International Journal of Engineering
Volume:17 Issue: 1, Feb 2004

The experimental study reported here is intended to evolve new designs of stilling basins for deep and narrow openings used as outlets. Several appurtenances such as grid, Impact wall, stepped wall, weir wall, sloping end sill and wedge shaped blocks are used to study their influence on the hydraulic performance of the stilling basins with an aim to propose efficient stilling basin models. All the models were tested at inflow Froude number Fr = 4.89 keeping a constant run time and same erodible bed material for each stilling basin model for comparison of the performance. The performance of each model was evaluated by observing the maximum depth of scour and its location after the end sill. A non-dimensional number named as Scour Index has been evolved for comparing the performance of the different stilling basin models. The use of wedge shaped blocks as a splitter block and baffle blocks reduced the depth of scour indicating a significant dissipation of energy and good flow conditions, downstream of the stilling basin.

Switched reluctance motor (SRM) drive has remarkable characteristics that make it attractive for high-speed applications. As the motor''s speed increases the shape of the current waveform changes in such way that limits the production of motoring torque. At high speeds, it is possible for the phase current never reaches the desired value due to the self e.m.f. of the motor, therefore, the torque falls off. In order to remedy this problem, the phase turn on angle is advanced in such way that the phase commutation begins sooner. Advancing the commutation angle offers the advantages of getting the current into the phase winding while the inductance of the phase is low, and also of having a little more time to get the current out of the phase winding before the rotor reaches the negative torque region. Since the SRM drive is a variable speed motor then, the amount of advancing for the turn on angle should be accomplished automatically according to the speed of the motor, meaning, as the motor speed increases so should the turn on angle and vice versa. In this respect, this paper introduces an electronic governor using a P.L.L. module in conjunction with a micro controller to achieve this task for a desired speed/advancement angle profile, which is considered to be linear in this study. The governor causes 0-14 degrees automatic adjustment in the turn on angle from stand still to a pre-set speed for a SR motor. A linear analysis of the current waveform for the motor under different advancements of the turn on angle has been performed and the plots are shown. Finally, the experimental results of employing the governor on a 6 x 4 SRM drive are presented.

A very low voltage 9th order linear phase baseband switched capacitor (SC) filter has been designed to be used as part of a cellular GSM (Global System Mobile) receiver. A Gaussian-to-6dB filter of the order of seven is chosen and a second order function is added to reduce the group delay variations around. The filter uses a fully differential topology to increase the dynamic range and reduce the clock feed-through noise and the distortion due to low voltage amplifier. Using a chopper stabilization technique in opamp design reduces the flicker noise. In order to reduce the charge injection two methods of delayed clock phases and dummy switches are used. The filter is realized by cascading the biquad sections. The filter has been designed in a 0.35μm CMOS technology and simulated with Hspice using BSIM 3V3 model. The filter operates at 2MHz sampling frequency and 1MHz chopping frequency with a corner frequency of 100KHz and 7mW power consumption.

Photonic band-gap (PBG) crystals offer new dimensions of freedom in controlling propagation of electromagnetic waves. The existence of stop-bands in the transmission characteristic of these crystals makes them a suitable element for the realization of many useful microwave and optical subsystems. In this paper, we calculate the propagation constant of a one-dimensional (1-D) photonic crystal by using an equivalent transmission-line network. The method is expanded for structures with arbitrary variation in relative permittivity. The effect of filling factor and relative permittivity on the width of the band-gap and its frequency is also investigated.

This paper presents a modified method for approximating nonlinear systems by a sequence of linear time varying systems. The convergence proof is outlined and the potential of this methodology is discussed. Simulation results are used to show the effectiveness of the proposed method.

Due to the importance of longest path analysis in networks of queues, we develop an analytical method for computing the steady-state distribution function of longest path in acyclic networks of queues. We assume the network consists of a number of queuing systems and each one has either one or infinite servers. The distribution function of service time is assumed to be exponential or Erlang. Furthermore, the source node can include an M/G/∞ queuing system. The length of the arcs connecting the nodes of the network is assumed to be independent random variables. In the proposed method, the network of queues is transformed into a relevant stochastic network. Then, we compute the distribution function of longest path from the source node to the sink node in the transformed stochastic network. This is done through solving a system of linear differential equations with non-constant coefficients, which is obtained from a related continuous-time Markov process.

In this paper we are to present a practical application of Axiomatic Design (AD) methodology, as a roadmap to lean production, in redesigning a car body assembly line. Axiomatic Design theory provides a framework to simplify the whole problem. According to the AD principles, a hierarchical structure has been developed. The developed structure originated in lean manufacturing principles and existing conditions of an assembly line, revealed that elimination of all kinds of waste is a prerequisite for other functional requirements. Several main sources of waste were recognized in the assembly line and some practical solutions are suggested to alleviate these problems. In the initial survey, it became obvious that high work-in-progress is the major problem of this assembly line, which is the symptom of an unbalanced flow. Two cells have more problems than others and require to be modified first: the door cell and the underbody cell. Based on the hierarchy, these cells are redesigned. In addition to interior space of the cells, two automatic material handling systems -overhead chain conveyor- are employed respectively to facilitate handling operation of these cells. Main Line is another part of the assembly line, have to being modified by adding spot welding robots. The proposed plan is justified both technically and economically to the managers of the assembly line.

To cope with fast changing customer requirements, industrial demands and to meet stringent specifications of customers Cellular Manufacturing Systems has become an effective tool in hands of manufacturers. Most of the published literature on cell formation earlier considers only the data available in the route sheets and ignored subproblems associated with cell formation. There is a need to develop an integrated approach for Cellular Manufacturing, which considers all the aspects. Present paper focuses on developing an integrated approach for Cellular Manufacturing. Proposed method considers workload, volume of production and processing times for machine cell and part family formation, which was ignored by past researchers. Proposed method has been tested on one of the largest public sectors in Asia and the benefits that can be obtained by implementation are reported.

A numerical study on mixing of hydrogen injected transversely into a supersonic air stream has been performed by solving Two-Dimensional full Navier-Stokes equations. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The main objectives of this study are to increase the mixing and combustion efficiencies, and the flame holding capability of a supersonic combustor. The performance of combustor has been investigated by varying the distance of injector position from left boundary keeping constant the backward-facing step height and other calculation parameters. The results show that the configuration for small distance of injector position has high mixing efficiency but the upstream recirculation can not be evolved properly which is an important factor for flame holding capability. On the other hand, the configuration for very long distance has lower mixing efficiency due to lower gradient of hydrogen mass concentration on the top of injector caused by the expansion of side jet in both upstream and downstream of injector. For moderate distance of injector position, large and elongated upstream recirculation can evolve which might be activated as a good flame holder.

A numerical study on mixing of hydrogen injected transversely into a supersonic air stream has been performed by solving Two-Dimensional full Navier-Stokes equations. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The main objectives of this study are to increase the mixing and combustion efficiencies, and the flame holding capability of a supersonic combustor. The performance of combustor has been investigated by varying the distance of injector position from left boundary keeping constant the backward-facing step height and other calculation parameters