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A coupled hydro-mechanical analysis for prediction of hydraulic fracture propagation in saturated porous media using EFG mesh-less method, Article Computers and Geotechnics ; Vol. 55, issue , January , 2014 , p. 254-266 ; Pak, A ; Soga, K ; Sharif University of Technology
The details of the Element Free Galerkin (EFG) method are presented with the method being applied to a study on hydraulic fracturing initiation and propagation process in a saturated porous medium using coupled hydro-mechanical numerical modelling. In this EFG method, interpolation (approximation) is based on nodes without using elements and hence an arbitrary discrete fracture path can be modelled.The numerical approach is based upon solving two governing partial differential equations of equilibrium and continuity of pore water simultaneously. Displacement increment and pore water pressure increment are discretized using the same EFG shape functions. An incremental constrained Galerkin...
Article Unsaturated Soils: Research and Applications - Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014 ; Vol. 1, issue , July , 2014 , p. 581-587 ; 978-1-138-00150-3 ; Pak, A ; Sharif University of Technology
Numerical modeling of the fully coupled phenomena of solid deformation-fluid flow in partially saturated porous media is of great interest in many branches of science and engineering. In this study, a new formulation based on one of the famous mesh-less methods, called Element-Free Galerkin (EFG), is developed to simulate the water and air movement through variably saturated soils. For this purpose, the governing partial differential equations including the equilibrium equation and mass conservation laws for each fluid phase are discretized in space using the same EFG shape functions. To enforce the essential boundary conditions, penalty method is employed. Temporal discretization is...
A novel three-dimensional element free Galerkin (EFG) code for simulating two-phase fluid flow in porous materials, Article Engineering Analysis with Boundary Elements ; Vol. 39, issue. 1 , 2014 , pp. 53-63 ; ISSN: 09557997 ; Pak, A ; Sharif University of Technology
In the past few decades, numerical simulation of multiphase flow systems has received increasing attention because of its importance in various fields of science and engineering. In this paper, a three-dimensional numerical model is developed for the analysis of simultaneous flow of two fluids through porous media. The numerical approach is fairly new based on the element-free Galerkin (EFG) method. The EFG is a type of mesh-less method which has rarely been used in the field of flow in porous media. The weak forms of the governing partial differential equations are derived by applying the weighted residual method and Galerkin technique. The penalty method is utilized for imposition of the...
Three-dimensional simulation of fully coupled hydro-mechanical behavior of saturated porous media using Element Free Galerkin (EFG) method, Article Computers and Geotechnics ; Volume 46 , 2012 , Pages 75-83 ; 0266352X (ISSN) ; Pak, A ; Sharif University of Technology
Meshless methods are a relatively new type of numerical methods that have attracted the attention of many researchers over the past years. So far, a number of meshless methods have been developed and applied to solve problems in various fields of engineering, including solid mechanics and geotechnical problems. The Element-Free Galerkin (EFG) method is adopted in this study for solving the governing partial differential equations of equilibrium and continuity of pore fluid flow for numerical simulation of coupled hydro-mechanical problems. For this purpose, the weak form of the governing equations is derived by applying the weighted residual method and Galerkin technique. The penalty method...
Article Geotechnical and Geological Engineering ; Volume 30, Issue 1 , Oct , 2012 , Pages 163-171 ; 09603182 (ISSN) ; Pak, A ; Sharif University of Technology
An experimental study is conducted to measure small-strain shear modulus of clay-cement mixture using bender element apparatus setup in a triaxial cell. Bender element tests were conducted on cement-treated soils and the results were analyzed to study the variation of shear modulus properties of soil specimens at different cement contents, confining pressures, curing times, and compaction moisture contents. Based on the obtained results increasing the cement ratio has a significant effect on the small-strain shear modulus of the treated soils, and this effect signifies with increasing the moisture content and curing time. Rates of shear modulus enhancements due to cement content, curing...
Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 114-126 ; 0266352X (ISSN) ; Pak, A ; Sharif University of Technology
In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the...
Article Particle-Based Methods II - Fundamentals and Applications, 26 October 2011 through 28 October 2011 ; 2011 , Pages 371-382 ; 9788489925670 (ISBN) ; Pak, A ; Sharif University of Technology
In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for 2D simulation of fluid flow in porous media comprising of movable circular particles. The developed model is used for simulation of sand production which is one of the important problems in petroleum industry. The numerical tool has proved to have the capability of investigating the mechanisms involved in sand production problem. The results show that the rate of sand production is strongly affected by flow rate and confining pressure
Pore scale study of permeability and tortuosity for flow through particulate media using Lattice Boltzmann method, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 35, Issue 8 , 2011 , Pages 886-901 ; 03639061 (ISSN) ; Pak, A ; Sharif University of Technology
In this paper, Lattice Boltzmann method (LBM) has been used to study the effects of permeability and tortuosity on flow through saturated particulate media and identify the relationships between permeability and tortuosity with other parameters such as particles diameter, grain specific surface, and porosity. LBM is a simple kinematic model that can incorporate the essential physics of microscopic and mesoscopic processes involved in flow through granular soils. The obtained results indicate that the 2D LB model, due to its inherent theoretical advantages, is capable of demonstrating that the porosity and specific surface are the most influential parameters in determining the intrinsic...
Numerical study of factors influencing relative permeabilities of two immiscible fluids flowing through porous media using lattice Boltzmann method, Article Journal of Petroleum Science and Engineering ; Volume 77, Issue 1 , 2011 , Pages 135-145 ; 09204105 (ISSN) ; Pak, A ; Sharif University of Technology
Relative permeability curves have practical implications in petroleum reservoir simulations. Study of the effects of reservoir wettability, pore shape geometry, and viscosity ratio of flowing fluids on the relative permeabilities is of great importance in reservoir modeling. In this paper, lattice Boltzmann method (LBM) is employed for analyzing the two-fluid flow in rigid porous media. The developed LBM code proved to be a robust numerical tool for analyzing the factors that influence the relative permeabilities of two immiscible fluids flowing through porous media. The numerically derived relative permeability curves demonstrate that in neutrally wet reservoirs, the effect of viscosity...
Numerical simulation of sand production experiment using a coupled Lattice Boltzmann-Discrete Element Method, Article Journal of Petroleum Science and Engineering ; Volume 135 , November , 2015 , Pages 218-231 ; 09204105 (ISSN) ; Pak, A ; Sharif University of Technology
In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for two-dimensional simulation of fluid flow in deformable particulate media comprising of movable circular particles. The developed LB-DE code is validated against the results of a bi-axial shear test as well as two well-known benchmark problems including settling of a circular particle under gravity force inside a viscous fluid, and motion of a neutrally buoyant particle released in a Poiseuille flow. The verified code is then utilized for simulation of "Sand Production" phenomenon which is of importance for oil producing wells in weakly cemented sandstone...
Numerical investigation on the behavior of the gravity waterfront structures under earthquake loading, Article Ocean Engineering ; Volume 106 , September , 2015 , Pages 152-160 ; 00298018 (ISSN) ; Pak, A ; Sharif University of Technology
Elsevier Ltd 2015
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...
Numerical investigation of the effects of porosity and tortuosity on soil permeability using coupled three-dimensional discrete-element method and lattice Boltzmann method, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 5 , May , 2015 ; 15393755 (ISSN) ; Pak, A ; Sharif University of Technology
American Physical Society 2015
Permeability of porous materials is an important characteristic which is extensively used in various engineering disciplines. There are a number of issues that influence the permeability coefficient among which the porosity, size of particles, pore shape, tortuosity, and particle size distribution are of great importance. In this paper a C++ GPU code based on three-dimensional lattice Boltzmann method (LBM) has been developed and used for investigating the effects of the above mentioned factors on the permeability coefficient of granular materials. Multirelaxation time collision scheme of the LBM equations is used in the simulator, which is capable of modeling the exact position of the...
Article Computers and Geotechnics ; Volume 37, Issue 3 , April , 2010 , Pages 267-279 ; 0266352X (ISSN) ; Pak, A ; Sharif University of Technology
Occurrence of liquefaction in saturated sand deposits underlying foundation of structure can cause a wide range of structural damages starting from minor settlement, and ending to general failure due to loss of bearing capacity. If the bearing capacity failure is not the problem, reliable estimation of the liquefaction-induced settlement will be of prime importance in assessment of the overall performance of the structure. Currently, there are few procedures with limited application in practice for estimation of settlement of foundations on liquefied ground. Therefore, development of a general relationship is important from the practical viewpoint. In this paper, the dynamic response of...
Numerical study of the coupled hydro-mechanical effects in dynamic compaction of saturated granular soils, Article Computers and Geotechnics ; Volume 37, Issue 1-2 , 2010 , Pages 10-24 ; 0266352X (ISSN) ; Pak, A ; Shahir, H ; Sharif University of Technology
Dynamic compaction is a widely used method for improvement of loose granular deposits. Its applicability in saturated layers generally considered to be less effective because of the fact that part of the applied energy is absorbed by pore water. Up to now the majority of numerical simulations have focused on the analysis of dynamic compaction in dry/moist soils. In this paper, a fully coupled hydro-mechanical finite element code has been developed and employed to evaluate the dynamic compaction effects on saturated granular soils. After verification of the results by comparing the numerical results with those measured in a real field case of DC treatment in a highway, some sensitivity...
A fully coupled element-free Galerkin model for hydro-mechanical analysis of advancement of fluid-driven fractures in porous media, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 40, Issue 16 , 2016 , Pages 2178-2206 ; 03639061 (ISSN) ; Pak, A ; Sharif University of Technology
John Wiley and Sons Ltd
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...
Article Soil Dynamics and Earthquake Engineering ; Volume 90 , 2016 , Pages 381-394 ; 02677261 (ISSN) ; Pak, A ; Ayoubi, P ; Sharif University of Technology
Elsevier Ltd 2016
In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully...
Numerical investigation of the effects of geometric and seismic parameters on liquefaction-induced lateral spreading, Article Soil Dynamics and Earthquake Engineering ; Volume 89 , 2016 , Pages 233-247 ; 02677261 (ISSN) ; Pak, A ; Sharif University of Technology
Elsevier Ltd 2016
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...
Article Meccanica ; Volume 51, Issue 3 , 2016 , Pages 517-536 ; 00256455 (ISSN) ; Pak, A ; Sharif University of Technology
Fully coupled flow-deformation analysis of deformable multiphase porous media saturated by several immiscible fluids has attracted the attention of researchers in widely different fields of engineering. This paper presents a new numerical tool to simulate the complicated process of two-phase fluid flow through deforming porous materials using a mesh-free technique, called element-free Galerkin (EFG) method. The numerical treatment of the governing partial differential equations involving the equilibrium and continuity equations of pore fluids is based on Galerkin’s weighted residual approach and employing the penalty method to introduce the essential boundary conditions into the weak forms....
An integrated SPH-polyhedral DEM algorithm to investigate hydraulic stability of rock and concrete blocks: application to cubic armours in breakwaters, Article Engineering Analysis with Boundary Elements ; Volume 84 , 2017 , Pages 1-18 ; 09557997 (ISSN) ; Pak, A ; Sharif University of Technology
In this paper, a combination of the Lagrangian meshfree method of SPH and Polyhedral DEM is presented to simulate the interaction between the free surface of water and solid objects possessing sharp edges and flat surfaces, such as armour units of breakwaters. Both SPH and DEM schemes are validated successfully against experimental data. The numerical scheme is utilized to inspect the stability of concrete cubic armours in rubble-mound breakwaters through systematic analyses with various geometrical parameters and environmental conditions. The numerical results regarding the required dimensions of the cubic blocks for providing stability of the armour units under the wave attack are compared...
Article Coastal Engineering ; Volume 121 , 2017 , Pages 145-157 ; 03783839 (ISSN) ; Pak, A ; Sharif University of Technology
Elsevier B.V 2017
This paper addresses numerically-derived tsunami wave loads on bridge superstructures using smoothed particle hydrodynamics (SPH), which is a type of mesh-free methods. Although there exist some relationships for the case of impinged loads on bridges exerted by regular (sinusoidal) waves, for the case of solitary waves such as tsunamis, no relation has yet been proposed in the literature. This shortcoming is partly due to the lack of understanding the mechanism of wave action on the bridge superstructures. In this study, three water depths, three wave amplitudes and four submergence depths of the deck are considered for the process of numerical investigation of tsunami-induced loads on...