ESTEGHLAL
Year:2004 | Volume:22 | Issue:2|Papers Count:15

Algorithmic skeleton has received attention as an efficient method of parallel programming in recent years. Using the method, the programmer can implement parallel programs easily. In this study, a set of efficient algorithmic skeletons is introduced for use in implementing parallel genetic algorithm (PGA).A performance model is derived for each skeleton that makes the comparison of skeletons possible in order to select the best one for the application. The performance of the selected skeleton can be increased by specifying the virtual topology required by the application. This is a novel approach with no precedent Nesting of skeletons used here is another novelty of the study which has been employed only in few previous studies.

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 reference 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.

In the current engineering practices, buildings are commonly designed for an effective lifetime of 50 years. This lifetime can increase the cost of buildings with short lifetimes and can reduce the safety level of buildings with large lifetimes. In this paper, a service-life factor has been defined Applying this factor into the nominal values of live, earthquake, wind, and snow loads, the effect of service-lifetime is taken into consideration. The study shows that the magnitude of seismic load can be reduced by 60% and those of other periodic loads by 30% for temporary buildings. An increase of 50% in the periodic loads was also observed for service-lifetime of 150- 200 years. These effects indicate a meaningful improvement in economy and safety of buildings if the service-life factor is considered

The new knee-braced frames (KBF) consiss of a moment resisting frame and diagonal braces connected to short knee elements. The lateral stiffness is provided by the frame and braces while flexural yielding of the knee elements provides the ductility. In this paper, the effects of geometric parameters on lateral elastic stiffness of KBF frames are studied and the suitable limits for these parameters are determined for the first time. Then, nonlinear dynamic seismic behavior of one kind of KBF frames (TKBF) and the effects of important parameters under Naghan and Elcentro earthquakes are studied and evaluated The seismic behavior of TKBF frames are compared with CBF and EBF frames. The results prove that suitably designed TKBF frames show better seismic behavior according to lateral nonlinear displacement, plastic hinge propagation, collapse mechanism, and vertical displacements of slabs, and, therefore, provide better stiffness and ductility requirements.

In this paper, dynamic and stability analysis of a flexible cam follower system is investigated Equation of motion is derived considering flexibility of the follower and camshaft. Viscous and Coulomb frictions are considered in the rocker arm pivot. The normalized equation of motion of the system is a 2d- order differential equation with periodic coefficients. Floquet theory is employed to study parametric stability of the system. Stability diagrams are presented and the effects of varying cam profiles and motion events on the stability of the system are compared Results show that viscous and Coulomb frictions stabilize the motion of the system.

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 k# - e#(RNG) 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.

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.

For implementation of the free surface boundary condition, a new subroutine has been introduced to an existing steady 3-D body fitted code. This code was previously written for steady flow simulation in closed ducts. The algorithm used in this subroutine reduces the instability problem according to the free surface wave generation. For code validation, it was applied to two different open channels. The results obtained for these test cases were compared with existing data. The comparison of the two sets of data was promising and proved that with this subroutine it is possible to predict the free surface position very well. The results of this routine were also compared with the symmetry boundary condition at the free surface for two mixing flows and it showed that, if the changes of the free surface elevation were small, the symmetry boundary condition could be considered as an accurate enough method

The microsegregation pattern of aluminium and silicon in the nodular cast irons has been investigated Microscopic analysis by EDX and EPMA indicates that there is inhomogeneity in the matrix of the as-cast experimental irons. Al is enriched at areas close to the graphite nodules, whereas the concentration of silicon is higher in the intercellular regions. Furthermore, the results obtained on the austenitised Al-alloyed ductile irons at 920 C at different holding times indicate that austenitising reduces the inhomogeneity of the as-cast microstructure and that after sufficient holding time, the matrix of Alalloyed ductile irons containing different Al concentrations can be virtually segregation free.

The purpose of this work was to production of ceramic thin films by using of Sol-Gel process. For this purpose deposition of Si02 on substrates of soda-lime glasses has been carried out. Coating treatments on prepared specimen were conducted in a Sol solution by means of dipping at various times. After drying and performing appropriate heat treatment on each sample, the thickness of coated layer was measured by means of roughness method Some of the specimens were also exposed to heat and chemical environment to evaluate the coating resistance in such media. SEM examination and EDAX and XRD analysis of coating layers was also conducted on some samples. The results indicated that by Sol-Gel method, it is easily possible to achieve thin layers in the scale of one-hundredth micron meter. Any change of the thickness layer on the surface is negligible and the quality of the coating is excellent. Also, experiments indicated that deposited coatings by Sol-Gel process, are stable and give enough durability in various environments.

In this study, colorimetric calibration of scanner has been done via perceptron neural network with three or jour layers by back propagation algorithm for colored polyester fabrics. The results obtained for random training samples are not satisfactory but application of selective training samples for L*a*b* or RGB leads to good results, with better results obtained for the L* a* b* method On the other hand, the color differences between calculation XYZ and real XYZ for unknown samples, are not only in agreement with the results of polynomials and regression methods, but are also better than the results obtained in previous studies where neural network had been used for colorimetric calibration of scanner.`