Year:2001 | Volume:35 | Issue:3 (73)|Papers Count:24

A narrow slot in the broad wall of a rectangular waveguide is analyzed in this work. The thickness of the wall as well as mutual effects and higher order modes are considered in the analysis. The method of moments is applied to a couple of integral equations using Green functions and appropriate boundary conditions. The tangential electric field on the upper and lower surfaces of the slot is, therefore, obtained. Sinusoidal functions are used as basis functions for expansion of these fields along with the Galerkin method. Using these basis functions, an accurate solution can be achieved and unlike other basis functions, a few terms are sufficient for a convergent solution.  The resulting matrices are therefore reduced in dimension with less computational time. Various arameters of the slot using analytical method is obtained and results are compared with the existing experimental data. These results show the accuracy of the method and are in close agreement with an error of about one percent.

A laboratory research was undertaken to study the penetration of coarse aggregate into soft seabed where they are used as embankment material. The samples of disturbed soft soil are prepared mixing a number of natural clays and water. The effects of separators, such as sandy layers and geosynthetics, have been also investigated. A new testing procedure has been used for the research utilizing a modified apparatus. It has been concluded that the size of aggregate and the shear strength of soft soil are very important parameters. The use of geosynthetic layers and for a layer of fine soil at the top of soft seabed could be essential when a high embankment with coarse material is going to be constructed.

Several bitumen samples were collected. These included 60/70 and 85/100 penetration grade bitumen's from the different refineries in Iran (i.e. refineries in Tehran, Isfahan, Shiraz, Tabriz and Arak). The primary standard tests were performed and the samples that met the local specifications were selected. In another study in Netherlands both standard and SHRP tests were performed on similar bitumens. Both mentioned tests were reported separately in a Bitumen Test Data Chart. It was shown that these had very close physical characteristics. For the samples in Netherlands, having performed the SHRP tests, the corresponding performance grade classification was noted. For the Iranian bitumen's, the standard test results were reported on the curves that were obtained in Netherlands (i.e. the curves showing correlation's between performance grade and penetration grade classification). From latter the relative SHRP performance grade class was obtained for Iranian bitumens. It was found that the 60/70 and 85/100 penetration grades corresponds to PG 64-22 and PG 58-22 class in SHRP classification, respectively.

Flow within road ditches, roof gutters, drainage conduits, wash-water trough flows in water and wastewater treatment plants, and side channel spillways are some practical examples of structures conveying spatially varied flow with increasing discharge. The water surface profile in such circumstances is an important factor in the design process. Accordingly, in order to decrease the water surface elevation along the channel, the bottom width of the channel is usually enlarged in the flow direction, this produces a non-prismatic channel. It has been mentioned that the presently available equations are applicable in prismatic as well as non-prismatic channels. The result of this study however, indicated that the presently available equations are sensitive to the position and the flow depth of the control section. This paper, based on the momentum principle, presents a new form of the governing equation for spatially varied flows with increasing discharge in non-prismatic channels. Also, the Newton- Raphson method was utilized to solve the proposed equation and the results of the model were verified with experimental data. Good agreements were observed between the computed values and the observed data, which indicates the validity of the proposed model

Development of the Iranian Code for Concrete Design of Buildings is an important achievement that has been made in the recent years. The safety factors and the formula that have been used in this code have been taken from codes of other countries, especially that of CSA A23.3- M84. Since the domestic conditions of building construction are different from those of other countries, it is necessary to evaluate the safety level of the code for Iranian workshops. In this study, conditions of more than 53 workshops in Tehran and its suburbs have been studied and relevant statistical data including concrete compressive strength, dimensions of concrete sections, yield strength, location and magnitude of reinforcing bars have been collected. By analyzing the data and doing risk analysis, it has been shown that the safety level for the Iranian code is lower than the assumed value. To reach the desired level of safety, some recommendations are made in this paper as to correct the load and resistance factors.

SMA actuators are a new kind of force-displacement actuators which act based on the unique property of shape recovery of the shape memory alloys. In this paper a mathematical model is presented for approximate responses of a novel thermally driven SMA actuator under arbitrary loading and boundary conditions. The actuator is a laminated composite beam made of SMA and elastomer layers, with a hollow rectangular cross section. The actuator has the ability to act in three dimensions, but here, modeling is done only for the 2-D conditions. The thermomechanical behavior 0f SMA layers is expressed using Tanaka and Nagaki's one-dimensional constitutive equation, together with a linear phase transformation kinetics. The thermoplastic behavior of elastomer layers is expressed by Hooke's law, in which the changes of the elastic modulus with temperature, is considered using an approximate linear function. The general form of the classic beam equations is used for the force-deformation relationships. This model gives explicit solutions for the structural response of actuator, including midplane-strain and curvature, in terms of the variable parameters such as activation temperatures, the layers' thicknesses, ... etc. A numerical example for a cantilever beam with hollow square cross-section subjected to a transverse concentrated load is presented. Results show that when the phase transformation starts in the heated SMA layer, significant changes in the actuator's response occurs due to strain recovery in it.

Cables have always been under consideration by engineers as a structural element. They have a low weight to strength ratio and they are also economic and these features makes them suitable for applications such as suspension bridges and roofs, Power transfer lines and so on. Despite these properties, what makes their analysis difficult is the nonlinear behavior due to geometry and material nonlinearity. In this work, the equilibrium equations for a cable network under distributed loading are derived considering the potential energy of the system and minimizing it using the variational procedure. Along with it the necessary and sufficient conditions for stability of the equilibrium configuration are obtained. Next a numerical procedure called "Dynamic Relaxation", which considers the equilibrium equations as dynamic equations of motion adding the mass and damping term, is used to solve the equations numerically. Several examples using this method are presented.

An approach for static and dynamic simulation of ball-end milling of die surfaces is presented in this paper. It has the capability of estimating the static and dynamic cutting forces and tool deflections for various cutting conditions. A commercially available geometric engine (ACIS) is used to represent the cutting edge, cutter and updated part. To determine cutting edge engagement for each tool rotational step, the intersections between the cutting edge and boundary of the contact face between tool and updated part are determined. The engaged portion of the cutting edge is divided into small differential oblique cutting edge segments and the static cutting force components are calculated by summing up the differential cutting forces. In dynamic simulation, the dynamic chip thickness is computed by summing up the static chip thickness, the tool deflection and the undulation left from the previous tooth. For calculating the ploughing forces, wu' s model is extended to the ball-end milling process. The total forces, including the cutting and ploughing forces, are applied to the structural vibratory model of the system and the dynamic deflections at the tool tip are predicted. A series of experiments were also performed to verify the proposed approach.

In this paper steady and unsteady conductive heat transfer in membrane walls of the boilers have been investigated. The furnace walls of the utility and large industrial boilers are constructed from membrane walls. The membrane walls consisting of parallel tubes connected longitudinally by fins have been considered. These types of the wall Insulated outside and exposed to the furnace on the other, constitute an effective means of transferring heat from furnace to the water circulating inside the tubes. Analysis of heat transfer in membrane walls. assemblies is an important step in design and sizing of the utility boiler's furnace. Because of geometric complexity and discontinuous properties of the fin-tube assembly, a numerical method is used, and for a simplified case of steady-state and no welding angle an analytical approach has been performed. The effect of the welding angle as well as fin width and thickness upon temperature distribution in the membrane walls have been considered. To obtain heat flux on the furnace sector of the tubes, the view factors between the flame considered as a parallel plane and the membrane walls has been evaluated. Also for the "Start up" of the boiler the distribution of temperature in membrane water-wall is obtained by finite element method and the effect of the tube thickness, fin thickness and width have been studied. It is also shown that the fin effectiveness as well as the insulated sector of the tube are closely related.

The instability of the patellofemoral joint in the transverse plane was studied in a two dimensional mathematical model with deformable contact surfaces. Articular surfaces, muscles, retinaculum and patellar tendon, and articular cartilage were simulated as orthogonal polynomials, strings with known forces, tensile springs, and a set of compression springs, respectively. The resulted nonlinear equations, including three equilibrium equations and one constraint equation for each cartilage spring, were solved using Newton-Raphson method. Results indicate that total dislocation of the patella only occurs if the joint's soft and hard tissues are both abnormal. Lateral displacement of the vastus medialis attachment to the patella, was appeared to be the most effective surgical procedure for treatment of patellar instability disorders.

Aromatic solutions containing N-Butylamine salts have sufficient thermo-chemical stability, wide polarization potential, high boiling point and acceptable dielectric coefficient suitable for electrolytic coating of the active metallic ions. In this study, nucleation/growth kinetics of thin metallic layers precipitated from copper containing N-Butylamine complexes dissolved in  naphthalene is investigated via cyclic voltammetry, chronoamperometry and electrochemical impedance frequency response method. Results indicate –an instantaneous three-dimensional electrochemical crystallization of copper concomitant with a diffusion-controlled growth regime. The diffusion coefficient of copper containing complex and the standard rate constant of the reaction are calculated from the data, which appear to be in the range of 3-6 x 10-6 cm2/s and 2-6 x 10-3 cm/s., respectively. The relatively small reaction as well as diffusion rates seem to be due to the complexion of copper ions with large aromatic legends.

Pentaerythritol (PE) is a tetravalent alcohol mainly used in painting (as alkyol resins) and military industries. PE is produced by reaction of acetaldehyde with formaldehyde in aqueous solution containing sodium hydroxide. The byproducts of the reaction are dipentaerythritol, sodium format and different linear and cyclic formals. Since the purpose of this work was the production of PE with high yield and high degree of purity, at first the effect of operating parameters on the production yield was studied and the optimum operating ranges for reaction temperature, reaction time and molar ratio of reactants were determined. In the next step, considering that the applications of PE necessitate high degree of purity, different methods of purification such as crystallization, hydrolysis through refluxing hydrochloric acids, adsorption with activated carbon and separation based on solubility difference were investigated. The results indicated that separation based on solubility difference is the most appropriate method and whenever combined with crystallization, can increase the degree of purity of PE up to 99/4 percent

In designing extraction columns many parameters must be considered such as dispersed phase local hold up. Prediction of dispersed phase hold up is one of the most important parameters in design. A laboratory spray and RDC columns are constructed for the experimental works. The selected chemical systems for no mass transfer experiments were Water-Toluene, Water-normal Heptane and Water-MIBK, with a variety of physical properties interfacial tension, viscosity and density. In all experiments, the oil phase was as dispersed phase and water phase as continuous phase. According to the experiments, it was found that dispersed phase local hold up increases in the columns as dispersed phase volumetric flow rate at a fixed continuous flow rate increases. As interfacial tension increases the dispersed phase local hold up in the columns increases as well. Static hold up can be neglected in spray columns because of no internal equipment's in the column although it is a little in the RDC column. Local hold up at different height of the columns is measured and analyzed. Series of experiments have been carried out in above-mentioned columns.

Thermosyphone is a kind of heat pipe consisting of a tube which after through degassing has been filled with the required working fluid under vacuum, the pipe is equipped with wide fines on both sides in order to absorb solar radiation, effectively. In order to eliminate conduction and convection heat transfer phenomena the tube is situated inside an evacuated glass bulb. In order to increase the efficiency and improve the design and working conditions of various types of heat pipes, a fundamental knowledge of the variation of operating parameters inside the heat pipes is necessary. In this paper, effective operating parameters of a thermosyphone heat pipe in uniform and steady condition are studied. These parameters include saturation temperature of the fluid inside the pipe, the variation of liquid and vapor flow rates inside the pipe and finally the pressure drop of liquid and vapor along the length of the pipe. The modeling is first started by writing an energy balance for the control volume of the pipe so that a first approximation for the above mentioned parameters is obtained. In this balance, depending on the type of fluid next to the condenser section and the type of heat transfer phenomena (free or forced convection) and also with due regards to the experimental correlations available, first the Nusselt number and then the heat transfer coefficient is calculated. From the latter, a first estimate of the required values for the liquid and vapor flow rates are found to be 0.222 and 0.0001126 Kg/s, respectively. The thickness of the film was determined to be 0.2 mm. In order to calculate the variations of the above mentioned parameters along the length of the tube, mass heat and momentum balances were written in next step for the control volumes on the liquid film, vapor phase and the system as a whole. Diagrams of these variations were obtained. The results were compared with both the data available in the literature and the experimental findings of a heat pipe constructed and operated for this purpose. Comparisons between the experimental and theoretical results showed a difference range of ±15%, which appears to show the suitability of the proposed model.

The present investigation concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by negative dc corona discharge. The corona creates negatively charged oxygen species, which react with methane and form methyl radicals. The products contain C2 hydrocarbones (acetylene, ethylene and ethane) and other. carbonaceous species including carbon deposits, CO2, H2O and syngas (H2+ CO). The conversion and selectivity of desired C2 products depend on the residence time (total feed flowrate) and the methane to oxygen ratio in the feed. All the experiments are conducted at room temperature and only with dc negative corona discharge (i.e, no oven or other heat source is used), and the temperature increases slightly (100-200 o C) due to the exothermic reactions and the discharge itself. According to the results: Methane conversion increases significantly with decreasing flowrate or increasing residence time, but C2 hydrocarbon selectivity decreases slightly and therefore, the yield of C2 hydrocarbons increases significantly. Moreover, increasing the methane to oxygen ratio at a constant flowrate leads to an increase in C2 selectivity. Also, the methane conversion and C2 yield go through a maximum at a methane to oxygen ratio of 5. The largest C2 yield is 23.1% with 35% methane conversion.and66% C2 selectivity at a flowrate of .5cm3/min (CH4O2=5, without any diluent), when the dc negative Corona with 4mA input power was used. The results suggest that dc gas discharge technique is a promising method for direct conversion of methane into more valuable hydrocarbons.

Fire-retarded and pure polymeric materials were subjected to heat fluxes of 25 and 50 kW/m2 using cone calorimeter. The approach of the flashover conditions were computed from Kokkala and Ostman models. The fire parameters needed to be . fed to the models were determined experimentally utilizing the method recommended by ISO/DIS5660 ASTM (E- 1359-90). The results show that the flashover time could be estimated from Kokkala method quite accurately. The flashover time for the pp was found to increase with the increase of Mg(OH)2 content. However with PE, the trend was found to be different.

The formation and deposition of coke III industrial pyrolysis quenching operation is a serious problem. One of the most important requirements for the plant operators of ethylene production is to have a prediction for the exchanger parameter such as outlet temperature and pressure and also the coke thickness inside the exchanger tubes. In the first, called chemical deposition, the coke formed by chemical reactions at higher temperature region is deposited at the first half of the tubes. In the second half of the tube, however due to the lower temperature (T<500 oC) the coke deposition increases due to the physical condensation of heavy poly-cyclic hydrocarbons condensed at this temperature region. This paper presents some of the results of a rigorous computer simulation of a naphtha pyrolysis quench cooler or Transfer Line Exchanger (TLX). The model incorporates existing molecular kinetic data for predicting coke formation rates in addition to the physical condensation of heavy aromatic hydrocarbons, and a semi empirical coke deposition model for the thermal and hydrodynamic behavior of the TLX. Finally, the model is used to simulate the operating performance of an industrial TLX in Arak petrochemical Complex and the results indicate a good match with full scale plant operating data.

Gas hydrates are crystalline compounds formed by inclusion of small gas molecules into a lattice constructed by water. Development of a mathematical model for qualitive quantitative description of hydrate crystal growth rate is the basic aim of this work. The difference between the temperature of crystal surface and that of the liquid bulk is employed as driving force of crystal growth. Parameters of model for hydrate formation from methane and ethane are calculated and it was shown that the heat transfer model combined with distribution of growing particles is capable of describing the experimental data.

Work index is a measure to define ores/minerals grindability which is significantly used in Bond (1952) to calculate the required energy of ores' comminution. Work index for any material is experimentally calculated under specific conditions and it is a certain value. To understand the effect of changing control screen in work index calculation, three different ores Alam-Kuh Pb-Zn ore, Sarcheshmeh Cu ore, and Abe-Gann region Dolomite were tested, using 425,212, 150 and 100 micron screens (totally 12 sets of tests). Results showed that the work index values increase with the increases of screen size. The relation between root of screen size and fines produced per revolution of mill and also, screen size and size of products out of which 80% passes through this size appeared to be linear for all three different ores. The constants of these linear equations were estimated using regression technique.

The objective of this paper is to identify the economic importance of Iranian industries by  multivariate analysis. This study is among the first in the world to examine the industrial sectors by two robust approaches, namely, Principal Component Analysis (PCA) and Data Envelopment Analysis (DEA). DEA is a mathematical programming approach and PCA is a multivariate statistical technique. Furthermore, the results of PCA is verified and validated by DEA through a nonparametric statistical test. The two methodologies are used to rank and analyze the Decision-Making Units (DMUs) which in our case are the industrial sectors. To achieve the above objective, first the industrial sectors are classified according to two-digit International Standard for Industrial Classification for all economics activities. ISIC is the most well known industrial classification format in the world. It is used by such international organization as UNIDO, UN and World Bank. ISIC classification ranges between two to four digit formats. This study considers the two digit format of industrial classification and further analysis (three and four digit) is left for a future research paper. Second, a comprehensive study was conducted to locate the most important economic shaping factors in the world, which were identified as eight  economic indicators such as value added per employee. The eight indicators are obtained (for PCA) by two output and four input measures (for DEA). The findings of PCA and DEA show the importance and influence of each of the eight indicators used in this study. Also, the industrial sectors (DMUs) are ranked to reveal the best and worst industrial sectors with respect to the selected indicators. In addition, the weak and strong points of each industrial sector are identified. This paper presents an integrated standard approach for economic assessment and ranking of industrial sectors in Iran and the world. Furthermore, for the first time the Iranian industrial sectors (and in the world) are analyzed and ranked by multivariate analyses according to international standards. Also, the results and rankings of PCA and DEA are verified and validated through Spearman test of correlation. The test shows a direct relationship between DEA and PCA, with Spearman test statistic rs = 0.873 which is very close to unity at ex = 0.05 level of significance. In summary, this paper presents a unique standard methodology for assessment and ranking of industrial sectors based on economic indicators. The structure and approach of this paper could be applied for other sectors in particular and other countries in general. The results of this study would help policy makers and top managers to have better understanding of their sectors with respect to economic factors. Also, designers and engineers could identify weak and strong points in regard to economic factors.