Journal of Advanced Materials in Engineering (Esteghlal)

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There are several sources for pressure oscillations in solid propellant rocket motors. Oscillatory flow field is one of them. Free shear layers in motor flow field cause vortex shedding. End edges of propellant grains and baffle edge in two-segmented motors are samples of such zones. These vortices move from their forming points and strike the field walls. The kinetic energy of vortices change to pressure, forming acoustical pressure oscillations. Acoustical characteristics of pressure oscillations such as frequency and amplitude change with the gradual change in the internal geometry of the motor. In this paper, the interaction between mean flow and acoustic field in a solid propellant rocket motor is studied numerically. Roe’s flux function in an unstructured grid strategy for solving compressible viscous flow equations show large changes in frequency of pressure oscillations in motor. Six different motor geometries are used for simulation of motor internal geometry at different burning times and grain configurations. Using this methodology, the frequency and intensity of pressure waves are well predicted. It is also shown that frequency jump from second longitudinal mode to the first is formed as a result of changes in the internal geometry.

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The compounds, lanthanium chromite, lanthanium magnetite and lanthanium ferric oxide were prepared through sol-gel methods in powdered form, then calcinated, peletized, and sintered at various temperatures. Electrical conductivity of these compounds was measured at various temperatures. The effectiveness of strontium as a dopant on electrical conductivity was also investigated. Electrical conductivity enhancement was observed in dopped compounds

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Air-jet weaving is an advanced weaving method with high efficiency and productivity. It is one of the most widely used methods of weaving in the world. In air-jet filling insertion, the motion of weft yarn is caused by friction between weft yarn and air blown through nozzle. After declamping and subjecting the yarn to air stream, its motion is not active but very complicated and influenced by structural properties of yarn and air stream factors. Researchers have tried to obtain the yarn motion equations in order to analyze and simulate the air-jet weft insertion system. The results could then be used in the optimization of weaving operation and machine design. In the present work, a single-nozzle loom was simulated by obtaining the weft yarn motion equation. The position, the velocity and the weft yarn tension graphs were obtained by numerical soloution of weft yarn motion equation. This analysis provided useful information for controlling the weft yarn tension in air-jet loom.

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The base isolation systems are among the passive control devices that have been used over the last three decades to limit the seismic-induced response of structures. In this regard, the Uniform Building Code provisions (UBC) has incorporated a special section for the seismic design of base isolated structures since its 1991 edition. Due to the importance of the behavior of these structures under seismic loading, and to evaluate the equivalent static analysis method of UBC97, a three dimensional, 4-story base-isolated structural model is selected. Considering 8 different types of the LRB base-isolation systems, the 8 structural models are designed using the UBC97 provisions for these structures. Extensive nonlinear dynamic time history analyses are performed for these structural models, using five pairs of earthquake components recorded on the SA and SB soil profile types according to the UBC97 provisions in the dynamic analyses, both the base isolation systems and the superstructure are allowed to behave nonlinearly (bilinear). The results indicate that the UBC97 suitably predicts the base shear force for the superstructure, but that it does not provide isolation systems. Also, underestimation of elastic force for the higher floors by UBC97, considered to be the main reason for the nonlinear behavior of the columns of these floors, revealed in the dynamic time history analyses. Besides, the corner and the center bearings’ displacement of the base floor predicted by the equivalent static method of the UBC94 were usually larger than their mean dynamic time history response. This issue has been appropriately modified in the UBC97. In addition, to provide the required strength capacity for the columns of the higher floors, an alternative shear force distribution over height for the base isolated structures is proposed. The results of the nonlinear dynamic analysis performed indicates that there is a closer match between the mean response of the structures designed by proposed shear force distribution and those obtained from the equivalent static method of the UBC97 provisions.

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Accurate estimate of flood flows at selected return periods is a fundamental step in flood control and design of hydraulic structures. Due to the inadequacy or unavailability of flood flow records in several western catchments of Iran, traditional regional flood frequency methods lead to remarkable estimate errors, particularly for long return periods. In this research, discriminant analysis is used to allocate catchments short of adequate records to defined regions, and rare discharges for the catchments are estimated subsequently. The discriminant model validation is evaluated and the results show low estimate errors.

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This paper presents the results of a recent project of IKCo’s research center to modify Paykan 1600’s rear suspension mechanism with the purpose of improving comfort, stability and handling qualities. The car was originally equipped with a solid rear axle with leaf springs. By replacing the original mechanism with a three-link mechanism with panhard bar and coil springs, the ride comfort and handling characteristics of the car were noticeably improved. 7DOF ride and 3DOF handling models were developed and analyzed to determine the important kinematic and dynamic effects of the new mechanism such as Roll Center and Roll Stiffness on vehicle responses. To verify analytical results, subjective tests were carried out on the vehicle. The results demonstrated remarkable improvement of the car’s dynamic behavior.

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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, , 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

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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 in 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.

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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 Current-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.

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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 150 ppm, average temperature of 26.9°C and under flow rates of 6 and 12 l.min-1 was more than 95% the results for average temperature of 20.5°C and the flow rates of 19.5 and 26 l.min-1 but 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 32.5 ppm

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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.

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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 proposed method in doing nonlinear analysis and in obtaining exact and accurate results.

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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 to fine aggregates (gravel to sand), i.e. 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.

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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. METAFONT 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 METAFONT 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.

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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 computer’s 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 PC’s 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.

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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.

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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, i.e. 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. Keywords: Heat Generation, Rubber, Contact Friction, Design, Finite Element, Viscoelastic Deformation

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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 Morrison’s equation. But for irregular flows where the flow pattern changes in each cycle, there is less overlap and the accuracy of Morrison’s 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 a pure mode, matching the experimental results. Keywords: Oscillating flow, Laminar flow about a cylinder, Numerical solution

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In 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. Keywords: Multiple Shooting Method Minimum time Thrust-Vectoring Maneuverability Aerodynamics

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Hydroxyapatite coatings have been used on metallic substrates in a variety of applications, including modifying the surface of human implants, bone osseointegration and biological fixation. 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 . Keywords: Hydroxyapatite coating, Dental endodontic implant, Osseointegration, Corrosion, Stainless steel, Cobalt base alloy