INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN)
Year:2007 | Volume:18 | Issue:3 (SUPPLEMENT OF MECHANIC AND ELECTRICAL ENGINEERING)|Papers Count:12

Base idea of adaptive control systems is to maintain performance index of control system in desired range while process dynamic has wide range of variation and in presence of disturbances. Power phase of flight of a ballistic missile or a launch vehicle is a manifest sample for this problem. But since trajectory of some of these missiles with good approximation is predictable, and variation of their parameters is slow and relatively deterministic, necessity of application of a complicate online adaptive method is not so reasonable. In this paper after presentation of gain scheduling as a simple and practical offline adaptive method, another simple offline adaptive method named as "decoupling of pitch (or yaw) control channel from missile's lateral velocity" is proposed. This adaptation Jaw leads to reduction of missile's sensitivity to wind disturbance. Non-linear six degree of freedom simulation and Simulink simulation results indicate suitable adaptation characteristics of this proposed simple and practical control law.

Two main problems in CDMA cellular systems are multiple access interference (MAI) and multipath fading. To alleviate these problems, two usually used methods are multiuser detection and space-time coding. In this paper, we study multi-user detection of CDMA signals in multiple transmit receive antenna systems. We propose some structures that use combinations of linear and non-linear multi-user detection techniques with space-time block coding method. Then, we compare the performance of the proposed receiver structures by computer simulations. We also compute the complexity of the proposed space-time multi-user detectors and compare them.

This paper focuses on the selection of ratings for capacitors and reactors used in single-tuned passive harmonic filters. System topology and working conditions has been considered. Also steady state, dynamic and transient simulations of an example HVDC system has been presented and finally ratings for filters components have been selected.

Base idea of adaptive control systems is to maintain performance index of control system in desired range while process dynamic has wide range of variation and in presence of disturbances. Power phase of flight of a ballistic missile or a launch vehicle is a manifest sample for this problem. But since trajectory of some of these missiles with good approximation is predictable, and variation of their parameters is slow and relatively deterministic, necessity of application of a complicate online adaptive method is not so reasonable. In this paper after presentation of gain scheduling as a simple and practical offline adaptive method, another simple offline adaptive method named as "decoupling of pitch (or yaw) control channel from missile's lateral velocity" is proposed. This adaptation Jaw leads to reduction of missile's sensitivity to wind disturbance. Non-linear six degree of freedom simulation and Simulink simulation results indicate suitable adaptation characteristics of this proposed simple and practical control law.

In this paper, operation, design and construction of a calorimetric system for measurement of electrical machine losses are described. Calculation of heat loss through the calorimeter walls are given both theoretically and experimentally. Specifications of the reference heater, calorimeter main fan, temperature measurement system and computer data acquisition system are given in this paper. Calibration of the constructed system using two heater methods is explained. Considering error for different parts, theoretical value for error is estimated to be 4.9% where, this value is experimentally found to be 5.6% (worst case) and 2.7% (in average). Using the described system, no-load losses of a 5.5kW induction motor are measured and compared with the measurement results obtained by a laboratory wattmeter. Accordingly, the average value of error is calculated to be less than 5%. This figure is comparable with other calorimetric methods as well as with conventional loss measurement methods. In this paper, some comments are proposed to improve the capability of the constructed loss measurement system.

The use of PSS in order to improve dynamical stability of the power systems has been recently increased. For this purpose, there are varieties of methods for determining the controller coefficients of the system stabilizers. If these coefficients are modified in each operational point by adaptive mechanism, the robust performance of the system is improved. In this paper, a new method for determining the coefficients of a self-tuning PSS with lead-lag controller based on pole assignment and pole-shifting techniques is presented. In the design procedure, the required identification in self-tuning regulator is performed by using active and reactive power values. Moreover, the properties of the proposed methodology are compared with self-tuning PID stabilizer whose coefficients are determined by using pole assignment technique. Then, the advantages of the proposed stabilizer in which parameter adaptation is accomplished based on the proposed self tuning method by combining the pole-assignment and pole-shifting techniques, is expressed with respect to other stabilizers. Finally, in order to show the effectiveness of the proposed methodology, some simulation results on a power system with definite parameters and different operational points are provided.

To design a safe substation grounding grid, it is necessary to compute the split factor of ground fault current and also current distribution in other possible paths. These may include earth wires of transmission lines, earthing resistance of towers and also grounding grid of adjacent" substations. In this paper, a novel, simple and accurate method is developed for the determination of split factor of earth fault current in RV substations. In the proposed algorithm grounding grid impedance of adjacent substations, different tower footing resistance, non similar double-circuit, more than one earth wires and different spans in transmission lines may be considered. Finally, the results are compared with the others and showed good agreement.

The duration of ignition delay plays an important role in performance, efficiency and the succeeding ignition period of diesel engine. Determining the duration of this period is mostly one of the problems in controlling combustion and engine design. The tests performed under full factorial design of experiments using a small direct injection diesel engine with operating variables; engine speed in 5 levels, engine load torque in 4 levels and fuel injection timing in 5 levels. In this study engine combustion parameters such as; peak cylinder pressure, maximum rate of cylinder pressure rise, maximum acceleration of cylinder pressure, peak rate of heat release, internal cylinder temperature and static and dynamic ignition delay were measured. The most effective parameters on ignition delay were found to be cylinder internal temperature, engine speed and peak rate of heat release, while peak cylinder pressure, maximum rate of cylinder pressure rise, maximum acceleration of cylinder pressure and engine load torque did not reveal any significant effect. Single variable regression analysis indicated that cylinder internal temperature, engine speed, peak rate of heat release and fuel injection timing correlate most with ignition delay. In this research work mathematical models single and multivariable for static and dynamic ignition delay with operating parameters of cylinder internal temperature, engine" speed and peak rate of heat release were estimated. The best model was static ignition delay having a coefficient correlation of (r =0.90) and maximum error of 1.32 ms. Statistical analysis indicated that the model is fully linear and parameters play an effective role individually. This model is extremely a new and its seems that the models presented by the other research hers so far do not predict the ignition delay period as accurate as this model for small direct injection diesel engines.

To increase the resolution of incremental encoders, interpolation circuits are used. Common interpolation methods decrease bandwidth of encoder output and increase response time which doesn't allow real time transfer of positioning information to a controller. Some of these methods require high quality input signals, as they are unable to compensate input signal errors. In this paper an interpolation method is proposed that is able to improve both resolution and accuracy of these encoders, while achieving high encoder output bandwidth and low response time. The experimental results show that the only limiting factors for the encoder output bandwidth are slew speed of encoder shaft (maximum mechanical speed of encoder shaft) and maximum scanning frequency of encoder head. The response time of the proposed interpolation circuit is a few nanoseconds that are small enough for most control applications.

Exact geometrical modeling and defining the accurate properties of the body tissues are the two parameters which increase the accuracy of a biomechanical finite element analysis. Regarding the lack of proper equipment and software in Iran, creating three- dimensional exact models using available means, is an important effort for getting more real results in a FE analysis. This study considered exact three dimensional modeling and analyzing the hard tissues with the focus on the first cervical vertebra (atlas). After creating a 3-D exact model of atlas using CT images of a cadaver, we studied the pattern of stress distribution in different positions of the head (flexion, normal, extension). The results of finite element analysis had a good compliance with clinical observations.

A 2-D numerical scheme for particle deposition on a rough surface is developed. The traditional method for roughness modeling is not used, and direct roughness simulation (DRS) is adopted. Averaged Navier Stock equations are solved by SIMPLE method, and RSTM is used to model Reynolds stresses. The fluctuation velocities that have calculated with DRS method are comparable with the experimental results. Lagrangian reference frame is utilized for particles simulation. Particle fluctuations are modeled by using a white noise. Drag, weight and Brownian forces are considered. The effects of particle size on dispersion and deposition rate are examined. The results show that the roughness plays an important rule in the particle deposition.