INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN)
Year:2005 | Volume:16 | Issue:3|Papers Count:18

Modeling and simulation of a wind farm power generation is an essential tool for the location of new farms. In this paper, control and distribution of reactive power in wind farms  made up with doubly fed induction generators (DFIG) is studied. After brief description of a wind turbine, dynamic model of a DFIG in the reference frame fixed to stator-flux linkage space phasor is developed and simulated. To robust control of reactive and active components of each generator power, Adaptive Nemo-Fuzzy Intelligent Systems (ANFIS) is used. After validation of the developed model, control of reactive power in a wind farm and its distribution between DFIG generators in various wind speeds are studied and the proposed Nemo-Fuzzy controller is used for the reactive power control in the wind farm. From the performed simulations it can be concluded that the Nemo-Fuzzy controller would be more efficient and robust in both cases: vector control of DFIG drive and control and distribution of wind farm reactive power.

Design of high efficiency power amplifier is a fundamental subject in the most of RF research centers. Fast advances in cellular communication systems especially with appearance of 3G mobile systems is a major motive for RF research center to invent to design and produce the handset with minimum consumption power. Although there are many parameters which affect on the consumption power of a handset, but the most important part is power amplifier. Essential parameter for all power amplifiers is linearity. As behavior of the transistor in large signal is naturally nonlinear, studying and modeling of the transistors nonlinearity are indispensable for precise and delicate design of the power amplifier. In this paper, nonlinear analysis is based on Volterra series. The results of the load-pull experiments and calculation are compared on various charts. There are excellent convergent between measured and calculation values.

In this paper, a closed-loop multi-channel Functional Neuromuscular Electrical Stimulation (FNS) system is designed and implemented for real-time control of the paralyzed limb. The system is used to acquire feedback information and to supply stimulation patterns for on-line activation of paralyzed muscles. The system is capable to modulate the current amplitude and pulse width, simultaneously. This feature offers fine movement control. The key feature that have to be considered in the design-of a closed-loop multi-channel neuromuscular electrical stimulation system is the reliability. The system needs to be easy to use and easy to implement any controller scheme. For implementing such a closed-loop FNS system, appropriate computer software is required. In our case, we used Matlab Simulink, Real-Time Workshop, and Real-Time Windows Target under Windows. The results of cyclic leg movement on a complete level T7 spinal cord injury paraplegic show that pulse width modulation produces more smooth movement than pulse amplitude modulation. For evaluating the capability of system for real-time control of the paralyzed limb, a PID controller is used. PID's coefficients are adjusted based on Ziegler-Nichols method. The results show that the system can adjust the parameters of stimulation signals according to control strategy. It is found that the PID controller could not control the knee joint angle for whole range of motion. Muscle fatigue is one of major problems in functional neuromuscular stimulation. The results show that the closed-loop control can control the knee-joint position during prolonged electrical stimulation.

Scheduling and sequencing problems are the most significant areas in production planning and are applicable to a number of service and manufacturing firms. Nowadays, one of the main objectives for every unit in an organization, its survival, present competitions, and in this global village is to increase the customer satisfaction. Thus, this issue has its effect on doing, the job for any organization. In this paper, the customer satisfaction is considered as the main objective function divided into three different objectives such as minimizing the maximum lateness, the number of tardy jobs, and the total late work. Due to the complexity of the associated mathematical model, a new heuristic algorithm, named three blocks (3B), is presented in this paper. To show the efficiency of the proposed algorithm, a number of test problems are generated at random and solved by the above algorithm. Finally, the obtained results are compared with the optimal solution in terms of the computational time and objective function values. However, it takes more than three hours to find the optimal solution for 9 jobs and more.

There are many references in decision making theory and other related subjects, but not so much in interactive aspects of decisions and decision makings .in this case, through soft system methodology, "analyzing the decision making network", is focused on by decision network, here, we mean: an interactive and unstructured network of decisions, in an organization.The whole network and subnetworks can be analysed through some general and individual criteria. The results leed to improve the action of an organization.

In this paper the use of neural networks for partitioning of adaptive, unstructured finite element meshes for parallel time-stepping finite element analysis is presented. The concept of mean filed annealing and its use in finding approximate solutions to combinatorial optimization problems is investigated. The application of mean field annealing neural network for the partitioning of finite element meshes is described. This partitioning is based on the recursive bisection approach. The mapping of the mesh bisection problem onto a recurrent neural network is presented. The use of a trained backpropagation neural network which can estimate the number of elements which will be produced inside each coarse element of a finite element mesh after mesh refinement is described. The solution quality and the computational time of solutions are demonstrated using a case study.

Business process reengineering (BPR) is a phenomenon in which through radical process redesign, some companies have achieved large scale improvements. However according to surveys more than 70 percent of firms face failure in BPR movements, due to high degree of risk and lack of coordination among involved peoples including actors, beneficiaries, and victims.One of the main reasons for that is high degree of resistance among the people those who face the real shock. Most BPR projects follow a top-down approach encouraging the human being across the firm to raise themselves against the project which makes BPR a tough challenge. The aim of this research is to develop a new methodology for BPR using MBO (management by objective) to help BPR overcome the cultural difficulties and resistance among the employees, in accepting the changes.To bring success to BPR projects, the employee must be thoroughly informed about the mission, objectives and goals of the movement . Organizational goal as well as individual goal must be announced, set and aligned in one direction n. BPR by MBO approach would facilitate employee involvement in change programs and help the BPR methodologies to overcome the weaknesses they face in terms of goal setting programs.In this research with considering BPR and MBO methodologies, a goal-oriented BPR model will be introduced which mixes both the methodologies to achieve the goals and objectives through BPR in organization using BPR & MBO interface to reduce the degree of resistance among employee and reach the mutual understanding between the top management and employees.

In this paper the effect of parameters such as thickness of plate, bolt diameter and bolt gage distance from beam flange and web on nonlinear behavior of bolted end-plate connection, is investigated. In this regard, ANSYS nonlinear structural software was used for analyzing connection models. The results of this research were verified with experimental results of one sample. In this study 30 models with different geometries were selected for nonlinear analysis. Moment-rotation curves were obtained for all the models and compared with each others.The results obtained showed that thickness of end-plate, configuration of holes and bolts, thickness of beam flange and web, presence of stiffeners, and bolt diameter affect the stiffness and strength of connection differently. Increasing in end-plate thickness and decreasing in distance between bolts and beam web, increase the stiffness of connection. Also, increasing in bolt diameter increases the stiffness of connection but not as much as the previous two parameters do.

Resistance to erosion in cohesionless sediment is a result of gravity only, but erosion of cohesive sediment is quite different. Before cohesive sediment can be eroded, the interparticle bond must be broken. Thus, a critical shear stress has to be exceeded before erosion of cohesive sediment can occur. The objective of this study is to determine the critical shear stress of erosion of cohesive sediment collected from bed of six khozestan irrigation channels, including Dasht-Evan, Hendijan, Veis, Shadegan, khalaf-Abad and Voseyleh. Experimental results are shown that shear stress of erosion for these channels varied from 0.96 N/M2 in Shadegan Channel, to 2.3 N/M2 in Hendijan Channel. Comparing the design shear stress of three of them, (Veis, Dasht-Evan, and Chamran (Voseyleh) with critical shear stresses of erosion obtain from experimental study indicate that for Veis and Dasht-Evan Channels the design values of shear stress are less than the values need to eroded the deposited sediment. Only for Chamran Channel the design shear stress is more than the critical shear stress. The main point of this study is that for designing channel in the area with fine particle size, it is very important to find the critical shear stress of erosion and use this value for correct hydraulic structures design.

In this research, the bucking of R.C. cooling towers of Shazand power plant as a typical cooling tower has been studied by using VGB recommendations due to wind load. In finite element analysis ANSYS 5.4 was used. The effect of columns on global buckling of the R.C. cooling towers has been ignored in most codes of practices except ACI. According to this research, in cooling towers with long columns, not only the buckling factors decrease considerably but in the first modes the columns buckle instead of the shell.

Since there are various and numerous parameters affecting individual mode choices, probably we can express that, certainly the recognition of the shortest possible decision making algorithms amid tremendous working parameters can be considered an essential step towards modal-split mode1ing. One of the latest and most authoritative mathematical instruments to ascertain the shortest decision making algorithms is rough-set theory. The said theory, firstly, was propounded by Pawlakin 1991. The current investigation studies the capabilities of the said theory in Modal-Split modeling. Also the present research aims to realize the most important parameters being decision-making regarding the individual mode choices and extract decision rules whereby the large amount of information, necessary for Modal-Split modeling, can be dwindled. In this research the compiler has attempted to detect the best algorithms of defined attributes, using Step-Wise method, concerning about behavioral specifications of the individual and his/her trip being able to delve the operational capability of rough-set theory. The results indicate the better and stronger performance of rough-set theory concerning the recognition of the best decision-making algorithms (Reducts). Meanwhile, the most important parameters affecting modal choice for Hamedan city as a case study is determined as well. The results shown in this work indicates that the rough-set theory is a more powerful tool comparing to Step-Wise method.

Influence of two types, Iranian and South African, of andalusite on the microstructure as well as physical and mechanical properties of bauxite-based low cement castable refractories was studied. During the heating of the samples under oxidizing atmosphere at 1400oC the mixture of mullite and silica rich glass phase evolved out of sillimanite minerals group. Different amount of bauxite grain (0-0.1 mm) were replaced by similar size of andalusite lead to improvement mechanical properties. It was found that the improvement of the mechanical properties of the refractory is because of the mullitization process during the firing. The X-Ray Diffraction tests showed that the use of Iranian in comparison to South African andalusite, caused higher amount of mullite formation in the samples.

Microalloyed medium carbon steels -have recently been used in the automotive industries, due to their low costs and high performances. Mechanical properties of these steels are controlled by controlling the chemical composition, preheating temperature and cooling rate. The aim of this research is to evaluate the effects of cooling rates on microstructure and mechanical properties of DIN: 38MnVS6 or IS038MnVS6 steel. Various samples were produced by changing the primary temperature and the cooling rates. The results show that the primary temperature has no significant effect, but the cooling rate has the main effect on the mechanical properties of the steel. The optimum cooling rate is obtained as 1.5°C/s. Due to the applied condition; the obtained mechanical properties of the steel are as below: Tensile strength 840 MPa, yield strength 600 MPa, elongation 20% and impact strength 80 J/cm3.

In the present work, the effect of aluminum on mechanical activation of hematite graphite- aluminum mixture has been investigated. Various amounts of aluminum powder (0 to 10 wt%) was added to hematite-graphite mixture (C/O=1 or 18.40 wt% graphite). Then, the mixture was mechanically treated by means of ball milling within different time periods, from 0 to 10 hours. XRD and SEM tests were carried out to study the effect of aluminum and milling time on activation mechanism of the mixture. It was found that existence of aluminum particles, as formable material, in the brittle hematite-graphite mixture could influence on the microscopic condition and subsequently on the behavior and intensity of mechanical activation of the mixture.

One of the main factors which determine the quality of concentrated iron for steel production is the phosphorus concentration in the final output of the iron processing plant (Iran steel requirement about %0.052). In this research, particle size, grinding and the degree of freedom of minerals are thoroughly investigated. This research is aimed at investigating the effect of particle size on the degree of freedom of minerals. Thus, first of all, the range of grinding of the output of SAG (Semi Auto Gen) mill and required intensity of magnetic field were determined, then the percentage of solid in the pulp and washing steps were optimized. The results indicated that in order to get a concentrate with appropriate quality, it is necessary the particles size of the output of SAG mill system to be reduced to 38 μm (D80 = 32 μm) and wet magnetite separators of 1200 gauss intensity and 25 rpm in four consecutive series to be used for washing the pulp with %35 solids. With the above conditions selection it is possible to obtain cumulative magnetite recovery of %76.59 with a phosphorus concentration of %0.052 and iron grade of % 69.14. To achieve the above conditions the processing plant should be redesigned for new ball mill, hydro cyclones and magnetic separators.

Characteristics of colored masterbatches have great effects on the quality of synthetic fibers. In this research work, the necessary suitable characteristic of the colored masterbatches for synthetic fibers have been studied. Two methods for characterization of internal and external masterbatches were used. In the first method a brabender internal mixer was used and parameters such as total energy, steady state energy, maximum torque, steady state torque were studied. Due to lack of knowledge of the formulation for the used masterbatches, this method was unable to provide an accurate evaluation for the quality of the masterbatches produced by different manufacturers. But it could be a useful method for evaluating the quality of masterbatches for a known manufacturer. The second method is based on optical microscopic analysis of the micrographs, which is a suitable criterion for qualitative analysis of the colored masterbatches. By optical analysis of the micrographs a quantitative criterion can be obtained.