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1.
J. M. Carcione 《国际地质力学数值与分析法杂志》1998,22(4):263-275
This work presents a numerical algorithm for solving crack scattering in a transversely isotropic medium whose symmetry axis is perpendicular to the crack surface. The crack is modelled as boundary discontinuities in the displacement u and the particle velocity v, of the stresses [κu+ζv], where the brackets denote discontinuities across the interface. The specific stiffness κ introduces frequency-dependence and phase changes in the interface response and the specific viscosity ζ is related to the energy loss. The numerical method is based on a domain decomposition technique that assignes a different mesh to each side of the interface, that includes the crack plane. As stated above, the effects of the crack on wave propagation are modelled through the boundary conditions, that require a special boundary treatment based on characteristic variables. The algorithm solves the particle velocity–stress wave equations and two additional first-order differential equations (two-dimensional case) in the displacement discontinuity. For each mesh, the spatial derivatives normal to the interface are solved by the Chebyshev method, and the spatial derivatives parallel to the interface are computed with the Fourier method. They allow a highly accurate implementation of the boundary conditions and computation of the spatial derivatives, and an optimal discretization of the model space. Moreover, the algorithm allows general material variability. © 1998 John Wiley & Sons, Ltd. 相似文献
2.
根据断裂动力学理论及弹性P波与裂缝相互作用的分析,利用混凝土的动态断裂韧度,研究了大体积混凝土深层或贯穿裂缝在爆炸应力波P波作用下的扩展,得到了含裂缝混凝土的安全质点振动速度,并讨论了P波频率及其入射角对安全质点振动速度的影响。结果表明,频率越低、入射角越大的应力波对混凝土裂缝的扩展作用越大,频率为10 Hz垂直入射条件下,混凝土裂缝不扩展的安全质点振动速度仅为0.95 cm/s,与水利水电工程施工组织设计手册中规定的混凝土重力坝、混凝土闸墩等大体积混凝土结构的安全振速5 cm/s有较大差距,含裂缝混凝土更加容易被破坏。 相似文献
3.
倾斜层状地层中速度模型对于震源精确定位具有重要意义。基于水平层状地层两点间的快速射线追踪法,分析了应力波在倾斜地层中的传播路径及规律。结合网格搜索法,提出了针对倾斜地层的微震定位算法,并与传统的基于单一速度模型的定位算法进行对比分析;探索性地采用了颗粒流理论构建地层数值模型,通过颗粒间的相互作用模拟应力波传播进行定位算法有效性验证。研究结果表明：（1）对于倾斜地层,基于简化弹性波等速传播规律的定位算法精度较差,单一速度模型不能满足复杂介质的定位要求;（2）采用倾斜分层速度模型并改进应力波传播路径的计算方法能有效提高倾斜地层的震源定位精度,同时分析了地层倾角以及地层数对算法精度的影响,表明定位误差与倾角、地层数成正比;（3）通过减小网格搜索法的网格尺寸可在一定程度上提高定位精度,合理的尺寸大小和搜索策略有助于网格搜索法在实际工程中的应用。建立的倾斜地层震源定位及其验证方法可为进一步研究复杂地层定位监测技术提供重要的理论和技术支撑。 相似文献
4.
Ambient relative humidity controls the stress-strain-time behaviour of granular media exhibiting particle breakage. Breakage is the result of crack propagation inside loaded particles. The DEM model developed uses the results of subcritical crack propagation in brittle rock to predict breakage and the subsequent structural rearrangement. Two closed-form solutions at grain level, stress distribution under diametrically opposed forces and the mode I crack propagation velocity, were included in the DEM formulation. Crack propagation velocity depends explicitly on relative humidity. The resulting model incorporates comminution and splitting modes of particle breakage as well as arbitrary grain shapes by means of aggregation of spherical microparticles. The model was first validated against a large diameter suction-controlled oedometer test on hard limestone crushed gravel. Direct tests on contact properties (local stiffness and friction) helped to validate the model. The model was then used to predict the response of large diameter suction-controlled triaxial tests on gravels having different (uniform) initial sizes. Time delayed deformations and wetting-induced collapse deformations under maintained load are also a natural outcome of the model. They were shown to follow quite accurately the experimental results. 相似文献
5.
开发一种改进损伤框架的粒子流算法,被称为核断裂的光滑粒子流法（kernel?broken smoothed particle hydrodynamics,KBSPH）,用于模拟地震条件下岩质边坡的裂纹扩展和变形破坏过程.在KBSPH中,提出一种改进的损伤框架,通过引入断裂标志来改进损伤粒子的核函数,使损伤粒子的虚拟应力键直接断裂,裂纹在断裂的应力键间生成,从而模拟岩石的裂纹扩展过程.在地震边界上采用了双层边界,将动力输入边界与黏滞边界分离.首先通过薄板振动实验验证KBSPH的动力特性.其次以单裂隙岩体单轴压缩试验验证KBSPH的断裂力学特性.最后模拟地震条件下多节理岩质边坡中裂纹扩展过程和动力响应.薄板振动实验验证了KBSPH的动力特性的准确性.单裂隙岩体单轴压缩试验,证明了KBSPH可以正确模拟预制裂隙尖端的翼型裂纹.通过对比以往数值模拟方法和现场案例,表明KBSPH正确揭示了加速度放大效应以及地震条件下岩质边坡的裂纹扩展过程.KBSPH避免了传统算法的网格畸变,损伤粒子应力分量重新分配的问题,降低了编程难度,提高了运行速率,可为SPH在地震条件下岩石力学中的应用和理解岩石断裂机理提供一定的参考. 相似文献
6.
We construct a new class of locally conservative numerical methods for two-phase immiscible flow in heterogeneous poroelastic media. Within the framework of the so-called iteratively coupled methods and fixed-stress split algorithm we develop mixed finite element methods for the flow and geomechanics subsystems which furnish locally conservative Darcy velocity and transient porosity input fields for the transport problem for the water saturation. Such hyperbolic equation is decomposed within an operator splitting technique based on a predictor–corrector scheme with the predictor step discretized by a higher-order non-oscillatory finite volume central scheme. The proposed scheme adopts an inhomogeneous dual mesh with variable cell size ruled by the local wave speed of propagation to compute numerical fluxes at cell edges. In the limit of small time steps the central scheme gives rise to a semidiscrete formulation for the water saturation capable of incorporating heterogeneous porosity fields and generalized flux functions including the water transport due to the solid phase velocity. Numerical simulations of a water-flooding problem in secondary oil recovery are presented for different realizations of the input random fields (permeability, Young modulus and initial porosity). Comparison between the accuracies of the proposed approach and the traditional one-way coupled hydro-geomechanical formulation are presented. The effects of the cross-correlation between the input random fields and compaction drive mechanism upon finger growth and breakthrough curves are also analyzed. A notable feature of the formulation proposed herein is the accurate prediction of the influence of geomechanical effects upon the unstable movement of the water front, whose evolution is dictated by rock heterogeneity and unfavorable viscosity ratio, without deteriorating the local conservative character of the numerical schemes. 相似文献
7.
在试验室进行裂纹稳定扩展及非稳定扩展的研究,其试验基座以楔形劈裂试验为基础改良而成,考虑材料的均质性,试验试体采用供铺设地板或建筑用外墙之天然石材。试验过程中利用裂缝应变片即时记录系统求出试体在稳定扩展及非稳定扩展下的裂纹扩展速度及其分形特性。结果表明,稳定扩展速度范围约在0.113～313.043 cm/s;非稳定扩展速度范围约在0.094～2 489.816 cm/s;亚临界分形维数范围约在0.994 3～1.036 6;起裂断裂韧性范围约在1.891 5～3.500 1 MPa?m1/2;分形亞臨界斷裂韌性范围约在2.063 6～3.712 8 MPa?m1/2。 相似文献
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9.
基于数值流形法（NMM）进行三维裂纹扩展分析研究,编写了相应的C++程序。充分发挥数值流形法在非连续变形分析领域的优势,不需要扩展有限元中的水平集和阶跃函数概念,应用数值流形法计算结果分析裂纹尖端线的破坏状况,对已有的非局部求迹法和三角形推进法进行简化和扩展,提出一种简化算法确定最终的新裂纹扩展面。应用简化算法对水平钱币型裂纹扩展问题进行数值模拟和对比分析研究。计算结果表明,基于数值流形法的三维裂纹扩展算法是可行的,采用简化处理之后,克服原有算法的不足,大大减少了新裂纹尖端线和新裂纹面的数目,降低了计算网格对新裂纹面的影响,提高了计算效率和扩大了应用范围。 相似文献
10.
中低围压或单轴压缩荷载条件下,可以将脆性岩石材料的裂纹扩展过程划分为原生裂纹压密、新生裂纹起裂并稳定扩展、不稳定裂纹扩展和交互贯通以及峰后5个主要发展阶段。含预制裂纹试样的直接观测法、应变监测、声发射（AE）监测、声波波速测试、CT（computerized tomography）扫描、微电镜观察等间接监测方法被用来研究裂纹起裂和扩展过程。本文基于在中、低围压以及单轴压缩荷载条件下,脆性岩石材料首先产生张拉裂纹,并优先沿加载方向发育的规律,提出采用声波波速连续测量方法进行岩石加载过程波速的连续观测,有助于分析裂纹扩展过程中声波波速的变化,为研究裂纹扩展过程提供一种间接测量手段。 相似文献
11.
岩体裂纹的水力劈裂是岩体开裂渗漏甚至施工涌水的重要影响因素之一,也是岩土工程界的研究热点。从断裂力学角度分析了爆破开挖对岩体含水裂纹扩展的扰动作用,结果表明,爆破开挖扰动下,岩体含水裂纹的扩展,与爆炸应力波强度及其入射角、地应力的大小与方向、孔隙水压大小、裂纹的倾角及断裂韧度等因素相关;爆炸应力波的作用,相当于增大了岩体裂纹中的孔隙水压力,每1 cm/s的峰值振动速度相当于增大100 kPa的孔隙水压力,爆破振动速度越大,所产生的爆破扰动荷载越大;岩体开挖引起的岩体裂纹近区地应力及其孔隙水压力的变化,对裂纹的失稳与扩展具有较复杂的影响,可改变裂纹的失稳扩展模式。 相似文献
12.
A numerical algorithm for simulation of 2-D (axis-symmetric) wave propagation using a multidomain approach is proposed. The method uses a cylindrical coordinate system, Chebyshev and
Fourier differential operators to calculate the spatial derivatives along the radial and vertical direction, respectively,
and a Runge–Kutta time-integration scheme. The numerical technique is based on the solution of the equations of momentum conservation
combined with the stress–strain relations of the fluid (drilling mud) and isotropic elastic media (drill string and formation).
Wave modes and radiated waves are simulated in the borehole-formation system. The algorithm satisfies the reciprocity condition
and the results agree with an analytical solution and low-frequency simulation of wave-propagation modes reported in the literature.
Examples illustrating the propagation of waves are presented for hard and soft formations. Moreover, the presence of casing,
cement, and formation heterogeneity have been considered. Since the algorithm is based on a direct (grid) method, the geometry
and the properties defining the media at each grid point, can be general, i.e., there are no limitations such as planar interfaces
or uniform (homogeneous) properties for each medium.
相似文献
13.
考虑非线性徐变的混凝土温度裂缝扩展过程模拟 总被引：1，自引：0，他引：1
混凝土温度应力超过相应龄期的抗拉强度一半时,混凝土的徐变变形不再与应力呈线性关系。采用一个混凝土非线性徐变模型来进行混凝土的温度应力计算,并给出了相应的算法。同时,吸取无网格方法在裂缝扩展模拟方面的优势,采用无网格方法对混凝土的温度裂缝过程进行了仿真计算。数值算例计算结果表明,所编制的无网格法程序具有较好的收敛性和可靠性,能够有效地模拟混凝土块在温度应力作用下的开裂发展过程,考虑混凝土非线性徐变效应后,在开裂时刻混凝土急剧增加的非线性徐变变形缓和了缝端的温度拉应力,使得相同龄期混凝土的裂缝深度和扩展速率要比只考虑混凝土线性徐变要小一些。 相似文献
14.
在岩土工程分析中求解精度控制常常是必需的,在数值流形法中可以通过控制数学覆盖网格的稀疏和覆盖位移的阶数来达到精度的要求。提出了基于等几何分析的数值流形方法,定义了相应的数学覆盖的构造形式,推导了基于二次B样条的9节点数值流形方法分析格式;针对基于Lagrange插值函数的4节点数值流形方法提出了基于T样条思想的数学覆盖网格的局部加密方法。算例计算结果表明,相对于4节点的数值流形方法,基于非均匀有理B样条的9节点数值流形方法具有更高的精度;基于T样条思想的加密网格在保持计算精度的前提下降低了自由度的数量,表明T样条加密是一种自然的局部加密算法。 相似文献
15.
One proposed geothermal heat extraction scheme relies on water circulation in a large vertical crack created by hydraulic fracturing in a hot dry impermeable rock mass. Water flow, heat convection and crack opening widths are analysed by finite elements. Governing field equations of the problem are first set up rigorously and then various small terms are identified and neglected, retaining the effects of pressure gradient, buoyancy, velocity head (kinetic energy) and head loss due to viscous friction in the water flow equation, and the effects of heat convection in water and heat conduction in rock in the heat transfer equation. The finite element scheme for water flow is based on a variational principle that is typical for diffusion problems, and for heat transfer it is based on the method of least-square residuals. The system of differential equations is highly non-linear. The non-linear terms and coefficients are treated in the fiaite element analysis as constant; the finite element analysisof, the steady-state pressures, fluxes and temperatures is then iterated, evaluating all non-linear terms and coefficients on the basis of the solution obtained in the previous iteration. Numerically calculated fields at various times after the start ofcooling are presented. They indicate some features favourable for the geothermal scheme, such as formation of eddy currents, and downward flux of water toward hotter rock. However, other important questions would have to be solved to gain full understanding, of this proposed geothermal scheme. 相似文献
16.
In a cracked material, the stress intensity factors (SIFs) at the crack tips, which govern the crack propagation and are associated with the strength of the material, are strongly affected by the crack inclination angle and the orientation with respect to the principal direction of anisotropy. In this paper, a formulation of the boundary element method (BEM), based on the relative displacements of the crack tip, is used to determine the mixed‐mode SIFs of isotropic and anisotropic rocks. Numerical examples of the application of the formulation for different crack inclination angles, crack lengths, and degree of material anisotropy are presented. Furthermore, the BEM formulation combined with the maximum circumferential stress criterion is adopted to predict the crack initiation angles and simulate the crack propagation paths. The propagation path in cracked straight through Brazilian disc specimen is numerically predicted and the results of numerical and experimental data compared with the actual laboratory observations. Good agreement is found between the two approaches. The proposed BEM formulation is therefore suitable to simulate the process of crack propagation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
17.
This paper presents a time integration scheme capable of simulating blast loading of relatively high frequency on porous media, using coarse meshes. The scheme is based on the partition of unity finite element method. The discontinuity is imposed on the velocity field, while the displacement field is kept continuous. The velocity discontinuity is postulated to occur in the time domain. The developed time integration scheme is unconditionally stable and has controllable numerical dissipation in the high frequency range. An important feature of the time scheme is that it allows for controlling the numerical damping in a consistent way. The time scheme has been implemented in combination with Biot’s theory of wave propagation in saturated porous media. Numerical examples have demonstrated that the proposed time scheme is, in addition to being accurate and stable, highly effective for coarse meshes. This makes the developed scheme suitable for large scale finite element analysis. 相似文献
18.
为了研究含缺陷胶结充填体的断裂特性,分别设置了裂纹偏置比为0、0.25、0.50、0.75,缝高比为0.10、0.25、0.50的胶结充填体试件进行三点弯曲试验,利用高速摄像机进行裂纹扩展模式全程捕捉,借助二维颗粒流软件PFC2D对充填体裂纹扩展全程、破断方式及断裂机制进行分析。试验结果表明：相同缝高比下,随着裂纹偏置比的增加,断裂峰值荷载越大;当偏置比一定时,随着缝高比的增加,断裂峰值荷载越小;裂纹偏置比在0、0.25和0.50时,裂纹从偏置处扩展,且随着偏置比的增加,偏折角增大;裂纹偏置比在0.75时,裂纹从中心处扩展;断裂裂纹可分为3个阶段,且呈锯齿状扩展并在发育的过程中不断有碎裂状颗粒产生和脱落。利用二维颗粒流模拟充填体试件的力链网络、速度场及破断方式,结合其宏观力学的试验结果进行对比分析,探讨了细观断裂机制,其断裂时的峰值荷载与试验值相差不超过3.8%。 相似文献
19.
对涡结构进行识别是紊流涡动力学研究的难题,为了降低涡识别方法对流速测量空间分辨率的要求,消除阈值对涡识别结果可能产生的影响,提出了基于二维平面流场的涡结构模式匹配方法。应用该方法对明渠紊流中涡结构的密度、涡量、半径和强度等特征参数和涡动力学特征进行了分析。结果表明,涡结构的密度和涡量沿水深逐渐减小,涡半径沿水深逐渐增大,涡结构的环量在近壁区迅速增大而随后基本维持稳定;在相同水深处,顺向涡密度大于逆向涡且具有更强的旋转运动;顺向涡的平均流场具有典型的发夹涡群特征,部分逆向涡与顺向涡在空间上具有相关关系。 相似文献
20.
岩（矿）心采取率低是单管取心钻进的主要问题。在钻进时由于冲洗液对岩心的冲刷作用,使岩（矿）心中的矿物颗粒不断被冲洗液带走,造成岩心缺失、岩心采取率过低。从钻具内部流速分布、冲洗液冲刷作用、岩心采取率、冲洗液携粉等角度出发,分析了单管钻进时造成岩心采取率过低的原因,采取分流、降速等方法,设计了一套可以在一定程度上提高岩心采取率的分水单管钻具,通过数值模拟,证明了该钻具在满足及时清除孔底岩粉的条件下,能使单管钻具中岩心周围冲洗液流速降低25%左右,进而解决常规单管钻进岩心采取率不足等问题。 相似文献