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Total 167 records

    Dynamic response of thin plates on time-varying elastic point supports

    , Article Structural Engineering and Mechanics ; Volume 62, Issue 4 , 2017 , Pages 431-441 ; 12254568 (ISSN) Foyouzat, M. A ; Estekanchia, H. E ; Sharif University of Technology
    Techno Press  2017
    Abstract
    In this article, an analytical-numerical approach is presented in order to determine the dynamic response of thin plates resting on multiple elastic point supports with time-varying stiffness. The proposed method is essentially based on transforming a familiar governing partial differential equation into a new solvable system of linear ordinary differential equations. When dealing with time-invariant stiffness, the solution of this system of equations leads to a symmetric matrix, whose eigenvalues determine the natural frequencies of the point-supported plate. Moreover, this method proves to be applicable for any plate configuration with any type of boundary condition. The results, where... 

    Stability of linear dynamic systems over the packet erasure channel: A co-design approach

    , Article International Journal of Control ; Volume 88, Issue 12 , May , 2015 , Pages 2488-2498 ; 00207179 (ISSN) Farhadi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    This paper is concerned with the stability of linear time-invariant dynamic systems over the packet erasure channel subject to minimum bit rate constraint when an encoder and a decoder are unaware of the control signal. This assumption results in co-designing the encoder, decoder and controller. The encoder, decoder, controller and conditions relating transmission rate to packet erasure probability and eigenvalues of the system matrix A are presented for almost sure asymptotic stability of linear time-invariant dynamic systems over the packet erasure channel with feedback acknowledgment. When the eigenvalues of the system matrix A are real valued, it is shown that the obtained condition for... 

    Linear spatial stability analysis of particle-laden stratified shear layers

    , Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 41, Issue 6 , 2019 ; 16785878 (ISSN) Khavasi, E ; Firoozabadi, B ; Sharif University of Technology
    Springer Verlag  2019
    Abstract
    Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes. These instabilities have an important role in the mixing process. In this work, the linear stability analysis in spatial framework is used to study the stability characteristics of a particle-laden stratified two-layer flow. The effect of parameters such as velocity-to-density thickness ratio, bed slope, viscosity as well as particle size on the stability is considered. A simple iterative method applying the pseudospectral collocation method that employed Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, the flow becomes stable for Richardson... 

    Bridged single-walled carbon nanotube-based atomic-scale mass sensors

    , Article Applied Physics A: Materials Science and Processing ; Volume 122, Issue 8 , Volume 122, Issue 8 , 2016 ; 09478396 (ISSN) Ali Akbari, H. R ; Shaat, M ; Abdelkefi, A ; Sharif University of Technology
    Springer Verlag 
    Abstract
    The potentials of carbon nanotubes (CNTs) as mechanical resonators for atomic-scale mass sensing are presented. To this aim, a nonlocal continuum-based model is proposed to study the dynamic behavior of bridged single-walled carbon nanotube-based mass nanosensors. The carbon nanotube (CNT) is considered as an elastic Euler–Bernoulli beam with von Kármán type geometric nonlinearity. Eringen’s nonlocal elastic field theory is utilized to model the interatomic long-range interactions within the structure of the CNT. This developed model accounts for the arbitrary position of the deposited atomic-mass. The natural frequencies and associated mode shapes are determined based on an eigenvalue... 

    Multi-objective robust design optimization (MORDO) of an aeroelastic high-aspect-ratio wing

    , Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 42, Issue 11 , 2020 Elyasi, M ; Roudbari, A ; Hajipourzadeh, P ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2020
    Abstract
    In this paper, a new approach for multi-objective robust optimization of flutter velocity and maximum displacement of the wing tip are investigated. The wing is under the influence of bending–torsion coupling and its design variables have different levels of uncertainty. In designing and optimizing wings with a high aspect ratio, the optimization process can be done in such a way to increase the flutter velocity, but this can increase the amplitude of the wing tip displacement to a point that leads to the wings damage and structural failure. Therefore, single-objective design optimization may lead to infeasible designs. Thus, for multi-objective optimization, modeling is based on the... 

    Mimicking the Hadamard discrete-time quantum walk with a time-independent Hamiltonian

    , Article Quantum Information Processing ; Volume 18, Issue 5 , 2019 ; 15700755 (ISSN) Khatibi Moqadam, J ; de Oliveira, M. C ; Sharif University of Technology
    Springer New York LLC  2019
    Abstract
    The discrete-time quantum walk dynamics can be generated by a time-dependent Hamiltonian, repeatedly switching between the coin and the shift generators. We change the model and consider the case where the Hamiltonian is time-independent, including both the coin and the shift terms in all times. The eigenvalues and the related Bloch vectors for the time-independent Hamiltonian are then compared with the corresponding quantities for the effective Hamiltonian generating the quantum walk dynamics. Restricted to the non-localized initial quantum walk states, we optimize the parameters in the time-independent Hamiltonian such that it generates a dynamics similar to the Hadamard quantum walk. We... 

    On the static and dynamic stability of thin beam conveying fluid

    , Article Meccanica ; Volume 54, Issue 11-12 , 2019 , Pages 1847-1868 ; 00256455 (ISSN) Askarian, A. R ; Abtahi, H ; Firouz Abadi, R. D ; Sharif University of Technology
    Springer Netherlands  2019
    Abstract
    In this paper, numerical investigation of the statical and dynamical stability of aligned and misaligned viscoelastic cantilevered beam is performed with a terminal nozzle in the presence of gravity in two cases: (1) effect of fluid velocity on the flutter boundary of beam conveying fluid and (2) effect of gravity on the buckling boundary of beam conveying fluid. The beam is assumed to have a large width-to-thickness ratio, so the out-of-plane bending rigidity is far higher than the in-plane bending and torsional rigidities. Gravity vector is considered in the vertical direction. Thus, deflection of the beam because of the gravity effect couples the in-plane bending and torsional equations.... 

    Free vibration of joined cylindrical–hemispherical FGM shells

    , Article Archive of Applied Mechanics ; Volume 90, Issue 10 , 2020 , Pages 2185-2199 Bagheri, H ; Kiani, Y ; Bagheri, N ; Eslami, M. R ; Sharif University of Technology
    Springer  2020
    Abstract
    Free vibration response of a joined shell system including cylindrical and spherical shells is analyzed in this research. It is assumed that the system of joined shell is made from a functionally graded material (FGM). Properties of the shells are assumed to be graded through the thickness. Both shells are unified in thickness. To capture the effects of through-the-thickness shear deformations and rotary inertias, first-order shear deformation theory of shells is used. The Donnell type of kinematic assumptions is adopted to establish the general equations of motion and the associated boundary and continuity conditions with the aid of Hamilton’s principle. The resulting system of equations is... 

    Vibrations and stability analysis of double current-carrying strips interacting with magnetic field

    , Article Acta Mechanica ; 2020 Hosseinian, A. R ; Firouz Abadi, R. D ; Sharif University of Technology
    Springer  2020
    Abstract
    Interactive vibrations and buckling of double current-carrying strips (DCCS) are investigated in this study. Considering the rotational and transverse deformation of the strip, four coupled equations of motion are obtained using Hamilton’s principle. Using the Galerkin method, mass and stiffness matrices are extracted and the stability of the system is determined by solving the eigenvalue problem. Effects of pretension and elevated temperature on the stability of DCCS are studied for three types of materials and various arrangements. Finally, the effect of horizontal or vertical distance between strips on the critical current value is investigated. According to the results, the effects of... 

    Modal analysis of the dynamic response of Timoshenko beam under moving mass

    , Article Scientia Iranica ; Volume 22, Issue 2 , 2015 , Pages 331-344 ; 10263098 (ISSN) Roshandel, D ; Mofid, M ; Ghannadiasl, A ; Sharif University of Technology
    Sharif University of Technology  2015
    Abstract
    In this study, the dynamic response of a Timoshenko beam under moving mass is investigated. To this end, vectorial form orthogonality property of the Timoshenko beam free vibration modes is applied to the EEM (Eigenfunction Expansion Method). The implication of the vectorial form series and an appropriate inner product of mode shapes in combination are focused for a beam with arbitrary boundary conditions. Consequently, significant simplifications and efficacy in the utilization of the EEM in eliminating the spatial domain is achieved. In order to comprise validation, the present study is compared with the DET (Discrete Element Technique) and the RKPM (Reproducing Kernel Particle Method)  

    First order perturbation solution for axial vibration of tension leg platforms

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 414-423 ; 10263098 (ISSN) Golafshani, A. A ; Tabeshpour, M. R ; Seif, M. S ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    The dynamic response of the leg (tether) of a Tension Leg Platform (TLP), subjected to axial load at the top of the leg, is presented. The structural model is very simple, but several complicated factors, such as foundation effect, buoyancy and simulated ocean wave load, are considered. As an application, the effect of added mass fluctuation on the dynamic response of the leg subjected to such a load is presented. This effect is important in the fatigue life study of tethers. A first order perturbation method is used, in order to formulate and solve the problem. The differential equation is solved by means of non-harmonic Fourier expansion, in terms of eigenfunctions obtained from a... 

    Intrinsic expressions for arbitrary stress tensors conjugate to general strain tensors

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 486-493 ; 10263098 (ISSN) Sohrabpour, S ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of... 

    A methodology for analyzing the transient reliability of systems with identical components and identical repairmen

    , Article Scientia Iranica ; Volume 14, Issue 1 , 2007 , Pages 72-77 ; 10263098 (ISSN) Amiri, M ; Ghassemi Tari, F ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    In this paper, the Markov models, eigenvectors and eigenvalue concepts are used to propose a methodology for analyzing the transient reliability of a system with identical components and identical repairmen. The components of the systems under consideration can have two distinct configurations, namely; they can be arranged in series or in parallel. A third case is also considered, in which the system is up (good) if k-out-of-n components are good. For all three cases, a procedure is proposed for calculating the transient probability of the system availability and the duration of the system to reach the steady state. © Sharif University of Technology, February 2007  

    New basis functions for wave equation

    , Article Scientia Iranica ; Volume 23, Issue 6 , 2016 , Pages 2928-2933 ; 10263098 (ISSN) Khorasani, S ; Sharif University of Technology
    Sharif University of Technology 
    Abstract
    The Differential Transfer Matrix Method is extended to the complex plane, which allows dealing with singularities at turning points. The results for real-valued systems are simplified and a pair of basis functions are found. These bases are a bit less accurate than WKB solutions but much easier to work with because of their algebraic form. Furthermore, these bases exactly satisfy the initial conditions and may go over the turning points without the divergent behavior of WKB solutions. The findings of this paper allow explicit evaluation of eigenvalues of confined modes with high precision, as demonstrated by few examples  

    Dynamic response of a non-uniform Timoshenko beam, subjected to moving mass

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 229, Issue 14 , October , 2015 , Pages 2499-2513 ; 09544062 (ISSN) Roshandel, D ; Mofid, M ; Ghannadiasl, A ; Sharif University of Technology
    SAGE Publications Ltd  2015
    Abstract
    In this article, the dynamic response of a non-uniform Timoshenko beam acted upon by a moving mass is extensively investigated. To this end, the eigenfunction expansion method is adapted to the problem, employing the natural mode shapes of a uniform Timoshenko beam. Moreover, the orthonormal polynomial series expansion method is successfully applied to the coupled set of governing differential equations pertaining to the dynamic behavior of non-uniform Timoshenko beam actuated by a moving mass. Some numerical examples are solved in which the excellent agreement of the two presented methods is illustrated  

    Complex modal analysis and coupled electromechanical simulation of energy harvesting piezoelectric laminated beams

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; 2018 ; 09544062 (ISSN) Pasharavesh, A ; Ahmadian, M. T ; Zohoor, H ; Sharif University of Technology
    SAGE Publications Ltd  2018
    Abstract
    In this paper, coupled electromechanical behavior of a vibrational energy harvesting system composed of a unimorph piezoelectric laminated beam with a large attached tip mass is investigated. To achieve this goal, first the electromechanically coupled partial differential equations governing the lateral displacement and output voltage of the harvester are extracted through exploiting the Hamilton’s principle. Considering vibration damping due to mechanical to electrical energy conversion, a complex modal analysis is performed to extract the complex eigenfrequencies and eigenfunctions of the system. Furthermore, an exact analytical solution is presented for the system response to the harmonic... 

    Complex modal analysis and coupled electromechanical simulation of energy harvesting piezoelectric laminated beams

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 233, Issue 7 , 2019 , Pages 2526-2537 ; 09544062 (ISSN) Pasharavesh, A ; Ahmadian, M. T ; Zohoor, H ; Sharif University of Technology
    SAGE Publications Ltd  2019
    Abstract
    In this paper, coupled electromechanical behavior of a vibrational energy harvesting system composed of a unimorph piezoelectric laminated beam with a large attached tip mass is investigated. To achieve this goal, first the electromechanically coupled partial differential equations governing the lateral displacement and output voltage of the harvester are extracted through exploiting the Hamilton’s principle. Considering vibration damping due to mechanical to electrical energy conversion, a complex modal analysis is performed to extract the complex eigenfrequencies and eigenfunctions of the system. Furthermore, an exact analytical solution is presented for the system response to the harmonic... 

    A screw dislocation near a damaged arbitrary inhomogeneity–matrix interface

    , Article International Journal of Damage Mechanics ; Volume 29, Issue 2 , 2020 , Pages 272-296 Kamali, M. T ; Shodja, H. M ; Masoudvaziri, N ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Abstract
    In the literature, the analytical solutions concerned with the interaction between screw dislocation and surfaces/interfaces have been mainly limited to simple geometries and perfect interfaces. The focus of the current work is to provide an approach based on a rigorous semi-analytical theory suitable for treatment of such surfaces/interfaces that concurrently have complex geometry and imperfect bonding. The proposed approach captures the singularity of the elastic fields exactly. A vast variety of the pertinent interaction problems such as dislocation near a multi-inhomogeneity with arbitrary geometry bonded imperfectly to a matrix, dislocation near the free boundaries of a finite elastic... 

    Free vibration analysis of a beam with an intermediate sliding connection joined by a mass-spring system

    , Article JVC/Journal of Vibration and Control ; Volume 22, Issue 4 , 2016 , Pages 955-964 ; 10775463 (ISSN) Hozhabrossadati, S. M ; Aftabi Sani, A ; Mofid, M ; Sharif University of Technology
    SAGE Publications Inc  2016
    Abstract
    In the free vibration analysis of beams, the inclusion of an intermediate sliding connection with an attached mass-spring system has not been yet treated. The present paper studies the free vibrations of uniform Euler-Bernoulli beams with an intermediate sliding connection and joined by a mass-spring system. Two different types of beams are considered. The Type 1 is attached with a single-degree-of-freedom mass-spring system and the Type 2 is attached with a two-degree-of-freedom mass-spring system. The ends of both beams are elastically restrained against rotation and translation. First, the eigenvalue problems including differential equations and boundary conditions are introduced. Then,... 

    Extraction of effective constitutive parameters of artificial media using Bloch modes

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 36, Issue 11 , 2019 , Pages 3226-3235 ; 07403224 (ISSN) Sheikh Ansari, A ; Rejaei, B ; Sharif University of Technology
    OSA - The Optical Society  2019
    Abstract
    The effective constitutive parameters of a three-dimensional periodic structure are calculated using its Bloch modes. These modes and their propagation constants are obtained from eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer of the structure. Effective bulk permittivity and permeability tensors of the medium are obtained when two of the Bloch modes are dominant, i.e., propagate without significant decay inside the medium. The effect of the strongly decaying Bloch modes, which are excited at the interface with a conventional medium, are included by means of surface impedance matrices. The results are in excellent agreement with full-wave electromagnetic...