ESTEGHLAL
Year:2003 | Volume:21 | Issue:2|Papers Count:17

Various methods are presented to control the attitude of satellite due to lack of information of YAW axis attitude so far.In this paper, a new method is used which is more general and is applicable to all types of satellites, with at least one controller. This method is not limited to YAW axis and can control the two other axes as well. One feature of this approach is the ability to be modified for large angle maneuvers for special applications. A new observer is also proposed for the controller, which causes the angle attitude to be kept in desirable values, with minimum control effect and more accuracy. Simulation results show that compare with methods using the complete all axis information, this approach is satisfactory.

Fabrication of an integrated circuit with smaller area, besides reducing the cost of manufacturing, usually causes a reduction in the power dissipation and propagation delay. Using the static CMOS technology to fabricate a circuit that realizes a specific logic function and occupies a minimum space, it must be implemented with continuous diffusion runs. Therefore, at the destine stage, an Eulerian path should be found for the logic function. Every discontinuity causes an increase in the area as well as a reduction in the clock rate and performance. The realization of a logic function using the static CMOS technology is done through different methods, most of which are based on the Uehara's method. In this paper, an algorithm is suggested that finds the Eulerian path and allows the implementation of the circuit with continuity in the diffusion region that results in minimum area. In a case where there is no Eulerian path, the possible sub-paths are found. In addition, the algorithm gives information that helps the layout generation.

In recent years, active filters have been considered and developed for elimation of harmonics in power networks. Comparing with passive, they are smaller and have better compensating characteristics and resistance to line distortions. In this paper, a novel idea based on adaptive filter theory in presented to develop an active filter to eliminate the distortions of an arbitrary signal. Using this idea, new methods of active power filters, are introduced to remove harmonic distortions in single phase power networks. Stability of these methods are analysed and the simulation results are shown. Design and implementation of this adaptive active filter are done and the performance and advantages of this technique are affirmed by the practical results. Exact estimation of amplitude, frequency and phase of input signal first harmonic is the most important advantage of this adoptive technique. Furthermore, this method is for canceling the harmonics of any arbitrary signal and can easily be modified for other systems, and three phase networks. Due to its adaptive nature, this technique can adapt itself with variations in environment and system parameters and be adjusted for optimal behaviour.

Knowledge is one of the most important organizations' assets. To manage knowledge effectively, it is necessary to be able to measure knowledge. There are few method for knowledge measurement with certain limitation. One important weakness of current method  is their insufficient attention to definition, dimensions and attributes of knowledge. In this paper, we propose a new method for measuring the level of an engineering organization's knowledge. According to our proposed method, the level of an organization's knowledge is a function of both "knowledge hierarchy" and "knowledge dimensions". The method is applied to an engineering organization to measure the level of knowledge at two different times and the result is presented.

In order to carry out experimental investigations on radial inflow gas turbine, a special test laboratory was designed and constructed at sharif University of Technology. This laboratory is introduced in the present paper and experimental procedures are elaborated on. Then, some test results are presented and discussed. The trends of performance characteristics math our expectation and show good agreement with the published research results in this field.

One of the basic equations to analyze the detonation of high explosives is the equation of state of the detonation products. Due to the very high pressure of the product, the direct measurement of the thermodynamic variables such as pressure or temperature is not possible. In this research, the parameters of BKW and HOM equations of state of detonation products are determined via experimental measurement of the detonation velocity. Comparing the calculated parameters show good agreement with the published results for a vast range of explosives.

A new method (thermal spokes) is proposed to simulate the guide rolls in FE analysis of the ring rolling process. So far this method is the only one, capable of calculating guide rolls reaction contact forces related to the stiffness of their, adjustment mechanism. The method is simple to use, does not introduce further nonlinearities and could be used in any kind of FE formulations. The method is successfully employed in FE analysis of rectangular and T-section rings. The results of the thermal spokes method, a new analytical method based on lever arm principle with experimental results are in good agreements. This analysis shows that the guide rolls greatly affect the process.

Due to the widespread applications of fiber reinforced polymer composites in various industries, the machining of these materials to reach the desired shapes, close tolerances and surface finish quality is of great importance. But the composite materials are anisotropic and are mostly prepared in laminated form and, therefore, they have special chip formation behaviour. Among the effective parameters in machining of these materials, the angle between the fibre orientation and machining direction and also the properties of fiber and matrix are of great significance. In the present paper, using the latest theories in the field of machining of FRP materials, a mathematical model to improve the feed rate as well as the cutting speed with respect to the fiber orientation has been introduced and, a computer package was developed for the 3-dimensional CNC machining of fiber composite materials. A number of composite pieces were fabricated and machined to check the output of the programme and the work pieces. Besides the reduction in the machining time, the machined work pieces had desired surface quality, while the common defects like matrix burning, delamination and fiber pullout were completely absent.

Titanium carbide is used as an attractive reinforcement to produce particulate metal matrix composites. One of the problems to use this carbide as a reinforcement in copper-based composites is the lack of wet ability in Cu-TiC system. This property improves as the C/Ti ratio in carbide decreases.  A practical method is presented in this paper to improve the dispersion of titanium carbide into liquid copper and emphasis is placed on the C/Ti ratio in the carbide. It was observed that the C/Ti  ratio in a raw mixture containing only Ti and C was equal to C/Ti ratio in the carbide after synthesis but when copper powder was added to the raw materials, this ratio was higher than the starting value. Regarding the relationship between the titanium carbide lattice parameter and the C/Ti ratio in the carbide and this ratio in the raw mixture, a graph was drawn that related the C/Ti ratio in the carbide to the raw mixture. In a master alloy containing 3Owt.% Cu, and the C/Ti=1, a network of agglomerated TiC particles with the same C/Ti ratio is formed which cannot be dispersed into liquid copper. When this ratio is decreased to 0.3, particulate titanium carbide with C/Ti =0.5 can be easily dispersed into liquid copper.

In recent years many different ways have been investigated by steel producers to increase ductility, impact strength and formability of steels. More important ways are steels with very low amounts of inclusion, small size inclusions and modified inclusions. In this study, experiments have been performed on the API-X42 steel produced by the electric arc furnace in Mobarekeh Steel Co. After the preparation of the melt in the electric arc furnace, it is taped in a 200 - ton ladle and ladle treatment was preformed in a ladle furnace (LF) in the steelmaking shop. In this study the effects of amount and the rate of CaSi wire addition on the shape and structure of inclusion were investigated. The optimum conditions for adding CaSi for inclusion shape control were also determined. Scanning electron microscope (SEM) and chemical energy analysis dispersive system (EDS) showed that adding calcium to the melt affects the chemical composition of inclusions present in steel melt. The effects of CaSi wire injection treatment, injection amount and inclusion shape control on the impact property and formability of steel were shown using charpy impact test.

The metallurgical and mechanical properties of Ti6Al4V/(WC-Co) friction welds have been investigated. The microstructure dose to the bondline comprised a mixture of acicular and equiaxed a plus ß phases. The diffusion of elements in the welded specimens has been detected. The fracture strengths of Ti6Al4V/(WC-Co) friction welds markedly improved when the cobalt content in the (WC-Co) carbide substrate increased.During the three-point bend testing of Ti6Al4V/WC-6 wt.%Co welds, the crack initiated at the bondline region at the periphery of the weld and then propagated into the brittle (WC-6 wt.%Co)substrate, while with the Ti6Al4V/WC-24 wt.%Co and Ti6Al4V/WC-24 wt.%Co welds, the crack initiated and propagated at the bondline region.

Application of gravity and magnetic separation methods to upgrade low grade Manganese ores from Venaj Mine has been reported elsewhere. This paper discusses the results of flotation tests, as well as combination of flotation and magnetic method to concentrate fine particles (less than 150 microns) of manganese ore. Results obtained from various direct and reverse flotation tests, using different types of reagents, indicated that manganese fines can not easily be concentrated by flotation. In this investigation, combination of direct flotation and magnetic separation for fine particles (finer than 150 microns) with 8.36% Mn, 34.11% SlO2 ,23.05% Fe2O3yielded a manganese concentrate with 26.78% Mn, 11.64% SiO2 20.37% Fe2O3 and 56% recovery. Desliming 10-15 micron particles prior to flotation tests improved product quality and the recovery.

In the present work the reflection behavior and the color appearance of acrylic yarns, as pile yarns used in carpet and piled fabrics, are considered along their lengths as well as their cross -sections. Differences between longitudinal and cross - sectional reflection behavior of yarns are measured in different yarn densities and hues and explained by the geometric model.The results of experimental work show that the average of reflectance and lightness values along yarns' length, with identical hue, are higher than values obtained from their cross -section, besides, the lightness values of cross-sectional of samples, with identical hue, increase when the density of yarns in holder cell increases. The metric chromas as well as the hue angles of samples, dyed with the same dyestuff are different in two directions and lead to color difference values between 3.35 and 27.84 under D65 Illumination and CIE 1964 standard observer in CIELAB color difference formula. The reflection differences between two directions are analyzed using the geometric model and it is found that they originated from different optical passes through the fibers in the mentioned modes.

This paper discusses the effective length factor of columns in Khorjini frames. In order to find this factor, a proper approximated method is proposed. In addition, accurate analysis is performed and the results are compared with those from the proposed technique. The comparison demonstrates the accuracy of presented FORMULATIONS. The proposed method is similar to Julian and Lawrence's, which is used for rigid frames.

Limitations on water resources and the high costs of new hydraulic structure construction intensify the need for an optimum operation of Iranian reservoir systems. For appropriable water distribution and management in a 9-reservoir system on the Kalamarz river, Mianeh basin optimizing mathematical models are applied. Considering the stochastic nature of river discharges and the constant amount of reservoir volume and farmland area, an optimum linear chance constrained model is programmed and run by GAMS software. This model is only used for within-year regulation. Using a linear yield regulation, operation parameters for request months and all reservoirs are derived by the model. Also, the model computes portions of river discharge diverted to each reservoir in different months and outflow from downstream for different months. Results show greater than 60 percent deficit that indicates the lack of sufficient attention to constructing an optimum reservoir volume and extensive development of farmlands for each reservoir.