Lamb波波包混叠分离方法的结构损伤定位

基于Lamb波信号延时累加的结构损伤成像方法具有结果准确、计算量小等优点,然而在复杂的航空结构中,Lamb波非常容易产生反射,由于Lamb波频散效应,导致多个波包混叠,从而影响定位的准确性。针对这些问题,提出了一种频散波包的分离补偿方法。首先,理论分析并得到了带有频散效应的波包混叠和函数模型,提出了和函数的隐变量参数求解方法;其次,采用数值仿真验证了算法对于波包分离和重构的有效性;最后,通过飞机复合材料加筋壁板的损伤定位实验验证了波包分离法在复杂边界条件下去除反射波伪损伤投影和频散补偿的能力,提升了损伤定位的准确度和成像的分辨率。     

基于压电晶片阵列的管中导波时反检测方法研究

为提高超声导波技术对管中小缺陷的检测能力,提出一种采用窄带高压脉冲激发安装在管道外表面的压电晶片阵列实现管中导波时间反转检测的新方法。该方法采用窄带脉冲同时激励沿管道表面轴对称安装的压电晶片阵列,从各压电晶片接收到的反射回波中提取含L(n, 2)模态的缺陷信息进行时间反转,并用获得的时反波再次激励阵列中对应压电晶片,整个阵列将同时接收到较单一L(n, 2)模态信号。试验结果表明,该方法能较好地抑制导波的频散、多模态特性,提高缺陷回波信噪比,增加对小缺陷的检测能力。同时,时反前、后所检测到的管道端面和缺陷反射回波的导波模态几乎相同,可采用特定频率的L(0, 2)模态群速度作为时反后缺陷波包的传播速度;且时反后的幅值最大的缺陷波包能重构窄带初始激励信号幅值最大的波包,可有效增加缺陷波包的辨识能力。     

基于PCA-WHMM的超声漏表面波频域合成孔径成像研究

超声漏表面波可用于检测表面或近表面缺陷,其非接触检测的优点易于实现自动化检测.但由于波型转换与传播衰减,漏表面波的回波幅值较小,不利于缺陷检测和成像.仿真分析了漏表面波的传播特性及缺陷回波特征,应用主成分分析分离回波信号中的干扰波,再利用小波域隐马尔可夫模型算法分离整段信号的系统噪声,联合两种方法提取漏表面波信号中的缺陷信息,最后通过频域合成孔径算法对漏表面波扫查数据进行了高分辨率图像重建.结果 表明,相比于传统B扫成像,基于PCA-WHIMM的超声漏表面波F-SAFT方法在回波信号平均信噪比上提高了10.05 dB,平均成像误差降低了26.3％,为金属表面及近表面缺陷检测提供了一种有效方法.     

厚截面CFRP孔隙超声脉冲反射检测方法

目前对碳纤维复合材料(carbon fiber reinforced plastic,简称CFRP)孔隙缺陷超声检测识别的研究主要以薄板型CFRP为对象,针对厚截面CFRP孔隙缺陷检测的需要,提出了基于超声脉冲反射背散射信号处理的孔隙缺陷识别方法。背散射信号特征分析结果表明,背散射信号由材料近表面共振结构噪声、信号指数型衰减成分、孔隙的反射和散射信号以及随机噪声组成。为得到孔隙的反射和散射信号,首先,利用提升小波变换良好的去噪能力除去背散射信号中的随机噪声;其次,设计低通滤波和自适应滤波分别除去信号中的共振结构噪声和衰减成分。对实验信号的处理结果表明,上述处理方法可以有效去除相应信号成分。在此基础上进一步提出了背散射信号幅值C扫描成像方法,将该成像方法应用于厚截面CFRP孔隙缺陷识别,可以有效识别试块中的含孔隙区域。     

混凝土超声检测技术的研究与实现

针对混凝土结构无损检测的需要,提出了一种超声激励脉冲产生的方法。由于超声波信号在混凝土中衰减快,为了提高检测系统的探测能力,增强回波信号,提高超声激励脉冲幅值,采用一种高频继电器实现了电磁脉冲源,并通过水和混凝土两种不同介质的无损检测试验验证其可用性。为了实现混凝土结构的高效精细检测,采用波包分解技术对检测数据处理分析,通过合成孔径技术成像,研制了系统样机。不同混凝土结构试块的检测成像试验表明,系统探测深度可达1m,可以较准确成像显示混凝土结构内部嵌入物的位置。     

基于空间相关性分数域的探地雷达回波信号增强方法研究

针对探地雷达回波中去除直达波和噪声干扰而削弱目标信号的问题,提出了一种基于空间相关性分数域的探地雷达回波信号增强方法,利用目标信号在临近测点之间的关联性,采用KL变换获得相关性特征值,根据相关性大的特征值重构目标图像,再将处理后的图像变换到分数域,通过分数阶傅里叶变换抑制直达波与噪声,最终得到目标回波增强的探地雷达图像。实验结果验证了所提方法的有效性。     

管道导波检测中的位移圆周分布调制方法

在研究管道导波检测中的位移圆周分布调制聚焦技术时,将存在的缺陷看作一个新的导波源,提出通过截取阵列中各传感器获得的检测信号中的缺陷反射回波及转换模态波包信息,分析该波源造成的波场在检测位置的位移圆周分布,从而得到将检测能量重新聚焦于缺陷所在圆周任一位置所需要的各激励信号幅值系数和时间延迟参数.有限元分析及试验表明,应用该方法,不仅可以减少运用位移圆周分布调制聚焦技术检测时的计算量,还可以灵活地应对检测过程中管道参数、传感器阵列及检测频率的变化,有利于该方法的推广和应用.     

一种基于宽带激励的虚拟时间反转方法

针对主动Lamb波监测中常见的低信噪比问题和传统时间反转方法降低监测信号空间分辨率的不足,提出一种采用宽带激励求取损伤散射路径传递函数的虚拟时间反转方法并应用于复杂结构的多损伤成像中.理论研究并经实验验证表明该方法不但能够有效实现Lamb波多损伤散射信号在相应损伤处聚焦增强,抑制了边界反射信号和噪声,提高了信噪比,而且与传统时间反转方法相比,提高了损伤聚焦波包的空间分辨率,增强了对于多个损伤的监测能力.最后的成像结果显示虚拟时间反转方法能够改善复杂板结构中两个近邻损伤的成像质量.     

奥氏体不锈钢小径管焊缝缺陷多模式超声复合全聚焦成像研究

奥氏体不锈钢广泛应用于重大装备的关键部件中,而焊缝是整个装备的薄弱部位。在考虑超声波的多路径和易发生波型转换的特性情况下,进行奥氏体不锈钢小径管焊缝多模式超声相控阵检测方法研究。通过数值仿真,对比分析4种不同直达波检测模式和8种不同底面一次反射波检测模式对小径管焊缝中典型缺陷的检出能力。基于优选出的一种直达波检测模式和一种底面一次反射波检测模式,发展了一种多模式复合全聚焦成像方法。在此基础上,进行奥氏体不锈钢小径管焊缝缺陷检测试验。结果表明,多模式复合全聚焦成像方法可以很好实现小径管中多种缺陷检测,与单一模式全聚焦成像相比,多模式复合全聚焦成像方法不仅可以提高成像的信噪比,且可以大大减小伪像的产生。项目研究工作为奥氏体不锈钢小径管焊缝检测提供了可行的技术方案。     

磁致伸缩液位传感器双检测线圈温度补偿与噪声抑制

为了校正扭转波速度、补偿温度、抑制脉冲电流噪声以及提高输出信号的信噪比,设计了一种双检测线圈结构应用于磁致伸缩液位传感器。推导了扭转波速度与温度的数学模型,得到了扭转波速度随温度的变化趋势;分析了单检测线圈结构存在温度影响测量结果与脉冲电流幅值大等问题。通过理论分析,最终的实验结果表明,与单检测线圈结构相比,双检测线圈结构能够快速计算扭转波速度,补偿温度对测量结果的影响,将脉冲电流噪声信号幅值降低至原来的1/27,测量误差由原来的0.18 mm降低至0.02 mm。双检测线圈结构为磁致伸缩液位传感器优化设计提供了理论指导。     

A novel method for construction of a point coordinate measuring instrument using ultrasonic waves

Point coordinate measuring instruments are applied in the geometric measurement of parts. In this instrument, ultrasonic waves are used for measuring distances using a method similar to the time-of-flight method. For improvement of the measurement resolution, an accurate value of the speed of sound is enhanced by using a phase-locked loop (PLL) circuit to generate a reference signal; this signal is dependent on the variation of the speed of sound. To measure the coordinate of a point, an ultrasonic signal is produced with a wireless transmitter on the surface of a part. The waves are received by a set of three ultrasonic receivers located at the corner of the room. By counting the pulses of that signal within a transmit-to-receive period, the distance between each pair of transducers can be determined. By increasing the coefficient of the frequency divider in the PLL, the output frequency increases and the resolution improves.     

Simultaneous data acquisition for improved performance in transit time difference ultrasonic flowmeters

Clamp-on ultrasonic transit time difference meters have many benefits for use in industry such as their non-intrusive nature, portability and ability to work with corrosive fluids. However, all transit time difference meters suffer from a sensitivity to changes in the speed of sound or flow profile in the fluid during the ultrasonic measurement. Trigger time jitter in the data acquisition electronics can also contribute to fluctuations in the output of the meter, since the upstream and downstream signals jitter back and forth in time independently of one another. Both of these mechanisms are a product of the method of data acquisition used, where one transducer is used as a generator and the signal is received on the other, then the other transducer is driven to send ultrasound the other way. A new method of performing the measurement is proposed in which the transducers are both driven simultaneously and the signal is received on both transducers at the same time, with the ultrasonic waves having passed through the same volume of fluid with the same flow profile. It is shown that fluctuations in the output of a flowmeter at constant flow rate can be reduced by over an order of magnitude compared to acquisition modes where the generation pulse and the start of data acquisition are not actively synchronised.     

A pulse ultrasonic gauge for measuring velocities of surface acoustic waves

A pulse broadband gauge designed for measurements of the velocities of surface acoustic waves is described. The gauge’s output signal is formed during mechanical translation of focused ultrasonic transducers relative to a specimen under study placed in an immersion liquid. A design of the device with line-focused lensless ultrasonic transducers for the frequency range 2–25 MHz is considered. The results of measurements of test samples are presented, and the algorithms for processing the output spatial-temporal signals for determining the frequency dependences of phase velocities of acoustic waves are described. Using a carbon steel sample as an example, it is shown that the random error component in acoustic-wave velocity measurements can be estimated as ±(2–8) and ±(1–3) m/s for longitudinal and lateral scanning modes, respectively.     

超声振动切削刀具设计

介绍频率40kHz,振幅在(10～35)μm范围可调的振动刀具的设计过程,该刀具选用通用信号发生器作为超声波信号源,对其(0～5)V正弦电压信号进行放大,输出幅值(0～350)V用于激励压电换能器,将超声电振荡转换成机械振动,对振动信号再经变幅杆机械放大,使刀具振动幅值达到(10～25)μm以上进行切削。利用该刀具切削工件的精度和表面粗糙度达到精密切削的效果,并且已进行了天然金刚石精细切削不锈钢零件的实验,切削后的刀具磨损量明显降低。     

Separated two-phase flow regime parameter measurement by a high speed ultrasonic pulse-echo system

In this work, a high speed ultrasonic multitransducer pulse-echo system using a four transducer method was used for the dynamic characterization of gas-liquid two-phase separated flow regimes. The ultrasonic system consists of an ultrasonic pulse signal generator, multiplexer, 10 MHz (0.64 cm) ultrasonic transducers, and a data acquisition system. Four transducers are mounted on a horizontal 2.1 cm inner diameter circular pipe. The system uses a pulse-echo method sampled every 0.5 ms for a 1 s duration. A peak detection algorithm (the C-scan mode) is developed to extract the location of the gas-liquid interface after signal processing. Using the measured instantaneous location of the gas/liquid interface, two-phase flow interfacial parameters in separated flow regimes are determined such as liquid level and void fraction for stratified wavy and annular flow. The shape of the gas-liquid interface and, hence, the instantaneous and cross-sectional averaged void fraction is also determined. The results show that the high speed ultrasonic pulse-echo system provides accurate results for the determination of the liquid level within +/-1.5%, and the time averaged liquid level measurements performed in the present work agree within +/-10% with the theoretical models. The results also show that the time averaged void fraction measurements for a stratified smooth flow, stratified wavy flow, and annular flow qualitatively agree with the theoretical predictions.     

Ultrasonic pig for submarine oil pipeline corrosion inspection

This paper introduces the design and development of an ultrasonic pig used for submarine oil pipeline corrosion inspection. Structure and functions of the equipment, as well as ultrasonic data acquisition system and off-line signal processing method are presented. The pig adopts a train-like structure including driver cups, batteries, ultrasonic transducers and data acquisition unit, which can detect and locate the corrosion of inspected pipeline. The data acquisition system is designed based on a digital signal processor and field programmable gate arrays structure to sample, process and compress the ultrasonic data and then store them in a hard disk. The off-line signal analysis method adopts a non-phase delay peak extraction algorithm to accurately calculate the pipe wall thickness. According to the thickness of each detected point, an ultrasonic image is traced by false color image, and then the potential defects are recognized by using a 3 × 3 grids template and classified according to American Petroleum Institute Standard. Both experimental and engineering testing results show that the pig is of perfect performance and could inspect defects greater than 10 × 10 mm² successfully. The article is published in the original.     

Requirements for choosing the parameters of broadband transducers for testing objects with high damping of ultrasonic signals

The main concepts of the theory of optimal signal processing as applied to tasks of ultrasonic testing of articles with high integral damping of acoustic vibrations are considered. The conditions for ensuring the optimal transfer coefficient of the receiving section of an ultrasonic flaw detector’s electroacoustic channel are formulated. The requirements for the characteristics of broadband piezoelectric transducers aimed at the insurance of undistorted transmission of ultrasonic signals are formulated.     

Comparison of the features of composite and mosaic piezotransducers for the ultrasonic testing of products with a high attenuation level of ultrasonic signals

The problem of the creation of stacked (mosaic and composite) broadband transducers that simultaneously provide a broad band and a high electroacoustic transduction efficiency is analyzed. The mosaic technology is shown to be optimal for the practical implementation of ultrasonic broadband low-frequency electroacoustic transducers. Being functionally flexible, the mosaic technology allows the development of numerous variants of electroacoustic transducers for the solution of different ultrasonic testing problems and, first of all, for the undistorted transduction of signals.     

基于互相关理论的时差法超声波流量检测系统

介绍一种时差法超声波流量检测系统.系统以两超声探头同侧V型安装方式.采集顺、逆流回波信号经插值后作互相关处理.由互相关函数的峰值得出两回波信号的时差,间接测出流量.插值算法的引入,提高了回波信号的时间分辨率实现了微小时差的测量.该系统测量精度高、统计特性好,在液压系统的测量中取得了较理想的效果.     

Ultrasonic Measurement of Cylindrical Roller–Bearing Lubricant Film Distribution with Two Juxtaposed Transducers

This article describes the measurement of lubricant film thickness distribution in a roller bearing by using two juxtaposed transducers, which are excited by a new ultrasonic pulse receiver with a maximum pulse repetition rate (PRR) of 100 kHz. The experimental results demonstrate the feasibility and advantage of this method with high PRRs. The influence of rotating speed and radial load on the measured film thickness are shown to be consistent with the theoretical predictions. Skewing of the roller in the bearing is observed. A combined trigger signal is proposed to reduce the influence of the cyclical vibration of the rotor.