Year:2002 | Volume:36 | Issue:2 (76)|Papers Count:17

In this paper a novel approach for optimal location, sizing and determining the service areas of HV/MV substations in a long-range planning period using pseudo dynamic methodology is presented. Costs of equipment, areas, cables in MV side and power loss are considered in cost function. Uncertainty in loads is modeled using LR fuzzy numbers in load points. For optimization procedure, genetic algorithm (GA) with a new coding is used. Load points splitting in each area between substations and infeasibility solutions are considered in search procedure. Based on this, software was developed and integrated into an optimization tool for substation allocation. The software was applied in many cases with satisfactory results.

Many of the current square root algorithms require an initial estimation of the result in order to start the computational process. Usually, for this purpose, a ROM based lookup table is employed, which occupies a relatively large space. In this paper an improved routine is presented which performs the initial estimation for the square root of real integer values with an error of less than six percent. In addition, an implementation method using FPGAs for floating point operands is proposed.

Transformers have found widespread use in power grids to reduce losses and improve voltage profile. Due to high cost, its optimum design has received attention in literature. Based on Genetic Algorithm (GA), a new approach is proposed in this paper in which a transformer may be optimally designed while various constraints are met. The capabilities of the approach is examined and verified for a typical distribution transformer.

Availability in a system means that users can access their expected services at expected times. Attacks on availability are called denial of service attacks. In this paper, we propose a novel categorization of these attacks. Based on the proposed categorization, we also propose and analyze some necessary principles for the design of protocols that are resilient against such attacks. We also show that some existing protocols in the TCP/IP protocol suite are not consistent with the proposed principles and, therefore, they are vulnerable. We then analyze some instances of such attacks and propose modifications in those protocols to make them compatible with the proposed principles which improve their resilience.

A new method for generation of artificial earthquake accelerograms from response spectra is proposed by Ghaboussi and Lin in 1997 using neural networks. In this paper the methodology has been extended and enhanced for data of Iran. For this purpose, first 40 records of Iran acceleration is chosen, then an RBF neural network which called generalized regression neural network (GRNN) learn the inverse mapping directly from the response spectrum to the Discrete Cosine Transform (DCT) of accelerograms. DCT has been used as an assisting device to extract the content of frequency domain. Learning of network is reasonable and a GRNN learns it in a few second. Outputs are presented to demonstrate the performance of this method and show its capabilities.

After a quick review of bolted connections in steel structures, flush end-plate type connection is introduced. Two-way connections made up of such kind have been analyzed using a three-dimensional (3D) inelastic finite element modeling. The model output compared well with available experimental tests. 65 cases of flush end-plate stiffened connections, then, used to study effects of connection parameters on its behavior. Finally Multiple-regression analysis procedure applied to derive Richard-Abbott power function parameters, which predicts moment-rotation curves for any selected connection, given the geometrical and mechanical properties

The strength of post-tensioned members of pre-stressed concrete structures is basically related to tensile strength of post-tensioned steel. For Protection against rusting, this steel is usually put in PVC or corrugated steel dust then ducts are filled with cement mortar. Nevertheless, due to incorrect method of filling, steel may be rusted. Besides, imperfect design of used mortar may lead to bleeding casing longevities, sometimes to the extent of the whole duct. Bleed voids are the main cause of steel rusting, because they provide paths for penetration and movement of salt solutions and other harmful chemical solutions through the ends of anchorage and existing cracks. This investigation presents a non-destructive test called "impact -echo" for studying the position of mortar inside these ducts and determining the location and size of voids. Theoretical and experimental studies indicate the high accuracy of the method in tracing and size determination of these voids. It has been shown in this study that information about existence and size of these voids can be obtained using studying the amount of reflected dominating frequency resulted from a mechanical impact on the surface of the concrete member.

In this paper a new approach is presented for analyzing the thermal behavior of rotary regenerator heat exchangers used in utility boilers. In this type of heat exchangers, due to the rotation of the solid matrix, the temperature of the fluids as well as heat exchange elements are functions of position and time. Energy equations for hot stream (gas) and cold stream (air) and the solid matrix have been solved using the Heat Blance Integral Method. The variation of physical properties of the cold and the hot fluids as well as the solid matrix has been considered. The results have been compared with existing data and the agreement appears to be reasonably good.

In the present study a Ti-B2 containing metal matrix composite has been made by mixing of two molten master alloys, Al-8%Ti and Al- 4%B. The weight ratio of Ti:B was selected in an appropriate portion to ensure the formation of TiB2 particles in aluminum matrix. The Al-8%Ti and Al-4%B master alloys were made by K2TiF6 and KBF4 salts in an induction furnace. The mechanism of formation of the TiB2 particles was studied by an optical microscope equipped with a Hot Stage, providing direct observation of phase transformation by recording real images. The study of phase transformation of solidified specimen microstructures was made by a scanning electron microscope coupled with EDAX analyzer. The results obtained from Hot Stage studies indicated that the boron atoms migrate easily towards TiAl3 particles to produce very fine TiB2 particles on the interface of TiAl3 particles and matrix alloy. Small atomic radius of boron and the ease of its diffusion may cause the readily access of boron on the interface and also formation of agglomerated TiB2 particles, as a result of exothermic reaction of TiB2 formation. The micro structural studies of the real-time observation showed that due to the high mobility of TiB2 particles and their easily separation from TiAl3 particles, the growth rate of these particles is high and penetration of boron into the TiAl3 particles leads to the replacement of agglomerated TiB2 particles (in a ring shaped) with large TiAl3 particles.

In this research, the effect of replacement of part of nickel and chromium by copper on hardness, impact strength and wear properties of martens tic white cast irons has been investigated. Samples made in infrared and cumolloy irons were cast and compared to Ni-hard iron used in industry. Results indicate that mechanical properties of these alloy are comparable to or even better than Ni-hard. Also, wear resistance is better than cumolloy and Ni-hard irons.

A new retrofit targeting procedure, based on pinch technology has been developed. The procedure considers existing structure and hydrodynamic system of a given network as two main constraint during targeting. The procedure uses a linear programming model to consider existing structure. The model finds a network structure that has maximum compatibility with existing structure. Furthermore, the procedure using the pressure drop equations, can consider decreasing the film coefficients of streams due to increasing network area. Good compatibility between old and new networks and non replacement of hydrodynamic equipment cause to the best use of capital in retrofit projects. The procedure has been checked by doing two case studies, in which the results compared to the established methods, and realized significant improvement

An effective method in the removal of metal ions from industrial wastewaters is the hollow fibers separation technology. In the common hollow fiber separation processes, liquid membranes together with chemical extract ants or water soluble chelating polymers are used for the removal of metal ions. In this study the application of a hybrid system consisting of natural zeolites and the hollow fiber membranes on the effective separation of nickel ions from synthetic wastewater was investigated. The hollow fibers used in this new technique were made of polysulfide in the ultra filtration range. The effect of different parameters, such as the initial metal concentration, feed flow rate and the quantity of the zeolite were studied on the efficiency of the separation process. The results showed that the presence of zeolite in the receiving phase, increased significantly the amount of nickel ions removed from the feed, comparing to the case where the zeolite was absent. Increasing the initial concentration of nickel in the wastewater raised the permeate flux, however, It had no effect on the total percentage of nickel ions removed. Mixing the aqueous receiving phase containing the zeolite, as well as higher flow rates of the feed through the lumen of the fibers, both significantly increased the rate and the percentage of the nickel ions removed.

In this paper the Meiduk copper ore body is first briefly described and its relevant parameters considered. An appropriate computer program is introduced and its virtues described. The computer program, first used in 1997, is subjected to analysis and the required data gathered from field investigations and experiments. These data include: geological and geotechnical parameters, characteristics of explosives used, environmental considerations etc. Burden is calculated using trimmed averaging method and the pattern of drilling and blasting is designed, using hand used method and the program introduced earlier. The results of these calculations are subjected to sensitivity analysis for fragmentation criteria and in particular, those obtained from two different methods compared. This comparison clearly demonstrates that the computerized method is of more accuracy and flexibility. This will help the mining engineer to minimize costs in varying conditions, whilst increasing blasting efficiency. The models introduced and results obtained could be used for Meiduk copper ore body and all similar situations, in order to obtain the optimum pattern for drilling and blasting.

Ground vibration due to blasting is the research subject of many investigations. A lot of works have been done in order to estimate the quality and quantity of this blasting outcome. Mathematical models proposed by various investigators are a noticeable result of these investigations. In this paper, the origin of these mathematical models are studied and the short comes are pointed out. With aid of real data a new empirical model has been proposed. This model is some modification of the previous ones with some different parameters. This investigation is based on analyzing the data obtained by operating 14 blasts in Sarcheshmeh Copper Mine whose data have been collected by seismographs installed in the area. In the proposed model, instead of the amount of charge exploded in each delay the amount of charge the vibration due to which is received in a certain time is concerned. This certain time has been determined to be 10ms for this mine. The application of the proposed model is compared with that of the previous models and with the real data. This comparison shows that the applicability of the new model is by far better than that of the previous ones.

The stability of underground excavations during and after construction is the main concern of geotechnical design engineers. Rock masses contain natural discontinuities, which may cause stability problems, therefore, most underground openings need to be stabilized to maintain their integrity during their service life. The best way to achieve this is through the use of reinforcement to help maintain the load-carrying capability of rock masses near excavation boundaries. Rock bolt is the most widely used type of reinforcement in rock engineering projects. Although numerous research on the bond capacity of a bolt is available but the detail study of the bond failure mechanism in this type of reinforcement has yet to be done. The main component of the bond capacity in rock bolts is mechanical interlocking, which after onset of slip, mobilizes the shear strength of the grout against the steel ribs. Similar to any rough interface, the most important factors controlling the shear strength at bolt-grout interface are confining pressure and grout properties. To study the pressure dependency of bond strength of a deformed bar, as well as the effect of cement shear strength and rib shape, a modified triaxial Hoek cell was designed to facilitate application of a radial confining pressure to a grouted bolt while pulling it axially. During the test, both axial displacement of the bolt as well as the radial dilation of the grout was monitored. Few deformed bolts were designed and manufactured to study the effect of the shape of the ribs. While pull out, the cement that is captured between lugs will shear which in turn emphasizes the importance of shear strength of the grout annulus. In this report, details of the laboratory test results are presented and conclusions are given based on the obtained results