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往复荷载作用下土体的广义塑性分析 总被引：2，自引：0，他引：2
针对往复荷载作用下土体变形和孔压发展的特点，应用能模拟低应力水平下塑性变形的边界面模型，将其线弹性卸载过程改进为弹塑性，从而建立土的边界面广义塑性本构理论，数值模拟结果与三轴试验数据吻合较好。 相似文献
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土的本构模型研究现状及发展趋势 总被引：2，自引：0，他引：2
从两方面总结了前人关于土体本构关系的成果以及目前的发展状况：一方面,从宏观现象学角度介绍了剑桥模型、弹性－硬化塑性模型以及为描述循环荷载条件下土的本构特性所建立的多重屈服面模型和边界模型;另一方面,阐述了土的微观结构和土微结构力学模型的研究状况。认为今后的土本械模型研究趋势必将与土的结构性研究紧密相联,成为２１世纪土力学的核心。 相似文献
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天然土体的初始各向异性通常可对其后继循环特性产生显著影响。现有考虑循环载荷作用的土体弹塑性模型,往往采用类似修正剑桥模型的椭圆形屈服面,已有研究表明,该椭圆形屈服面因其拉伸弹性区域偏大,针对天然K0固结状态的土体,其计算精度较差。基于新近提出的广义各向同性硬化准则,在边界面方程中引入初始各向异性张量,并采用空间滑动面破坏准则（SMP）的变换应力法,建立了能考虑饱和黏土初始各向异性的循环边界面塑性模型。分别针对等压和偏压固结的饱和黏土静、动三轴试验进行模拟,结果表明,该模型能合理反映土体的初始各向异性及其后继循环动力特性。 相似文献
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堆积层滑坡作为一种非线性系统变形演化规律复杂，准确量化坡体形变过程中滑移面边界变化、降雨入渗边界、水头边界和流量边界等重要参数是堆积层滑坡变形破坏机理研究的基础。此项研究基于电阻率成像技术，可依据岩土体成分、结构的不同和地层间电性的差异实现快速、多维剖面成像，并通过深度神经网络建立了浅层高分辨率电阻率成像数据和各类监测数据的“时间-空间-属性”邻近域特征信息统一表达矩阵，实现了各监测项空间权重的快速收敛。在此基础上，用逐层、逐个递推式回归分析方法分析深层电阻率成像数据，准确构建了反映堆积层滑坡形变过程的内部结构多维电性特征模型。试验证明，该方法有效地提高了各类边界参数基于地电信息成像监测结果的实时性和准确性，为堆积层滑坡形变破坏机理研究提供理论与方法支撑。 相似文献
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边界面模型在MARC中的开发实现及应用 总被引：1，自引：1，他引：0
介绍了一个简化的边界面动本构模型及其在通用有限元软件MARC中开发实现的技术。通过对循环单剪试验的模拟验证了程序的可靠性和模型的表现。基于所添加的边界面模型,对一均质场地进行了非线性动力反应分析,并和等效线性动力反应分析的结果进行了对比,表明了模型和分析方法的有效性。最后以一理想土坝为例说明了用所添加的本构模型进行土石坝非线性动力反应分析的方法,并给出了相应的结果。 相似文献
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基于地质剖面构建三维地质模型的方法研究 总被引：5，自引：0，他引：5
地质剖面是三维地质建模的重要数据源,运用地质剖面构建三维地质模型的方法应用较为广泛。在模型构建之前,统一确定模数据的坐标系和比例足,建立原始资料数据库。构建三维地质模型的关键是不同地质界面。本文详细介绍了模型边界面、断层面、地层界面、岩体界面等4种主要地质界面的构建流程与方法,尤其对褶皱构造、地层界面的断层效应、复杂岩体界面等的构建进行了重点阐述按模型边界面(模型的底界面和四周边界面)、DEM面、断层面、其他地质界面的顺序依次构建地质界面,构建断层面和其他地质界面时严格按先新后老的顺序。运用已构建好的地质界面按先新后老的顺序逐个、依次建立单个地质体,再将所有地质体的面模型组合成整个模型的面模型。通过对面模型进行网格(实体)填充和对网格赋予相应的属性值,最终构建三维地质模型。 相似文献
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根据断裂条件和充填质条件，基于理性力学观点，研究断层面对地震子波的反射和透射问题。先将断层面用弹塑性接触面模型加以力学描述，应用增量波动概念引出地震波的边界条件，然后得到断层面的理论反射系数和透射系数。结果表明，断层面反射依赖于充填质的力学属性；并且在流体充填时，断层面对透射波表现为带通滤波特性。据此可以用于检测断层含水性。 相似文献
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《岩土力学》2017,(4):1203-1210
为了研究层流状态下粗糙单裂隙面的渗流特性,基于格子Boltzmann方法,建立了压力作用下单裂隙面渗流的数值模型。采用D2Q9模型模拟离散速度分布方向,在宏观尺度上,上、下边界设置为不透水边界(u_x=u_y=0),左、右边界为压力边界(左侧压力p_(in)大于右侧压力p_(out))在微观尺度上,左、右边界及光滑裂隙表面采用非平衡态外推格式,粗糙裂隙表面采用标准反弹格式。编制了相应的计算程序,验证了光滑平板裂隙流的立方定律。采用分段随机裂隙长及裂隙宽的方法生成了粗糙裂隙面,并基于格子Boltzmann方法研究了不同粗糙裂隙面方案的渗流特性。研究结果表明:对于粗糙裂隙面,渗流特征极大程度取决于裂隙表面形貌,随着相对粗糙度的增加,裂隙渗流规律明显偏离立方定律。为此,考虑裂隙面相对粗糙度的影响,根据不同裂隙粗糙面方案的数值计算结果,提出了层流状态下粗糙裂隙面渗流的立方定律修正公式,为系统研究复杂粗糙裂隙的水力特性奠定了一定的基础。 相似文献
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Numerical studies of subduction zone dynamics on a regional scale usually use a limited spatial extent for their models and therefore need to define boundary conditions on all model edges. These boundary conditions imply a choice for the mechanical and thermal state of the surrounding regions which may influence the evolution of the model system. We investigate the role of the surface and lateral boundary conditions for simple mechanical subduction models using a standard finite element method. We find that subduction is only possible if the slab can decouple from the surface. This decoupling can be achieved by a true free surface, a free-slip surface with a weak crust for the subducting plate, or a free-slip surface with a layer of low viscosity, low density material (‘sticky air’) between the model surface and the crust. Models of slab dynamics that employ a free-slip surface reproduce trench migration, slab sinking velocities and slab geometry of models with a free surface, as long as they use either a weak crust, which can be viscous, viscoelastic and/or brittle, or a ‘sticky air’ layer. The vertical topography will however not be reproduced for free-slip models without a ‘sticky air’ layer. For ocean–ocean convergent models we find that the application of inflow boundary conditions at the edges of the subducting or overriding lithosphere controls trench motion and the geometry of the subducting slab. Inflow on the overriding side causes trench retreat and a slab resting on the lower mantle, whereas inflow restricted to the subducting side can cause trench advance and a slab which folds on the lower mantle. 相似文献
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Although there has been significant progress in the seismic imaging of mantle heterogeneity,the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models.To address this question,we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns.A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow,without imposing prescribed surface velocities(i.e.,plate-like boundary condition).As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip(rigid) boundary condition.A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved,and its geographical location is fixed during the evolution of mantle flow.Considering the impact of different assumed surface boundary conditions(rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure.Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term,stable pattern of thermal heterogeneity in the lowermost mantle that resembles the presentday Large Low Shear Velocity Provinces(LLSVPs),especially below the Pacific.The evolution of subduction zones may be,however,influenced by the mantle-wide flow driven by deeply-rooted and longlived superplumes since Archean times.These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs.We find there is no need for dense chemical ’piles’ in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly.Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise. 相似文献
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We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones. 相似文献
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This paper presents a new scheme that can be used to overcome the overshooting effect, one of the well known problems occurs during application of bounding surface plasticity models in numerical analysis of boundary value problems. The scheme is based on definition of clouds of loading surfaces with a specific margin of strains within which unloading does not accompanied kinematic hardening. The basic concept of the scheme is introduced and the methodology and the relevant step by step algorithm to implement this scheme are presented. This scheme has been incorporated in the UNSW bounding surface model and implemented in a finite difference code and used to simulate cyclic triaxial tests as well as complicated monotonic and dynamic boundary value problems. The satisfactory performance of the scheme is demonstrated and its efficiency is discussed thorough these simulations. 相似文献
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辽河油田锦99块沙河街组四段上亚段杜家台油层是典型的扇三角洲前缘沉积,主要由扇三角洲前缘水下分流河道和河道砂坝组成。依据高分辨率层序地层学和储层构型理论,采用层次分析方法,对锦99块沙四上亚段扇三角洲前缘砂体构型界面进行了层次表征。综合利用岩心资料和测井资料,识别出11种岩相类型和4种岩相组合。根据高频湖泛面、冲刷面、粒序突变面和岩相转换面将沙四上亚段Ⅰ3砂层组和Ⅱ1砂层组划分为6个短期旋回、15个超短期旋回。在等时格架内,建立了扇三角洲前缘储层5级构型界面层次,层次界面以三级和四级为主,四级界面分布较稳定,三级界面零星分布。总结出两种层次界面分布模式:较稳定分布的界面和随机型分布的界面。储层层次分析为研究区构型约束建模提供了依据。 相似文献
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S. M. N. Shojaee O. Uzol Ö. Kurç 《International Journal of Environmental Science and Technology》2014,11(1):59-68
This paper presents the design, computational analysis and experimental study of passive device configurations which utilized in the Ankara Wind Tunnel to simulate the atmospheric boundary layer within the test section. The study here is part of a joint project between the Aerospace and Civil Engineering Departments at Middle East Technical University, which involves testing of high-rise building models in the Ankara Wind Tunnel. The design consists of spires and rows of cubical surface roughness elements at the inlet. The preliminary computational analysis shows that the current design may provide the desired boundary layer thickness at about 4.0 m downstream of the test section inlet, which leaves enough room for the building models to be placed in the test section. This study also helps obtaining a preliminary understanding of the boundary layer development and reducing the tunnel operation time and cost during the actual experimentation phase. At the end, experimental results show acceptable results of this study. 相似文献
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The use of spectral analysis-based exact solutions to characterize topography-controlled groundwater flow 总被引：2，自引：1，他引：1
Spectral analysis enhances the ability to analyze groundwater flow at a steady state by separating the top boundary condition into its periodic forms. Specifically, spectral analysis enables comparisons of the impact of individual spatial scales on the total flow field. New exact spectral solutions are presented for analyzing 3D groundwater flow with an arbitrarily shaped top boundary. These solutions account for depth-decaying, anisotropic and layered permeability while utilizing groundwater flux or the phreatic surface as a top boundary condition. Under certain conditions, groundwater flow is controlled by topography. In areas where the groundwater flow is controlled by the topography, the unknown water table is often approximated by the topography. This approximation induces a systematic error. Here, the optimal resolution of digital elevation models (DEMs) is assessed for use as a top boundary in groundwater flow models. According to the analysis, the water-table undulation is smoother than the topography; therefore, there is an upper limit to the resolution of DEMs that should be used to represent the groundwater surface. The ability to represent DEMs of various spectral solutions was compared and the results indicate that the fit is strongly dependent on the number of harmonics in the spectral solution. 相似文献
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Nucleation and growth of kink bands 总被引：1，自引：0，他引：1
L.E. Weiss 《Tectonophysics》1980,65(1-2)
The geometric and strain properties of an ideal kink band in a perfectly plastic material with one slip surface are determined and two plausible modes by which a kink band can grow while maintaining these properties are presented. The first mode involves change in the orientation of the boundary surface of the kink band as it broadens. In the second mode the initial orientation of this boundary surface is maintained during broadening.A theoretical model is proposed for kink band formation in three stages: first, in an elastically strained material with a suitably oriented planar anisotropy; a small nucleus is either present or develops, and grows in thickness by one or the other or by both of the growth modes; second, as some critical thickness is reached, this nucleus propagates longitudinally until the excessive elastic distortion surrounding its ends is sufficiently relieved, or until the boundary of the body is reached; and third, the band widens by lateral migration of its boundaries, most probably by mode 2 growth.It is proposed that the direction of longitudinal propagation—and hence the orientation of the kink band with respect to principal normal stress—is decided by the value of a, the kink angle, in the nucleus at the time the critical thickness for propagation is reached. A further proposal is that this value of a is in turn decided by a principle of maximum plastic work: the instantaneous increment in strain or in volume within a nucleus is always the one for which the instantaneous increment in plastic work is a maximum at constant deviatoric stress.Calculations based on this theory for the two growth modes working either separately or together as competing processes yield three models of kink band nucleation in reasonable agreement with published experimental data. The most appealing of these models physically is one in which early mode 1 growth is replaced by mode 2 growth as the increments in mechanical work for the two modes become equal. 相似文献
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The main objective of this work is to develop a novel moving‐mesh finite‐volume method capable of solving the seepage problem in domains with arbitrary geometries. One major difficulty in analysing the seepage problem is the position of phreatic boundary which is unknown at the beginning of solution. In the current algorithm, we first choose an arbitrary solution domain with a hypothetical phreatic boundary and distribute the finite volumes therein. Then, we derive the conservative statement on a curvilinear co‐ordinate system for each cell and implement the known boundary conditions all over the solution domain. Defining a consistency factor, the inconsistency between the hypothesis boundary and the known boundary conditions is measured at the phreatic boundary. Subsequently, the preceding mesh is suitably deformed so that its upper boundary matches the new location of the phreatic surface. This tactic results in a moving‐mesh procedure which is continued until the nonlinear boundary conditions are fully satisfied at the phreatic boundary. To validate the developed algorithm, a number of seepage models, which have been previously targeted by the other investigators, are solved. Comparisons between the current results and those of other numerical methods as well as the experimental data show that the current moving‐grid finite‐volume method is highly robust and it provides sufficient accuracy and reliability. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献