坝基岩体块度特征研究

岩体块度特征是岩体完整性评价的重要指标, 通常用岩石质量指标RQD来表征。但是RQD是有不足之处的, 岩体基本块度的概率分布、块度百分比、RQDt、块度指数RBI等参数是描述岩体块度特征的重要补充, 它们更全面地、更深入地表征了岩体的完整性, 丰富了岩体质量评价的定量指标。本文以金沙江下游溪洛渡水电站工程坝基岩体块度调查统计资料为基础, 对岩体基本块度的概率分布、块度百分比、RQDt、块度指数RBI等岩体块度特征进行了深入研究。     

基于分维理论的爆炸焊接界面形貌的定量表征

以爆炸焊接界面形貌为研究对象,利用分形理论研究其界面特征。运用三维超景深显微镜获得界面形貌图像,利用Matlab图像分析技术对界面形貌进行二值化处理,基于分形理论计算图像分维值以及多重分维谱。由分维值及多重分形谱的物理意义可知,轮廓分维值是对界面不规则程度宏观度量,而多重分形谱能定量表征界面的起伏程度及高度分布。因而,通过对界面结构进行分形几何分析,可实现界面形貌定量表征,弥补当前定性分析的不足。     

用灰关联分析方法确定影响岩体爆破质量的主要因素

用灰关联分析方法确定影响岩体爆破质量的主要因素。在简介灰关联分析原理及其计算方法后,通过实例计算与分析,得到各影响因素的主次关系。并且发现:节理裂隙岩体中的爆破块度指标主要受爆区内节理裂隙分布特征的控制;其次,也与均质岩体中的爆破一样,影响块度分布的主要因素是炮孔间距、排距和最小抵抗线等。     

金川Ⅲ矿区岩体分类及其力学特性参数预测

本文针对金川Ⅲ矿区岩体质量及参数,并在11个钻孔数据资料的基础上,采用数学统计和数值模型来分别分析矿区岩体质量和力学参数的特征。对11个钻孔的资料进行详细的统计分析,进行每一个钻孔不同深度的岩体节理裂隙统计和岩体分类评价,并由此获得了建立矿块力学参数模型的数据。再建立表征整个岩体特性的三维力学模型,并揭示了矿块力学特性的分布特性和变化规律。此研究为崩落法采矿设计和数值模拟提供可靠的依据。     

计算露天矿台阶爆破块度分布的三维数学模型

本文提出一个实用的计算台阶爆破块度分布的三维数学模型。模型根据应力波理论,计算出应力波能量的三维分布,以岩石破碎单位表面能指标作纽带,首先求算出均质连续弹性台阶岩体的爆破块度分布。在此基础上模型进一步考虑到存在各种地质构造弱面和前次爆破破坏弱面的实际情况,运用概率统计方法最终求算得到实际的台阶岩体的爆破块度分布。根据此模型编制的BMMC程序,经用美国矿业局R.A.狄克和我们自己的小台阶爆破实验数据进行验算,电算得到的理论块度分布与实际的爆破块度分布吻合得相当好。     

炸药单耗对爆破块度分布影响的理论探讨

基于爆破块度分布的分形特征,从理论上推导了炸药单耗与爆破块度分布均匀性指数的关系,对爆破块度分布的预测具有重要的指导意义。     

裂隙岩体损伤局部化破坏分岔模型及其应用

采用概率统计方法分析节理裂隙岩体的几何特征，定义了反映裂隙岩体几何特征的组构张量．基于不可逆热力学理论，通过裂纹扩展的细观分析，得出了损伤的发展机理和演化方程，把损伤演化和裂隙的几何特征的变化联系起来，建立了弹塑性损伤本构关系．为分析含有节理裂隙岩体在发生局部化破坏时的特征，通过对发生局部化时的裂隙岩体的分析。构造了适用于节理裂隙岩体局部化分析的不连续分岔模型．利用非线性规划数值解法，可以得出局部化破坏的方向特征．在有限元方法中，根据该模型给出了节理裂隙岩体相关的算例，分析表明该模型用于分析裂隙岩体的局部化破坏是有效的．     

岩石爆破破碎能耗随抵抗线的变化规律

针对爆炸荷载下岩体破碎块度和有用功能耗及能耗利用率问题,运用断裂力学、分形基础理论分析和模型实验等方法,对爆炸荷载下岩体破碎块度和能耗利用率随最小抵抗线的变化规律开展了系统的分析研究。研究结果表明:在模型实验条件下,破碎块度分形维数在1.2～1.7之间,随最小抵抗线增大呈现较好的线性衰减趋势;破碎能耗随最小抵抗线呈现先增加后降低的趋势,爆炸能量利用率在4.57%～12.51%之间,趋势与能耗值一致,模型实验中能耗利用率存在最大值;破碎块度与能耗利用率变化趋势相反,说明在最小抵抗线变化过程中存在一个最佳值,使得破碎块度和能耗利用率均处于最优状态,模型实验中这一最佳值为160 mm,是装药直径的26.7倍。该研究结果可为提高爆炸能利用率理论分析及工程中降低大块率的设计和施工提供理论依据。     

基于数字摄影测量的结构面信息表征及应用研究

结构面的存在直接影响岩体的强度、变形特征及破坏机制。为探究夏甸金矿矿区结构面的存在对岩体力学参数和岩体质量情况的影响,利用数字摄影测量技术快速获取研究区域结构面几何信息,并通过三维建模、激光扫描技术以及VR-Platform虚拟现实平台实现了结构面二维几何信息的真三维表征。基于此,利用广义Hoek-Brown强度准则分析计算了各研究区域的岩体力学参数,并根据岩体基本质量指标BQ值进行了岩体质量分级评价。结果表明,夏甸金矿岩体力学参数指标和岩体质量指标均较好;矿体下盘距离矿体方向越远,岩体完整性系数和岩体力学参数越低;利用广义Hoek-Brown强度准则计算所得岩体力学参数除内摩擦角外数值均与前期试验所得数据基本一致,计算所得岩体内摩擦角度偏大的原因,可能是其未考虑结构面自身的颗粒直径和形态等对岩体内摩擦角的影响。     

室爆破法采石级配预测

引入岩体裂隙分布的统计理论，探讨了爆堆岩块的分形特性，从统计岩体力学及爆炸分形的角度建立爆炸过程并对硐室爆破进行级配分析，级配预测结果和实际工程吻合较好。     

Simulation and experimental analysis of melt pool evolution in laser engineered net shaping

In this work, the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping (LENS) process is analyzed. Firstly, the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made. Then, the establishment process of the multi-physical field model of the melt pool is introduced in detail. It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile, space temperature gradient, and time temperature gradient. Meanwhile, some parameters, such as the 3D morphology and surface fluid field of the melt pool, which are not obtained in the online measurement experiment, are analyzed. Finally, the influence of changing the scanning speed on the profile, peak temperature, and temperature gradient of the single-line melt pool is also analyzed, and the following conclusions are obtained: With the increase in scanning speed, the profile of the melt pool gradually becomes slender; The relationship between peak temperature and scanning speed is approximately linear in a certain speed range; The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed, and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.     

Surface Strain Measurements Using a 3D Scanning Laser Vibrometer

Three-dimensional scanning laser vibrometers enable extremely accurate non-contact measurement of the three-dimensional displacements on the surface of structures. This paper looks at the feasibility of using such a scanning laser vibrometer for the non-contact measurement of dynamic strain fields across the surface of a planar structure subjected to in-plane loading. Issues such as laser head alignment and choice of differentiation filter parameters are discussed. Finally, experimental results of two test specimens are presented which clearly demonstrate the significant potential of this new experimental technique as well as highlighting several limitations.     

A Numerical Approach for Non-Linear Moisture Flow in Porous Materials with Account to Sorption Hysteresis

A numerical approach for moisture transport in porous materials like concrete is presented. The model considers mass balance equations for the vapour phase and the water phase in the material together with constitutive equations for the mass flows and for the exchange of mass between the two phases. History-dependent sorption behaviour is introduced by considering scanning curves between the bounding desorption and absorption curves. The method, therefore, makes it possible to calculate equilibrium water contents for arbitrary relative humidity variations at every material point considered. The scanning curves for different wetting and drying conditions are constructed by using third degree polynomial expressions. The three coefficients describing the scanning curves is determined for each wetting and drying case by assuming a relation between the slope of boundary sorption curve and the scanning curve at the point where the moisture response enters the scanning domain. Furthermore, assuming that the slope of the scanning curve is the same as the boundary curve at the junction point, that is, at the point where the scanning curve hits the boundary curve once leaving the scanning domain, a complete cyclic behaviour can be considered. A finite element approach is described, which is capable of solving the non-linear coupled equation system. The numerical calculation is based on a Taylor expansion of the residual of the stated problem together with the establishment of a Newton–Raphson equilibrium iteration scheme within the time steps. Examples are presented illustrating the performance and potential of the model. Two different types of measurements on moisture content profiles in concrete are used to verify the relevance of the novel proposed model for moisture transport and sorption. It is shown that a good match between experimental results and model predictions can be obtained by fitting the included material constants and parameters.     

基于医学影像的血流动力学分析

随着计算机成像技术的发展,计算机断层扫描(CT)和核磁共振(MRI)已经广泛应用于临床,特别是血管类疾病的诊断,比如动脉狭窄、血管瘤、血管畸形等。除了可以提供高分辨率的静态图像,先进的MRI技术还可以通过时间序列直接反映血流动力学的变化。而基于计算机成像和三维重建技术,血流动力学的参数又可以通过计算流体力学的方法进行详细的分析。如何将血流动力学参数和临床诊断相结合是近年来在转化医学领域研究的热点。文中将结合文献调研和作者自己的研究工作对基于医学图像的血流动力学分析进行综述,并探讨未来的研究方向。     

Medical image based hemodynamic analysis

随着计算机成像技术的发展,计算机断层扫描(CT)和核磁共振(MRI)已经广泛应用于临床,特别是血管类疾病的诊断,比如动脉狭窄、血管瘤、血管畸形等.除了可以提供高分辨率的静态图像,先进的MRI技术还可以通过时间序列直接反映血流动力学的变化.而基于计算机成像和三维重建技术,血流动力学的参数又可以通过计算流体力学的方法进行详细的分析.如何将血流动力学参数和临床诊断相结合是近年来在转化医学领域研究的热点.结合文献调研和作者自己的研究工作对基于医学图像的血流动力学分析进行综述,并探讨未来的研究方向.     

Fracture behavior of a cohesive soil under crushing stress loading

In this study the concepts of engineering fracture mechanics are used to investigate the behavior of cohesive soil crumbling. Prior to the analysis, the physical structure was investigated using the electron scanning method. Cohesive soil-crushing tests were conducted to evaluate the fracture parameters. The results of both phenomenal and experimental approaches indicated that the concept of engineering fracture mechanics can be applied to evaluate soil fracture leading to crumbling.     

A scanning PIV method for fine-scale turbulence measurements

A hybrid technique is presented that combines scanning PIV with tomographic reconstruction to make spatially and temporally resolved measurements of the fine-scale motions in turbulent flows. The technique uses one or two high-speed cameras to record particle images as a laser sheet is rapidly traversed across a measurement volume. This is combined with a fast method for tomographic reconstruction of the particle field for use in conjunction with PIV cross-correlation. The method was tested numerically using DNS data and with experiments in a large mixing tank that produces axisymmetric homogeneous turbulence at \(R_\lambda \simeq 219\) . A parametric investigation identifies the important parameters for a scanning PIV set-up and provides guidance to the interested experimentalist in achieving the best accuracy. Optimal sheet spacings and thicknesses are reported, and it was found that accurate results could be obtained at quite low scanning speeds. The two-camera method is the most robust to noise, permitting accurate measurements of the velocity gradients and direct determination of the dissipation rate.     

Fabricating Parameters Optimization of High Frequency Grating by Multi-scanning Electron Beam Method

The electron-beam moiré method uses a high frequency grating to measure microscopic deformation. Increasingly fine gratings are being developed to achieve increasingly high resolutions in microscopic stress analysis. In this study, we improve the electron grid fabricating technique by using a common scanning electron microscope (SEM). An error analysis for the multi-scanning grating was performed by a sampling moiré method. The grating manufacturing parameters strongly affect the superfine grating quality. A high accelerating voltage or a short working distance yield better results generally. A set of optimal parameters is suggested based on a minimum-error criterion. A cross-line grid with a frequency of 10,000 lines/mm and a parallel grating with a frequency of 13,000 lines/mm were successfully fabricated.     

冻融循环作用下沥青混凝土分形断裂特性研究

沥青混凝土作为一种主要的路面材料,暴露于外部寒冷环境下冻融损伤是不可避免的。通过对经历不同冻融循环次数的沥青混凝土试件进行CT扫描,采用数字图像处理技术对CT灰度图像进行处理分析,可获得其内部冻融损伤情况。基于分形理论量化表征了冻融循环作用下内部裂纹扩展的几何特征。沥青混凝土经过冻融循环后的断裂韧性被认为是决定其力学性能损伤程度的关键指标,建立了考虑分形特征的临界裂纹应力、应力强度因子和断裂韧性方程。研究发现：平均分形维数反映了冻融循环过程中的波动特征;断裂韧性由裂纹几何参数决定;弹性模量、临界开裂应力及断裂韧性等力学参数随冻融循环次数的增加而逐渐减弱。

     

塔河油田超埋深碳酸盐岩油藏基质的力学试验研究

碳酸盐岩油气藏在全球范围内分布广泛,其中30%以上为缝洞型碳酸盐岩油气藏。在我国缝洞型油藏占已探明的碳酸盐岩油藏储量的2/3,是今后增储的主要领域。为准确揭示碳酸盐岩油藏基质的力学特性,本文以塔河油田奥陶系油藏地层为研究背景,通过现场深孔钻井取样得到埋深达5300~6200m的碳酸盐岩油藏基质岩样,并通过力学试验首次获得超埋深碳酸盐岩油藏基质的弹模、泊松比、抗压强度、抗拉强度、粘聚力、内摩擦角等力学参数,借助电镜扫描试验揭示出超埋深碳酸盐岩的微细观破裂机制。该项研究成果可为分析碳酸盐岩油藏溶洞的垮塌破坏机理提供有效的试验参数。