[en] Cloud-to-ground lightning strokes can include dangerous overvoltage on power distribution overhead lines. In this paper, a new algorithm is propagated within a distribution network including nonlinear apparatus. The coupling between the lightning channel and the overhead line is based on an antenna theory model and employs the method of moment for solving the governing electric field integral equation. The computed induced overvoltage is then used in the electromagnetic transient program to analyze its propagation within the distribution network. In this regard, the accuracy of the new coupling method is demonstrated by comparing the calculated induced over voltages using the new method and those obtained using the conventional methods. Simulation results are presented to show how the induced overvoltage is penetrated in a typical distribution network, consisting of overhead lines and underground cables, a distribution transformer protected by surge arresters and a three-phase resistive load

[en] In this paper, vibrational behavior of bodies of revolution with different types of structural faults is studied. Since vibrational characteristics of structures are natural properties of system, the existence of any structural faults causes measurable changes in these properties. Here, this matter is demonstrated. In other words, vibrational behavior of a body of revolution with no structural faults is analyzed by two methods of I) numerical analysis using super sap software, II) Experimental model analysis, and natural frequencies and mode shapes are obtained. Then, different types of cracks are introduced in the structure, and analysis is repeated and the results are compared. Based on this study, one may perform crack detection by measuring the natural frequencies and mode shapes of the samples and comparing with reference information obtained from the vibration analysis of the original structure with no fault

[en] This paper is dealing with refractory earth of North Semnan. Having an area of 2000 square kilometers, Semnan province is mainly formed by sedimentary rocks with a verity of refractory earth, red earth and kaolin containing heavy minerals. The refractory earth of this area contains a considerable rate of aluminum oxide in shape of dia spore minerals, behemoth and gybsite along with heavy minerals of iron and titanium. To improve the quality of refractory earth, in order to be used in related industries, these minerals have to be separated. To assess the quality of refractory earth of North Semnan as the raw materials of refractory industries, their genesis and mineralogy properties have been precisely studied. Based on the rate of aluminium oxide of the refractory earth of North Semnan mines, a suitable mineral deposit has been selected for more investigation. Using XRD and X RF methods along with electronic and photo microscopes, the refractory earth and heavy minerals of them have been assessed. The elementary laboratory experiments of fragmentation and magnetic separation have been performed. It has been proved that the iron minerals can be separated and, therefore, the quality of the refractory earth can be improved. The separation of titanium minerals has to be investigated with other methods

[en] In this paper a least square numerical method is presented for the solution of the junction of cylindrical waveguides. First, the electromagnetic fields in the input, output and the aperture waveguides are expressed by their modal expansions. Then, using the boundary conditions on the tangential electric and magnetic fields over the waveguide junction, an error function is constructed which is a positive definite quadratic function of the modal amplitudes. The unique minimum point of this error function may be obtained by the inverse of a hermitian matrix. This method of least squares is applied to parallel- plate and also rectangular waveguide junctions including conducting diaphragms. The outputs from computer implementations are compared with the data in the literature. In the present version of method of least squares similar to the method of moments for the solution of waveguide junction problems, the phenomenon of relative convergence appears, where the relative number of modes in various sections of the waveguide has a definite effect on convergence of the numerical methods and should be selected in proportions to the size of the waveguides. On the other hand, in the customary method of least squares, a weighting factor appears in the error function, which has a definite effect on the solution and the conservation of power and reaction should be used to determined its correct value. Therefore, there is an uncertainty of the solution of the waveguide junction problems by the various versions of the method of least squares, and it is necessary to adopt appropriate measures to reduce errors

[en] One of the most effective method used in protecting gas turbine blade against hot corrosion and oxidation is the employment of enriched chromium coatings. The effect of processing parameters such as time and chemical compositions of coating on its structure and hot corrosion resistance were evaluated in this work. Pack cementation method was used at 1100 ^deg^for various time. Structure of coating was examined using the light and electron microscopy to evaluate hot corrosion resistance of the coated specimens, that were subjected to hot corrosion test at 850 'deg' for 528 hr s along with an uncoated sample. The corroded surfaces of the samples were studied using light and electron microscopes as well as XRD analysis. The results show that by increasing both the amount of chromium in the pack and time of operation, hot corrosion resistance of coating increases. However, the mechanical properties of the coated samples were adversely affected by increasing the surface concentration of chromium and/or thickness of coating more than a certain amount. Therefore, it is essential to optimize the time and chromium concentration in order to obtain the best mechanical and hot corrosion properties

[en] A Valid boiler model is a tool for the improvement of the steam generation control system and hence results boiler efficiency enhancement. However, methods of obtaining such a model are not readily found in the open literature and are often specific to a particular plant. This paper presents boiler model using a new method in system identification called ^Subspace methods^. This method is shown to provide an accurate state space model for boiler in a few numbers of operations, directly from input-output data without any prior knowledge of the system equations and any requirement to several stages of testing

[en] A great number of engineering problems about nuclear fusion have to be solved before it's real life application in energy generation be economically reasonable. Tokamaks are presently the most successful apparatus in magnetic confinement of plasma and performing the nuclear fusion. The control of the plasma position is one of the basic necessities in proper working of Tokamaks. Having a relatively precise model of the position variations with respect to control voltages is compulsory in the design of appropriate controllers. In this paper a simple model of the plasma position in Damavand Tokamak has been presented and then the stability of the closed loop system is investigated in the presence of uncertainties in the plasma as well as the controller parameters

[en] The Method assumes linear elastic material behavior, but takes into account the changes of geometry due to applied load. Such a formulation makes it possible to study the change of the crack tip geometry and its effect on the local stress and displacement fields during the process of static loading. The solution obtained for a sharp crack provides finite stresses and strains at the crack tip, which becomes blunt soon after application of the load. Closed from displacement solution is also obtained. A finite element commercial code, ANSYS, is used to simulate the crack behavior on a remote tension stress. It is shown that the displacement solution obtained form the present method agrees very well with Finite Element Method solution. However, because of high stress gradient close to the tip, the stress given by Finite Element Method at the tip is not reliable. A method is proposed which uses the Finite Element Method to obtain the final shape of the crack along with the closed from stress solution presented here. Results from present solution are used to predict the plastic zone size based on Irwin method of LEFM. It is shown that prediction of plastic zone provided by the stress distribution of the present solution is in good agreement with the experimental results

[en] For pumping viscous fluids like oil and petrochemical products, by using the centrifugal pumps, fluid flow rate and pumping head are smaller than that of water, while the required power is increased. This is due to increased frictional losses in impeller passages. The characteristic curves for pumps, offered by different manufacturers are exclusively for water and can not be valid for viscous fluids. In the present project a centrifugal pump manufactured by pump iran has been tested on a test bed for different industrial oils as well as water. In order to investigate the effect of different design parameters on pump characteristics, a new impeller has been designed with reduced number of blades, the shroud has been taken away and with new dimensions for blades. The results obtained from different oil tests indicate that head, capacity and efficiency are increased. The numerical simulation of fluid flow inside the passage of impellers for two model by fluent code confirmed the results of hydraulic tests

[en] In this paper, a methodology is presented to determine the optimal sensor choice for active control of surge in multi-stage axial flow compressors. In this method, the compression system is modeled based on the conservation equations of mass, momentum and energy. The model is then linearized at unstable steady-state points, and the Linear Quadratic Gaussian controllers are designed to stabilize the compression system. The effects of different sensor types and locations on active stabilization process are then investigated for both low and high compressor speeds. Based on this sensor placement methodology, the sensor location and type are selected in order to minimize the estimation error and air bleed mass flow. The results are presented to show the effectiveness of the methodology. These results show that the proper sensor location is dependent on the compressor rotational speed and the instability origination