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    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.... 

    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... 

    Tight bound on the stability of control systems over parallel gaussian channels using a new joint source channel coding

    , Article 2019 Iran Workshop on Communication and Information Theory, IWCIT 2019, 24 April 2019 through 25 April 2019 ; 2019 ; 9781728105840 (ISBN) Sanjaroon, V ; Motahari, A. S ; Farhadi, A ; Khalaj, B. H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    In this paper, we address the stability problem of a noiseless linear time invariant control system over parallel Gaussian channels with feedback. It is shown that the eigenvalues-rate condition which has been proved as a necessary condition, is also sufficient for stability over parallel Gaussian channels. In fact, it is proved that for stabilizing a control system over the parallel Gaussian channels, it suffices that the Shannon channel capacity obtained by the water filling technique is greater than the sum of the logarithm of the unstable eigenvalues magnitude. In order to prove this sufficient condition, we propose a new nonlinear joint source channel coding for parallel Gaussian... 

    Estimation and stability over AWGN channel in the presence of fading, noisy feedback channel and different sample rates

    , Article Systems and Control Letters ; Volume 123 , 2019 , Pages 75-84 ; 01676911 (ISSN) ; https://www.sciencedirect.com/science/article/abs/pii/S0167691118301993 Sanjaroon, V ; Farhadi, A ; Khalaj, B. H ; Motahari, A. S ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    This paper is concerned with estimation and stability of control systems over communication links subject to limited capacity, power constraint, fading, noisy feedback, and different transmission rate rather than system sampling rate. A key issue addressed in this paper is that in the presence of noisy feedback associated with channel, which models transmission of finite number of bits over such links as is the case in most practical scenarios, the well-known eigenvalues rate condition is still a tight bound for stability. Based on an information theoretic analysis, necessary conditions are derived for stability of discrete-time linear control systems via the distant controller in the mean... 

    Magneto-mechanical stability of axially functionally graded supported nanotubes

    , Article Materials Research Express ; Volume 6, Issue 12 , 2019 ; 20531591 (ISSN) Ebrahimi Mamaghani, A ; Mirtalebi, H ; Ahmadian, M. T ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Abstract
    In this paper, size-dependent vibration analysis of axially functionally graded (AFG) supported nanotubes conveying nanoflow under longitudinal magnetic fields are performed, aiming at performance improvement of fluid-interaction nanosystems. Either the density or the elastic modulus of the AFG nanotube varies linearly or exponentially along the axial direction. Based on the nonlocal continuum theory, the higher-order dynamical equation of motion of the system is derived considering no-slip boundary condition. Galerkin discretization technique and eigenvalue analysis are implemented to solve the modeled equation. The validity of the simplified model is justified by comparing the results with... 

    Magneto-mechanical stability of axially functionally graded supported nanotubes

    , Article Materials Research Express ; Volume 6, Issue 12 , 2019 ; 20531591 (ISSN) Ebrahimi Mamaghani, A ; Mirtalebi, H ; Ahmadian, M. T ; Sharif University of Technology
    Institute of Physics Publishing  2019
    Abstract
    In this paper, size-dependent vibration analysis of axially functionally graded (AFG) supported nanotubes conveying nanoflow under longitudinal magnetic fields are performed, aiming at performance improvement of fluid-interaction nanosystems. Either the density or the elastic modulus of the AFG nanotube varies linearly or exponentially along the axial direction. Based on the nonlocal continuum theory, the higher-order dynamical equation of motion of the system is derived considering no-slip boundary condition. Galerkin discretization technique and eigenvalue analysis are implemented to solve the modeled equation. The validity of the simplified model is justified by comparing the results with... 

    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
    Abstract
    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... 

    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... 

    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... 

    An adaptive sampling technique to correct large passivity violations

    , Article 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, Sydney, NSW, 14 December 2008 through 17 December 2008 ; 2008 ; 9781424441624 (ISBN) Porkar, B ; Vakilian, M ; Shahrtash, M ; Sharif University of Technology
    2008
    Abstract
    Rational functions for approximation of the admittance matrix elements of a linear power system/component are used to increase the computational efficiency for the analysis of electromagnetic transients. The challenge in this regard is passivity enforcement of the resultant model to guarantee numerical stability of the analyses. The main cause of passivity violation of the equivalent model of a passive system/ component, in a specific frequency region, is the selection of unsuitable and/or insufficient number of frequency samples for fitting. The more severe the passivity violations are, the more effort is required to enforce passivity. This paper presents an adaptive sampling technique for... 

    Extracting single trial visual evoked potentials using iterative generalized eigen value decomposition

    , Article Proceedings of the 8th IEEE International Symposium on Signal Processing and Information Technology, ISSPIT 2008, 16 December 2008 through 19 December 2008, Sarajevo ; 2008 , Pages 233-237 ; 9781424435555 (ISBN) Hajipour, S ; Shamsollahi, M. B ; Mamaghanian, H ; Abootalebi, V ; IEEE Signal Processing Society and IEEE Computer Society ; Sharif University of Technology
    2008
    Abstract
    The activity generated in the brain in response to external stimulations which is named the evoked potential (EP) is typically buried in the background EEG. Because of the low signal to noise ratio ofEPs, it is difficult to record single trial evoked potentials. The traditional technique which is based on ensemble averaging destroys the dynamic information of single trials. In this paper, a new method has been proposed based on generalized eigen value decomposition to extract single trial EPs from single channel EEG recordings. The extraction of the N75-P100-N135 complex in simulated and actual visual evoked potentials is mainly taken under consideration. To illustrate the effectiveness of... 

    Two-dimensional model of melt flows and interface instability in aluminum reduction cells

    , Article Light Metals 2008, New Orleans, LA, 9 March 2008 through 13 March 2008 ; 2008 , Pages 443-448 ; 01470809 (ISSN); 9780873397100 (ISBN) Kadkhodabeigi, M ; Sharif University of Technology
    2008
    Abstract
    We derive a new non-linear two dimensional model for melt flows and interface instability in aluminum reduction cells. This model is based on non-linear de St. Venant shallow water equations and contains the main features of an aluminum reduction cell. In this model we consider linear friction terms but in a new way that has not been considered in previous works. Our results are in good agreement with the results of simulation of viscous flow. This model is applicable both in determination of melt flows in molten aluminum and cryolite layers and also in finding the extreme limit for stability of interfacial waves in an aluminum reduction cell  

    Wireless multicasting using network coding

    , Article 2006 1st Workshop on Operator-Assisted (Wireless-Mesh) Community Networks, OpComm 2006, Berlin, 18 September 2006 through 19 September 2006 ; 2006 ; 1424406927 (ISBN); 9781424406920 (ISBN) Eslami, A ; Khalaj, B. H ; Sharif University of Technology
    2006
    Abstract
    In this paper, we consider the network coding in networks with broadcast channels (called hypernetworks) as the first step for applying network coding to wireless networks. We first prove a Max-Flow Min-Cut theorem for such networks. While we propose an algorithm to achieve this bound, we will introduce new definitions and provide sufficient tools to extend many of the theorems stated for flows in wireline networks to the case of hypernetworks. As an example, we will extend the Max-Flow Min-Cut condition for feasibility of the point-to-point connection in wireline networks to the case of hypernetworks. Then, we will extend the algebraic approach of Koetter and Medard in [3] to the... 

    Validation of a new MCNP-ORIGEN linkage program for burnup analysis

    , Article Progress in Nuclear Energy ; Volume 63 , 2013 , Pages 27-33 ; 01491970 (ISSN) Kheradmand Saadi, M ; Abbaspour, A ; Pazirandeh, A ; Sharif University of Technology
    2013
    Abstract
    The analysis of core composition changes is complicated by the fact that the time and spatial variation in isotopic composition depend on the neutron flux distribution and vice versa. Fortunately, changes in core composition occur relatively slowly and hence the burnup analysis can be performed by dividing the burnup period into some burnup spans and assuming that the averaged flux and cross sections are constant during each step. The burnup span sensitivity analysis attempts to find that how much the burnup spans could be increased without any significant deviation in results. This goal has been achieved by developing a new MCNP-ORIGEN linkage program named as MOBC (MCNP-ORIGEN Burnup... 

    Estimation and stability over AWGN channel in the presence of fading, noisy feedback channel and different sample rates

    , Article Systems and Control Letters ; Volume 123 , 2019 , Pages 75-84 ; 01676911 (ISSN) Sanjaroon, V ; Farhadi, A ; Khalaj, B. H ; Seyed Motahari, A ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    This paper is concerned with estimation and stability of control systems over communication links subject to limited capacity, power constraint, fading, noisy feedback, and different transmission rate rather than system sampling rate. A key issue addressed in this paper is that in the presence of noisy feedback associated with channel, which models transmission of finite number of bits over such links as is the case in most practical scenarios, the well-known eigenvalues rate condition is still a tight bound for stability. Based on an information theoretic analysis, necessary conditions are derived for stability of discrete-time linear control systems via the distant controller in the mean... 

    Nonlinear aeroelastic response of slender wings based on Wagner function

    , Article Thin-Walled Structures ; Volume 46, Issue 11 , 2008 , Pages 1192-1203 ; 02638231 (ISSN) Shams, Sh ; Sadr Lahidjani, M. H ; Haddadpour, H ; Sharif University of Technology
    2008
    Abstract
    This paper presents a method for nonlinear aeroelastic analysis of Human Powered Aircraft (HPA) wings. In this type of aircraft there is a long, highly flexible wing. Wing flexibility, coupled with long wing span can lead to large deflections during normal flight operation; therefore, a wing in vertical and torsional motion using the second-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic theory based on Wagner function is used for determination of aerodynamic loading on the wing. Combining these two types of formulations yields the nonlinear integro-differentials aeroelastic equations. Using the Galerkin's... 

    Towards obtaining more information from gas chromatography-mass spectrometric data of essential oils: An overview of mean field independent component analysis

    , Article Journal of Chromatography A ; Volume 1217, Issue 29 , 2010 , Pages 4850-4861 ; 00219673 (ISSN) Jalali Heravi, M ; Parastar, H ; Sereshti, H ; Sharif University of Technology
    2010
    Abstract
    Mean field independent component analysis (MF-ICA) along with other chemometric techniques was proposed for obtaining more information from multi-component gas chromatographic-mass spectrometric (GC-MS) signals of essential oils (mandarin and lemon as examples). Using these techniques, some fundamental problems during the GC-MS analysis of essential oils such as varying baseline, presence of different types of noise and co-elution have been solved. The parameters affecting MF-ICA algorithm were screened using a 25 factorial design. The optimum conditions for MF-ICA algorithm were followed by deconvolution of complex GC-MS peak clusters. The number of independent components (ICs) (chemical...