DCM 相位梯度提取技术在光力学图像信息识别中的应用

为解决相位去包裹对光力学图像处理的影响问题,本文将一种直接从数字编码傅立叶变换或相移条纹图中逐相素提取相位梯度的方法应用于光力学图像信息识别中。该方法是一个广泛应用于光纤传感器中的微分正交乘法器(DCM)的正、余弦相位检波技术。这一技术算法简单,不需计算反正切,不受相位去包裹方法标准的限制,非常适于应用在以相位梯度作为最终所需识别的信息的光力学图像处理中。本文以载波等达因条纹图应力场计算及四幅图相移等达因法求板的接触应力为例,对该技术在光力学图像信息识别中的应用进行了论证。     

基于锁相循环投影的物体形貌检测

本文提出将相位锁定循环技术应用于栅线投影方法,将规则栅线投影到物体表面得到变形栅线,用相位锁定循环法解调含有物体表面高度信息的位相。用该法不需传统的相位去包裹,即可完成对二维栅线图扫描,从而确定其相位。通过对典型试件的检测,得到了比较满意的结果。     

三维物体形貌检测图像处理中的小波数字滤波技术

傅里叶变换轮廓术和相移法是投影栅法测物体三维形貌的两种重要方法。相移法需要精密的移相装置,且需采集一幅以上的图像,在应用中受到一定限制。而傅里叶变换轮廓术只需一幅图像便可计算出各点相位值,测量精度高,测量范围广,因而得到广泛运用。最大测量范围受到高度分布h(x,y)在与光栅线垂直向上变化率的限制,即面形变化剧烈的物体易产生相邻谱区的混合,不易测准。本文提出的基于小波数字滤波的傅里叶变换法,可以将物体的可测梯度提高3倍。因为利用小波技术对变形栅线图进行处理后,滤去了直流分量和高频分量,得到的相对栅线图只剩下基频分量。采用小波数字滤波与傅里叶变换轮廓术相结合的方法,用小波变换去除直流成分和高频成分,从而提高了物体的可测精度,降低了对滤波器的设计要求,能较好地将物体的相位信息分离出来。本文给出了这种算法的理论分析和计算机模拟试验的结果。     

单步辛算法的相位误差分析及修正

若一个算法的幅值误差和相位误差都不累加，则该算法就是最理想的算法， 但这样的算法难以构造. 辛几何算法解决了幅值误差的累加问题，但相位误差累加问题仍然 存在. 给出了单步隐式辛算法相位误差的精确估计公式，提出了简单而实用的修正方法. 以 Euler中点隐式辛差分格式为例，针对几个线性动力学系统，对相位误差进行了数值分析和 修正.     

条纹投影法中考虑伽马非线性影响的相移编码去包裹方法

条纹形貌测量方法中广泛存在相位去包裹问题,相移编码去包裹方法兼顾了时间类方法逐点分析的鲁棒性和空间类方法的高效性,但是容易受到投影仪的伽马非线性影响.本文通过使用有限谐波模型近似非线性影响下的条纹图像,得到了一种考虑非线性影响的相移编码去包裹方法,在不增加编码图像数量的条件下能稳健地实现不连续物体的形貌测量,而且有效抑...     

一种不受相位噪声影响的模态参数识别法

本文提出了一种根据幅值频响数据来识别模态参数的频域识别法.该方法首先通过识别幅值频响函数模型来得到传递函数的零点和极点.鉴于不同结构系统可以有完全相同的幅值频响函数,文中提出了由相位频响数据来判定传递函数零点的号性,以唯一确定传递函数,从而消除了相位噪声对模态参数识别结果的影响.作为例子,文中给出了计算机模拟实验例子和滚动轴承支承动态参数识别的应用实例.     

数字全息干涉相位导数计算的研究

应变测量对材料评估与分析非常重要。通过计算数字全息干涉的相位导数可实现应变测量。本文针对数字全息干涉相位导数提取问题,对数字剪切法和基于二维伪维格纳法进行研究。数字剪切法通过对干涉复相量的数字平移实现剪切,确定干涉相位导数,而二维伪维格纳法则通过对干涉复相量的二维伪维格纳分布变换,由变换模极值对应的频域参数确定相位导数。数字剪切法需干涉复相量的数字剪切过程,还需相位去包裹。由于激光散斑噪声的影响,直接数字剪切法处理效果较差,通过对剪切干涉复相量滤波,能较好消除散斑噪声影响。二维伪维格纳法无需数字剪切和相位去包裹,就可同时得到2个方向的干涉相位导数,但处理时间较长,处理效果较差。最后,用数字全息干涉法对四周固定、中心加载铝圆盘进行了实际测量,并分别用数字剪切法和二维伪维格纳法进行了分析。结果表明,滤波数字剪切法处理时间适中,处理效果较好。     

开放剪切流空间全局动力学与空间相位斑图间的关系

开放流动空间动力学可基于两类全局能量关系式进行研究;而空间相位斑图则可通过互谱空间演化加以测定。全局能量关系式以时间Fourier系数的形式建立流场任意两点问速度脉动能量间的关系,籍此可定义全局意义上的线性、非线性和线性一非线性机制。基于轴对称剪切流、变密度轴对称圆射流以及平面对称剪切流的实验发现：轴对称旋涡结构的配对由线性、线性一非线性机制表征,对应有序空间相位斑图;并且能量可通过线性一非线性机制在具有相同相速度的扰动间传递。螺旋结构由线性机制表征,对应有序相位斑图。全局自激励振荡由非线性的能量共振表征,对应无序相位斑图。籍此,有序空间相位斑图对应线性和线性一非线性机制;而混沌相位斑图则对应非线性机制。     

Galileo/GPS组合接收机载波相位定位方法

鉴于载波相位观测量可提供高精度定位信息的特点，采用扩展卡尔曼滤波和载波相位组合观测值相结合的方法，提出了一种适合Galileo／GPS组合接收机的载波相位定位方法。通过扩展卡尔曼滤波给出精确的载波相位不足整周的相位值，并且在模糊度保持为整数的前提下，根据一定的组合标准论述了具有相应特性的组合观测值，给出一些典型的组合，通过这些组合后的观测值可以容易地解算整周模糊度。最后对结果进行了分析。     

基于参考面的包裹次数减少的最小不连续法加速

在投影栅三维形貌测量中,相位解调得到的相位主值包裹在(-π,π)范围内,需要进行相位去包裹处理。Gdeisat提出了基于包裹次数减少的最小不连续相位去包裹加速,但无论是采用频域方法还是空域方法减少相位包裹次数,Gdeisat方法在实际操作中都存在操作复杂,计算量较大,精度有限的问题。针对以上问题,本文提出了一种基于参考面的包裹次数减少的最小不连续相位去包裹算法。首先分别投影和采集参考面和待测物面的变形条纹图,然后由四步相移法进行相位解调得到待测物和参考面的包裹相位;再由待测物和参考面的包裹相位,通过简单的复数除法运算,直接减少待测物包裹相位的包裹次数;最后利用最小不连续法去包裹,得到连续相位。该方法不仅省掉了Gdeisat方法中包裹次数减少的复杂操作,而且能消除测量系统的相位畸变。进行了实验验证,实验结果表明本文方法是可行的。     

A Novel Phase Shifting Technique of Coherent Gradient Sensing Method for Measuring Crack-tip <Emphasis Type="Italic">K</Emphasis>-Dominance

A novel phase shifting method for coherent gradient sensing (CGS) is proposed to automate fringe processing. The phase shifting of CGS interferograms can be simply realized by placing three plane-parallel plates sequentially between the two gratings in the traditional CGS method. The phase shifting method is deduced theoretically and the full-field wrapped phase value can be calculated accurately from four or more interferograms. A calibration test that determines the elasto-optic constant for a polymethyl methacrylate (PMMA) sheet is implemented as a verification experiment. Results show the proposed phase shifting method is valid for transmission CGS measurement. As an application, the proposed phase-shifted CGS method is applied to measure the crack tip K-dominance in a PMMA sheet. In addition, the phase shifting method is shown to be valid for reflective CGS measurement.     

条纹投影形貌测量的品质评估位相展开

0Introduction Phaseunwrappingisrelatedtomanyresearchdisciplinesincludingopticalmetrology,synthetic apertureradar,acousticimaging,magneticresonanceimaging(MRI)andmicrowaveinterferometry.AnexcellenttextbookbyGhigliaandPritt[1]presentedthefundamentaltheoryan…     

Quality Guided Phase Unwrapping for Fringe Projection Profilometry

0Introduction Phaseunwrappingisrelatedtomanyresearchdisciplinesincludingopticalmetrology,synthetic apertureradar,acousticimaging,magneticresonanceimaging(MRI)andmicrowaveinterferometry.AnexcellenttextbookbyGhigliaandPritt[1]presentedthefundamentaltheoryandvariousalgorithms ofphaseunwrapping.Thispaperwillfocusonasocalledquality guidedphaseunwrappingapproach.Inthisapproach,aqualitymapgeneratedbyacertainphasequalityevaluationcriterionisincorporated toguidetheunwrappingprocess.Attheprimitivesta…     

频率向导的单幅散斑条纹图位相提取方法

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.      

Coupling of discrete-element method and smoothed particle hydrodynamics for liquid-solid flows

Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.     

Non-invasive Mechanical Measurement for Transparent Objects by Digital Holographic Interferometry Based on Iterative Least-Squares Phase Unwrapping

A non-invasive measurement method for transparent objects using digital holographic interferometry based on iterative least-squares phase unwrapping is presented. Holograms are captured and processed by digital method. The phase reconstructed from holograms is wrapped. Continual and real phase is obtained by phase unwrapping. In this paper iterative unwrapping of phase difference is combined with least-squares unwrapping to eliminate errors. The relations between the phase variation of object wave and the thickness deformation and stress of transparent object are given. A polymethyl methacrylate (PMMA) specimen with a hole under uniform tensile force is tested by this method. The experimental results are in accordance with the theoretical ones. That means the method is correct.     

Simultaneous velocity field measurements in two-phase flows for turbulent mixing of sprays by means of two-phase PIV

This paper describes a novel derivative of the PIV method for measuring the velocity fields of droplets and gas phases simultaneously using fluorescence images rather than Mie scattering images. Two-phase PIV allows the simultaneous and independent velocity field measurement of the liquid phase droplets and ambient gas in the case of two-phase flow mixing. For phase discrimination, each phase is labelled by a different fluorescent dye: the gas phase is seeded with small liquid droplets, tagged by an efficient fluorescent dye while the droplets of the liquid phases are tagged by a different fluorescent dye. For each phase, the wavelength shift of fluorescence is used to separate fluorescence from Mie scattering and to distinguish between the fluorescence of each phase. With the use of two cross-correlation PIV cameras and adequate optical filters, we obtain two double frame images, one for each phase. Thus standard PIV or PTV algorithms are used to obtain the simultaneous and independent velocity fields of the two phases. Because the two-phase PIV technique relies on the ability to produce two simultaneous and independent images of the two phases, the choice of the labelling dyes and of the associated optical filter sets is relevant for the image acquisition. Thus a spectroscopic study has been carried out to choose the optimal fluorescent dyes and the associated optical filters. The method has been evaluated in a simple two-phase flow: droplets of 30–40 μm diameter, produced by an ultrasonic nozzle are injected into a gas coflow seeded with small particles. Some initial results have been obtained which demonstrate the potential of the method.     

A Cartesian grid method for two‐phase gel dynamics on an irregular domain

We develop a numerical method for simulating models of two‐phase gel dynamics in an irregular domain using a regular Cartesian grid. The models consist of transport equations for the volume fractions of the two phases, polymer network and solvent; coupled momentum equations for the two phases; and a volume‐averaged incompressibility constraint. Multigrid with Vanka‐type box relaxation scheme is used as a preconditioner for the Krylov subspace solver (GMRES) to solve the momentum and incompressibility equations. Ghost points are used to enforce no‐slip boundary conditions for the velocity field of each phase, and no‐flux boundary conditions for the volume fractions. The behavior of the new method, including its rate of convergence, is explored through numerical experiments for a problem in which strong phase separation develops from an initially (almost) homogeneous phase distribution. We also use the method to explore situations, motivated by biology, which show that imposed boundary velocities can cause substantial redistribution of network and solvent. Copyright © 2010 John Wiley & Sons, Ltd.     

Full-field automatic evaluation of an isoclinic parameter in white light

In this paper, a technique for full-field evaluation of the isoclinic parameter is presented. It combines the phase-shifting method with true color imaging technology to minimize the interaction between isoclinic and isochromatic fringes. The paper also shows how the proposed technique can be suitably integrated with known methods for evaluating the retardations. Furthermore, a digital algorithm for filtering wrapped phase data obtained by general phase-shifting techniques is presented.     

A coupled model for simulation of the gas–liquid two-phase flow with complex flow patterns

A new model coupling two basic models, the model based on interface tracking method and the two-fluid model, for simulating gas–liquid two-phase flow is presented. The new model can be used to simulate complex multiphase flow in which both large-length-scale interface and small-length-scale gas–liquid interface coexist. By the physical state and the length scale of interface, three phases are divided, including the liquid phase, the large-length-scale-interface phase (LSI phase) and the small-length-scale-interface phase (SSI phase). A unified solution framework shared by the two basic models is built, which makes it convenient to perform the solution process. Based on the unified solution framework, the modified MCBA–SIMPLE algorithm is employed to solve the Navier–Stokes equations for the proposed model. A special treatment called “volume fraction redistribution” is adopted for the special grids containing all three phases. Another treatment is proposed for the advection of large-length-scale interface when some portion of SSI phase coalesces into LSI phase. The movement of the large-length-scale interface is evaluated using VOF/PLIC method. The proposed model is equivalent to the two-fluid model in the zone where only the liquid phase and the SSI phase are present and to the model based on interface tracking method in the zone where only the liquid phase and the LSI phase are present. The characteristics of the proposed model are shown by four problems.