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复合单元法动力分析初步研究 总被引：1，自引：0，他引：1
复合单元法是一种适用于不连续介质结构分析的数值计算方法,优点是建立网格时不用考虑结构中不连续面,计算时能离散模拟不连续面。在复合单元法静力计算模型的基础上,提出了复合单元的动力分析方法。给出了复合单元动力分析的质量矩阵和阻尼矩阵的具体表达式,通过质量矩阵、刚度矩阵和阻尼矩阵将分布于复合单元内部的惯性力和阻尼力分别转移到复合单元的广义节点上。建立了惯性力、阻尼力、动力荷载及弹性力作用下的复合单元动力系统的控制方程组。以一个基岩内含有两条断层的混凝土重力坝模型地震为例,采用复合单元法动力分析程序进行计算,其结果与有限单元法解吻合得较好,说明所提出方法的正确性和有效性。 相似文献
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简述了复合单元法的基本原理和算法,该方法的主要优点在于可以明显地减少前处理的工作量和难度,且可以与有限单元很好地耦合在一个系统中。介绍了宝珠寺重力坝的物理模型超载试验。分别采用三维弹黏塑性复合单元法和三维弹黏塑性有限单元法对宝珠寺重力坝的超载工况进行了数值试验,并与物理试验进行比较。结果表明,三种方法得到的特征点位移吻合得较好,两种数值试验方法的整体位移和应力也基本一致。研究验证了复合单元法的正确性,也说明了该算法的主要优点：前处理简单,计算精度与有限单元法相当,同时还证实了复合单元单元法可以较好地解决复杂岩基上重力坝的变形与破坏问题。 相似文献
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针对塑料排水板(PVD)安装热源能提升PVD性能、加速竖井地基固结这一工程现象,基于热-水-应力 (T-H-M) 三场全耦合的有限元方法来模拟利用热源进行地基处理新技术(PVTD)。首先,以微分形式与等效弱形式分别给出T-H-M耦合控制方程,并推导出其有限元方程组。然后在多场耦合有限元软件中建立饱和土的T-H-M全耦合模型,并通过与已有解析解比较,验证了模型正确性。最后,对一个经典有涂抹区的竖井地基算例,分不耦合温度(UT)、耦合温度但不考虑其对饱和土物性影响(CT)、耦合温度考虑温度对饱和土渗透性影响(CTP) 3种情况进行固结计算分析。研究结果表明,相对于无热源竖井地基,CT情况下由于热源产生的附加孔隙水压力,固结速度略有下降;CTP情况下,由于热源有效改善涂抹区的渗透性能,竖井地基固结速率明显加快。上述研究结论从理论上较好地阐明了PVTD的作用机制。 相似文献
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The finite element method (FEM) and the boundary element method (BEM) are two well established numerical methods used for the analysis of underground openings. The advantages of both the methods are utilized by adopting FEBEM in which finite elements are coupled with boundary elements. A coupling procedure is presented in this paper. In using FEBEM, the effect of the location of interface boundary between finite element and boundary element regions, effect of Poisson's ratio and effect of stress ratio are discussed. It is shown that Poisson's ratio and stress ratio have significant effect on the accuracy of the results. Different discretization schemes are discussed to study their effect on accuracy and computation time. The use of different material properties in the FE region is presented. A comparative study is made with FEM for all the cases. It is shown that use of FEBEM is more advantageous than FEM. 相似文献
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Mohammad Wasiul Bari Mohamed A. Shahin 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(1):37-48
A stochastic approach that investigates the effects of soil spatial variability on stabilisation of soft clay via prefabricated vertical drains (PVDs) is presented and discussed. The approach integrates the local average subdivision of random field theory with the Monte Carlo finite element (FE) technique. A special feature of the current study is the investigation of impact of spatial variability of soil permeability and volume compressibility in the smear zone as compared to that of the undisturbed zone, in conjunction with uncoupled three-dimensional FE analysis. A sensitivity analysis is also performed to identify the random variable that has the major contribution to the uncertainty of the degree of consolidation achieved via PVDs. The results of this study indicate that the spatial variability of soil properties has a significant impact on soil consolidation by PVDs; however, the spatial variability of soil properties in the smear zone has a dominating impact on soil consolidation by PVDs over that of the undisturbed zone. It is also found that soil volume compressibility has insignificant contribution to the degree of consolidation estimated by uncoupled stochastic analysis. 相似文献
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加锚节理岩体有着复杂的细部结构和力学行为,常规的数值模型很难满足模拟这种力学行为的要求。进一步发展了笔者建立的加锚岩体的复合单元法,提出加锚节理岩体的复合单元法研究。在不考虑锚杆、节理等细部结构的情况下划分网格,分别定义了加锚岩体复合单元、不连续岩体复合单元和加锚节理岩体复合单元,并建立了其数值模型。同时,在复合单元中还定义了不同材料介质的子单元用来模拟加锚节理岩体内复杂的细部构造。对加锚节理复合单元法进行了理论推导和算例研究,通过与常规有限单元法计算结果的比较,表明了加锚节理岩体复合单元法的合理性,同时也突出体现了其前处理简便的优势。 相似文献
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大规模超长群桩基础工作性能的数值模拟 总被引：3，自引：0，他引：3
超长桩基础在土木工程中的应用越来越多,但对其工作性状的研究相对滞后。以某超长群桩基础工程为例,用三维非线性有限元方法分析了超长单桩及群桩的工作性能。计算中桩、土和承台的有限元模型均用8节点六面体等参单元,桩-土界面用有厚度的接触面单元模拟;混凝土的应力-应变关系用线弹性模型,土体用非线性Duncan-Chang弹性模型模拟;承台施工过程用分级加荷的方法模拟,承台混凝土的硬化过程用变化模量的方法模拟。计算结果表明,超长单桩的承载性状属摩擦桩,其桩身失稳的原因是桩侧土体的破坏;在群桩基础中,不同位置基桩的工作性能不完全相同,承台周边桩的工作性能与单桩类似,而与内部桩的差别较大;现行规范中推荐的群桩效应系数和有限元计算结果间存在较大差别,表明现行规范可能不适用于超长群桩基础,对超长群桩基础的工作性能进行深入研究是必要的。 相似文献
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A new development of the scaled boundary finite element method for wave motion in layered half-space
The scaled boundary finite element method (SBFEM) developed by Wolf and Song has shown certain parallels to the finite element method (FEM) and boundary element method (BEM). Because of its semi-analytical nature, SBFEM is particularly suitable for the analysis of wave propagation in unbounded domains. This paper makes a certain modification of the standard SBFEM. A new idea of scaling surface instead of a scaling center is introduced to formulate the governing SBFE equations for the analysis of wave propagation in multilayered half-space, which leads to simplifying the modeling and saving considerably the computational effort. In addition, by employing the proposed approach, some problems encountered in engineering practice, which are difficult to deal with by the conventional SBFEM, for example, 3D foundation impedance on half-space with irregular geographical features, can be effectively solved. The proposed approach also helps to simplify the solution of shell structures. Numerical examples are provided to validate the accuracy and efficiency of the proposed approach. 相似文献
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This paper presents a finite element procedure for the analysis of consolidation of layered soils with vertical drain using general one‐dimensional (1‐D) constitutive models. In formulating the finite element procedure, a Newton–Cotes‐type integration formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (Modified Newton) iteration scheme. The proposed procedure is then applied for the consolidation analysis of a number of typical problems using both linear and non‐linear soil models. Results from this simplified method are compared with those from a fully coupled consolidation analysis using a well‐known finite element package. The average degree of consolidation, excess porewater pressure and average vertical effective stress are almost the same as those from the fully coupled analysis for both the linear and non‐linear cases studied. The differences in vertical effective stresses are tolerable except for the values near the vertical drain boundaries. The consolidation behaviour of soils below a certain depth of the bottom of vertical drain is actually one‐dimensional for the partially penetrating case. Therefore, there are not much differences in whether one uses a one‐dimensional model or a three‐dimensional model in this region. The average degree of consolidation has good normalized feature with respect to the ratio of well radius to external drainage boundary for the cases of fully penetrating vertical drain using a normalized time even in the non‐linear case. Numerical results clearly demonstrate that the proposed simplified finite element procedure is efficient for the consolidation analysis of soils with vertical drain and it has better numerical stability characteristics. This simplified method can easily account for layered systems, time‐dependent loading, well‐resistance, smear effects and inelastic stress–strain behaviour. This method is also very suitable for the design of vertical drain, since it greatly reduces the unknown variables in the calculation and the 1‐D soil model parameters can be more easily determined. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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弹性地基梁法常用于研究土和结构的相互作用,对于均布荷载和边界条件简单的弹地基梁,采用理论解即可方便地进行计算。侧向荷载作用下桩体、嵌入式挡墙一般根据弹性地基梁理论进行分析,并假定基床系数随深度增加。对于基床系数呈线性分布或呈均匀分布但边界条件复杂的弹性地基梁理论求解困难,通常采用有限差分法或有限单元法近似求解。采用有限单元法计算线性分布基床系数弹性地基梁时,若单元划分数量不够,就存在计算精度不足的问题。采用加权余量法推导了更为精确的2节点5次位移函数和相应的单刚矩阵,得出了线性分布荷载作用下挠度的5次多项式近似解,从而实现只需划分很少的单元数,节点位移及单元内位移的分布即可达到较高的计算精度,极大地提高了计算效率,单元内力的分布可直接由位移函数导出,简化了后处理计算程序。 相似文献
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A new method, the η or ‘eta’ method, for modeling consolidation by vertical and horizontal drains is presented. The approach is applicable in one, two and three dimensional as well as axisymmetric cases. Material and geometry properties are familiar from unit cell vertical drain analysis and are consistent across dimensions. An uncoupled finite element method (FEM) program is used to test the efficacy of the new approach. Because drains are not explicitly modeled in the finite element mesh, mesh complexity and computational time are greatly reduced. Unlike existing plane strain matching methods there is no special transformation of permeability or drain properties. The analyses conducted indicate that the η method provides an efficient and consistent means of modeling drains in any dimension. 相似文献
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Xiao Ma Setare Hajarolasvadi Gabriele Albertini David S. Kammer Ahmed E. Elbanna 《国际地质力学数值与分析法杂志》2019,43(1):317-338
The finite element method (FEM) and the spectral boundary integral method (SBI) have both been widely used in the study of dynamic rupture simulations along a weak interface. In this paper, we present a hybrid method that combines FEM and SBI through the consistent exchange of displacement and traction boundary conditions, thereby benefiting from the flexibility of FEM in handling problems with nonlinearities or small-scale heterogeneities and from the superior performance and accuracy of SBI. We validate the hybrid method using a benchmark problem from the Southern California Earthquake Center's dynamic rupture simulation validation exercises.We further demonstrate the capability and computational efficiency of the hybrid scheme for resolving off-fault heterogeneities by studying a 2D in-plane shear crack in two different settings: one where the crack is embedded in a high-velocity zone and another where it is embedded in a low-velocity zone. Finally, we discuss the potential of the hybrid method for addressing a wide range of problems in geophysics and engineering. 相似文献
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刚性块体极限分析上限法常应用于岩土工程稳定性研究,然而应用时需假定刚性块体破坏模式并递推繁琐的几何关系。为此,提出一种适应性更广的基于非线性规划模型的刚体平动运动单元上限有限元法,并解决了其优化模型初始值的确定问题。通过引入有限单元思想,将计算区域离散成刚体单元,同时以单元速度和节点坐标作为决策变量,由上限定理建立非线性规划模型获得上限解。利用编制的上限有限元程序进行边坡和浅埋隧道稳定性算例验证,表明运动单元上限有限元法能调整速度间断线至较优方位,所得破坏模式特征鲜明,上限解精度高,可广泛应用于边坡、隧道等稳定性分析研究。 相似文献
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Strain gradient implies an important characteristic in localized damage deformation, which can be observed in the softening state of brittle materials, and strain gradients constitute the basic behaviours of localization failure area of the materials. The most important point in strain gradient is its damaging function including an internal length scale, which can be used to express the scale effects of mechanical responses of brittle rock mass. By extending the strain gradient theory and introducing an intrinsic material length scale into the constitutive law, the authors develop an isotropic damage model as well as a micro‐crack‐based anisotropic damage model for rock‐like materials in this paper. The proposed models were used to simulate the damage localization under uniaxial tension and plain strain compression, respectively. The simulated results well illustrated the potential of these models in dealing with the well‐known mesh‐sensitivity problem in FEM. In the computation, elements with C1 continuity have been implemented to incorporate the proposed models for failure localization. When regular rectangle elements are encountered, the coupling between finite difference method (FDM) and conventional finite element method (FEM) is used to avoid large modification to the existing FEM code, and to obtain relatively higher efficiency and reasonably good accuracy. Application of the anisotropic model to the 3D‐non‐linear FEM analysis of Ertan arch dam has been conducted and the results of its numerical simulation coincide well with those from the failure behaviours obtained by Ertan geophysical model test. In this paper, new applications of gradient theories and models for a feasible approach to simulate localized damage in brittle materials are presented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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The concurrent multiscale method, which couples the discrete element method (DEM) for predicting the local micro‐scale evolution of the soil particle skeleton with the finite element method (FEM) for estimating the remaining macro‐scale continuum deformation, is a versatile tool for modeling the failure process of soil masses. This paper presents the separate edge coupling method, which is degenerated from the generalized bridging domain method and is good at eliminating spurious reflections that are induced by coupling models of different scales, to capture the granular behavior in the domain of interest and to coarsen the mesh to save computational cost in the remaining domain. Cundall non‐viscous damping was used as numerical damping to dissipate the kinetic energy for simulating static failure problems. The proposed coupled DEM–FEM scheme was adopted to model the wave propagation in a 1D steel bar, a soil slope because of the effect of a shallow foundation and a plane‐strain cone penetration test (CPT). The numerical results show that the separate edge coupling method is effective when it is adopted for a problem with Cundall non‐viscous damping; it qualitatively reproduces the failure process of the soil masses and is consistent with the full micro‐scale discrete element model. Stress discontinuity is found in the coupling domain. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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正交各向异性岩体裂纹扩展的扩展有限元方法研究 总被引：1，自引：0，他引：1
石油开采和非常规天然气开采等领域经常遇到页岩、砂岩等沉积岩,这类岩石材料往往具有正交各向异性特征。采用扩展有限元方法研究了正交各向异性岩体裂纹扩展问题,并基于Matlab平台编写了数值计算程序Betaxfem2D。将由复变函数法得到的裂纹尖端渐进位移场作为裂尖位移增强函数,用相互作用积分法计算混合模式应力强度因子,采用修改后的最大周向拉应力扩展准则确定裂纹扩展方向。与传统有限元方法的对比表明,扩展有限元方法达到相同计算精度需要的自由度少,节省计算机时。分别采用扩展有限元程序和传统有限元程序模拟了岩石试件4点弯曲试验,二者所得结果一致。数值试验表明：随着正交材料坐标系与空间坐标系夹角α的增大,裂纹扩展方向角? 按照周期为? 的近似正弦函数的规律变化;保持剪切模量和泊松比不变时,正弦函数的值域随着弹性模量比值E1 /E2的减小而缩小,但相位基本保持不变;研究沉积岩断裂力学问题时,岩石的正交各向异性特征不可忽略。 相似文献
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面向对象有限元程序设计及其VC++与Matlab混合编程实现 总被引：1，自引：1，他引：1
应用面向对象方法来研究有限元,是对有限元新方法的有益尝试和创新性发展。通过对比面向过程和面向对象的程序设计方法,讨论了面向对象方法与有限元程序设计相结合的优点,并简要回顾了国内外面向对象的程序设计方法的研究进展。应用面向对象的程序分析方法,建立了三维脆塑性有限元分析类库。采用VC 和Matlab混合编程的手段,设计了基于Windows98/2000/NT操作平台的面向对象的三维脆塑性有限元分析软件,成功地分析了国内某大型水电站地下硐室群围岩稳定性,验证了该面向对象有限元分析程序的有效性和实用性。 相似文献