International Journal of Engineering
Volume:23 Issue: 1, Jan 2010

The problem of steady, laminar and incompressible natural convection flow in an octagonalenclosure was studied. In this investigation, two horizontal walls were maintained at a constant hightemperature, two vertical walls were kept at a constant low temperature and all inclined walls wereconsidered adiabatic. The enclosure was assumed to be filled with a Bousinessq fluid. The studyincludes computations for different Prandtl numbers Pr such as 0.71, 7, 20 and 50 whereas the Rayleighnumber Ra was varied from 103 to 106. The pressure-velocity form of Navier-Stokes equations andenergy equation were used to represent the mass, momentum and energy conservations of the fluidmedium in the enclosure. The governing equations and boundary conditions were converted todimentionless form and solved numerically by penalty finite element method with discretization bytriangular mesh elements. Flow and heat transfer characteristics were presented in terms of streamlines,isotherms and average Nusselt number Nu. Results showed that the effect of Ra on the convection heattransfer phenomenon inside the enclosure was significant for all values of Pr studied (0.71-50). It wasalso found that, Pr influence natural convection inside the enclosure at high Ra (Ra > 104).

A collocation method with the modified equilibrium on line method (ELM) forimposition of Neumann and Robin boundary conditions is presented for solving the two-dimensionalacoustical problems. In the modified ELM, the governing equations are integrated over the lines onthe Neumann (Robin) boundary instead of the Neumann (Robin) boundary condition equations. Inother words, integration domains are straight lines for nodes located on the Neumann boundary.Numerical examples of two-dimensional acoustical problems are presented to demonstrate thestability, accuracy and convergence of the proposed method.

Substrate noise generated by digital circuits on mixed-signal ICs can disturb the sensitiveanalog/RF circuits, such as Low Noise Amplifier (LNA), sharing the same substrate. This paperinvestigates the adverse impact of the substrate noise on a high frequency cascode LNA laid out on alightly doped substrate. By studying the major noise coupling mechanisms, a new and efficientmodeling method is proposed to predict, prior to processing, the LNA performance degradation due tothe substrate noise. Our simulations prove that the model can estimate the magnitude of the spurioussignals appearing at the output spectrum of the 5 GHz LNA, within an acceptable error of 13%.

The increasing consumption of electricity over time forces different countries to establishnew power plants and transmission lines. There are various crisp single-objective mathematicalmodels in the literature for the long-term power generation and transmission expansion planning tohelp the decision makers to make more reasonable decisions. But, in practice, most of the parametersassociated with the input data, such as forecasted demands for electricity consumption, economic andtechnical characteristics of new evolving generating and transmission technologies are imprecise(fuzzy) in nature. Moreover, making such strategic decisions require considering several objectivessimultaneously and applying appropriate multi-objective programming approach to yield severalcompromise solutions. In this paper, we take into account these main characteristics of the problem inour proposed model. Also, the maintenance cost of generation units is modeled in such a way thathandles its increasing nature over operating periods. Consequently, we propose a new fuzzy multiobjective mixed integer linear programming model (FMOMILP) for integrated power generation andtransmission expansion planning problem. After applying the effective strategies to convert theoriginal FMOMILP into an equivalent single objective crisp one, through an illustrative example weshow that the results obtained by proposed fuzzy model is more reliable than the crisp one. Finally,some concluding remarks are also provided.

In this paper we examine fluctuation and frequency of the governing equation ofoscillator with odd and even nonlinearities without damping and we present a new efficientmodification of the He’s homotopy perturbation method for this equation. We applied standard andmodified homotopy perturbation method and compare them with the numerical solution (NS), also weapplied He’s Energy balance method (EBM) for study frequency of this equation. By comparemodified homotopy perturbation method with numerical solution we find that this modified homotopyperturbation method works very well for the wide range of time and boundary conditions fornonlinear oscillator, and comparison of the result obtained using this method for frequency with thoseobtained by Energy balance method reveals that the former is very effective and convenient. The newmodified method accelerates the rapid convergence of the solution, reduces the error solution andincreases the validity range for fluctuation and frequency.

With the aim of extending the use of integrated variational principles on fluid and deckplate to the large deflection analysis of floating roofs، this paper investigates the significance of theflexural and membrane components in the formulations of the deck plate. Applying integratedvariational principles on deck plate and fluid facilitate the treatment of the compatibility ofdeformation between floating roof and supporting liquid. Analysis results showed that differentassumptions about deck plate formulation were commonly used in the literature which resulted inconsiderably different deflection and stress patterns on the floating roof. The results showed thatmodeling of the deck plate as a flexural element rather than membrane، by eliminating the need fornonlinear analysis، gave reasonable results for deflections and stresses in the deck plate. Finally، asimple and efficient procedure using linear finite element code analyzes of the floating roofs،considering only the flexural stiffness was developed.

The effect of imposed magnetic field on natural convection in a tilted cavity with partially active walls was investigated numerically. The active part of the right side wall was at a higher temperature than the active part of the left side wall and were moving on vertical walls relative to each other. The top، the bottom and the remaining parts of the side walls were insulated. The magnetic field was perpendicular to the side walls. The SIMPLER algorithm was used to indicate the pressure gradient in the momentum equations. Flow field and heat transfer were predicted for fluid with Pr = 0. 71 and a wide range of the governing parameters such as Rayleigh number between 104 and 106، Hartmann number between 0 and 100، aspect ratio between 0. 5 and 2 and inclination angle between 0°and 90°. The average Nusselt number decreased with an increase of Hartmann number and increased with an increase of Rayleigh number. The maximum heat transfer rate was occurred for the middle–middle thermally active locations while heat transfer was poor for the bottom-top thermally active locations.

The Ocean has provided a new avenue in the quest for renewable energy. One potentialsource of energy is marine current, which is harnessed using either vertical or horizontal axis turbines.This paper describes a particular type of vertical axis turbine which is suitable for low current velocityapplications. The simulation of Savonius-type turbine, which hitherto has never been proposed formarine current energy application, is presented in this paper. A 3D computational model was builtand analyzed using a Computational Fluid Dynamic analysis using proprietary software. The overlapratio is identified as one of the important factors in Savonius turbine performance. This paperprovides results of the investigation for a range of overlap ratios between 0.1 and 0.6 and it was foundthat the maximum torque can be obtained at overlap ratio of 0.21.

Nanofluids, in which nano-sized particles (typically less than 100 nm) are suspended in liquids, have emerged as a possible effective way of improving the heat transfer performance of common fluids. In this paper a numerical study is performed to analyze the wall shear stress and heat transfer coefficient of γAl2O3-water nanofluids under laminar forced convection through a circular pipe. It is assumed that the distribution of nanoparticles in the flow field is nonhomogeneous. The results obtained show that addition of γAl2O3 nanoparticles to pure water effectively enhances the convective heat transfer. Moreover, the wall shear stresses are increased. The increasing rate of heat transfer depends on the volume concentration such that for the lowest and highest values of particle volume concentration 0.03 and 0.05, considered in this study, the heat transfer enhancement is approximately 23% and 40%, respectively. Also, compared with the available experimental data, the model used in this work is capable to predict the increasing rate of heat transfer of nanofluids properly.

The purpose of this work is to assess and develop experimental techniques that allowwicking measurement over a wide range of textiles. Various kinds of fabrics, nonwoven layers and anelectro spinning nylon layer were used as the test materials. A syringe is used to drop a 0.02 g spot ofdistilled water on the sample and a digital camera to take pictures simultaneously. When the wickingprocess stops, the images are processed and the increase in wicking area is measured using Matlab 7.4and a set of image processing tools. It is shown that the newly developed technique is able to test thewicking behavior of various kinds of textiles with different thickness.