A finite element algorithm for parameter identification of material models for fluid saturated porous media     

R. Mahnken  P. Steinmann 《国际地质力学数值与分析法杂志》2001,25(5):415-434

In this contribution an algorithm for parameter identification of geometrically linear Terzaghi–Biot‐type fluid‐saturated porous media is proposed, in which non‐uniform distributions of the state variables such as stresses, strains and fluid pore pressure are taken into account. To this end a least‐squares functional consisting of experimental data and simulated data is minimized, whereby the latter are obtained with the finite element method. This strategy allows parameter identification based on in situ experiments. In order to improve the efficiency of the minimization process, a gradient‐based optimization algorithm is applied, and therefore the corresponding sensitivity analysis for the coupled two‐phase problem is described in a systematic manner. For illustrative purpose, the performance of the algorithm is demonstrated for a slope stability problem, in which a quadratic Drucker–Prager plasticity model for the solid and a linear Darcy law for the fluid are combined. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Modeling permeability in imperfectly layered porous media. II. A two-dimensional application of block-scale permeability     

J. M. T. Stam  W. Zijl 《Mathematical Geology》1992,24(8):885-904

In the previous paper (Zijl and Stam, 1992), a theory has been developed to calculate the nine components of the three-dimensional intrinsic permeability tensor on the scale of a grid-block from a local-scale, predominantly layered subsurface. The resulting block-scale expressions can be written as a perturbation series of which the first term, or zeroth-order solution, coincides with the conventionally applied arithmetic and harmonic averages over the layers of the subsurface. The derived expressions permit the calculation of the diagonal and off-diagonal terms of the permeability tensor. In the present paper, these expressions will be applied in some numerical examples. Two basic two-dimensional hypothetical permeability distributions are adopted, and the various terms of the theoretical expressions are calculated. The results will be used to derive guidelines to discern the situations where higher order solutions can be neglected, and where conventional harmonic and arithmetic averages give a good estimate of the permeability on grid-block scale.  相似文献   

Role of heat and water transport in frost heaving of fine-grained porous media under negligible overburden pressure     

Yoshisuke Nakano  Kaoru Horiguchi 《Advances in water resources》1984,7(2):93-102

An equation accurately describing the rate of frost heave is derived by using the mixture theory of continuum mechanics. It is shown that the rate of frost heave is determined mainly by the rate of heat removal and the rate of water intake. When the phase equilibrium holds in the system, the relation between the rate of heat removal and the rate of water intake is shown to depend mainly on the phase composition data of a given medium.By studying reported experimental data, it is found that the phase equilibrium may hold until th rate of heat removal reaches a certain critical value. When the rate of heat removal exceeds this critical value, the phase equilibrium may possibly be disrupted for some media.  相似文献   

Study of transient poroviscoelastic soil motions by semi-analytical and numerical approaches     

A. Mesgouez  G. Lefeuve-Mesgouez 《Soil Dynamics and Earthquake Engineering》2009

In this paper, the authors compare results obtained by semi-analytical and numerical approaches for the dynamic response of a poroviscoelastic soil under transient loads. The behaviour of the medium is governed by complete Biot formalism. The semi-analytical approach is based on Helmholtz decompositions and Fourier transforms, and yields exact solid and fluid displacements in the transformed domain. The numerical approach uses a C++$\mathrm{C}++$ object oriented programming finite element–finite difference code. Both methods give concurring results. Moreover, influence of viscous coupling on the response of the ground and visualization of the compressional wave of the second kind are discussed.  相似文献   

非饱和土广义有效应力原理   总被引：4，自引：1，他引：3  

赵成刚  蔡国庆 《岩土力学》2009,30(11):3232-3236

综述了非饱和土有效应力的沿革,并就非饱和土有效应力的研究和发展中存在的问题进行了讨论。基于多相孔隙介质理论推导得到的变形功的表达式,提出了非饱和土广义有效应力原理。该原理认为,由非饱和土中的单应力变量的有效应力或双应力变量理论很难唯一地确定非饱和土的变形和强度。广义有效应力原理实质上就是要综合考虑影响非饱和土变形和强度的三种广义应力以及与其对偶的广义变形,给出考虑因素更为全面、理论基础更为坚实的广义有效应力原理。它为非饱和土基本性质的研究和本构方程的建立奠定了坚实而科学的理论基础。  相似文献   

Modelling of contaminant transport through landfill liners using EFGM     

R. Praveen Kumar  G. R. Dodagoudar 《国际地质力学数值与分析法杂志》2010,34(7):661-688

Modelling of contaminant transport through landfill liners and natural soil deposits is an important area of research activity in geoenvironmental engineering. Conventional mesh‐based numerical methods depend on mesh/grid size and element connectivity and possess some difficulties when dealing with advection‐dominant transport problems. In the present investigation, an attempt has been made to provide a simple but sufficiently accurate methodology for numerical simulation of the two‐dimensional contaminant transport through the saturated homogeneous porous media and landfill liners using element‐free Galerkin method (EFGM). In the EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no characterization of the interrelationship of the nodes is needed. The EFGM employs moving least‐square approximants to approximate the function and uses the Lagrange multiplier method for imposing essential boundary conditions. The results of the EFGM are validated using experimental results. Analytical and finite element solutions are also used to compare the results of the EFGM. In order to test the practical applicability and performance of the EFGM, three case studies of contaminant transport through the landfill liners are presented. A good agreement is obtained between the results of the EFGM and the field investigation data. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Assessment of acceleration modelling for fluid‐filled porous media subjected to dynamic loading     

B. Lenhof  P. Kettil  K. Runesson  N.‐E. Wiberg 《国际地质力学数值与分析法杂志》2008,32(2):109-119

The purpose of this paper is to examine the importance of different possible simplifying approximations when performing numerical simulations of fluid‐filled porous media subjected to dynamic loading. In particular, the relative importance of the various acceleration terms for both the solid and the fluid, especially the convective contribution, is assessed. The porous medium is modelled as a binary mixture of a solid phase, in the sense of a porous skeleton, and a fluid phase that represents both liquid and air in the pores. The solid particles are assumed to be intrinsically incompressible, whereas the fluid is assigned a finite intrinsic compressibility. Finite element (FE) simulations are carried out while assuming material properties and loading conditions representative for a road structure. The results show that, for the range of the material data used in the simulations, omitting the relative acceleration gives differences in the solution of the seepage velocity field, whereas omitting only the convective term does not lead to significant differences. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

On the dissipation of atmospheric alfvén waves in uniform and non-uniform magnetic fields     

L. M. B. C. Campos 《地球物理与天体物理流体动力学》2013,107(4):193-215

Abstract

We deduce the dissipative Alfvén wave equation in a medium stratified in one direction, with a transverse magnetic field, in the presence of dissipation by fluid viscosity and electrical resistance; the dissipative Alfvén wave equation generalizes earlier results for homogeneous (Cowling, 1960) and inhomogeneous (Campos, 1983a) media, and corrects an error in the literature (Heyvaerts and Priest, 1983). The wave equation is solved exactly in two cases: a uniform magnetic field, and a magnetic field decreasing with height. In both cases the mean state is assumed to be isothermal, with a constant rate of ionization, so that the magnetic diffusivity is constant, but the dynamic viscosity increases with height. There are therefore two regions, a low- (high-) altitude region where electrical resistance dominates fluid viscosity (or vice versa), and an asymptotic regime relevant to the uppermost (lowermost) layers. The two regions are separated by a transition layer, across which the wave field is continuous and whose structure is expressible by hypergeometric functions, with different arguments in the low- and high-altitude regions, and over the whole altitude range. These exact solutions allow the amplitude and phase of the wave field to be plotted as a function of height for a variety of magnetoatmospheric mean states. They show that wave dissipation is more localized and intense when the magnetic field decreases with height than when it is uniform.  相似文献   

FLAC3D在边坡变形过程可视化中的应用     

卢志强  冷洋洋 《贵州地质》2012,29(1):52-55

利用FLAC3D对边坡进行数值模拟,分别对对沙子岭边坡降雨前及降雨后的边坡变形过程进行模拟,显示处了边坡的变形发生在基岩中软弱层的位置,因受地表水体入渗造成软弱层软化现象,而导致力学性能迅速降低,坡体并沿着物质分异面发生剪切破坏的过程,该模拟过程与边坡实际变形基本一致,反映了FIAC3D在边坡变形预测预报中具有较好的应用前景。  相似文献   

Variational inequalities for modeling flow in heterogeneous porous media with entry pressure     

R. Helmig  A. Weiss  B. I. Wohlmuth 《Computational Geosciences》2009,13(3):373-389

One of the driving forces in porous media flow is the capillary pressure. In standard models, it is given depending on the saturation. However, recent experiments have shown disagreement between measurements and numerical solutions using such simple models. Hence, we consider in this paper two extensions to standard capillary pressure relationships. Firstly, to correct the nonphysical behavior, we use a recently established saturation-dependent retardation term. Secondly, in the case of heterogeneous porous media, we apply a model with a capillary threshold pressure that controls the penetration process. Mathematically, we rewrite this model as inequality constraint at the interfaces, which allows discontinuities in the saturation and pressure. For the standard model, often finite-volume schemes resulting in a nonlinear system for the saturation are applied. To handle the enhanced model at the interfaces correctly, we apply a mortar discretization method on nonmatching meshes. Introducing the flux as a new variable allows us to solve the inequality constraint efficiently. This method can be applied to both the standard and the enhanced capillary model. As nonlinear solver, we use an active set strategy combined with a Newton method. Several numerical examples demonstrate the efficiency and flexibility of the new algorithm in 2D and 3D and show the influence of the retardation term. This work was supported in part by IRTG NUPUS.  相似文献