Showing 657 results for Type of Study: Research
A. Monshi,
Volume 16, Issue 1 (7-1997)
Abstract
This new method which is worked out in Isfahan University of Technology, makes it possible to analyze the phases quantitatively in minerals and powdered materials by X Ray Diffraction and without any reference material. To identify n unknown phases, n different combinations of phases, from fine and coarse fractions, or etc., must be obtained. Amorphous phases should not exist. Intensity ratios of selected peaks of different phases to the suitable peak of added substances are plotted against the weight ratio of unknown material to substances. The phase is used to eliminate the effect of absorption in measurements. After detecting the slopes of linear plots which pass through the origin, n equations are obtained which are solved for n unknown coefficients. The quantitative phase analysis is subsequently performed in all n samples. If reference materials are available for some phases, n is reduced. The method is to analyze three phases MgO, CaO, Ca(OH)2 with substance CaF2, in magnesite – dolomite, partially hydrated refractories.
J. Mahdavi and A Emaadi,
Volume 16, Issue 1 (7-1997)
Abstract
Power electronic converters are non-linear time-dependent systems whose exact analysis without the use of computers is very difficult, and even using computer softwares requires a long time. Use of the state space averaging method, as will be mentioned, in addition to simplifying the analysis procedure which is a result of converting a time-dependent system to a time-independent one, reduces the required computation time considerably. But this method is not applicable to circuits for which small variations of state variables does not apply, since it is not able to follow rapid and large changes. Therefore, we make use of a developed method in which we consider the average of the state variables as well as adding the harmonics. This more general method can basically be adjusted to various arbitrary wave forms, and is based upon a Fourier series time-dependent display for a sliding window of the given waveform. In this paper, after introducing the developed state space averaging method, results of applying this method to various basic DC/DC and DC/AC converters will be mentioned, and also effects of some parameters on the quality of model will be discussed.
A. A. Bidokhti and A. R. Mohamadnejad,
Volume 16, Issue 1 (7-1997)
Abstract
A small salt gradient solar pond with an average surface area of 1.8 m2 and depth of 0.8m has been tested. The depths of storage, gradient and surface zones are 0.3, 0.27 and 0.07m, respectively. The temperature of the storage zone for the summer days reaches its maximum of 65˚ C after about 8 days. Daily variation of the storage zone temperature was about 8˚C which is due to small volume of this zone. The thermal absorption of the pond varies between 35 to 20 percent of the total solar radiation, depending on the temperature of the storage zone. Salinity of the storage zone is about 200 gr/kg and the density gradient of the gradient zone is about 5x10-3 gr/cm4 which with typical fluid velocity of the convective zone gives a Richardson number, Ri, of order of 104. Erosion of the gradient zone based on this Ri is about 2.5 cm/month which is in agreement with the observations. Although the temperature of the storage zone reaches high values, with sloped wall, no sign of double diffusive convection was observed.
A. Meghdari and F. Fahimi,
Volume 16, Issue 2 (1-1998)
Abstract
Recently a method has been developed to decouple the equations of motion for multi-rigid body systems. In this paper, the method is first studied, then the equations of motion for a planar two degree-of-freedom robot with flexible joints are carried out using Lagaranges equations and Kanes equation with congruency transformations. Finally, the results obtained from both methods are throroughly compared.
A. Heydari, S. Hatefi-Pour and A.a. Ahangar,
Volume 16, Issue 2 (1-1998)
Abstract
In the last quarter of the century, a substantial amount of research work has been conducted on optimization of energy consumption by refrigeration systems and on proper design and construction of household refrigerator-freezers. The importance of such energy optimization schemes stems from the environmental impacts of Freon (R-12) used as the working refrigerant in household refrigerator – freezers as well as the enormous energy consumed by such appliances. International regulations for the replacement of Ozone-depleting refrigerants, such as the Montreal Protocol, as well as the Iranian regulations regarding reduced energy consumption of energy consuming products have motivated research on the optimum design of household refrigerator-freezers. In this paper, research works aimed at analytical modeling and also the experimental works conducted to determine design methods of energy efficient refrigerator- freezers in Iran will be presented. Using the numerical method developed for this purpose, a parametric analysis of the components of a refrigerator-freezer manufactured in Iran will be presented and the reduced energy consumption by the selected appliance and its increased efficiency will be discussed. The influence of replacing R-12 with its substitute refrigerant (R-134a) on the energy consumption and efficiency of the typical refrigerator is also presented.
M.azhari and S. Hooshdar,
Volume 16, Issue 2 (1-1998)
Abstract
The spline finite strip method (S.F.S.M.) for buckling analysis of plates and plate assemblies subjected to longitudinal compression and bending, transverse compression as well as shear is described. The method allows for the boundary conditions. Local buckling coefficients of plates with different boundary conditions under compression, bending and shear are calculated. Convergence studies with increasing number of section knots are described. The method is also applied to study the elastic local buckling interaction of bending and shear for plates with different aspect ratios.
M. M. Saadatpour and D. Mokhalefi,
Volume 16, Issue 2 (1-1998)
Abstract
This paper may be regarded as a new numerical method for the analysis of triangular thin plates using the natural area coordinates. Previous studies on the solution of triangular plates with different boundary conditions are mostly based on the Rayleigh-Ritz principle which is performed in the Cartesian coordinates. Consequently, manipulation of the geometry and numerical calculation of the integrals are time consuming and tedious. In this paper a new approach is developed to analyze triangular plates by the Ritz method, using interpolation functions in the area coordinates. The geometry is presented in a natural way by mapping a parent triangle and the integrals are evaluated analytically. In this approach, the convergence is always assured due to the completeness of interpolating polynomials. Several examples are presented and the results are compared with other available data.
S. A. Hoseini,
Volume 16, Issue 2 (1-1998)
Abstract
Warp and weft spacing and its coefficient of variation affect the physical properties of fabrics such as fabric hand, frictional and mechanical properties. In this paper the weft and warp spacing and its coefficient of variation for plain weave is calculated using Fourier transforms. Different methods have been used in this work including autocorrelation function. First, two dimensional power spectrum of the gray level image of the fabric was estimated using Fourier transforms. Then, inverse Fourier transform was used to calculate the two dimensional autocorrelation function. Finally, from autocorrelation function and autospectral density the periodicity of the warps and the wefts were calculated. The results from ACF and microscopic methods yielded a significant correlation factor (r2). Thus image processing coupled with application of fourier transforms can be considered as a new method and a good substitute for the microscopic method.
M. Shamanian, M. Salehi and F. Ashrafizadeh,
Volume 16, Issue 2 (1-1998)
Abstract
The use of Fe-Al intermetallic compound coatings has been investigated in order to improve the tribological behaviour of carbon tool steel. The coatings were formed by a pack cementation process and subsequently diffusion annealing at 900˚C in an argon controlled atmosphere. The optimum diffusion time was selected on the basis of optimum thickness and tribological behaviour.
The microstructure and the phases developed on the surface were identified by metallography, microhardness, X-ray diffraction (XRD), microanalysis (EDX) and glow discharge optical spectroscopy (GDOS) techniques. Experimental results indicate that a three layer coating is formed on the surface of the aluminized specimens, the outermost layer being identified as Fe2Al5 and the underlying layers as FeAl and Fe3Al. A two layer coating was formed on the surface of the aluminized and subsequently diffusion annealed specimen at the optimum time. The FeAl and Fe3Al have been formed on and below the surface, respectively.
The results from wear testing indicate that these coatings improve the wear and frictional behaviour of carbon steel significantly. The predominant wear mechanisms of diffusion annealed specimens were identified as delamination and oxidative wear.
M. A. Golozar,
Volume 16, Issue 2 (1-1998)
Abstract
In this paper, the nucleation and growth of diamond/diamond-like coatings on austenitic (AISI 316) and ferritic (AISI 430) stainless steel substrates have been investigated using torch technique. The effects of substrate surface preparation has also been studied. The quality of coatings produced has been examined using optical and scanning electron microscopy, X-ray diffraction, Raman spectroscopy and atomic force microscopy.
The results obtained revealed very good crystalline grains and coating on austenitic and clusters of semi-and non-crystalline particles on ferritic stainless steel substrates. It was also observed that mechanical polishing and/or chemical etching would increase the nucleation density. The nucleation density was a function of substrate temperature, as well.
M. Kahrizi, A. Heidary and M. Kyvanfar,
Volume 16, Issue 2 (1-1998)
Abstract
Analysis of aperture-coupled microstrip antennas with a superstrate using space domain closed form Greens functions is presented. Integral equations are derived from applying the boundary conditions on the radiating patch, across the aperture, and on the microstrip feedline. The computation of space domain greens functions is performed using the closed-form. The solution of the integral equations is based on the method of moments. The information about the input impedance of the antenna is extracted from the electric current distribution on the microstrip feedline using the matrix pencil technique. The radiation pattern is obtained from the electric current distribution on the antennas patch utilizing the asymptotic forms of sommerfeld integrals. The effect of considering a superstrate for different thicknesses and dielectric constants are examined. Numerical results are compared with other published and experimental results. The results show good agreement with prerions data.
M. H. Rahimian and M. Farshchi,
Volume 16, Issue 2 (1-1998)
Abstract
The objective of this research is to develop an accurate numerical method to be used in showing the deformation of a liquid fuel droplet in a convective field. To simultaneously solve the internal liquid droplet flow field as well as the external gas phase flow field, a nonstaggered rectangular grid system without any coordinate transformation is used. Transition from the gas field to the liquid field is performed through consistent balancing of kinematic and dynamic conditions at the liquid-gas interface. An implicit fractional step-type method is used to capture pressure and velocity field with proper coupling at low Mach number limit. To show the accuracy of the method, the solution of the driven cavity flow and flow over a solid cylinder is presented. Next, two phase flow field solution of moving and deforming droplet in a gaseous surrounding, with appropriate surface tracking, is presented. While gas Reynolds number and Weber number are shown to play an important role in droplet deformation, liquid Reynolds number and density ratio have no significant effect.
Ch. Dehghanian and A. Shabzendeh Azari,
Volume 16, Issue 2 (1-1998)
Abstract
Effectiveness of furfural as an organic inhibitor in 5 percent hydrochloric acid which is used in acid pickling of steel was evaluated. Lungmuir, Frumkin and Flory-Huggins isotherms [1, 2] were used to determine the parameters of effective adsorption, free energy and entropy of adsorption. Furfural indicated an inhibition less than 17 percent in concentrations of 0.001 mole per liter for a duration of two hours at temperatures of 50, 60 and 70 degrees centigrade. Steel was protected up to 90 percent in concentration of 0.08 mole per liter at temperature of 70 degrees centigrade in 5 percent hydrochloric acid solution. Adsorption of furfural on the steel surface obeyed lungmuir isotherm.
S. Gh. Etemad,
Volume 17, Issue 1 (7-1998)
Abstract
The Galerkin finite element method is used to solve the three dimensional continuity, momentum and energy equations for laminar Newtonian and power-law model non-Newtonian flow through horizontal circular tube. The governing equations are non-dimensionalized with respect to specific variables and converted into algebraic equations using appropriate elements. To accelerate convergence a combination strategy of fixed iteration and Newton-Raphson methods are employed. Uniform wall temperature as well as constant wall heat flux are used as thermal boundary conditions. Apparent friction factor and incremental pressure drop and also Nusselt number are obtained for a wide range of power-law indices. The effects of thermal boundary conditions and Prandtl number on heat transfer characteristics are presented and discussed.
M. Aghdasi, F. Mokhatab Rafiei and G. Moslehi,
Volume 17, Issue 1 (7-1998)
Abstract
This paper presents a summary of the results from the simulation of a given two-stages production system which uses JIT. The system consists of an assembly line with two automated assembly cells and two assembly stock points and one manufacturing cell with three manufacturing stock points for storing reserved parts and one receiving stock. Carts with fixed capacity are used for handling the parts. A kanban is attached to each cart. The minimum number of kandbans required to operate the system without shortage in stock are estimated. The effects of changing the demands mean and its variation on the number of carts are also investigated. Finally, a different simulation model is developed for the same production system using conventional job shop decipline and some main characteristics have been compared to the results, from the first model.
A. Memariani, G. Moslehi,
Volume 17, Issue 1 (7-1998)
Abstract
Flow shop sequencing problem is included in NP-hard problems and a number of heuristic methods have been developed to solve it. Most of these methods are offered for the crisp processing time. However fuzzy algorithm is appropriate for the problems with fuzzy processing time. This paper presents a method in which an algorithm is used to minimize make span of flow shop with fuzzy processing time by taking advantage of fuzzy mathematics. This method is based on the behavior of the decision maker who can make either pessimistic or the most likely decisions. The algorithm includes proper relations and corresponding results.
K. Mirtalaei and S.s. Mahini,
Volume 17, Issue 1 (7-1998)
Abstract
At present, the tubular structural systems are mainly used in tall buildings to withstand earthquake loads. Although it is possible to analyse the structure by finite element methods using standard three dimensional programs, the system is generally time-consuming and expensive in the primary design work. In this paper, for the analysis of Framed-Tube systems, a simple method was studied and developed for Bundled-Tube systems and corresponding formulas for horizontal and vertical deflections were obtained. By replacing the discrete structure with and equivalent tube or replacing the multicell tube with orthotropic plates and making simple assumptions regarding the stress distributions in the structure, simple Closed-Form solutions using the were obtained. Standard load cases including uniformly distributed load, triangularly distributed load, and point load at the top were applied. By this method, a new computer program was developed, called TSAP (Tubular Structural Analysis Program). The <> results were compared with more accurate results obtained by famous finite element computer programs. The runtime for this program was about 2% of the runtime for other existing programs.
H. Shakib,
Volume 17, Issue 1 (7-1998)
Abstract
In this study a series of ambient vibration tests on the triple ferrocement elevated water tanks with 150 cubic meters volume, is carried out. In order to verify the dynamic characteristics of full, half-full and one full tanks (mass eccentric system), the different arrangements of sensors are used. The effects of base rotation are also considered in the tests. Natural frequencies and mode shapes obtained from tests are compared to the mathematical model of the tanks using finite element method. In order to verify the effect of different assumptions on the design forces, the revised mathematical model is analyzed by spectral method. The results indicate that base rotation causes the change of design forces especially in the vicinity of the base of system.
H. Haji-Kazemi and M. Arab,
Volume 17, Issue 1 (7-1998)
Abstract
In this paper a new element for analysis of thin-walled structures is presented, and the effects of secondary shear stresses on longitudinal displacements are examined. Since the Interpolation Functions are based on non-uniform torsional differential equations, the analysis of stiffness matrix is facilitated. Therefore, its ability to produce accurate results with the least number of elements is considerably improved. Furthermore, this element can be used in the analysis of all kinds of thin-walled, straight or curved beams with open or closed sections.
B. Farhanieh, M. Golafshani and S. Ekrami,
Volume 17, Issue 1 (7-1998)
Abstract
One method of solving the governing equations of fluid flow about complex geometries is to use multi-zonal method. In this method the overall domain is divided into small number of simpler domains. In each zone, the flow field is solved independently of other zones. The boundary conditions for connecting zones are enforced to convey the necessary linkage. This multi – zonal procedure has been applied into a finite- volume body – fitted code. This code employs collocated variable arrangement and Cartesian velocity components. The accuracy of the method was also established by comparing the calculated results with the numerical and experimental results available in the open literature of cavity flow and flow over a backward – facing step. The flow field around Alavian sliding gate is investigated using the present method. The velocity vectors, streamlines and pressure contours are plotted for various opening ratios of the gate. The drag forces induced due to the pressure field around the gate were calculated and compared with the experimental data.
