فهرست مطالب
International Journal of Engineering
Volume:16 Issue: 1, Feb 2003
- Transactions : A : Basic
- تاریخ انتشار: 1382/01/11
- تعداد عناوین: 11
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Pages 1-20This study is concerned with the numerical analysis, formulation, programming and computation of steady, 3D conservation equations of reacting laminar flow heat and mass transfer in ducts of arbitrary cross-sections. The non-orthogonal boundary-fitted coordinate transformation method is applied to the Cartesian form of overall-continuity, momenta, energy and species-continuity equations, parabolized in the axial direction. The boundary conditions are also transformed accordingly. Applying a novel feature of the solution procedure, the contravariant velocity components are introduced into the transformed equations while the physical Cartesian velocity components are retained as dependent variables of the velocity field in the equations. The transformed equations are integrated over 3D control-volumes, followed by differencing the convective and diffusive terms by upwind and central-difference schemes respectively. A modified version of the SIMPLER algorithm is introduced in the solution procedure and a line-by-line TDMA algorithm is employed for the solution of discretization equations. A computerprograme is developed for the generation of non-orthogonal grids corresponding to Patankar’s B-type arrangement in the transformed plane. A general computer programme in FORTRAN is developed for the solution of flow, heat and mass transfer problems for laminar reacting flows in straight ducts of arbitrary cross-sections. The model and computer codes are validated by theoretical, experimental and numerical results from various sources. The computer programs are employed for studies in the analysis of hydrodynamics and heat transfer in the entrance regions of ducts of arbitrary cross-sections for Newtonian and non-Newtonian fluids and ultimately for simulation of production of polystyrene in arbitrary cross-sectional duct reactors.
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Pages 21-28Modeling and optimization of synthesis gas production via the non-catalytic partial oxidation of methane (NCPO) were studied by minimizing of Gibbs free energy, and comparison studies were carried out to analyze the mechanism of syngas production. For this purpose, concentrations of CO2 and H2O in the feed were optimized in specified pressure and temperature, such that the hydrogen to carbon monoxide ratio in the product was set between 1.98 and 2.02 (suitable ratio for FT and methanol synthesis process) and concentration of CH4 in the product was less than 1.5%. The predictions obtained by this simulator were in agreement with the experimental data as well as the AspenPlus® package results.
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Pages 29-40This paper describes the various frequency domain methods which may be used to analyze experiments data on the force experienced by a circular cylinder in wave and current to estimate drag and inertia coefficients for use in Morison’s equation. An additional approach, system identification techniques (SIT) is also introduced. A set of data obtained from experiments on heavily roughened circular cylinders in waves and simulated current has been analyzed by all these techniques. The resulting force coefficients are then used to predict the force from separate experiments-results, which have not used in the analysis. The root mean square error and bias in the estimation of maximum force in each wave cycle is used a measure of predictive accuracy and as a basis for comparing the analysis techniques. The case when wave particle kinematics must be inferred from water surface elevation is also considered. It is found that when water particle kinematics are not possible to be measured directly and have to be inferred from surface elevation then using a system identification approach, the predictive errors increase considerably.
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PROBE-FED RECTANGULAR DIELECTRIC RESONATOR ANTENNAS: THEORETICAL MODELING AND EXPERIMENTSPages 41-46A Rectangular Dielectric Resonator Antenna (RDRA) is theoretically analyzed using the Conventional Dielectric Waveguide Model (CDWM), numerically simulated using the High Frequency Structure Simulator (HFSS) based on the Finite Element Method (FEM) software package and experimentally investigated with the consideration of the fundamental mode TE 111. Antenna parameters under investigation include resonance frequency, radiation patterns, directivity, Q-factor, impedance bandwidth and cross polarization level. The results for a specific resonator are presented and compared with those obtained by experiments. It is concluded that the CDWM can be used for a first order estimation of the antenna parameters, but more accurate results can be obtained using the FEM for radiation patterns.
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Pages 47-56In the present investigation transient, G x/G/m queuing model with balking and reneging has been studied. The diffusion process with elementary return boundary has been used for modeling purpose. The probability density function (p. d. f.) for the number of customers in the system has been obtained. In special case, the steady state results that tally with those of Kimura and Ohsone have been established as a limiting case.
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Pages 55-60Complexity is one of the most important issues of any production planning. The increase in complexity of production planning can cause inconsistency between a production plan and an actual outcome. The complexity generally can be divided in two categories, the static complexity and the dynamic complexity, which can be computed using the ant ropy formula. The formula considers the probability of a system in different scenarios in which it can happen and based on the formula it computes the complexity of the system. However, the method is not able to make a difference between the complexities of different scenarios such as busy, idle, setup, etc. This paper presents a new algorithm to compute the complexity of a static production planning. Our method ranks the importance of the complexity for each scenario and then computes the complexity of the overall system.
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Pages 59-72The relationship between velocity of chemical reactions with activities or concentrations of their reactants, temperature and pressure and the mechanisms through which the reactions proceed are of interest to many scientists and engineers. The purpose of this article is to introduce a computer software that is developed for calculation, classification and collection of such data. The application of this software to the homogeneous and heterogeneous processes occurring in porous and non-porous media of flat, cylindrical or spherical geometry is tested. The software is capable of assisting the professional process design engineers as well as the general process kinetic investigators.
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Pages 71-78The effects of using both directions and directional subdividing on adaptive gridembedding on the computational time and the number of grid points required for the same accuracy are considered. Directional subdividing is used from the beginning of the adaptation procedure without any restriction. To avoid the complication of unstructured grid, the semi-structured grid was used. It is used to solve three test cases, transonic and supersonic inviscid flows in channels with circular arc bump and with convergent part. The Euler equations are integrated to steady state by an explicit, finite volume, Ni’s Lax-Wendroff type. In this work, multi-grid technique is applied to increase the convergence rate. The directional subdividing is more complex than both directions subdividing. However, the results show that for the same accuracy, directional subdividing considerably reduces the number of grid points and the computational time.
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Pages 79-88one of the simplest numerical integration method which provides a large saving in computational efforts, is the well known one-point Gauss quadrature which is widely used for 4 nodes quadrilateral elements. On the other hand, the biggest disadvantage to one-point integration is the need to control the zero energy modes, called hourglassing modes, which arise. The efficiency of four different anti-hourglassing approaches, Flanagan (elastic approach), Dyna3d, Hansbo and Liu have been investigated. The first two approaches have been used in 2 and 3-D explicit codes and the latters have been employed in 2-D implicit codes. For 2-D explicit codes, the computational time was reduced by 55% and 60% for elastic and Dyna3d, respectively. However, for 3-D codes the reduction was dependent on the number of elements and was obtained between 50% and 70%. Also, the error due to the application of elastic methods was less than that for Dyna3d when the results were compared with those obtained from 2-points Gauss quadrature. Nevertheless, the convergence occurred more rapidly and the oscillations were damped out more quickly for Dyna3d approach. For implicit codes, the anti-hourglassing methods had no effect on the computations and therefore a 2-points Gauss quadrature is recommended for implicit codes as it provide the results more accurately.
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Pages 89-98The paper begins by outlining the role and importance of coal as a source of energy and in the steel industry. It briefly describes the longwall method of working together with the conventional machinery used in the method. A mathematical model is then proposed that shows the relationship between the gradient of the coal seam, that of the face and the entries to the panel. Determination of a model that mathematically shows the economically best location for the longwall panel with regards to the seam gradient is the core section of the paper which is accomplished by introducing an objective function and devising its component models. The model is then subjected to sensitivity analysis. The results can assist the mining engineer in determining the most economic location for the longwall panels.
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Pages 99-108Irregularities are inherent to virtually all fibers, including the conventional textile fibers, the high-performance brittle fibers and newly developed nano-fibers. These irregularities can fall into two main categories: dimensional or geometrical irregularity (external) and structural irregularity (internal). For natural fibers such as wool, diameter variation along fiber length is atypical example of fiber dimensional or geometrical irregularity, while the presence of flaws and defects within a fiber signifies structural irregularity. The irregularities of fibers are bound to have major impact on the mechanical behavior of fibers. In recent years, there has been a growing awareness of the importance of this particular fiber attribute – fiber irregularity, particularly the within-fiber diameter variation. Instruments have been developed to accurately measure fiber diameter variations. In addition, with the development of computing technology, numerical modeling technique has been applied to examine the impact of fiber irregularity on fiber mechanical properties.This paper reviews research progress in the area of fiber geometrical irregularity and its effect on important fiber mechanical properties.