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    How particle shape affects the flow through granular materials

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 85, Issue 3 , 2012 ; 15393755 (ISSN) Nemati Hayati, A ; Ahmadi, M. M ; Mohammadi, S
    2012
    Abstract
    Flow through the pores of granular materials has many instances in practice. Therefore, it is interesting to realize how some parameters, such as the shape of the particles affect the passing flow. Following the recent mathematical theory proposed by the authors, this paper deals with the issue of how tortuosity and permeability are influenced by the particle shape. Comparison of the results with the experimental data reveals the competency of the theory in predicting the impact of particle geometry  

    Mixed mode fracture analysis of adiabatic cracks in homogeneous and non-homogeneous materials in the framework of partition of unity and the path-independent interaction integral

    , Article Engineering Fracture Mechanics ; Vol. 131, issue , 2014 , Pp. 100-127 ; ISSN: 00137944 Goli, E ; Bayesteh, H ; Mohammadi, S ; Sharif University of Technology
    Abstract
    In this paper, the path independent interaction integral has been implemented in the framework of the extended finite element method for mixed mode adiabatic cracks under thermo-mechanical loadings particularly in orthotropic non-homogenous materials. The mesh insensitivity and increased accuracy due to the thermal and displacement asymptotic analytical solutions are discussed and the contour independency of the interaction integral is investigated in different examples. Finally, the problem of crack propagation in orthotropic FGM materials under the thermal loading is investigated to assess the accuracy and robustness of proposed approach  

    Stability of a predator-prey system with prey taxis in a general class of functional responses

    , Article Acta Mathematica Scientia ; Volume 36, Issue 1 , 2016 , Pages 62-72 ; 02529602 (ISSN) Yousefnezhad, M ; Mohammadi, S. A ; Sharif University of Technology
    Elsevier  2016
    Abstract
    In this paper, a diffusive predator-prey system with general functional responses and prey-tactic sensitivities is studied. Providing such generality, we construct a Lyapunov function and we show that the positive constant steady state is locally and globally asymptotically stable. With an eye on the biological interpretations, a numerical simulation is performed to illustrate the feasibility of the analytical findings  

    Developing new enrichment functions for crack simulation in orthotropic media by the extended finite element method

    , Article International Journal for Numerical Methods in Engineering ; Volume 69, Issue 10 , 2007 , Pages 2150-2172 ; 00295981 (ISSN) Asadpoure, A ; Mohammadi, S ; Sharif University of Technology
    2007
    Abstract
    New enrichment functions are proposed for crack modelling in orthotropic media using the extended finite element method (XFEM). In this method, Heaviside and near-tip functions are utilized in the framework of the partition of unity method for modelling discontinuities in the classical finite element method. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore, mesh generation is directly performed ignoring the existence of any crack while the method remains capable of extending the crack without any remeshing requirement. Furthermore, the type of elements around the crack-tip remains the same as other parts of... 

    Crack analysis in orthotropic media using the extended finite element method

    , Article Thin-Walled Structures ; Volume 44, Issue 9 , 2006 , Pages 1031-1038 ; 02638231 (ISSN) Asadpoure, A ; Mohammadi, S ; Vafai, A ; Sharif University of Technology
    2006
    Abstract
    An extended finite element method has been proposed for modeling crack in orthotropic media. To achieve this aim a discontinuous function and two-dimensional asymptotic crack-tip displacement fields are used in a classical finite element approximation enriched with the framework of partition of unity. It allows modeling crack by standard finite element method without explicitly defining and re-meshing of surfaces of the crack. In this study, fracture properties of the models are defined by the mixed-mode stress intensity factors (SIFs), which are obtained by means of the domain form of the interaction integral (M-integral). Numerical simulations are performed to verify the approach, and the... 

    Modeling crack in orthotropic media using a coupled finite element and partition of unity methods

    , Article Finite Elements in Analysis and Design ; Volume 42, Issue 13 , 2006 , Pages 1165-1175 ; 0168874X (ISSN) Asadpoure, A ; Mohammadi, S ; Vafai, A ; Sharif University of Technology
    2006
    Abstract
    The problem of crack modeling in 2D orthotropic media is considered. The extended finite element method has been adopted for modeling and analyzing a crack and its domain numerically. In this method, first the finite element model without any discontinuities is created and then the two-dimensional asymptotic crack-tip displacement fields with a discontinuous function are added to enrich the finite element approximation using the framework of partition of unity. The main advantage is the ability of the method in taking into consideration a crack without any explicit meshing of the crack surfaces, and the growth of crack can readily be applied without any remeshing. Mixed-mode stress intensity... 

    Extended finite element method in an orthotropic cracked medium

    , Article 8th International Conference on Computational Plasticity: Fundamentals and Applications, COMPLAS VIII, Barcelona, 5 September 2005 through 7 September 2005 ; Issue PART 2 , 2005 , Pages 1110-1113 ; 849599979X (ISBN); 9788495999795 (ISBN) Asadpoure, A ; Mohammadi, S ; Vafai, A ; Sharif University of Technology
    2005

    Analytical Solution for Isothermal Flow in a Shock Tube Containing Rigid Granular Material

    , Article Transport in Porous Media ; Volume 93, Issue 1 , 2012 , Pages 13-27 ; 01693913 (ISSN) Hayati, A. N ; Ahmadi, M. M ; Mohammadi, S ; Sharif University of Technology
    2012
    Abstract
    Analytical solution of shock wave propagation in pure gas in a shock tube is usually addressed in gas dynamics. However, such a solution for granular media is complex due to the inclusion of parameters relating to particles configuration within the medium, which affect the balance equations. In this article, an analytical solution for isothermal shock wave propagation in an isotropic homogenous rigid granular material is presented, and a closed-form solution is obtained for the case of weak shock waves. Fluid mass and momentum equations are first written in wave and (mathematical) non-conservation forms. Afterwards by redefining the sound speed of the gas flowing inside the pores, an... 

    Comparative study of different excitation signals on Mel-generalized cepstral synthesis filters

    , Article 2011 International Symposium on Artificial Intelligence and Signal Processing, AISP 2011, 15 June 2011 through 16 June 2011 ; June , 2011 , Pages 15-19 ; 9781424498345 (ISBN) Bahaadini, S ; Sameti, H ; Mohammadi, S. H ; Sharif University of Technology
    2011
    Abstract
    In speech production systems, the vocal tract is modeled by a filter and glottal pulse by an excitation signal. In most traditional systems impulse train or noise is used as the excitation. In this paper the effects of different excitation signals on Mel-generalized cepstral filters (LPC, warped LPC, mel cepstral and ML cepstral) are studied. Excitation signals with different pulse shapes are used. Furthermore, based on voicing power, noise factor is added to the excitation signals. Totally 600 different experiments with different filter types, number of coefficients, pulse shapes, pulse widths and noise power are preformed. Synthesized speech is evaluated by PESQ measure. A number of pulse... 

    Analytical derivation of tortuosity and permeability of monosized spheres: A volume averaging approach

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 83, Issue 2 , February , 2011 ; 15393755 (ISSN) Ahmadi, M. M ; Mohammadi, S ; Hayati, A. N ; Sharif University of Technology
    2011
    Abstract
    Macroscopic properties of granular materials are important in modeling a variety of flow and transport phenomena in many fields of science. Determination of these parameters has always been an issue among both researchers and engineers, mainly in view of tortuosity and permeability. This paper presents analytical functions for the tortuosity and permeability of monosized sphere arrays based on a volume averaging approach and eliminates some ambiguities by modification of the original representative elementary volume model. Veracity of the proposed formulations has been illustrated through comparisons with the latest available results on the subject. Good agreement is found  

    Formulation of differential transfer matrix method in cylindrical geometry

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 25 January 2010 through 28 January 2010 ; Volume 7597 , January , 2010 ; 0277786X (ISSN) ; 9780819479938 (ISBN) Jiani, M ; Khorasani, S ; Rashidian, B ; Mohammadi, S ; Sharif University of Technology
    2010
    Abstract
    Transfer and scattering matrix methods are widely in use for description of the propagation of waves in multilayered media. When the profile of refractive index is continuous, however, a modified formulation of transfer matrices does exist, which provides a complete analytical solution of the wave phenomena in such structures. Previously reported variations of the so-called Differential Transfer Matrix Method (DTMM) had been limited to Cartesian geometry where layered media form one-dimensional structures and plane waves are used as basis functions. In this work, we extend the formalism to cylindrical geometry with radial symmetry, in which Bessel functions need to be employed as basis... 

    Effect of defects on the local shell buckling and post-buckling behavior of single and multi-walled carbon nanotubes

    , Article Computational Materials Science ; Volume 79 , November , 2013 , Pages 736-744 ; 09270256 (ISSN) Eftekhari, M ; Mohammadi, S ; Khoei, A. R ; Sharif University of Technology
    Abstract
    The local buckling behavior of perfect/defective and single/multi-walled carbon nanotubes (CNTs) under axial compressive forces has been investigated by the molecular dynamics approach. Effects of different types of defects including vacancy and Stone-Wales (SW) defects and their configurations on CNTs with different chiralities at room temperature are studied. Results show that defects largely reduce the buckling stress and the ratio of immediate reduction in buckling compressive stress of the defective CNT to the perfect one, but have little influence on their compressive elastic modulus. SW defects usually reduce the mechanical properties more than vacancy defects, and zigzag CNTs are... 

    Stability improvement of a dynamic walking system via reversible switching surfaces

    , Article Multibody System Dynamics ; 2017 , Pages 1-19 ; 13845640 (ISSN) Tehrani Safa, A ; Mohammadi, S ; Naraghi, M ; Alasty, A ; Sharif University of Technology
    Abstract
    Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be... 

    Stability improvement of a dynamic walking system via reversible switching surfaces

    , Article Multibody System Dynamics ; Volume 43, Issue 4 , 2018 , Pages 349-367 ; 13845640 (ISSN) Tehrani Safa, A ; Mohammadi, S ; Naraghi, M ; Alasty, A ; Sharif University of Technology
    Abstract
    Inspired by the effects of a switching surface on the stability of passive dynamic walking (Safa and Naraghi in Robotica 33(01):195–207, 2015; Safa et al. in Nonlinear Dyn. 81(4):2127–2140, 2015), this paper suggests a new control strategy for stabilization of dynamic bipedal locomotion. It verifies that the stability improvement of a dynamic walking system is feasible while preserving the speed, step-length, period, natural dynamics, and the energy effectiveness of the gait. The proposed control policy goes behind the three primary principles: (i) The system’s switching surface has to be replaced by a new one if an external disturbance is induced. (ii) The new switching surface has to be... 

    Assisted passive snake-like robots: Conception and dynamic modeling using Gibbs-Appell method

    , Article Robotica ; Volume 26, Issue 3 , 2008 , Pages 267-276 ; 02635747 (ISSN) Vossoughi, G ; Pendar, H ; Heidari, Z ; Mohammadi, S ; Sharif University of Technology
    2008
    Abstract
    In this paper, we present a novel structure of a snake-like robot. This structure enables passive locomotion in snake-like robots. Dynamic equations are obtained for motion in a horizontal plane, using Gibbs-Appell method. Kinematic model of the robot include numerous nonholonomic constraints, which can be omitted at the beginning by choosing proper coordinates to describe the model in Gibbs-Appell framework. In such a case, dynamic equations will be significantly simplified, resulting in considerable reduction of simulation time. Simulation results show that, by proper selection of initial conditions, joint angles operate in a limit cycle and robot can locomote steadily on a passive... 

    The non-linear effect of oil polarity on the efficiency of low salinity waterflooding: A pore-level investigation

    , Article Journal of Molecular Liquids ; January , 2021 ; 01677322 (ISSN) Golmohammadi, M ; Mohammadi, S ; Mahani, H ; Ayatollahi, S ; Sharif University of Technology
    Elsevier B. V  2021
    Abstract
    Oil polarity is an important property impacting the efficiency of low salinity waterflooding (LSWF). It directly affects fluid/fluid and rock/fluid interactions, controlling the interfacial properties and forces. However, the current findings in the literature on the effect of concentration of polar components on oil recovery by LSWF are contradictory. Therefore, the main objective of this paper is to investigate how the type of non-polar fractions and the concentration of acidic polar oil constituents change the trapped oil saturation at the pore-scale during LSWF. In this regard, we conducted a series of microfluidics LSWF experiments in both secondary and tertiary modes, using clay-free... 

    Conception and dynamic modeling of an assisted passive snake-like robot using Gibbs-Appell method

    , Article DETC2005: ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Long Beach, CA, 24 September 2005 through 28 September 2005 ; Volume 7 B , 2005 , Pages 863-870 ; 0791847446 (ISBN); 9780791847442 (ISBN) Vossoughi, G ; Heidari, Z ; Pendar, H ; Mohammadi, S ; Sharif University of Technology
    American Society of Mechanical Engineers  2005
    Abstract
    In this paper we present a novel planar structure of a snake-like robot. This structure enables passive locomotion in snake-like robots through an auxiliary link in joint and a torsional spring. Dynamic equations are derived, using Gibbs-Appell method. Kinematic model of the robot include numerous non-holonomic constraints, which can be omitted at the beginning by choosing proper coordinates to describe the model in Gibbs-Appell framework. In such a case, dynamic equations will be significantly simplified, resulting in significant reduction of simulation time. Simulation results show that, by proper selecting initial conditions, joint angles operate in a limit cycle and robot can locomote... 

    Graph centrality algorithms for hardware trojan detection at gate-level netlists

    , Article International Journal of Engineering, Transactions A: Basics ; Volume 35, Issue 7 , 2022 , Pages 1375-1387 ; 17281431 (ISSN) Hashemi, M ; Momeni, A ; Pashrashid, A ; Mohammadi, S ; Sharif University of Technology
    Materials and Energy Research Center  2022
    Abstract
    The rapid growth in the supply chain of electronic devices has led companies to purchase Intellectual Property or Integrated Circuits from unreliable sources. This dispersion in the design to fabrication stages of IP/IC has led to new attacks called hardware Trojans. Hardware Trojans can bargain information, reduce performance, or cause failure. Various methods have been introduced to detect or prevent hardware Trojans. Machine learning methods are one of these. Selecting the type and number of input variables in the learning algorithm has an important role in the performance of the learning model. Some previous hardware Trojan detection studies have used structural gate-level features to... 

    Infrastructure aware heterogeneous-workloads scheduling for data center energy cost minimization

    , Article IEEE Transactions on Cloud Computing ; Volume 10, Issue 2 , 2022 , Pages 972-983 ; 21687161 (ISSN) Haghshenas, K ; Taheri, S ; Goudarzi, M ; Mohammadi, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2022
    Abstract
    A huge amount of energy consumption, the cost of this usage and environmental effects have become serious issues for commercial cloud providers. Solar energy is a promising clean energy source, to provide some portion of the Internet data center's (IDC's) energy usage which can reduce environmental effects and total energy costs. Moreover, due to the high energy consumption of the cooling system, considering cooling power in job scheduling can provide efficient solutions to reduce total energy consumption. In this article, we investigate the problem of minimizing the energy cost of an IDC and propose an algorithm which schedules heterogeneous IDC workloads, by considering available renewable... 

    The non-linear effect of oil polarity on the efficiency of low salinity waterflooding: A pore-level investigation

    , Article Journal of Molecular Liquids ; Volume 346 , 2022 ; 01677322 (ISSN) Golmohammadi, M ; Mohammadi, S ; Mahani, H ; Ayatollahi, S ; Sharif University of Technology
    Elsevier B.V  2022
    Abstract
    Oil polarity is an important property impacting the efficiency of low salinity waterflooding (LSWF). It directly affects fluid/fluid and rock/fluid interactions, controlling the interfacial properties and forces. However, the current findings in the literature on the effect of concentration of polar components on oil recovery by LSWF are contradictory. Therefore, the main objective of this paper is to investigate how the type of non-polar fractions and the concentration of acidic polar oil constituents change the trapped oil saturation at the pore-scale during LSWF. In this regard, we conducted a series of microfluidics LSWF experiments in both secondary and tertiary modes, using clay-free...