فهرست مطالب

  • Volume:8 Issue: 1, 2020
  • تاریخ انتشار: 1398/11/12
  • تعداد عناوین: 6
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  • Abbas Rahi * Pages 1-8
    The vibration analysis is an important step in the design and optimization of microsensors. In most of the cases, COMSOL software is employed to consider the size-dependency on the dynamic behavior in the MEMS sensors. In this paper, the Modified Couple Stress Theory (MCST) is used to capture the size effect on dynamic behavior in a microsensor with two layers of the silicon and piezoelectric. The governing equations of the system and also associated boundary conditions are derived based on the MCST and using Hamilton’s principle by obtaining the total kinetic and potential energies of the system. Then, the obtained governing equations are solved using an analytical approach to determine the natural frequencies of the system. The first, second and third natural frequencies of the microsensor are determined using an analytical approach. Finally, the natural frequency variations of the system are presented with respect to different values of the system parameters such as dimensionless parameters of the sensor geometric, the thickness of the silicon and piezoelectric layers and also the dimensionless material length scale parameter. The obtained results show that the material length scale parameter values and also the length, width, and thickness of each layer of the sensor are extremely effective on the vibration characteristics of the piezoelectric cantilever-based Micro Electro Mechanical System (MEMS) sensors. Also, the results show that the first natural frequency of the microsensor will decrease with either increasing dimensionless material length scale parameter or decreasing the thickness of silicon and piezoelectric. This analytical approach presents an efficient method to predict the dynamic behavior of microsensors and consequent optimization in their design procedure.
    Keywords: Free vibration, MEMS, Microsensor, Modified couple stress theory, Piezoelectric, Size-dependency
  • Ramadan Abdullah Mohamed, Abdelraheem Mahmoud Aly, Sameh Elsayed Ahmed *, Mahmoud Sayed Soliman Pages 9-22

    In this article, a numerical investigation of magnetohydrodynamic non-Newtonian nanofluid flow on a stretching sheet through an isotropic porous medium. The effects of both non-linear thermal radiation and heat generation/absorption were studied on distributions of velocity, temperature and concentration. On the other side, the governing partial differential equations have been transformed by using suitable similarity transformations into a system of ordinary differential equations and then solved, numerically by using the fourth order Runge-Kutta method with shooting technique. The principal findings of the study showed up that the effect of both Darcy number and magnetic field on the velocity profile is decreasing, while the impacts of both non-linear thermal radiation and heat source/skin on temperature are increasing and decreasing on concentration distribution respectively. Numerical solutions were calculated for the skin fraction, local Nusselt number and local Sherwood number for values of all important physical parameters.

    Keywords: Magnetohydrodynamic (MHD), Nanofluid, Porous media, Stretching surface, thermal radiation
  • Roozbeh Pouyanmehr, Reza Ansari, Mohammad Kazem Hassanzadeh Aghdam * Pages 23-31

    The purpose of the present work is to analyze the modulus of elasticity of graphene (Gr) sheet-reinforced metal matrix nanocomposites (MMNCs) using a homogenized model based on the Mori-Tanaka micromechanics approach. The main focus is to investigate the effects of Gr sheet agglomeration on the MMNC macroscopic elastic modulus. Also, the role of aligning Gr sheets in the mechanical performance of MMNC is explored. It is found that a small amount of Gr sheets can increase the elastic properties of the MMNCs. Addition of 5% by volume fraction of Gr sheet in an aluminum (Al) matrix improves the MMNC elastic modulus by 31%. The mechanical properties of MMNCs are very sensitive to the Gr sheet agglomeration. Formation of sheet agglomeration can significantly decrease the MMNC elastic modulus. It is observed that the Gr sheet alignment plays a superior role in enhancing the MMNC elastic properties. Generally, alignment of Gr sheets leads to the maximum level of MMNC mechanical properties in axial direction. As compared to the uniform dispersion type, aligning the 5 vol% Gr sheets can improve the elastic of Al nanocomposite by as much as 20%. The elastic modulus calculated from the present micromechanical model for different types of MMNCs is compared with available experimental data. In addition, the results from the Mori-Tanaka method are also compared with other analytical results acquired from semi-empirical Halpin-Tsai (H-T) model and the rule of mixture (ROM).

    Keywords: Agglomeration, Elastic properties, Graphene sheet, Metal matrix nanocomposite, Micromechanics
  • Sajjad Seifoori *, Fatemeh Abbaspour, Ehsan Zamani Pages 32-38
    In this study, an impact behavior of spherical striker on a double-walled carbon nanotube (DWCNT) is presented based on a three degree of freedom spring-mass model and the finite element (FE) simulations. The semi-analytical solution of the transverse impact of a striker on a DWCNT is investigated by using the elasticity nonlocal theory of Euler-Bernoulli (EBT) and Timoshenko (TBT) nanobeams. The spring-mass system with spring constant is used that involves shear and bending deformation. The van der Waals (vdW) interaction between two layers of a DWCNT is included in the analytical model. The results of this analysis are compared with the results of the FE simulation.  The results from the spring-mass model demonstrated good agreement with FE simulation for various values of a DWCNT dimension, chirality, boundary condition, number of layered and also striker parameters such as mass and velocity. The DWCNT independent of vdW interaction is more flexible than DWCNT with vdW forces.
    Keywords: Double-Walled Carbon Nanotube, FE simulation, Impact, spring-mass system
  • Hadi Mohammadi Hooyeh *, Ali Mohammadi Hooyeh, Hasan Afshari Pages 39-60
    In this study, the free vibration analysis of smart vibration control (SVC) systems based on Reddy – Levinson model and modified strain gradient theory is developed. This system consist of a micro beam at middle and two magneto-electro-elastic (MEE) composite micro beams at top and bottom which connected by enclosing elastic medium and simulated by Winkler and Pasternak foundation. The effects of the lower MEE composite micro beam in the absence of upper MEE composite micro beam and also the effect of both MEE composite micro beams together on the dimensionless natural frequency of the middle micro beam are evaluated. It is shown that the presence of both MEE composite micro beams together have less dimensionless natural frequency than presence of lower MEE composite micro beam alone. The results of this work can be useful to analysis, design and manufacture intelligent micro-systems to hamper resonance phenomenon or as a sensor to control the dynamic stability of micro structures.
    Keywords: Free Vibration analysis_Reddy - Levinson model_Smart vibration control system_three micro-_micro-composite beams
  • Mohammad Kazem Moayyedi * Pages 61-70
    In this article, a coupled computational framework is presented for the numerical simulation of mass transfer under the effects of natural convection phenomena in a field contains water-copper Nano-fluid. This CFD model is build up based on accurate algorithms for spatial derivatives and time integration. The spatial derivatives have been calculated using first order upwind and second order central differencing approaches. Also, time integration is performed using the fourth order Runge-Kutta method. A parametric reduced order model is developed to compute the whole flow field under the effects of some important parameters. This model is constructed using POD-snapshots method based on Karhunen-Loeve decomposition. The POD modes have been calculated based on the solution of an eigenvalues problem. The obtained eigenfunctions are POD modes which are arranged using energy-based criteria based on total kinetic energy of the flow field. This approach leads to the model order reduction procedure, and the outcome model can be used as a surrogate model of CFD high order model. The results obtained from the reduced order model show close agreements to the benchmark DNS data and proving high accuracy of the proposed model.
    Keywords: Computational Fluid Dynamics, Model Order Reduction, Nano-fluid, natural convection