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61.
Ming Ruisen 《Acta Mechanica Sinica》1996,12(3):251-262
Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the
estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending
waves. In a two-dimensional quasi-longitudinal wave field, the intensity vector is the sum of the effective intensity vector
and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities
and in the measurement, it is measured by a pair of two-transducer arrays. In a onedimensional quasi-longitudinal wave field,
the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and
it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from
bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain
a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately
measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves.
The project supported by the National Natural Science Foundation of China 相似文献
62.
本文应用激光多普勒测速仪对二种转盘萃取塔模型进行切向速度、轴向速度和湍流度测量。实验结果表明,在RDC是切向速度比较大,因而有较大的搅拌效果,它的内部流场比较均匀稳定,有利于传质,所以RDC是广泛应用于化学工业中的一种液-液萃取设备。 相似文献
63.
Dan N. Borza 《Experimental Mechanics》2002,42(4):432-438
Electronic holography is a well-established technique used in real-time, non-contact, whole-field displacement measurements.
When using the real-time, time-averaged method for vibration measurments, the quantitative interpretation of dense fringe
patterns is difficult because of speckle noise. Even when speckle-reducing procedures are used, such as multiple-frame averaging
or rotation of the illumination beam, the remaining speckles and decreasing visibility of higher-order Bessel fringes are
serious limitations. The primary objective of this paper is to present a new realtime, interferometric method for mechanical
vibration measurements and the associated quantitative interpretation. The fringe pattern obtained by this method is quasi-binary
and half as dense as in the time-averaged method. The method greatly improves the overall visibility (contrast, resolution)
of vibration fringe patterns without any sacrifice in the real-time capabilities. Quantitative fringe interpretation is straightforward
and based on binary fringe tracking. It allows quantitative measurements in situations where the time-averaged fringe processing
fails. 相似文献
64.
Peng Cheng Ph.D. Michael A. Sutton Hubert W. Schreier Ph.D. Student Stephen R. McNeill 《Experimental Mechanics》2002,42(3):344-352
A full-field speckle pattern image correlation method is presented that will determine directly the complete, two-dimensional
deformation field during the image correlation process on digital images obtained using computer vision systems. In this work,
a B-Spline function is used to represent the object deformation field throughout the entire image area. This is an improvement
over subset-based image correlation methods by implicitly maintaining position and derivative continuity constraints among
subsets up to a specified order. The control point variables within the B-Spline deformation function are optimized iteratively
with the Levenberg-Marquardt method to achieve minimum disparity between the predicted and actual deformed images. Results
have shown that the proposed method is computationally efficient, accurate and robust. The general framework of this method
can be applied ton-dimensional image correlation systems that solve for multi-dimension vector fields. 相似文献
65.
66.
In speckle photograph technology, to determine the displacement of the points on the surface of the measured body, the conventional
method is to put the film which has recorded the speckle patterns before and after displacement into a system of optical Fourier
transforms. After filtering on the spectrum plane, the experimentalist can obtain the displacement information from the interference
pattern on the image plane. Instead of setting up a complex optical Fourier transform system, we consider the speckle field
as a light intensity function of 2 dimensions, which will change with different positioning of the points. After working on
the function's discrete Fourier transform (DFT), according to one of the properties of Fourier transformation, the displacement
of the measured point is involved in the phase of its spectrum. Having extracted the displacement information from the phase,
we obtain the distribution of the displacement field. In this paper, we deduce the expression for the displacement field by
using Fourier transformation under conditions of both equal and unequal displacement and show their applications. 相似文献
67.
用PVDF实时测量激光诱导的冲击波压力 总被引:4,自引:1,他引:4
本文用自己研制的PVDF(polyvenylidenfluoride)压电传感器测量了0.2mm厚铝和2.08mm厚T300/环氧复合材料中激光诱导的冲击波压力,首次获得了这些材料中激光冲击波压力的时间演化波形。实验在中国科大强激光实验室的YAG脉冲激光器上进行,激光波长1.06μm,脉宽33ns,靶面平均功率密度为109W/cm2量级。从所得数据估计了表面入射压力,其值与已有结果符合良好。实验结果证实,PVDF压电传感器频响高,量程宽,多次使用重复性好,可有效应用于激光冲击波压力的实时测量 相似文献
68.
单镜头三维粒子成像测速 总被引:2,自引:2,他引:2
本文提出了一种用单镜头进行三维流场测量的方法,建立了包括摄录系统、数字图象处理及识别系统及流动装置的3D-SCPIV系统。完成了现有条件下的原理性定量测量实验。 相似文献
69.
A method for the detection of small masses with the aid of a longitudinally vibrating band is described and further applications, e.g. for viscosity and humidity measurement are discussed. The complex Young's modulus of the band can also be determined. 相似文献
70.
本文报告了明渠非定常水流垂向结构的实验研究,通过 LDV 激光测速,我们给出了非定常水流的速度削面,湍流度,Eulerian质量输运速度的垂向分布。实验结果表明:在非定常周期很长时非定常流动的速度剖面,湍流强度及其粗糙度的影响基本上与定常流动相一致,当非定常流动为纯往复流动时,存在一个逆时针方向的环流,这种环流有利于底部的质量输运。 相似文献