Showing 306 results for Co
B. Ghasemi,
Volume 21, Issue 1 (7-2002)
Abstract
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.
Keywords: Convection, Natural, Forced, Cavity, Rayleigh, Ventilate
M.farzin, M. Salmani-Tehrani and S.h. Hashemolhoseini,
Volume 21, Issue 1 (7-2002)
Abstract
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 analysis 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.
Keywords: Cold Roll-Forming, Nonlinear Finite Element Analysis, Local Buckling
M. Jafarboland, H. R. Momeni and N. Sadati,
Volume 21, Issue 2 (1-2003)
Abstract
Various methods are presented to control the attitude of satellite due to lack of information of yaw axis attitude so far.
In this paper, a new method is used which is more general and is applicable to all types of satellites, with at least one controller.
This method is not limited to YAW axis and can control the two other axes as well. One feature of this approach is the ability to be modified for large angle maneuvers for special applications.
A new observer is also proposed for the controller, which causes the angles attitude to be kept in desirable values, with minimum control effort and more accuracy. Simulation results show that compare with methods using the complete all axis information, this approach is satisfactory.
Keywords: Attitude control, PID controlley, BIBO stability, pseudo observer
S. Samavi, A. Torkian and P. Khadivi,
Volume 21, Issue 2 (1-2003)
Abstract
Fabrication of an integrated circuit with smaller area, besides reducing the cost of manufacturing, usually causes a reduction in the power dissipation and propagation delay. Using the static CMOS technology to fabricate a circuit that realizes a specific logic function and occupies a minimum space, it must be implemented with continuous diffusion runs. Therefore, at the design stage, an Eulerian path should be found for the logic function. Every discontinuity causes an increase in the area as well as a reduction in the clock rate and performance.
The realization of a logic function using the static CMOS technology is done through different methods, most of which are based on the Uehara's method. In this paper, an algorithm is suggested that finds the Eulerian path and allows the implementation of the circuit with continuity in the diffusion region that results in minimum area. In a case where there is no Eulerian path, the possible sub-paths are found. In addition, the algorithm gives information that helps the layout generation.
Keywords: VLSI, Uehara's method, Static CMOS, Continous diffusion, Standard cell.
S. M. R. Khalili, M. Zohouri and A. Khorrami,
Volume 21, Issue 2 (1-2003)
Abstract
Due to the widespread applications of fiber reinforced polymer composites in various industries, the machining of these materials to reach the desired shapes, close tolerances and surface finish quality is of great importance. But the composite materials are anisotropic and are mostly prepared in laminated form and, therefore, they have special chip formation behaviour. Among the effective parameters in machining of these materials, the angle between the fiber orientation and machining direction and also the properties of fiber and matrix are of great significance. In the present paper, using the latest theories in the field of machining of FRP materials, a mathematical model to improve the feed rate as well as the cutting speed with respect to the fiber orientation has been introduced and, a computer package was developed for the 3-dimensional CNC machining of fiber composite materials. A number of composite pieces were fabricated and machined to check the output of the programme and the work pieces. Besides the reduction in the machining time, the machined work pieces had desired surface quality, while the common defects like matrix burning, delamination and fiber pullout were completely absent.
Keywords: Fiber composite Materials, Machining, Software, Cutting force, fiber orientation
M. Alizadeh and H. Edriss,
Volume 21, Issue 2 (1-2003)
Abstract
In recent years many different ways have been investigated by steel producers to increase ductility, impact strength and formability of steels. More important ways are steels with very low amounts of inclusion, small size inclusions and modified inclusions. In this study, experiments have been performed on the API-X42 steel produced by the electric arc furnace in Mobarekeh Steel Co. After the preparation of the melt in the electric arc furnace, it is taped in a 200-ton ladle and ladle treatment was preformed in a ladle furnace (LF) in the steelmaking shop. In this study the effects of amount and the rate of CaSi wire addition on the shape and structure of inclusion were investigated. The optimum conditions for adding CaSi for inclusion shape control were also determined. Scanning electron microscope (SEM) and chemical energy analysis dispersive system (EDS) showed that adding calcium to the melt affects the chemical composition of inclusions present in steel melt. The effects of CaSi wire injection treatment, injection amount and inclusion shape control on the impact property and formability of steel were shown using charpy impact test.
Keywords: Inclusion shape control, calcium treatment, ladle furnace and inclusion modification
M. Rezaiee – Pajand and S. Payman,
Volume 21, Issue 2 (1-2003)
Abstract
This paper discusses the effective length factor of columns in Khorjini frames. In order to find this factor, a proper approximated method is proposed. In addition, accurate analysis is performed and the results are compared with those from the proposed technique. The comparison demonstrates the accuracy of presented FORMULATIONS. The proposed method is similar to Julian and Lawrence's, which is used for rigid frames.
Keywords: Khorjini Frame, Effective Length, Bifuraction Load, Rotational Stiffness, Matrix Structural Analysis, Column Factor.
M. T. Sattari, S. S. Eslamian and A. Abrishamchi,
Volume 21, Issue 2 (1-2003)
Abstract
Limitations on water resources and the high costs of new hydraulic structure construction intensify the need for an optimum operation of Iranian reservoir systems. For appropriate water distribution and management in a 9-reservoir system on the Kalamarz river, Mianeh basin optimizing mathematical models are applied. Considering the stochastic nature of river discharges and the constant amount of reservoir volume and farmland area, an optimum linear chance constrained model is programmed and run by GAMS software. This model is only used for within-year regulation. Using a linear yield regulation, operation parameters for request months and all reservoirs are derived by the model. Also, the model computes portions of river discharge diverted to each reservoir in different months and outflow from downstream for different months. Results show greater than 60 percent deficit that indicates the lack of sufficient attention to constructing an optimum reservoir volume and extensive development of farmlands for each reservoir.
Keywords: Multi-reservoir system, optimal operation optimizing Models, linear chance constrained model
J. Soltani and F. Katiraei,
Volume 22, Issue 1 (7-2003)
Abstract
In this paper, using a personal computer (PC), the practical implementation of scalar and vector control methods on a three–phase rotor surface- type permanent magnet synchronous machine drive is discussed. Based on the machine dynamic equations and the above control strategies, two block diagrams are presented first for closed-loop speed controlling of the machine drive/system. Then, the design and implementation of hardware circuits for power, insulating, and signal matching stages are explained along with a description of the written software program for the servo drive system control. These circuits are
used to produce the drive inverter switching pulses. To supply the machine drive, the sinusoidal, uniform sampling and step-trapezoidal PWM voltage source inverters are examined. For closed loop speed control of the drive system, the stator currents and rotor speed signals (in scalar control method only the rotor speed) are sampled on-line. After filtering, buffering and matching operations, these signals are transferred to a personal computer port via a high frequency sampling and high resolution A/D converter. It is worth mensioning that both methods of controlling mathematical calculations is done by computer. Finally, the practical and computer simulation results obtained are demonstrated.
Keywords: Machine Drive, Synchronous Machine, Permanent Magnet, Rotor Surface Type, Scalar and Vector Control, Voltage – Source Inverter, Control by PC.
H. Farzanehfard and A. Pakizeh Moghadam,
Volume 22, Issue 1 (7-2003)
Abstract
Soft Switcing techniques have recently been applied in the design of dc-ac converters, in order to achive better performance, higher efficiency, and power density. One of the soft switching techniques uesd in inverters is resonant dc links. These topologies have some disadvantages such as irregular current peaks, large voltage peaks, uncotrollble pulse width, etc. Another soft switching method in inverters is using Quasi –resonant links, which have PWM modulation capability. Inverters with series or parallel Quasi-resonant dc links use several quasi-resonant current or voltage pulses, respectively, to produce PWM modualation. In this paper an inverter with a novel Quasi-resonant series dc link is introduced. This topology enables current source inverters to have characteristics such as resonant pulse peak limition and pulse width controllability. This circuit provides the inverter with two to three ranges of PWM control capability which increases the switching time control in a larger range.
Various operational modes of this novel Quasi-resonant dc link is analyesed and then the circuit losses is calculated. Finally, simulation results by PSPICE software is presented to justify the circuit operation.
Keyword: Inverter, Soft switching, Novel quasi-series resonant link, increasing control areas, Losses
F. Torkamani Azar and M. Zanjani,
Volume 22, Issue 1 (7-2003)
Abstract
Recently, image processing technique and robotic vision are widely applied in fault detection of industrial products as well as document reading. In order to compare the captured images from the target, it is necessary to prepare a perfect image, then matching should be applied. A preprocessing must therefore, be done to correct the samples’ and or camera’s movement which can occur during the capturing of images. The Radon Transform technique is applied in this study which is inherently invariant to any movement, such as dislocation and rotation which leads to scale changing. According to this technique, simple methods are proposed to determine the degree of movement. Results of computer simulation show the priority of the proposed
method to other techniques. The accuracy of the proposed algorithm is less than 0.1 degree and is applicable to different segments such as texts, tables, drawings, …, which are prepared in different writing languages by different devices such as digital camera, scanner, fax, and printer.
Keywords: Image processing, Image matching, Radon Transform, Skew detection documents, Computer application in industry.
A. Gholami and M. Mirzai,
Volume 22, Issue 1 (7-2003)
Abstract
Overhead transmission lines are influenced by different factors which are mostly electrical and mechanical. These factors can cause problems for lines, distortions in network and outage of line. In designing transmission lines mechanical properties are evaluated after selecting a suitable conductor and clearance with regard to electrical properties. In lines designing, an important mechanical parameter for estimating of phase distance is oscillations. Strong wind or ice fall from conductor surfaces or simultaneous presence of ice and wind may cause different oscillations. These oscillations are classified to aeoliane, galloping, and swing. Aeoliane is of high frequency (5-100Hz) and low amplitude (about a few centimeters), galloping is of low frequency (0.1 to 0.3Hz) and high amplitude (about of span sagging), also swing is of horizontal oscillation. In this paper, the mechanism of conductor galloping oscillation and its different types are described. Also these oscillations are simulated on the typical span by personal computer.
Keywords: Galloping, Overhead transmission lines, Single conductors, Modeling
M. R. Banan and A. Fouladi,
Volume 22, Issue 1 (7-2003)
Abstract
This paper presents a new super-element with twelve degrees of freedom for latticed columns. This elements is developed such that it behaves, with an acceptable approximation, in the same manner as a reference model does. The reference model is constructed by using many Solid elements. The cross section area, moments of inertia, shear coefficient and torsoinal rigidity of the developed new element are derived. Since the reference model has a large number of degrees of freedom (especially for nonlinear cases), computation of the equivalent essential parameters of the proposed element is very time consuming, so, a model using only beam elements is also presented. For the super element, a general purpose program is developed that is capable of performing linear and nonlinear analysis of 3D-frames with latticed columns. In order to derive the essential parameters of the proposed super-element, many latticed columns are analyzed while shear deformations are taken into consideration. Using these essential equivalent parameters approximate relations are proposed for the compution of parameters of any latticed column based on geometric characteristics. Finally, to show the accuracy of the proposed element, several examples are presented.
Keywords: Finite elements, Super-element, Latticed column, Shear deformations, 3D-frames
M. Vafaeian,
Volume 22, Issue 1 (7-2003)
Abstract
A finite element program based on elastic –plastic model of Mohr-Coulomb criterion was used to evaluate the bearing capacity coefficients of soil under shallow strip flexible footing . The results were compared with others’ analytical results and it was found that the present study could offer quite consistent and rather precise values for the bearing capacity coefficients .
The effect of different parameters such as E , υ, φ ,ψ ,γ , type of mesh idealization ,type of elements ,type of load distribution at the footing base have been examined and some new results obtained and discussed. The main conclusion can be summarized as : that the values of bearing capacity coefficients for any particular amount of friction angle should not be expressed as a single number solely dependent on the friction angle ,but the accurate values must be considered as the values dependent on some other effective parameters , which have been mentioned above .
Keywords : soil bearing capacity , finite element , Mohr-Coulomb , shallow footing
M. Kalantar and G. Fantozzi,
Volume 22, Issue 1 (7-2003)
Abstract
Dense Silicon nitride was investigated to determine the effect of its microstructural parameters and densification on thermo-mechanical properties and thermal stress resistance to fracture initiation during a hot or cold mechanical and thermal shock testing. The different materials and microstructures were obtained by changing the parameters such as the type of the powder, additive, forming process and sintering condition. Maximum crack growth and thermal shock resistance of dense Si3N4 are achieved after complete conversion of the aàB transformation, and after the change in grain morphology towards elongated
grain and the relative crystallization of the second phases have been obtained. The characteristics are obtained by a high a phase content of the starting powder, high Y2O3, and sintering condition of higher temperature (2000ْC), longer soaking times (1h) and load application at the beginning of the thermal cycle.
Keywords: Silicon nitride, Thermo- mechanical properties, Thermal shock resistance, Crack propagation resistance
M. Jafarboland, H. R. Momeni and N. Sadati,
Volume 22, Issue 1 (7-2003)
Abstract
Designing a robust tracking control for a non-linear MIMO system with uncertainty is one of the most complicated control problems. In this paper, sliding mode changed to non-linear controllable canonical form by input-output linearization. This, sliding surfaces can be defined in a way that we can de-couple equations and indicate the sliding conditions of multi-variable controller system. The uncertain parameters will be estimated properly and the input equation improved to apply the restricted input condition. The control law will be improved in a way that in addition to increasing the tracking accuracy inside the boundary layer, the speed of convergence will increase outside of the boundary layer. In order to satisfy the balance of the filter, the thickness of the adaptive boundary layer is used. Thus, a robust tracking control is designed which can trace the angle
of attitude of satellite for maneuvers with a very large angle (180 deg.) on a piece-wise smooth path. Finally, the simulation results are compared with Elmali & Olgac’s methods and it is shown that despite decreasing control signals, the tracking accuracy increases by several ten times.
Keywords: Attitude, Control, Sliding-mode control, Non-linear System, Input-Output Linearzation
J. Soltani and N. R. Abjadi,
Volume 22, Issue 2 (1-2004)
Abstract
In this paper, based on feedback linearization control method and using a special PI (propotational integrator) regulator (IP) in combination with a feed-forward controller, a three-phase induction servo-drive is speed controlled. First, an observer is employed to estimate the rotor d and q axis flux components. Then, two input-output state variables are introduced to control the dynamics of torque and the magnitude of the rotor flux independently. In addition, based on the model refrence adaptive system (MRAS) and the recursive least square (RLC) error techniques, the rotor time constant and the mechnical parameters (J, R) are simultaneously estimated. Finally, the efficiency of the proposed method is confirmed against results from computer simulation.
Keywords: Adaptive speed ontrol, Inducation servo-drive, Feedback linearization, IP controller, Model reference, Adaptive
system, Recursive least square.
Sasan Azadi, Hamidreza Momeni, and Ahmadreza Sharafat,
Volume 22, Issue 2 (1-2004)
Abstract
The objective of this study is to design a robust direct model reference adaptive controller (DMRAC) for a nonlinear cardiovascular model over a range of plant parameters representing a variety of physical conditions. The direct adaptive controllers used in thisd study require the plant to be almost strictly positive real (ASPR) that is, for a plant to be controlled there must exist a feedback gain such that the resulting closed loop system is strictly positive real. We designed a new compensator so that the system composed of the cardiovascular plant and the compensator satisfy the ASPR condition.
Numerous studies in the past have considered a small range of gain variations of the cardiovascular system. In most cases, the controller was designed based on variations in either time delay or plant gains. Many of these workers treated the cardiovascular system as a single-input single output (SISo) plant in which the control output was Mean Arterial Pressure (MAO). We treated the cardiovascular system as a multi-input multi-output (MIMO) plant in which both the MAP and Cardiac Output (CO) are simultaneously controlled.
In this study, a new linear model is presented that provides a better approximation thanthe one the original linear model does. By doing so and utilizing the DMRAC algorithm, we could satisfy the stability conditions for the nonlinear model while satisfactory responses obtained under every possible condition for the cardiovascular nonlinear model.
Keywords: Adaptive control, Cardiovascular system, Blood pressure, Cardiac output
A. Saboonchi and S. Kheradmand,
Volume 22, Issue 2 (1-2004)
Abstract
This paper presents a numerical solution for a changing combustor geometry. The effects of the geometric change on the main parameters of the chamber are considered. For this purpose the original geometry and the new one are simulated numerically by a 3-D CFD code and the results are compared. Finally, comments are presented regarding this change. A model is used for turbulence modeling and an eddy dissipation model for reaction. Effect of thermal radiation is considered through solving an extra transport equation. The DO model is used to obtain radiation intensity.
E. Hajidavalloo,
Volume 22, Issue 2 (1-2004)
Abstract
In this paper,
the application of evaporative cooling for refrigeration cycle to reduce power consumption in hot climates is emphasized. Experimental and analytical investigations were performed in order to specify the effect of evaporative cooling condenser instead of the commonly used air cooling condenser in window-air-conditioners. Evaporative condenser can reject more heat, thereby preventing the reduction of cooling capacity and increasing power consumption of window-air-conditioners during very hot seasons. Two designs were developed for evaporative condensers. In the direct injection design, water is injected on the condenser coil directly while in the media pad design, water is injected on the media pad installed before the condenser. Thermodynamic properties of the systems after modification were measured and compared with the ordinary situation. Analysis of the results show that using these methods, the coefficient of performance increases by about 25% and power consumption decreases by about 13%. It is also anticipated that further modifications in these designs may yield better results
