long-span cable-stayed bridge with the SHM system. In the example, reliability indices of the bridge's stiffening girder at the stage after repair and replacement after 18 years of operation, and the damaged stage are evaluated.     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance, 简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer, 简称PZT)进行主动激励,通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态;然而EMI方法容易受到环境工况变化的影响,导致结构损伤的误报。针对此问题,采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征,将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列,根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性,开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明,协整消除了动态应力对EMI方法的影响,当铝梁内存在持续变化的应力时,仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响,及时准确地进行结构损伤识别。     

基于肖特基势垒二极管的太赫兹固态倍频源和检测器研制

本文基于GaAs肖特基势垒二极管以及混合集成电路工艺,对太赫兹固态倍频和检测技术开展了研究.文章结合肖特基势垒二极管物理结构,采用电磁场仿真软件和电路仿真软件相结合的综合分析方法,对各模块电路进行优化设计,研制出了高倍频效率的倍频源和高灵敏度的检测器(检波器和谐波混频器).0.15THz检波器测得最高检波电压灵敏度1600mV/mW,在0.11~0.17THz灵敏度典型值为600mV/mW,切线灵敏度优于-29dBm.0.15THz二倍频器测得最高倍频效率7.5%,在0.1474~0.152THz效率典型值为6.0%.0.18THz二倍频器测得最高倍频效率14.8%,在0.15~0.2THz效率典型值为8.0%.0.15THz谐波混频器测得最低变频损耗10.7dB,在0.135~0.165THz变频损耗典型值为12.5dB.0.18THz谐波混频器测得最低变频损耗5.8dB,在0.165~0.2THz变频损耗典型值为13.5dB,在0.21~0.24THz变频损耗典型值为11.5dB.     

结构健康监测无线传感网络同步采集研究

无线传感网络时间同步和同步采集预同步后,采用物理初始化相对(Physical time,Initialize time,Relative time,PIR)时间分离法,以及时间戳和数据包序号相结合的数据包结构,并对时间信息建立柔性优化模型。该同步采集方法可获取准确的时间信息,具有适用高频采集和低功耗的特点,保障了结构健康监测中同步采集时间信息和场域诊断的可靠性。     

Electro-Mechanical Impedance (EMI)-Based Incipient Crack Monitoring and Critical Crack Identification of Beam Structures

Fatigue-induced damage is often progressive and gradual in nature. Fatigue is often deteriorated by corrosion in ageing structures, creating maintenance problems, and even causing catastrophic failure. This ushers the development of structural health monitoring (SHM) and nondestructive evaluation (NDE) systems. Recent advent of smart materials applicable in SHM alleviates the shortcomings of the conventional techniques. Autonomous, real-time, remote monitoring becomes possible with the use of smart piezoelectric transducers. For instance, the electro-mechanical impedance (EMI) technique, employing piezoelectric transducers as collocated actuators and sensors, is known for its ability in damage detection and characterization. This article presents a series of lab-scale experimental tests and analysis to investigate the feasibility of fatigue crack detection and characterization employing the EMI technique. This study extends the work by Lim and Soh [1 Y. Y. Lim and C. K. Soh . Smart Materials and Structures 20 : 125001 ( 2011 ).[Crossref], [Web of Science ®] , [Google Scholar]] to incorporate the phases involving crack initiation and critical crack. It is suggested that the EMI technique is effective in characterizing fatigue induced cracking, even in its incipient stage. Micro-crack invisible to the naked eyes can be detected by the technique especially when employing the higher frequency range of 100–200 kHz. A quick and handy qualitative-based critical crack identification method is also suggested by visually inspecting the admittance frequency spectrum.     

基于阻抗技术的压电元件自损伤检测-

为了保证结构健康监测系统的有效运行,基于压电阻抗技术原理,提出了一种压电传感、驱动元件自损伤检测方法.通过研究压电元件等效电容值(压电元件导纳虚部数值)的变化,判别压电元件是否破损及其与主体结构之间是否剥离,并在悬臂梁结构上进行压电元件自损伤检测试验.结果表明,相比压电元件完好的情况,各频率下压电元件电纳值随脱粘部分面积的增加而上升,随破裂部分面积的增加而下降,并且损伤程度和等效电容变化量成比例关系,与理论分析结果吻合较好.     

Optimization of SAW-type Surface Wave Ultrasonic Sensors for Ultrasonic SHM

Surface acoustic waves (SAW) are particularly suited for effectively monitoring and characterizing a structure’s surfaces (condition of the surface, coating, thin layer, micro-cracks, etc.), and in some cases it is necessary to permanently keep the sensors on the structures to enable continuous monitoring. This article focuses on the optimization of SAW-type interdigital sensors (or IDT sensors for InterDigital Transducer) because they can largely address this issue. Initially, the ability of piezoelectric materials (lead zirconate titanate [PZT] and Niobate de lithium) to generate SAW is studied by modeling. Then a design of an IDT sensor is defined and optimized for the generation of SAW on a substrate. Parameters such as electrode’s periodicity, thickness of piezoelectric plate, and type of contact between the plate and the substrate, are studied. Finally, experimental results are compared with those obtained by modeling.