Sharif Digital Repository

In recent years, there has been a growing interest in the simulation and analysis of piezoelectric transducers with the he help of equivalent electrical circuit simulations (EECS). This paper has been devoted to study of such approach for two designed and fabricated ultrasonic sandwich transducers. By using analytical analysis, the dimensions of components of the two piezoelectric transducers were determined for the assumed resonance frequencies of 30 kHz and 40 kHz. Then, by using a two dimensional finite element model, and regarding two different modeling techniques for the transducers and by application of a current source which was connected directly to the piezoelectric pieces of the... 

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... 

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... 

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... 

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... 

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  

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... 

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... 

Experimental studies have indicated that the small strain shear modulus, Gmax, of unsaturated silt and clay has a greater amount during imbibition than during drainage, when presented as a function of matric suction. However, due to material properties and inter-particle forces, different behavior is expected in the case of sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drainage, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during imbibition. In the study presented herein, an effort has been made to compare the Gmax behavior of specimens of silt and sand during... 

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.... 

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... 

Hydraulic fracturing is a complicated phenomenon in which deformation of the porous medium and fluid leak-off to the surrounding area take place simultaneously. Their interaction therefore must not be overlooked. Modeling of this phenomenon in isothermal conditions requires analysis of soil deformation and crack and pore fluid pressure interaction. In this paper, a numerical scheme is presented for analysis of soil stresses and deformations and fluid flow in a coupled manner. This scheme is also used to detect the fracture in the medium. Our model was used in simulating a set of hydraulic fracturing experiments. These experiments were performed on compacted hollow cylindrical specimens under... 

Improved methods of constructing wells and producing wells are one of the keys to increasing field profitability. In the areas of well construction and well productivity optimization, many of the problems encountered are related to the geomechanics of the reservoir and the overlying layers; these problems include well-bore stability, sand production and hydraulic fracturing. Hydraulic fracturing is a complicated phenomenon in which deformation of the porous medium and fluid leak-off to the surrounding area take place simultaneously. Their interaction, therefore, must not be overlooked. In the past, some experimental researchers performed laboratory investigations on the phenomenon of... 

In composite liners, geomembrane and low permeability soil layer exhibit distinct physical and chemical properties. The combination of these two can, therefore, be used to construct a proper barrier that confines waste materials. In this study, the total permeability of geomembrane is calculated as summation of the leakage through defects and permeability of the intact geomembrane. Then, based on numerical analyses, the influence of geomembrane on liner performance is specified. On the other hand, the existence of soil barrier in composite liner can significantly reduce the amount of leakage through holes and defects in geomembrane. The performance of the liner with different thicknesses of... 

Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness, joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under constant normal load conditions. Shear stress-shear... 

Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings dams plays a major role. Most of the tailings dams require some kinds of remedial actions during their operational lifetime, among which heightening is the most common. In the first stage of the remedial provisions for Sarcheshmeh Copper Complex tailings dam in Iran, it has been decided to use hydrocyclone method to provide suitable construction material due to the high cost associated with using borrow materials for heightening of the dam. To undertake this project a series of laboratory experiments was performed to determine the copper 'original tailings' and 'cycloned... 

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... 

In this article, behavior of cantilever retaining walls with various flexibilities, which retain saturated cohesive soil behind, is studied using numerical modeling. Generally, pattern of lateral earth pressure behind retaining walls is complex and this complexity becomes greater for clayey soils. In this investigation, effects of different wall bending stiffnesses, and backfill drainage conditions on the failure height and on the lateral earth pressure are investigated using finite elements. Comparison between the obtained results from numerical simulation and those based on empirical or conventional design methods indicate that soil-structure interaction and c drainage conditions play... 

Mine tailings are the most common materials that are used in construction of tailings dams. Due to high level of environmental hazard and serious consequences that are associated with tailings dam failure, proper design of tailings dams is an important factor in mining industry. Water level fluctuation, change in permeability of dam foundation, seismic loads, and excessive settlements are the most common reasons of failure, particularly in upstream type tailings dams. Due to low shear strength of wet tailings, drying of tailing material is very common in practice during the dam construction. In hot climate, the received solar energy at the soil surface converts to soil heat flux, air heat... 

Evaluating the seismic active earth pressure on retaining walls is currently based on pseudo-static method in practices. In this method, however, it is not simple, choosing an appropriate value for earthquake coefficient, which should fully reflect the dynamic characteristics of both soil and loading is an important problem. On the other hand, by using only two extra dynamic parameters that are shear wave velocity of soil and predominant frequency of probable earthquake, one can benefit from another more accurate tool called pseudo-dynamic method to solve the problem of earth pressure. In this study in the framework of limit equilibrium analysis, pseudo-dynamic method has been applied into...