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Evaluation of variable permeability model in simulation of seismic behavior of uniform level and gently sloping sand layers
, Article Earth Sciences Research Journal ; Volume 24, Issue 3 , 2020 , Pages 328-336 ; Seyfi, S ; Shahir, H ; Sharif University of Technology
Universidad Nacional de Colombia
2020
Abstract
In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface...
Thick planar domain wall: Its thin wall limit and dynamics
, Article International Journal of Modern Physics D ; Volume 16, Issue 4 , 2007 , Pages 629-640 ; 02182718 (ISSN) ; Khakshournia, S ; Mansouri, R ; Sharif University of Technology
2007
Abstract
We consider a planar gravitating thick domain wall of the λφ4 theory as a space-time with finite thickness glued to two vacuum space-times on each side of it. Darmois junction conditions written on the boundaries of the thick wall with the embedding space-times reproduce the Israel junction condition across the wall in the limit of infinitesimal thickness. The thick planar domain wall located at a fixed position is then transformed to a new coordinate system in which its dynamics can be formulated. It is shown that the wall's core expands as if it were a thin wall. The thickness in the new coordinates is not constant anymore and its time dependence is given. © World Scientific Publishing...
Numerical investigation into the effects of geometrical and loading parameters on lateral spreading behavior of liquefied layer
, Article Acta Geotechnica ; 2013 , Pages 1-13 ; 18611125 (ISSN) ; Seyfi, S ; Ghassemi, A ; Sharif University of Technology
2013
Abstract
Numerical simulation of liquefaction-induced lateral spreading in gently sloped sandy layers requires fully coupled dynamic hydro-mechanical analysis of saturated sandy soil subjected to seismic loading. In this study, a fully coupled finite element model utilizing a critical-state two-surface-plasticity constitutive model has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the well-known VELACS project. Lateral spreading phenomenon has been...
Lensing effects in inhomogeneous cosmological models
, Article Physical Review D - Particles, Fields, Gravitation and Cosmology ; Volume 79, Issue 10 , 2009 ; 15507998 (ISSN) ; Khoeini Moghaddam, S ; Mansouri, R ; Sharif University of Technology
2009
Abstract
Concepts developed in the gravitational lensing techniques such as shear, convergence, tangential, and radial arcs maybe used to see how tenable inhomogeneous models proposed to explain the acceleration of the universe models are. We study the widely discussed Lemaitre-Tolman-Bondi (LTB) cosmological models. It turns out that for the observer sitting at origin of a global LTB solution the shear vanishes as in the Friedmann-Robertson-Walker models, while the value of convergence is different, which may lead to observable cosmological effects. We also consider Swiss-cheese models proposed recently based on LTB with an observer sitting in the Friedmann-Robertson-Walker part. It turns out that...
Model checking MANETs with arbitrary mobility
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) ; Volume 8161 LNCS , April , 2013 , Pages 217-232 ; 03029743 (ISSN) ; 9783642402128 (ISBN) ; Ahmadi, S ; Fokkink, W ; Movaghar, A ; Sharif University of Technology
Springer Verlag
2013
Abstract
Modeling arbitrary connectivity changes of mobile ad hoc networks (MANETs) makes application of automated formal verification challenging. We introduced constrained labeled transition systems (CLTSs) as a semantic model to represent mobility. To model check MANET protocol with respect to the underlying topology and connectivity changes, we here introduce a branching-time temporal logic interpreted over CLTSs. The temporal operators, from Action Computation Tree Logic with an unless operator, are parameterized by multi-hop constraints over topologies, to express conditions on successful scenarios of a MANET protocol. We moreover provide a bisimilarity relation with the same distinguishing...
When do colliding bubbles produce an expanding universe?
, Article Physical Review D - Particles, Fields, Gravitation and Cosmology ; Volume 69, Issue 10 , 2004 ; 15507998 (ISSN) ; Bucher, M ; Ghassemi, S ; Glanois, F ; Sharif University of Technology
2004
Abstract
It is intriguing to consider the possibility that the big bang of the standard (3+1)-dimensional cosmology originated from the collision of two branes within a higher dimensional spacetime, leading to the production of a large amount of entropy. In this paper we study, subject to certain well-defined assumptions, under what conditions such a collision leads to an expanding universe. We assume the absence of novel physics, so that ordinary (4+1)-dimensional Einstein gravity remains a valid approximation. It is necessary that the fifth dimension not become degenerate at the moment of collision. First the case of a symmetric collision of infinitely thin branes having a hyperbolic or flat...
Simulation of Two-Fluid Flow Through Particlulate Porous Media Contaning Moving Particles at Pore Scale Using Combined LB-DE Method
, Ph.D. Dissertation Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
A considerable number of engineering applications deal with flow of fluid(s) through particulate porous media. For certain engineering problems, fluid flow may displace and even dislodge the solid particles from the mass where a fluid-particle flow occurs. The complexity of involving processes which should be studied at the scale of moving particles transforms the analyses of these problems towards a difficult engineering task. Characteristics of solid grains such as size and shape and properties of the flowing fluid(s) such as viscosity and surface tension play essential roles in the behavior of fluid-particle systems. Also, when fluid flows through porous media, secondary processes such as...
Investigation of Dynamic Response of Shallow Foundations on Sandy Soil to Horizontal Harmonic Loading by Physical Model Tests
, M.Sc. Thesis Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor)
Abstract
The most important step in current dynamic analysis of machine foundations is determining dynamic impedance functions. Impedance functions are defined as ratios of applied force or moment to induced displacement or rotation angle of foundation. In this research, horizontal dynamic response of foundation on homogeneous halfspace was investigated using physical modeling. Soil medium was built in a 1mx1mx0.8m steel box whose interior walls were covered by 0.1m of sawdust (a material with high damping). In order to prevent possible reflection of waves, this cover was extended to the box bottom with 0.2 m thickness. Sand raining method was used to build soil medium. In this method, with...
Coupled lattice boltzmann - Discrete element method for numerical modelling of sand production
, 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
2011
Abstract
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
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
Elsevier
2015
Abstract
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 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
2011
Abstract
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...
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
2011
Abstract
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...
Investigation of the Effects of Corrosive Environments on Mechanical and Microstructural Properties of Polymer and Portland Cement Concrete
, M.Sc. Thesis Sharif University of Technology ; Toufigh, Vahab (Supervisor)
Abstract
Polymer concrete is well-known for the quick repair of concrete structures and pavement. Many concrete structures such as bridges, offshore, and pavements are under cyclic loads when they are exposed to different environmental conditions during their lifespan. However, there are relatively few studies on the durability of Polymer concrete. The durability and fatigue performance of these structures are significant issues that should be considered. This study aims to investigate the long-term environmental effects on the mechanical properties of Polymer concrete. Therefore, polymer and ordinary cement concrete specimens were prepared and exposed to four chemical solutions with pH values of...
Durability of epoxy polymer and ordinary cement concrete in aggressive environments
, Article Construction and Building Materials ; Volume 234 , 2020 ; Toufigh, V ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Polymer concrete is well-known for quick repairing of concrete structures and pavement. However, there are relatively few studies on the durability of epoxy polymer concrete (EPC). This study aims to investigate the long-term environmental effects on the mechanical properties of EPC. Therefore, EPC and ordinary cement concrete (OCC) specimens were prepared and exposed to four chemical solutions with pH values of 2.5, 7, 12.5 and artificial seawater in intervals of 1, 3, 6, 9 and 12 months. Epoxy resin (10 and 12% by weight) and Portland cement were used as binder phase in EPC and OCC specimens, respectively. Scanning electron microscopy (SEM) was additionally applied to investigate the...
Modeling routing protocols in ad hoc networks
, Article 13th International Computer Society of Iran Computer Conference on Advances in Computer Science and Engineering, CSICC 2008, Kish Island, 9 March 2008 through 11 March 2008 ; Volume 6 CCIS , 2008 , Pages 419-426 ; 18650929 (ISSN); 3540899847 (ISBN); 9783540899846 (ISBN) ; Movaghar, A ; Sharif University of Technology
2008
Abstract
Regarding increasing popularity of Ad hoc networks, the routing protocols employed in these networks should be validated before deployment. Formal methods are used nowadays to find defects in protocols specification. In this paper, we explain different methods of formal modeling and verification of routing protocols of ad hoc networks. We derive the key concepts that are vital in modeling ad hoc network protocols and then modify process algebra, appropriate for verifying protocols at network layer. This process algebra implements mobility behaviors of underlying infrastructure implicitly in the semantics of broadcasting. The semantics of broadcast communication also abstracts away the...
A novel approach towards control of exoskeletal systems as an assistive device for human's upper extremity
, Article JICTEE 2014 - 4th Joint International Conference on Information and Communication Technology, Electronic and Electrical Engineering ; 2014 ; Jahed, M ; Sharif University of Technology
2014
Abstract
With increasing importance of exoskeletons as rehabilitation apparatuses, suitable and delicate control strategies has received much attention. In order to control the exoskeleton, there should be a complete understanding of torques produced by the limb itself which makes the musculoskeletal modeling of the limb essential but also complex. In addition, the musculoskeletal model can be used to discover the user's desired movement to control the exoskeleton. In this paper a complete musculoskeletal model for the elbow with two degrees of freedom is developed and simulated. Next the model is used to determine user's desired movement. Finally based on this evaluation, an exoskeleton model is...
Control of Exoskeletal System in Coordination with Upper Extremity System
, M.Sc. Thesis Sharif University of Technology ; Jahed, Mehran (Supervisor)
Abstract
With technological advances in fabrication and control of prosthesis and assistive devices the importance of such systems has increased drastically. On the other hand the appropriate coupling of these devices, especially the exoskeletal systems with the upper or lower extremities is of immense importance as it is an integral part of the control system. In particular, the control strategy and its ability to adapt the exoskeletal system with the existing and physiological functionality of the user, is an integral part of the system requirement. In the controller implementation, a number of methods are proposed including using the excitation signal, similar to the existing neuromuscular system....
A new linear adjacency approach for facility layout problem with unequal area departments
, Article Journal of Manufacturing Systems ; Volume 37, Part 1 , October , 2015 , Pages 93-103 ; 02786125 (ISSN) ; Neghabi, H ; Sharif University of Technology
Elsevier
2015
Abstract
In this study a new version of adjacency, which provides a more flexible layout design, is proposed. In the proposed version, departments which are nonadjacent yet close to each other are considered to be adjacent with a smaller adjacency rating. It is shown that the proposed adjacency is a generalized version of the traditional adjacency. A mathematical programming model is developed for the proposed facility layout problem. To show the flexibility and efficacy of the proposed model, a computational study is conducted. The solution of an illustrative example as well as the solutions of several test problems, reveal flexibility and efficacy of the proposed model
A priority based genetic algorithm for nonlinear transportation costs problems
, Article Computers and Industrial Engineering ; Volume 96 , 2016 , Pages 86-95 ; 03608352 (ISSN) ; Hashemi, Z ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this manuscript, a vehicle allocation problem involving a heterogeneous fleet of vehicles for delivering products from a manufacturing firm to a set of depots is considered. Each depot has a specific order quantity and transportation costs consist of fixed and variable transportation cost. The objective is to assign the proper type and number of vehicle to each depot route to minimize the total transportation costs. It is assumed that the number of chartering vehicle types is limited. It is also assumed that a discount mechanism is applied to the vehicles renting cost. The discount mechanism is applied to the fixed cost, based on the number of vehicles to be rented. A mathematical...
Prioritized K-mean clustering hybrid GA for discounted fixed charge transportation problems
, Article Computers and Industrial Engineering ; Volume 126 , 2018 , Pages 63-74 ; 03608352 (ISSN) ; Hashemi, Z ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The problem of allocating different types of vehicles for transporting a set of products in an existing transportation network, to minimize the total transportation costs, is considered. The distribution network involves a heterogeneous fleet of vehicles each with the given capacity and with a variable transportation cost and a fixed cost with a discounting mechanism. Due to nonlinearity of the discounting mechanism, a nonlinear mathematical programming model is developed. A prioritized K-mean clustering encoding is introduced to designate the distribution depots distances, their demands, and the vehicles’ capacity. Using this priority clustering, a heuristic routine is developed by which...