Journal of Advanced Materials in Engineering (Esteghlal)

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Due to improvements in computational resources, interest has recently increased in using implicit scheme for solving flow equations on 3D unstructured grids. However, most of the implicit schemes produce greater numerical diffusion error than their corresponding explicit schemes. This stems from the fact that in linearizing implicit fluxes, it is conventional to replace the Jacobian matrix in the dissipation term by its constant spectral radius. The objective of the present study is to develop a modified implicit solver based on Roe scheme so that its numerical dissipation is as much as the explicit one. In the proposed scheme, the Krylov subspace method with a LU decomposition preconditioner (GMRES+LU-SGS) is used to solve the linear systems. The efficiency of this method is shown by presenting some examples at the end.

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The present paper contains the test results of a planing catamaran model. The aim of the tests was to study the effect of hydrofoil in these types of crafts. First, experiments were carried out on the bare body (i.e. without hydrofoils) to obtain non-dimensional hydrodynamic resistance coefficient versus speed. Then, the model with hydrofoils, by various locations and attack angles were subjected to tests and the results were compared with those from the tests with the bare body. Results show that great reduction in hydrodynamic resistance of hydrofoil-supported catamaran is accessible especially at high speeds. In addition, hydrofoils positioning is important and un-suitable designs may result in instability in motion and increased in hydrodynamic resistance.

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Neutral stability limits for wake flow behind a flat plate is studied using spectral method. First, Orr-Sommerfeld equation was changed to matrix form, covering the whole domain of solution. Next, each term of matrix was expanded using Chebyshev expansion series, a series very much equivalent to the Fourier cosine series. A group of functions and conditions are applied to start and end points in the mathematical domain of the solution so as to avoid error accomulation at these points. The scheme ends with two matrices which result from the Orr-Sommerfeld equation. These matrices are solved, in conjunction, with boundary conditions ending up with a curve of neutral points of stability for an assumed velocity profile. Results are compared with other existing numerical methods and experiments, and the accuracy of the method is confirmed.

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In this paper an analytical model for cold rolling of strip has been described. This model is developed based on the slab method of analysis and the hydrodynamic lubrication. The characteristics of rolling are obtained from the equations of equilibrium and the plate was allowed to strain harden assuming that the lubricant behaves as a Newtonian fluid. The shear stress to the plate is obtained by calculating the thickness of the lubricant film by employing a viscosity-pressure-temperature relation. The governing equations are obtained by composing these relations and the final differential equations have been solved. From the solution of the final equation, the rolling force، torque and shear stress to the plate are calculated. To verify the validity of the proposed model, these values are compared with experimental and analytical results of other investigators. It was also noted that by employing the proposed analytical model, a large amount of computation time and costs are saved

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In this paper, the Radiation Transfer Equation(RTE) for a non-gray gas between two large parallel planes has been solved and the temperature distribution obtained. With the RTE, solution heat fluxes are also determined. Since and are two components of most combustion products, the problem has been solved for these two gases. The results were, whenever possible, compared with data reported elsewhere. Since the simulation of exact absorbing bands has been used, it can be claimed to be relatively close to exact solution. From the results otained, it can be maintained that treating, the above mentioned gases as a gray gas could cause considerable errors in the determination of temperature distribution and heat fluxes. The error would be more for water vapour than for carbon dioxide.

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An experimental investigation on heat transfer coefficient is presented from three horizontal tubes in a vertical array in a duct for 500

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The 25Cr-35Ni heat resistant steel has been widely used when resistance to oxidation and creep rapture at elevated temperatures is required. In this paper, the microstructural effect on the weldability of this alloy is investigated. The results of this study indicate that this steel has a perfect weldability in the as cast condition but does not possess good weldability in the aged condition. The as cast microstructure of 25Cr-35Ni steel consists of austenite matrix and a network of primary carbides, while the aged condition consists of austenite matrix and y primary and secondary carbides. The morphological change of primary carbides and the secondary carbides precipitate formation, reducing the elongation and ductility of aged steel, should have enhanced the steel susceptibility to cracking, particularly in the area of the eutectic carbides, and hence, the reduced weldability of the steel. The cracking observed was of the intergranular type and spread along the eutectic carbides. It was found that the carbides in the as cast steel consisted of NbC and M23C6, whereas that of the aged steel also exhibited Ni16Nb6Si7 and M23C6 carbides

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Reductive leaching was used to dissolve metals, especially cobalt, present in Fars Tidar mine,. In this paper, cobalt ore was leached with sulphuric acid in the presence of phenol to determine the effects of various factors on leaching. These factors included temperature, acid concentration, time, phenol content, pulp density, and interaction between some of the parameters. The results indicated that temperature was more effective on SN ratio (Signal to Noise ratio) which was found to be about 80%. The effecst of time and acid concentration on SN ratio were also determined at about 8% and 4 %, respectively. Although the effect of phenol content on cobalt leaching was too low but dissolution of cobalt decreased in the absence of phenol. Therefore, it was concluded that phenol was one of the factors in effective the leaching process. Anyway, three parameters including temperature, acid concentration, and time were selected as more effective parameters. Consequently optimum conditions can be obtained with high levels content of temperature, acid concentration, and time with low levels of phenol and pulp density.

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The presence of defects in cold mercerizing of cotton goods led to the creation of a new method, called hot mercerizing in which caustic soda solution is used at a high temperature. Hot mercerizing is successfully used in cotton blended with some other fibers. In cotton/polyester blend fabrics, this treatment serves a dual purpose: subjectively, it imparts a silklike soft handle to the polyester and brings about mercerizing of the cotton. In this work, the mercerizing operation with caustic soda solution was performed on a 65/35 polyester/cotton fabric in sixteen different temperatures (from 15°C to 90°C), in two states: with tension and without tension. Finally, the effect of temperature of treatment on some properties of fabric such as tensile properties, weight loss, and shrinkage have been studied. Alkali treatment cause weight loss in cotton/polyester blend fabrics, the main part of the weight loss attributed to the polyester component of the blend. Increasing temperature leads to a corresponding increased in weight loss. The resulting weight loss leads to more yarn release and consequently, to the improvement of the drape and soft handle in the fabric. However, it decreases the tensile strength and causes weakness of the fabric, therefore, an optimum of temperature must be considered. In the alkali treatment, the internal stresses in the fabric can be released. Release of tension in the fabric causes shrinkage, particularly in the warp direction. The effect of tension on properties of cotton/polyester blend fabric is not considerable in alkali treatment.

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Regarding the importance of ring spinning method among spinning systems, great potentials exist for research about on the improvement of the quality and properties of ring spun yarn. This study aims to improve yarn quality by changing the shape and dimensions of spinning triangle through forming a groove in the middle zone of the front darfting roller with a curvature of 5 to 7 mm. For the top drafting roller, we used an elastic O-Ring with dimensions similar to those of the groove. With this change, the geometry of spinning triangle is expected to change as an Euclidean geometry to a half cone Riemannian shape. The results show improvement in yarn tenacity, elongation at break, yarn evenness and faults, shape of spinning baloon, decrease in yarn tension and yarn breakage, improvement in fiber packing in the yarn cross section, more evenness in the yarn count and twist, and, finally, better inter-structure compared to the normal ring spun yarn.

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Continuous welded turnouts are important for CWR track through the railway station. According to equivalent resistance and non-linear theories and the principle of force diagram, a new method of theoretical calculation for continuous welded turnouts was developed. The continuous welded turnouts designed and installed according to the new theory behaved fairly well. The data collected on sites basically agreed with those of theoretical calculation. It was proved that the calculation theory is correct and values of calculation parameters are reasonable.

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Being economical and performing well under cyclic loads, steel sections filled with concrete have been widely used in structural buildings. Extensive studies and experiments have been conducted to investigate the influence of different parameters and loadings on the behavior of these structural components. Based on the data available from previous experiments and studies, this paper discusses the behavior of composite columns. The results of 3D-non-linear finite element analysis of thin-walled steel sections filled with concrete are presented. Lastly, comparisons are made between results from finite element analysis and experimental data available about the specimens. Using a trial and error method, the finite element model was calibrated and was used to evaluate the capacity of specimens that were not tested in the laboratory. The capacities of the sections were calculated based on the LRFD design method. The results are compared to evaluate the accuracy of the proposed method. Because of the increase in the use of high strength materials in structures, the effects of increase in concrete and steel strengths on the behavior of composite columns are discussed in this paper. Also the effects that the change in the thickness of the steel shell may have on the behavior of composite columns are argued.

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Silica fume has been largely used in concrete in recent decades due to its effect on improvement of strength and durability of concrete. On the other hand, attention has been recently paid to the use of limestone powder as a substitute for part of cement in concrete, basically because of its low price and its positive effect on the durability of concrete. The aim of the current study is the investigation of the interactive effect of silica fume and limestone powder on the compressive strength of concrete and the optimization of the mix design. To do so, 27 mix designs including 3 water-to-cementitious materials ratios (W/CM=0.25, 0.3 and 0.4) 3 silica fume-to-cementitious materials ratios (SF/CM=%0, %5 and %10) and 3 limestone powder-to-cement ratios (LP/C=%0, %15 and %30) were used and 28-day compressive strength of the cubic concrete specimens were determined. Then, the interactive effect of silica fume and limestone powder on compressive strength of concrete was investigated using isoresponse curves. Furthermore, the optimization of the mix design for concretes containing silica fume and limestone powder was carried out using “cost effective factor” (CEF) which is defined compressive strength divided by cost of concrete.

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Exergy analysis is based on combined first and second laws of thermodynamics and is a useful tool to analyze the energy systems in a better and more realistic way than an energy analysis, based on the first law of thermodynamics. Combination of exergy from thermodynamics with conventional concepts from engineering economy which is referred to as thermo-economy (exergo-economy) is a valuable tool to analyze the energy systems in a better way. In this paper, efforts are made to apply the concept of thermo-economy to analyze two power cycles (a combined Gas and Steam cycle and a conventional steam power plant). In this analysis, the results of an exergy calculation are combined with the economic aspects such as investment costs, fuel costs, and also operation and maintenance costs. The goal of this study is to show how to implement the concept of thermo-economy to these cycles and also how to estimate the price of the product (electric power generated). Assessment of the components exergy destruction costs is a second objective in this study. Results obtained from this analysis clearly show the effect of the cost breakdown and the component performance on the price of the final product. Comparison of the price of the product in these cycles shows that the combined cycle is superior to the conventional steam power plant.

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A higher bustle temperature in midrex direct reduction process is always desirable due to its positive effect on the productivity and DRI quality. The limit of the bustle temperature is related to the sticking or clustering behaviour of oxide pellets during the reduction in the reactor. It has been well estabilished that coating of oxide pellets by a refractory material decreases its tendency to clustering. In this study, the clustering behaviour of oxide pellets (produced from Golegohar-Chadormalu iron ore) during redution at different temperatures was investigated. The effect of coating with different amounts of hydrated lime on the clustering behaviour was also examined. Microscopic examination of coated pellets shows a porous, non-continious layer of Ca(OH)2 being fromed on the surface of the pellets. The clustering tendency of coated pellets, measured by the standard sticking test at pilot scale, was much lower, compared with normal (uncoated) pellets, while their reducibility was the same.

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Stator flux oriented vector control of induction motor (IM) drives for speed sensorless control has several advantages. But the application of a pure integrator for the flux estimation is difficult due to the presence of measurement noise and dc offset. To overcome these problems, some have used a programmable cascaded low pass filter (PCLPF). In this paper, it is shown that some problems still exist and some new problems arise from this approach. In order to solve these problems, a novel compensation method is proposed. In this scheme, the dc offset is detected and subtracted from the estimated flux along d and q axes. The simulation results show that it works well in the low speed region as well as in the transient state. The oscillation of the torque and the estimated flux are also reduced notably when the torque reference changes rapidly.

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In the last few years, Run-to-Run (R2R) control techniques have been developed and used to control various processes in industries. These techniques combine response surface, statistical process control, and feedback control techniques. The R2R controller consists of a linear regression model that relates input variables to output variables using Exponentially Weighted Moving Average (EWMA). In this paper, we have developed a R2R controller model based on quality costs. The model consists of finding optimum weight of EWMA procedure in R2R controllers with respect to conformities and nonconformities costs. The validity and performance of the developed model were tested using a real case study in an optic industry application.

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The new techniques in seismic design of structures are usually attributed to high damping ratios. In such systems, the assumption of classical (i.e. proportional) damping is not valid and in most cases they should be considered as Non-classical systems. Since the analytical tools for studying the behavior of such structures are not easily available, the present work attempts to find the limits, in which, a non-classical system can be approximated as a classical one. This is accomplished, first, by introducing the mass participation factor for non-classical systems. Subsequently, a relevant spectrum analysis technique such systems is developed. Using the spectrum analysis technique, the limitation of damping ratios in which two different types of Mass Isolated structures can be approximated as classical ones are determined. The results indicate that in the usual range of damping capacity for such structures, a well distribution of dashpots along the height of the system considerably reduces the non-classical characteristics of the structure.

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This paper presents the complete algorithm of site response analysis of nonhomogeneous topographic structures using transient two-dimensional boundary element method (BEM). Seismic behaviour of various topographic features including canyon, half plane, sedimentary filled valley and ridge sections, subjected to incident SV and P waves are analysed. The analysis shows the efficiency of the proposed algorithm and its advantage over common transformed domains methods in forming a basis for extension to non-linear behaviour.

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The study of two-phase fluid flow behavior in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions and other similar conduits is of great importance. A two-phase mixture flowing in a pipe can exhibit several interfacial geometries such as bubbles, slugs or films, depending on the fluid and hydrodynamic properties of flow. The main variables, giving rise to a variety of flow patterns, include relative discharge rate of fluids and the pipe slope. The flow patterns mostly attainable with air and water include stratified include and slug patterns. In this paper, the experimental results of pressurized water tunnel model are presented. The results include pressure transient and its variations for different hydraulic and geometric properties. It is shown that trapped and released air can cause tremendous pressure surges in the system and, eventually, may cause failure in systems (e.g. the maximum pressure inside the pipe would reach up to 10 times of upstream hydrostatic pressure). Finally, relations for forecasting maximum and minimum pressure in these situations are presented as a function of mean pressure, flow characteristics and pipe geometry.