فهرست مطالب

  • Volume:2 Issue:2, 2010
  • تاریخ انتشار: 1389/04/26
  • تعداد عناوین: 9
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  • M. Jalaal, E. Esmaeilzadeh, G. Ahmadi Page 63
    Transport and sedimentation of spherical and non-spherical solid particles in quiescent fluids play significant roles in many separation processes and powder industries. Current work investigates the spherical and conical shape falling solid particles in a stationary viscous fluid. First, the flow around a falling solid sphere was simulated and the results were compared with the experimental data and empirical correlations. Then, the flow around conical shaped particles with the same volume and different aspect ratios were analyzed. The simulation results were presented for different Reynolds numbers, Re, aspect ratios, λ, and sphericity, ψ. Recirculation zone was generated above the particle in low-viscosity fluid environments. The simulation results showed that the length of the wake region was increased by reduction of viscosity (increase or Reynolds number). Also for conical particles, higher sphericity caused smaller drag coefficient and increase of tip angle, increased the drag coefficient. Correlations were presented for drag coefficients for particles, based on the Reynolds number and aspect ratio.
    Keywords: Transport, sedimentation of spherical, non spherical solid particles in quiescent fluids play
  • G. A. Sheikhzadeh, V. Rahmani, M. R. Babaei, M. A. Mehrabian Page 79
    The effect of an imposed magnetic field on natural convection in a tilted cavity with partially active walls is investigated numerically. The active part of the bottom wall is at a higher temperature than the active part of the top wall and are moving on horizontal walls relative to each other. The left, right and the remaining parts of the top and bottom walls are insulated. The magnetic field is parallel to active walls. The governing equations are discretized using the hybrid scheme. The resulting algebraic equations are coupled and simultaneously solved using TDMA algorithm. The SIMPLER algorithm is used to indicate the pressure gradient in the momentum equations. Flow field and heat transfer are predicted for Pr=0.71 and a wide range of the governing parameters such as: Rayleigh number between 104 and 106, Hartman number between 0 and 100, and inclination angle between 0 and 90 degrees. The average Nusselt number decreases with an increase of Hartman number and increases with an increase of Rayleigh number. The maximum heat transfer rate is occurred for the middle– middle thermally active locations while heat transfer is poor for the left-right and right-left thermally active locations.
    Keywords: Magnetic Field, Natural Convection, Partially Active Walls, Cavity
  • M. Ardebilipour, A. Ebrahimzadeh Page 89
    Signal identification plays an important role for various applications and purposes. In this paper, we addressed a problem that did not receive great attention in the literature: numerical classification of signals that propagated through fading channels. We concentrated on the mobile application, and on fast time-selective dispersive channel with no pre-channel estimation. We present two novel systems for the same problem. The first one is based on the phase of the signal, and the approach taken is decentralization that named phase based signal type classifier (PBMC). The second classifier is based on the phase difference of the signal (for eliminating a constant phase offset) named phase difference based signal type classifier (PDBMC). Numerical simulations shows both structures suggest easy and very good solutions for the problem of automatic MPSK signal classification in fast time-selective dispersive channel even in low SNR.
    Keywords: Numerical Methods, Signal Type Identification, Dispersive Channels, Decentralization, Phase Histogram
  • A. Noorpoor, S. Sharif Page 109
    In this article, aerodynamic and heat transfer efficiency of an Automotive Aluminum radiator with louvered fins is investigated by numerical simulation and the obtained results are compared with tunnel results. To find out the behavior of the fins, symmetric conditions is used for a fin with two halves of tubes on its top and bottom. To estimate the mass flow rate of each tube in a 40 tube radiator, a simple 2D model is constructed and the real geometry of the inlet and outlet reservoirs are considered in it. At the end, water flow inside a tube with different mass flow rates is considered that for convection heat transfer of the air side in it, a user defined function is used. The results show that this method has small error with respect to tunnel test results that is caused by neglecting the end effects of the radiator geometry.
    Keywords: Aluminum Radiator, Louvered Fins, Wind Tunnel Test, Symmetry
  • B. Ataie, Ashtiani, N. Nekouee Page 119
    Due to the sparseness of the available data for wind-wave hindcasting, temporal and spatial gaps exist in wind input data. Also, for the sake of convenience and reduction of computational efforts, the available wind field data may be simplified when used in numerical simulations of wave generation. Although this simplification is computationally economical, the wave characteristics obtained from the numerical simulations may be compromised. This study investigates the extent of influence for wind data simplification on the characteristics of wind-generated waves by considering two case studies. SWAN (SWAN Group, [25]), a third generation wave prediction model specialized for coastal and inland waters, are applied to hindcast wave regime. Lake Oroumieh in Iran and Lake Michigan in USA are considered as case studies. The effect of temporal wind variations are assessed by comparing predicted wave heights using the wind-rose and wind time-series as input data for Lake Oroumieh. A noticeable difference in the maximum significant wave height and period is observed between the results of the two prediction cases. The simulation results of the wind-rose case predict a wave height approximately 100% higher than the case with wind time-series data. In Lake Michigan the influence of the spatial variation of wind input data has been evaluated by comparing the predicted wave heights from simulation of surface spatially varied wind field to that of the constant wind over the whole lake area. Therefore in practical designs, considering local wind effects and storms by using satellite data catchments, buoys, ships reports and meteorological stations can play a significant role in reducing the final project costs.
    Keywords: Wind, Wave Hindcasting, Numerical Simulation, Wave Prediction Model
  • M.J. Maghrebi Page 133
    Direct numerical simulation of three–dimensional incompressible plane free shear flow is performed. Mass and momentum equations are solved in a domain which is finite in the streamwise direction (x), doubly infinite in the cross–stream direction (y) and homogeneous in the spanwise direction (z). In the x direction a high-order compact finite differencing scheme is used. In the y and z directions, a mapped spectral method and a Fourier spectral method are used, respectively. The numerical results for several known cases are computed and compared with their (analytical or experimental) solutions. This is performed to establish and verify the accuracy of the numerical code. Results indicate that the accuracy of the direct numerical simulation is excellent for the class of free shear flow in general and plane wake flow in particular. The code can be used as a perfect tool to investigate turbulence for the class of free shear flow problems.
    Keywords: DNS, Spatially Developing, Free Shear Flow, Diffusion Equation, Stuart Vortices
  • M. Nakhaei, A. Ghannad Page 143
    The effect of soil-structure Interaction on hysteretic energy demand of buildings under an ensemble of 24 earthquake ground motions recorded on alluvium sites is investigated. The building is modeled as a single-degree-of-freedom oscillator resting on flexible soil. The soil beneath the building is considered as a homogeneous elastic half space and is modeled via the concept of Cone Models. A parametric study is done using the aspect ratio of the building as well as a non-dimensional frequency as a representative of the structure to soil stiffness ratio. Making use of an optimization procedure, non-dimensional scaling indices are derived to minimize the average coefficient of variation of energy spectra. This is done separately for each spectral region. The results due to individual scaled records are then averaged and presented in the form of energy spectra. It was concluded that generally the dissipated hysteretic energy decreases under SSI effect except for the rare cases of short-period slender buildings. The energy drop is more significant for squatty buildings located on soft soils. The variations are more sensible in the acceleration and velocity spectral regions and usually minor in the displacement region.
    Keywords: Soil, Structure Interaction, Hysteretic Energy, Cone Models, Energy Spectra
  • N. Fallah Page 155
    In this paper two finite volume based formulations for the bending analysis of beam type structures are presented. The first formulation, which is a mixed type one, deals with the analysis of Bernoulli beam in which shear deformations are neglected. The second formulation, displacement based formulation, concerns with the analysis of Timoshenko beam in which shear effects are included in the analysis. Capability of both formulations in terms of accurate predictions of displacement field is investigated in several test problems. The numerical results reveal that: the predictions of both approaches show monotonic convergence to the analytical solutions, the shear locking is not observed in the analysis of thin Timoshenko beam models by using the second approach and finally in the tapered beam test problems of Bernoulli beam models the first method predicts more accurate results than the finite element counterpart with the same mesh.
    Keywords: Finite volume, Bernoulli beam, Timoshenko beam, Shear locking
  • R. Gharraei, E. Esmaeilzadeh, M. R. Heirani Nobari Page 165
    Electrohydrodynamic conduction pumping of dielectric liquid film using flush mounted electrodes has been investigated numerically. Numerical modeling has been performed for pure n-heptane with known ion mobilities. Plumley’s model for field enhancement of neutral molecules dissociation rate, has been used which is based on experimental measurements of n-heptane conductivity in the high field strengths. Numerical simulation has been performed for various electrode arrangements in order to investigate the importance of effective factors on flow rate of conduction pumps. Comparison of numerical results with experimental data indicates the good accuracy of numerical modeling. Numerical results show that the net flow generation is principally due to the mismatch of ions mobility and asymmetry of electrodes play a minor role in the conduction pumping of n-heptane.
    Keywords: Electrohydrodynamic, Pumping, Plumleys Model, n heptane