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    Design, modeling and optimization of a novel two DOF polymeric electro-thermal micro-actuator

    , Article Applied Mechanics and Materials ; Vol. 307 , 2013 , pp. 112-116 ; ISSN: 16609336 ; ISBN: 9783037856598 Sheikhbahaie, R ; Alasty, A ; Salarieh, H ; Sharif University of Technology
    Abstract
    In this paper, design, simulation and optimization of a novel electrothermally-activated polymeric microactuator capable of generating combination of bidirectional lateral and rotational motions are presented. The composite structure of this actuator is consisted of a symmetric meandered shape silicon skeleton, a SU8 thermal expandable polymer and a thin film chrome layer heater. This actuator is controlled by applying appropriate voltages on its four terminals. With the purpose of dimension optimization, a numerical parametric study is executed. The modeled actuator which is 1560 ?m long, 156 ?m wide and 30 ?m thick, demonstrates a remarkable lateral displacement of 23 ?m at power... 

    Numerical study of the effects of process parameters on tool life in a cold radial forging process

    , Article Scientia Iranica ; Vol. 21, issue. 2 , 2014 , p. 339-346 Afrasiab, H ; Movahhedy, M. R ; Sharif University of Technology
    Abstract
    Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axles, and for creating internal profiles in tubes. Due to very large forging loads, the tool should withstand high stress and wear. Therefore, the success of the forging process depends upon recognition of the die failure factors and optimization of the tool working conditions that enhance tool life. In this study, the effect of process parameters on tool life in the cold radial forging process is investigated using nonlinear three dimensional finite element modeling. Wear and mechanical fatigue are considered as the main modes of tool failure, and a parametric study on the... 

    Free vibration of moderately thick conical shells using a higher order shear deformable theory

    , Article Journal of Vibration and Acoustics, Transactions of the ASME ; Vol. 136, issue. 5 , Jul , 2014 Firouz-Abadi, R. D ; Rahmanian, M ; Amabili, M ; Sharif University of Technology
    Abstract
    The present study considers the free vibration analysis of moderately thick conical shells based on the Novozhilov theory. The higher order governing equations of motion and the associate boundary conditions are obtained for the first time. Using the Frobenius method, exact base solutions are obtained in the form of power series via general recursive relations which can be applied for any arbitrary boundary conditions. The obtained results are compared with the literature and very good agreement (up to 4%) is achieved. A comprehensive parametric study is performed to provide an insight into the variation of the natural frequencies with respect to thickness, semivertex angle, circumferential... 

    Numerical investigation into the effects of geometrical and loading parameters on lateral spreading behavior of liquefied layer

    , Article Acta Geotechnica ; 2013 , Pages 1-13 ; 18611125 (ISSN) Pak, A ; Seyfi, S ; Ghassemi, A ; Sharif University of Technology
    2013
    Abstract
    Numerical simulation of liquefaction-induced lateral spreading in gently sloped sandy layers requires fully coupled dynamic hydro-mechanical analysis of saturated sandy soil subjected to seismic loading. In this study, a fully coupled finite element model utilizing a critical-state two-surface-plasticity constitutive model has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the well-known VELACS project. Lateral spreading phenomenon has been... 

    Investigation of free surface flow generated by a planing flat plate using smoothed particle hydrodynamics method and FLOW3D simulations

    , Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 227, Issue 2 , 2013 , Pages 125-135 ; 14750902 (ISSN) Ghadimi, P ; Dashtimanesh, A ; Farsi, M ; Najafi, S ; Sharif University of Technology
    2013
    Abstract
    In this article, smoothed particle hydrodynamics method is applied in order to study the free surface flow generated by two-dimensional planing flat plate. For this purpose, a two-dimensional smoothed particle hydrodynamics code is developed and validated by the well-known dam breaking problem. Four trim angles and three different velocities are considered to perform a parametric study to examine their physical effects. The obtained results from smoothed particle hydrodynamics are compared against the corresponding Reynolds-averaged Navier Stokes solutions. It is observed that at lower velocities, there exists a good agreement between the smoothed particle hydrodynamics and Reynolds-averaged... 

    Dynamic responses of intervertebral disc during static creep and dynamic cyclic loading: A parametric Poroelastic finite element analysis

    , Article Biomedical Engineering - Applications, Basis and Communications ; Volume 25, Issue 1 , 2013 ; 10162372 (ISSN) Nikkhoo, M ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
    2013
    Abstract
    Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic... 

    Electroosmotic flow of viscoelastic fluids through a slit microchannel with a step change in wall temperature

    , Article Journal of Heat Transfer ; Volume 135, Issue 2 , 2013 ; 00221481 (ISSN) Sadeghi, A ; Veisi, H ; Saidi, M. H ; Asghar Mozafari, A ; Sharif University of Technology
    2013
    Abstract
    Thermally developing electroosmotically generated flow of two viscoelastic fluids, namely the PTT and FENE-P models, through a slit microchannel is considered. Both the viscous dissipation and Joule heating effects are taken into account and a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. Expressions for the dimensionless temperature and Nusselt number in the form of infinite series are presented. In general, the resultant eigenvalue problem is solved numerically; nevertheless, an analytical solution is presented for the regions close to the entrance. A parametric study reveals that increasing amounts of the Peclet number... 

    Application of elastically supported single-walled carbon nanotubes for sensing arbitrarily attached nano-objects

    , Article Current Applied Physics ; Volume 13, Issue 1 , 2013 , Pages 107-120 ; 15671739 (ISSN) Kiani, K ; Ghaffari, H ; Mehri, B ; Sharif University of Technology
    Abstract
    The potential application of SWCNTs as mass nanosensors is examined for a wide range of boundary conditions. The SWCNT is modeled via nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The added nano-objects are considered as rigid solids, which are attached to the SWCNT. The mass weight and rotary inertial effects of such nanoparticles are appropriately incorporated into the nonlocal equations of motion of each model. The discrete governing equation pertinent to each model is obtained using an effective meshless technique. The key factor in design of a mass nanosensor is to determine the amount of frequency shift due to the added nanoparticles. Through an inclusive parametric... 

    Electrokinetically driven fluidic transport of power-law fluids in rectangular microchannels

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Volume 414 , 2012 , Pages 440-456 ; 09277757 (ISSN) Vakili, M. A ; Sadeghi, A ; Saidi, M. H ; Mozafari, A. A ; Sharif University of Technology
    2012
    Abstract
    Electroosmosis is the predominant mechanism for flow generation in lab-on-chip devices. Since most biofluids encountered in these devices are considered to be non-Newtonian, it is vital to study the flow characteristics of common non-Newtonian models under electroosmotic body force. In this paper, the hydrodynamically fully developed electroosmotic flow of power-law fluids in rectangular microchannels is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A thoroughgoing parametric study reveals that the Poiseuille number is an increasing function of the channel aspect ratio, the zeta potential, the... 

    Thermally developing electroosmotic flow of power-law fluids in a parallel plate microchannel

    , Article International Journal of Thermal Sciences ; Volume 61 , 2012 , Pages 106-117 ; 12900729 (ISSN) Sadeghi, A ; Saidi, M.H ; Veisi, H ; Fattahi, M ; Sharif University of Technology
    2012
    Abstract
    The present investigation considers the thermally developing electroosmotic flow of power-law fluids through a parallel plate microchannel. Both the viscous dissipation and Joule heating effects are taken into account and a step change in wall temperature is considered to represent physically conceivable thermal entrance conditions. Expressions for the dimensionless temperature and Nusselt number in the form of infinite series are presented. In general, the resultant eigenvalue problem is solved numerically; nevertheless, an analytical solution is presented for the regions close to the entrance. A parametric study reveals that increasing amounts of the Peclet number result in higher wall... 

    Equivalent linearization of non-linear soil-structure systems

    , Article Earthquake Engineering and Structural Dynamics ; Volume 41, Issue 13 , 2012 , Pages 1775-1792 ; 00988847 (ISSN) Esmaeilzadeh Seylabi, E ; Jahankhah, H ; Ghannad, M. A ; Sharif University of Technology
    Wiley  2012
    Abstract
    The concept of equivalent linearization, in which the actual nonlinear structure is replaced by an equivalent linear single-degree-of-freedom (SDOF) system, is extended for soil-structure systems in order to consider the simultaneous effects of soil-structure interaction (SSI) and inelastic behavior of the structure on equivalent linear parameters (ELP). This is carried out by searching over a two-dimensional equivalent period-equivalent damping space for the best pair, which can predict the earthquake response of the inelastic soil-structure system with sufficient accuracy. The super-structure is modeled as an elasto-plastic SDOF system whereas the soil beneath the structure is considered... 

    Assessment of a practical technique for active control of sound using microphone and speaker

    , Article Scientia Iranica ; Volume 19, Issue 4 , 2012 , Pages 1005-1012 ; 10263098 (ISSN) Joghataie, A ; Raoufi, M ; Sharif University of Technology
    Elsevier  2012
    Abstract
    In this analytical study, it has been desired to develop a practical and simple control mechanism to control, at a given point and its neighborhood, the sound arriving from a distant source, assuming that a primary pure-tone sound pressure is propagated from a relatively far distance. The control model consists of a microphone as a sensor for measuring the sound pressure and a loud speaker for applying the control force. Corresponding equations have been developed to determine an optimum control force, and afterwards a parametric study on the factors affecting the control results has been performed. The results show that the control system can significantly reduce low frequency sound... 

    Thermodynamic model for prediction of performance and emission characteristics of SI engine fuelled by gasoline and natural gas with experimental verification

    , Article Journal of Mechanical Science and Technology ; Volume 26, Issue 7 , July , 2012 , Pages 2213-2225 ; 1738494X (ISSN) Mehrnoosh, D ; Asghar, H. A ; Asghar, M. A ; Sharif University of Technology
    2012
    Abstract
    In this study, a thermodynamic cycle simulation of a conventional four-stroke SI engine has been carried out to predict the engine performance and emissions. The first law of thermodynamics has been applied to determine in-cylinder temperature and pressure as a function of crank angle. The Newton-Raphson method was used for the numerical solution of the equations. The non-differential form of equations resulted in the simplicity and ease of the solution to predict the engine performance. Two-zone model for the combustion process simulation has been used and the mass burning rate was predicted by simulating spherical propagation of the flame front. Also, temperature dependence of specific... 

    Evaluation of flapping wing propulsion based on a new experimentally validated aeroelastic model

    , Article Scientia Iranica ; Volume 19, Issue 3 , 2012 , Pages 472-482 ; 10263098 (ISSN) Pourtakdoust, S. H ; Aliabadi, S. K ; Sharif University of Technology
    2012
    Abstract
    To evaluate the propulsion system capabilities of a Flapping Micro Air Vehicle (FMAV), a new aeroelastic model of a typical flexible FMAV is developed, utilizing the Euler-Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV, as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV, as well as an instrumented test stand for the online measurement of forces, flapping angle and power consumption, has been constructed. The experimental results are... 

    A parametric study using two design methodologies for pressure jet and swirl injectors

    , Article IEEE Aerospace Conference Proceedings ; 2012 ; 1095323X (ISSN) ; 9781457705564 (ISBN) Mazaheri, K ; Morad, M. R ; Shakeri, A. R ; Sharif University of Technology
    2012
    Abstract
    One of the most important subsystems in the air-breathing engines is the atomizers, which break the fuel into many droplets. It is well known that atomization quality has a significant influence on combustion characteristics such as stability limits, efficiency, and pollutant emission. Both jet and swirl injectors are applicable in gas turbine engines. The latter have been widely used for combustion chambers and the former are usually employed for fuel injection in the afterburner part. Since experimental and numerical study of atomizers could be complex and costly, a design methodology of atomizers based on empirical relations is still very advantageous and effective in reducing... 

    Analysis of nanofluid heat transfer in parallel-plate vertical channels partially filled with porous medium

    , Article International Journal of Thermal Sciences ; Volume 55 , 2012 , Pages 103-113 ; 12900729 (ISSN) Hajipour, M ; Molaei Dehkordi, A ; Sharif University of Technology
    Abstract
    In this article, mixed-convective heat transfer of nanofluids in a vertical channel partially filled with highly porous medium was studied. In the porous region, the Brinkman-Forchheimer extended Darcy model was used to describe the fluid flow pattern. Different viscous dissipation models were also applied to account for viscous heating. At the porous medium-fluid interface, interfacial coupling conditions for the fluid velocity and temperature were used to derive the analytical solution using a two-parameter perturbation method. The model used for the nanofluids incorporates the effects of Brownian motion and thermophoresis. With constant wall temperature, velocity and temperature profiles... 

    Dynamics of a delaminated timoshenko beam subjected to a moving oscillatory mass

    , Article Mechanics Based Design of Structures and Machines ; Volume 40, Issue 2 , Apr , 2012 , Pages 218-240 ; 15397734 (ISSN) Kargarnovin, M. H ; Ahmadian, M. T ; Jafari-Talookolaei, R. A ; Sharif University of Technology
    2012
    Abstract
    This paper presents dynamic response of a delaminated composite beam under the action of moving oscillatory mass. The Poisson's effect, shear deformation and rotary inertia have been considered in this analysis. We have used the constrained mode model to simulate the behavior between the delaminated surfaces. Based on this model, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes for the delaminated beam. Then, the forced response is determined by employing the modal series expansion technique. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literature. Moreover, the... 

    Heat transfer characteristics of mixed electroosmotic and pressure driven flow of power-law fluids in a slit microchannel

    , Article International Journal of Thermal Sciences ; Volume 53 , 2012 , Pages 71-79 ; 12900729 (ISSN) Babaie, A ; Saidi, M. H ; Sadeghi, A ; Sharif University of Technology
    2012
    Abstract
    Thermal transport characteristics of electroosmotic flow of power-law fluids in the presence of pressure gradient through a slit microchannel are studied in this paper. Considering a fully developed flow with a constant wall heat flux as the boundary condition, the governing equations are numerically solved by means of the finite difference method. A complete parametric study is done in order to investigate the effects of different flow parameters on the thermal behaviors of the flow. The results show that the non-Newtonian characteristic of the fluid can influence the thermal behaviors of the flow by affecting the rate of heat convection and viscous dissipation; however, its influence... 

    Three-dimensional elasticity analysis of functionally graded rotating cylinders with variable thickness profile

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 226, Issue 3 , 2012 , Pages 585-594 ; 09544062 (ISSN) Ghafoori, E ; Asghari, M ; Sharif University of Technology
    Abstract
    A three-dimensional elasticity solution for the analysis of functionally graded rotating cylinders with variable thickness profile is proposed. The axisymmetric structure has been divided in several divisions in the radial direction. Constant mechanical properties and thickness profile are assumed within each division. The solution is considered for four different thickness profiles, namely constant, linear, concave, and convex. It is shown that the linear, concave, and convex thickness profiles have smaller stress values compared to a constant thickness profile. The effects of various grading indices as well as different boundary conditions, namely solid, free-free hollow and fixed-free... 

    Dynamic behavior of pile foundations under cyclic loading in liquefiable soils

    , Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 114-126 ; 0266352X (ISSN) Rahmani, A ; Pak, A ; Sharif University of Technology
    Abstract
    In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the...