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141.
借助一个简单的大陆与大陆碰撞模型,即把两个大陆的碰撞简化为两个粘弹性块体的碰撞,两个块体之间的不连续变形面对应两个大陆之间的碰撞断裂带,运用三维粘弹性拉格朗日非连续变形有限元(LDDA)方法,通过分析模型中不连续变形面的存在对两个粘弹性块体碰撞变形的影响,探讨了大陆碰撞断裂带的倾角和摩擦系数对两个大陆碰撞变形影响的一般规律,给出了大陆碰撞变形的一些显著的特点。尽管运算模型的几何尺寸、边界条件等参考了印度和欧亚大陆碰撞的实际特征,但所得结果适用于更一般的情况。研究结果表明,碰撞断裂带倾角和摩擦系数对陆-陆碰撞变形有着重要的影响。当断裂带倾角在15~30°时,两个大陆板块碰撞导致的仰冲板块一侧隆升高度相对更大,利于形成高大的山脉,其中以15°倾角对应的仰冲板块一侧隆升最高;当断裂带倾角在30~45°时,两个大陆板块碰撞导致的俯冲板块的俯冲深度相对更深,利于形成深陷的盆地,其中以45°倾角对应的俯冲陆块一侧俯冲最深;当断裂带倾角≥75°时,两个大陆板块之间的相对俯冲和仰冲作用变得不明显。碰撞断裂带摩擦系数越小,碰撞过程中两个大陆板块之间相对俯冲和仰冲作用越强,形成高大的山脉和深陷的盆地要求碰撞断裂带摩擦系数≤0.2。从大陆与大陆碰撞变形构造特征看,除发育前陆盆地-山脉系统外,在仰冲陆块一侧靠近造山带后缘还发育呈不对称结构的挤压性凹陷,当两个大陆板块碰撞断裂带倾角在15~30°时,该类型凹陷更容易形成,其中以30°倾角对应的凹陷最深,反映其形成可能是大陆碰撞过程中陆块之间相对俯冲和仰冲运动的综合结果。  相似文献   
142.
滑坡运动过程仿真分析   总被引:2,自引:0,他引:2  
滑坡是一个动态过程,滑坡体的运动是一个集滑动,转动,拉张等运动方式的复杂运动过程,传统的极限平衡和计算和有限元分析均无法描述滑坡的运动学特点和运动过程。非连续变形分析(DDA)是最近发展起来的一种新的离散数值分析方法。该方法基于块体的运动学理论及数值分析,可以开展块体的静力和动力学计算。应用非连续变形分析方法对长江三峡区新滩滑坡的运动全过程进行了数值模拟研究,模拟方案充分依据该滑坡的地质,地形特征,按不同岩土体和地质结构面类型进行块体单元的划分,共划分成504个块体单元。模拟结果表明,新滩滑坡是以斜坡中部姜家坡一带的局部破坏为其运动的开始阶段,并进一步牵引上部滑体和推动下部滑体。代表性块体单元的位移变化曲线和滑动速度变化曲线反映了滑动过程中滑坡体块体系统的变形是非连续的,各处块体的动态形态各异,从而很好地再现了新滩滑坡的整个动态过程,揭示了滑坡的运动机制。  相似文献   
143.
A Boundary Element based Discontinuous Deformation Analysis (BE‐DDA) method is developed by implementing the improved dual reciprocity boundary element method into the open close iterations based DDA. This newly developed BE‐DDA is capable of simulating both the deformation and movement of blocks in a blocky system. Based on geometry updating, it adopts an incremental dynamic formulation taking into consideration initial stresses and dealing with external concentrated and contact forces conveniently. The boundaries of each block in the discrete blocky system are discretized with boundary elements while the domain of each block is divided into internal cells only for the integration of the domain integral of the initial stress term. The contact forces among blocks are treated as concentrated forces and the open–close iterations are applied to ensure the computational accuracy of block interactions. In the current method, an implicit time integration scheme is adopted for numerical stability. Three examples are used to show the effectiveness of the algorithm in simulating block movement, sliding, deformation and interaction of blocks. At last, block toppling and tunnel stability examples are conducted to demonstrate that the BE‐DDA is applicable for simulation of blocky systems. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
144.
The interaction of an advancing hydraulically loaded crack and in situ fracture network can yield highly complex patterns. We model the connectivity of cells in a finite element domain and in a fracture network by a simplicial complex data structure. The complete adjacency information between cells is determined by one level down facet and one level up cofacet neighborhood information. Combined with a disjoint set data structure, explicit algorithms are derived to efficiently track network connectivity and load transfer between independent fracture sets. We also propose an approach to regularize the application of hydraulic load to newly intersected in situ cracks to smoothen the transition of pressure on intersected cracks from ambient to hydraulic pressure and to avoid the sudden loading of the entire length of these cracks. Numerical results demonstrate the performance of crack connectivity and load transfer models and the effect of regularization model. The results show that as the angle between an incoming hydraulically loaded crack and an in situ crack increases, the effect of in situ crack shifts from slight realignment to diversion/offsetting of the loaded crack. As the angle difference approaches the normal angle, the loaded crack tends to penetrate through the in situ crack. The proposed schemes are also used for transient simulation of 2D reservoirs with multiple perforations surrounded by in situ cracks with and without a bias in the distribution of their orientation. It was shown that from 2 perforations with angles closer to in situ cracks at low loading rates to all perforations at higher loading rates can result in active hydraulic crack propagation. The h‐adaptive method of asynchronous space‐time discontinuous Galerkin method is used to exactly track complex fracture patterns in these dynamic fracture simulations.  相似文献   
145.
Updating the block configuration on the basis of additive decomposition and its linearized expression of the displacement increment leads to the low calculation accuracy of the original discontinuous deformation analysis (DDA) and false volume expansion. In this study, the displacement expressions of a small deformation, a large rotation, and the corresponding velocity and acceleration terms on the basis of the initial configuration are presented using multiplicative decomposition. With the use of the principle of virtual work, the stiffness matrix, mass matrix, and force vector of blocks are obtained. Compared with the original DDA, each of the block deformation parameters has obvious physical meaning as a parameter of mechanics, which can be obtained by adding the incremental deformation components of each time step directly without co-ordinate transformation. Moreover, the proposed modification automatically considers the block deformation produced by centrifugal and Coriolis forces. The analysis of some typical numerical examples have verified the accuracy of the strain and stress calculated by the proposed method, and the current configuration is updated by the total displacements, which completely overcomes the false volume expansion and provides reasonable linear strains.  相似文献   
146.
An extensive examination of the discontinuous deformation analysis (DDA) in block dynamic sliding modeling is carried out in this paper. Theoretical solutions for a single block sliding on an arbitrarily inclined plane by applying the horizontal/vertical seismic loadings to the sliding block as acceleration time histories or to the base as constraint displacement time histories are derived. As compared with the theoretical solutions, for a single block sliding, the DDA predicts the sliding displacements and block interaction forces accurately under various base incline angles and friction angles under both the harmonic loadings and a real seismic loading. The vertical seismic component may influence the block sliding displacements to different extent, and the DDA can capture these phenomena successfully and give accurate results. For the calculation of the single block relative sliding, both the theoretical and the DDA solutions indicate that applying the seismic accelerations as constraint displacement time histories (derived by integrating the seismic accelerations twice) to the base is equivalent to applying the seismic accelerations as volume forces to the sliding block in the opposite directions. The DDA modeling also demonstrates that this conclusion still stands for the case of multi‐block sliding. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
147.
土壤湿度直接作用于植被的呼吸、蒸腾和各种化学反应,是生态气象学的重要的环境因素。降雨和蒸发作为土壤湿度的两个重要扰动因子,对其进行定性的理论分析及定量的数值分析具有重要意义,尤其在半干旱和干旱地区。蒸发对土壤湿度具有持续的耗散作用,可以视为连续的,而降雨作为湿度补充作用具有脉冲效应。为阐释降雨和蒸发对土壤湿度的影响,该文通过建立脉冲降雨—蒸发对土壤湿度响应模型,并对其进行定性分析,得到此微分方程系统的周期解的充分条件。在此基础上,通过Forcal对方程参数拟合,并以Maple作为数值分析工具,对此系统进行数值模拟。  相似文献   
148.
We compare the factors which affect the movement of Tibetan Plateau by building three types of finite element models: an elastic materials (M-EC), a continuous model composed by non-linear materials (M-PC), and an elastic model with discontinuous fault movements (M-ET). Both in M-ET and M-EC, the materials in Qiangtang and Lhasa block are elastic, and in M-ET, discontinuous movement of faults is considered for evaluating the effects of strike-slip faults. In model M-PC Druker-Prager plastic materials are us...  相似文献   
149.
As a hybrid method, the nodal‐based discontinuous deformation analysis (NDDA) greatly improves the stress accuracy within each DDA block by coupling a well‐defined finite element mesh inside the DDA block; at the same time, the NDDA inherits the unique block kinematics of the standard DDA method. Each finite element mesh line inside the DDA block is treated as a potential crack, which enables the transformation of the block material from continuum to discontinuum through the tensile and shear fracturing mechanism. This paper introduces a double minimization procedure into the NDDA method to further improve the accuracy of the stresses evaluated at the finite element mesh lines and thus to obtain a more realistic fracture model. Three numerical examples are employed to demonstrate the improved stress accuracy by the implemented double minimization procedure and the accuracy and capability of the enhanced NDDA method in capturing brittle fracturing process. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
150.
L. Sun  B. Teng  C.F. Liu 《Ocean Engineering》2008,35(8-9):920-930
The phenomenon of irregular frequencies is a puzzle in the course of calculating the interaction of waves and structures by the boundary element method. To remove the irregular frequencies, the modified integral domain method is adopted, and continuous higher order elements and partial discontinuous higher order elements are used for discretization. By these means, the effects of the irregular frequencies are effectively removed. Effective strategies have been adopted to deal with singular integrals and nearly singular integrals at different situations. The numerical results of the horizontal wave force on a uniform cylinder in the first order and second order diffraction problems show that the present method has a good validity. At the same time, the influence of collocation parameter on accuracy of numerical results is examined in detail.  相似文献   
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