ESTEGHLAL
Year:2001 | Volume:20 | Issue:1|Papers Count:17

New Page 1 Trigonometric functions are among the most useful functions in the digital signal processing applications. The design introduced in this paper computes the trigonometric functions by means of the systolic arrays. The method for computing these functions for an arbitrary angle, θ, is the CORDIC algorithm. A simple standard cell is used for the systolic array. Due to the fixed inputs, in some cases, a number of the cells are optimized. The control unit and a read only memory are the essential parts of any CORDIC implementation. The introduced hardware does not use any of these two structures, which makes it a simple and expandable design.

New Page 1 In this paper, a new method is proposed for the speed control of a three-phase current forced synchronous machine drive. This metohd is based on the use of an approximate constant commutation safety margin angle ill the output thyristor bridge of the drive system as well as on the compenastion of stator magnetization reaction. The commutation process in the output converter of the machine drive is naturally performed by means of the rotor induced emfs in the stator winding. In comparsion with other speed control methods reported for these types of drives, this method is more stable and robust. In additon, higher efficency and power factor can be achieved for the synchronous machine drive through this method. The impacts of rotor damper windings on the drive system performance are also explained in the paper.

New Page 1 In this paper, a new method based on genetic-fuzzy algorithm for multi-objective optimization is proposed. This method is successfully applied to several multi-objective optimization problems. Two examples are presented: the first example is the optimization of two nonlinear mathematical functions and the second one is the design of PI controller for control of an induction motor drive supplied by cuent-Source-Inverter(CSI). Step response of the system is considered and controller parameters are designed based on multi-objective optimization technique. Rise-time, maximum over-shoot, settling time and steady state error are considered as objective functions. The simulation results of the new method for induction motor speed control and optimization of two nonlinear mathematical functions are compared with the results obtained from other methods {4,14,15}, which shows better performance.

New Page 1 In order to evaluate the performance of biofilter for H2S removal from contaminated air, a 120 ×14 cm column biofilter was constructed using clear polyacrylic material in conjunction with H2S production and control systems. The column was divided into four stages using perforated plates. The column was packed with a mixture of mushroom compost and snail shell (4:1). The performance of biofilter was evaluated during 4 months of operation under various flow rates and H2S concentrations in ambient temperature. According to the results, the removal effeciency of H2S in polluted air for concentrations of up to 150ppm, average temperature of26.9"C and under flow rates of6 and 12 Lmin-I was more than 95%; the results for average temperature of 20.5"C and the flow rates of 19.5 and 261.min-1but constant H2S concentration was more than 85%. The maximum removal rate (Vm)was measured as 0.075 g S/kg-dry compost.h and average saturation constant (Ks)was 32.5ppm.

New Page 1 Zoning the pollution of a river may be the first or even the most important step in water quality management. In order to resolve its pollution, fuzzy clustering analysis may be used whenever a composite classification of water quality, incorporates mutiple parameters. In such cases, the technique may be used as  a complement or an alternative to comprehensive assessment. In fuzzy clustering analysis, the classification is achieved through a fuzzy relation. After a fuzzy similiarity matrix has been, established and the fuzzy relation stabilized, a dynamic clustering chart can be developed Given a suitable threshold, the appropriate classification ,is worked out. A. general methodology for fuzzy clustering analysis is developed and illustrated with a case study of water quality evaluation for the Zayandeh -Rood river, the results of which have been represented in a pollution zoning manner.

New Page 1 ABSTRACT-Due to- their dual behavior under tension and compression, structures with tension-only members show non-linear behavior. To analize such structures, it is necessary to use a nonlinear analysis scheme. Nonlinear analysis methods generally use gradual loading techniques with/without modification of stiffness matrix of the structure. These methods, in addition to being time consuming algorithms, are iterative and may not always lead to exact results. In this paper, an innovative technique is presented that conducts the nonlinear analysis in one step without any modification in stiffness matrix and! or load vector and gives exact results. The proposed method conducts nonlinear analysis "via solution of a Quadratic Programming problem that, in turn, is established based on some simple static rules and superposition principle. It superimposes the results of linear elastic analysis for external loads and some weighted (yet unknown) self-equilibrating unit loads. The outcome of QP problem is the unknown weights of unit loads from which internal forces are obtained. Two solved examples have been provided to show the capabilities of the ptoposed method in doing nonlinear analysis and in obtaining exact and accurate results.

New Page 1 The paper presents the results of casting and testing of  264 GFRC specimens. The glass fibers were 25 mm long, with the aspect ratio (L/D) ranging between 1250 and 3570. The parameters studied were the ratio (by weight) of fibers to cement, i.e. F/C=0%,1.5%, 3%, and 4.5%, and the ratio of coarse tofine aggregates (gravel to sand), Le. G/S=1.1 ,0.7 and 0.2. In total, 12 mix designs were selected for GFRC specimens while the water-cement ratio was constant and equal to W/C=0.4.The balling of glass fibers in the mix was overcome by using adequate and sufficient antistatic agents. The specimens were tested under compressive, tensile and flexular loading at the ages of 7 and 28 days. Furthermore, the modulus of elasticity and the absorption of the concretes were determined. Finally, the mechanical and physical properties of the GFRC specimens were analysed and an empirical expression describing the modulus of elasticity of the GFRC was proposed.

New Page 1 Solving traffic equilibrium problem, or "traffic assignment", as the last step in Transportation Planning, distributes OD trip demands of a transportation network over the network links with regard to Traffic Equilibrium Law, and estimates the link flows. in formulations of traffic equilibrium which are based on path saving, the memory consumption is considerably affected by the number of effctive OD pairs (ODs with non zero demand), thus making it impossible to solve a real life transportation problem in a computers conventional memory This paper attempts to present some methods to show that, reducing the number of effective OD pairs and compensating for the error, it is possible to solve a real life traffic equilibrium problem in a reasonable amount of computer memory and up to an acceptable precision. To do so, the traffic equilibrium problem of the city of Mashhad, as a case of a real life problem, is considered and The Aashtiani complementary algorithm which requires path saving is applied to solve the problem. Solving such a problem in a PCs conventional memory is normally impossible. Nevertheless, the methods presented in this paper allow us to solve it in a conventional memory. Comparison between the results of these methods with the original answer shows that the errors generated via these methods are quite low and acceptable. A brief comparison is finally made among the different methods.

New Page 1 In this paper, a fast method for automatic generation and scientific design of Persian letters is proposed. Scientific typeface design is an approach in which fonts are described by mathematical curves with well defined parameters, where these parameters can be automatically tuned. META FONT is a language suitable for the type of design used in this work. This language is particularly useful in designing Persian fonts because it can be used to simulate the pen movements of a calligrapher through automatic conversion of the scanned bitmap image of a font into a META FONT program, which can in turn, produce the font at a high quality. A complete software has been implemented based on these algorithms that works interactively with the user to facilitate the font design.

In this paper the problem of minimum cost communication network design is considered where the costs are piecewise linear concave. Several methods are compared: Simulated Annealing method, a heuristic based on the method proposed by Minoux, and a lagrangian method based on lower bounding procedure.

New Page 1 One of the great enemies of rubber compounds is heat. Heat will cause chemical and physical degradation of vulcanized rubber as well as a considerable loss in its strength. A major source of heat generation in a tire is due to internal friction resulting from the viscoelastic deformation of the tire as it rolls along the road. Another source of heat generation in a tire is due to its contact friction with the road. Prediction of the temperature rise at different parts of the tire will help to detect the behavior of the tire as regards its strength and its failure. In the present work, initially the data required for the thermal analysis of the tire are determined which include:- the thermal conductivity of rubber compounds, the tire rolling resistance and its heat build-up rate. The thermomechanical analysis of a typical tire then follows based on the thermodynamics of an irriversible process. The mechanical dissipatives, Le. the hystersis losses are assummed to be the major source of heat in the mathematical formulation. A finite element code is developed for two-dimensional heat transfer analysis of the tire. The results obtained show that the highest temperature rise will occur on the carcass-tread interface in a tire specially at heavy loading and under high speed conditions.

New Page 1 In this paper, the oscillating two-dimensional laminar flow about a cylinder and the oscillation of a cylinder in still water are studied. A finite volume method is applied to solve the Navier Stokes equations using SIMPLEC algorithm on a body fitted co-located O-type grid. In this study, the non-dimensional flow numbers, Keulegan-Carpenter and Stokes numbers are chosen over a range where different laminar flow regimes are normally three-dimensional The results of this simulation and comparison with numerical and experimental works indicate the good capability of this two-dimensional model in showing the various regimes of. flow patterns and vortex shedding. Considering the forces exerted on the cylinder, this study shows that in cases where the flow is of a regular type, there is a good match between longitudinal force presented by this work and the one calculated through. Morrisons equation. But for irregular flows where the flow pattern changes in each cycle, there is less overlap and the accuracy of Morrisons equation is reduced. Studying the time variation of the transversal force gives accurate information about the vortex shedding and its frequency in each cycle and mode changing. Since the flow mode changes continuously with time, the average of transversal and longitudinal forces on consecutive cycles is not a good representation of the force exerted on the cylinder. On the other hand, the model has satisfactorily reproduced the time variation of the tranversal and longitudinal forces of apure mode, matching the experimental results.

New Page 1 this paper, some results are provided for minimum time roll about velocity vector maneuvering with thrust-vectoring and aerodynamic control in effect. The mathematical model for attitude motions of the aircraft is developed. First order necessary conditions for optimality using Pontryagen principle is applied, and the existence of an extreme family of solutions for the maneuver is shown. Multiple shooting method is used to obtain the numerical results. An estimate of maneuver time reduction resulting from thrust-vectoring is obtained.

New Page 1 Hydroxyapatite coatings have been used on metallic substrates in a variety of applications, including modifying the surface of human implants, bone osseointegration and biologicalf1Xlltion. In this paper, the effects of various kinds of metallic substrate on clinical and pathological results of in vivo tests are presented. Four kinds of endodontic ,implants; i.e, stainless steel, cobalt base alloy, plasma sprayed hydroxyapatite coated stainless steel, plasma sprayed hydroxyapatite coated cobalt base alloy were prapared and implanted in mandibular canine of cats. After a healing period of 4 months, investigation by SEM and histopathological interpretation and evaluation showed significant differences in tissue response and osseointegration between coated and non-coated metallic implants. It was concluded that the results were affected by the kind of metallic substrate.

New Page 1 Zinc was electrodeposited from an acidic sulphate solution on commercial steel sheet substrates galvanostatically at 10,20, and 100 mA/cm2. The steel substrates had an average roughness number of 1.34 microns and a high percentage of its grains had their (111)planes parallel to the plate surface. During electrodeposition at 10 mA/cm2, on some specimens, there was an intense potential fluctuation around -870 m V vs Saturated Calomel Electrode (SCE). During this period zinc hydroxide precipitated on the surface. After a certain time, the potential dropped to -1020 for zinc deposition. Zinc nuclei were seen to precipitate from zinc hydroxide. Increasing current density changed nucleation mode from progressive to instantaneous, and also changed the size, morphology, and texture of zinc deposits.

New Page 1 Articulated liquid cargo vehicles transporting inflammablefuels and dangerous chemical products require special consideration when traveling on urban roads or cruising at highway speeds. The road safety and handling of these kinds of vehicles may be adversely affected when negotiating sharp turns or travelling on slippery roads, which may result in either lateral instabilities or complete rollover of these tanker vehicles. Moreover, directional instabilities in these kinds of vehicle may also introduce an excessive yaw swing or may initiate the jack- knifing of the articulated tanker trucks. In order to overcome the instabilities of these tanker vehicles, installation of lateral baffles in the form of separating walls in the tanker were considered. The static roll and yaw plane models of these vehicles including lateral translation of the liquid inside the tank were developed. Using the static roll model, the rollover threshold of the vehicle is analyzed and the effect of these separating walls on the stability of the vehicle is studied. The yaw plane model is then used to predict the transient response and stability of the tanker vehicle under various road maneuvers. The governing differential equations were solved numerically to obtain the simulation results and optimum values of the parameters.