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1.
This paper is concerned with small strain measurement utilizing the numerical processing of digital images. The proposed method
has its theoretical basis in digital signal analysis and, from a methodological point of view, it can be considered as an
extension to digital images of the wellknown white light speckle photography technique. That conventional method is based
on the analysis of photographic plates that are exposed twice (before and after the specimen deformation) with the image of
a random speckle pattern that has been previously printed on the test piece surface. The digital speckle correlation advantages
consist of requiring a very simple specimen preparation and, mainly, of allowing the strain field computation just by numerical
elaboration of the acquired images.
In this paper, the theoretical basis of the technique and some valuable improvements to the known analogous methodologies
are presented. Finally, test results for an application of digital speckle correlation are shown and advantages and disadvantages
of the technique are elaborated. In addition, further developments in this area are discussed. 相似文献
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A novel subpixel registration algorithm with Gaussian windows is put forward for accurate deformation measurement in digital image correlation technique. Based on speckle image quality and potential deformation states, this algorithm can automatically minimize the influence of subset sizes by self-adaptively tuning the Gaussian window shapes with the aid of a so-called weighted sum-of-squared difference correlation criterion. Numerical results of synthetic speckle images undergoing in-plane sinusoidal displacement fields demonstrate that the proposed algorithm can significantly improve displacement and strain measurement accuracy especially in the case with relatively large deformation. 相似文献
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A genetic algorithm particle pairing technique for 3D velocity field extraction in holographic particle image velocimetry 总被引:1,自引:0,他引:1
This research explores a novel technique, using Genetic Algorithm Particle Pairing (GAPP) to extract three-dimensional (3D)
velocity fields of complex flows. It is motivated by Holographic Particle Image Velocimetry (HPIV), in which intrinsic speckle
noise hinders the achievement of high particle density required for conventional correlation methods in extracting 3D velocity
fields, especially in regions with large velocity gradients. The GA particle pairing method maps particles recorded at the
first exposure to those at the second exposure in a 3D space, providing one velocity vector for each particle pair instead
of seeking statistical averaging. Hence, particle pairing can work with sparse seeding and complex 3D velocity fields. When
dealing with a large number of particles from two instants, however, the accuracy of pairing results and processing speed
become major concerns. Using GA’s capability to search a large solution space parallelly, our algorithm can efficiently find
the best mapping scenarios among a large number of possible particle pairing schemes. During GA iterations, different pairing
schemes or solutions are evaluated based on fluid dynamics. Two types of evaluation functions are proposed, tested, and embedded
into the GA procedures. Hence, our Genetic Algorithm Particle Pairing (GAPP) technique is characterized by robustness in velocity
calculation, high spatial resolution, good parallelism in handling large data sets, and high processing speed on parallel
architectures. It has been successfully tested on a simple HPIV measurement of a real trapped vortex flow as well as a series
of numerical experiments. In this paper, we introduce the principle of GAPP, analyze its performance under different parameters,
and evaluate its processing speed on different computer architectures.
Received: 7 September 1997/Accepted: 3 February 1998 相似文献
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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
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基于遗传算法的GPS姿态测量技术 总被引:5,自引:0,他引:5
提出了一种新的GPS载波相位姿态测量搜索技术。它是一种基于遗传算法(Genetic Algorithm,GA),采用二值编码,最佳保留(Elitist Model)选择机制和模糊度函数法的适应度函数,并以分级方式(粗搜索GA和精搜索GA)进行最优搜索,实现GPS姿态快速测定。试验结果表明:该方法对复杂搜索之间的搜索效率高,速度快,并且对周跳不敏感。 相似文献
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Measurement of out-of-plane deformation is significant to understanding of the deflection mechanisms of the plate and tube structures.In this study,a new surface contouring technique with color structured light is applied to measure the out-of-plane deformation of structures with one-shot projection.Through color fringe recognizing,decoding and triangulation processing for the captured images corresponding to each deformation state,the feasibility of the method is testified by the measurement of elastic deflections of a flexible square plate,showing good agreement with those from the calibrated displacement driver.The plastic deformation of two alloy aluminum rectangular tubes is measured to show the technique application to surface topographic evaluation of the buckling structures with large displacements. 相似文献
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Micro- and Nanoscale Deformation Measurement of Surface and Internal Planes via Digital Image Correlation 总被引:1,自引:0,他引:1
T. A. Berfield J. K. Patel R. G. Shimmin P. V. Braun J. Lambros N. R. Sottos 《Experimental Mechanics》2007,47(1):51-62
The digital image correlation (DIC) technique is successfully applied across multiple length scales through the generation
of a suitable speckle pattern at each size scale. For microscale measurements, a random speckle pattern of paint is created
with a fine point airbrush. Nanoscale displacement resolution is achieved with a speckle pattern formed by solution deposition
of fluorescent silica nanoparticles. When excited, the particles fluoresce and form a speckle pattern that can be imaged with
an optical microscope. Displacements are measured on the surface and on an interior plane of transparent polymer samples with
the different speckle patterns. Rigid body translation calibrations and uniaxial tension experiments establish a surface displacement
resolution of 1 μm over a 5×6 mm scale field of view for the airbrushed samples and 17 nm over a 100×100 μm scale field of
view for samples with the fluorescent nanoparticle speckle. To demonstrate the capabilities of the method, we characterize
the internal deformation fields generated around silica microspheres embedded in an elastomer under tensile loading. The DIC
technique enables measurement of complex deformation fields with nanoscale precision over relatively large areas, making it
of particular relevance to materials that possess multiple length scales. 相似文献
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通过对散斑计量法原理分析、数学描述及观测实例的论述,证明激光散斑法是研究煤矿地下结构物相似模型变形状态的一种新的无损检测技术,若采用白光作为光源,该项技术可用于二维变形场的实地测试。 相似文献
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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
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Two new techniques making use of the scattered-light speckle pattern have been developed which yield the displacements on an arbitrary interior plane of a 3-D body. When a sheet of coherent light passes through a transparent 3-D body, a small fraction is scattered. This scattered light produces a speckle pattern in an imaging system. By recording two superimposed images of this speckle pattern, one before and one after body deformation, the displacements on the interior illuminated plane can be found. The technique of scattered-light photography uses a single illuminating beam and is sensitive to displacements greater than one speckle diameter, approximately 3 μm. Scattered-light speckle interferometry uses two illuminating beams and is sensitive to displacements greater than one half the wavelength of light being used, approximately 0.2 μm. With both techniques, the double-exposed speckle photograph is optically processed to yield displacement information. With both techniques, the maximum displacement measurable is limited by correlation requirements between the two speckle patterns. Experimental results are presented demonstrating the two new techniques. 相似文献
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A technique has been developed for measuring three-dimensional instantaneous drop profiles on rough surfaces. The surface
is illuminated using a laser and images are captured of the resulting speckle pattern with and without the drop in place.
The analysis consists of finding the contact line, measuring the deformation of the speckle field caused by refraction of
light at the drop surface, then reconstructing the drop using simulated annealing optimization to find the drop shape whose
shift vector field best matches the one measured. An error analysis of the technique was performed using a Monte Carlo technique
and comparisons to sideview drop images for a large sample of drops. Mean contact angle measurement error was found to be
−1.6° with a 1 − σ error bound of −6.9°, +2.0°. 相似文献
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Electronic Speckle Pattern Interferometry (ESPI) provides a sensitive technique for measuring surface deformations. The technique
involves comparison of the speckle phase angles within surface images measured before and after material deformation. This
phase angle comparison requires that the speckle positions be consistent in all images. A lateral shift between image sets
of just one pixel substantially degrades ESPI measurements, while a shift of two or more pixels typically causes complete
decorrelation and compromises the measurement entirely. To prevent such rigid body motions, the specimen and the optical system
must be rigidly fixed. This requirement typically impedes use of the ESPI method in applications outside laboratories or where
it is necessary to remove the specimen from the optical setup between ESPI measurements. Here, Digital Image Correlation (DIC)
is used to track speckle motion caused by specimen displacement between ESPI phase stepped image sets. The measured image
set can then be mathematically shifted to restore the original speckle locations, thereby recorrelating the ESPI measurement.
Examples are presented where ESPI measurements are successfully made with specimen shifts over 60 pixels. 相似文献
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S. Yoshida I. Muhamed M. Pardede R. Widiastuti Muchiar B. Siahaan A. Kusnowo 《Theoretical and Applied Fracture Mechanics》1997,27(2):137
Deformation and fracture of aluminum alloys are studied using a unique optical technique. This technique is based on a new optical pattern that we recently discovered in a fringe system generated by speckle pattern interferometry. The investigation has revealed that the optical pattern represents a band structured deformation called the mesoband which is substantially related to stress concentration. Described in detail are the Characteristics of this optical pattern; they are explained in connection with the development of plastic deformation and fracture behavior. Several features of this optical pattern are presented that manifest some important mechanical states of the material in the prefracture stage and they can be used to predict the location and timing of a fracture. 相似文献
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Electronic shearography (ES), a laser interferometry technique, has the potential for large-scale structural inspection and
for identifying cracks and strain anomalies. A system based on this technology could possibly be used for noninvasive inspection
of structures with high insensitivity and robustness. One major problem is the existence of largerigid body motions in typical
engineering structures such as bridges and high-rise buildings. These rigid-body motions are large enough to cause a complete
decorrelation of the characteristic speckle pattern that is obtained by illuminating the object surface. This nullifies any
possibility of interference between speckled images obtained at different stages of loading, as is necessary for interferometry
applications. A systematic study was conducted to characterize the speckle pattern obtained from typical civil structures
as a function of the illumination and imaging system. Experiments were carried out to quantify speckle decorrelation as a
function of object motion and instrumentation characteristics. A fracture mechanics based finite element (FEM) analysis was
carried out on an existing fractured bridge to determine the strains and displacements. The results of these studies were
subsequently used to define the parameters of a structural inspection system based on ES for field applications. 相似文献
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《Comptes Rendus de l'Académie des Sciences》2001,329(12):897-900
From kinematic observations by granularity in whiting light mode based on a technique of digital speckle images correlation, the behaviour in tension of a reactive powders concrete is studied. The measures show several localisation areas of the deformation fields and the role of the fibres in the transmission of the stresses in the neighbourhood of a damaged area. 相似文献
20.
基于时序变形预测的数字图像相关加速方法 总被引:1,自引:0,他引:1
利用数字图像相关求解连续变形物体的位移场和应变场时,会遇到处理速度非常慢的问题,原因是相关算法计算量大且忽略了物体在时间轴上的变形规律。本文提出了一种基于变形预测的数字图像相关方法,该方法利用物体在时间轴上的变形规律,通过已经得到的变形值来预测后面时刻的变形初值。首先分析了物体在时间轴上的变形规律,然后结合实际应用对其进行修正,得到物体下一步变形的初值,最后通过NR方法(Newton-Raphson Method)得到物体的位移场和应变场。通过计算机模拟和金属试件拉伸实验并结合GPU(Graphic Processing Unit)编程验证了该方法的有效性。计算机模拟和金属试件拉伸实验的计算结果表明,该方法能够在计算精度保持不变的情况下,使计算速度提高4~7倍。 相似文献