Sharif Digital Repository

In this paper, a numerical model is developed for the fully coupled hydro-mechanical analysis of deformable, progressively fracturing porous media interacting with the flow of two immiscible, compressible wetting and non-wetting pore fluids, in which the coupling between various processes is taken into account. The governing equations involving the coupled solid skeleton deformation and two-phase fluid flow in partially saturated porous media including cohesive cracks are derived within the framework of the generalized Biot theory. The fluid flow within the crack is simulated using the Darcy law in which the permeability variation with porosity because of the cracking of the solid skeleton... 

Dynamic compaction is a widely used soil improvement method in dry and/or saturated soils. Despite its vast application, its design basis is still empirical and the mechanisms that are involved in the procedure are not fully understood. A fully coupled dynamic finite element code has been developed in order to clarify the ambiguities in the process and predict the strain/displacement field in the ground, determine depth and degree of improvement, and also calculate the pore pressure variation during the process. This model can be used as a rational design tool for dynamic compaction projects  

Abstract Lateral Spreading, which usually occurs as a consequence of liquefaction in gently sloped loose saturated sand layers, is known to be a major source of earthquake-induced damages to structures such as quay walls, bridge piers, pipelines, and highway/railways. Therefore evaluation of the liquefaction potential and using appropriate methods for prediction of the adverse consequences of lateral spreading is of great importance. In this study, numerical modeling has been used to study lateral spreading phenomenon behind rigid waterfront structures. Coupled dynamic field equations of the extended Biot's theory with u-P formulation are used for simulating the phenomenon. A fully coupled... 

Hydraulic fracturing (HF) of underground formations has widely been used in different fields of engineering. Despite the technological advances in techniques of in situ HF, the industry uses semi-analytical tools to design HF treatment. This is due to the complex interaction among various mechanisms involved in this process, so that for thorough simulations of HF operations a fully coupled numerical model is required. In this study, using element-free Galerkin (EFG) mesh-less method, a new formulation for numerical modeling of hydraulic fracture propagation in porous media is developed. This numerical approach, which is based on the simultaneous solution of equilibrium and continuity... 

The lateral movement of a liquefiable soil layer on gentle slopes is the most visible and devastating type of liquefaction-induced ground failure. Recent earthquakes have shown that this phenomenon causes severe damages to coastal structures, pier of the bridges and life-lines by exerting large lateral forces on the structures. In this paper coupled dynamic field equations of extended Biot's theory with u-p formulation are used for simulating the phenomenon and the soil behavior is modeled by a critical state two-surface plasticity model for sands. Furthermore, in this study variation of permeability coefficient during liquefaction is taken into account. The permeability coefficient is... 

A fully coupled formulation of thermo-fluid shape design problems has recently been developed in which the unknown nodal coordinates appear explicitly in the formulation of the problem. This "direct design" approach is, in principle, generally applicable and has been successfully applied in the context of potential and Euler flow models. This paper focuses on the direct design of ducts using the ideal flow model and may be considered as an addendum to the paper entitled "Direct Design of Ducts" [1]. However, a cell-vertex finite volume method is used and a different boundary condition implementation technique is applied, as compared to the method presented in the previous paper. The other... 

The multiphysics process of the electromagnetic (EM) radiation induced from an embedded nanofiber scatterer subjected to SH-waves is of interest. By discarding the commonly employed electroquasistatic approximation, the fully-coupled elastodynamics and Maxwell's equations have been solved simultaneously within the mathematical framework of piezoelectric surface elasticity theory. Certain subtleties regarding the introduced interface characteristic lengths that make the examination of the size effect on the EM radiated power, scattering cross section, fundamental resonance frequency, and distribution of the magnetic field possible will be discussed. The obtained results can be helpful for... 

In this paper, a fully coupled numerical model is developed for the modeling of the hydraulic fracture propagation in porous media using the extended finite element method in conjunction with the cohesive crack model. The governing equations, which account for the coupling between various physical phenomena, are derived within the framework of the generalized Biot theory. The fluid flow within the fracture is modeled using the Darcy law, in which the fracture permeability is assumed according to the well-known cubic law. By taking the advantage of the cohesive crack model, the nonlinear fracture processes developing along the fracture process zone are simulated. The spatial discretization... 

In this paper, a numerical model is developed for the fully coupled analysis of deforming porous media containing weak discontinuities which interact with the flow of two immiscible, compressible wetting and non-wetting pore fluids. The governing equations involving the coupled solid skeleton deformation and two-phase fluid flow in partially saturated porous media are derived within the framework of the generalized Biot theory. The solid phase displacement, the wetting phase pressure and the capillary pressure are taken as the primary variables of the three-phase formulation. The other variables are incorporated into the model via the experimentally determined functions that specify the... 

The coupling of rock and thermal stresses along with fluid pressure are particularly important in fractured rock masses, since stress-induced changes in permeability can be large and irreversible under perturbations resulting from various natural and induced activities. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Three cases of overbalanced, underbalanced, and balanced drilling fluid pressure conditions are employed. The... 

Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u-P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modelled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class 'B' analysis of a centrifuge...