Development and assessment of a single-image fringe projection method for dynamic applications

A single-image fringe projection profiling method suitable for dynamic applications was developed by combining an accurate camera calibration procedure and improved phase extraction procedures. The improved phase extraction process used a modified Hilbert transform with Laplacian pyramid algorithms to improve measurement accuracy. The camera calibration method used an accurate pinhole camera model and pixel-by-pixel calibration of the phase-height relationship. Numerical simulations and controlled baseline experiments were performed to quantify key error sources in the measurement process and verify the accuracy of the approach. Results from numerical simulations indicate that the resulting phase error can be reduced to less than 0.02 radians provided that parameters such as fringe spacing, random measured intensity noise, fringe contrast and frequency of spatial intensity noise are carefully controlled. Experimental results show that the effects of random temporal and spatial noise in typical CCD cameras for single fringe images limits the accuracy of the method to 0.04 radians in most applications. Quantitative results from application of the fringe projection method are in very good agreement with numerical predictions, demonstrating that it is possible to design both a fringe projection system and a measurement process to achieve a prespecified accuracy and resolution in the point-to-point measurement of the spatial (X, Y, Z) positions.     

Estimating deflection of a simple beam model using fiber optic bragg-grating sensors

In this paper, we develop a method to estimate the bridge deflection using fiber optic Bragg-grating (FBG) strain sensors. For most structural evaluation of bridge integrity, it is very important to measure the geometric profile, which is a major factor representing the global behavior of civil structures, especially bridges. In the past, because of the lack of appropriate methods to measure the deflection curve of bridges on site, the measurement of deflection has been restricted to just a few discrete points along the bridge, and the measuring points have been limited to the locations installed with displacement transducers. However, by applying classical beam theory, a formula is rearranged to estimate the continuously deflected profile by using strains measured directly from several points. In addition, FBG strain sensors, which are electromagnetic, noise-free and multipoint measurable, are employed to obtain flexural strains more accurately and stably. The regression analysis is performed to obtain a strain function from the measured strain data. Finally, the deflection curve can be estimated by applying the strain function to the formula. An experimental test has also been carried out to verify the developed method.     

面载荷识别的TSVD正则化方法

线性系统的响应可以表示为单位脉冲响应函数与动态载荷的卷积分,经离散后得到载荷识别反问题。引入TSVD正则化方法处理反问题的不适定性,对不同噪声的实测响应进行了面载荷的反演求解,并对识别精度做出了分析。算例表明,TSVD正则化方法对响应误差的适应性强,识别精度高。     

Surface profiling using sequential sampling and inverse methods. Part I: Mathematical background

A novel method is presented for measuring the height profile of the surface of an object, even in the presence of relative motion between the surface and the height sensors. The method involves making height measurements of the surface using several sensors arranged along the scanned surface. The surface profile and the relative motions are mathematically separated by observing that the surface features appear sequentially among the sensor data, while the relative motions appear simultaneously. The proposed linear inverse technique overcomes several limitations of existing profiling methods based on curvature measurements. In contrast with other inverse calculations, the results are quite stable, with noise in the results only about twice the measurement noise. Regularization is introduced as a means of smoothing noise and for achieving solutions for ill-posed cases. This paper focuses on the profile calculation of one-sided objects, and initially uses the assumption that the rigid relative motion between object and sensors is purely translational.     

Effect of the measurement volume in turbulent pipe flow measurement by the ultrasonic velocity profile method (mean velocity profile and Reynolds stress measurement)

 The ultrasonic velocity profile measurement method has some favorable advantages over the conventional flow measurement methods, such as measurement of the instantaneous velocity profile over the measuring line and its applicability to opaque liquids. The method has another advantage of being non-intrusive. Hence, it is applicable to various flow conditions, although it requires a relatively large measurement volume. In this paper, the effects of the measurement volume on the mean velocity profile and the Reynolds stress measurement have been investigated for fully developed turbulent flows in a vertical pipe. The results were then compared with data obtained by direct numerical simulation. Received: 9 March 2000 / Accepted: 27 March 2001 Published online: 29 November 2001     

势问题的重构核粒子边界无单元法

将重构核粒子法和势问题的边界积分方程方法结合,提出了势问题的重构核粒子边界无单元法. 推导了势问题的重构核粒子边界无单元法的公式,研究其数值积分方案,建立了重构核粒子边界无单元法的离散化边界积分方程,并推导了重构核粒子边界无单元法的内点位势的积分公式. 重构核粒子法形成的形函数具有重构核函数的光滑性,且能再现多项式在插值点的精确值,所以该方法具有更高的精度. 最后给出了数值算例,验证了所提方法的有效性和正确性. }      

基于新息自适应卡尔曼滤波算法的多类型结构响应重构

为改善传统卡尔曼滤波KF(Kalman filter)算法在过程噪声方差和测量噪声方差未知的情况下响应重构精度降低甚至发散的问题，提出了一种基于新息自适应卡尔曼滤波IAKF(innovation-based adaptive Kalman filter)算法的多类型响应重构方法。首先根据新息统计特性对卡尔曼滤波增益和状态估计误差协方差矩阵进行实时自适应调整；然后利用有限测点的加速度传感器的测量数据，结合模态法对结构各个位置的加速度、速度、位移以及应变进行响应重构；最后对起重机桁架和简支梁分别进行数值模拟和试验分析。结果表明，该方法能够有效地调整过程噪声方差并估计测量噪声方差，未测点的重构响应时程曲线与计算响应或测量响应时程曲线吻合良好。     

A Finite Element-based Heuristic Estimation of Local Preform Permeability for Resin Transfer Molding

Uniformity of fabrics significantly affects the resin flow behavior in the resin transfer molding (RTM) process. Due to fabric defects or improper fiber preform preparation/loading, non-uniformity in fabric structure frequently occurs in RTM processing and creates local permeability variations. Such variations often lead to unbalanced resin flow patterns and thus result in defects of finished composite parts. In RTM process modeling, an accurate estimation of the whole field permeability profile of the fiber preform is critical for predicting resin flow pattern correctly. In this article, a finite element-based heuristic computing method is introduced for estimating the in situ whole-field isotropic permeability profile of the preform using a steady flow of gas. Compared with conventional approaches, this method is effective in measuring local permeability variations and applicable to molds with complex 2-D geometries, as well as diverse injection strategies. Several case studies were presented with experimental designs and numerical computations to illustrate the effectiveness and efficiency of the method.     

基于提升小波变换和互相关函数的梁式桥损伤检测

为了有效地提取梁式桥的损伤特征,提出了一种将提升小波变换与互相关函数幅值向量相结合的损伤识别的方法。首先利用提升小波变换将车载作用下梁桥结构的加速度响应分解到单阶模态上,再对提升重构后得到的第一阶响应进行互相关处理,利用提出的损伤指标来进行损伤定位。通过数值仿真和模拟实验,验证了方法的有效性,讨论了噪声及测点稀疏对识别结果的影响,结果表明该方法具有良好的噪声鲁棒性。另外,在综合考虑经济性和识别结果准确性的情况下,给出了合理的测点布置方式。     

畸变信号的反演修正在同步测压中的应用

本文说明了同步测压所包含的主要内容以及一套实用的同步测压系统的组成,分析了通过传压管道传递的压力信号产生畸变的原因,指出对畸变信号进行反演修正是同步测压过程中必不可少的关键环节。利用频域修正的方法可以对压力分布同步测量中的畸变信号进行反演,以消除输出信号的幅值误差和相位差,保证各个测压通道得到的信号在时间上具有良好的同步性。这样就可以通过对脉动压力分布进行面积加权积分,得到脉动气动力的时间历程。在对畸变信号进行反演修正时,得到测压系统的频率响应函数是关键,本文介绍了利用比较法来标定频响曲线的装置和方法。并通过实验演示了反演修正的效果,表明本文所采用的同步测压装置具有非常好的同步性能。     

Variation method for acoustic wave imaging of two dimensional targets

IntroductionAcousticwaveimaginghasagreatpotentialtobeappliedtonondestructivetesting ,medicalimaging ,geologicalprospectingandmaterialscienceetc.,andvariousimagingmethods,eachpossessingitsownpeculiarities,havebeenproposed .In 1 992 ,Moghaddam[1]putforwarda…     

Displacement fields denoising and strains extraction by finite element method

Optical full-field measurement methods are now widely applied in various domains. In general, the displacement fields can be directly obtained from the measurement, however in mechanical analysis strain fields are preferred. To extract strain fields from noisy displacement fields is always a challenging topic. In this study, a finite element method for smoothing displacement fields and calculating strain fields is proposed. An experimental test case on a holed aluminum specimen under tension is applied to validate this method. The heterogeneous displacement fields are measured by digital image correlation (DIC). By this proposed method, the result shows that the measuring noise on experimental displacement fields can be successfully removed, and strain fields can be reconstructed in the arbitrary area.     

Parametrically Excited Vibration of a Timoshenko Beam on Random Viscoelastic Foundation jected to a Harmonic Moving Load

The vibration response of a Timoshenko beam supported by a viscoelastic foundation with randomly distributed parameters along the beam length and jected to a harmonic moving load, is studied. By means of the first-order two-dimensional regular perturbation method and employing appropriate Green's functions, the dynamic response of the beam consisting of the mean and variance of the deflection and of the bending moment are obtained analytically in integral forms. Results of a field measurement for a test track are utilized to model the uncertainty of the foundation parameters. A frequency analysis is carried out and the effect of the load speed on the response is studied. It is found that the covariance functions of the stiffness and the loss factor both have the shape of an exponential function multiplied by a cosine function. Furthermore, it is shown that in each frequency response there is a peak value for the frequency, which changes inversely with the load speed. It is also found that the peak value of the mean and also standard deviation of the deflection and bending moment can be a decreasing or increasing function of the load speed depending on its frequency. An erratum to this article is available at .     

SH波与功能梯度材料静止裂纹的相互作用

利用功能梯度材料剪切模量和密度的指数模型，利用积分变换－积分方程方法，对无限大体SH波作用下的功能梯度材料理解纹进行了求解。通过理论分析给出了裂纹尖端的动应力强度因子，通过数值计算给出了材料的剪切模量梯度，频率对动应力强度因子的影响。     

METHOD OF GREEN＇S FUNCTION OF CORRUGATED SHELLS

By using the fundamental equations of axisymmetric shallow shells of revolution, the nonlinear bending of a shallow corrugated shell with taper under arbitrary load has been investigated. The nonlinear boundary value problem of the corrugated shell was reduced to the nonlinear integral equations by using the method of Green＇s function. To solve the integral equations, expansion method was used to obtain Green＇s function. Then the integral equations were reduced to the form with degenerate core by expanding Green＇s function as series of characteristic function. Therefore, the integral equations become nonlinear algebraic equations. Newton＇ s iterative method was utilized to solve the nonlinear algebraic equations. To guarantee the convergence of the iterative method, deflection at center was taken as control parameter. Corresponding loads were obtained by increasing deflection one by one. As a numerical example,elastic characteristic of shallow corrugated shells with spherical taper was studied.Calculation results show that characteristic of corrugated shells changes remarkably. The snapping instability which is analogous to shallow spherical shells occurs with increasing load if the taper is relatively large. The solution is close to the experimental results.     

用有限积分计算曲率复杂分布下的结构挠度

有限积分法是Brown和Trahair在求解微分方程时采用的数值解法, 其核心环节是已知函数z= z(x)的导函数z′ =z′(x)的某些值的情况下数值分析z的方法. 由曲率φ计算挠度, 实质意义上是由z″计算z的数学问题. 基于有限积分法给出的z与z″之间及z′与z″之间的数值关系, 通过矩阵运算推导得到了挠曲矩阵,通过引入转换式φ= -z″得到了曲率挠度关系式, 讨论了几种常见边界条件下的曲率挠度关系, 提出了曲率复杂分布情况下结构挠度计算的有限积分方法.     

变刚度梁挠度曲线的Green函数法求解

在变刚度梁的线弹性问题中,求解梁受静力荷载的挠度曲线常用解法有积分法与单位荷载法.本文从变刚度梁挠度曲线的微分方程出发,给出了变刚度梁挠度曲线的Green函数法解答,并分析了该解法的优点.从推导结果可以看到,本文提出的公式具有统一、精确、简洁、适合电算的特点,在编制杆系结构计算软件中将具有重要应用价值.     

简支梁振台的理论解及位移测试

利用由机械振动理论推导出的等截面简支梁的理论解,推导出了带集中质量的简支梁振动台的理论解,并通过分析动态条件下简支梁的位移与应变之间的关系,证明了:在动态条件下梁的位移与应变之间存在很好的正比关系。利用梁的位移与应变之间正比关系,如果在梁上适当位置粘贴应变片,通过测试应变就能准确地测得梁的动态位移。本文通过实例证明了该方法确实可行,理论解与实测结果非常吻合。这为简支梁的动态测试提供了有效而简便的方法。     

超静定梁?柱的解析解研究

本文采用渐进积分法研究了超静定梁?柱的弯曲问题. 首先建立超静定梁?柱的四阶挠度微分方程, 考虑到边界条件和连续光滑条件, 采用连续分段独立一体化积分法求解得到了挠度的精确解析解. 为了满足工程设计需要, 构造了超静定梁?柱的四阶挠度微分迭代方程, 选取无轴向力作用时超静定梁的挠曲线作为梁的初函数, 将初函数代入梁的四阶挠度微分迭代方程进行积分, 利用边界条件和连续光滑条件确定积分常数, 得到下一次迭代挠度函数, 依次进行迭代积分运算. 计算出了最大挠度、最大转角和最大弯矩等用轴向力放大系数表示的多项式解析函数解. 本文选取了两种边界条件下受分布力作用的超静定梁?柱进行分析, 计算结果表明, 当超静定梁?柱所受的轴向力小于欧拉临界力的1/2时, 迭代六次误差就可以控制在1%以内; 不仅梁?柱最大位移和最大内力的大小随轴向力的增大而增大, 而且其位置也随轴向力的增大而发生迁移. 本文的研究对揭示轴向力对超静定梁?柱变形和内力的影响有重要意义, 为超静定梁?柱的实际设计提供了一定的理论基础.      

加窗傅里叶滤波和相干增强扩散在条纹去噪中的比较分析

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。