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Total 113 records

    Field Scale Characterization of Geological Formations Using Percolation Theory

    , Article Transport in Porous Media ; Vol. 92, issue. 2 , March , 2012 , p. 357-372 ; ISSN: 1693913 Sadeghnejad, S ; Masihi, M ; Shojaei, A ; Pishvaie, M ; King, P. R ; Sharif University of Technology
    Abstract
    The connectivity of high conductivity pathways in geological formations depend on the spatial distribution of geological heterogeneities that may appear on various length scales. Appropriate modeling of this is crucial within in hydrology and petroleum systems. The approach taken in this study is to use percolation theory to quantify the connectivity, hydraulic conductivity, and breakthrough time behavior between an injector and a producer within such systems. In particular, a three-dimensional overlapping sandbody model is considered which assumes that the geological formation can be split into either conductive flow units (i. e., good sands) or non-conductive units (i. e., poor sands). The... 

    Assessment of 2DH and pseudo-3D modelling platforms in a large saline aquatic system: Lake Urmia, Iran

    , Article Hydrological Processes ; Vol. 28, Issue. 18 , 2014 , pp. 49534970 ; ISSN: 10991085 Zeinoddini, M ; Tofighi, M. A ; Bakhtiari, A ; Sharif University of Technology
    Abstract
    The main objective of this paper is to provide comparative quantitative examinations on the capabilities of two-dimensional horizontal and pseudo-three-dimensional (3D) modelling approaches for simulating spatial and temporal variability of the flow and salinity in Lake Urmia, Iran. The water quality in the lake has been an environmentally important subject partly because this shallow hypersaline aquatic ecosystem is considered to be one of the largest natural habitats of a unique multicellular organism, Artemia urmiana. This brine shrimp is the major food source for many of the protected and rare shorebirds that visit the lake. A.urmiana can grow and survive in certain ranges of salinity,... 

    Nonlinear seismic assessment of steel moment frames under bidirectional loading via endurance time method

    , Article Structural Design of Tall and Special Buildings ; Vol. 23, issue. 6 , April , 2014 , p. 442-462 ; ISSN: 15417794 Valamanesh, V ; Estekanchi, H. E ; Sharif University of Technology
    Abstract
    In this paper, considering horizontal components of seismic excitation, an algorithm for the nonlinear multi-component analysis of building structures by the Endurance Time (ET) method is proposed, and results of the ET method for various steel moment frames with one to seven stories are verified by comparing with the results from Nonlinear Time History Analysis with use of two different sets of ground motions. In addition, several parameters such as eccentricities and irregularities in structure, rotational and lateral stiffness, effect of hysteresis type and ductility have been considered for sensitivity analysis on results, obtained by ET method. Results show that on the basis of... 

    A new correlation on the MEXICO experiment using a 3D enhanced blade element momentum technique

    , Article International Journal of Sustainable Energy ; Vol. 33, issue. 2 , 2014 , pp. 448-460 ; ISSN: 14786451 Mahmoodi, E ; Jafari, A ; Schaffarczyk, A. P ; Keyhani, A ; Mahmoudi, J ; Sharif University of Technology
    Abstract
    The blade element momentum (BEM) theory is based on the actuator disc (AD) model, which is probably the oldest analytical tool for analysing rotor performance. The BEM codes have very short processing times and high reliability. The problems of the analytical codes are well known to the researchers: the impossibility of describing inside the one-dimensional code the three-dimensional (3D) radial flows along the span-wise direction. In this work, the authors show how the 3D centrifugal pumping affects the BEM calculations of a wind turbine rotor. Actually to ascertain the accuracy of the analytical codes, the results are compared with rotor performance, blade loads and particle image... 

    Three-dimensional simulation of urine concentrating mechanism in a functional unit of rat outer medulla. I. Model structure and base case results

    , Article Mathematical Biosciences ; Vol. 258 , 2014 , pp. 44-56 ; ISSN: 00255564 Sohrabi, S ; Saidi, M. S ; Saadatmand, M ; Banazadeh, M. H ; Firoozabadi, B ; Sharif University of Technology
    Abstract
    The urine formation and excretion system have long been of interest for mathematicians and physiologists to elucidate the obscurities within the process happens in renal tissue. In this study, a novel three-dimensional approach is utilized for modeling the urine concentrating mechanism in rat renal outer medulla which is essentially focused on demonstrating the significance of tubule's architecture revealed in anatomic studies and physiological literature. Since nephrons and vasculatures work interdependently through a highly structured arrangement in outer medulla which is dominated by vascular bundles, a detailed functional unit is proposed based on this specific configuration.... 

    A study on thermal responses, microstructural issues, and natural aging in gas tungsten arc welding of AA2024-T4

    , Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Vol. 228, issue. 3 , 2014 , p. 413-421 Sarmast, A ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
    Abstract
    In this study, a three-dimensional model has been utilized for predicting thermal responses during tungsten arc welding of AA2024-T4 plates in which double ellipsoidal heat source model was employed to consider the moving torch in the model. Furthermore, tensile and hardness tests and microstructural evaluations have been carried out to investigate the mechanical properties and the microstructures within the welded metal. The results show that there is a region inside the heat-affected zone where hardness increases while in some parts of this region having temperatures higher than 250 C the hardness decreases significantly. Furthermore, natural aging occurs after welding; however, its... 

    Unsupported advance length in tunnels constructed using New Austrian Tunnelling Method and ground surface settlement

    , Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 37, Issue 14 , 2013 , Pages 2170-2185 ; 03639061 (ISSN) Nemati Hayati, A ; Ahmadi, M. M ; Hajjar, M ; Kashighandi, A ; Sharif University of Technology
    2013
    Abstract
    Tunnels constructed using New Austrian Tunnelling Method (NATM) are always based on certain round (unsupported) advance lengths, after which, the temporary lining is placed. The settlement of the ground surface resulting from such construction is of high significance in design and practice. The existing data in this respect, however, is scarce. It is the aim of this paper to propose a semi-analytical procedure based on three-dimensional finite element analyses to predict the maximum surface settlement of the ground in NATM tunnels under different combinations of tunnel diameter, overburden depth, round length and soil and lining properties. The comparison of the results with three case... 

    Prediction of the yielding moment of flush endplate splice connections using finite element modeling

    , Article Scientia Iranica ; Volume 20, Issue 2 , 2013 , Pages 270-277 ; 10263098 (ISSN) Mohamadi Shooreh, M. R ; Mofid, M ; Sharif University of Technology
    2013
    Abstract
    This paper presents the results of parametric analyses of the yielding moment (My) of Bolted Flush Endplate Beam (BFEB) splice connections using Finite Element Modeling (FEM) tools. The connection components were modeled using three-dimensional brick elements, while contact between the endplates was modeled using Coulomb friction. Materials for beam, endplate and bolts were considered to behave non-linearly. Finite element results with three experimental and numerical studies were compared, and all indicated good agreement, which is also briefly reviewed in this paper. Using verified FEM, fairly large parametric studies, based on the practical configuration of BFEB connections, were carried... 

    Effect of considering stability requirements on antagonistic muscle activities using a musculoskeletal model of the human lumbar spine

    , Article 2013 20th Iranian Conference on Biomedical Engineering, ICBME 2013 ; 2013 , Pages 260-264 Hajihoseinali, M ; Nickpour, H ; Arjmand, N ; Farahmand, F ; Sharif University of Technology
    2013
    Abstract
    The recruitment pattern of trunk muscles is determined using a three-dimensional model of the spine with two joints and six symmetric pairs of muscles in which both equilibrium and stability requirements are satisfied. Model predictions are verified using Anybody Modeling System (AMS) and Abaqus. The model is used to test the hypothesis that antagonistic muscle activities are necessary for the spinal stability. The model with stability constraints predicts muscle activities greater than those predicted without stability consideration. In agreement with experimental data, the stability-based model predicts antagonistic muscle activities. It is shown that spinal stability increases with trunk... 

    Prediction of particle deposition in the respiratory track using 3D-1D modeling

    , Article Scientia Iranica ; Volume 19, Issue 6 , December , 2012 , Pages 1479-1486 ; 10263098 (ISSN) Monjezi, M ; Dastanpour, R ; Saidi, M. S ; Pishevar, A. R ; Sharif University of Technology
    2012
    Abstract
    Airflow simulation of the whole respiratory system is still unfeasible due to the geometrical complexity of the lung airways and the diversity of the length scales involved in the problem. Even the new CT imaging system is not capable of providing accurate 3D geometries for smaller tubes, and a complete 3D simulation is impeded by the limited computational resources available. The aim of this study is to develop a fully coupled 3D-1D model to make accurate prediction of airflow and particle deposition in the whole respiratory track, with reasonable computational cost and efficiency. In the new proposed method, the respiratory tree is divided into three parts to be dealt with using different... 

    A meshless EFG-based algorithm for 3D deformable modeling of soft tissue in real-time

    , Article Studies in Health Technology and Informatics, 9 February 2012 through 11 February 2012 ; Volume 173 , February , 2012 , Pages 1-7 ; 09269630 (ISSN) ; 9781614990215 (ISBN) Abdi, E ; Farahmand, F ; Durali, M ; Sharif University of Technology
    2012
    Abstract
    The meshless element-free Galerkin method was generalized and an algorithm was developed for 3D dynamic modeling of deformable bodies in real time. The efficacy of the algorithm was investigated in a 3D linear viscoelastic model of human spleen subjected to a time-varying compressive force exerted by a surgical grasper. The model remained stable in spite of the considerably large deformations occurred. There was a good agreement between the results and those of an equivalent finite element model. The computational cost, however, was much lower, enabling the proposed algorithm to be effectively used in real-time applications  

    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) Samimi, S ; Pak, A ; Sharif University of Technology
    2012
    Abstract
    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... 

    Experimental and theoretical evaluations of thermal histories and residual stresses in dissimilar friction stir welding of AA5086-AA6061

    , Article International Journal of Advanced Manufacturing Technology ; Volume 61, Issue 1-4 , 2012 , Pages 149-160 ; 02683768 (ISSN) Jamshidi Aval, H ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
    2012
    Abstract
    In this work, the thermomechanical responses during the dissimilar friction stir welding of aluminum alloys have been evaluated employing a three-dimensional model and the finite element software ABAQUS. Furthermore, welding experiments have been conducted under different working conditions and the temperature variations during and after welding as well as the produced residual stresses in various positions of the welded samples were measured using hole-drilling technique. The model results were then examined by experimental data, and a reasonable agreement was observed. It is found that tool rotational speed significantly affects the amount of maximum tensile residual stress while traverse... 

    Field scale characterization of geological formations using percolation theory

    , Article Transport in Porous Media ; Volume 92, Issue 2 , 2012 , Pages 357-372 ; 01693913 (ISSN) Sadeghnejad, S ; Masihi, M ; Shojaei, A ; Pishvaie, M ; King, P. R ; Sharif University of Technology
    2012
    Abstract
    The connectivity of high conductivity pathways in geological formations depend on the spatial distribution of geological heterogeneities that may appear on various length scales. Appropriate modeling of this is crucial within in hydrology and petroleum systems. The approach taken in this study is to use percolation theory to quantify the connectivity, hydraulic conductivity, and breakthrough time behavior between an injector and a producer within such systems. In particular, a three-dimensional overlapping sandbody model is considered which assumes that the geological formation can be split into either conductive flow units (i. e., good sands) or non-conductive units (i. e., poor sands). The... 

    Dynamic behavior of pile foundations under cyclic loading in liquefiable soils

    , Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 114-126 ; 0266352X (ISSN) Rahmani, A ; Pak, A ; Sharif University of Technology
    Abstract
    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... 

    Prediction of temperature distribution in dissimilar arc welding of stainless steel to carbon steel

    , Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 226, Issue 1 , October , 2012 , Pages 117-125 ; 09544054 (ISSN) Ranjbarnodeh, E ; Serajzadeh, S ; Kokabi, A. H ; Fischer, A ; Sharif University of Technology
    Abstract
    In this work, a three-dimensional model has been proposed to predict temperature distribution and weld-pool shape during dissimilar arc welding of low-carbon steel (CK4) and ferritic stainless steel (AISI 409). The model has been developed using the finite-element software ANSYS, while in the analysis, the effects of process parameters, as well as dilution, in the weld pool have been considered. To verify the predictions, welding experiments were conducted under different welding conditions, and the model results were then compared with the measured weld-pool geometry; a reasonable consistency was observed  

    Proposal of a new design for valveless micropumps

    , Article Scientia Iranica ; Volume 18, Issue 6 , December , 2011 , Pages 1261-1266 ; 10263098 (ISSN) Afrasiab, H ; Movahhedy, M. R ; Assempour, A ; Sharif University of Technology
    2011
    Abstract
    A new design for a valveless micropumping device has been proposed that integrates two existing pumping technologies, namely, the wall induced traveling wave and the obstacle-type valveless micropump. The liquid in the microchannel is transported by generating a traveling wave on the channel, while the placing of two asymmetric trapezoid obstacles, along the centerline of the channel inlet and outlet, leads to a significant (up to seven times) increase of the net flow rate of the device. The effectiveness of this innovative design has been proved through a verified three-dimensional finite element model. FluidStructure Interaction (FSI) analysis is performed in the framework of an Arbitrary... 

    Study on effect of residual stress distributions on kinetics of static strain aging after cold rolling

    , Article Materials Science and Technology ; Volume 27, Issue 11 , 2011 , Pages 1620-1626 ; 02670836 (ISSN) Koohbor, B ; Serajzadeh, S ; Sharif University of Technology
    Abstract
    In the present research, the effect of residual stress distribution on the static strain aging (SSA) phenomenon in cold rolled steel was investigated. A three-dimensional model was employed to evaluate the residual stress distributions within the rolled strips, and hole drilling experiments were also performed to verify the data obtained from the mathematical model. Hardness and tensile tests were then performed on the cold rolled samples at different temperatures and aging periods, and the results of these tests were utilised to assess SSA behaviour after different rolling programs. The results show that SSA occurs within the cold rolled steel in the employed aging period, and its kinetics... 

    A multiple-point statistics algorithm for 3D pore space reconstruction from 2D images

    , Article Advances in Water Resources ; Volume 34, Issue 10 , October , 2011 , Pages 1256-1267 ; 03091708 (ISSN) Hajizadeh, A ; Safekordi, A ; Farhadpour, F. A ; Sharif University of Technology
    2011
    Abstract
    Fluid flow behavior in a porous medium is a function of the geometry and topology of its pore space. The construction of a three dimensional pore space model of a porous medium is therefore an important first step in characterizing the medium and predicting its flow properties. A stochastic technique for reconstruction of the 3D pore structure of unstructured random porous media from a 2D thin section training image is presented. The proposed technique relies on successive 2D multiple point statistics simulations coupled to a multi-scale conditioning data extraction procedure. The Single Normal Equation Simulation Algorithm (SNESIM), originally developed as a tool for reproduction of... 

    New modeling for moment-rotation behavior of bolted endplate connections

    , Article Scientia Iranica ; Volume 18, Issue 4 A , August , 2011 , Pages 827-834 ; 10263098 (ISSN) Mohamadi Shoore, M. R ; Mofid, M ; Sharif University of Technology
    2011
    Abstract
    A new exponential model to depict the moment-rotation (M-θ) relationship of Bolted Endplate Connections (BEC) is proposed. The proposed model represents an approach to the prediction of M-O curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The presented model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. By employing simplified connection behavioral models to estimate the connection M-θ behavior, analytical expressions for evaluating major connection parameters, such as initial...