فهرست مطالب

Scientia Iranica
Volume:19 Issue: 3, 2012

  • Transactions B: Mechanical Engineering
  • تاریخ انتشار: 1390/11/13
  • تعداد عناوین: 11
|
  • B. Sajadi, M.H. Saidi Page 431
    In the past two decades, microfluidic systems have become more appealing due to their wide applications in many areas, such as electronics, biotechnology, medicine, etc. Recently, the advantages of using the bubble growth phenomenon as a robust actuator in microfluidic devices have directed research interests towards the investigation of various applications. In this research, a new transient thermo-hydraulic model has been developed for bubble growth in confined volumes. The present model has been used to describe the pumping effect produced by the bubble growth and collapse phenomenon in microchannels. The results show relatively good agreement with experimental data. This study is useful in getting a better understanding of the bubble growth mechanism in confined volumes, and its application as a reliable micro actuator.
    Keywords: Microchannel, Explosive evaporation, Thermo, hydraulic modeling, MEMS
  • M. Sheikholeslami, H.R. Ashorynejad, D.D. Ganji, A. Yi, Ldi, Ri, M Page 437
    The three-dimensional problem of steady fluid deposition on an inclined rotating disk is illustrated in this study. The governing non-linear partial differential equations are reduced to the nonlinear ordinary differential equations system by similarity transform. The analytical solution applied to solve this system is the Homotopy Perturbation Method (HPM). The velocity and temperature profiles are shown and the influence of Prandtl number and rotation ratio on the flow field and the Nusselt number are discussed in detail. The validity of our solutions is verified by the numerical results.
    Keywords: Rotating disk, Condensation film, Heat, mass transfer, Film thickness, Homotopy perturbation method
  • M. Soleymani, M. Montazeri, Gh, R. Amiryan Page 443
    Vehicle ride comfort is a function of the frequency content of transmitted vibrations to passengers from road irregularities. However, this frequency content varies with vehicle speed fluctuations, which occur under real traffic conditions. The design of an adaptive active suspension system, in order to simultaneously improve ride comfort and travel suspension under various traffic conditions, is addressed in this paper. For this purpose, using a full-vehicle model, with eight degrees of freedom, two separate fuzzy controllers are designed for front and rear suspensions. The parameters of the fuzzy controllers are then tuned for various traffic conditions of a driving pattern, using a multi-objective Pareto-optimal solution. The optimization objectives are: the ride comfort index, evaluated according to the ISO 2631-1 standard, and the maximum suspension travel. Simulation results prove that the multi-objective fuzzy controller conventionally tuned, based on the constant speed driving pattern, results in simultaneous improvement of ride comfort, travel suspension and energy consumption. However, this controller does not work optimally under all traffic conditions. On the other hand, the proposed adaptive multi-objective controller not only results in optimal ride comfort and travel suspension under various traffic conditions, but also leads to a considerable drop in active suspension energy consumption.
    Keywords: Fuzzy logic controller, Adaptive, Traffic conditions, Genetic algorithm, Multi, objective, Pareto, Full, vehicle model
  • H. Khazaei, A.R. Teymourtash, M. Malek, Jafarian Page 454
    In this paper, energy separation effects in a vortex tube have been investigated using a CFD model. A numerical simulation has been undertaken, due to the complex structure of flow. The governing equations have been solved by the FLUENT™ code in a 2D compressible and turbulent model. Three turbulent models, namely, RSM, Standard k-epsilon and Spalart–Allmaras, have been used. The Spalart–Allmaras turbulent model, which is the first equation, was not so bad in predicting temperature results, although the Standard k-epsilon model better predicts the results in most regions. The effects of geometrical parameters have been investigated. The results have shown that the hot outlet size and its shape do not affect the energy distribution in the vortex tube, and a very small diameter will decrease the temperature separation. Different kinds of gas have been examined for the vortex tube, and it was concluded that using helium as a refrigerant produces the largest energy separation.
    Keywords: Vortex tube, Numerical method, Standard k, epsilon, Spalart–Allmaras, RSM, Different gases
  • O.B. Yaakob, A. Nasirudin, M.P. Abdul Ghani, T. Mat Lazim, M.A. Abd Mukti, Y.M. Ahmed Page 463
    The wake wash from passing ships can cause environmental damage. The wake wash is an important issue for naval architects and shipbuilders in concentrating on more environmentally friendly designs. This paper presents results of a parametric study of catamaran hull form to obtain low wake wash hull form configurations or low speed inland waterway boats. The study uses a Computational Fluid Dynamics (CFD) simulation, and model experiments were carried out for validation of the CFD software set-up. The study concentrates on the asymmetric catamaran hull form. The investigation is conducted on two configurations of hull form; Flat Side Inward (FSI) and Flat Side Outward (FSO) configurations. The investigation is conducted on a hull form with a Length to Beam (L/B) ratio of 12.2, 15.2 and 18.3 and a Separation to Length (S/L) ratio of 0.2, 0.3 and 0.4. The results based on wave height criteria at various longitudinal cuts have shown that the FSO configuration has a lower wake wash compared with the FSI configuration. Considering L/B and S/L ratios, hull forms with a larger separation or higher L/B ratios produce lower wave heights.
    Keywords: Wake wash, Catamaran, CFD, Model experiment, Wave profile
  • S.H. Pourtakdoust, S. Karimain Aliabadi Page 472
    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 initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new aeroelastic coordinates are introduced. In this reduced design space, new generalized performance curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter, as a function of reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional ideas of utilizing intelligent variable stiffness materials and/or an active morphing technology for the sustained flight of FMAVs.
    Keywords: Flapping air vehicle, Aeroelastic model, Propulsion, Experimental study, Parametric study, Dimensionless parameter
  • S. Erkaya, I. Uzmay Page 483
    An experimental study is proposed to investigate the effects of balancing and link flexibility on the dynamics of a mechanism with imperfect revolute joints, that is, joints having radial clearance. A planar slider-crank mechanism, widely used in vehicle engines, is used in the experimental investigation. Bearing vibrations are considered to evaluate the reflection of balancing and link flexibility effects on a mechanism having two revolute joints with clearance. On the other hand, these vibrations are measured to clarify how the balancing and link flexibility feature can decrease the undesired effects of joint clearances. For this purpose, three accelerometers, an analyzer and a PC are used for measuring the related vibrations on the main frame. The experimental results show that joint clearance leads to sudden changes in motion characteristics of the mechanism. During small time intervals, these sudden changes cause forces to impact in the joints of the mechanism with clearance. This also leads to some vibration peaks, and increases the vibration amplitudes. Furthermore, the flexibility feature of the mechanism link has a crucial role in decreasing additional vibration arising from joint clearance. Also, the undesired effects of clearance are reduced to some degree by using the balancing.
    Keywords: Joint clearance, Slider, crank mechanism, Link flexibility, Balancing, Bearing vibration
  • E. Barati, Y. Alizadeh Page 491
    The paper deals with the minimum value of a fracture load, with respect to the notch root radius, in plates weakened by U-notches under Mode I loading. It has been found that the fracture load has a minimum value at a critical value of the notch root radius (ρ), using four criteria, namely, Mean Stress (MS), maximum tangent stress or Point Stress (PS), Critical Strain-Energy (CSE) and Averaged Strain-Energy Density (ASED). Using a characteristic length (lch), which is a function of material properties, the results showed that the dimensionless critical notch root radius (ρ/lch)cr depended on w/a ratio (the specimen width to the notch depth), Poisson ratio, and loading condition (tensile or bending loading) under Mode I loading. In other words, according to these criteria, a notch root radius different from zero exists, providing a minimum fracture load. Therefore, a crack is not more dangerous rather than a U-notch under Mode I loading. This critical notch root radius is important for a quasi-brittle material, but may not be significant for brittle ones in practical engineering situations. Good agreement was found between theoretical predictions and experimental results on Al356-T6.
    Keywords: U_notch_Fracture load_Mode I loading_Failure criteria
  • S. Sattarzadeh, A. Jahangirian Page 503
    An implicit mesh-less method is developed for calculation of compressible flows around three dimensional complex geometries. The algorithm is applied directly to the differential form of the governing equations using least-square formulation. A dual-time implicit time discretization scheme is developed, and the computational efficiency is enhanced by adopting accelerating techniques, such as local time stepping, residual smoothing and enthalpy damping. Two different artificial dissipation techniques are employed for stability preservation and it is shown that the scalar one is more efficient in terms of accuracy and computational time. The capabilities of the method are demonstrated by flow computations around different geometries under subsonic and transonic flow conditions. Results are presented which indicate good agreement with experimental and other reliable numerical data. The method is shown to reduce computational time by about 50% compared with the alternative explicit method.
    Keywords: Mesh, less method, Implicit method, Compressible flow, 3D geometries
  • M. Baghani, M. Fattahi, A. Amjadian Page 513
    In this paper, an analytical solution for the nonlinear free vibration of a conservative oscillator is presented. The nonlinear governing equation is solved by employing the Variational Iteration Method (VIM). This method is based on the use of Lagrange multipliers for identification of optimal values of parameters in a function. Obtained results reveal that the proposed method is very effective, simple and exact. In the present investigation, the results of this method are compared with those of the Homotopy Analysis Method (HAM), as well as those predicted by the Runge–Kutta method. The excellent accuracy of the obtained results is demonstrated by comparing them with available analytical and numerical results available in the literature. Furthermore, the numerical results for different particular cases of the problem are presented. The effects of different parameters on the ratio of nonlinear to linear natural frequency of the system are also studied. Consequently, the proposed analytical solution can be used as an efficient tool to study the effects of the material or geometrical parameters in the modeling of devices consisting of nonlinear conservative oscillators for their design and optimization, which requires a large number of simulations.
    Keywords: Variational iteration method, Nonlinearity, Lagrange multiplier, Free vibration, Exact solution
  • A. Nematollahi, E. Shirani, I. Mirzaee, M.R. Sadeghi Page 519
    In this study, Lumen Surface Concentration (LSC) of Low Density Lipoprotein (LDL) particles in arteries with a permeable wall and up to 60% stenosis under steady state conditions, for Newtonian and non-Newtonian fluids, has been numerically investigated. The results show the Concentration Polarization (CP) phenomenon. Also, an increase in wall suction velocity (high blood pressure) and a reduction in Wall Shear Stress (WSS) are introduced as factors for an increase in LSC. Maximum LSC are observed for 40% stenosis.
    Keywords: Atherosclerosis, Mass transfer, LDL, Carotid artery, Non, Newtonian fluid