ESTEGHLAL
Year:2002 | Volume:21 | Issue:1|Papers Count:17

In a de-regulated open access environment, reactive power is one of the ancillary services which must be provided by an Independent System Operator (ISO). In this paper, a new algorithm is proposed in which reactive power resources areinitially so tuned that optimum security in terms of voltage profile and voltage stability are achieved while at the same time, the system losses are minimized. The resulting optimization case is solved as an Extended Multi-objective Optimal Power Flow (EMOPF) problem using Lexico Graphic Method (LGM). Thereafter, using the concept of Fair Resource Allocation (FRA), the reactive powers generated are distributed among existing transactions so that the costs incurred are properly and fairly recovered. The algorithm is successfully tested on a typical power system.

Because of extreme local saturation at pole tips of excited phase and uncircular shape of rotor and stator, a Swithed Reluctance Motor (SRM) does not have a simple and accurate mathematical model. Therefore, the output control of this motor requires a robust controller which is not based on an accurate model of the process. Fuzzy controllers, to some extent, will satisfy these requirements. Teta-on and teta-off are controller outputs. The output of teta-off controller is proportional to the speed error. For teta-on controller we consider three different structures. Teta-on controller is a Variable Structure Controller (VSC) which contains two parts: coarse controller which is used when the speed error is large and its output causes large changes in teta-on angle. This part of the controller is similar to a fuzzy PI controller. The other part of the controller is a fine controller and is used when the speed error is low. The fine controller increases the speed of response and reduces the speed error to zero. This part is similar to a fuzzy I or PI controller. Finally, exprimental results of no-load and underload speed controls are demonstrated. The fuzzy controller robustness to measurement noise and parameter uncertainty is also studied.

In this paper, two algorithms have been developed for allocation and size determination of Active Power Filters (APF) in power systems. In the first algorithm, the objective is to minimize harmonic voltage distortion. The objective in the second algorithm is to minimize the new APF injection currents while satisfying harmonic Standards. Genetic algorithm is proposed for these two optimization problems. The simulation results for an 18-bus system show the effectiveness of the genetic algorithm for these two optimization problems.

A mathematical model has been analyzed for in-situ bioremediation with the purpose of remediating organic contaminated soil. Oxygen rich water when passed through the porous media of soil activates the aerobic microorganisms, leading to the biodegradation of the organic content. The model equations comprise three convection-dispersion partial differential equations and one ordinary differential equation. Dimensional analysis of the model equations has been performed and the solution of these equations has been conducted using the finite difference method. The effects of insufficient oxygen supply, growth of biomass and resistance to contaminant migration on the rate of biodegradation have been analyzed by numerically solving the equations.The results from the numerical simulation indicate that the rate of biodegradation of contaminants in soil may be constrained not only by insufficient oxygen supply, but also by resistance to contaminant migration within the pore network.

A Two-phase model for configuring a cellular manufacturing system is proposed. In phase (I), for the first time, number of cells is considered as a decision variable. In phase (II), pursuing two different objectives, one minimization of under load and the other, maximization of similarity of parts within a group, the design procedure is performed. As one cannot have these two objects together, a heuristic algorithm based on cellular similarity coefficient and integration of two objects is proposed. The results confirmed that the proposed heuristic procedure has reasonable outcomes.

In most stochastic inventory models, such as continuous review models and periodic review models, it has been assumed that the stockout period during a cycle is small enough to be neglected so that the average number of cycles per year can be approximated as D/Q, where D is the average annual demand and Q is the order quantity. This assumption makes the problem more tactable, but it should not be adopted when the backorder and lost sales penalty costs are relatively small. In this paper, considering a continuous review inventory model, we relax the above assumption and we explicitly take into account the stockout period when computing the expected cycle length. Further, we consider the effect of using exact number of cycles rather than using approximate number of cycles in a continuous review inventory model.

In most cases, structural engineers assume a concrete floor to be a rigid diaphragm. Although this simplification is in most cases acceptable, it should be noted that such an assumption may be distrusted due to certain problems. Concrete structures with staggered shear walls are among those whose analysis should be conducted with special concern for the behavior of their floor diaphragms. However, in the structures with staggered shear walls, the horizontal shear due to lateral loads is transmitted to the lower stories through the floor diaphragm since the walls are not usually located over each other in consecutive stories. Therefore, the rigidity of the floor diaphragm is of great importance. In the present study, a parametric analysis was performed to investigate the effect of the rigidity of the floor diaphragm on the load-carrying procedure of the structures with staggered shear walls. The investigated parameters were the number of stories, the ratio of length to width of the plan, and the thickness of walls and diaphragms. Furthermore, the study was carried out for both rectangular and I-shape plans. All analyses were dynamically performed by ANSYS 5.4 using acceleration spectrum recommended by Iranian Building Code Standard No. 2800. Finally, the behavior of these structures and comparison of the frequencies, the maximum lateral displacements and the shear in the walls and columns as the responses of rigid and flexible diaphragms were highlighted and outlined.

As a result of the limitations in the application of Darey Law (V=ki) to linear-laminar flow regime, through porous media and due to tire fact that in coarse alluviums, the Reynolds number may exceed its critical value, the so-called Laplas equatioll cannot be used for precise analyses of coarse granular foundations. A more general relationship is. therefore Required for such cases. However, a common relationship between piezometric gradient "i" and the approach velocity "v" within porous media shown as i=m It" leads to major difficulties in undertaking complicated tests to determine tlte values of m and n. It is shown that by combining the above-mentioned relationship with the continuity equation, a differential equation may be obtained to give piezometric hem/ and a potential function j, which, in turn, lead to the uplift force distributions and the seepage quantities through porous media. To overcome difficulties associated with m and n estimations in the model and as a result of fulfilling, extensive research programme, afresh and reliable procedure has been developed and explained to assess m and n by means <!simple stepped pump-out test. The practicial applicability of the method for a given confined aquifer is also examined. Find in indicates that the proposed procedure a) makes the use of the differential equation for turbulent flow in porous media possib and b) provides means to determine the nonlinear equation parameters (m&n) at an acceptable precision. The computed values the parameters are also submitted.

The importance of the equipment and secondary systems in seismic design and performance evaluation is well recognized and has been the subject of many studies. In all of the estudies, earthquakes considered as a single component, and in most of them the primary system is considered as shear building. Most attention has been concentrated on the response of secondary systemand its response spectrum. In this paper, the transfer function for absolute acceleration of the secondary system is outlined The squared modulus of transfer function relates the power spectral density function of the input (excitation) to the output (response), which is useful in the study af the various dynamic parameters of the system. In addition to the transfer function, the autoco elation and power spectral density functions of absolute acceleration of the secondary system are obtained. Earthquake is considered as a multi-component system and the necessary formulation is developed for the calculation of these functions as well as the critical angle with and without interaction between the two systems. The damping of the system is considered as proportional in the decoupled analysis and nonproportianal in the coupled analysis. The formulation developed has been illustrated by considering a ten-story torsional building. Various parameters such as eccentricity, correlation between components, tuning interaction and nonproportinal damping are studied. Results show that eliminating the effect of multicomponentness of earthquake can cause large errors especially at large eccentricities.

An extensive experimental investigation to understand the aerodynamic behavior of wrap around in (WAF) missile configuration has been conducted Various tests using at first a standard model (TTCP)in the transonic wind tunnel of Imam Rouein University has been performed The tunnel has a test section of 60´60 cm and can operate at Mach numbers of 0.4 £ M¥£ 2.2 and at attack angles of - 4° £a£100. Experimental longitudinal results are compared with those of NASA and an engineering code. The results for TTCP model are in good agreement. After gaining confidence on the TTCP results, a new model of WAF rocket was designed, built and tested this paper compares the results of two models tested under the same conditions.

The internal flow circulation dynamics of a liquid drop moving in a co- or counter-flowing gas stream has been numerically studied. The present work is concerned with the time accurate numerical solution of the two phase flow field at the low Mach number limit with an appropriate volume tracking method to capture motion and deformation of a liquid drop. It is shown that relative velocity between gas and liquid and the parameters controlling the deformation of the drop have the strongest influence on its internal circulation, too. The effects of the liquid Weber number, ranging from 8 to 32, and of gas stream Reynolds number, ranging from 1 to 20 are studied. It was revealed that the largest and the most lasting internal circulation are observed in drops with small deformation in high Reynolds number gas streams. In the case of counter-flowing gas stream, there is a strong internal circulation inside the liquid drop. The locations of the gas separation points on the drop are strongly influenced by the internal circulation of the drop, resulting in a complex wake dynamics.

In this study, “Buckling Limit of Strain” (B.L.S.) is introduced as one of the most important limiting factors in cold roll forming process. B.L.S. is calculated by the finite element procedure. Then for two particular processes with existing analytic and experimental results, B.L.S. has been determined and evaluated. LUSAS 12.3 is used for finite element analysis. The results show that when buckling of the sheet metal is the limiting factor, B.L.S. is in good agreement with practical limits. It has also been shown that flower pattern can be well predicted when B.L.S. is obtained and this idea is another new outcome from this study. Using this criterion to define and determine B.L.S. and to design the flower pattern is a new concept accomplished for the first time.

In this paper, mixed forced and natural convection heat transfer in a rectangular cavity has been numerically studied. The cavity receives a uniform heat flux from one side and is ventilated with a uniform external flow. The external flow enters the cavity from the heated side and leaves the cavity from the opposite side. The velocity and temperature fields and heat transfer rate are determined by solving the two-dimensional continuity, momentum and energy equations. In this research, steady-state flow with constant Reynolds number, Re=100, is considered. Rayleigh number is in the range of 0£Ra£107. First, the results are presented for a cavity with constant aspect ratio, AR=2, and four different inlet and exit opening positions. Then cases with a fixed opening position and different aspect ratios including 0.1, 0.25, 1, 4 and 10 are modeled. In the cavities with opening in the bottom or cavities with aspect ratios less than one, the results show weak effects of natural convection on heat transfer. This research has been done for air as a working fluid (Pr = 0.71). In some cases, the results are compared with those from previous studies.

In electric arc furnace steel making units, the essential parameters are reducing price, increasing production and decreasing environmental pollution. Electric arc furnaces are the largest users of electric energy in industry. The most important techniques that can be used to reduce the electric energy consumption in electric arc furnaces are scarp preheating. Stirring use of burners and hot charge and foamy slag. Between these methods, the use of foamy slag is the most useful and economical factor. Foamy slag can reduce the amount of energy, electrodes, refractory consumption, and tap to tap time while it also increases productivity.In this study, method of production and optimum conditions for foamy slag in a 200-ton electric arc furnace was investigated. The use of foamy slag in this research can reduce the electric energy consumption from 670 to 580 kwh/t and the melting time from 130 to 115 min. and that the electric power in put can be increased. It also shows that with foamy slag, the optimum amount of Fe Din slag is 20-24 percent and the optimum basicity is 2-2.2.

Observations of the Caspian Sea during August-September 1995 are used to develop a three dimensional numerical model to be used in calculating temperature and current. The model has variable grid resolution and horizontal smoothing that filters out small scale vertical motion. Data from the meteorological buoy network on the Caspian Sea are combined with routine observations at first-order synoptic station around the lake to obtain hourly values of wind stress and pressure fields. The hydrodynamic model of the Caspian Sea has 6 vertical levels and a uniform horizontal grid size of 50 km. The model is driven with surface fluxes of heat and momentum derived from observed meteorological data. The model was able to reproduce all the basic features of the thermal structure in the Caspian Sea and larger-scale circulation patterns tended to be anticyclone, with anticyclone circulation within each sub-basin. The results matched observation data.