炮管内表面加工质量的动态测量

主要介绍应用超声波在传播过程中,在不同媒质界面各个反射波之间的时间差与超声波在媒质中的传播速度和媒质的尺寸关系,来刹量炮管的厚度;通过测量炮管的厚度变化来测量炮管内径的尺寸.检测系统通过扫描炮管的外表面,对工件尺寸和涂层厚度进行测量、监控;并能根据检测到的各点表面的测量数据,在计算机上进行三维成像.     

脉冲多普勒天气雷达数据质量控制之解速度模糊处理

在雷达硬件标定正确的情况下,多普勒天气雷达基数据的质量主要受到3个因素的影响[1]。这3个因素分别是地物杂波、距离折叠和速度模糊。在本文中我们主要分析了其中的速度模糊现象出现的原因,着重介绍交错脉冲法（也叫双脉冲重复频率法,即DPRF）解速度模糊,同时结合3830天气雷达解速度模糊的特点,证明了交错脉冲法可以有效地扩大无模糊测速范围。     

Measurement of tissue motion.

A number of ultrasonic methods are available for the detection of tissue motion as it occurs physiologically in the body. The detection of echoes from within the body in less than 1 ms after the initial transmission of ultrasound and the Doppler effect have enabled a range of instrumentation to be developed. The subject owes a great deal to advances in transducer design, electronics and computer technology. Over many years fast B-mode imaging and M-mode traces of boundary position versus time have been the main clinical tools. Currently new sophisticated detection and imaging techniques are being produced based on the Doppler effect and on tracking motion in tissue images. The measurement of several velocity components is permitting velocity vectors to be determined more completely, adding to accuracy. Not surprisingly, cardiology is the main field of application but there are other areas of interest, e.g. vascular, musculo-skeletal and foetal function studies.     

Surface wave velocity measurement using reflections from laser scribed grooves

The measurement of ultrasonic surface wave (USW) velocity is difficult using the pulse overlap method (POM) in the presence of an externally applied stress. Coupling variations between the sample and the transducer cause nonuniform distortions of the two received pulses which makes the overlap condition difficult to determine over an extended stress range. The adaptation in this paper of a single transducer configuration to generate and detect the USW eliminates coupling variations between two or more transducers. In addition, two parallel, precisely positioned and contoured grooves are laser scribed on the sample surface to provide the necessary overlap echoes. Since both echoes are reflected only once by identical grooves and are equally affected by the distortions due to coupling variations, the overlap condition is relatively unaffected by the external stress and the accuracy of the USW velocity measurement is increased significantly.     

基于超声波的工件内层表面加工质量的检测

超声波在传播过程中,反射波的时间差与被测量物体的厚度成正比。采用超声波反射波脉冲信号的时间差,来检测工件涂层后内层表面的加工质量,并根据扫描工件表面的测量数据,在计算机上进行三维成像。因此,采用超声波反射波脉冲信号可以完成工件内层表面加工的测量与监测。     

Accurate ultrasound speed measurement using an MLS-modulated continuous wave

The continuous wave shows greater potential than the pulse signal to achieve high-accuracy ultrasound speed measurement thanks to its stronger noise resistance. However, the accuracy of ultrasound speed measurement would deteriorate if echoes exist in the received continuous wave. This paper presents an applicable method using the maximum length sequence-modulated continuous wave. The present method improves the accuracy of ultrasound speed measurement further by resisting echoes. The time delay between the received signal and the transmitted signal is estimated accurately by combining the cross-correlation, parabolic interpolation and phase shift technique. Moreover, both the inherent delays induced by physical system and the path length of ultrasound are expediently corrected through least square estimation. As a result, accurate time of flight and ultrasound speed measurement are achievable. For example, the standard deviation of ultrasound speed measurement in distilled water is less than 0.003 m/s, and the deviation between the ultrasound speed measurement and the reference is less than 0.04 m/s.     

Analysis of Ultrasound Propagation in a Metal Rod by Using Finite Element Method

A metal rod is used in the high temperature testing for ultrasonic propagation and heat output,but the trailing echoes generated by ultrasonic penetration through the metal rod seriously affect the recognition and extraction of characteristic signals.According to the phenomenon,the Finite Element Method(FEM)is used to analyze ultrasonic penetration through a metal rod,the reason of the trailing echoes and the regularity of ultrasonic signals.The motion equation of ultrasonic propagation in a metal rod is established and calculated,then the simulation signals and instantaneous cartographies of the process are obtained.Based on the results of the analysis,it can be concluded that the intervals of the trailing echoes are determined by the rod’s diameter and wave velocity.In practical applications,the FEM is used to analyze ultrasonic propagation in the designed buffer rod at first.Based on the characteristics of the simulation signals,the material and dimension are adjusted and selected,aiming to identify the characteristic echo and trailing echoes in time domain and extract characteristic echo from the ultrasonic signals available.     

Device for improving ultrasonic transit time measurements with standard pulse echo equipment

A simple and inexpensive device is described which in conjunction with conventional pulse echo equipment allows the direct measurement of the time interval between the zeros of selected individual cycles in different echoes with an accuracy better than 0.2 ns.     

A novel approach to multi-path ultrasonic transit time flow meter based on measurement model analysis to improve accuracy

Ultrasonic transit time flow meter (UTTFM) is commonly used in a wide range of applications. It is commonly believed amongst researchers, industrialists, and standard committee members that due to nonuniform flow velocity distribution inside the pipe (flow velocity profile) the measured flow velocity using UTTFM needs to be corrected by the flow profile. Mathematical analysis of UTTFM measured quantity shows that UTTFM measures flow correctly when flow is fully developed or laminar. However, the measurement results using flow profile correction factor produces erroneous values. The UTTFM measurement model assessment shows, when flow is not fully developed, there are unknown quantities contributed by flow velocity in the axial and diametrical direction to measurement results. These unknown quantities lead to erroneous measurement results when it is simply corrected by flow profile. Assessment of the UTTFM error model shows that using multi-path UTTFM can significantly reduce the impact of the unaccounted quantities and improve accuracy. A novel approach to UTTFM design utilizing multiple acoustic paths (using different planes and transmitting angles) is proposed to reduce potential error for UTTFM. This approach is consistent with the general measurement modeling method with incomplete information recommended by JCGM GUM-6:2020.     

Microscale mechanisms of ultrasound velocity measurement in metal melts

Ultrasound Doppler velocimetry (UDV) is a powerful, widely used technique for measuring flow in metal melts. However, UDV in metal melts suffers from substandard reliability because its operation depends on phenomena that are poorly understood. In this study, we investigate the poorly characterized source of bulk echoes in metal melts and the corresponding mechanisms of ultrasound signal deterioration. We present evidence from electron microscopy and ultrasound measurements that oxide inclusions are the main source of bulk echoes in gallium. By measuring their terminal velocity, we estimate the mean size of echoing objects in gallium to be 58–64 μm, implying that Mie scattering is the dominant scattering mechanism. By comparing UDV measurements in which signals were transmitted directly into the fluid, to others in which signals were transmitted through a vessel wall, we show evidence that there are two distinct mechanisms for signal degradation: the loss of echoing objects from the bulk and the deterioration of acoustic coupling and wetting at the transducer surface. We suggest stirring vigorously and using indirect-contact UDV measurement strategy to mitigate the signal degradation in metal melts.     

Terahertz scanning techniques for paint thickness on CFRP composite solid laminates

Terahertz ray (T-ray) scanning applications are promising tools. The use of T-ray for nondestructive evaluation was investigated on composite materials. In this characterization procedure, electromagnetic properties, such as the refractive index, were analyzed. The estimates of properties are in good agreement with known data. We successfully demonstrated the characteristics of T-ray propagating through Carbon fiber-reinforced plastic (CFRP) composites to acquire the refractive index by using the characterized material properties. A T-ray technique was developed for measuring paint thickness on CFRP laminates. Good results were obtained from tests performed on standard paint samples with thickness starting from approximately 100 μm. The method was based on reflection mode measurement with time of flight. Another method developed for measuring paint thickness using resonance frequencies was utilized to determine paint thickness on composite laminates. The paint thickness deduced from resonance frequencies agrees well with the result obtained directly from time-domain echoes.     

Relative position finite-time coordinated tracking control of spacecraft formation without velocity measurements

This paper investigates finite-time relative position coordinated tracking problem by output feedback for spacecraft formation flying without velocity measurement. By employing homogeneous system theory, a finite-time relative position coordinated tracking controller by state feedback is firstly developed, where the desired time-varying trajectory given in advance can be tracked by the formation. Then, to address the problem of lack of velocity measurements, a finite-time output feedback controller is proposed by involving a novel filter to recover unknown velocity information in a finite time. Rigorous proof shows that the proposed control law ensures global stability and guarantees the position of spacecraft formation to track a time-varying reference in finite time. Finally, simulation results are presented to illustrate the performance of the proposed controller.     

Results of high resolution slip measurements in a fretting experiment

An optical method of slip measurement in a fretting experiment has been developed which allows the measurement of slip amplitude to ±0.95 μm. Average sliding velocities of fretting interfaces during each 1.9 μm of relative motion can be calculated from the slip measurement data. Results on 4130 steel indicate that previously reported temperature variations of the fretting interface closely follow the pattern of the instantaneous sliding velocity of the interface, as is expected for frictional heating. The pattern of sliding velocity versus time is very regular from one fretting cycle to the next. It is concluded that any welding or adhesion which occurs at the interface is either on such a small scale that it does not disrupt the regular motion of sliding parts or is so infrequent in occurrence that it was not observed in any of the present experiments.     

High-accuracy ultrasonic temperature measurement based on MLS-modulated continuous wave

Ultrasonic temperature measurement has the potential to improve measurement accuracy by increasing the length of a received signal due to its excellent performance with noise resistance. However, when the distance between the transmitter and receiver is limited, the received signal can be polluted by strong multiple echoes, which can significantly degrade temperature accuracy. This paper proposes a method for high-resolution ultrasonic temperature measurement. With the use of a maximum length sequence (MLS)-modulated continuous wave, the obstructive effect of echoes is effectively suppressed. A hybrid method is employed for accurate time-of-flight (TOF) estimation by incorporating both cross-correlation and phase shift (PS), which is the basis of highly accurate temperature measurement. The experimental results in distilled water show that the proposed method estimates TOF with a standard deviation of less than 0.3 ns, and temperature errors consistently remain within ±0.04 °C.     

基于全加速度计惯性测量单元的微震颤测量技术研究

对基于全加速度计惯性测量单元的微震颤测量技术进行研究和分析,设计了测量系统的方案并研制了实验样机,惯性测量单元采用9加速度计的配置形式;推导了加速度计输出的比力方程,提出了将积分法和开方法结合起来求解角速度的算法;给出了利用四元数求解捷联矩阵的数值求解方法和在惯性坐标系下载体系上任意位置在任意时刻坐标的数值求解方法。     

用激光外差技术高精度测量目标速度

搭建了外差探测实验平台,分别选用漫反射目标及类简谐运动模型作匀转速运动及变速运动的测量目标,应用激光外差探测技术实现了对匀转速运动及变速运动物体的速度测量.在匀转速测量过程中,同时采用外差探测法和振幅调制法测量了漫反射目标正负两个方向转动的速度,共得到133组不同的转速结果.通过调整实验系统,亦实现了对类简谐运动目标的...     

传播衰减法测平板阻尼

通过研究无限板上速度响应的传播衰减规律,发展了一种测试损耗因子的工程方法,并将其推广到周边简支板结构。同时给出了利用此方法的无限板上的远场条件和周边简支板的远场条件和边界条件。     

基于虚拟仪器技术和互相关原理的流体流速测量仪

本文采用虚拟仪器技术和互相关原理相结合．研制了流体流速测量仪。该方法利用待测两路信号的通道中信号与信号的相关性．信号与噪声之间．噪声与噪声之间不存在相关性．通过求两通道中信号与信号的互相关系数．得到两个信号的时延．从而得到流场的速度值。并对该流速测量仪进行了理论分析，全面阐述了基于虚拟仪器技术和互相关原理流体流速测量仪的实现过程。给出了对应硬件和基于LabVIEW编写的核心程序，并对结果误差进行了分析。     

An investigation of a constant-bandwidth hot-wire anemometer

A model for a constant-bandwidth hot-wire anemometer and experimental testing of such a anemometer prototype are presented in this article. During the testing, an approximately constant anemometer transmission bandwidth, and good conformity between the model and the real measurement system were achieved. The system developed and outlined herein allows for minimization of the dynamic errors that arise during the measurement of rapidly changing flow velocity fluctuations, in which the mean velocity changes significantly. However, the electronic circuitry needs to be extended, and some additional parameters are required for the anemometer adjustment process. It appears that the results obtained are sufficient for a positive evaluation of the capabilities of the developed measurement system in a wide range of metrological applications.     

A mathematical model of ultrasonic cross correlation flow meters based on industrial experience

A new model for Ultrasonic Cross Correlation Flow Meters (USCCFM) has been developed as result of industrial experience at Ontario Power Generation (OPG). Industrial applications of USCCFM have encountered cases where the frozen pattern model failed. The new model is based on the mathematical properties of turbulent velocity fields and correlation functions. It contains a proof that USCCFM measurement in a particular situation is successful, if and only if certain mathematical conditions are satisfied. In this document, the term “successful” means that the USCCFM is able to obtain a consistent cross correlation peak, and a stable time delay from the flow condition; otherwise the measurement is considered unsuccessful. This model applies to all measurement conditions encountered so far.