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.     

高压输电线路巡检机器人机械本体设计

对国内外已提出的高压架空输电线路巡检机器人机械本体机构的特点进行综述.在此基础上提出了新型的高压输电线路巡检机器人行走及越障机构,并对高压线路巡检机器人的发展趋势做了论述.     

吊臂式巡线机器人悬吊姿态自平衡机构的研究

文中针对目前应用较为广泛的吊臂式巡线机器人在跨越线缆附件时所出现的姿态失稳现象进行了研究,从机构学的角度研制了相应的俯仰失稳自平衡机构、侧倾失稳自平衡机构,并分析了其工作原理.通过理论分析和实验验证,证明了上述自平衡机构的实用性和可行性,为电力巡线机器人的应用推广奠定了坚实的基础.     

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 × 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 signal-to-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.     

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.     

输电线路巡检机器人的设计与控制系统研究

文章介绍了一种新型的履带式高压输电线路巡检机器人,阐述了基于递阶控制理论的分级控制系统结构设计和基于规则库模型的专家控制系统控制策略,仿真验证了机器人越障动作过程的正确性。     

超声导波虚拟相控聚焦方法研究

虚拟相控聚焦方法是一种新型的超声导波聚焦方法.针对现有时间反转聚焦方法与相控聚焦方法所需的多通道同步激励-接收设备研发难度大且成本高的现状,采用实验室现有单通道设备,利用多次激励-接收所采集的多组数据通过信号处理方法等效出多通道同步设备精确控制激励延迟所产生的相控聚焦效果.通过该方法与时间反转聚焦方法的聚焦效果有限元仿真与实验对比表明,该方法在现有实验设备基础之上,将缺陷回波幅度放大了2倍之多,获得了和时间反转聚焦方法相差不大的聚焦效果,同时,对检测区域进行成像,实现了缺陷的二维定位.     

在GSM网络中实现高压电力线路检测

根据目前高压输电线路分布广、作业环境恶劣的现状。本文介绍了基于GSM网络的无线检测系统,以现有成熟的GSM系统作为数据无线传输网络,在各分机与控制中心间采用AT指令集以短消息方式实现数据传输,实现了高压电力线路污秽情况的远程自动化实时监测,为线路状态检修提供了决策依据,大大提高了线路运行的安全性和输电线路技术管理水平。该系统具有精度高、稳定性强、抗干扰能力强、应用范围广、操作简便、免维护等优点,在实际检测中达到了良好的效果。     

管道导波时反聚焦检测系统的设计与实现

在分析管道中超声导波时反聚焦原理的基础上,设计并实现了一套适合激励压电换能器阵列,并对管道中超声导波能量在缺陷处进行时间-空间聚焦的时反聚焦检测系统.该系统实现的关键技术为:改进DDS( direct digital synthesis)结构,实现脉冲激励电路对时反特征信号进行合成发射;采用脉冲方式,实现小体积大输出功率的宽带线性功放电路;通过时反聚焦检测过程,实现管道中超声导波能量在缺陷处的时间-空间聚焦.采用该系统进行八通道时反聚焦检测实验,其结果表明,对于所用的含缺陷的管道而言,在特定的检测条件下,缺陷回波信号的幅值相对常规检测可提高246％,并且很好地抑制了导波的频散和多模态特性,提高了回波信号的信噪比.     

基于高频柱面超声导波的螺栓轴向应力测量

基于金属杆件中高频超声导波的传播特性,提出使用柱面导波高阶不同模态群速度比值的单探头螺栓轴向应力测量方法。使用数值方法求解考虑晶粒散射衰减的Pochhammer-Chree方程,得到了导波群速度衰减系数频散曲线,并分析了其在高频区的传播规律。结合非线性声学以及弹性力学理论,推出基于群速度比值的螺栓轴向应力测量方法。搭建超声应力测量平台,讨论了脉冲超声激励下的实测导波信号特点并提出使用经验小波算法对信号进行模态分解,有效获取了信号中特定模态的群速度。使用该方法以及传统的纵横波声时比法进行了螺栓轴向应力对比标定和测量实验,结果表明前者平均测量误差约为4%,其精度明显高于传统方法(平均测量误差6%)且具有更简便的测量流程。     

超声导波在管道检测中信息处理分析研究

本文主要介绍超声导波检测工作原理以及导波检测中信息处理分析的方法,包括缺陷区域定位和疑似缺陷识别、腐蚀程度判断等。通过站场的实际操作表明,运用软件分析处理可以标识管道外形明显特征（如焊缝）的位置,能够对架空管道、埋地管道和防腐层、套管内部管道的腐蚀程度做初步判断,对管道维修起到一定指导作用。     

功率超声在线数字化检测方法

检测功率超声设备的负载阻抗为分析和研究负载阻抗对超声设备的影响提供依据.本文提出一种方法,在大功率驱动超声设备正常工作的同时,通过数字信号采集及后续的FFT变换和频域特性分析,得到超声设备在工作状态下的负载阻抗信息.通过实验验证,此方法可以较好地检测超声设备的带负载情况.     

电磁超声全向导波换能器辐射控制方法研究

针对传统电磁超声全向导波换能器因导波内、外辐射致使检测回波信号复杂及信噪比低的问题,设计了一种新型电磁超声全向导波换能器(OUT-EMAT)结构,研究了换能器双线圈结构参数、双激励源控制方法,实现了导波辐射强度与方向控制。根据电磁超声全向换能器理论,建立波动位移叠加的数学模型,并对设计的OUT-EMAT性能进行仿真计算及实验。研究结果表明：与传统全向EMAT相比,OUT-EMAT内、外辐射导波强度之比由1∶1变为2∶9;其外辐射导波强度增加了100%,内辐射导波强度抑制了55.6%;增强了检测回波信噪比,降低了信号复杂度,提高了裂纹缺陷定位准确度;为有效识别裂纹缺陷提供了一种新方法,对实际工程应用具有指导意义。     

基于复合左／右手传输线的双频功分器

本文介绍了一种新型的基于复合左／右手（CRLH）传输线理论的双频功分器设计方法,该功分器工作于900MHz和1800MHz。用集总电感和电容元件构成的复合左／右手传输线在900MHz和1800MHz的相移分别是超前和滞后90°。完全可以替代传统功分器中的四分之一波长阻抗变换传输线,且具有占用面积小和可设计工作于任意两个频率的优点。在双频工作的现代无线通信系统中有很广阔的应用前景。     

Efficient registration for precision inspection of free-form surfaces

Precision inspection of free-form surface is difficult with current industry practices that rely on accurate fixtures. Alternatively, the measurements can be aligned to the part model using a geometry-based registration method, such as the iterative closest point (ICP) method, to achieve a fast and automatic inspection process. This paper discusses various techniques that accelerate the registration process and improve the efficiency of the ICP method. First, the data structures of approximated nearest nodes and topological neighbor facets are combined to speed up the closest point calculation. The closest point calculation is further improved with the cached facets across iteration steps. The registration efficiency can also be enhanced by incorporating signal-to-noise ratio into the transformation of correspondence sets to reduce or remove the noise of outliers. Last, an acceleration method based on linear or quadratic extrapolation is fine-tuned to provide the fast yet robust iteration process. These techniques have been implemented on a four-axis blade inspection machine where no accurate fixture is required. The tests of measurement simulations and inspection case studies indicated that the presented registration method is accurate and efficient. This work was supported primarily by the NSF Engineering Research Center for Reconfigurable Manufacturing Systems as part of the Engineering Research Centers Program of the National Science Foundation under NSF Award Number EEC 95-29125.     

Multibody dynamics study on galloping of power transmission line

When the power transmission line (PTL) passes through a region of high mountains and heavy snowfall, maintaining the stability of the PTL and avoiding sleet jump and galloping are necessary. In this study, PTL is modeled as the mass-spring-damper system by using the multi-body dynamics analysis program, RecurDyn. The lumped mass model is compared with the finite element model based on deflection. To analyze the dynamic behavior of the PTL under icing and wind conditions, we obtained a damping coefficient for a multibody model from the free vibration test and Rayleigh damping theory. The icing cross-section of the transmission line is assumed to have ellipse and triangle shapes. The aerodynamic coefficients for each cross-section are derived by using the commercial CFD program, ANSYS Fluent. The occurrence of galloping is simulated for each shape according to the attack angle. Results indicate that the dynamic behavior of the PTL and the galloping conditions such as the icing shape, thickness, and attack angle, can be analyzed. Furthermore, the effects of each factor are evaluated. In the elliptical icing section, the effect of icing thickness is high; whereas in the triangular icing section, the wind velocity highly affects galloping.     

基于分离谱技术的自适应带通滤波法在超声检测中的应用

超声检测是无损检测的一项重要内容,本文通过分析超声波检测反射回波的特点,结合线性带通滤波法和非线性分离谱滤波法的优缺点,应用了一种可利用于超声检测的有效的滤波方法——基于分离谱技术的自适应带通滤波法,并通过实际检测的钢板超声信号进行验证表明该方法具有良好的效果。文章内容涉及超声检测、自适应滤波和分离谱等。     

High temperature integrated ultrasonic shear and longitudinal wave probes

Integrated ultrasonic shear wave probes have been designed and developed using a mode conversion theory for nondestructive testing and characterization at elevated temperatures. The probes consisted of metallic substrates and high temperature piezoelectric thick (>40 microm) films through a paint-on method. Shear waves are generated due to mode conversion from longitudinal to shear waves because of reflection inside the substrate having a specific shape. A novel design scheme is proposed to reduce the machining time of substrates and thick film fabrication difficulty. A probe simultaneously generating and receiving both longitudinal and shear waves is also developed and demonstrated. In addition, a shear wave probe using a clad buffer rod consisting of an aluminum core and stainless steel cladding has been developed. All the probes were tested and successfully operated at 150 degrees C.     

磁致伸缩纵向导波管道检测数值建模与分析

检测模型是磁致伸缩纵向导波检测技术发展的基石。现有磁致伸缩纵向导波检测模型存在不包含接收过程和不包含静态磁场计算等不足,难以满足设计优化接收传感器、增强导波检测信号等方面的研究需求。因此,以磁致伸缩纵向导波管道检测为背景,分析激励和接收过程中的控制方程,在此基础上建立了包括激励过程、声场传播和接收过程的有限元模型。分别采用仿真和实验分析了接收线圈的提离效应,仿真和实验结果吻合较好,验证了该数值模型的正确性。     

基于无人机巡查的电站征地红线智能分析系统

以丰富水电站征地红线管控手段为目的,设计了基于无人机巡查的电站征地红线智能分析系统。该系统信息采集模块使用固定翼无人机搭载摄像机方式采集水电站征地红线图像,并通过无线数传子模块和无线图传子模块将征地红线图像以及无人机飞行信息传输至地面控制模块和智能分析与展示模块内。地面控制模块基于卫星通讯主站、运营商基站以及通信卫星组成的5G信号网络,利用无人机测控子模块控制执行巡检拍摄任务。智能分析与展示模块接收到征地红线图像后,使用图像预处理子模块计算征地红线坐标后,使用3Dmax软件构建征地红线三维模型,利用该模型提取征地红线特征点后,将其输送至智能分析子模块,该模块使用尺度不变特征变化算法对征地红线图像特征进行匹配,得到征地红线智能分析结果。实验结果表明:该系统在应用过程中可有效分析水电站征地红线特征匹配情况,具备较强的应用性。