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1.
用曲线大窗口平滑散斑条纹图的方法研究 总被引:5,自引:0,他引:5
提出一种计算条纹方向的简单算法,以及通过条纹方向图获得沿条纹方向的曲线窗口并对散斑条纹图进行曲线大窗口滤波的方法.实验表明此方法较好地消除了散斑条纹图的噪声,同时尽量减小了对条纹结构的损害.为从单幅散斑条纹图中应用条纹中心线法或全灰度法进一步提取相位场的后处理,奠定了良好的基础. 相似文献
2.
对图像进行滤波或称平滑是干涉条纹图像处理中的一项重要工作。一幅未经处理的原始图像或多或少存在着不同程度的噪声干扰,特别是散斑和Insar干涉条纹图,信噪比很低,难以处理。本文针对光测力学中光学干涉方法得到的条纹图,提出了一种新的滤波方法条纹等值线窗口滤波,并对这种滤波方法进行了研究讨论,提出了几种确定等值线窗口的不同方法。这种滤波方法根据干涉条纹图不同断面上灰度分布的不同特点,选择沿条纹走向的条纹等值线窗口进行滤波,在最大消除条纹图噪声的同时,也能保证对条纹损伤最小。摄像测量技术正在迅速发展和得到广泛应用,在国防试验和航天飞行任务中发挥着不可替代的作用。本文也介绍了作者近年来在该领域所做的应用研究,包括在火箭、导弹发射试验,冲击、碰撞等过程中的动态目标运动测量;针对航天航空和力学工程领域的视频图像实时分析;飞行器三维运动测量;基于投影条纹的物体三维形貌精密测量方法研究;以及对接航天器位置和姿态的实时测量。在这些应用中都实现了高精度测量。 相似文献
3.
This paper proposes a specific application of the approach recently proposed by the authors to achieve an autonomous and robust
adaptive interrogation method for PIV data sets with the focus on the determination of mean velocity fields. Under circumstances
such as suboptimal flow seeding distribution and large variations in the velocity field properties, neither multigrid techniques
nor adaptive interrogation with criteria based on instantaneous conditions offer enough robustness for the flow field analysis.
A method based on the data ensemble to select the adaptive interrogation parameters, namely, the window size, aspect ratio,
orientation, and overlap factor is followed in this study. Interrogation windows are sized, shaped and spatially distributed
on the basis of the average seeding density and the gradient of the velocity vector field. Compared to the instantaneous approach,
the ensemble-based criterion adapts the windows in a more robust way especially for the implementation of non-isotropic windows
(stretching and orientation), which yields a higher spatial resolution. If the procedure is applied recursively, the number
of correlation samples can be optimized to satisfy a prescribed level of window overlap ratio. The relevance and applicability
of the method are illustrated by an application to a shock-wave-boundary layer interaction problem. Furthermore, the application
to a transonic airfoil wake verifies by means of a dual-resolution experiment that the spatial resolution in the wake can
be increased by using non-isotropic interrogation windows. 相似文献
4.
0Introduction Phaseunwrappingisrelatedtomanyresearchdisciplinesincludingopticalmetrology,synthetic apertureradar,acousticimaging,magneticresonanceimaging(MRI)andmicrowaveinterferometry.AnexcellenttextbookbyGhigliaandPritt[1]presentedthefundamentaltheoryan… 相似文献
5.
0Introduction Phaseunwrappingisrelatedtomanyresearchdisciplinesincludingopticalmetrology,synthetic apertureradar,acousticimaging,magneticresonanceimaging(MRI)andmicrowaveinterferometry.AnexcellenttextbookbyGhigliaandPritt[1]presentedthefundamentaltheoryandvariousalgorithms ofphaseunwrapping.Thispaperwillfocusonasocalledquality guidedphaseunwrappingapproach.Inthisapproach,aqualitymapgeneratedbyacertainphasequalityevaluationcriterionisincorporated toguidetheunwrappingprocess.Attheprimitivesta… 相似文献
6.
频率向导的单幅散斑条纹图位相提取方法 总被引:1,自引:0,他引:1
提出一种基于条纹频率向导的单幅散斑条纹图位相提取技术,可对一般的散斑条纹图进行自动化位相提取. 该方法利用加窗傅里叶运算求得散斑条纹图的条纹频率,并在条纹频率的向导下对散斑条纹图的位相进行提取. 数值模拟和实验结果证实了这一方法的有效性. 相似文献
7.
一种通过条纹方向图提取散斑条纹中心线的方法 总被引:3,自引:2,他引:1
在光测力学中,如何从单幅散斑干涉条纹图中消除散斑噪声,高精度自动提取相位信息,是一项较困难的工作。本文提出了一种计算条纹方向的简单算法,以及通过条纹方向图提取散斑条纹中心线的方法。实验表明此方法对高噪声的散斑条纹图非常有效。 相似文献
8.
在光测力学中,条纹图正则化是进一步提取条纹位相信息的重要基础。对于散斑条纹图来说,正则化的过程还需能够有效地抑制散斑噪声。本文提出一种基于多通道滤波技术的散斑条纹图正则化方法。通过使用多个Gabor滤波通道对散斑条纹图进行滤波,并且引入与条纹对比度有关的权重因子把各个滤波通道的滤波结果叠加起来,最终得到滤除了散斑噪声的正则化条纹图。数值模拟和实验结果表明,该方法在将散斑条纹图正则化的同时能够有效地滤除条纹图中的散斑噪声,为进一步提取条纹位相奠定了良好的基础。 相似文献
9.
The isochromatic fringe patterns surrounding an intersonically propagating interface crack are developed and characterized using the recently developed stress field equations. A parametric investigation is conducted to study the influence of various parameters such as the crack-tip velocity and the contact coefficient on the isochromatic fringe patterns. It has been observed that the crack-tip velocity has a significant effect on the size and shape of isochromatic fringe patterns. The contact coefficient, on the other hand, does not affect the fringe pattern significantly. The paper also presents a numerical scheme to extract various parameters of interest such as the series coefficients of the stress field, the contact coefficient and the dissipation energy. The results show that the crack growth is highly unstable in the intersonic regime, and the energy dissipation decreases monotonically with increasing crack-tip velocity. The experimental data fit well with the recently proposed fracture criterion for intersonic interfacial fracture. 相似文献
10.
数字剪切散斑相关条纹图的形成及其分析 总被引:3,自引:1,他引:3
本文提出了用线性相关计算形成高可见度的数字剪切散斑相关条纹图的方法,为相关条纹图的自动分析奠定了良好的基础。文中还推导了附加位相与物光反射镜转角的关系,使精确地计算附加位相成为可能。同时还介绍了任意附加位相的三步相移技术。最后给出了用线性相关计算法形成的相关条纹图及计算出的位相图。 相似文献
11.
光学干涉测量具有非接触、高精度和全场测量的优点,能对形变、折射率、位移等信息进行测量。噪声滤除是光学干涉测量产生的条纹图像处理的一个关键问题。加窗傅里叶滤波(Windowed Fourier Filtering,WFF)与自适应加窗傅里叶滤波(Adaptive Windowed Fourier Filtering,AWFF)是有效的频域去噪算法。相干增强扩散(Coherence Enhancing Diffusion,CED)则是基于偏微分方程的空域去噪算法。针对条纹去噪问题,比较了WFF、AWFF和CED在不同密度和不同噪声类型的条纹图上的表现,分析了它们的适用条纹类型。 相似文献
12.
An interferometric-fiber-optic sensor and an efficient fringe-detection scheme are described. The fiberoptic interferometer
consists of two fibers; they are labeled the reference fiber and the sensing fiber. The reference fiber is arranged in a circular
pattern, whereas the sensing fiber is arranged in an ‘S’ pattern. These fibers are exposed to the same strain field and each
experiences a strain-induced phase shift. A difference in the phase shift between the two fibers indicates a change in strain.
The strain-induced phase difference causes the interferometrically produced fringes to shift spatially. Analysis shows that
the number of fringes passing an arbitrary point on a screen (the detection point) is linearly related to the strain in the
fiber. In this analysis, the strain sensor is assumed to be perfectly bonded so that the fibers experience the same strain
field as the specimen. It is further assumed that the sensor covers a sufficiently small area so that the strain can be considered
constant over the entire strain sensor. Also, the phase change produced by transverse strain components (with respect to the
fiber) induced by the specimen is assumed negligible compared to the phase changes attributable to the axial strain components.
A cantilever beam was used as a specimen. Experimentally determined strains correlated well with the strains predicted by
beam theory.
The fringe-detection scheme described is a high-speed fringe counter. The speed of this counter is necessary to detect vibrational
phase noise which is invisible to the human eye. Two photodiodes detect the fringes, and a logic circuit counts the fringe
shifts, both strain and noise induced. Since noise is random in nature, it can be averaged out. This fringe detector exhibits
good sensitivity and is the key to moving the sensor from the laboratory to the field. 相似文献
13.
《International Journal of Solids and Structures》2006,43(5):1189-1200
Local deformation field and fracture characterization of mode I V-notch tip are studied using coherent gradient sensing (CGS). First, the governing equations that relate to the CGS measurements and the elastic solution at mode I V-notch tip are derived in terms of the stress intensity factor, material constant, notch angle and fringe order. Then, a series of CGS fringe patterns of mode I V-notch are simulated, and the effects of the notch angle on the shape and size of CGS fringe pattern are analyzed. Finally, the local deformation field and fracture characterization of mode I V-notch tip with different V-notch angles are experimentally investigated using three-point-bending specimen via CGS method. The CGS interference fringe patterns obtained from experiments and simulations show a good agreement. The stress intensity factor obtained from CGS measurements shows a good agreement with finite element results under K-dominant assumption. 相似文献
14.
This paper presents a PIV (particle image velocimetry) image processing method for measuring flow velocities around an arbitrarily
moving body. This image processing technique uses a contour-texture analysis based on user-defined textons to determine the
arbitrarily moving interface in the particle images. After the interface tracking procedure is performed, the particle images
near the interface are transformed into Cartesian coordinates that are related to the distance from the interface. This transformed
image always has a straight interface, so the interrogation windows can easily be arranged at certain distances from the interface.
Accurate measurements near the interface can then be achieved by applying the window deformation algorithm in concert with
PIV/IG (interface gradiometry). The displacement of each window is evaluated by using the window deformation algorithm and
was found to result in acceptable errors except for the border windows. Quantitative evaluations of this method were performed
by applying it to computer-generated images and actual PIV measurements. 相似文献
15.
16.
A method is described for the rapid, accurate determination of residual stresses from a holographic interference fringe pattern.
The pattern is generated by the displacement field caused by localized relief of residual stresses via the introduction of
a small, shallow hole into the surface of a component or test specimen. The theoretical development of the holographic method
is summarized. An example is given showing how the method can be applied to a typical experimentally observed fringe pattern
to determine principal residual stresses and directions. 相似文献
17.
Analysis and treatment of errors due to high velocity gradients in particle image velocimetry 总被引:1,自引:0,他引:1
This paper deals with errors occurring in two-dimensional cross-correlation particle image velocimetry (PIV) algorithms (with window shifting), when high velocity gradients are present. A first bias error is due to the difference between the Lagrangian displacement of a particle and the real velocity. This error is calculated theoretically as a function of the velocity gradients, and is shown to reach values up to 1 pixel if only one window is translated. However, it becomes negligible when both windows are shifted in a symmetric way. A second error source is linked to the image pattern deformation, which decreases the height of the correlation peaks. In order to reduce this effect, the windows are deformed according to the velocity gradients in an iterative process. The problem of finding a sufficiently reliable starting point for the iteration is solved by applying a Gaussian filter to the images for the first correlation. Tests of a PIV algorithm based on these techniques are performed, showing their efficiency, and allowing the determination of an optimum time separation between images for a given velocity field. An application of the new algorithm to experimental particle images containing concentrated vortices is shown. 相似文献
18.
二维相移逻辑云纹法—条纹图全自动处理的一种方法 总被引:1,自引:2,他引:1
本文报告的二维相移逻辑云纹法,可对二维全场条纹图,进行全自动处理。这种方法用了经典云纹的概念,运用了相移的思想,用计算机进行逻辑运算,从而获得了全场条纹图上任意点的信息,为后续的运算提供了方便。这种方法可用于若干种条纹图的处理。 相似文献
19.
《力学快报》2016,(1)
Although the structured light system that uses digital fringe projection has been widely implemented in three-dimensional surface profile measurement, the measurement system is susceptible to non-linear error. In this work, we propose a convenient look-up-table-based(LUT-based) method to compensate for the non-linear error in captured fringe patterns. Without extra calibration, this LUT-based method completely utilizes the captured fringe pattern by recording the full-field differences. Then, a phase compensation map is established to revise the measured phase. Experimental results demonstrate that this method works effectively. 相似文献
20.
基于小波分析的条纹图滤波方法 总被引:2,自引:0,他引:2
本文提出了一种新颖的干涉条纹图非线性滤波方法,可以选择性地在频域图像的不同区域选用不同的滤波方式,在滤掉图像中大部分散斑噪声的同时,能够减少信息的损失,使图像的内部边界仍然保持清晰。文中首先简介了正交小波变换的原理,然后介绍了去除散斑噪声的具体算法,最后给出了计算机模拟去噪声的结果 相似文献