共查询到20条相似文献，搜索用时 734 毫秒
1.
The effect of nonaxisymmetric elasticheterogeneities on the mechanical stability of a nearly axisymmetricvolcanic structure, with particular reference to Mt. Vesuvius (Italy) is investigated. This is done solving numerical models using a finite element codein the framework of linear elasticity. The models include gravity,anisotropic depth-dependent regional stress, the edifice, thepossible presence of a pressurized feeding system and of heterogeneities inthe elastic behavior of country rocks. The criteria to assessinstability are the development of tensile stresses and, in compression, theNavier–Coulomb criterion. The presence of asymmetric heterogeneous structureswith lateral elastic contrast has been considered by solvingthree-dimensional (3D) models. To have computationally tractable models, axis-symmetric models were solved first, considering lateral symmetricheterogeneities of different shapes and sizes around the symmetry axis. This allowed us to assess the minimum size of smallermodels (submodels) to be developed in 3D. Thesubmodels were then solved including asymmetrical heterogeneities.In all the analyzed cases, the main characteristics of theinstabilities/stabilities found with the 3D asymmetric models are verysimilar to those found by the analogous symmetric models.Moreover, the presence of sharp lateral elastic contrast at shallow depthappear to produce a greater instability on the flanks of the volcanicedifice. 相似文献
2.
We developed an anisotropic effective theoretical model for modeling the elastic behavior of anisotropic carbonate reservoirs by combining the anisotropic self-consistent approximation and differential effective medium models. By analyzing the measured data from carbonate samples in the TL area, a carbonate pore-structure model for estimating the elastic parameters of carbonate rocks is proposed, which is a prerequisite in the analysis of carbonate reservoirs. A workflow for determining elastic properties of carbonate reservoirs is established in terms of the anisotropic effective theoretical model and the pore-structure model. We performed numerical experiments and compared the theoretical prediction and measured data. The result of the comparison suggests that the proposed anisotropic effective theoretical model can account for the relation between velocity and porosity in carbonate reservoirs. The model forms the basis for developing new tools for predicting and evaluating the properties of carbonate reservoirs. 相似文献
3.
Wan Zheng 《地震工程与工程振动(英文版)》2015,14(2):229-238
A simple cyclic elastoplastic constitutive model for sand is proposed based on the UH model for overconsolidated clay. The proposed model has the following features. First, in order to describe the stress-induced anisotropy in sand, a rotational hardening rule is introduced for the evolution of the yield surface axis with development of plastic deviatoric strain in the principal stress space. Second, the relationship between the rotational axis and stress-induced anisotropy is modeled by introducing the slope of rotational axis into the yield function. The fl atness of the yield surface can be determined by the slope of rotational axis. Finally, a revised unifi ed hardening parameter is proposed to incorporate the stress-induced anisotropy. The model capability in describing the cyclic response of sand is verifi ed by comparing the simulations with available test results. 相似文献
4.
5.
A. Schubnel O. Nishizawa K. Masuda X. J. Lei Z. Xue Y. Guégen 《Pure and Applied Geophysics》2003,160(5-6):869-887
— A set of experiments on four samples of Oshima Granite at 15, 40 and 60 MPa confining pressure have been performed in order to investigate the damage behavior of granite submitted to deviatoric stress. In addition an experiment on one sample of Toki Granite at 40 MPa confining pressure was performed, in order to compare and elucidate the structural effects. Using acoustic emission data, strain measurements and elastic wave velocities allow to define consistently a damage domain in the stress space. In this domain, microcracking develops. The microcracking process is, in a first stage, homogeneous and, close to failure, localized. Elastic wave velocities decrease in the damage domain and elastic anisotropy develops. Using Kachanov's model (1993), elastic wave velocities have been inverted to derive the full second-order crack density tensor and characterize the fluid saturation state from the fourth-order crack density tensor. Crack density is strongly anisotropic and the total crack density close to failure slightly above one. The results indicate that the rock is saturated in agreement with the experimental conditions. The model is thus shown to be very appropriate to infer from elastic wave velocities a complete quantitative characterization of the damaged rock. 相似文献
6.
二维横各向同性弹性随机介质中的波场特征 总被引：9，自引：4，他引：5
本文通过交错网格有限差分正演．模拟了平面地震波在二维横各向同性弹性随机介质模型中的传播及其自激自收时间记录．为研究横各向同性弹性随机介质模型中的波场特征,我们在五个不同的时间区段上,分别计算剖面的三个统计特征(横向中心频率、纵向中心频率、波场能量相对值)．这样,对应每一个横各向同性弹性随机介质模型．均可计算得到15个不同的波场特征量．我们通过在二维横各向同性弹性随机介质中的正演模拟．研究当自相关长度以及介质的各向异性系数变化时,对应的上述波场特征量的变化特点．证实了在随机介质模型中．各向异性系数的变化会引起波场记录上的某些统计特征的变化,归纳得出了若干结论． 相似文献
7.
Characterizing the effect of elastic interactions on the effective elastic properties of porous,cracked rocks 
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下载免费PDF全文 Elastic interactions between pores and cracks reflect how they are organized or spatially distributed in porous rocks. The principle goal of this paper is to understand and characterize the effect of elastic interactions on the effective elastic properties. We perform finite element modelling to quantitatively study how the spatial arrangement of inclusions affects stress distribution and the resulting overall elasticity. It is found that the stress field can be significantly altered by elastic interactions. Compared with a non‐interacting situation, stress shielding considerably stiffens the effective media, while stress amplification appreciably reduces the effective elasticity. We also demonstrate that the T‐matrix approach, which takes into account the ellipsoid distribution of pores or cracks, can successfully characterize the competing effects between stress shielding and stress amplification. Numerical results suggest that, when the concentrations of cracks increase beyond the dilute limit, the single parameter crack density is not sufficient to characterize the contribution of the cracks to the effective elasticity. In order to obtain more reliable and accurate predictions for the effective elastic responses and seismic anisotropies, the spatial distribution of pores and cracks should be included. Additionally, such elastic interaction effects are also dependent on both the pore shapes and the fluid infill. 相似文献
8.
Discrete Element Modeling of Stress and Strain Evolution Within and Outside a Depleting Reservoir 总被引：1，自引：0，他引：1
Stress changes within and around a depleting petroleum reservoir can lead to reservoir compaction and surface subsidence,
affect drilling and productivity of oil wells, and influence seismic waves used for monitoring of reservoir performance. Currently
modeling efforts are split into more or less coupled geomechanical (normally linearly elastic), fluid flow, and geophysical
simulations. There is evidence (from e.g. induced seismicity) that faults may be triggered or generated as a result of reservoir
depletion. The numerical technique that most adequately incorporates fracture formation is the DEM (Discrete Element Method).
This paper demonstrates the feasibility of the DEM (here PFC; Particle Flow Code) to handle this problem. Using an element
size of 20 m, 2-D and 3-D simulations have been performed of stress and strain evolution within and around a depleting reservoir.
Within limits of elasticity, the simulations largely reproduce analytical predictions; the accuracy is however limited by
the element size. When the elastic limit is exceeded, faulting is predicted, particularly near the edge of the reservoir.
Simulations have also been performed to study the activation of a pre-existing fault near a depleting reservoir. 相似文献
9.
We examine the one-dimensional direct current method in anisotropic earth formation. We derive an analytic expression of a simple, two-layered anisotropic earth model. Further, we also consider a horizontally layered anisotropic earth response with respect to the digital filter method, which yields a quasi-analytic solution over anisotropic media. These analytic and quasi-analytic solutions are useful tests for numerical codes. A two-dimensional finite difference earth model in anisotropic media is presented in order to generate a synthetic data set for a simple one-dimensional earth. Further, we propose a particle swarm optimization method for estimating the model parameters of a layered anisotropic earth model such as horizontal and vertical resistivities, and thickness. The particle swarm optimization is a naturally inspired meta-heuristic algorithm. The proposed method finds model parameters quite successfully based on synthetic and field data. However, adding 5 % Gaussian noise to the synthetic data increases the ambiguity of the value of the model parameters. For this reason, the results should be controlled by a number of statistical tests. In this study, we use probability density function within 95 % confidence interval, parameter variation of each iteration and frequency distribution of the model parameters to reduce the ambiguity. The result is promising and the proposed method can be used for evaluating one-dimensional direct current data in anisotropic media. 相似文献
10.
The phase and group velocity surfaces are essential for wave propagation in anisotropic media. These surfaces have certain features that, especially, for shear waves result in complications for modelling and inversion of recorded wavefields. To analyse wave propagation in an anisotropic model, it is important to identify these features in both the phase and group domains. We propose few characteristics for this analysis: the energy flux angle, decomposed in the polar and azimuth angle correction angles and enhancement factor, which is able to characterize both singularity points and triplication zones. The very simple equation that controls the triplications is derived in the phase domain. The proposed characteristics are illustrated for elastic and acoustic anisotropic models of different symmetry classes. 相似文献
11.
Tuan Nguyen-Sy Quy-Dong To Minh-Ngoc Vu The-Duong Nguyen Thoi-Trung Nguyen 《Geophysical Prospecting》2020,68(8):2557-2578
This paper aims to demonstrate that the elastic stiffnesses and the anisotropic parameters of rocks can be accurately predicted from geophysical features such as the porosity, the density, the compression stress, the pore pressure and the burial depth using relevant machine learning methods. It also suggests that the extreme gradient boosting method is the best method for this purpose. It is more accurate, extremely faster to train and more robust than the artificial neural networks and the support vector machine methods. Very high R-squared scores was obtained for the predicted elastic stiffnesses of a relevant dataset that is available in the literature. This dataset contains different types of rocks, and the values of the features are in large ranges. An optimal set of parameters was obtained by considering an appropriate sensitivity analysis. The optimized model is very easy to implement in Python for practical applications. 相似文献
12.
Jin-Yong Gui Jian-Hu Gao Xue-Shan Yong Sheng-Jun Li Bin-Yang Liu Wan-Jin Zhao 《应用地球物理》2015,12(4):523-532
Variation of reservoir physical properties can cause changes in its elastic parameters. However, this is not a simple linear relation. Furthermore, the lack of observations, data overlap, noise interference, and idealized models increases the uncertainties of the inversion result. Thus, we propose an inversion method that is different from traditional statistical rock physics modeling. First, we use deterministic and stochastic rock physics models considering the uncertainties of elastic parameters obtained by prestack seismic inversion and introduce weighting coefficients to establish a weighted statistical relation between reservoir and elastic parameters. Second, based on the weighted statistical relation, we use Markov chain Monte Carlo simulations to generate the random joint distribution space of reservoir and elastic parameters that serves as a sample solution space of an objective function. Finally, we propose a fast solution criterion to maximize the posterior probability density and obtain reservoir parameters. The method has high efficiency and application potential. 相似文献
13.
《Advances in water resources》2002,25(4):371-387
To determine the origin of fractional flow dimensions identified from the results of pumping tests in fractured reservoir, the geometric specificities of synthetic networks are compared to flow dimensions obtained from simulated pumping tests. The modeled reservoirs studied in this paper constitute a system of orthogonal fractures generated by using a pseudo-random process controlled by simple mechanical rules. Flow induced by pumping is simulated while considering the intersections between discontinuities as pipes with various apertures. In many cases, the simulations result in fractional flow dimension although the flow-path network is not self-similar at different scales. We also show that the range of pipe conductance can affect early-time flow behavior although late-time flow behavior appears to be insensitive to the latter. Finally we propose an explanation for the fractional dimension of flow while considering the spatial distribution of interconnections between flow paths. 相似文献
14.
以一多层框架结构停车场的地基基础为研究对象,分析其在将来可能发生大地震中的动力特性。除地基可能出现的液化,还包括地震中的瞬时沉降及地震后地基长期固结沉降,尤其是不均匀沉降。采用水土耦合2维有限元分析法,对研究领域的地基基础及上部结构进行整体建模。计算中采用的地震波为一三连动人工地震波,最大加速度为182gal,主震持续150s。为比较不同的基础形式对地基液化和沉降的影响,对采用长桩和密集型短柱两种基础形式做分析比较。有限元计算中,采用能反映其地层土交变移动特性的弹塑性本构模型来描述土的动力学特性,桩基础和上部框架结构采用梁单元模型,密集型短柱基础采用弹性单元模型。结果表明,除地震中地基的液化,震后随着超孔隙水压的消散,地基基础长期不均匀沉降也是不可忽略的重要问题。 相似文献
15.
Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou George D. Bouckovalas 《Soil Dynamics and Earthquake Engineering》2010
This paper presents the constitutive relations and the simulative potential of a new plasticity model developed mainly for the seismic liquefaction analysis of geostructures. The model incorporates the framework of critical state soil mechanics, while it relies on bounding surface plasticity with a vanished elastic region to simulate the non-linear soil response. Key constitutive ingredients of the new model are: (a) the inter-dependence of the critical state, the bounding and the dilatancy (open cone) surfaces on the basis of the state parameter ψ, (b) a (Ramberg–Osgood type) non-linear hysteretic formulation for the “elastic” strain rate, (c) a discontinuously relocatable stress projection center related to the “last” load reversal point, which is used for mapping the current stress point on model surfaces and as a reference point for introducing non-linearity in the “elastic” strain rate and finally (d) an empirical index of the directional effect of sand fabric evolution during shearing, which scales the plastic modulus. In addition, the paper outlines the calibration procedure for the model constants, and exhibits its accuracy on the basis of a large number of laboratory element tests on Nevada sand. More importantly, the paper explores the potential of the new model by presenting simulations of the VELACS centrifuge tests of Models No 1 and 12, which refer to the free-field liquefaction response of Nevada sand and the seismic response of a rigid foundation on the same sand, respectively. These simulations show that the new model can be used successfully for the analysis of widely different boundary value problems involving earthquake soil liquefaction, with the same set of model constants calibrated on the basis of laboratory element tests. 相似文献
16.
Plasticity model for sand under small and large cyclic strains: a multiaxial formulation 总被引：1，自引：0，他引：1
Achilleas G. Papadimitriou George D. Bouckovalas 《Soil Dynamics and Earthquake Engineering》2002,22(3):15
This paper presents the multiaxial formulation of a plasticity model for sand under cyclic shearing. The model adopts a kinematic hardening circular cone as the yield surface and three non-circular conical surfaces corresponding to the deviatoric stress ratios at phase transformation, peak strength and critical state. The shape of the non-circular surfaces is formulated in accordance with the experimentally established failure criteria, while their size is related to the value of the state parameter ψ. To simulate cyclic response under small and large shear strain amplitudes without a change in model parameters, it was found necessary to introduce: (a) a non-linear hysteretic (Ramberg–Osgood type) formulation for the strain rate of elastic states and (b) an empirical index of the effect of fabric evolution during shearing which scales the plastic modulus. This index is estimated in terms of a macroscopic second-order fabric tensor, which develops as a function of the plastic volumetric strain increment and the loading direction in the deviatoric plane. Comparison of simulations to pertinent data from 27 resonant column, cyclic triaxial and cyclic direct simple shear tests provide a measure for the overall accuracy of the model. 相似文献
17.
地应力的精确预测是对页岩地层进行水平井钻井轨迹设计和压裂的基础.本文在分析页岩构造特征的基础上,提出了适用于页岩地层的岩石物理等效模型的建立流程,并以此为基础实现了最小水平地应力的有效预测.首先,通过分析页岩地层的矿物、孔隙、流体及各向异性特征,将其等效为具有垂直对称轴的横向各向同性介质,进行了页岩岩石物理等效模型的构建;然后建立了页岩地层纵横波速度经验公式,并将该经验公式与岩石物理等效模型均应用于实际页岩工区的横波速度预测中,二者对比表明,本文中建立的页岩气岩石物理等效模型具有更高的横波预测精度,验证了该模型的适用性;最后,利用该模型计算各弹性刚度张量,进而实现了页岩地层最小水平地应力的预测,与各向同性模型估测结果对比表明,该模型预测的最小水平地应力与地层瞬间闭合压力一致性更高,且储层位置更为明显,具有较高的实用性. 相似文献
18.
根据模型试验相似比尺和桩土间应力协调要求,用机制砂、河砂、水泥、石粉等配置了40组（每组6个）低强度、低弹性模量的圆柱形微混凝土相似材料试件。测试结果表明：微混凝土具有和原型混凝土大致相同的应力应变阶段和破坏模式,可以模拟原型结构的力学行为和变形、破坏特征。砂率和石粉取代率不同时,微混凝土试件的轴压强度和弹性模量在较大范围内变化;砂率较合适时,同一配合比微混凝土6个试件的强度和弹性模量一致性较好。微混凝土可以满足不同比尺模型试验对相似材料力学性质稳定、力学参数可以在较大范围内调整的要求。 相似文献
19.
Changes in geophysical properties caused by fluid injection into porous rocks: analytical models 下载免费PDF全文
下载免费PDF全文 Steven R. Pride James G. Berryman Michael Commer Seiji Nakagawa Gregory A. Newman Donald W. Vasco 《Geophysical Prospecting》2017,65(3):766-790
Analytical models are provided that describe how the elastic compliance, electrical conductivity, and fluid‐flow permeability of rocks depend on stress and fluid pressure. In order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites, the models require a population of cracks to be present in a possibly porous host phase. The central objective is to obtain a consistent mean‐field analytical model that shows how each modeled rock property depends on the nature of the crack population. The crack populations are described by a crack density, a probability distribution for the crack apertures and radii, and the averaged orientation of the cracks. The possibly anisotropic nature of the elasticity, conductivity, and permeability tensors is allowed for; however, only the isotropic limit is used when comparing to laboratory data. For the transport properties of conductivity and permeability, the percolation effect of the crack population linking up to form a connected path across a sample is modeled. However, this effect is important only in crystalline rock where the host phase has very small conductivity and permeability. In general, the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable. 相似文献
20.
Based on the consistency-viscoplastic constitutive model,the static William-Warnke model with three-parameters is modified and a consistency-viscoplastic William-Warnke model with three-parameters is developed that considers the effect of strain rates. Then,the tangent modulus of the consistency viscoplastic model is introduced and an implicit backward Elure iterative algorithm is developed. Comparisons between the numerical simulations and experimental data show that the consistency model properly provides the uniaxial and biaxial dynamic behaviors of concrete. To study the effect of strain rates on the dynamic response of concrete structures,the proposed model is used in the analysis of the dynamic response of a simply-supported beam and the results show that the strain rate has a significant effect on the displacement and stress magnitudes and distributions. Finally,the seismic responses of a 278 m high arch dam are obtained and compared by using the linear elastic model,as well as rate-independent and rate-dependent William-Warnke three-parameter models. The results indicate that the strain rate affects the first principal stresses,and the maximal equivalent viscoplastic strain rate of the arch dam. Numerical calculations and analyses reveal that considering the strain rate is important in the safety assessments of arch dams located in seismically active areas. 相似文献