数字图像相关方法若干关键问题研究进展

本文报道了作者及其所在课题组近期在数字图像相关(DIC)测量方法上取得的重要研究进展。主要包括:(1)通过对DIC方法中反向组合高斯-牛顿算法的理论误差分析,提出了新的理论误差公式,进一步证明了反向组合高斯-牛顿算法在提高计算速度和测量精度方面的综合优势;(2)采用提出的理论误差公式,发展了数字散斑场的优化及制作方法,保证了测量结果的一致性和正确性;(3)基于相机阵列和图像拼接技术,发展了超分辨率数字图像相关方法,大大提高了DIC测量方法的应变测量分辨率;(4)提出了大视场条件下的三维系统标定方法,实现了三维测量系统的外参实时标定和多相机测量系统中相机位姿的自动矫正;(5)研制了便携式原位三维测量仪和多尺度DIC测量系统,实现了三维实时数字图像相关测量,进一步满足了DIC方法在工业在线检测和医学领域中的应用需求。     

MESHLESS METHOD OF DUAL RECIPROCITY HYBRID RADIAL BOUNDARY NODE METHOD FOR ELASTICITY

Combining the radial point interpolation method （RPIM）, the dual reciprocity method （DRM） and the hybrid boundary node method （HBNM）, a dual reciprocity hybrid radial boundary node method （DHRBNM） is proposed for linear elasticity. Compared to DHBNM, RPIM is exploited to replace the moving least square （MLS） in DHRBNM, and it gets rid of the deficiency of MLS approximation, in which shape functions lack the delta function property, the boundary condition can not be applied easily and directly and it＇s computational expense is high. Besides, different approximate functions are discussed in DRM to get the interpolation property, in which the accuracy and efficiency for different basis functions are compared. Then RPIM is also applied in DRM to replace the conical function interpolation, which can greatly improve the accuracy of the present method. To demonstrate the effectiveness of the present method, DHBNM is applied for comparison, and some numerical examples of 2-D elasticity problems show that the present method is much more effective than DHBNM.     

A Procedure for the Accurate Determination of Sub-Core Scale Permeability Distributions with Error Quantification

We present a new method for non-destructively calculating sub-core scale permeability distributions within a core. The new method integrates experimentally measured capillary pressure data and sub-core scale saturation and porosity data collected using a computed tomography-scanner, to construct an accurate and unique sub-core scale permeability distribution. Using this procedure, it is possible to conduct highly refined simulations of core flooding experiments without typical assumptions requiring the core to be homogeneous, or relying on inaccurate porosity-based methods for estimating permeability distributions. The calculation procedure is described and results from two example rock cores are presented, a Berea Sandstone and a sandstone from the Otway Basin Pilot Project in Australia. Drainage coreflooding experiments of carbon dioxide ( $\text{ CO }_{2})$ CO 2 ) injection into water are first conducted on both cores and permeability distributions are calculated using the experimental data. Numerical simulations of the very same experiments are then conducted to demonstrate the accuracy of the calculated sub-core scale permeability distribution. Results from both cores show that the input sub-core scale saturation distributions are predicted with an $R^{2}$ R 2 correlation of greater than 0.93. This is compared to having no correlation when using simple porosity-only based permeability distributions, or assuming homogeneous core properties (Krause et al., SPE J 16(4):768–777, 2011). The uniqueness of the calculated permeability distribution is then demonstrated by calculating permeability distributions for the same core using data collected at different $\text{ CO }_{2}$ CO 2 injection fractional flows. Results show that the two independently calculated permeability distributions agree within the limits of experimental measurement error.     

Numerical modeling of carbon/carbon composites with nanotextured matrix and 3D pores of irregular shapes

A multiscale modeling approach is utilized to evaluate the contribution of irregularly shaped three-dimensional pores to the overall elastic properties of carbon/carbon composites. The degree of anisotropy of a carbon matrix depends on nanotexture, which is defined by manufacturing conditions. Elastic properties of the matrix are predicted assuming a Fisher distribution of orientations of graphene planes with respect to the pyrolytic carbon deposition direction. X-ray computed microtomography is employed to identify pores in a sample of carbon/carbon composite. The pores have highly irregular shapes so that micromechanical modeling based on the analytical solutions of elasticity becomes inapplicable. Thus, the cavity compliance tensor of an individual pore is found numerically by finite element method, and then used in a micromechanical modeling procedure. Examples of pores in isotropic and transversely isotropic pyrolytic carbon matrices are considered. The accuracy of pore approximation by ellipsoidal shapes is evaluated.     

A Semi-analytical Model for Pressure-Dependent Permeability of Tight Sandstone Reservoirs

In tight gas reservoirs, permeability is pressure dependent owing to pore pressure reduction during the life of the reservoir. Empirical models are commonly used to describe pressure-dependent permeability. In this paper, it was discussed a number of issues which centered around tight sandstone pressure-dependent permeability experiment, first to apply core aging on permeability test and then to develop a new semi-analytical model to predict permeability. In tight sandstone permeability test experiment, the microinterstice between core and sleeves resulted in over estimation of dependency of permeability on pressure. Then, a new semi-analytical model was developed to identify the relation between permeability and fluid pressure in tight sandstone, which indicates there is a linear relation between pore pressure changes and the inverse of permeability to a constant power. Pressure-dependent permeability of 8 tight sandstone core samples from Ordos Basin, China, was obtained using the modified procedure, and results were perfectly matched with the proposed model. Meanwhile, the semi-analytical model was also verified by pressure-dependent permeability of 16 cores in the literature and experiment results of these 24 cores were matched by empirical models and the semi-analytical model. Compared with regression result of commonly used empirical models, the semi-analytical model outperforms the current empirical models on 8 cores from our experiment and 16 cores from the literature. The model verification also indicates that the semi-theoretical model can match the pressure-dependent permeability of different rock types. In addition, the permeability performance under reservoir condition is discussed, which is divided into two stages. In most tight gas reservoirs, the permeability performance during production is located in stage II. The evaluation result with proposed experiment procedure and the stress condition in stage II will reduce permeability sensitivity to stress.     

Towards petascale spectral simulations for transition analysis in wall bounded flow

An efficient parallel spectral method for direct numerical simulations of transitional and turbulent flows is described in this paper. The parallelization is classically based on a bidimensional domain decomposition, but has been specifically developed for a solenoidal Fourier–Chebyshev spectral approximation where in one Fourier direction, the number of modes is very large compared with the two other directions. The approach therefore differs from classical libraries developed for cubic Fourier boxes. The strategy uses message‐passing interface (MPI) for message‐passing among nodes and is fairly portable. One of the originalities of this paper is the use of an efficient hybrid programming with MPI for internodes communications and a coarse grain parallelism using OpenMP for core shared‐memory computation, instead of the classical hybrid programming with MPI and a fine granularity parallelism at the loop level with OpenMP directives. This hybrid parallelism has been tested on the recent generation of high‐performance parallel supercomputers involving a few tens of cores per node. Performances are evaluated on different low‐frequency and high‐frequency processors massively parallel platforms. We demonstrate that spectral methods, which are known to be inherently ill‐fitted for the new generation of high‐performance distributed‐memory computers, can be implemented efficiently using this hybrid programming with good scalability and a very fast wall‐clock time per iteration. New numerical experiments are therefore now accessible on petascale computers, while keeping the attractive features of spectral methods such as accuracy, exponential convergence, computational efficiency and conservative properties. This is illustrated by a direct numerical simulation of the transition of the boundary layers developing from the entrance section of a plane channel and interacting to merge into a fully turbulent flow. Copyright © 2012 John Wiley & Sons, Ltd.     

基于核磁共振孔隙划分的致密油藏自发渗吸原油可动性研究

自发渗吸驱油是致密油藏提高采收率的有效手段,但不同的孔隙划分方法会导致原油可动性精细定量表征存在差异性.基于此,以鄂尔多斯盆地延长组致密油藏为研究对象,开展了四种典型致密岩心的自发渗吸驱油实验,利用基于核磁共振分形理论的流体分布孔隙精细划分方法,区分了致密砂岩岩心孔隙类型,明确了不同类型岩心孔隙结构对原油可动性和自发渗吸驱油速率的控制特征.研究结果表明不同类型岩心自发渗吸模拟油动用程度介于22.07%～33.26%,核磁共振T2谱双峰型岩心自发渗吸模拟油动用程度高于单峰型岩心;不同类型致密砂岩岩心中流体分布孔隙可初步划分出P1和P2两种类型, P1类型孔隙则可进一步划分出P1-1, P1-2和P1-3三种亚类型孔隙;致密砂岩岩心中P1和P2类孔隙中模拟油均有不同程度的动用, P1类孔隙作为致密岩心中主要孔隙,尤其是P1类孔隙中P1-2和P1-3类孔隙的数量决定了自发渗吸模拟油动用程度;P1-1, P1-2和P1-3类孔隙结构差异性对自发渗吸模拟油动用程度起决定性作用,较小尺寸孔径孔隙较大的孔隙结构差异性不仅提升了自发渗吸模拟油动用程度,而且提升了自发渗吸驱油速率;流体可动性指数较高的P...     

基于图像分析法的水稻茎秆力学性能测量与分析

水稻茎秆力学性能的准确描述是水稻抗倒伏力学分析的关键。由于茎秆是由生物活性材料组成的形状不规则柔性结构,传统的测试方法难以对其力学性能进行准确测量。以南方水稻为研究对象,采用拉伸试验机对水稻茎秆进行了拉伸试验。首先采用传统的应变片方法测量应变,继而探索采用图像分析法实现非接触、高精度地测量水稻茎秆的截面尺寸、拉伸变形。用数字摄像机记录不同荷载水平下试件表面的数字图像,采用数字图像相关分析法(DIC)进行分析,通过两种方法计算茎秆的轴向应变;将完成拉伸实验的试件切片,采集其横截面的数字图像,通过数字图像分析技术得到其几何特性,并对大量实验数据进行了统计分析,实现了对水稻茎秆弹性模量、抗弯刚度等的合理描述。实验结果表明,采用传统的应变片测量求得的水稻茎秆的弹性模量的离散性极大,超出样本差异性的范围,而采用数字图像分析方法得到的弹性模量、抗弯刚度的结果有一定的离散性,但分布比较合理,比较准确地反映了水稻茎秆相关的力学性能。     

PRECISE INTEGRAL ALGORITHM BASED SOLUTION FOR TRANSIENT INVERSE HEAT CONDUCTION PROBLEMS WITH MULTI-VARIABLES

IntroductionIHCPs (InverseHeatConductionProblems)arecloselyassociatedwithmanyengineeringaspects,andwelldocumentedintheliteratures,coveringtheidentificationsofthermalparameters[1,2 ],boundaryshapes[3],boundaryconditions[4 ]andsource_relatedterms[5 ,6 ]etc .Howeveritseemsthatonlylittleworkisdirectlyconcernedwithmulti_variablesidentificationsbyauthors’knowledge.Tsengetal.presentedanapproachtodeterminingtwokindsofvariables[7],butonlygavefewnumericalexamplestodeterminethemsimultaneously .Thesol…     

3-D simulation of spatial stress distribution in an AZ31 Mg alloy sheet under in-plane compression

A complete 3-D crystal plasticity finite element method (CPFEM) that considered both crystallographic slip and deformation twinning was applied to simulate the spatial distribution of the relative amount of slip and twin activities in a polycrystalline AZ31 Mg alloy during in-plane compression. A microstructure mapping technique that considered the grain size distribution and microtexture measured by electron backscatter diffraction (EBSD) technique was used to create a statistically representative 3-D microstructure for the initial configuration. Using a 3-D Monte Carlo method, a 3-D digital microstructure that matched the experimentally measured grain size distribution was constructed. Crystallographic orientations obtained from the EBSD data were assigned on the 3-D digital microstructure to match the experimentally measured misorientation distribution. CPFEM captured the heterogeneity of the stress concentration as well as the slip and twin activities of a polycrystalline AZ31 Mg alloy during in-plane compression.     

Practical Method for Analysis of Immiscible Displacement in Laboratory Core Tests

Abstract. An accurate analytical interpretation method to determine the Leverett function (f_w)and its derivative (f_w) from immiscible displacement data in core plugs is presented. Linear equations are developed to describe the displacement processes occurring before and after breakthrough. A quadratic function is introduced to represent the saturation distribution along the cores. The relationships derived in this study can be used for analysis of core tests involving constant injection rates and constant pressure differences. The applicability, practicality, and accuracy of the new analytical method are verified by means of the experimental data obtained in the present study and by those reported in the literature.     

康托洛维奇-里茨杂交法及其应用

本文将Kantorovich法与Ritz法进行适当组合,吸收了二者的主要优点,提出了康托洛维奇法的一种改进方法.以二维问题为例,Kantorovich法在一个方向(例如y方向)的分布完全预先选定,这含有很大的主观任意性,因而限制了近似解的精度,改进法则在y方向仿Ritz法改进为一个含有若干个自由参数的分布函数,由于增加了近似解的自由度,故可改善解的精度.对Kantorovich法的另一改进是在计算高阶近似解时,通过逐项求解待定函数避免了求解更高阶微分方程或含更多方程的方程组,减少了计算量,降低了计算难度.用改进法求解了固体力学里的矩形截面柱体扭转问题和四边固支矩形板的弯曲问题,通过算例充分说明了此方法的特点和优越性.     

A study of boundary integral method for a type of nonlinear problem based on generalized quasilinearlization theory

非线性泊松问题在热传导和多孔催化粒子的扩散反应等问题中是非常常见的,为此,利用广 义拟线性化迭代理论,提出了一种非线性泊松问题的新的数值迭代方法. 该方法将非线性方 程转化成一序列线性方程的迭代,其优点是初始值的选取具有一定的理论基础,并且在一定 的初始值条件下,迭代结果将单调地收敛于非线性问题的解. 将此迭代方法与边界元和双互 易杂交边界点方法结合,并用于非线性泊松问题的求解,比较了两种方法的结果精度,收敛 速度及不同初始值下的稳定性. 结果显示,基于拟线性化的双互易杂交边界点法具有较高的 稳定性和计算效率,并且收敛速度为平方阶.     

Transition radiation in a nonlinear and infinite one-dimensional structure: a comparison of solution methods

Transition zones in railway tracks are locations with a significant variation of track properties (i.e. foundation stiffness) encountered near structures such as bridges and tunnels. Due to strong amplification of the track’s response, transition zones are prone to rapid degradation. To investigate the degradation mechanisms in transition zones, researchers have developed a multitude of models, some of them being very complex. This study compares three solution methods, namely an integral-transform method, a time-domain method, and a hybrid method, with the goal of solving these systems efficiently. The methods are compared in terms of accuracy, computational efficiency, and feasibility of application to more complex systems. The model employed in this paper consists of an infinite, inhomogeneous, and piecewise-linear 1-D structure subjected to a moving constant load. Although the 1-D model is not particularly demanding computationally, it is used to make qualitative observations as to which method is most suitable for the 2-D and 3-D models, which could lead to significant gains. Results show that all three methods can reach similar accuracy levels, and in doing so, the time-domain method is most computationally efficient. The integral-transform method appears to be efficient in dealing with frequency-dependent parameters, while the time-domain and hybrid methods are efficient in dealing with a smooth nonlinearity. For multi-dimensional models, if nonlinearities and inhomogeneities are considered throughout the depth, the time-domain method is likely to be most efficient; however, if nonlinearities and inhomogeneities are limited to the surface layers, the integral-transform and hybrid methods have the potential to be more efficient than the time-domain one. Finally, although the 1-D model presented in this study is mainly used to assess the three methods, it can also be used for preliminary designs of transition zones in railway tracks.

     

规划-迭代型弹塑性摩擦接触多极边界元法

提出基于多极展开法的规划-迭代型的高度非线性方程的IGMRES(m)高效求解法,并建立其收敛性理论。本法适用于三维弹塑性摩擦接触多极边界元法,有效处理弹塑性摩擦接触迭代的繁杂和费时问题。数值试验证明,本求解法在确保数值精度的前提下,可减少迭代次数,显著提高计算效率。     

改进广义移动最小二乘近似的无网格法

无网格法是求解微分方程定解问题的一种新数值方法.移动最小二乘近似只要求近似函数在各节点处的误差的平方和最小,对近似函数导数的误差没有任何约束.而广义移动最小二乘近似要求近似函数及其导数在所有节点处的误差的平方和最小.为了降低计算工作量,本文构造了要求近似函数在全部节点处和任意阶导数在部分节点处误差的平方和最小的改进广义移动最小二乘近似.数值计算显示本文提供的方法关于函数值和各阶导数值都具有很高的精度.     

结合数码显微镜的数字散斑相关方法精度分析及应用

结合数字散斑相关方法和一种新型的显微镜数码显微镜,提出了一种测量多晶材料晶粒尺度面内变形的新方法,并通过零变形校准实验、重聚焦实验和平移实验等一系列验证实验分析了该方法的精度和实用性.作为应用实例,对一种镍基合金试件进行了单向拉伸和疲劳实验,得到了晶粒尺度下具有较大应变梯度的应变分布图像.结果表明,该方法能够得到精确的位移测量数据,是一种理想的测量晶粒尺度变形的光测方法.     

波动数值模拟的一种显式方法——一维波动

本文提出了波动时域数值模拟的一种新的显式方法,并通过一维非规则网格节点递推公式的建立说明此方法。为了阐明应用此法构建高精度、稳定递推公式的可行性,详细论述了一维均匀网格标量波动数值模拟的精度和稳定性;提出了构建时空精度皆为 阶( 为正整数)的稳定递推公式的技术途径,并以构建二阶(M=1)和四阶(M=2)公式为例予以说明。最后,通过算例详细说明了本文理论结果。     

Two-Phase Flow Properties Prediction from Small-Scale Data Using Pore-Network Modeling

The objective of this work is to evaluate the prediction accuracy of network modeling to calculate transport properties of porous media based on the interpretation of mercury invasion capillary pressure curves only. A pore-scale modeling approach is used to model the multi-phase flow and calculate gas/oil relative permeability curves. The characteristics of the 3-D pore-network are defined with the requirement that the network model satisfactorily reproduces the capillary pressure curve (P_c curve), the porosity and the permeability. A sensitivity study on the effect of the input parameters on the prediction of capillary pressure and gas/oil relative permeability curves is presented. The simulations show that different input parameters can lead to similarly good reproductions of the experimental P_c, although the predicted relative permeabilities K_r are somewhat widespread. This means that the information derived from a mercury invasion P_c curve is not sufficient to characterize transport properties of a porous medium. The simulations indicate that more quantitative information on the wall roughness and the node/bond aspect ratio would be necessary to better constrain the problem. There is also evidence that in narrow pore size distributions pore body volume and pore throat radius are correlated while in broad pore size distributions they would be uncorrelated.     

Hybrid Meta-Model Based Design Space Differentiation Method for Expensive Problems

In this work,a hybrid meta-model based design space differentiation(HMDSD)method is proposed for practical problems.In the proposed method,an iteratively reduced promising region is constructed using the expensive points,with two different search strategies respectively applied inside and outside the promising region.Besides,the hybrid meta-model strategy applied in the search process makes it possible to solve the complex practical problems.Tested upon a serial of benchmark math functions,the HMDSD method shows great efficiency and search accuracy.On top of that,a practical lightweight design demonstrates its superior performance.