Year:2000 | Volume:34 | Issue:2 (68)|Papers Count:14

The traditional methods used so far for modeling, analysis, and control of systems are generally based on determining the differential equations governing the system and the designing based on some mathematical methods and algorithms. Recent investigations and studies show that, with the use of some approximations, the most complicated systems can easily be analyzed and controlled without actually being involved in a sophisticated computation or on exact mathematical model. In systems made by man, the efforts in implementing methods similar to Ruman reasoning is the basis of introducing the expert control systems and the artificial intelligence. In this paper, the qualitative control is introduced as one of the recent methods of achieving this objective, the nature of qualitative reasoning, its applications and advantages are discussed and compared with the fuzzy control, which is one of commonly used methods in artificial intelligence.

It is of prime importance to obtain information about irregular patterns on the output control chart of a semiconductor manufacturing process as well as to be able to predict the occurrence of such patterns. Here, processing of the gate in a 27MHz submicron GaAs MESFET of a monolithic microwave integrated circuit is chosen as an example, the method for extracting control charts, use of process data is described and the time series and neural network methods are used to predict the patterns. Unlike equip mental based modeling this method can predict slow changes in the output. Time series modeling of the output is done by classical Box-Jenkins. The ability to predict the irregular patterns as well as the effect of the forecasted length is investigated, using an optimum neural network model and a series of simulation.

In this paper maximum average torque operation and minimum pulsating torque operation of single phase induction motors are analyzed. An optimal method is then proposed to achieve a desirable motor performance including both a high average torque and a law pulsating torque over the entire motor speed range. A single adjustable capacitor and a switching power electronic device are used to indicabe the optimum value of the capacitor at every speed. Extensive  simulation results show the superior performance of the motor under the proposed method over the maximum average torque, minimum pulsating torque and two-capacitor methods.

The paper presents an investigation on the behavior of a plate with variable thickness and simple boundaries under in plane compressive loads using energy, finite differences, and finite elements methods. The more important parameters affecting such behavior, are the spatial location of the corrosion patch, the corroded surface and thickness at corroded place. These are studied through changing them at practical ranges, and the more critical cases are indicated. At first the critical load of plate is calculated using energy and finite differences methods which is a basic parameter in all such studies. To consider the effect of mid plane variation due to corrosion, FEM is employed via ALGOR software. The geometric and material non-linearity are taken into account and the effect of progressive corrosion on gradual strength reduction is traced.

In this paper, the behavior of RC beams deficient in shear capacity and strengthened by using post-tensioning technique was investigated by conducting flexural tests on over twenty-four beams. The beams were 80x150 mm in cross section and 1800mm long. Test variables include: concrete strength (ƒc') ; shear span to effective depth ratio (aid); longitudinal tensile reinforcement (ρ); level of post - tensioning as a percentage of ƒc' ; presence of shear reinforcement; use of continuous plates, and presence of shear crack. Beam specimens were made with ƒc' of 35 and 50 MPa, shear span of L/4 and L/6, and reinforcement ratio based on seismic design. The level of post - tensioning in location of shear crack potential is 0.04 ƒc' and 0.07 ƒc'. Test results indicate that a post-compression stress as low as 0.04fc' in shear critical region increases shear strength significantly. It also changes failure mode from brittle shear to ductile bending. Moreover, influence of other parameters is very limited at this level of post-compression. Theoretical evaluation of behavior of beams strengthened in the critical region is based on Mohr's theory. The analysis shows that this method of strengthening is very effective, and is capable of providing ductile flexural behavior in beams with inadequate shear strength. 

In this paper, Urea synthesis reactor is simulated by using UNIQUAC equation of state at high pressure and temperature. The UNIQUAC equation is very suitable at this condition. The extended model presented for simulation of reactor is based on series of stirred tanks. The effective parameter on conversion of CO2 and Urea production is surveyed by reactor simulation. Also, results of simulation were compared with operating data of Urea reactor of National petrochemical company in Khorasan (NPC-Khorasan). The comparison showed good agreement with plant data.

The kinetics of reaction between HTPB (Hydroxyl Terminated Polybutadiene) and IDI (Toluene Diisocyanate) bas been investigated. Back procedure is used for determination of extent of reaction. In this procedure the additives will not disturb the experiments. The reaction was only investigated up to gel point, because of unreproducibility for postgel samples. The extent of reaction was measured at four different temperatures for polymeric binder and the constants of apparent second order rate equation were obtained. Because of different situation of isocyanate groups in TO! a break appears in the said quadratic curves. Also cure ratio parameter (R or equivalent ratio of NCO to OH) was varied, but the effect of variation of this ratio on the rate of reaction was not very much sensible (R was varied from 0.84 to 0.95). Finally the effect of Ammonium perchlorate was studied. It is found that as the extent of this additive is increased, its reducing effect of reaction rate will increase, and as Ammonium perchlorate sizing becomes larger the rate of reaction will decrease.

In this paper a mathematical model based on the finite element method is presented to predict the strain field and the roll-force during hot strip rolling process. The model is capable to predict the effect of various factors such as work hardening of rolled metal, variation of temperature during hot rolling, rolling speed, and friction on the strain field within the rolled metal. To verify the validity of the model, a comparison was made between the theoretical and the experimental results of hot rolling of steel strip. A good agreement was found between the two sets of results.

Machining of industrial parts made from austempered ductile iron (ADI) is both time and money consuming. Therefore, control of dimensional changes during heat treatments of ductile iron as to reduce machining process has received much of interest. In this research austenitization temperature effects on the dimensional changes are studied; the reasons behind these  dimensional changes were discussed as well. In this regard, the as cast cylindrical specimens were austenitized at 870, 900 and 920°C followed by austempering at 315°C. Optical and scanning electron microscope (SEM) equipped with EDX and image analyzer were used to explain the reasons of dimensional changes. The results show that increase of austenitization temperature increases the dimensional changes due to increase of volumetric fraction of matrix and porosities around nodular graphites.

In this paper, the results are presented of the experiments and the data reduction schemes for evaluation of the mode-I interlaminar fracture energy of unidirectional glass/epoxy composites. All tests, including the material elastic properties tests, are performed according to the ASTM standard practices. In the interlaminar fracture tests, the double cantilever beam (DCB) specimens are employed. Several data reduction schemes are used for calculating the mode-I fracture energy. It is found that the accuracy of the experimental delamination length data has a great effect on the calculated fracture energy. A novel method is then introduced which is capable of determining the fracture energy without using delamination length data which are the most error prone part of the test data. The method is based on the previously developed finite element modeling of delamination growth in the specimen. The modeling technique makes the practical use of linear elastic fracture mechanics incorporating the strain energy release rate analysis. It is shown that the new method can practically be used for calculating the interlaminar fracture energy and/or evaluating the DCB test accuracy.

The free and forced nonlinear vibration of the fixed and simply supported, orthotropic annular plates with stepwise are investigated. Assuming harmonic oscillations, and utilization of Ritz-Kantorovich method the time variable is eliminated. Hence, the governing nonlinear partial differential equations for the axisymmetric vibration of annular plate are reduced to a set of ordinary nonlinear differential equations. The finite difference method together with multidimensional Newton Raphson method is used for solution of problem. The initial guesses for starting the solution are obtained from the linear solution of plate. Modes shapes, frequency, bending and membrane stresses for two case of fixed and simply supported are compared. For particular problem, finite difference gives the same results as those of shooting method with less intervals (points) chosen for numerical solutions.

The objective of this paper is to develop an accredited computer simulation model for an assembly workshop of the largest electric motors manufacturer in Iran. To achieve the above objective, the workshop was visited several times. Moreover, the processes and operations of the workshop in general and each workstation in particular were studied. The data related to process times, defectives nd scraps, repair and maintenance and production rates were collected by cooperation of the Industrial Engineering unit and by referring to historical data and time studies. Conceptual models of the workshop were developed through flow process chart, logic diagram and schematic diagram. In addition, station technical sheets. Are designed to illustrate the main characteristics of each workstation. A computer simulation was developed by Slam system simulation language. The outputs and structures of the model were verified and validated against the actual system. Also, a t-test was used to compare the outputs of the system being studied with that of simulation model. The Industrial Engineering unit of the system also accredited the model. Finally, a set of optimizing alternatives based on sensitivity analysis was proposed to the management. The simulation methodology has several benefits for the workshop. The past, present and future of the system can be analyzed and second, the effects of specific parameters such as increased demand can be easily evaluated. Furthermore, before any additional investment or making physical changes in the workshop, the effects of various changes may be predicted.

A new method is described for gravimetric determination of gold as tetra phyenlarsnium aurichloride, (C6H5)4As, AuCl4. Accuracies ranged from 0.4% to 0.6% for sample sizes between 0.2 and 4mg., with Analytical Factor FAu=0.2728. This method is used for analyse of metallic aurates with their prepration and thermolysis