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    Transversals in long rectangular arrays

    , Article Discrete Mathematics ; Volume 306, Issue 23 SPEC. ISS , 2006 , Pages 3011-3013 ; 0012365X (ISSN) Akbari, S ; Etesami, O ; Mahini, H ; Mahmoody, M ; Sharifi, A ; Sharif University of Technology
    Elsevier  2006
    Abstract
    In this paper it is shown that every m × n array in which each symbol appears at most (mn - 1) / (m - 1) times has a transversal, when n ≥ 2 m3. © 2006 Elsevier B.V. All rights reserved  

    A novel numerical method to model the dynamic underbalanced perforation process

    , Article Society of Petroleum Engineers - Abu Dhabi International Petroleum Exhibition and Conference 2020, ADIP 2020, 9 through 12 November ; 2020 Mohajeri, S ; Alizadeh, A ; Zeinali, M ; Rajabi, H ; Madani, M ; Sharif University of Technology
    Society of Petroleum Engineers  2020
    Abstract
    The final goal in a perforation operation is achieving the maximum production and reducing perforation damage, using optimal completion process. The Dynamic Underbalanced Perforation (DUP) as one of the more recent completion technologies minimizes or even eliminates the perforation crushed zone by optimizing the well's dynamic underbalance. Dynamic underbalance is a transient underbalance process that occurs immediately after creation of the perforation tunnels. The modeling of this process is essential in designing the optimal configuration of the perforation charges to evaluate the perforation efficiency. In this study we propose a novel and efficient numerical method, to optimize the... 

    Widespread chaos in rotation of the secondary asteroid in a binary system

    , Article Nonlinear Dynamics ; Volume 81, Issue 4 , September , 2015 , Pages 2031-2042 ; 0924090X (ISSN) Jafari Nadoushan, M ; Assadian, N ; Sharif University of Technology
    Kluwer Academic Publishers  2015
    Abstract
    The chaotic behavior of the secondary asteroid in a system of binary asteroids due to the asphericity and orbital eccentricity is investigated analytically and numerically. The binary asteroids are modeled with a sphere–ellipsoid model, in which the secondary asteroid is ellipsoid. The first-order resonance is studied for different values of asphericity and eccentricity of the secondary asteroid. The results of the Chirikov method are verified by Poincare section which show good agreement between analytical and numerical methods. It is also shown that asphericity and eccentricity affect the size of resonance regions such that beyond the threshold value, the resonance overlapping occurs and... 

    Reliable nonlinear hybrid simulation using modified operator splitting technique

    , Article Structural Control and Health Monitoring ; 2018 ; 15452255 (ISSN) Zakersalehi, M ; Tasnimi, A. A ; Ahmadizadeh, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    One of the main challenges of hybrid simulation is developing integration methods that not only provide accurate and stable results but also are compatible with the hybrid simulation circumstances. This paper presents a novel enhanced integration technique for hybrid simulation termed “modified operator splitting” (MOS) method. The main aim of the MOS technique is to improve the precision of the operator splitting (OS) method by reducing the corrector step length, where initial stiffness is utilized instead of actual stiffness. For this purpose, a new algorithm is proposed, which makes a more precise estimation of the predictor displacement; thus minimizes the effect of the corrective... 

    Solar radiation on domed roofs

    , Article Energy and Buildings ; Volume 41, Issue 11 , 2009 , Pages 1238-1245 ; 03787788 (ISSN) Faghih Khorasani, A. R ; Bahadori, M.N ; Sharif University of Technology
    2009
    Abstract
    Solar radiation received and absorbed by four domed roofs was estimated and compared with that of a flat roof. The domed roofs all had the same base areas, and equal to that of the flat roof. One of the roofs considered was the dome of the St. Peter's Church in Rome. Compared with the other roofs considered, this dome had a higher aspect ratio. It was found that all domed roofs received more solar radiation than the flat roof. Considering glazed tiles to cover a selected dome in Iran and the dome of the St. Peter's Church, it was found that the solar radiation absorbed by these roofs is reduced appreciably. In the case of the dome of St. Peter's Church, the amount of radiation absorbed was... 

    Reliable nonlinear hybrid simulation using modified operator splitting technique

    , Article Structural Control and Health Monitoring ; Volume 26, Issue 1 , 2019 ; 15452255 (ISSN) Zakersalehi, M ; Tasnimi, A. A ; Ahmadizadeh, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2019
    Abstract
    One of the main challenges of hybrid simulation is developing integration methods that not only provide accurate and stable results but also are compatible with the hybrid simulation circumstances. This paper presents a novel enhanced integration technique for hybrid simulation termed “modified operator splitting” (MOS) method. The main aim of the MOS technique is to improve the precision of the operator splitting (OS) method by reducing the corrector step length, where initial stiffness is utilized instead of actual stiffness. For this purpose, a new algorithm is proposed, which makes a more precise estimation of the predictor displacement; thus minimizes the effect of the corrective... 

    Reliable nonlinear hybrid simulation using modified operator splitting technique

    , Article Structural Control and Health Monitoring ; Volume 26, Issue 1 , 2019 ; 15452255 (ISSN) Zakersalehi, M ; Tasnimi, A. A ; Ahmadizadeh, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2019
    Abstract
    One of the main challenges of hybrid simulation is developing integration methods that not only provide accurate and stable results but also are compatible with the hybrid simulation circumstances. This paper presents a novel enhanced integration technique for hybrid simulation termed “modified operator splitting” (MOS) method. The main aim of the MOS technique is to improve the precision of the operator splitting (OS) method by reducing the corrector step length, where initial stiffness is utilized instead of actual stiffness. For this purpose, a new algorithm is proposed, which makes a more precise estimation of the predictor displacement; thus minimizes the effect of the corrective... 

    Numerical Simulation and Modeling of Thermosyphon Using PIV Method

    , M.Sc. Thesis Sharif University of Technology Bastankhah, Majid (Author) ; Saeedi, Mohammad Hassan (Supervisor)
    Abstract
    Heat pipe is a device with several applications in various industries such as electronics cooling, nuclear and renewable technologies. This apparatus transfers heat from a hot source to a cold one. Thermosyphon is a special type of heat pipe that transmits heat using gravitational forces. Although scholars have performed many experiments on thermosyphon, mostly they were about the thermal characteristics of thermosyphon and rarely the hydraulic specifications of thermosyphon have been investigated. But it is clear that these two specifications (thermal, hydraulic) relate to each other closely and detailed study about their interaction may bring out better results. In this thesis, initially a... 

    Continuous neural network with windowed Hebbian learning

    , Article Biological Cybernetics ; Volume 109, Issue 3 , June , 2015 , Pages 321-332 ; 03401200 (ISSN) Fotouhi, M ; Heidari, M ; Sharifitabar, M ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    We introduce an extension of the classical neural field equation where the dynamics of the synaptic kernel satisfies the standard Hebbian type of learning (synaptic plasticity). Here, a continuous network in which changes in the weight kernel occurs in a specified time window is considered. A novelty of this model is that it admits synaptic weight decrease as well as the usual weight increase resulting from correlated activity. The resulting equation leads to a delay-type rate model for which the existence and stability of solutions such as the rest state, bumps, and traveling fronts are investigated. Some relations between the length of the time window and the bump width is derived. In... 

    New point-to-face contact algorithm for 3-D contact problems using the augmented Lagrangian method in 3-D DDA

    , Article Geomechanics and Geoengineering ; Volume 4, Issue 3 , 2009 , Pages 221-236 ; 17486025 (ISSN) Beyabanaki, S. A. R ; Mikola, R. G ; Biabanaki, S. O.R ; Mohammadi, S ; Sharif University of Technology
    Abstract
    This paper presents a new point-to-face contact algorithm for contacts between two polyhedrons with planar boundaries. A new discrete numerical method called three-dimensional discontinuous deformation analysis (3-D DDA) is used and formulations of normal contact submatrices based on the proposed algorithm are derived. The presented algorithm is a simple and efficient method and it can be easily coded into a computer program. This approach does not need to use an iterative algorithm in each time step to obtain the contact plane, unlike the ‘Common-Plane’ method applied in the existing 3-D DDA. In the present 3-D DDA method, block contact constraints are enforced using the penalty method.... 

    A parametric study on the effects of surface explosions on buried high pressure gas pipelines

    , Article Engineering Solid Mechanics ; Volume 5, Issue 4 , 2017 , Pages 225-244 ; 22918744 (ISSN) Adibi, O ; Azadi, A ; Farhanieh, B ; Afshin, H ; Sharif University of Technology
    Growing Science  2017
    Abstract
    Underground gas pipelines are one of the vital parts of each country which surface blasts can break down such pipelines, making destructive explosions and threatening the safety of neighborhood structures and people. In this paper, to enhance the safety of these lines, response of a buried 56-inch diameter high pressure natural gas pipeline to a surface blast was numerically investigated. Besides, the effects of: i) explosive mass, ii) pipeline thickness, iii) burial depth and iv) concrete protective layer on pipeline deformation were parametrically studied. To simulate the problem according to actual explosion events, geometries were modeled in real scales, pipeline properties were... 

    Evaluation of heat conduction in a laser irradiated tooth with the three-phase-lag bio-heat transfer model

    , Article Thermal Science and Engineering Progress ; Volume 7 , 2018 , Pages 203-212 ; 24519049 (ISSN) Falahatkar, S ; Nouri-Borujerdi, A ; Mohammadzadeh, A ; Najafi, M ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this study, a dental short pulse laser with a Gaussian beam profile was applied normally to the top surface of a mineral organ i.e. the human tooth for a root canal therapy. A numerical method of finite difference is adopted to solve the time-dependent heat transfer equation. The real boundary conditions of thermal insulation on the sharp segment of the root canal and periodic heat flux on the top boundary of the tooth were applied. The comparison of a three-phase-lag (TPL) bio-heat transfer model with other heat transfer studies has shown that this new bio-heat model (TPL) could accurately predict the thermal behaviour of a non-homogeneous structure such as the human tooth. It was... 

    Stress behaviour across human tooth by temperature gradient resulting of laser irradiation

    , Article Journal of Mechanical Engineering and Sciences ; Volume 14, Issue 1 , 2020 , Pages 6218-6228 Falahatkar, S ; Nouri Borujerdi, A ; Najafi, M ; Sharif University of Technology
    Universiti Malaysia Pahang  2020
    Abstract
    The authors report the simulation of temperature distribution and thermally induced stress in the premolar tooth under ND-YAG pulsed laser beam. The Three-Phase-Lag (TPL) non-Fourier model is proposed to describe the heat conduction in the human tooth with nonhomogeneous inner structures. A premolar tooth comprising enamel, dentin, and pulp with real shapes and thicknesses are considered and a numerical method of finite difference was adopted to solve the time-dependent TPL bio-heat transfer, strain and stress equations. The surface heating scheme is applied for simulation of laser therapy. The aim of this laser therapy is that the temperature of pulp reaches to 47oC. The results are... 

    Asymmetric wave propagation in a transversely isotropic half-space in displacement potentials

    , Article International Journal of Engineering Science ; Volume 46, Issue 7 , 2008 , Pages 690-710 ; 00207225 (ISSN) Khojasteh, A ; Rahimian, M ; Eskandari, M ; Pak, R. Y. S ; Sharif University of Technology
    2008
    Abstract
    With the aid of a complete representation using two displacement potentials, an efficient and accurate analytical derivation of the fundamental Green's functions for a transversely isotropic elastic half-space subjected to an arbitrary, time-harmonic, finite, buried source is presented. The formulation includes a complete set of transformed stress-potential and displacement-potential relations that can be useful in a variety of elastodynamic as well as elastostatic problems. The present solutions are analytically in exact agreement with the existing solutions for a half-space with isotropic material properties. For the numerical evaluation of the inversion integrals, a quadrature scheme... 

    Some basis-free expressions for stresses conjugate to Hill's strains through solving the tensor equation AX + XA = C

    , Article International Journal of Solids and Structures ; Volume 45, Issue 11-12 , 2008 , Pages 3584-3595 ; 00207683 (ISSN) Asghari, M ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    2008
    Abstract
    In the present paper, some new and compact basis-free expressions are derived for representing stresses conjugate to the Lagrangean Hill's strain measures. Solving a tensor equation in the form of AX + XA = C, a rather simple general expression is obtained for the conjugate stresses in the case of distinct principal stretches. The result decomposes the conjugate stresses additively into two parts, such that one part is coaxial with the right stretch tensor while another part is orthogonal to it. An expression for the case of double-coalescent principal stretches is also obtained. As an example of the general results, simple expressions are obtained for the stress conjugate to the logarithmic... 

    Material removal simulation of aluminum compound tubes with incorporating real unloading behavior

    , Article 2007 ASME Pressure Vessels and Piping Conference, PVP 2007, San Antonio, TX, 22 July 2007 through 26 July 2007 ; Volume 3 , 2008 , Pages 195-201 ; 0277027X (ISSN); 0791842819 (ISBN); 9780791842812 (ISBN) Mohammadi, M ; Farrahi, G. H ; Hoseini, S. H ; Sharif University of Technology
    2008
    Abstract
    Real loading- unloading behavior of an A5083 aluminum alloy was recorded experimentally. This real behavior was incorporated in the variable material properties (VMP) numerical algorithm to predict residual stresses resulted from autofrettage and shrink fit in two kinds of autofrettage compound tubes. Using an analytical method, residual stresses induced by bore material removal via machining were calculated. Using developed VMP code and isotropic hardening rule in both autofrettage compound tubes, residual stresses resulted from shrink fit and autofrettage processes and via post machining, were estimated. Machining process simulation was performed for 10 mm bore material removal. ANSYS... 

    A study on the cross-sectional profile of flat rolled wire

    , Article Journal of Materials Processing Technology ; Volume 200, Issue 1-3 , 2008 , Pages 325-330 ; 09240136 (ISSN) Kazeminezhad, M ; Karimi Taheri, A ; Kiet Tieu, A ; Sharif University of Technology
    2008
    Abstract
    In this research the cross-sectional profile of flattened wires after flat rolling are calculated for different reductions. The empirical formulation, analytical formulation and numerical method have been used to predict the cross-sectional profile. Also, the theoretical results are compared with the experimental data. It has been found that the numerical method is able to predict the lateral spread, the width of contact area, and the curvature radius in all ranges of the reduction in height with a good accuracy, while the other methods exhibit a reasonable accuracy only for a limited range of height reduction. All results of the methods show that with increasing the reduction in height, the... 

    A numerical method for solving nth-order boundary-value problems

    , Article Applied Mathematics and Computation ; Volume 196, Issue 2 , 2008 , Pages 889-897 ; 00963003 (ISSN) Hesaaraki, M ; Jalilian, Y ; Sharif University of Technology
    2008
    Abstract
    In this paper, we consider the solution of an nth order boundary-value problem. We solve this problem by changing the problem to a system of two integral-differential equations and using the variational iteration method. By giving three examples and comparing with the other methods, the efficiency of the method will be shown. © 2007 Elsevier Inc. All rights reserved  

    Optimal point removal in closed-2PM labeling

    , Article Information Processing Letters ; Volume 105, Issue 3 , 2008 , Pages 108-113 ; 00200190 (ISSN) Rostamabadi, F ; Sadeghi, I ; Ghodsi, M ; Khosravi, R ; Sharif University of Technology
    2008
    Abstract
    An optimal labeling where labels are disjoint axis-parallel equal-size squares is called 2PM labeling if the labels have maximum length each attached to its corresponding point on the middle of one of its horizontal edges. In a closed-2PM labeling, no two edges of labels containing points should intersect. Removing one point and its label, makes free room for its adjacent labels and may cause a global label expansion. In this paper, we construct several data structures in the preprocessing stage, so that any point removal event is handled efficiently. We present an algorithm which decides in O (lg n) amortized time whether a label removal leads to label expansion in which case a new optimal... 

    Effect of EPB tunnelling on surface settlement

    , Article Annual Conference of the Canadian Society for Civil Engineering 2007: Where the Road Ends, Ingenuity Begins, Yellowknife, NT, 6 June 2007 through 9 June 2007 ; Volume 2 , 2007 , Pages 1003-1012 Sadaghiani, M. H ; Aliari, Y ; Sharif University of Technology
    2007
    Abstract
    Settlement is one of the most important effects of tunnelling. In order to minimize this effect, it is necessary to arrange for circumstances to keep the strain and stress state of undisturbed soil within a tight limit. To achieve this, it is common nowadays to use closed face pressurized shields such as EPB TBMs. In this type of shield, face stability and ground settlement control is maintained by pressurizing the tunnel face with adjustment of cutter head thrust and muck removal discharge. In this paper, numerical modeling of excavation of twin tunnels in Tabriz subway is addressed with respect to the effect of EPB tunnelling in settlement control. Settlement and lining thrust are...