基于希尔伯特变换的湍流随机相位差解调算法研究

根据大气光学湍流的光纤干涉测量技术原理及其信号表现形式,提出了一种基于希尔伯特(Hilbert)变换的动态相位差解调算法.数值模拟结果表明,该算法能够解调出波形相位差和符合湍流频谱特征的随机相位差,且绝对误差小于10(-3),与相关法的解调结果一致.两者对比分析表明,Hilbert变换算法无需设定相关长度,对信号无平滑...     

数字体图像相关方法中的残余灰度场计算研究

残余灰度场是变形前后数字体图像中对应体素点的灰度之差。在基于有限单元的全局数字体图像相关（DVC）方法中,残余灰度场作为计算区域各体素点匹配质量的目标函数,可直接计算获得,并可用于材料内部损伤演化或裂纹扩展的精细表征。然而,当前广泛使用的基于图像子体块的局部DVC只能获得计算区域内各离散计算点的位移、应变和相关系数信息,无法直接计算区域内各体素点的残余灰度。相较于相关系数和变形信息,残余灰度场可实现逐体素的匹配质量评价,在内部损伤或裂纹扩展的可视化观测和准确定位方面具有显著优势。为能在局部DVC中获得残余灰度场信息,提出一种简单有效的残余灰度场计算方法。该方法基于三维Delaunay四面体剖分算法,并利用有限元框架对局部DVC离散计算结果进行稠密插值,以获取逐体素连续位移场,并将其用于变形体图像校正。模拟和真实实验结果表明,基于局部DVC测量结果后处理计算获得的残余灰度场不仅可以实现精准的损伤定位,还能观测到裂纹形貌以及界面脱黏行为。所提方法弥补了当前局部DVC在精细化匹配质量评价方面的不足,有望拓展该方法在材料和结构内部损伤观测和定位中的应用。     

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To calculate the phase shift, zero-crossing detection, digital correlation method and FFT are commonly used. Tests on the three algorithms show that, they can obtain phase shift accurately in dozens of microseconds delay, but resources and time cost are different. Zero-crossing detection needs more resources, but less time. FFT has large resource occupancy and latency. Digital correlation method is just the opposite to FFT, but detecting phase reverse is difficult.     

高阶色散介质的改进移位算子时域有限差分方法

提出一种适用于高阶Debye,Drude,Lorentz及其混合模型的改进移位算子的时域有限差分(SO-FDTD)方法。从介质极化率函数出发,将其写成一阶或二阶有理分式求和的形式,并在随时间步推进计算的过程中,通过引入中间变量和设置临时变量,克服了常规SO-FDTD将高阶模型直接转化为有理分式所导致的计算复杂性和内存占用量大的问题。同时,改进SO-FDTD方法的时域推进计算步骤具有通用性,克服了常规递归卷积(RC-FDTD)方法对各种高阶模型具有不同计算公式,因而不能形成通用计算程序的问题。最后,通过空气-高阶色散介质界面的反射系数计算验证了算法的有效性和通用性。     

高阶色散介质的改进移位算子时域有限差分方法

提出一种适用于高阶Debye,Drude,Lorentz及其混合模型的改进移位算子的时域有限差分(SO-FDTD)方法。从介质极化率函数出发,将其写成一阶或二阶有理分式求和的形式,并在随时间步推进计算的过程中,通过引入中间变量和设置临时变量,克服了常规SO-FDTD将高阶模型直接转化为有理分式所导致的计算复杂性和内存占用量大的问题。同时,改进SO-FDTD方法的时域推进计算步骤具有通用性,克服了常规递归卷积(RC-FDTD)方法对各种高阶模型具有不同计算公式,因而不能形成通用计算程序的问题。最后,通过空气-高阶色散介质界面的反射系数计算验证了算法的有效性和通用性。     

一种基于数字信号处理技术的改进通用色散介质移位算子时域有限差分方法

借鉴数字信号处理技术中的无限脉冲响应滤波器实现的思想,提出一种适用于通用色散介质的改进移位算子时域有限差分（shift operator finite-difference time-domain,SO-FDTD）方法.与原SO-FDTD方法相比,改进的SO-FDTD方法内存占用减少33%以上,同时计算时间也有所减少.最后通过一阶、二阶色散介质雷达散射截面计算验证了方法的通用性和有效性. 关键词： 时域有限差分 色散介质 移位算子     

Time shift and superposition method for solving transient radiative transfer equation

Due to the long-time transient response of pulse irradiation, the computational time required for solving transient radiative transfer (TRT) is often very long, especially for the case in which the boundary is subjected to continuous pulse train and the geometry is complicated. In addition, sometimes, before actual experiments are carried out, a suitable pulse shape or type often needs to be selected by numerical simulation and comparison. Because the numerical solution of TRT needs to be repeated many times, the selection processes is very time-consuming. In this paper, by considering that the TRT equation and its initial and boundary conditions are linear, a time shift and superposition method is developed for solving TRT equation in non-emitting media, in which only the transient response of a short square pulse needs to be solved, and the solution of TRT under any pulse shape can be constructed by time shift and then superposition using the basis solution of the short square pulse. Three numerical examples are studied to illustrate the peformance of the superposition method in solving TRT problems. The results show that the superposition is effective, accurate and very suitable for solving TRT in the medium subjected to a series of pulse train.     

On the use of the digital image correlation method for heterogeneous deformation measurement of porous solids

In this paper, several crucial issues arising from the application of the digital image correlation (DIC) method to the measurement of heterogeneous deformation of porous solids are discussed. To handle samples with complex geometry, the performance of the two commonly employed DIC methods, namely the subset-based DIC and the finite-element based DIC methods are first evaluated and compared. A combined DIC approach and an adaptive DIC approach suitable for samples with discontinuities/holes are then proposed. Aluminum plates with circular holes subject to compressive loading are employed to evaluate the accuracy of the proposed methods. It has been found that in addition to other factors such as the number of pixels and speckle size, the orientation of the camera lens also plays an important role on the measurement accuracy. A calibration method for the adjustment of camera orientation is proposed, which leads to a good agreement between the experimentally measured displacements and finite element simulation results. Another finding of the presented work is that for relatively stiff specimens, the deformation of the loading system itself must be considered in order to obtain an accurate displacement.     

数字图像相关技术的综合算法及其在断裂力学中的应用

鉴于散斑图的随机噪声和相关搜索运算过程仍是当今影响相关图像技术所获结果精度与计算速度两大有待研究解决的主要问题,提出一种基于小波变换、序惯相似度检测和统计相关算法三者相结合的新算法。其基本原理是应用小波变换对变形前后的散斑图进行滤波平滑处理;利用序惯相似度检测算法进行粗搜索,找到可能的匹配点;在可能的匹配点应用统计相关法进行细搜索,最终找到匹配点的位置。基本实验、计算和应用表明,这种算法在消除噪声和提高运算速度等方面,取得了良好的效果。     

Large deformation measurement scheme for 3D digital image correlation method

Difficulties often arise for digital image correlation (DIC) technique when serious de-correlation occurs between the reference image and the deformed image due to large deformation. An updating reference image scheme could be employed to deal with large deformation situation, however that will introduce accumulated errors. A large deformation measurement scheme, combining improved coarse search method and updating reference image scheme, is proposed in this paper. For a series of deformation images, the correlation calculation begins with a seed point and spreads out. An improved coarse search method is developed to calculate the initial correlation parameters for the seed point, which guarantees that the correlation calculation can be carried out successfully even in large deformation situation. Only for extremely large deformation, the reference image is updated. Using this method, not only extremely large deformation can be measured successfully but also the accumulated error could be controlled. A polymer material tensile test and a foam compression test are used to verify the proposed scheme. Experimental results show that up to 450% tensile deformation and 83% compression deformation can be measured successfully.