Search for: eigenvalues-and-eigenfunctions
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    Buckling of the composite cracked cylindrical shells subjected to axial load

    , Article 2003 ASME International Mechanical Engineering Congress, Washington, DC, 15 November 2003 through 21 November 2003 ; Volume 470 , 2003 , Pages 87-93 ; 0277027X (ISSN) Vaziri, A ; Nayeb Hashemi, H ; Estekanchi, H. E ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2003
    Cylindrical shells constitute the main structural components in pressure vessels and pipelines. Cylindrical shells made of fiber-reinforced composites are now being considered in the design of many components due to their high specific strength and stiffness. Buckling is one of the main failure considerations, when designing the cylindrical shells. The buckling behavior of the composite cylindrical shells can severely be compromised by introducing defect in the structure, due to high stress field generated around these defects. Defects could be generated during service due to cyclic loading or during manufacturing. A reliable operation of these structures require to understand the effects of... 

    Unified basis-free relation between two stress tensors conjugate to arbitrary Hill's strain measures

    , Article ASME PVP2006/ICPVT-11 Conference, Vancouver, BC, 23 July 2006 through 27 July 2006 ; Volume 2006 , 2006 ; 0277027X (ISSN); 0791837823 (ISBN); 9780791837825 (ISBN) Asghari, M ; Naghdabadi, R ; Sharif University of Technology
    American Society of Mechanical Engineers(ASME)  2006
    The concept of energy conjugacy for stress and strain measures states that a stress tensor T is conjugate to a strain measure E if T: Ė provides the rate of change of the internal energy per unit reference volume of the body in an adiabatic process. The applications of the conjugate stress and strain measures are in the development of the basic relations in nonlinear analysis of solids. In this paper using eigenprojection method, unified explicit basis-free relation between two arbitrary stress tensors T(f) and T (g), respectively conjugate to two measures of Hill's strains is determined. The result is valid for arbitrary dimension of the Euclidean inner product space and for all cases of... 

    Optimal pinning controllability of complex networks: Dependence on network structure

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 1 , January , 2015 ; 15393755 (ISSN) Jalili, M ; Askari Sichani, O ; Yu, X ; Sharif University of Technology
    American Physical Society  2015
    Controlling networked structures has many applications in science and engineering. In this paper, we consider the problem of pinning control (pinning the dynamics into the reference state), and optimally placing the driver nodes, i.e., the nodes to which the control signal is fed. Considering the local controllability concept, a metric based on the eigenvalues of the Laplacian matrix is taken into account as a measure of controllability. We show that the proposed optimal placement strategy considerably outperforms heuristic methods including choosing hub nodes with high degree or betweenness centrality as drivers. We also study properties of optimal drivers in terms of various centrality... 

    Optimal exploitation of the resource in remote state preparation

    , Article Physical Review A ; Volume 102, Issue 1 , 15 July , 2020 Nikaeen, M ; Ramezani, M ; Bahrampour, A ; Sharif University of Technology
    American Physical Society  2020
    Transmission efficiency (TE) of remote state preparation (RSP) with a shared quantum state and one bit of classical communication is considered. Following Dakić et al. [Nat. Phys. 8, 666 (2012)10.1038/nphys2377], the encoding and decoding operators of the protocol are restricted to the physically relevant classes of projective measurements and unitary operators, respectively. It is shown that contrary to the previous arguments, the quadratic fidelity as well as the linear fidelity could be a valid figure of merit to quantify the TE of RSP. Then, the TE of the protocol in terms of both linear and quadratic fidelities is evaluated in a fully optimized scenario which includes the maximization... 

    Exact solutions for universal holonomic quantum gates

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 1 , 2004 , Pages 012320-1-012320-5 ; 10502947 (ISSN) Karimipour, V ; Majd, N ; Sharif University of Technology
    American Physical Society  2004
    Implementation of local quantum gate on specific qubits in an array of qubits by carrying a Hamiltonian around a closed loop is discussed. A family of isospectral Hamiltonians with the same spectrum of the projection operator on the main array is constructed by choice of a suitable curve. For every single qubit gate acting on the k-th qubit, a local operator Xk acts nontrivially on the ancilla and the qubit. Imbedding appropriate operators for a suitable set of qubit gates comprises of a universal set of quantum gates. In tensor product of the array one can enact holonomically any set of gates on any subset of qubits  

    Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique

    , Article Applied Physics Letters ; Volume 117, Issue 6 , 2020 Mohammadi, K ; Movahhedy, M. R ; Shishkovsky, I ; Hedayati, R ; Sharif University of Technology
    American Institute of Physics Inc  2020
    Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then... 

    A new reduced-order modeling approach based on fluid eigenmodes and boundary element method

    , Article 23rd AIAA Applied Aerodynamics Conference, Toronto, ON, 6 June 2005 through 9 June 2005 ; Volume 2 , 2005 , Pages 1245-1252 ; 10485953 (ISSN) Behbahani Nejad, M ; Nobari, A. S ; Shahverdi, H ; Haddadpour, H ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2005
    This paper presents a new reduced-order modeling approach based on boundary element method. In this approach the eigenvalue problem of the unsteady flows is defined based on the unknown wake singularities. By constructing this reduced-order model, the body quasi-static eigenmodes are removed from the eigensystem and it is possible to obtain satisfactory results without static correction technique when enough eigenmodes are used. In addition to the conventional method, Eigenanalysis and reduced-order modeling of unsteady flows over a NACA 0012 airfoil and a wing with NACA 0012 section are performed using this new ROM method. Numerical examples are presented that demonstrate the accuracy and... 

    Reduced-order modeling of unsteady flows without static correction requirement

    , Article Journal of Aircraft ; Volume 42, Issue 4 , 2005 , Pages 882-886 ; 00218669 (ISSN) Behbahani Nejad, M ; Haddadpour, H ; Esfahanian, V ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2005
    A new reduced-order modeling approach is presented. This approach is based on fluid eigenmodes and without using the static correction. The vortex lattice method is used to analyze unsteady flows over two-dimensional airfoils and three-dimensional wings. Eigenanalysis and reduced-order modeling are performed using a conventional method with and without the static correction technique. In addition to the conventional method, eigenanalysis and reduced-order modeling are also performed using the new proposed method, that is, without static correction requirement. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the proposed method. Based on the... 

    Bending-torsional stability analysis of aerodynamically covered pipes with inclined terminal nozzle and concurrent internal and external flows

    , Article Journal of Fluids and Structures ; Volume 94 , 2020 Askarian, A. R ; Rahmanian, M ; Haddadpour, H ; Dehghani Firouz Abadi, R ; Sharif University of Technology
    Academic Press  2020
    Stability analysis of a cantilevered pipe with an inclined terminal nozzle as well as simultaneous internal and external fluid flows is investigated in this study. The pipe is embedded in an aerodynamic cover with negligible mass and stiffness simply to streamline the external flow and avoid vortex induced vibrations. The structure of pipe is modeled as an Euler–Bernoulli beam and effects of internal fluid flow including flow-induced inertia, Coriolis and centrifugal forces and the follower force induced by the exhausting jet are taken into account. In addition, neglecting the compressibility effect and using the unsteady Wagner model, aerodynamic loading is determined as a distributed... 

    Investigation of thrust effect on the vibrational characteristics of flexible guided missiles

    , Article Journal of Sound and Vibration ; Volume 272, Issue 1-2 , 2004 , Pages 287-299 ; 0022460X (ISSN) Pourtakdoust, S. H ; Assadian, N ; Sharif University of Technology
    Academic Press  2004
    In this paper the effect of thrust on the bending behaviour of flexible missiles is investigated. For this purpose, the governing equations of motion of a flexible guided missile are derived following the Lagrangian approach. The missile is idealized as a non-uniform beam where the bending elastic deflections are modelled using the method of modal substitution. The vehicle (time varying) bending modeshapes and natural frequencies are determined by modelling variable mass and stiffness distributions with thrust and mass burning effects accounted for. To solve this problem the missile is divided into several segments of uniform stiffness, density and axial force distribution. This approach... 

    Robust regulation and tracking system design for multivariable control of the tape transport mechanism

    , Article Microsystem Technologies ; Vol. 18, Issue. 5 , 2012 , pp. 557-573 ; ISSN: 09467076 Moradi, H ; Bakhtiari-Nejad, F ; Alasty, A ; Sharif University of Technology
    Tape mechanisms must be able to transport the tape with a constant velocity for achieving high rate of data transfer. In this paper, a multivariable model of tape transport mechanism including the take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. To achieve desired performance,pole-placement approach based on general canonical control form (GCCF) is used. Instead of using expensive tension sensors, an observer is designed. A regulator system is developed for disturbance rejection; and a modified integral control is designed for perfect tracking of desired setpoints in tape speed and tensions. Since the real dynamic model associates... 

    Connectedness of users-items networks and recommender systems

    , Article Applied Mathematics and Computation ; Vol. 243 , 2014 , Pages 578-584 ; ISSN: 00963003 Gharibshah, J ; Jalili, M ; Sharif University of Technology
    Recommender systems have become an important issue in network science. Collaborative filtering and its variants are the most widely used approaches for building recommender systems, which have received great attention in both academia and industry. In this paper, we studied the relationship between recommender systems and connectivity of users-items bipartite network. This results in a novel recommendation algorithm. In our method recommended items are selected based on the eigenvector corresponding to the algebraic connectivity of the graph - the second smallest eigenvalue of the Laplacian matrix. Since recommending an item to a user equals to adding a new link to the users-items bipartite... 

    The effects of nonlinearities on the vibration of viscoelastic sandwich plates

    , Article International Journal of Non-Linear Mechanics ; Vol. 62 , 2014 , Pages 41-57 ; ISSN: 00207462 Mahmoudkhani, S ; Haddadpour, H ; Navazi, H. M ; Sharif University of Technology
    The nonlinear free and forced bending vibration of sandwich plates with incompressible viscoelastic core is investigated under the effects of different source of nonlinearities. For the core constrained between stiffer layers, the transverse shear strains, as well as the rotations are assumed to be moderate. The linear and quadratic displacement fields are also adopted for the in-plane and out-of-plane displacements of the core, respectively. The assumption of moderate transverse strains requires a nonlinear constitutive equation which is obtained from a single-integral nonlinear viscoelastic model using the assumed order of magnitudes for linear strains and rotations. The 5th-order method... 

    The multiplicity of Laplacian eigenvalue two in unicyclic graphs

    , Article Linear Algebra and Its Applications ; Vol. 445 , 2014 , pp. 18-28 Akbari, S ; Kiani, D ; Mirzakhah, M ; Sharif University of Technology
    Let G be a graph and L(G) be the Laplacian matrix of G. In this paper, we explicitly determine the multiplicity of Laplacian eigenvalue 2 for any unicyclic graph containing a perfect matching  

    Axial-torsional vibrations of rotating pretwisted thin walled composite beams

    , Article International Journal of Mechanical Sciences ; Vol. 80 , 2014 , pp. 93-101 ; ISSN: 00207403 Sina, S. A ; Haddadpour, H ; Sharif University of Technology
    Axial-torsional vibrations of rotating pretwisted thin-walled composite box beams exhibiting primary and secondary warping are investigated. Considering the nonlinear strain-displacement relations, the coupled nonlinear axial-torsional equations of motion are derived using Hamilton's principle. Ignoring the axial inertia term leads to differential equation of motion in terms of elastic torsion in the case of axially immovable beams. Centrifugal load in the presence of material anisotropy and pretwist angle leads to an induced static torque. The nonlinear equation should be linearized about the corresponding equilibrium state to obtain the linear differential equation of motion. Extended... 

    Linear analysis of the stability of particle-laden stratified shear layers

    , Article Canadian Journal of Physics ; Vol. 92, issue. 2 , 2014 , pp. 103-115 ; ISSN: 00084204 Khavasi, E ; Firoozabadi, B ; Afshin, H
    Hydrodynamic instabilities at the interface of stratified shear layers could occur in various modes and have an important role in the mixing process. In this work, the linear stability analysis in the temporal framework is used to study the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The effect of parameters, such as bed slope, viscosity, and particle size, on the stability is also considered. The pseudospectral collocation method employing Chebyshev polynomials is used to solve two coupled eigenvalue equations. Based on the results, there are some differences in the... 

    Inverse vibration problem for un-damped 3-dimensional multi-story shear building models

    , Article Journal of Sound and Vibration ; Volume 333, Issue 1 , 6 January , 2014 , Pages 99-113 ; ISSN: 0022460X Dolatshahi, K. M ; Rofooei, F. R ; Sharif University of Technology
    Various researchers have contributed to the identification of the mass and stiffness matrices of two dimensional (2-D) shear building structural models for a given set of vibratory frequencies. The suggested methods are based on the specific characteristics of the Jacobi matrices, i.e., symmetric, tri-diagonal and semi-positive definite matrices. However, in case of three dimensional (3-D) structural models, those methods are no longer applicable, since their stiffness matrices are not tri-diagonal. In this paper the inverse problem for a special class of vibratory structural systems, i.e., 3-D shear building models, is investigated. A practical algorithm is proposed for solving the inverse... 

    Collective dynamics of interacting particles in unsteady flows

    , Article SIAM Journal on Applied Dynamical Systems ; Vol. 13, Issue. 1 , 2014 , pp. 194-209 ; ISSN: 15360040 Abedi, M ; Jalali, M. A ; Sharif University of Technology
    We use the Fokker-Planck equation and its moment equations to study the collective behavior of interacting particles in unsteady one-dimensional flows. Particles interact according to a longrange attractive and a short-range repulsive potential field known as Morse potential. We assume Stokesian drag force between particles and their carrier fluid and find analytic single-peaked traveling solutions for the spatial density of particles in the catastrophic phase. In steady flow conditions the streaming velocity of particles is identical to their carrier fluid, but we show that particle streaming is asynchronous with an unsteady carrier fluid. Using linear perturbation analysis, the stability... 

    Re-interpreting simultaneous buckling modes of axially compressed isotropic conical shells

    , Article Thin-Walled Structures ; Vol. 84 , November , 2014 , pp. 360-368 ; ISSN: 02638231 Shakouri, M ; Spagnoli, A ; Kouchakzadeh, M. A ; Sharif University of Technology
    Elastic stability of shell structures under certain loading conditions is characterized by a dramatically unstable postbuckling behavior. The presence of simultaneous 'competing' buckling modes (corresponding to the same critical buckling load) is understood to be largely responsible for such behavior. In this paper, within the framework of linear bifurcation eigenvalue analysis and Donnell shallow shell theory, the presence of simultaneous buckling modes in axially compressed isotropic cones is determined using the semi-analytical method of Galerkin. The results are presented in the plane of the dimensionless reciprocal meridional and circumferential buckling half wavelengths, and are... 

    Thickness optimization of polyurethane floor insulation based on analysis of the heat transfer in a multi-layer

    , Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 3, issue , 2014 Moosavi, A ; Saidi, M. H ; Reshadi, M ; Sharif University of Technology
    During the year, due to weather conditions, the temperature fluctuations at surface level cause problems in underground pipes as a result of freezing water. One of the best prevention strategies is the use of polyurethane floor insulation for keeping the temperature of clay above zero degrees Celsius. In this study to calculate the minimum thickness of polyurethane insulation layer, the differential equation of energy is solved based on principle of separation of variables using imaginary eigenvalues for consistency with the temperature distribution in multi-layer consist of asphalt, gravel and polyurethane with finite thickness and clay as a semiinfinite medium with periodic thermal...