International Journal of Engineering
Year:2004 | Volume:17 | Issue:3 (TRANSACTIONS B: APPLICATION)|Papers Count:10

A pressure-based implicit procedure to solve the Euler and Navier-Stokes equations on a nonorthogonal mesh with collocated finite volume formulation is described. The boundedness criteria for this procedure are determined from Normalized Variable diagram (NVD) scheme. The procedure incorporates the eddy-viscosity turbulence model. The algorithm is tested for inviscid and turbulent transonic aerodynamic flows around airfoils for different Mach number and angle of attack where the results are compared with other existing numerical solutions for inviscid flow and with experiment and another numerical solution for the turbulent case. The comparisons show that the resolution quality of the NVD scheme is considerable.

The purpose of this paper is to analyze the effect of a particular control doctrine applied to the service mechanism of a queuing process with lapse. It is assumed that the service discipline is FCFS (first come, first served), arrival process is Poisson, service time distribution is exponential, service process is one phase and the capacity is infinite. It is also assumed that the customer may give up joining the system when the queue is overcrowded. Expressions are obtained for queue length probabilities for describing control performance. The aim of which is to decrease customer’s expectancy time via incorporation of a service cost structure. The model is executed by two control methods, namely the single level control and double level hysteretic control. Finally, the results are compared with each other through solving a numerical example.

In this paper, we consider the call admission problem in cellular network with two classes of voice users. In the first part of paper, we introduce a two-threshold guard channel policy and study its limiting behavior under the stationary traffic. Then we give an algorithm for finding the optimal number of guard channels. In the second part of this paper, we give an algorithm, which minimizes the number of channels subject to hard constraints on the blocking and dropping probabilities of calls. Finally, we propose an optimal prioritized channel assignment for multi-cells cellular networks with two classes of voice users.

This paper presents an efficient modeling method, based on the microstrip lines theory, for the coupling between a sub­strate backplane and a device contact. We derive simple closed-form formulas for rapid extraction of substrate parasitics. We use these formulas to model spiral inductors as important substrate-noise sources in mixed-signal systems. The proposed model is verified for the frequencies up to 35 GHz, and is easily adaptable to CAD tools.

When depth of flow past a river bridge exceeds opening under the bridge, the flow under the bridge becomes pressurized. The water is directed downward and under the bridge deck, causing increase in velocity and shear stress on the bed thereby increasing bed scour. This is termed as Pressure Flow Scour. The present study investigates the phenomenon of pressure flow scour resulting from a submerged bridge deck over an unprotected erodible bed. Velocity of approaching flow, depth of flow, degree of submergence and width of bridge are some of the parameters that are likely to affect the scour under a submerged bridge. The effect of fluctuations in the flow depth on the depth of scour increases with decrease in constriction. The experimental data of Edward et al. (1) has been merged with the present study and a conceptual relation is developed between scour depth and degree of submergence in the form of scour fraction and constriction ratio. For incipient flow conditions on the upstream of a submerged bridge, the final clearance under the bridge is equal to the depth of approaching flow. The study has been extended to include effect of unsteady flow in the form of a hydrograph, Interference of two similar submerged bridges, Interference of a submerged bridge with an un-submerged pier and a submerged bridge in conjunction with a circular bridge pier.

This report is the result of a research project on a pavement management system that was preformed by the Transportation Division of Iran University of Science and Technology. Information used in the project was collected from 20 zones of the Tehran Municipality. Any maintenance and repair system for roads is normally compared of a number of general and coordinated activities in conjunction with programming, designing, construction, maintenance, evaluation, and research on road pavement. Prediction of pavement condition is one of the most important parts of such system. Prediction models have their application at the network level as well as project level activities. At the network level it is used in predicting the condition for budget planning. While in project level it is used in economical analysis. Many factors have been used to determine the pavement condition. These factors are the design life of the pavement, loading, climatic condition, and the type of roadway. In order to plan for future improvements, you need to predict the future condition of the pavement. In this paper, factors affecting the prediction of pavement condition are discussed. A model is developed exclusively for Tehran, based on the distress data collected of pavement condition.

The influence of compaction water content on the structure has been well known for clayey soils, but has never been studied for granular materials. In this paper the structure of a non-plastic till and the effect of compaction moisture is investigated by means of water retention curve study, scanning electron microscopy and mercury intrusion porosimetry tests. The results show that when compacted on the dry side of the optimum water content, the porous system is characterized by a relatively uniform medium pores, while in case of compaction on the wet side, pores size is very diversified and the numerous small pores dominate the porous system. The difference in the structure was also approved by measuring the rigidity and the coefficient of permeability showing a less rigidity and permeability in case of compaction on the wet side.

Treatment of wastewater containing carbohydrates by Pichia saitoi growing on beet molasses was investigated in a well-mixed continuous tank as an alternative to bulking control.The yeast strain that used in this work was isolated from non-alcoholic beverage industrial wastewater, with a view on TOC removal compared with other strains in previous study.In this research the isolated yeast showed high COD and TOC removal at three hydraulic retention times, HRT= 48, 24 and 18 hours.Maximum COD and TOC reductions were obtained at HRT=48 hours, which were 96% and 88%, respectively.The influent COD and TOC were 2500 and 148 mg/l, respectively.The pH maintained for synthetic wastewater was about 9.The changes of pH within the aeration tank at each HRT was monitored.Effects of organic loading rate (OLR) on COD and TOC reduction efficiencies were studied in this work.Aeration rate was between 0.2-0.25 vvm, which was very low in comparison to the other studies.This yeast strain had high settling ability (maximum SVI was observed at 60 ml/g) and also high F/M ratios (maximum of F/M was 2.9 kg COD/kg MLSS.day).

In this paper, we study N-policy for a finite population Bernoulli feedback queueing model for machine repair problem with degraded failure. The running times of the machines between breakdowns have an exponential distribution. The repair times of the machines are independent and identically distributed random variables. If at any time a machine fails, it is sent to the repairman for repairing, the repairman restores the machine to the state as before failure. When the failed machine finds the repairman busy upon its failure, it has to wait until its turn as repairman stores only one machine at a time. When all the standby components are used, the failure of components occurs in a degraded fashion. To obtain the steady-state probabilities, the supplementary variable is introduced and a recursive method is employed. Some performance measures viz. expected number of down machines, expected number of machines waiting for repair in the queue, expected number of operating machines, expected number of spare machines, machine availability, etc. are established. Some special cases are deduced that match with the earlier existing results. To provide sensitivity analysis, numerical experiment is performed.

Analysis and practical implementation of the regular symmetric sampled three-phase PWM inverter waveform has been presented in this paper. It is digitally implemented on a Xilinx field programmable gate array FPGA, and the essential considerations involved in the feasibility of using a Xilinx XC4008E software-based to generate PWM has been discussed. All the necessary Xilinx hardware/software techniques and programs required to implement and generate three-phase Pulse Width Modulation (PWM) are developed in detail, and demonstrated using practical results from an experimental Xilinx board. The techniques developed and presented in this paper are readily applicable to other currently available Xilinx chips. Simulation and experimental results of grid-connected inverter are presented. From the simulation and experimental results it is confirmed that the harmonic distortion of the output current waveform of the inverter fed to the grid is within the stipulated limits laid down by the utility companies