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    Numerical properties of second order integration algorithms for plasticity models

    , Article Research and Applications in Structural Engineering, Mechanics and Computation - Proceedings of the 5th International Conference on Structural Engineering, Mechanics and Computation, SEMC 2013 ; 2013 , Pages 443-448 ; 9781138000612 (ISBN) Jahanshahi, M ; Sharif University of Technology
    2013
    Abstract
    Investigating the behavior of materials in plastic limit is very important in different fields of engineering. Due to the simplicity of implementation and numerical stability, implicit types of algorithms are conventionally used to deal with plasticity problems. The backward Euler method as a first order accurate algorithm has proven very efficient for integrating the rate form of differential equations governing the behavior of different plasticity models. However, it is desirable to have algorithms with superior performance and quadratic rate of convergence compared with backward Euler method. Many second order integration algorithms have been proposed in the literature which are majorly... 

    Numerical assessment of a double step integration algorithm for J 2 plasticity with Armstrong-Frederick evolution of back stress

    , Article Scientia Iranica ; Volume 19, Issue 5 , 2012 , Pages 1168-1179 ; 10263098 (ISSN) Jahanshahi, M ; Sharif University of Technology
    2012
    Abstract
    In this work a double step algorithm is presented for the integration of equations governing the behavior of von Mises material in plastic limit. The isotropic and kinematic hardenings employed are of general type and the evolution of back stress follows the Armstrong-Frederick rule. Theoretical and numerical aspects are discussed in detail and a comparison is made with the classical backward Euler method  

    Second order integration algorithms for j2 plasticity with generalized isotropic/kinematic hardening

    , Article Asian Journal of Civil Engineering ; Volume 13, Issue 2 , April , 2012 , Pages 203-232 ; 15630854 (ISSN) Jahanshahi, M ; Sharif University of Technology
    AJCE  2012
    Abstract
    In this work four algorithms are presented for the integration of equations governing the behavior of von Mises material in plastic limit. Two of them are single-step and the others are double-step algorithms. Single-step algorithms are straight forward extension of backward Euler method or midpoint rule while double-step algorithms are a combination of two. In past similar algorithms were proposed for special cases of isotropic/kinematic hardening; however the algorithms presented in this work are applicable to general isotropic/kinematic hardening laws. Theoretical as well as numerical aspects are presented for all integration schemes and elaborated for double-step algorithms which are... 

    A compatible mixed finite element method for large deformation analysis of two-dimensional compressible solids in spatial configuration

    , Article International Journal for Numerical Methods in Engineering ; Volume 123, Issue 15 , 2022 , Pages 3530-3566 ; 00295981 (ISSN) Jahanshahi, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2022
    Abstract
    In this article, a new mixed finite element formulation is presented for the analysis of two-dimensional compressible solids in finite strain regime. A three-field Hu–Washizu functional, with displacement, displacement gradient and stress tensor considered as independent fields, is utilized to develop the formulation in spatial configuration. Certain constraints are imposed on displacement gradient and stress tensor so that they satisfy the required continuity conditions across the boundary of elements. From theoretical standpoint, simplex elements are best suited for the application of continuity constraints. The techniques that are proposed to implement the constraints facilitate their... 

    Plastic Analysis of Two Dimensional Frames using Ant Colony Algorithms

    , M.Sc. Thesis Sharif University of Technology Pouraghajan, Marjan (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In previous decades, easy access to material and low cost human power allow the product process to be performed in a preferred way. The limit in amount of material, economy, and the efficiency of the model has not been influential like these days. Today, the effective use of material and consideration of an economic model have great importance. It is obvious that a process of designing implies optimizing which the range of its using is also continuing in many engineering sciences. Many optimization issues contain discrete nature. Many of searching spaces that we encounter in the real world applications are not necessarily continuous as a condition which has crucial importance for classic... 

    Application of Isogeometric Analysis in Determining Stress Distribution at the Tip of a Crack

    , M.Sc. Thesis Sharif University of Technology Zandinia, Meysam (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    Isogeometric Analysis is one of the new methods for solving partial differential Equations which has special advantages compared to conventional methods such as the finite Element method. Some of these benefits can be used to approximate the geometry and solving the Equations governing the behavior of materials. Calculating the stress intensity factor at the tip of the Crack using classical method such as finite element method is done as well as IGA and gives Acceptable Results in linear range. Studying how to calculate these coefficients in combination with Isogeometric analysis method and comparing results with FEM due to novelty of the approach can have considerable importance for... 

    Using Base Isolators in Bridges to Reduce the Dynamic Forces of Piers and Abutments

    , M.Sc. Thesis Sharif University of Technology Kohani Khoshkbijari, Reza (Author) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    In recent years, the application of base isolation as a seismic design strategy for reducing the effects of earthquake ground motion has become an advantageous method and much effort has been devoted to base isolation research and there has been a growing acceptance of this approach. In this research, the effect of using base isolators in reducing the dynamic forces of piers and abutments of bridges is studied. More specifically double-span bridges are the target of this research. After modeling a regular bridge in a typical analysis program, it is excited by different earthquake accelerograms and then the effect of using base isolators in dissipating the earthquake energy is investigated  

    The Influence of Information Presentation and Risk Attitude on Asset Allocation in Financial Markets

    , M.Sc. Thesis Sharif University of Technology Jahanshahi, Mahmoud (Author) ; Akhavan Niaki, Taghi (Supervisor)
    Abstract
    In this work, effects of information aggregation on risk attitude of Iranian individuals is being studied through two experiments. In these experiments a risk-free asset with a guaranteed revenue and a risky asset is introduced to each individual. Then the individual has to allocate a certain amount of money between two assets. In both experiments three treatments of control, separation and aggregation are defined in a way that the degree of information aggregation increases respectively. Given the specific treatment assigned to each individual, complementary information is presented, in orderto finalize the decision. Next a financial market simulation for a five year horizon is conducted to... 

    On the efficiency of artificial neural networks for plastic analysis of planar frames in comparison with genetic algorithms and ant colony systems

    , Article Neural Computing and Applications ; 2016 , Pages 1-19 ; 09410643 (ISSN) Jahanshahi, M ; Maleki, E ; Ghiami, A ; Sharif University of Technology
    Springer-Verlag London Ltd  2016
    Abstract
    The investigation of plastic behavior and determining the collapse load factors are the important ingredients of every kinematical method that is employed for plastic analysis and design of frames. The determination of collapse load factors depends on many effective parameters such as the length of bays, height of stories, types of loads and plastic moments of individual members. As the number of bays and stories increases, the parameters that have to be considered make the analysis a complex and tedious task. In such a situation, the role of algorithms that can help to compute an approximate collapse load factor in a reasonable time span becomes more and more crucial. Due to their... 

    Continuous synthesis of barium sulfate nanoparticles in a new high-speed spinning disk reactor

    , Article Industrial and Engineering Chemistry Research ; Volume 58, Issue 36 , 2019 , Pages 16597-16609 ; 08885885 (ISSN) Jahanshahi Anboohi, J ; Molaei Dehkordi, A ; Sharif University of Technology
    American Chemical Society  2019
    Abstract
    A new high-speed spinning disk reactor (HSSDR) was proposed and tested successfully. In this regard, barium sulfate (BaSO4) nanoparticles were synthesized using reactive crystallization processes. In this reactor, the rotational disk speed was varied from 5000 to 15 000 rpm. The effects of various design and operating parameters such as the rotational disk speed, feed entrance radius, volumetric flow rate of feed solutions, supersaturation, and free ion ratio were investigated in detail. The mean particle size (MPS) and specifications of the synthesized barium sulfate were investigated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and powder X-ray... 

    Three-particle deterministic secure and high bit-rate direct quantum communication protocol

    , Article Quantum Information Processing ; Volume 12, Issue 7 , 2013 , Pages 2441-2451 ; 15700755 (ISSN) Jahanshahi, S ; Bahrampour, A ; Zandi, M. H ; Sharif University of Technology
    2013
    Abstract
    A scheme for deterministic secure and high bit-rate direct communication without resorting to a distinct control interval is proposed. It utilizes three entangled qubits, and presents higher bit transfer rate of information and higher security. The security of protocol is asserted by introducing a security control for each transferred bit. The protocol is investigated for a class of individual attacks and it is explicitly showed that the protocol has a high security even in the presence of channel loss  

    Blokus Duo game on FPGA

    , Article roceedings - 17th CSI International Symposium on Computer Architecture and Digital Systems, CADS 2013 ; 2013 , Pages 149-152 ; 9781479905621 (ISBN) Jahanshahi, A ; Taram, M. K ; Eskandari, N ; Sharif University of Technology
    IEEE Computer Society  2013
    Abstract
    There are a number of Artificial In elligence (AI) algorithms for implementation of 'Blokus Duo' game. We needed an implementation on FPGA, and moreover, the design had to respond under a given time constraint. In this paper we examine some of these algorithms and propose a heuristic algorithm to solve the problem by considering intelligence, time constraint and FPGA implementation limitations  

    A coarse-graining approach for modeling nonlinear mechanical behavior of FCC nano-crystals

    , Article Computational Materials Science ; Volume 172 , 1 February , 2020 Jahanshahi, M ; Vokhshoori, M ; Khoei, A. R ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    The ever-increasing growth of nano-technology has elevated the necessity for development of new computational methods that are capable of evaluating large systems at nano-scale. The existing techniques, such as the molecular dynamics, lack the ability to simulate large systems of practical size and time scales. In order to provide a realistic simulation of large models, the multi-scale methods such as coarse-graining, have therefore become very popular. The coarse-grained models have mostly been used to simulate large biomolecules, such as proteins, lipids, DNA and polymers. In this paper, the Iterative Boltzmann Inversion (IBI) coarse-graining technique is applied to FCC nano-crystals; the... 

    A hierarchical hyperelastic-based approach for multi-scale analysis of defective nano-materials

    , Article Mechanics of Materials ; Volume 140 , January , 2020 Jahanshahi, M ; Ahmadi, H ; Khoei, A. R ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    In this paper, a continuum–atomistic multi-scale method is presented in modeling the nonlinear behavior of nano-materials under large deformation. In order to identify an appropriate strain energy function for crystalline nano-structures with different percentages of spherical voids, the hyperelastic method is employed for specimen whose behavior is determined based on the molecular dynamics analyses. In the atomistic level, the EAM many-body potential is employed to model the interactions between the atoms of Al RVEs. The atomistic strain energy density curves and surfaces are generated by applying the uniaxial, biaxial and simple shear deformations to the boundaries of RVEs. The material... 

    A new model for estimation of the critical properties of alkanes

    , Article Theoretical Foundations of Chemical Engineering ; Volume 39, Issue 1 , 2005 , Pages 78-80 ; 00405795 (ISSN) Pazuki, G. R ; Mokhatab, S ; Jahanshahi, V ; Sharif University of Technology
    2005
    Abstract
    A simple model is proposed to estimate the critical properties of alkanes-temperature, pressure, and volume. This model is dependent on normal boiling and molecular weight of hydrocarbons. The model has been expanded based on a Taylor series in the form of a polynomial function of normal boiling. Because methane has the simplest structure among hydrocarbons, this model has been calculated around methane. The coefficients of this model were assumed in the form of a linear function of molecular weight. These parameters can be obtained from regression between experimental results and results from this model. By a comparison of this model and previous models, it is shown that this model is... 

    Security enhanced direct quantum communication with higher bit-rate

    , Article International Journal of Quantum Information ; Volume 11, Issue 2 , 2013 ; 02197499 (ISSN) Jahanshahi, S ; Bahrampour, A. R ; Zandi, M. H ; Sharif University of Technology
    2013
    Abstract
    A scheme for deterministic secure direct communication based on ping-pong protocol without restricting the security control only to a distinct control mode and debate via classical channel is proposed. It utilizes an entangled pair of qubits and presents a higher bit-rate transfer of information together with a higher security than ping-pong protocol. The security of protocol is enhanced by introducing a control factor for each message mode. It is explicitly showed that the protocol has a high degree of security against a class of individual attacks, and successfully resolves the famous Wojcik attack  

    A hierarchical thermo-mechanical multi-scale technique for modeling of edge dislocations in nano-crystalline structures

    , Article Computational Materials Science ; Volume 141 , 2018 , Pages 360-374 ; 09270256 (ISSN) Jahanshahi, M ; Khoei, A. R ; Heidarzadeh, N ; Jafarian, N ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    In this paper, a hierarchical multi-scale technique is developed to investigate the thermo-mechanical behavior of nano-crystalline structures in the presence of edge dislocations. The primary edge dislocations are generated by proper adjustment of atomic positions to resemble discrete dislocations. The interatomic potential used to perform atomistic simulation is based on the Finnis-Sinclair embedded-atom method as many-body potential and, the Nose-Hoover thermostat is employed to control the effect of temperature. The strain energy density function is obtained for various representative volume elements under biaxial and shear loadings by fitting a fourth order polynomial in the atomistic... 

    Properties Evaluation of Self-Consolidating Concrete Containing Rice Husk Ash

    , M.Sc. Thesis Sharif University of Technology Nourbakhsh, Ali (Author) ; Jahanshahi, Mohsen (Supervisor) ; Shams, Mohammad Reza (Co-Advisor)
    Abstract
    The Self-Consolidating (Compacting) Concrete (SCC) is a high performance concrete. Due to preventing it from segregation, SCC is known by its need to higher dosage of super plasticizer and viscose modifying agents. This increases the cost and reduces the popularity of SCC in construction industry. In this thesis, the production of Rice Husk Ash (RHA) from a controlled burning process using a special designed furnace, and cement replacement feasibility in the concrete mixture by low cost RHA, as an active pozzulanic additive have been investigated. Finding an appropriate ratio of replacement with cement for RHA and further effects on mechanical properties of SCC have been evaluated. The... 

    Determination of the Plastic Zone at the Tip of a Crack in Pressure-Sensitive Materials Using RKPM

    , M.Sc. Thesis Sharif University of Technology Malgard, Afsaneh (Author) ; Mohammadi Shoja, Hossein (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    This project presents an outline of the crack tip stress fields in the presence of a plastic enclave around a growing fatigue crack using RKPM and Drucker-Prager criterion for pressure sensitive materials such as concrete and rock. Two distinguished features of RKPM are the arbitrarily high order smoothness and the interpolation property of the shape function which has kronecker delta property at the associated nodes. This method has proved to handle extreme material deformation and moving discontinuities. For the frictional materials such as rock in geotechnical engineering, a non-associated or associated Drucker- Prager plasticity model is appropriate for modeling its constitutive... 

    Application of Shape Memory Alloys (SMA) in Re-Centering the Base-Isolated Steel Structures under Near Field Earthquake Excitation

    , M.Sc. Thesis Sharif University of Technology Ahmadnejhad, Mahmoud (Author) ; Rahimzadeh Rofooei, Fayaz (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    Base isolation system is an efficient passive structural control approach to save the structures from the harms of earthquakes. The base isolated systems help to reduce the base shear by increasing the period of the structures, as well as dissipating the seismic input energy by its inherent damping mechanism [1]. However, the residual displacement of the base isolation systems resulted from strong ground motions would remain as a main obstacle in its regular serviceability after the main event. In that regard different isolating devices have been introduced to resolve the problem of the remaining permanent displacement. On the other hand, Shape Memory Alloys (SMAs) are among the newly...