超声导波相移追踪的回波辨识方法

超声导波的多模式和频散特性使得其回波分析与定位异常复杂,在导波传播的模型解析的基础上,提出了一种基于频率相位追踪的回波辨识方法。首先,选取指定模式的直接散射信号的频域相位作为参考相位,将被分析信号各个波包的频域相位用参考相位进行归一化处理,得到各个波包相对参考波包传播距离的归一化阶次;然后,结合回波信号的传播路径分析,达到对各个波包定位辨识的目的。数值仿真和实验也验证了该方法的可行性和有效性。     

超声导波检测技术的发展、应用与挑战

回顾了近三十年的超声导波技术发展及应用,阐述了导波的频散现象及其求解方法,深入分析了导波激励的力学加载原理和模态选择原则。论述了导波的传感激励方法与装置,并比较了各种激励接收方法的特点与应用场合。对超声导波在板类、管类和复合材料中的应用进行了评述,并从提高缺陷检测能力的角度,介绍了时间反转法和相控阵法在超声导波技术中的应用。最后总结了当前导波技术面临的机遇与挑战。     

基于时间反转的管道导波缺陷参数辨识方法

针对导波检测中的缺陷辨识问题,通过对不同缺陷的时间反转导波检测缺陷反射率随时间反转信号截取窗宽变化关系的研究,确定缺陷散射波场中各导波模态的能量分布规律,并据此提出一种基于时间反转的管道导波检测缺陷辨识方法。在数值模拟的基础上,选择适当的特征参数用于表征反射率—窗宽关系曲线,建立与缺陷特征相对应的关系曲线样本库,并通过聚类分析方法在库中寻找到与待检测缺陷特征最为接近的样本。结果表明,该方法可达到评判缺陷特征的目的,为最终实现缺陷反演奠定基础。     

管道缺陷的超声导波检测研究

针对管道缺陷与超声导波交互的特点,为解决在管道超声导波检测中的缺陷定位困难、轴向尺寸无法量化等繁琐和耗时严重等问题,设计了自发自收和一发一收两种管道缺陷的超声导波检测平台,对特定环形缺陷进行管道超声导波检测进行了研究,探究了环形缺陷的轴向长度和径向深度对超声导波检测的影响。结果表明:采用自设计的超声导波检测平台可实现管道缺陷的定位检测及轴向尺寸定量检测,缺陷的轴向长度主要影响缺陷回波的形态,缺陷的径向深度主要影响回波的能量。     

超声导波在缺陷弯管上的数值模拟研究

采用数值模拟的方法对弯管结构进行了分析.通过对4种不同弯曲半径弯管的特性进行分析,最终选定70 kHz作为导波的激励频率;通过对不同周期信号在弯管中的特征进行分析,选定激励信号的周期为5.通过对不同弯曲角度弯管进行分析,L(0,2)模态导波经过弯管时会发生模态转换,转换为F(1,2)模态;在弯管内侧与外侧进行检测发现存...     

基于群速度校准的超声导波技术及在复合材料缺陷检测中的应用

由于在复合材料板中传播的超声导波具有偏斜效应,使得理论群速度与试验测得的群速度不一致,因此需要对群速度幅值和传播方向进行校准。数值计算复合材料板中超声导波频散方程得到S0模态各个方向的理论相速度频散曲线。运用群速度校准法则对S0模态群速度幅度和传播方向进行修正。校准后的理论群速度与试验测得的群速度较为吻合。试验中采用频率200 kHz的S0模态对碳纤维复合材料板中的模拟缺陷进行检测。结果显示采用校准后群速度和试验测得的群速度可准确定位缺陷,且具有很好的一致性。因此,采用群速度校准法则可有效提高各向异性复合材料结构中超声导波的缺陷定位和识别能力。     

超声导波在管中传播的理论分析与试验研究

采用分布式PZT传感器在管中激励和接收超声导波。根据在管状波导中传播的超声波具有频散现象及多模态特征,选择具有单一频率的特定信号激励超声波,使其频散最小;同时采用分布式传感器抑制不同模态的波型。其试验结果与理论预测相吻合。     

超声导波在高压蒸汽管道缺陷检测中的应用

为了提高高压蒸汽管道超声检测的效率,研究了超声导波在高压蒸汽管道缺陷检测中的应用。通过试验对比,设计并实践了高频导波换能器,确定了高压蒸汽管道高频导波检测灵敏度,为实现高压蒸汽管道快速检测提供了一种方法。     

半解析有限元法求解钢轨中超声导波频散曲线

钢轨中超声导波的频散曲线是采用超声导波技术进行无缝线路钢轨完整性检测的重要参考依据.通过传统的有限元模态分析方法,无法求解得到钢轨中超声导波完整的频散曲线,针对这一问题,采用了半解析有限元方法.求解时假设导波在钢轨中以简谐振动的方式传播,仅对钢轨的横截面采用三角形单元进行有限元网格划分,经理论推导得到超声导波在钢轨中传播的波动方程,通过求解特征方程,得到波数与频率的值,进而获取频率与相速度、群速度的关系,绘制出频散曲线.通过求解得到的特征向量还可以分析各导波模态的振动特性.实验结果表明,半解析有限元法求解得到的我国无缝线路CHN60钢轨的频散曲线与实际线路测试结果有很好的一致性.     

空心圆管中导波频散特性与检测频率选择

频散是长距离管道导波检测中影响检测频率选择的重要因素。通过分析空心圆管中纵向模态导波的频散特性,探讨导波检测常用模态L(0, 2)和L(0, 1)的频率选择问题。根据导波频散现象,建立缺陷回波分辨距离与激励信号参数间的量化关系,分析检测频率优化选择问题。以导波频散引起的信号分辨距离为依据,计算不同几何尺寸管道中L(0, 2)和L(0, 1)导波非频散段的限制频率。结果表明,限定或最小化缺陷回波分辨距离,可获得最佳的导波激励信号周期及检测频率或频段。随着管道几何尺寸变化,得到L(0, 2)和L(0, 1)导波频散特性变化的几个重要结论。当管道内径壁厚比不小于4时,L(0, 2)导波低限频率与管道直径的乘积约为4.0 MHz•mm,高限频率与壁厚的乘积约为1.06 MHz•mm。对于小口径管中的L(0, 1)导波,其高限频率与直径的乘积约为0.81 MHz•mm。这些简单的函数关系为管道检测时快速确定非频散段频率范围提供参考。     

Optimization of excitation frequency and guided wave mode in acoustic wavenumber spectroscopy for shallow wall-thinning defect detection

In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, acoustic wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.     

导波雷达液位计在方家山核电站的应用

液位测量是核电站自动控制系统中重要组成部分。导波雷达液位计基于电磁波的时域反射(TDR)原理,具有受环境影响小、测量精度高等诸多优点。方家山项目是导波雷达液位计第一次在二代改进型核电站核岛厂房进行应用。通过研究,报告了导波雷达液位计在方家山项目中的选型与应用,阐述了导波雷达液位计的工作原理、性能特点、使用注意问题以及在ASG系统液位测量方面的应用。     

Damage identification in composite materials using ultrasonic based Lamb wave method

The paper presents an ultrasonic based Lamb waves propagation method for identifying and measuring the damage location in a material for SHM. The present work determines the experimental and analytical effects of various parameters on the sensitivity of damage detection and a methodology is proposed for estimating and measuring the location of damage in the test specimens. An experimental setup is used for generating A_o Lamb waves by calibrating ultrasonic pulse generation for optimal value of the parameters. The experiment is performed on two carbon fiber reinforced plastic bars in both undamaged and damaged state, where the two damaged states are (1) having a cut partway through the bar, perpendicular to the long axis of the bar and (2) having a circular hole. The Lamb wave propagation parameters are calibrated using the ultrasonic pulse generator test setup and the method was compared with direct measured values of ultrasonic instrument.     

On a defect identification method based on monitoring the structure and peculiarities of surface wave fields

A special technique is proposed for processing detected signals. The technique uses an adjustable orthonormal basis and makes it possible to effectively identify defects by monitoring the structure and peculiarities of surface wave fields.     

Time reversal method for guided wave inspection in pipes

The application of the time reversal method in pipe-like structures based on finite element method (FEM) is investigated. A steel pipe model measuring 70 mm x 3.5 mm is used to analyze the reflection coefficient of the L(0,2) mode with the time reversal process. Simulation results show that the time reversal array method is beneficial to the improvement of the signalto-noise ratio of a guided wave inspection system. As the intercepting window is widened, more energy is included in re-emitted signals, which leads to a large reflection coefficient of the L(0,2) mode. In parallel, a circumferential locating method based on the time reversal method is described. The time reversal process used for guided wave inspection leads to the temporal and spatial focusing. When the time reversal signals are re-emitted, the angular profile obtained at the axial location of the defect can be used to determine the circumferential location of the defect. Except for a pipe with one defect, the circumferential locating method has been verified on another pipe model with two defects. Meanwhile, the elements number of the time reversal array has been discussed for enhancing the discrimination of the defect circumferential location.     

有级动态补偿及谐波滤波系统在北钢的应用

本系统采用有级功率因数动态补偿及谐波滤波装置，其主要特点是在国内首次采用了自动投切控制器，很好地解决了无功倒送问题，消除了谐波危害，使系统有功容量增加，使一总降功率因数罚款降至0，为公司创造了十分可观的经济效益。     

海洋平台吊机波浪补偿系统研究

为消除在两船吊放货物的过程中波浪对作业船舶的影响,以主动式波浪补偿反馈控制系统作为研究对象,分析了补偿原理和位移测量原理,推导了传递函数.通过仿真结果表明,伪微分控制完全满足波浪补偿控制系统的要求.     

A reference standard of defect compensation for leather transactions

Defects exist on natural leather surfaces and they usually cannot be eliminated during processing. No international criterion specifies the compensatory counting for calf leather surface defects. So complicated negotiation causes additional cost and argument between suppliers and purchasers. The objective of this article is to establish a compensatory standard of leather defects for finished leather transactions. We start by collecting 170 samples of defective leather and classify the leather defects into seven types. By using digital image processing techniques, we can identify the defects and group nearby defects into a larger scrap area. The area of leather falling into disuse can be calculated. The compensatory standard corresponding to each type of leather defect is then defined. The established compensatory standard for finished leather transactions is evaluated for simulated practical leather transaction. Simulation results showed that the proposed approach is useful and beneficial for practical leather transactions.     

Effect of dispersion compensation on FBG sensing systems’ performance

This paper introduces the use of a fiber-optic communication system for interrogation and transmission of data from fiber Bragg grating (FBG) sensors. Signal coding and dispersion compensation methods, usually used in communication systems, are used to improve the sensing system’s performance. Moreover, communication system parameters are used to assess the improvement in the FBG sensing performance. This is done through the determination of the profiles of Q-factor and eye diagrams. The sensors considered in the simulations are strain sensors subjected to a wide range of strains. The results obtained show a clear improvement of the sensing system with symmetrical compensation. The proposed method is suitable for applications where fiber-optic links are available near both the sensing location and information-collection and-processing unit, even if these two are hundreds of kilometers apart. A good example of where such a system can be applied is the oil industry. The rigs are usually very far from headquarters, but both might be close to a fiber node. Published in Russian in Pribory i Tekhnika Eksperimenta, 2006, No. 3, pp. 115–118. This text was submitted by the authors in English.     

Chirp信号及其在超声导波检测中的应用

传统的超声导波激励信号为窗函数调制的正弦波信号,其突出优点是频带窄,从而可以最大限度地抑制频散.但是此种信号在扫频测试和多模态、多频段检测中将需要逐次变换中心频率,且为达到较高的信噪比,每次测量采集时均需几十甚至上百次的平均,耗时耗能.提出了线性chirp和Gaussian-chirp2种信号作为超声导波激励信号.线性chirp信号频带宽,通过对其检测接收信号进行后处理,可得到等同于传统的窗函数调制的正弦波信号激励时的检测接收信号,且被调制的正弦波频率可以为线性chirp信号频带范围内任意频率,特别适用于扫频测试和多模态、多频段检测.Gaussian-chirp信号幅频特性与高斯窗调制的正弦波信号完全相同,但单次测量即可达到常规激励信号上百次平均采集的信噪比,测量过程省时节能.实验采用2片置于铝板表面的压电晶片激励产生兰姆波,分别验证了2种chirp信号激励超声导波及其信号后处理方法的有效性.