International Journal of Engineering
Volume:15 Issue: 3, Sep 2002

The non-orthogonal boundary-fitted coordinate transformation method is applied to the solution of steady three-dimensional momentum and energy equations in laminar flow to obtain temperature field and Nusselt numbers in the thermal entry region of straight ducts of different cross sectional geometries. The conservation equations originally written in Cartesian coordinates are parabolized in the axial direction and then transformed to the non-orthogonal curvilinear coordinate system to handle arbitrary duct geometries. The transformed equations are discretized using the control-volume finite-difference approach in which the convective and diffusive terms are discretized by the upwind and central difference schemes respectively. The discretization equations are solved by a line-by-line TDMA algorithm. Numerical results of Nusselt numbers and temperature profiles are obtained for constant wall temperature boundary condition and Pr = 6.78.

Power stations with high heads are nowadays almost without exception designed so as to have one pipeline, or a few pipelines, supplying the water to the turbines. The penstocks are connected to a distributor, which has the task of distributing the flow with the lowest possible losses of energy to the individual turbines. The function and location of this section of the plant make it understandable that its safety is regarded as a matter of outstanding importance. Careful selection of materials, followed by continuous and extremely meticulous inspections of work-pieces and production processes enable the manufacturer to rule out unwarrantable risks as regards materials. Furthermore, well-substantiated method of computation and experimental stress investigations make it possible to control stresses occurring in the complicated bifurcations. Thus adequate safety and economical design of the construction are ensured by suitable matching of stress levels to the properties of the materials used. The experimental work included over the two of three types of different sickle rib geometries on non-symmetric wye-branch upon certain critical flow conditions are presented. The objectives of the studies were to determine the influence of the geometry and size of sickle rib on head losses in Karun I conical wyes. The prototype of wye consists of six conical at the main and three extended cylindrical, one for inflow and two for out flow. The scale of model is 1:25 which three types of sickle ribs can be assembled on the model.

A new market based approach for transmission expansion planning in deregulated environments is presented in this paper. In this approach, transmission-planning decisions are made based on the electric power market conditions. The main contribution of this research is 1) Introducing a new probabilistic tool for analyzing the electric market conditions, 2) Defining new criteria for ranking transmission expansion plans according to their effects on improving the competition and facilitating fairly access to cheap generation, and 3) Presenting a new algorithm for transmission expansion planning in deregulated environments using the above tool and criteria. The characteristics of this approach are 1) It encourages competition and provides fairly access to cheap generation, 2) It considers the uncertainties including uncertainty in loads, uncertainty in bid of generators, uncertainty in availability of IPPs, and uncertainty in wheeling transactions, 3) It is a value based approach instead of cost based.

The objective of this paper is three fold. First, a general framework for development of total ergonomics model is introduced. Second, it is described how total ergonomics model may be applied in practice to intensify the productivity and working conditions of manufacturing systems. Third, it is shown whether the total ergonomics model is superior to the conventional ergonomics approach. This study is among the first to examine total ergonomics components in a manufacturing system. Total ergonomics model considers conventional ergonomics factors as well as management and organizational factors. The total factors are defined as teamwork, information flow, information exchange, training (accident prevention and mitigation and safety in addition to conventional training), management skills and organizational procedures. Control room operation and maintenance department of a large thermal power plant is chosen as the case of our study. To achieve the above objectives, an integrated approach based on total ergonomics factors is developed. Second, it is applied to the power plant and the advantages of total ergonomics approach are discussed. Third, the impact of total ergonomics factors on local factors is examined through non-parametric statistical analysis. Moreover, the importance and impacts of total ergonomics factors are shown through Cramer''s Phi coefficient and Kruskal-Wallis test. It is shown that total ergonomics model is much more beneficial than conventional approach. It should be noted that the traditional ergonomics methodology is not capable of locating the findings of total ergonomics model. The distinguished aspect of this study is the employment of a total system approach based on integration of the conventional ergonomics factors with management and organizational factors.

This paper develops a method for solving the single product multi-period production-planning problem, in which the production and the inventory costs of each period arc concave and backlogging is not permitted. It is also assumed that the unit variable cost of the production evolves according to a continuous time Markov process. We prove that this production-planning problem can be Stated as a problem of finding the dynamic shortest path from the source node to the sink node, Finally, we apply the stochastic dynamic programming to find the dynamic shortest path from the source node to the sink node and obtain the optimal production scheduled for each period.

In the present study, we analyze the multi-channel service system with ordered entryfrom finite-source and finite-storage at each channel. The arrival and service rates are assumedto be state dependent. The steady state probabilities of the system are obtained by usingChapmann-Kolmogorov equations. Some other performance indices viz. utilization of servers,expected number of units in the system and expected number of units at each channel have beenderived. A computational algorithm is developed to determine the optimal allocation of storagespace facilitated in front of three heterogeneous servers. Sensitivity analysis has been carried outto study the effect of variation of different parameters on the system performance.

The initial stage of fretting fatigue crack growth is significantly influenced by tangential force induced by fretting action along the contact surface where a mixed-mode crack growth is involved. Fretting crack behavior of aluminum alloy 2024 was studied, taking into account the problem of contact asperities. Finite element was used for the determination of the stress field near the contact surface and the stress intensity factor. The results showed that tensile stress maxima are situated at the trailing edge of the contact zone. Experimental results showed that the crack initiates from the trailing edge of the contact zone too. The crack extension angle was calculated and compared with experimental results at different normal loads. The stress intensity factor increased with increasing friction. The crack initially grows in combined mode I and II before deflecting to mode I plane. Delamination, one of the wear mechanisms, has been observed in our experiments too.

Laminar natural convection from an array of horizontal isothermal cylinders confined between two vertical walls, at low Rayleigh numbers, is investigated by theoretical and numerical methods. The height of the walls is kept constant, however, number of the cylinders and their spacing, the distance between the walls and Rayleigh number have been varied. The optimal spacing (confining walls) and the maximum Nusselt number predicted theoretically are validated by means of numerical simulations. It has been shown that with increasing the number of cylinders or their spacing the optimal spacing will increase. In addition, increasing the Ra number decreases the optimal spacing of the walls.

A finite-volume model has been developed to study incompressible forced flow heat transfer of air over a circular cylinder in cross flow. An artificial compressibility technique is applied to couple the continuity to the momentum equations. The proposed explicit finite-volume method (FVM) uses a novel discretization in time and space. The governing equations are solved by time-marching using a new third- order algorithm at each time level. The discretization of the viscous and thermal conduction terms are very simplified using the new scheme instead of common methods. The new scheme is similar to the Jameson''s flux averaging in the convective terms, while for viscous and thermal conduction terms, the first- order derivatives are averaged in the vicinity of two cells. The proposed model is able to converge at higher Reynolds numbers up to 101000. The numerical results agree well with the available experimental and numerical data. The proposed FVM is capable of capturing the flow details at wide range of Reynolds numbers.