International Journal of Engineering
Volume:23 Issue: 1, Feb 2010

A probabilistic seismic hazard assessment in terms of Arias intensity is presented for the city of Tehran. Tehran is the capital and the most populated city of Iran. From economical, political and social points of view, Tehran is the most significant city of Iran. Many destructive earthquakes happened in Iran in the last centuries. Historical references indicate that the old city of Rey and the present Tehran have been destroyed by catastrophic earthquakes at least 6 times. Existence of active faults like North of Tehran, Mosha and North and South of Rey is the main causes of seismicity of this city. Seismicity parameters on the basis of historical and instrumental earthquakes for a time period, from 4th century BC to the present time are calculated using Tavakoli’s approach and Kijko method. The earthquake catalogue with a radius of 200 km around Tehran has been used to calculate seismicity parameters. Iso-intensity contour lines maps of Tehran on the basis of different attenuation relationships are plotted. They display the probabilistic estimate of Arias intensity with Rock and Soil beds for the return periods of 72, 224, 475, 2475 years. SEISRISKIII software has been employed for seismic hazard assessment. Effects of different parameters such as seismicity parameters, length of fault rupture relationships, and attenuation relationships are considered using logic tree.

An experimental study of the effect of silt and influence of cell confinement on the bearing capacity of circular footings on silty sand was carried out. Laboratory experiments on clean sand and sand containing silt up to 25 % were performed. Cells with different heights and diameters were used to confine the silty sand. The effect of proportion of silt in sand, cell diameter, cell height and the embedded depth of footing were studied. Initially, the response of a footing without cellular support was determined and then compared with that of footing with cellular support. The results indicate that the bearing capacity of circular footing can be appreciably increased by soil confinement. It was interpreted that such confinement resists lateral displacement of soil underneath the footing. It leads to a significant improvement in the bearing capacity of the footing. The cell–soil footing behaves as one unit for small cell diameters, while this pattern was no longer observed with large diameter cells. Results of model-scale footing tests show that bearing capacity decreases with fines. It is due to fact that on the increase of silt while density increases but increase in compressibility offsets the effect of density. The cell height, depth, and diameter that give the maximum bearing capacity improvement are presented and discussed.

In this paper، tuning of power system stabilizer (PSS) and thyristor controlled series capacitor (TCSC) is studied. The analysis of mode controllability is used to select the effective location for TCSC. The performances of TCSC equipped with a proportional-integral-derivative controller (P-I-D controller) and proportional-integral-derivative power system stabilizer (P-I-D PSS) are investigated. The dynamic responses considering TCSC equipped with a P-I-D controller and P-I-D PSS are compared with considering TCSC equipped with a phase lead-lag controller and conventional power system stabilizer (CPSS). The controllers design problem is formulated as an optimization problem. The genetic algorithm (GA) is used to search for optimal settings of controller parameters. Analysis reveals that the TCSC equipped with P-I-D controller and P-I-D PSS give better dynamic performances.

The paper proposes an algorithm to calculate the switching angles using harmonic elimination PWM (HEPWM) scheme for voltage source inverter. The algorithm is based on curve fittings of a certain polynomials functions. The resulting equations require only the addition and multiplication processes; therefore, it can be implemented efficiently on a microprocessor. An extensive angle error analysis is carried out to determine the accuracy of the algorithm in comparison to the exact solution. To verify the workability of the technique, an experimental voltage source inerter was constructed. Since the proposed HEPWM algorithm is simple and fast, it is implemented using a low cost, 16-bit microprocessor.

In the present work، the behavior of Cu-Cr powder mixtures during mechanical alloying has been studied. The powder mixtures with 1، 3 and 6 weight percents of Cr in Cu were treated. They were milled in a ball mill with two different speeds of 250 and 500 rpm using equal numbers of 1 and 2 centimeters balls. The weight ratio of balls to powders was 10 to 1 under argon atmosphere. Ethanol was used as the process control agent and milling times were 4، 12، 48 and 96 hours. After every hour of milling، a half–an–hour stop was applied to avoid temperature rise. The milled powder mixture was evaluated by a scanning electron microscope equipped with energy dispersive spectroscopy and an optical microscope equipped with image analyzer. Results have shown profound effects of milling conditions (the change in time، speed، etc.) on the behavior of milled powders.

In the present study, Thermo-Reactive Deposition method (TRD) in a molten bath was used to form niobium carbide coating on AISI L2 steel. The coating was formed in five different composition of borax (Na2B4O7), boric acid (B2O3), and ferro-niobium. For all of the five compositions of molten bath, niobium carbide coating treatment was carried out at 1173 K, 1273 K, and 1373 K for 2, 4 and 8 hours. The thickness of coating ranged between 3.6 ± 0.1 µm to 33.6 ± 0.5 µm depending on the bath composition, treatment time, and temperature. Kinetic study of the formation of NbC coating demonstrated that for the molten baths containing 10 wt.% ferro-niobium or more, growth of the coating is under the controled of by diffusion. For such molten baths, the activation energy of the process was estimated to be 122.5 kJ/mol. A practical formula to estimate the coating thickness in these molten baths has been suggested.

Increasingly restrictive emission regulations and renewed focus on energy efficiency drive the current researches to find alternative fuels and their related better combustion strategies. In this regard, dual fuel engines, in which natural gas fuel is used as a main fuel and diesel fuel is employed as a pilot fuel, have received considerable attention. However, poor fuel utilization efficiencies and high emissions of HC and CO may be encountered at light loads. This study focuses on improving the aforementioned drawbacks. Exhaust gas recirculation (EGR) and its inherent thermal energy can be used as an effective way to improve the performance and emission parameters of these engines at part load conditions. Therefore, in the laboratory of authors, an experimental work was conducted on an IDI Lister (8-1) dual fuel engine to investigate the effects of different levels of EGR temperature on combustion process, performance and emissions of these engines. The amount of EGR conducted into the engine was altered but its temperature level was considered constant at 10 and 50 percents of full load of engine. Results of this work show that the ignition delay and combustion durations shorten sufficiently by increasing EGR percentage and its temperature to a specified level. Also, CO and UHC emissions reduce whereas NOx emission increases but not too much for low percentage of EGR. Moreover, by employing low percentage of EGR, performance and emission parameters show better behavior in comparison with high percentage of EGR at a constant temperature.