فهرست مطالب

  • Volume:47 Issue: 2, 2016
  • تاریخ انتشار: 1395/09/11
  • تعداد عناوین: 12
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  • M. Sharififar *, S. A. A. Akbari Mousavi Pages 129-136
    Rectangular waveguide is one of the earliest types of transmission lines. Rectangular waveguide can be produced by hot extrusion process. In this paper, the hot extrusion process of CuZn5 rectangular waveguide was investigated by Finite Element Method (FEM). In addition, Genetic Algorithm (GA) was used to optimize the die geometry and process conditions to achieve the lowest magnitude of extrusion force. Die geometry was introduced in terms of die length and billet hole diameter under various frictional conditions. It was found that die length and billet hole diameter had contradictory effects on the extrusion force. The experimental study was also carried out to verify the accuracy of estimated results.
    Keywords: Extrusion, Finite Element Method, Genetic Algorithm, Optimization, Rectangular Waveguide
  • Naser Kordani *, Abdolhossein Fereidoon, Mehdi Divsalar, Ali Farajpour Pages 137-150
    In this paper, a numerical solution procedure is presented for the free and forced vibration of a piezoelectric nanowire under thermo-electro-mechanical loads based on the nonlocal elasticity theory within the framework of Timoshenko beam theory. The influences of surface piezoelectricity, surface elasticity and residual surface stress are taken into consideration. Using Hamilton’s principle, the nonlocal governing differential equations are derived. The governing equations and the related boundary conditions are discretized by using the differential quadrature method (DQM). The numerical results are obtained for both free and forced vibration of piezoelectric nanowires. The present results are validated by available results in the literature. The effects of the nonlocal parameter together with the other parameters such as residual surface stress, temperature change and external electric voltage on the size-dependent forced vibration of the piezoelectric nanowires are studied. It is shown that the nonlocal effect (small scale effect) plays a prominent role in the forced vibration of piezoelectric nanowires and this effect cannot be neglected for small external characteristic lengths. The resonant frequency increases with increasing the residual surface stress. In addition, as the surface elastic constant increases, the resonant frequency of PNWs increases, while the surface piezoelectric constant has a decreasing effect on the resonant frequency.
    Keywords: Piezoelectric nanowire, Forced vibration, Small scale effect, Surface effects
  • Mohammad Hossein Bayati *, Morteza Shahravi Pages 151-158
    Many people experience vibration effects on whole-body throughout their lives frequently. Vibrating energy absorbed is exposed all-body caused with vibration hazard in the vertically on body and biodynamic responses from body in speed 2.37 to 5.14 m/s could captivate with car seat on user body, so the vibration energy transferred to a seated people body. In this paper, the human body is modeled as a series/parallel 4 DOF dynamic models of system and use Lagrange equation for calculate head and neck equation and investigation the effect of vibration energy absorbed in whole body. The hybrid model is analyzed with Matlab software for vertical vibration responses and vibration energy absorption. It is shown improvement seat vehicle cause, drastically ameliorate the tolerance to high-intensity vibrations in the 0.8 Hz range with reducing the maximum amplitude ratios and relative displacements of the body.
    Keywords: Transient analysis, People body vibration, Vibration answer, Mathematical model
  • Mohammad Zakeri *, Reza Attarnejad, Amir Mohsen Ershadbakhsh Pages 159-180
    The accuracy and efficiency of the elements proposed by finite element method (FEM) considerably depend on the interpolating functions namely shape functions used to formulate the displacement field within the element. In the present study, novel functions, namely basic displacements functions (BDFs), are introduced and exploited for structural analysis of nanobeams using finite element method based on Eringen’s nonlocal elasticity and EulerBernoulli beam theory. BDFs are obtained through solving the governing differential equation of motion of nanobeams using the power series method. Unlike the conventional methods which are almost categorized as displacement-based methods, the flexibility basis of the method ensures true satisfaction of equilibrium equations at any interior point of the element. Accordingly, shape functions and structural matrices are achieved in terms of BDFs by application of merely mechanical principles. In order to evaluate the competency and accuracy of the proposed method with different boundary conditions, several numerical examples with various boundary conditions are scrutinized. Carrying out several numerical examples, the results in stability analysis, free longitudinal vibration and free transverse vibration show a complete accordance with those in literature.
    Keywords: Nanobeams, size-effect, Basic Displacement Functions (BDFs), Free Vibration, instability analysis
  • Borhan Beigzadeh *, Mahdi Halabian Pages 181-194
    The use of magnetic fields in targeted drug delivery, especially for treatment of cancers and tumoral regions, is one of the significant techniques in the field of modern methods of treatment. Considering that many vital biological tissues have been located deep in the body, then for targeted drug delivery and effective treatment in these tissues, it is required to bring therapeutic agent to the desired location and focus on that location. The purpose of this study is to evaluate the static magnetic field interaction with hemodynamic properties of blood flow containing a magnetic carrier substance as a bio magnetic fluid. The finite element method (FEM) is used for 2D numerical simulation of magnet with different tip shapes and evaluating of external static magnetic field and its effects on the blood flow with aforementioned properties. The results show that the static magnetic fields generated from magnets with different tip shapes have different effects on the distribution of the fluid velocity field. Furthermore it can be concluded that when magnetic field flux density is concentrated around the magnet tip, the intensity of these hemodynamic effects become more concentrated within the fluid and the location of the magnet tip on the tissue, though the hemodynamic variables have been changed.
    Keywords: Static Magnetic Field, Hemodynamic Properties, Blood Flow, Magnetic Particles
  • Seyed Abdolkarim Payambarpour *, Hossein Shokouhmand Pages 195-207
    Heat and mass transfer, in this paper, is considered in one-row heat exchanger, that fins are hotter than air flow and water is added to fins. Related governing equations are derived by analyzing a two-dimension model in a unique cell of a heat exchange. These equations are numerically solved by finite difference method. Heat transfer and efficiency under partially wet surface are calculated by changes in thickness of water layer on the fins and wet percentage region of fin with constant airflow characteristics. In this study, Lewis Number as unity and water vapor saturation as parabolic are assumed. Obtained results show that increasing in thickness of fin leads to increasing thermal resistance; therefore, efficiency of fin decreases. But thickness of water layer dose not play a significant role in fin efficiency when water layer covering the surface of fins is thin or it covers a small region of fins because thermal resistance of water is not comparable with thermal conductivity of fin material. But where thickness of water layer is comparable with fin pitch or more surface of fins is wetted, fin efficiency and heat transfer change obviously because of increasing thermal resistance and changing in air flow velocity that cause more decreasing in efficiency of fins.
    Keywords: Heat exchanger, partially wet-surface, Thickness of water layer
  • Hadi Ramin *, Mohammad Pourjafar Pages 209-218
    Unsteady slip-flow of second grade non-Newtonian electrically conducting fluid over an oscillating sheet has been considered and solved numerically. A second-order slip velocity model is used to predict the flow characteristic past the wall. With the assumption of infinite length in x-direction, velocity of the fluid can be assumed as a function of y and t, hence, with proper variable change partial governing equations are converted to ordinary differential equations, and resulting equations are solved numerically. Fourth-order finite difference scheme is used to solve the transformed governing equations. The effects of magnetic field applied on surface, slip flow parameters, frequency of oscillating, mass suction or injection and elastic second number on the velocity distribution are shown graphically and discussed. With increase of slip flow parameter, unlike that of other parameters, thickness of the fluid affected by motion of boundary will decrease. It is also realized that both injection and suction of mass on the sheet, will increase amplitude of velocity.
    Keywords: Unsteady flow, MHD flow, second order fluid, slip parameters
  • Kia Dastani, Mahdi Moghimi Zand * Pages 219-230
    In the current study, the effects of Casimir force and squeeze film damping on pull-in instability and dynamic behavior of electrostatically actuated nano and micro electromechanical systems are investigated separately. Linear elastic membrane theory is used to model the static and dynamic behavior of the system for strip, annular and disk geometries. Squeeze film damping is modeled using nonlinear Reynolds equation. Both equation of motion and nonlinear Reynolds equation are first nondimensionalized, and then discretized and solved by means of finite element method. Static pullin analysis is performed and validated by previous researches, and then dynamic pull-in values are investigated and compared with static pull-in parameters. In the next step, the effect of squeeze film damping, ambient pressure and Casimir force on the system dynamics is studied. Results show significant effect of Casimir force and squeeze film damping on the system behavior which is considerable for fabrication and design
    Keywords: MEMS, NEMS, pull-in instability, Squeeze film damping, Casimir force, linear elastic membrane, FEM
  • P. Ghabezi *, M. Farahani Pages 231-239
    Adhesive bonding technology is being used in a variety of modern industries, including the automotive, aerospace, maritime, construction, defense and so on. On the other side, polymeric nano - composites attracted both academic and industrial interests in the past decades. The scope of this paper is experimental investigation on the effects of the addition of Alpha-alumina nanoparticles to the woven glass / epoxy composite and Araldite 2015 adhesive on the mechanical properties of the composite adhesive bonded joints. In this study, vacuum assisted resin transfer molding was used to fabricate experimental samples and to fabricate composite samples, 6 glass-fiber layers with a surface density of 200 g/m2 were used. The study of the influences of the addition of Alpha-alumina nanoparticles with different weight ratios to glass/epoxy composites suggests that the maximum values of the ultimate strength, elongation, toughness, and Young’s modulus belong to the samples with the weight ratios of 0.43, 1, 1, and 2.1%, respectively. The experimental results from the shear tensile test show that the incorporation of 0.74 wt% of nanoparticles to the adhesive increases the joint strength by about 14%.
    Keywords: Adhesive Joint, Composite, Nanoparticle, Mechanical Properties, VARTM
  • Saeid Shakki, Mahdi Moghimi Zand * Pages 241-246
    Typically two configurations are used for energy harvesting with different advantages: piezoelastic and piezomagnetoelastic. Best performance of the piezoelastic configuration is when the excitation frequency is close to the resonance frequency. If the input frequency slightly deviates from the natural frequency, the generated power is severely decreased. To tackle the problem, the piezomagnetoelastic configuration has been introduced. This configuration can be used near the non-resonant frequencies. This paper examines the effects of frequency and damping in the two above-mentioned configurations. The results of the study indicate that with increasing the damping, the harvested energy decreases. Also the results show that at higher frequencies, piezomagnetoelastic operation is better than the piezoelastic one; but at low frequencies, piezoelastic configuration is the better option.
    Keywords: Piezoelastic, piezomagnetoelastic, energy harvesting
  • Rouhollah Hosseini *, Maryam Nouri Pages 247-259
    The most promising method for micro scale energy scavenging is via vibration energy harvesting which converts mechanical energy to electrical energy. Using piezoelectric cantilevers is the most common method for vibration energy harvesting. Changing the shape of the cantilevers can lead to changing the generated output voltage and power. In this work vibration energy harvesting via piezoelectric resonant unimorph cantilevers is studied and new design for obtaining more efficient piezoelectric energy harvester is suggested. This study provides comprehensive analysis of the output voltage relationships and deducing a considerable precise rule of thumb for calculating resonance frequency in cantilever-type unimorph piezoelectric energy harvesters using Rayleigh method. The analytical formula, is then analyzed and verified by FEM simulation in ABAQUS. The analytical data was found to be very close to simulation data. A key finding is that among all the unimorph trapezoidal V-shaped cantilever beams with uniform thickness, the triangular tapered cantilever, can lead to highest resonance frequency and by increasing the ratio of the trapezoidal bases, the resonance frequency decreases. These new findings provide guidelines on system parameters that can be manipulated for more efficient performance in different ambient source conditions.
    Keywords: Vibration energy harvesting, Unimorph Piezoelectric vibrator, Trapezoidal V-shaped cantilever, Triangular beam, Resonant frequency
  • Ahmadreza Azadi *, Keivan Torabi Pages 261-271
    Natural vibration analysis of plates represents an important issue in engineering applications. In this paper, a new and simplify method for vibration analysis of circular and rectangular plates is presented. The design of an effective robust controller, which consistently attenuates transverse vibration of the plate caused by an external disturbance force, is given. The dynamics of the plate is modeled as a distributed parameter system. We have studied the control vibration of the plate using quantitative feedback theory method by determining the transfer functions between various factors of control system. In this method we have developed the general distributed parameter system method for uncertainty problem for simply supported rectangular plate and clamped circular plate. The quantitative feedback method is one of the robust control methods which is capable to solve problems despite structural and non-structural uncertainty. Quantitative Feedback Theory introduces the new technique to design one-point feedback controllers for distributed parameter systems. The results demonstrate that the control law provided a significant reduction in the plate vibration. The numerical simulation of the designed controller demonstrates that the QFT controller can consistently attenuate the vibration compared to a passive system.
    Keywords: Vibration, control, rectangular plate, circular plate, quantitative feedback theory