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61.
Although recognized as important, measures of connectivity (i.e. the existence of high-conductivity paths that increase flow and allow for early solute arrival) have not yet been incorporated into methods for upscaling hydraulic conductivities of porous media. We present and evaluate a binary upscaling formula that utilizes connectivity information. The upscaled hydraulic conductivity (K) of binary media is determined as a function of the proportions and conductivities of the two materials, the geometry of the inclusions, and the mean distance between them. The use of a phase interchange theorem renders the formula equally applicable to two-dimensional media with inclusions of low K and high K as compared with the matrix. The new upscaling formula is tested on two-dimensional binary random fields spanning a broad range of spatial correlation structures and conductivity contrasts. The computed effective conductivities are compared to what is obtained using self-consistent effective medium theory, the coated ellipsoids approximation, and to a streamline approach. It is shown that, although simple, the proposed formula performs better than available methods for binary upscaling. The use of connectivity information leads to significantly improved behavior close to the percolation threshold. The proposed upscaling formula depends exclusively on parameters that are obtainable from field investigations. 相似文献
62.
讨论了一类偶数阶四点边值问题正解的存在性,借助Leggett-Williams不动点定理和不等式技巧,得到了该边值问题至少存在三个和任意奇数个正解的充分条件. 相似文献
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主要研究奇异非线性二阶诺伊曼边值问题的正解个数.应用比较原理、最大值原理和上界方法得出了在一定条件下,该问题恰好有5个正解的结果. 相似文献
65.
水平浅埋条形锚板极限抗拔力上限计算 总被引:1,自引:1,他引:1
作为一种提供抗拔力的基础形式,锚板在实际工程中有广泛的应用。在上限定理的基础上,根据线性破坏准则,对锚板上的填土建立机动容许的速度场,运用关联流动法则以及速度边界条件求解条形锚板极限抗拔力的上限解。把锚板上填土的抗剪强度指标c、? 作为变量参数,对锚板上部填土建立两种新的含有变量的容许速度场。根据外力功率与内部耗能相等原理,求出极限抗拔力的目标函数与约束条件,并根据“序列二次规划算法”对该问题进行优化。将研究结果与已有文献资料进行分析比较,可以证明本文方法的有效性。参数分析结果表明:在同样条件下,两种破坏模式的极限抗拔力差别不大;岩土体密实度、抗剪强度指标c、?、锚板埋深率和锚板几何形状对锚板承载能力和锚板抗拔破坏区域均有较大的影响。 相似文献
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This paper develops a novel return mapping algorithm for the numerical integration of general isotropic finite strain elastoplastic constitutive models for geomaterials. The constitutive formulation is founded on multiplicative decomposition of the deformation gradient. The logarithmic strain measure as well as the exponential approximation of the plastic flow rule is utilized to restore the standard infinitesimal format return mapping algorithm. Central to the algorithm is the exploitation of a set of three mutually orthogonal unit base tensors for the representation of constitutive relations and the corresponding integration of the rate form of the constitutive equations. The base tensors constitute a local cylindrical coordinate system in the principal space, which allows to formulate the return mapping algorithm in the three‐dimensional space and reduce the dimension of the problem to be analyzed from six down to three. With the proposed approach, direct determination of the principal axes and the transformation procedure between the general space and the principal space, as required in traditional spectral decomposition, are avoided. Furthermore, the matrices that are involved in the inversion evaluation take simple forms, leading to extremely easy inverse computation. As a result, the consistent tangent operator can be streamlined into a form simpler and more compact than those by conventional integration methods. Following the formulation of the integration procedure, a numerical experiment is performed to assess the accuracy and efficiency of the proposed algorithm. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
68.
Navin Chandra 《Planetary and Space Science》2004,52(8):747-760
The non-linear stability of the triangular libration point L4 of the restricted three-body problem is studied under the presence of third- and fourth-order resonances, when the more massive primary is a triaxial rigid body and source of radiation. In this study, Markeev's theorems are applied with the help of Moser's theorem. It is found that the stability of the triangular libration point is unstable in the third-order resonance case and in the fourth-order resonance case, this is stable or unstable depending on A1 and A2, and a source of radiation parameter α, where A1, A2 depend upon the lengths of the semi-axes of the triaxial rigid body. 相似文献
69.
基于岩土塑性极限分析上限理论的基本原理,考虑预应力锚索的加固效应,分析了单预应力锚索加固措施条件下边坡的稳定性特性,并由此探讨了多预应力锚索共同加固边坡的稳定性能量分析方法。结合强度折减技术,采用内点迭代方法和序列二次规划优化迭代法对锚固边坡安全系数目标函数进行了能量耗散最小化意义上的优化计算。典型算例的分析计算表明:锚索加固效应可以有效地提高边坡的稳定性,预应力锚索设置位置对边坡安全系数、临界滑裂面位置和锚索长度有显著影响。综合考虑锚索设置位置对边坡安全系数和锚索长度的影响,单锚索的最优设置位置应位于边坡中下部区域。采用多排锚索加固既可以保证边坡的安全储备,也可有效避免局部稳定性问题。 相似文献
70.