桥梁拉索表面缺陷的分布式机器视觉检测

介绍了一种桥梁拉索表面损伤缺陷的分布式视觉检测系统。系统以DSP(Digital Signal Processor)芯片TMS320DM642(简称DM642)为核心处理器,协同控制辅助机械装置,实现拉索表面缺陷检测。提出并采用改进的中值滤波对CCD采集到的拉索表面图像进行图像预处理,采用改进的Sobel边缘检测算法对缺陷进行边缘检测;对分割后的缺陷目标进行决策判别,实现桥梁拉索表面缺陷的智能检测。实验结果表明,系统可检测出桥梁拉索表面损伤面积大于1cm2的缺陷,处理速度达到了5cm/s,满足了快速有效的检测要求。     

光纤Bragg光栅传感器在桥梁工程中的应用

本文概述了光纤Bragg光栅传感器(FBG)的组成、原理、类型及特点，介绍了目前光纤Bragg光栅传感器在国外桥梁工程中的研究及应用情况以及国内应用实例，并分析了现有应用的不足之处，指出了光纤Bragg光栅传感器在桥梁结构健康监测应用中的发展方向。     

分布式光纤传感器在预应力结构健康监测中的应用研究

介绍了国内外分布式光纤传感器应用于桥梁等大型预应力混凝土结构进行安全监测的现状,讨论了光纤传感器在大型预应力等结构健康监测应用中的发展前景。     

桥梁振动的激光干涉测量方法

为了实现对新建桥梁的质量检测及现有桥梁健康状况的定期检查,分析和评估桥梁结构振动特性,掌握抗震性能变化情况和趋势,本文提出了激光干涉测量桥梁振动频率的方法,克服了现有测量方法精度低、电磁干扰大、传输距离受限等缺点.实现了对桥梁振动情况的检测,为桥梁勘测提供了重要的分析数据,结构简单、测量精度高、应用前景广阔.     

铝合金材料腐蚀损伤的声发射评价

为了研究如何利用声发射(AE)技术监测飞机主结构件的腐蚀损伤从而为确定飞机日历寿命提供科学依据。首先介绍了航空铝合金材料在加速腐蚀过程中的AE信号特征,说明如何利用AE技术来监测腐蚀损伤,进而讨论如何对材料的安全性能和剩余寿命进行评估。试验表明, AE能比超声和涡流等常规无损检测方法更早地发现铝合金材料的腐蚀损伤。通过研究加速腐蚀过程中腐蚀损伤程度及腐蚀AE信号随加速腐蚀时间的变化规律,获得了腐蚀损伤与AE参数之间的变化关系。说明AE技术可用于探测早期腐蚀、研究腐蚀发展规律及监测和评估腐蚀损伤方面。     

Lamb波多特征参数的复合材料损伤程度 评估方法*

航空航天飞行器、风电等工程机械结构的安全性保障至关重要,复合材料等新材料的大量应用,进一步提升了对结构健康监测的难度和要求。裂纹、脱层等复合材料结构典型损伤形成机理复杂、易扩展,损伤程度累积严重时会造成结构的突然失效。面向复合材料结构的损伤监测与诊断,现有的方法大多很难实现对结构损伤程度的跟踪评估,进而无法对结构的安全性评价提供依据。采用Lamb波监测理论,基于其传播距离远、对小损伤敏感等特点,通过研究分析典型损伤对Lamb波结构响应信号传播的多个特征作用过程和机理,采用多尺度分析,提取结构损伤时频域多特征参数;借助于神经网络的非线性映射能力,构建多特征复合材料结构损伤程度评估模型,实现对不同程度下典型结构损伤的评估。在环氧玻璃纤维复合材料板结构上的实验验证结果表明：提取的Lamb波时频域多特征参数,对不同程度典型损伤有一定的敏感性,所构建的损伤程度评估系统可以较为有效的实现损伤的程度估计。     

基于近场辐射声压信号的索力识别方法

为准确、快速获取拉索结构索力,该文提出利用结构近场固定位置辐射声压信号对拉索进行索力测试的方法。基于动力学理论推导出结构振动加速度响应与其近场辐射声压响应的线性比例关系,并根据希尔伯特-黄变换推导了声压响应信号与结构频率的关系。对单根拉索依次施加3种不同工况的初始张拉力,并对结构中心表面处施加一瞬时脉冲力,使拉索受迫振动发声,通过对结构近场范围内拉索振动辐射声压进行测量,进而获得不同工况下不同位置声压响应信号,并探讨了在有高斯噪声干扰情况下通过希尔伯特-黄变换方法获取拉索固有频率的可靠性。数值模拟分析验证了该方法能较为准确地得到拉索固有频率并利用索力计算实用公式有效地计算出索力值,为实际工程中拉索索力测试提供了一种新的简单有效的方法。     

正交异性钢桥面板声发射波三维谱元法模拟及损伤定位*

针对大跨度桥梁正交异性钢桥面板的疲劳损伤评估与结构健康监测需求,开展基于声发射波场谱元法模拟的大型复杂板类结构损伤定位研究。采用Legendre高阶插值三维时域谱元法模拟声发射波在正交异性钢桥面板中的传播过程,验证了其内部显著的反射、衍射和频散现象,并代替人工预断铅实测试验获得大量声发射数据。然后,利用赤池信息准则判定声发射波到达各传感器的时间,通过高斯过程回归建立到达时差与声发射源位置的关系模型,用于未知损伤的定位监测。数值模型实验结果表明,赤池信息准则和高斯过程回归改进的时差图法在正交异性钢桥面板中的平均定位误差为37.3 mm(25 dB信噪比工况),平板的定位精度高于U肋。谱元法模拟有望代替繁琐的预断铅实测试验,提升声发射时差图系列损伤定位方法的实用性。     

光学薄膜抗激光损伤研究发展

随着大能量/高功率激光器的发展需求日益突出,光学薄膜的激光损伤阈值逐步成为激光器发展的瓶颈,受到国内外高能激光器研究领域的广泛关注。阐述了光学薄膜激光的损伤机理、激光损伤阈值测试平台及方法,结合自身研究成果,综述性分析了国内外光学薄膜抗激光损伤技术与手段研究的发展情况,主要包括离子束预处理、离子束与退火后处理、虚设保护层等;重点提出了磁过滤结合激光沉积的复合沉积技术,并建议加速推动无缺陷沉积的原子层沉积技术,为大幅提高光学薄膜抗激光损伤能力、满足当前需求提供了理论基础。     

基于声发射的光学元件损伤监测方法研究

光学元件损伤是限制激光通量水平提高的重要因素之一。为快速、准确地检测光学元件损伤是否产生,支撑光学元件循环修复策略的使用,研究并提出了基于声发射技术的光学元件损伤检测方法,通过研究光学元件损伤产生的声发射信号特征,判断光学元件是否发生损伤,使用一种基于二次相关和相关峰精确插值（FICP）的时延估计算法,通过仿真验证了该算法的可行性,结合时差定位原理建立了损伤位置求解方法,并通过实验进行了验证。研究结果表明:该方法能从监测信号中快速地获得损伤的位置估计,其平均定位误差为8.61 mm,计算时间为0.143 s/次,对大口径光学元件的损伤在线监测具有应用潜力。     

高强度钢手工焊接后过程的声发射实时监测研究

本针对实际工艺中使用的高强度钢，重点对手工焊接的冷却过程利用声发射技术进行实时监测。本次试验是和先前在不同型号的钢板在手工焊接过程中所产生的声发射信号进行比较的基础上进行的，主要目的是寻找高强度钢在手工焊接的冷却中所产生的活性裂纹在冷却阶段的声信号特征。     

Applications of optical fibre Bragg gratings sensing technology-based smart stay cables

Stay cable is one of the most critical structural components of a bridge. However, it readily suffers from fatigue damage, corrosion damage, and their coupled effects. Thus, health monitoring of stay cables is important for ensuring the integrity and safety of a bridge. A smart stay cable assembled with optical fibre Bragg grating (OFBG) strain and temperature sensors was proposed in this study. To protect the OFBG sensors against breakage in application, the OFBG sensors were first incorporated into a glass-fibre-reinforced polymer (GFRP) bar (GFRP-OFBG bar) when the bar was fabricated. To fabricate cables assembled with OFBG sensors, several GFRP-OFBG bars were inserted into the hollows of steel wires and fixed with the steel wires together at the anchorages of the cable. Therefore, the GFRP-OFBG bars can consistently deform with the steel wires in a cable and the smart stay cable can sense its own strain and temperature through OFBG sensors. The fabrication procedure of the smart stay cable was developed and the self-sensing property of the smart stay cable was calibrated. Finally, the application of the smart stay cables on the Tianjing Yonghe Bridge was demonstrated. The fatigue accumulative damage of the smart stay cables was evaluated based on field monitoring strain.     

Modern acoustic emission technique and its application in aviation industry

This paper proposes the concept of modern acoustic emission (MAE) technique and describes its application in aviation industry. Modern AE is characterized by the combination of AE parameter and waveform analysis based on the understanding of AE source mechanism, the property of sound wave propagation and the interaction between sound wave and the medium in which the sound wave is propagating. Another feature of MAE is characterized by the application of so-called fully digital AE apparatus with low noise, high speed of data transmission and accurate AE source locating capability. MAE is merely an imagination without the realization of the advanced fully digital AE instrument. The application of MAE in monitoring the conditions of aircraft structures during a fatigue test was taken as an example for showing the important role played by AE. Roles of AE in the evaluation of (environment-related) corrosion damage of aircraft were also presented.     

铝与钢摩擦时声发射参数与正压强之间的关系

材料不同,声发射信号的特点不同。为了提高声发射技术在监测摩擦过程中的应用水平,研究不同材料的声发射信号的特点是必要的。本文研究了铝与45钢摩擦时产生的声发射信号的特点,实验研究结果表明:在铝与45钢的摩擦过程中,相对运动速度对于正压力与声发射信号之间的关系有较大的影响;低速下,正压力与声发射信号之间无规律可言;高速下,随着正压力的增加,声发射信号各参数是增加的。     

Effects of operating conditions on the Acoustic Emissions (AE) from planetary gearboxes

In the last decade, the use of acoustic emissions has received growing acceptance for its application in machine condition monitoring. This is because it offers good possibilities to diagnose failures at early stages and low rotational speeds. The use of acoustic emissions for condition monitoring of gears, however, is still an active field of research, because several questions remain unanswered. One of these questions is the effect of operating conditions on the AE generated during gear meshing. In this work, the results of experiments carried out on a non-faulty planetary gearbox test bench are presented. A planetary gearbox is considered, because of its usual application on machines subjected to variable operating conditions. The effects of lubricant temperature, load and rotational speed are investigated. The conclusions obtained from the experiments are used for the analysis of the AE measured on the planetary gearbox of a bucket wheel excavator.     

A stereo-fiberscope with a magnetic interlens bridge for laryngeal observation.

A stereoscopic method of observation of the larynx and the pharynx during speech utterances has been devised, making use of fiber-optic cables and a magnetic bridge. The cables are inserted via the subject's nostrils. The bridge makes the two objective lenses at the tips of the cables abut within the pharynx near the uvula, and the two images viewed through the separate lenses at the prescribed mutual distance are recorded on each frame of a 16-mm film side by side for computer processing of the three-dimensional data.     

Seeded fault detection on helical gears with acoustic emission

Acoustic emission (AE) is one of many technologies for health monitoring and diagnosis of rotating machines such as gearboxes. Although significant research has been undertaken in understanding the potential of AE in monitoring gearboxes this has been solely applied to spur gears. This report presents an experimental investigation that assesses the effectiveness of AE in identifying seeded defects on helical gears; the first known attempt. Additionally vibration analysis has performed to study the effect of seeded defect on the vibration signature of the meshing gears.     

Toward a probabilistic acoustic emission source location algorithm: A Bayesian approach

Acoustic emissions (AE) are stress waves initiated by sudden strain releases within a solid body. These can be caused by internal mechanisms such as crack opening or propagation, crushing, or rubbing of crack surfaces. One application for the AE technique in the field of Structural Engineering is Structural Health Monitoring (SHM). With piezo-electric sensors mounted to the surface of the structure, stress waves can be detected, recorded, and stored for later analysis. An important step in quantitative AE analysis is the estimation of the stress wave source locations. Commonly, source location results are presented in a rather deterministic manner as spatial and temporal points, excluding information about uncertainties and errors. Due to variability in the material properties and uncertainty in the mathematical model, measures of uncertainty are needed beyond best-fit point solutions for source locations. This paper introduces a novel holistic framework for the development of a probabilistic source location algorithm. Bayesian analysis methods with Markov Chain Monte Carlo (MCMC) simulation are employed where all source location parameters are described with posterior probability density functions (PDFs). The proposed methodology is applied to an example employing data collected from a realistic section of a reinforced concrete bridge column. The selected approach is general and has the advantage that it can be extended and refined efficiently. Results are discussed and future steps to improve the algorithm are suggested.     

Modeling and analysis of the in-plane vibration of a complex cable-stayed bridge

The in-plane vibration of a complex cable-stayed bridge that consists of a simply-supported four-cable-stayed deck beam and two rigid towers is studied. The nonlinear and linear partial differential equations that govern transverse and longitudinal vibrations of the cables and transverse vibrations of segments of the deck beam, respectively, are derived, along with their boundary and matching conditions. The undamped natural frequencies and mode shapes of the linearized model of the cable-stayed bridge are determined, and orthogonality relations of the mode shapes are established. Numerical analysis of the natural frequencies and mode shapes of the cable-stayed bridge is conducted for various symmetrical and non-symmetrical bridge cases with regards to the sizes of the components of the bridge and the initial sags of the cables. The results show that there are very close natural frequencies when the bridge model is symmetrical and/or partially symmetrical, and the mode shapes tend to be more localized when the bridge model is less symmetrical. The relationships between the natural frequencies and mode shapes of the cable-stayed bridge and those of a single fixed–fixed cable and the single simply-supported deck beam are analyzed. The results, which are validated by commercial finite element software, demonstrate some complex classical resonance behavior of the cable-stayed bridge.     

DYNAMIC ANALYSIS OF LARGE-DIAMETER SAGGED CABLES TAKING INTO ACCOUNT FLEXURAL RIGIDITY

For the purpose of developing a vibration-based tension force evaluation procedure for bridge cables using measured multimode frequencies, an investigation on accurate finite element modelling of large-diameter sagged cables taking into account flexural rigidity and sag extensibility is carried out in this paper. A three-node curved isoparametric finite element is formulated for dynamic analysis of bridge stay cables by regarding the cable as a combination of an “ideal cable element” and a fictitious curved beam element in the variational sense. With the developed finite element formulation, parametric studies are conducted to evaluate the relationship between the modal properties and cable parameters lying in a wide range covering most of the cables in existing cable-supported bridges, and the effect of cable bending stiffness and sag on the natural frequencies. A case study is eventually provided to compare the measured natural frequencies of main cables of the Tsing Ma Bridge and the computed frequencies with and without considering cable bending stiffness. The results show that ignoring bending stiffness gives rise to unacceptable errors in predicting higher order natural frequencies of the cables, and the proposed finite element formulation provides an accurate baseline model for cable tension identification from measured multimode frequencies.