AMIRKABIR
Year:2002 | Volume:13 | Issue:49|Papers Count:26

An three level production planning and control method is developed and examined. In the first level with the use of a mathematical model, optimum planning period is determined and passed to te next level. The two last levels which perform production cpntrol function are ha sed on three principals: separation between due dates, operational considerations andfull utilization of the cell felcxibility. A simulation medel based on the proposed method has been huilt. Classic loading rules have been redefined with respect to the concept of balanced workload. The resultsfor these reules have shown similar behdvior as compared to the results for classic rules.

A direct Monte Carlo Method is used to simulate the effect of tri-and tetra-functional branching on molecular weight distribution in emulsion polymerization of butadiene. Butadiene polymerization due to high extent of transfer to C=C bonds of polymer chains, can be used as a modeL to study the effect of tri-and tetra-functional branching on Polymer Microstructure. In this simulation, elementary reactions included propagation, chain transfer to Monomer, termination by disproportionation, transfer to C-H bonds (BN3) and C=C bonds (BN4) of growing and dead polymer chains. The initial polymerization volume of the simulation was 105 nm3. The ratio of monomer to initiator concentration and initiator to polymer particles were 500 and 2.5,  respectively. As the conversion was increased from 20% to 75%, the molecular weight  distribution became bimodal. The maximum of the second peak of the bimodal distribution moved to higher molecular weights as the conversion was increased. Tetra-functional branching had little effect on number average molecular Weight, but it had a significant effect on weight average molecular weight. Therefore, weight average molecular weight is more suitable for characterization of emulsion polymerization systems with high extent of tetra-functional branching.

In this resarch after constructing a membrane electrode selective to hexadecylpyridinium ion, the micellization process both in the absence and presence of dicyclohexyI18-Crown-6 was studied. considering DCH18C6 as a nonionic surfactant, thermodynamic model ofbinary mixed micelle solutions was applied for mixed solutions of DCH18C6 and HDP+. Activity Coefficients of components in a micellar phase were evaluated with Regular Solution Theory (RST). CMC of DCH18C6 was evaluated from extrapolating the curve of real mixed solution CMC vs. mole fraction of crown ether. On the base of above assumptions the interaction parameter of such mixed system was evaluated as (b=-8.88 kT) which implies a strong synergism effect between DCH18C6 and HDP+ resulted from their head group ion dipole interactions.

This paper deals with the problem of H ∞ control of singularly perturbed linear continuous-time systems. The authors' attention is focused on the robust regulation of the system based on a new modeling approach under the assumption of norm-bounded ness of the fast dynamics. In this approach, the fast dynamics may be treated as norm-bounded disturbance. Hence, the synthesis is performed for only the dominant or certain dynamics of the singularly perturbed system. It is shown that, in spite of coupling between the uncertain dynamics and dominant dynamics, the designed H ∞ controller stabilizes the overall closed - loop system, in the presence of norm-bounded disturbances. Finally, the proposed methodology in this paper is applied to a single-link flexible manipulator with six modes of deflection as fast dynamics.

In order to improve the wear and corrosion resistance as well as the hardness of 304 stainless steel (SS) for mechanical use, surface treatment derived from those applied in mechanical engineering industries were investigated. Surface characterization according to the different ion implantation showed that corrosion and wear resistances were strongly improved. In the same way, micro hardness was significantly increased after ion implantation.

Researchers and practicing engineers have come to this realization that different mixtures should be used for different climate and traffic conditions. Rutting is one of the main performance related types of distress in areas where the asphalt pavement is subjected to heavy axle loads and high temperature. In this research various types of SMA mixtures were tested to evaluate their effectiveness for inhibiting rutting. The variables in the laboratory tests were aggregate gradation, nominal maximum aggregate size, asphalt binder content, and the type of binder thickener. Two types of asphalt binder thickener, namely mineral fiber and crumb rubber were used. The results of this investigation revealed that special test methods should be devised for proper evaluation of these mixes.

Adsorption of p-Cresol, Benzoic acid and Nitro Benzen by activated carbon from dilute aqueous solutions was carried out under controlled pH conditions at 310k. In acidic conditions, well below the pKa of all solutes, it was observed that the adsorbate solubility and the electron density of its aromatic ring were the influencing factors on the extent of the adsortion by affecting the extent of London dispersion forces. In higher solution pH conditions, on the other hand, it was found that the electrostatic forces played a significant role on the extent of adsorption. The Effect of ph must be considered from its combined effects on the carbon surface and on the solute molecules. It was found that the uptake of the molecular forms of the aromatic solutes was dependent on the substituents of the aromatic ring. Adsorption of the solutes in higher pH Values was found to be dependent on the concentration of anionic form of the solutes. All isotherms were fitted into Freundlich isotherm Equations.

Multi-Attribute Decision Making (MADM) models are applied to solve the selection problems with different and usually conflicting attributes. The uncertainty involved in the parameters of the model is due to judgment of Decision Maker (DM) and is usually introduced, using fuzzy theory. The MADM model proposed in this paper considers not only the uncertainty, of the DM judgments, but also the amount of DM's certainty on his judgments. The proposed model called as "Two-Dimensional MADM Model uses a new parameter, i.e. Certainty Factor, (CF), besides the judgments to show the certainty to those judgments. The propsed model inspired from expert systems domain, which is pioneer of using CF index in decision-making, process. This paper also proposes two methods to solve the two-dimensional MADM model, which are called as "one-stage" and" two-stage" methods. The experiments conducted have shown that considering the CF index causes an in crease in increase in the precision and simplicity of decisions.

Regarding the vast application of cut-off walls in different structures, their behavior under Different executive conditions have been investigated by numerical methods. Using finite element method with nonlinear models, the effects of excavation layers thickness, installation of anchors on deformation, lateral stress and internal forces of the walls L are studied.

In the extraction of number of metal with high unit price such as gold of certain types of sulfidic minerals in the ore makes some difficulties in the way of using common processes such as cyanidation. With reference to the diversity of biotechnology area, many researche have been conducted using microorganisms for treating the refractory ores. Certain groups of bacteria have capacity to use inorganic materials such as minerals to obtain energy for their metabolic activites and living. Considering oxidation and/or solubilization of the sulfidic minerals these reactions could cause the loss of integration of the sulfidic network and result is the liberation of gold from its encapsulating materix. Microbial solubilization and/or oxidation are the basis for using bioleaching process as a pretreatment of refractory gold bearing sulfide ores prior to the cyanidation. In this research a mixed cultures of mesoPhiliC chemolitoautotrophic bacteria (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans) have been used to conduct batch bioleaching of sulfidic pyrite of Motah mine, - Isphahan. With reference to biological function (s) of each of these three individual bacterial species on iron and sulfur fractions of the pyrite sample the amount of iron extracted was measured and by obtaining the time coures of iron dissolution by the mixed cultures - rate of the bioleaching was determined. Comparing these results with that from using only T. ferrooxidans, one could see some improvements. The roles of each of these bacteria in reference to the suggested mechanism and with regards to the results obtained in this resarch have been discussed. All of these show the positive functions of mixed - hacterial cultures relative to mono - bacterial culture in bioleaching of sulfidic pyrite. Similar findings have heen reported by a number of reseachers, the results of this work thus cold he emphesized in this way.

A model has been developed for unsteady-state simulation of non isothermal, gas absorption with chemical reaction in packed columns. The model is based upon the two film theory in each time step and finite difference technique is used to solve the governing system of partial differential equations. The constructed model is capable to predict the concentration of all components in both gas and liquid phases as well as the temperature of each phase along the bed in dynamic and the final steadystate. Results of the model, subjected to various forcing functions were compared with the experimental data obtained from a pilot-plant gas absorption unit, where CO2 was removed from an AIR--- CO2 mixture into an aqueous monoethanolamine (MEA) solution.

Today durability and consideration of maintenance and repair methods of concrete structures have become necessary in the design procedures. These are not only important in the design stages, but also necessary for management. Carbonation of concrete is the major factor for initiation of steel reinforcement corrosion. This type of deterioration exists in the southern regions of Iran, especially in the hot-marine environment of Persian Gulf. In this paper, a deterministic model of concrete carbonation, based on the experimental data, was proposed. Then by using the Monte Carlo simulation technique, a stochastic model for the depth of carbonation of concrete was developed. The advantage of the presented models is the contribution of condensed silica fume as a relatively new pozzolan, which was not found in the past investigations.

This paper is concerned with the optimization of velocity response of structures. Since a few research have been done in the field of velocity response optimization so far, using different optimization approaches for simple structures can provide an insight into the behaviour of the velocity response of such structures. The problem reported here seeks the optimum heights of a simply supported beam for maximizing its tip velocity when released from a deflected state. The problem has been solved using two zero-order methods, the Evolutionary Program and the Genetic Algorithm (GA), and a first-order method, DFP. The results of these three methods have been compared against each other. The best result has been obtained using the GA, which yields to a 428% improvement in the tip velocity with respect to a uniform beam. The dynamic analysis has been carried out using the ANSYS5.4 program.

In this Paper the formulation and properties of Fire-resistant coatings, which were made and tested ih the Building and Housing Research Center laboratories (BHRC), are reported. Different samples were produced from gypsum, perlite, LECA, blast furnace slag, pumice, and silica fume. In the absence of fire resistance test furnaces, the basic concepts related to fire resistance performance of materials have been used to plan the test setting and analyse the behaviour of formulated materials. Thermal properties of the samples were examined with the thermal analysis equipment, including DTA, TG and dilatometery methods. The effect of high temperatures on the behaviour of samples was also studied by means of laboratory furnaces. In. addition, the physical and mechanical properties of samples were tested and compared with standard specifications of plasters.

Discharge coefficient of a semicircular labyrinth weir is a function of total head, effective length of crest and discharge coefficent. Discharge coefficient of such a weir is influenced by total head over the weir, height of weir, radius of weir, thickness of weir and shape of crest. In this paper the effect of imporant parameters affecting discharge coefficient are investigated. It was found that by increasing the radio us of weir, discharge coefficient increases. The rate of variations of discharge coefficient decreases by increasing depth of flow and finally maintain a constant value.Appropriate equations for discharge coefficient are introduced. New method of design is introduced.

In the last two decades, Neural Network modeling has become a subject of much interest and its application in research work has provided vast improvements. Metameric indices at their best, deviate by approximately %35 (PF/4=36) from visual assessments, In the present article, the application of Artificial Neural Network for quantification of metamerism has been studied. Data from 98 real metmeric pairs with visual assessment values were used for training of network. Many type of networks with different architecture, activation function and input were exassment deviating only by 20% (PF/4=20) and can therefore be a good potential candidate as examined to achieve the best results, the final trained network showed a good degree of correlation mith visual assessmet a substitute for previously proposed metmetric indices

In this paper, the applicability of higher order wavelet transforms in detection of the local and transient phenomena hidden in vibration signals is investigated. Such phenomena may be, caused by a small defect in a mechanical system, such as a gearbox. It is shown that the spectrum analysis, based on an FFT algorithm, is unable to detect such events. Therefore, a method for, detection of inital and small defects gives certain advantages over other ethods.Although some researchers have investigated the fault detection problem using the wavelet transforms, their works are mainly restricted to the lower order wavelet transforms like D2 to D8 Despite the complexity of obtaining the higher order basic wavelet functions such as D18, and D20 in this investigation it is shown that the higher order wavelet transfroms have more capabilities with respect to the lower ones. In fact, various signals have been analyzed using the different orders of wavelets, and the results have been compared. The results show the great ability of the higher order wavelets to detect the above mentioned local events. ,

Polyunsaturated fatty acids (PUFA) in the marine oils make them very useful in the, preventation and treatment of cardiac diseases and cancer. The PUFA are used as an additive, to the nutrition diets for the pregnant women to increase the infants" IQ. To test whether the liver and/or tissue of sharks from Presian Gulf might be a source of commercially valuable, PUFA and other fatty acids, 5 sharks were caught from Persian Gulf waters near the Bushehr, Port. The lipid from livers and tissues was extracted using the Bligh & Dyer method, and, analyzed for fatty acids by gas chromatography. The lipid content of livers and tissues was 3-, 58.8% and 0.8-2.04%, respectively. The w-3 fatty acids in the sharks livers and tissues oils were 18.027-29.814% and 2.21-20. 512 %, respectively. The wide variation in the lipid content and fatty acid composition of the sharks liver and tissue oils is due to parameters such as kind age, migration conditions, total weight and weight of liver of the species. The notable values lipid content and w-3 fatty acids in the sharks in Persian Gulf impliy that the fish can be, considered as the main source of the so-called fatty acids.

Modeling of a rock mass containing a joint set has been studied in this paper. The model has been analysed on the basis of joint element, linear behaviur for intact rock, and non- linear behaviur for the joints. Difference in behavior of a single joint in a rock mass with behaviur of a rock mass containing a joint set is evaluated and discussed.A computer program has been prepared for analysis of rock mass with a joint set which is able to analyze stresses and deformations both in intact and jointed rock mass. A number of rock mass models containing one joint, two parallel joints and tree parallel joints are analyzed and various factors affecting rock mass have been assessed.

In this paper vibration analysis for local faults and transient phenomena detection, using multiwavelet systems is developed. Unlike the scalar wavelet systems in which their coefficients are scalar parameters, the transformation parameters of multiwavelet systems are vector valued, and their calculation requires some special techniques. In this investigation, having considered the technique used to obtain the scalar wavelet system coefficients as well as the orthogonality of the scale and wavelet functions of multiwavelet systems, the transformation coefficients of the multiwavelet system are calculated, and then some artificial vibration signals are analyzed using the multiwavelet system. The results are compared with those obtained through the scalar wavelet systems and frequency analysis techniques. The combination of the contributions of the analyzed signal at different levels of the multiscale and multiwavelet function spaces results in original signal which shows the validity of the results. One of the main advantages of the multiwavelet systems over the scalar wavelet systems is their ability to analyze the signal in more frequency intervals. Using this property, the detection of the local and transient phenomena from the vibration signals, which may be caused by a small and local defects in a mechanical system, may be performed more efficiently.

An approach for modeling of cutting force in ball-end milling process is presented in this paper. This model has the capability of estimating the cutting forces 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 with 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 cutting force components are calculated by summing up the differential cutting forces. A series of experiments were performed to verify the proposed approach.

The Transmission line Matrix (TLM) method is a powerful tool for mode ling of lectromagnetic wave propagation in complex structures. This method needs a large amount of memory and computation time for studying open region problems. In order to reduce the necessary memory capacity and computation time in 3D-TLM, generally two strategies are used First, using absorbing boundary conditions to limit the space dimension of the problem, and second using an efficient scattering algorithm with minimum algebric computation. This article discusses various type of symmetrical condensed node (SCN). Efficient implementations of the scattering procedure in the various SCN are given. Computational time and requirements of different TLM nodes are compared. Comparsion of results of simulation with analytical and experimental shows very good agreement.

An three level production planning and control method is developed and examined. In the first level with the use of a mathematical model, optimum planning period is determined and passed to te next level. The two last levels which perform production cpntrol function are based on three principals: separation between due dates, operational considerations and full, utilization of the cell flecxibility. A simulation medel based on the proposed method has been  built. Classic loading rules have been redefined with respect to the concept of balanced workload. The results for hese reules have shown similar behavior as compared to the results for classic rules.