IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:1999 | Volume:23 | Issue:1|Papers Count:8

A method is presented to predict the onset of knock and associated performance of a spark ignition engine when primarily fuelled with gaseous fuels such as methane. It gives guidelines for choosing the best operating conditions to obtain maximum power just before the onset of knock. A two-zone predictive combustion model was developed based on an estimate of the effective duration of the combustion period and the mass burning rate for any set of operating conditions. The unburned end gas preignition chemical reaction activity is described by a detailed chemical reaction kinetic scheme. The variation with time of the value of a formulated dimensionless knock parameter K is calculated. This parameter relates the total energy released within the end gas due to autoignition reaction activity per unit of corresponding instantaneous volume relative to total energy release per cylinder volume that would take place normally due to regular flame propagation. When knocking is encountered, the value of K builds up to a sufficiently high value that exceeds an acceptable limit. Under normal operating conditions, the value remains throughout the combustion period at comparatively low levels.

A fuzzy-set based power system stabilizer is proposed to enhance the stability of a power system. The controller parameters are optimized using Genetic Algorithm (GA). An Artificial Neural Network (ANN) is then trained so that the controller parameters are selftuned based on operating conditions. The performance of the proposed approach has been assessed by simulating it on a single machine infinite busbar system.

This paper establishes a relationship between two techniques for the control of current controlled induction motors, namely scalar control with flux loop and direct vector control. This is accomplished through theoretical comparison of the governing equations that relate the input and the output signals in the respective controllers. In traditional scalar control, the controller outputs are [IS] and ωe while in vector type they are Isds and Isqs. In each method two signals are produced which define the reference current. It is desirable to improve these two controllers, so that similar information is derived for the reference current. With this achievement, it will be shown how an existing scalar controller may be converted to a vector control type (with improved responses) by software modifications. Computer simulation is demonstrated for a typical 3 HP motor.

In this paper, the total stability of specific fuzzy control systems is studied. The plant of the system is assumed to be a linear system and the fuzzy controller is of Sugeno type. The stability analysis is based on some newly developed theorems that guarantee sufficient conditions for the total stability of the system. The analysis results are applied to the stabilization problem of an unstable plant.

This paper develops a new adaptive control law for rigid robotic manipulators, which is computationally very fast and therefore suitable for real-time implementations. This globally convergent adaptive controller is a modified version of the original scheme presented earlier, but results in simpler design conditions in comparison with the previous work in this area. The convergence properties of the proposed scheme are established through a basic theorem, using the theory of passive dynamic systems. Other aspects of this paper, such as a new general lemma on passive systems, which is utilized in proof of the basic theorem, and a procedure for determining the design parameters, are also of interest. This algorithm is simulated on a digital computer and the results confirm theoretical studies.

Application of a new control strategy on actuators used in electromagnetic vehicle suspension systems has been studied in this paper. The vehicle is modeled as a quarter car in which the unsprung mass is supported by two vertically arranged electromagnetic actuators having a nonlinear behavior. The nonlinear actuators, having forces proportional to the square of the electric current and inversely proportional to the square of their distances from the mass, are controlled using a simple and feasible control strategy named "Performance Based Time-Delay". It is shown that this control strategy can result in excellent system performance compared to the conventional passive suspension system or other control strategies implemented in active suspension systems. The vibrations due to road roughness are controlled by changing magnetic fluxes of the actuators. Less required computational steps, use of an on-line digital computer, overall system simplicity, and achievement of a better response to larger high frequency disturbances are among the advantages of the system controller.

In this paper the principles of the Ramberg-Osgood expression and the Masing criterion for cyclic loading are described. Modifications to the Ramberg-Osgood expression are reviewed and suggested methods for parameter determination in this equation are presented. The application of the expression for first cycle behavior is illustrated. A common degradation criterion is described and, by representing other researchers test results, it is shown that the criterion might not be generally applicable. A new degradation model is proposed which is found to be more representative than the other model. A model for predicting cyclic pore pressures for normally consolidated soil is also described. The parameters required for this model have been described in detail and its applicability in predicting cyclic behavior of Shiraz silty clay is presented.

Some common methods, such as 75% of full demand (75%), shortage index (SI), modified shortage index (MSI) and planned deficit at specific dry years (PD) were compared with a proposed method of constant water deficit (CWD) for a 30×106 m3 reservoir of the Ardak dam located northwest of Mashhad (Khorasan province of Iran). In each case the optimum downstream area for a cropping pattern of wheat, barley, sugarbeet and corn was determined. The amount and net value (NV) of actual yield, net present value (NPV) and benefit to cost (B/C) ratio were computed for each scenario, using dated water production functions of different crops, accompanied with suitable sensitivity indices. Optimum intra-seasonal water allocation under PD was made by applying the nonlinear programming scheme. The results of this study showed that the methods of 75%, SI, and MSI are neither appropriate since they do not account for actual crop yield obtained under water deficit, and nor are they practical in real time. On the other hand, the inappropriateness of the PD method is attributed to its impossible utilization for an actual reservoir and also to its theoretical shortcomings. In contrast, the proposed method of CWD for the whole period of operation can be used in reservoir operation management, while it is coupled with optimum intra-seasonal water allocation based on a nonlinear programming scheme. This study also shows that the CWD method is more appropriate for the economical operation of the reservoir.