共查询到19条相似文献,搜索用时 62 毫秒
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讨论了驻波法测空气中声速的实验,分别用相位比较法和李萨如图法来确定超声波波长.在不同温度条件下测量了声速并与理论值进行比较,实验结果显示测量温度接近室温时实验值与理论值基本一致,测量温度与室温相差较大时实验值与理论值偏差较大. 相似文献
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有限元方法已成为分析螺纹螺栓结构的有力手段,但已有的工作基本都将螺纹结构简化为二维的,基于三维模型的研究还很少。但螺纹的三维螺旋型结构特征,则势必要求进行三维分析。 相似文献
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空气中的声速随着温度的变化而变化,本文利用生活中的器材(有限长直管)自制简易实验装置,借助手机APP作为声音发射器和频率接收器,在管内中部区域形成恒温条件,实现了驻波法对不同温度下声速的测量,在测量范围内相对误差不超过2%.这种基于传统物理实验的拓展,在特殊居家环境下亦可进行,有利于物理实验线上自主学习模式的开展,促进学习者的综合素质和实践创新能力的提升. 相似文献
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为获取液体介质的声速值,设计了一种测定流体声速的实验方法,该方法利用时差式超声波流量计和标准流量校验设备同时对封闭管道中的液体进行流速测量,分别得到流速的测量值和真实值,从而计算出超声波流量计的仪表系数,并以此导出了一定条件下液体介质的声速值随仪表系数的变化关系式.利用该方法测量给出了0.17 MPa下四氧化二氮(N2O4)在7.6-19.4 ℃、偏二甲肼((CH3)2NNH2)在6.5-25.2 ℃范围内的流体声速值,并为其他液体介质的声速测量提供了借鉴.
关键词:
超声波流量计
声速
仪表系数
温度 相似文献
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高强度螺栓轴向预紧力(轴力)的测量在工程应用中具有重要意义。使用电磁超声波对螺栓轴力检测时对超声回波声时测量精度要求较高,传统互相关估计法对超声回波声时估计易因噪声干扰发生估计错误,无法满足轴力测量精度要求。本文针对互相关法对电磁超声测量信号声时估计存在不准确的问题,提出了Gabor时频滤波法。通过螺栓轴力测量实验采集测量信号,对测量信号进行Gabor变换,在时频域中进行滤波,再对去噪后的信号进行互相关估计测得信号的声时,进而计算出螺栓轴力。实验表明:Gabor时频滤波法能有效地滤除电磁超声信号中的噪声,改善互相关估计的稳定性,提高螺栓轴力测量的准确率。 相似文献
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Effect of wood properties on within-tree variation in ultrasonic wave velocity in softwood 总被引:2,自引:0,他引:2
The radial variations in the velocity of longitudinal waves propagating through Japanese cedar and Japanese cypress were experimentally investigated. In addition, the tracheid length (TL), microfibril angle (MFA), air-dried density (AD), and moisture content (MC) were measured in order to determine the effect of wood properties on velocity variations within the wood trunk. For both species, the longitudinal wave velocities measured in the longitudinal direction (VL) exhibited minimum values near the pith. For Japanese cedar, VL increased from 3600 m/s toward the bark and soon attained a constant value (=4500 m/s). On the other hand, for Japanese cypress, VL kept increasing from 4000 m/s near the pith to 4800 m/s at the bark. These radial variations in VL coincided with those in the tracheid length. VL exhibited strong correlations with TL and MFA with a significant level of (p < 0.01). These findings suggest that the TL and MFA greatly affect the radial variation in the ultrasonic wave velocity in softwood. 相似文献
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S. Sankarrajan S. Aravindan R. Yuvakkumar K. Sakthipandi V. Rajendran 《Journal of magnetism and magnetic materials》2009,321(21):3611-3620
Nd1−xSrxMnO3 perovskite manganite material with different compositions (x=0.31, 0.35, 0.37, 0.39 and 0.41) have been prepared employing solid-state reaction technique. The ultrasonic velocities and attenuation of the above samples have been measured employing through transmission method operated at a fundamental frequency of 5 MHz over wide range of temperatures. The temperature dependence of ultrasonic velocities, attenuation, relative percentage variation in velocities and elastic constants show an interesting anomaly in all compositions. The observed anomalies in ultrasonic parameters at Tc in all compositions have been revealed in terms of existence of ferromagnetic (FM) state. Similarly, the anomalies at Tco show the transition from FM to charge-ordered antiferromagnetic (AFM) state. The observed results have been used to explore the competitions between FM and AFM. 相似文献
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Methods of measuring ultrasonic wave velocity in an elastic sample require data on the thickness of the sample and/or the distances between the transducers and the sample. The uncertainty of the ultrasonic wave velocity measurements generally depends on that of the data available. Conversely, to determine the thickness of a material, it is necessary to have a priori information about the wave velocity. This problem is particularly hard to solve when measuring the parameters of biological specimens such as bones having a greater acoustical impedance contrast (typically 3-5 MRayl) than that of the surrounding soft tissues (typically 1.5 MRayl). Measurements of this kind cannot easily be performed. But obtaining the thickness of a bone structure and/or the ultrasonic wave velocity is a important problem, for example, in biomechanical field for the calculation of elastic modulus, or in acoustical imaging field to parameterize the images, and to reference the grey or color level set to a physical parameter.The aim of the present study was to develop a method of simultaneously and independently determining the velocity of an ultrasonic wave in an elastic sample and the wave path across the thickness of this sample, using only one acquisition in pure transmission mode. The new method, which we have called the “Wavelet-Based Processing” method, is based on the wavelet decomposition of the signals and on a suitable transmitted incident wave correlated with the experimental device, and the mathematical properties such as orthonormality, of which lend themselves well to the time-scale approach. By following an adapted algorithm, ultrasonic wave velocities in parallelepipedic plates of elastic manufactured material and the apparent thicknesses were both measured using a water tank, a mechanical device and a matched pair of 1 MHz ultrasonic focused transducers having a diameter of 3 mm, a focal length of 150 mm and beam width of 2 × 2 mm at the focus (mean temperature 22°). The results were compared with those obtained with a conventional Pulse-mode method and with the control values, to check their validity. Measurements performed on bovine and human dry cortical bone samples are also presented to assess the limitations of the method when it is applied to elastic biological samples, including those of an equal-wavelength size (≈1.5 mm). The thicknesses and the ultrasonic wave velocities were then measured in this kind of (quasi-) parallelepipedic elastic materials with an mean estimated error ranged from 1% to 3.5% compared to the referenced values. 相似文献
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Longitudinal and transverse wave attenuation coefficients are obtained in a simple integral form for ultrasonic waves in cubic polycrystalline materials with elongated grains. Dependences of attenuation on frequency and grain shape are described in detail. The explicit analytical solutions for ellipsoidal grains in the Rayleigh and stochastic frequency limits are given for a wave propagating in an arbitrary direction relative to ellipsoid axes. The attenuation exhibits classic frequency dependence in those frequency limits. However, the dependence on the grain shape in the stochastic limits is unexpected: it is independent of the cross-section of the ellipsoidal grains and depends only on the grain dimension in the propagation direction. In the Rayleigh region attenuation is proportional to effective volume of the ellipsoidal grain and is independent of its shape. A complex behavior of attenuation on the grain shape/size and frequency is exhibited in the transition region. The results obtained reduce to the classic dependences of attenuation on parameters for polycrystals with equiaxed grains. 相似文献