Directivity analysis of ultrasonic waves on surface defects using a visualization method

Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in one direction. The directivity is expressed as the relationship between the propagation direction and its sound pressure. The directivity of an ultrasonic wave is related to the choice of probe arrangement, testing sensitivity and scanning pitch, and correct measurement of defect size and location. This paper investigated the directivity of ultrasonic waves, which are scattered from a slit defect located in simulated butt weld joint using a visualization method. When the defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. When the ratio of defect size to wavelength is greater than 1.5, measured directivities almost agree with the theoretical directivity. The directivity of shear waves scattered from the slit defect varied according to probe direction (Far defect, Near defect). The angle of reflection wave became similar to angle of incidence as the height of excess metal in welded joint increased.     

Simulation and experimental study of the sensor emitting frequency for ultrasonic tomography system in a conducting pipe

Ultrasonic tomography techniques provide flow visualization capability, non-invasively and non-intrusively, to enhance the understanding of complex flow processes. There is limited ultrasonic research in tomography imaging systems in the tomogram analysis of fluid flow in a conducting pipe because of a high acoustic impedance mismatch, which means that very little ultrasonic energy can be transmitted through the interface. The majority of industrial pipelines are constructed from metallic composites. Therefore, the development and improvement of ultrasonic measurement methods to accommodate a stainless steel pipe are proposed in this paper. Experimental and simulation distribution studies of the ultrasonic emitting frequency in acrylic versus stainless steel pipes were studied, measured and analyzed. During the simulation, ultrasonic transducers were placed on the surface of the investigated pipe to inspect the ultrasonic sensing field. The distribution of the sound wave acoustic pressure was simulated based on the physical dimensions and parameters of the actual experimental hardware set-up. We developed ultrasonic acoustic models using the finite element method with COMSOL software, and experiments were carried out to validate the simulation results. Finally, by performing the static phantoms tests, a feasibility study of ultrasonic tomography system was presented to investigate the void fraction of liquid column inside a stainless steel pipe.     

Modeling of ultrasonic testing in butt joint by ray tracing

Ultrasonic wave generation and propagation were modeled to simulate an ultrasonic test. A ray model was used for the modeling. Actual sound pressure distribution of the incident wave from an angle probe was analyzed using an ultrasonic visualization method to incorporate the actual sound pressure distribution in the model. In this method, the sound pressure was expressed by the density of rays and the reflection coefficient of ultrasonic beams. Reflection and mode conversion of rays were computed by the Snell’s law. Simulation programs for the problem of ultrasonic testing of a butt joint are built using this ray modeling. Simulation results for ultrasonic wave scattering from a defect and A-scan display in ultrasonic testing agreed with the actual experiment results.     

Fundamental uncertainty analysis of flowrate measurement using the ultrasonic Doppler velocity profile method

The present paper describes a fundamental uncertainty analysis for a flowrate measurement in a pipe using an ultrasonic Doppler velocity profile method and an evaluation of the estimated uncertainty by an actual flow calibration. The uncertainties are estimated for internal factors originating from the measurement equipment; UVP provided by Met-Flow sa. and external factors depending on on-site measurements, such as the inclination angle of the ultrasonic transducer. The relative expanded uncertainty due to internal factors is estimated to be 0.34% with a coverage factor of 2. The relative external uncertainty including external factors is estimated to be from 0.42% to 2.13% depends on the inclination angle of the transducer. The results of the actual flow calibration under the same condition as the uncertainty analysis are within the range of uncertainty considering the internal factors.     

双参数非线性概率模型的板材腐蚀精度估计

针对金属板腐蚀在线超声动态检测时探头抖动致使超声波入射角变化,引起测量精度低的问题,建立双参数超声波水浸检测误差修正的非线性概率模型,结合函数逼近理论补偿超声入射角引入误差。采用基函数加权组合与三阶拉格朗日插值结合方法,同时对超声波入射角、界面声程双参数与工件声程的函数关系进行最小二乘曲线拟合,得出入射角与检测误差的非线性相关关系。通过对误差补偿算法中非线性概率模型入射角与界面声程变量的迭代运算,利用折射角反向求解入射角,解决检测中超声波入射角不确定问题。在水层厚度30～45 mm范围内,对不同厚度铝板进行检测,结果表明,经模型补偿处理,超声波以0°～8°角入射,板材检测精度为1%,为有效提高腐蚀精度估计提供依据。     

Measurement of steam flow rates using a clamp-on ultrasonic flowmeter with various wetness fractions

Most of the heat in industrial plants is supplied by steam. To minimize energy waste, measuring the steam flow rates in existing pipes is important. Clamp-on ultrasonic flowmeters are used for this purpose, for which the sensors are attached to the pipe wall. However, flow conditions that can be used are limited because the signal-to-noise ratio of the ultrasonic signal in a steam flow is low. Furthermore, the steam wetness increases with heat losses, which may affect measurement results. Therefore, flow rate measurements in wet steam flows using clamp-on ultrasonic flowmeters have not been fully established. In this study, steam flow rates with various wetness fractions and system pressures were measured using a laboratory-made clamp-on ultrasonic flowmeter. The results show that flow rates in wet steam could be determined within a 10% error under general conditions in a steam piping system, although the conversion factor from line-average to area-average velocities was calibrated in superheated conditions, and the speed of sound in saturated conditions at each pressure was used. However, the error of the flow rates tended to increase with the wetness fraction and was biased toward positive values. The speed of sound and liquid volume fraction were evaluated at different wetness fractions. The flow rate error due to the change in sound speed was less than 1%, and 1.2% of the flow rates were overestimated owing to the liquid volume fraction. The velocity distribution in wet steam was considered different from that in the superheated steam owing to the existence of the liquid phase, and the change in velocity profile may lead to an overestimation of the steam flow rates in the wet steam condition.     

Neural network approach to ultrasonic flow measurements

Mathematical models and numerical methods offer a flexible tool to investigate flow disturbance effects on flowmeters of different types. In this paper a simple neural network based approach has been used to study the velocity profile dependence of ultrasonic flowmeters. Neural networks have been used in two ways: to interpolate the velocity profiles in the points needed for the modelling of ultrasonic flow measurement, and to compute the weights for different paths of multipath ultrasonic flowmeters. In the former case two types of neural networks, multilayer perceptron networks and radial basis function networks, have been investigated. In the latter case, a single layer neural network with linear neurons is first trained with known velocity profiles, and the weights determined by the network have then been used in the computation of the errors in other piping configurations. The results have been compared with the errors computed with the weights for different paths given in Pannel CN, Evans WAB, Jackson DA. A new integration technique for flowmeters with chordal paths, Flow Measurement and Instrumentation 1990;1:216–224.     

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.     

An accurate air temperature measurement system based on an envelope pulsed ultrasonic time-of-flight technique

A new microcomputer based air temperature measurement system is presented. An accurate temperature measurement is derived from the measurement of sound velocity by using an ultrasonic time-of-flight (TOF) technique. The study proposes a novel algorithm that combines both amplitude modulation (AM) and phase modulation (PM) to get the TOF measurement. The proposed system uses the AM and PM envelope square waveform (APESW) to reduce the error caused by inertia delay. The APESW ultrasonic driving waveform causes an envelope zero and phase inversion phenomenon in the relative waveform of the receiver. To accurately achieve a TOF measurement, the phase inversion phenomenon was used to sufficiently identify the measurement pulse in the received waveform. Additionally, a counter clock technique was combined to compute the phase shifts of the last incomplete cycle for TOF. The presented system can obtain 0.1% TOF resolution for the period corresponding to the 40 kHz frequency ultrasonic wave. Consequently, with the integration of a humidity compensation algorithm, a highly accurate and high resolution temperature measurement can be achieved using the accurate TOF measurement. Experimental results indicate that the combined standard uncertainty of the temperature measurement is approximately 0.39 degrees C. The main advantages of this system are high resolution measurements, narrow bandwidth requirements, and ease of implementation.     

Broadband electrostatic acoustic transducer for ultrasonic measurements in liquids

A broadband capacitive electrostatic acoustic transducer (ESAT) has been developed for use in a liquid environment at megahertz frequencies. The ESAT basically consists of a thin conductive membrane stretched over a metallic housing. The membrane functions as the ground plate of a parallel plate capacitor, the other plate being a dc biased electrode recessed approximately 10 mum from the electrically grounded membrane. An ultrasonic wave incident on the membrane varies the membrane-electrode gap spacing and generates an electrical signal proportional to the wave amplitude. The entire assembly is sealed for immersion in a liquid environment. Calibration of the ESAT with incident ultrasonic waves of constant displacement amplitude from 1 to 15 MHz reveals a decrease in signal response with increasing frequency independent of membrane tension. The use of the ESAT as a broadband ultrasonic transducer in liquids with a predictable frequency response is promising.     

Velocity vector profile measurement using multiple ultrasonic transducers

This paper proposes a new technique that enables the measurement of the velocity vector in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on the ultrasonic velocity profiling by using multiple transducers. A two-dimensional system was constructed and successfully applied to an actual flow field for two-dimensional velocity vector measurements. To estimate the influence of the existence of a wall, acoustic field under the developed system was calculated by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure the two-directional velocity components of a periodic velocity fluctuation in the wake of a cylinder as an example of unsteady flow. Temporal variation of velocity vector profiles well represent the velocity fluctuation, and vorticity distribution, which is obtained from the spatial distribution of velocity vector, well represents the vertical motion in the wake.     

基于空间脉冲响应的超声换能器声场研究

以空间脉冲响应为理论基础,建立了换能器空间声压模型,通过求任意时刻相交弧长对应圆心角的方法,计算了圆形和矩形换能器的脉冲响应函数,并仿真了其声轴线平面、横截面和声轴线的声压分布,通过与理论声压对比,仿真结果可以准确地反映换能器在空间辐射的声场。该方法对优化换能器设计参数和无损检测工艺、提高超声检测分辨率和可靠性有重要意义,也适用于其他形状换能器声场的计算。     

High flow-rate ultrasonic seeder

Application of optical techniques to gaseous flows usually requires seeding the fluid with tracers sufficiently small to follow the flow, added in suitable concentrations. This work describes the design and manufacture of a seeder based on ultrasonic atomization of aqueous solutions or other fluids of similar viscosity, capable of operating in a continuous way with high atomization rates. It includes a dozen piezoceramic disks that oscillate at 1.65 MHz, generating droplets with Sauter mean diameter in the range of 4–5 μm and rates over 0.6 g/s when working with water. To test its performance, the device has been used to seed a simple free air jet issuing from a 3.5 cm diameter pipe. Initially the seeding density is very satisfactory, but if only water is nebulized the droplets evaporate in a short time and the concentration becomes too low when moving downstream. The situation can be greatly improved mixing the water with a less volatile liquid. Here, a small percentage of glycerol (5% in volume) has been added to the water to extend the droplet lifetime, although in general, atomization rate strongly decreases when increasing the liquid viscosity. The seeded flow has been visualized, and the 3D velocity field has been successfully measured using stereoscopic particle image velocimetry.     

超声波气体流量计的管道模型仿真和误差分析

为满足不断发展的超声波气体流量计测量精度的需要,改进传感器的设计精度和有效降低安装测试及样机调试成本,针对制约超声波气体流量计测量精度主要误差源之一的管道流场分析问题,结合计算机建模数值仿真技术及实验技术对其流场设计参数以及弯管安装条件等对超声波测量误差产生原因进行定量分析.理论研究和仿真实验结果表明,可以量化分析气体超声波流量计流场误差产生的原因、范围,并通过限定流场修止系数更有效地降低其测量误差,这项研究对该超声波气体流量计的优化设计和工程应用具有一定的指导意义.     

A highly accurate ultrasonic ranging method based on onset extraction and phase shift detection

The opposite-type ultrasonic ranging application is widely used in spatial 3D coordinates measurement systems. The traditional phase shift (PS) estimation based on multi-frequency ultrasonic pulse is a highly accurate ranging method but has high requirement to the transducers and signal processing algorithm. This paper proposes a novel opposite-type ultrasonic ranging method with single frequency pulse. It can estimate the time of flight (TOF) roughly through extracting the signal’s onset based on self-correlation and correct the TOF accurately through detecting the phase shift between the transmission and reception signals. In order to reduce the noise disturbance to this algorithm, a new de-noising method based on wavelet decomposition is presented, and the de-noising effect is analyzed by MATLAB simulation. Finally, three separate ultrasonic ranging experiments were designed to validate the effects of wavelet de-noising, PS detection and temperature field compensation. The accuracy of distance measurement can achieve 0.5 mm for the distance up to 5000 mm.     

超声波流量计中反射装置的声-固耦合分析

对超声波流量计中的反射装置进行有限元模拟计算,利用声-固耦合的方法将流体域内的声压和固体域中的结构变形联系起来。在流体域内求解Helmholtz方程,得到的声压作用于固体表面使得超声波反射装置受到载荷,而结构变形在固体边界的法向上产生结构化加速度。选取一款超声波流量计的反射装置并将其置于无限大空间中,通过一个球体对计算区域进行分割得到有限元计算区域,将超声波换能器简化为垂直入射计算区域的平面波。通过对硬边界、铝材料和不锈钢的模拟结果进行对比,分析3种情况下超声波传播过程中3条路径上的声压级变化,得出固体域的结构变形对超声波传播过程中声压分布产生影响;不锈钢材料宜作为反射装置的材料。     

Measurement of solid propellant burning rates by analysis of ultrasonic full waveforms

The measurement of solid propellant burning rates using ultrasound requires the simultaneous acquisition and analysis of ultrasonic signals and pressure data simultaneously in a wide range of pressure values during the process of propellant burning. Recently, this method has been proposed as an effective approach based on an analysis of full waveforms of ultrasonic signals together with a laboratory prototype system in which the proposed approach has been implemented. However, this prototype system had limitations in terms of data processing speed and signal processing procedures. To overcome such limitations, in the present study, we develop a dedicated, high speed system that can acquire ultrasonic full waveforms and pressure data up to 2,000 times per second. Our system can also estimate the burning rate as a function of pressure using a special software based on ultrasonic full waveform analysis. This paper describes the approach adopted in this high speed system, along with the burning rate measurement results obtained from three propellants with different burning characteristics. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Sung-Jin Song received a B.S. degree in Mechanical Engineering from Seoul National University, Seoul, Korea in 1981, a M.S. degree in Mechanical Engineering from Korea Advanced Institute of Science and Technology in 1983, and a Ph.D in Engineering Mechanics from Iowa State University, Ames, Iowa, USA in 1991. He has worked at Daewoo Heavy Industries, Ltd., Inchoen, Korea for 5 years from 1983, where he has been certified as ASNT Level III in RT, UT, MT and PT. He has worked at Chosun University, Gwangju, Korea as Assistant Professor for 5 years from 1993. Since 1998 he has been at Sungkyunkwan University, Suwon, Korea and is currently Professor of Mechanical Engineering.     

Measurement range expansion of continuous wave ultrasonic anemometer

This study was conducted to expand the measurement range of a continuous wave ultrasonic anemometer (CWUA) that uses phase difference measurement. A CWUA has a narrower measurement range than conventional ultrasonic anemometers because it can measure the phase difference up to the half-cycle of the used ultrasonic signals. In this study, a method of expanding the measurable range of the phase difference using a phase delay circuit and a frequency divider was developed. Through experiments, it was found that this method doubled or quadrupled the measurement range when the method was used. Furthermore, an algorithm for determining the validity of the measurement data by comparing them with the previous data was implemented with a wind velocity measurement error of less than ±1 μs to solve the problem caused by the use of the frequency divider and to produce a stable measurement system.     

基于互相关理论的超声波气体流量测量电路系统

介绍一种基于互相关理论的超声波流量测量电路系统。该系统以数字信号处理器(DSP)为核心,通过采集上、下游流动信号并做互相关运算,计算出互相关函数峰值对应的渡越时间,间接测出流量。采用抛物线插值计算互相关函数峰值,减少测量误差。它对流场不敏感,测量精度高,在气体的测量实验中,取得了比较理想的效果。     

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.