Sharif Digital Repository

In this study, behavior of softening after hot tensile and hot rolling processes in isothermal and non-isothermal conditions in AA5083 Aluminium alloy has been simulated using cellular automata. Also effect of temperature and strain rate in hot tensile test and effect of temperature and strain in hot rolling has been investigated. First distribution of temperature in material using the finite element method computed and used as initial temperature in CA and computing the static recovery in hot tensile. Also for hot rolling, computing static recovery and CA are used for initial temperature in ABAQUS. For investigating effect of dynamic recovery and recrystallization, the neural network has... 

In this thesis, engine performance parameters such as power, torque, fuel consumption and in-cylinder pressure are investigated with considering ignition timing in order to achieve the minimum value of knock index. The implemented methods include engine dynamometer tests and simulating vehicle powertrain in GT- POWER software. Based on the acceptable precision of the GT-POWER model, it can be used to predict the engine performance in other ignition timings. Final results prove that for wide open throttle status altering the ignition timing to reach the minimum possible value impact differently on the engine performance so that in low engine speeds for basic and new ignition timings, a... 

In some of the austenitic stainless steels, the strain-induced martensite transformation occurs during the deformation processing owing to instability of austenite phase at low temperatures. In this study, formation of strain-induced martensite as well as the impact of strain path on the rate of martensite transformation in 316L austenitic stainless steel were investigated. At first, the multi-pass cold rolling experiments at room temperature and -8 ℃ were conducted in which both direct and reverse rolling layouts were taken into account. Then, as the third path, the uni-axial tensile loading with an appropriate strain rate was considered. After that, in order to examine the mechanical and... 

In this work, the deformation behavior of an Aluminium-Magnesium alloy i.e. AA5052, in different temperature ranges was studied experimentally and theoretically. For this purpose, uniaxial tensile tests were carried out in the temperature range of 25°C to 450°C and under strain rates of 0.001 "s-1" to 0.05 "s-1" . Also, the occurrence of dynamic strain aging and dynamic softening mechanisms of the alloy were taken into account. It was observed that the dynamic strain aging occurred in the temperature range of 25°C to 125°C while the corresponding activation energy was defined as 46.2 kJ/mol which is close to migration of Mg atoms in aluminum. At hot deformation region, different softening... 

Chaos theory examines complex systems whose output results in large changes by applying small changes to the initial conditions. In other words, some seemingly accidental phenomena for which we have not yet found a reason can be justified with the help of chaos theory. The strong dependence of the response to the initial conditions is one of the most important features of turbulent systems, but their quasi-random behavior will be independent of these conditions after some time. Chaotic systems, as an important branch of nonlinear dynamic systems, behave close to stochastic systems. Perhaps the most important similarity between the two systems is the existence of invariant probability density... 

In this work a mathematical model has been developed to predict large deformation of work piece in friction stir welding process. Commercially finite element package; ABAQUS is used to solve the governing equations while an elasto-viscoplastic materials behavior is utilized in the model. The model is capable of considering the effects of process parameters such as welding speed and tool geometry on various aspects of the process including temperature and stress distribution within the work piece as well as tool, and velocity and strain fields with in the work piece. Experimental works have been carried out to assess the accuracy of the model and also to determine the effects of various... 

In the present study, a 3D combustion chamber was simulated using FLUENT6.32. The objectives were to obtain detailed information on the combustion characteristics and NO formation in the furnace, and also to examine the effect of Oxygen enrichment on the combustion process. The combustion chamber has internal dimensions of 60 cm wide, 90 cm high and 190 cm long. The fuel pipe diameter is 1.25 cm and the air pipe diameter is 3.5 cm. The 3-D Reynolds Averaged Navier Stokes (RANS) equations together with standard k-ε turbulence model are solved by Fluent 6.3. Air/fuel flow rate ratio is varied as 1.3, 3.2 and 5.1 and the oxygen enriched flow rates are 28, 54, 68 lit/min. NO emission was... 

The application of internal combustion engine is vast in different context, such as transportation and power generation. Therefore to investigation of these objects and the importance of flame front development, a combustion chamber with constant volume is designed and manufactured. The chamber designing is based on the experimental knowledge and numerical simulation of chamber and glasses. The combustion chamber made of stainless steel and contained transparent quartz glasses in both side of it to provide the ability of using schlieren photography method and investigation of flame. The great advantage of present chamber is the capability of different type of combustion, including fuel and... 

In this work, wind farm layout optimization problem is dealt with a new approach. The aim of this work is maximizing the output power of a wind farm by considering wake loses. Layout optimization minimizes the wake loses regarding the wind direction. Three different wind scenarios including different wind direction angles, wind direction blowing probabilities and Weibull distribution parameters for wind speed are assumed. Since, the problem is nonlinear and constrained, imperialist competitive algorithm is used as a modern and powerful algorithm for continuous optimization problems. The optimization outcomes indicate that imperialist competitive algorithm yields promising results.... 

In this study, hot extrusion of AA2017-10%SiC¬p composite during deformation process and effect of deformation parameters on mechanical properties have been investigated. At the first step, hot compression tests have been carried out to obtain the flow behavior of the material at different temperatures and strain rates. The activation energy of hot deformation was calculated 296 Kj/mol. In the next step, by using a finite element model in ABAQUS software and the results of uniaxial hot compression test behavior of AA2017 and AA2017-10%SiC¬p during hot and warm extrusion have been investigated. By using it temperature gradient and velocity field and strain distribution were predicted. In the... 

Softening behavior containing static recovery and static recrystallization in isothermal and non-isothermal conditions in aluminum 1050 after cold rolling has been simulated using Cellular Automata(CA). The effect of strain pass on recrystallization process has been investigated. The finite element method was employed to simulate 1,2 and 3 pass rolling processes and compute the stored energy distribution and transferred to the CA model. For the initial microstructure the topologic deformation and site-saturated nucleation has been considered. For non-isothermal conditions the thermal model has been utilized to compute temperature distribution and decreasing in stored energy due to... 

In this research, non-isothermal annealing process at temperatures ranging between 400°C to 830 °C was investigated in warm and cold-rolled austenitic stainless steel 304L. First, the wide variety of austenitic to martensitic structure was produced by the multi-pass rolling process at room temperature -8 °C, 200 °C, and 280°C. The n exponent in Olson-Cohen equation was governed 2.83 after non-linear curve fitting to assess the fraction of deformation-induced martensite as a function of strain. Afterward, Abaqus/Explicit method was utilized to achieve the stored energy and plastic strains distribution through the thickness. Then, Cellular automata and Galerkin-finite element models were... 

In this research, the extrusion of composite AA6061-SiC has been investigated and the temperature distribution field and energy required for the process has been predicted. In this regard, to predict the flow behavior of material, hot extrusion tests conformed at various ranges of temperatures and strain rates. Afterward, the finite element method coupled with the upper bound technique to calculate the temperature distribution and energy required during hot extrusion. This model has also used for wire drawing and cold extrusion processes. The present model is capable of considering various process parameters such as speed of extrusion, reduction and the initial billet/die temperature on the... 

For optimum designing of dry friction clutch, we should taking into account a lot of parameters, in order to the clutch have good efficiency in torque transmission and power train. These parameters include: the type of friction plate and the mechanical properties, Clutch geometry, diaphragm spring and its ability to make pressure. In this project, the goal is the analysis of effect of different parameters in clutch's temperature distribution and effect of these issues in torque transmission. In next step, the clutch's temperature distribution analyzed by changing the friction plate (ceramic), pressure applied and relative round in order to gain optimum properties of clutch. These works done... 

The purpose of present work is to study the effect of different parameters on the solar chimney used in ventilation. Experimental model and numerical model were used to achieve this goal. First, the model was numerically analyzed by Fluent software using Boussinesq approximation. The results of numerical modeling were validated by the empirical model. Finally, the numerical model can be used to investigate the effects of parameters which modeling is not possible by the empirical model for any reason. Experimental modeling was performed on a chimney with height and width of 180 and 62 cm, respectively. The thickness and angle of chimney in both experimental and numerical methods varied from 5... 

The purpose of this study is to determine a function which estimate fuel/air equivalence ratio distribution inside combustion chamber of spark ignition engine for pollution minimization and maximum efficiency. To do this, we developed a code by which, we are able to model one SI engine cycle.
Seven distributions for fuel/air equivalence ratio were examined which include: Homogeneous, linearly decreasing, linearly increasing, sinusoidal increasing and decreasing, sinusoidal decreasing and increasing, cosinusodal decreasing, and cosinusodal increasing. The average fuel/air equivalence ratio for all of these distributions was 0.85.
The results for indicated power showed that,... 

Design hybrid systems to supply electrical energy for off grid domestic consumer in the remote villages in Iran are the main objective of this work. The hybrid systems considered in this study consist of photovoltaic array, wind turbine, battery and diesel generator. Measured wind speed data used for wind turbine energy production model. The hybrid system optimized to supply 6, 14, 20, 40 and 60 families in Bojnoord, Moorchehkhoort, Kish, Langrood, Khash and Meshkinshahr. The main purpose of optimization is to find the economic system, able to fulfill the energy requirements of a given load distribution; so Iran’s current economy and cost, considered. The optimized results for studied cities... 

Three-dimensional cell culture and forming multicellular aggregates is superior over traditional monolayer approaches due to better mimicking in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform sized multicellular aggregates. Restoring cartilage to healthy state is difficult due to low cell density and hence low regenerative capacity. Currently used platforms are not compatible with clinical translation and require dedicated handling of trained personnel. However, when engineering and implanting cell microaggregates in a higher concentration, new cartilage is efficiently... 

Resistance spot welding is one of the types of sheet metal joining processes used in many industries, such as automotive, home appliances, and aviation. In the direct welding of aluminum to steel, brittle intermetallic compounds are formed, which is necessary to control the thickness of these intermetallic compounds to improve welding properties. Using an aluminum-clad layer can effectively reduce the thickness of intermetallic compounds by reducing the heat generation at the steel-aluminum interface. This research aims to investigate experimentally and theoretically the welding of aluminum-clad steel sheet to Al-Mg aluminum sheet by resistance spot welding process with finite element method... 

The residential construction projects are an important and extraordinary part of the economy of Iran. Due to their important role and lots of problems that these kinds of projects face, this research was conducted. Delay is one of the main problems in these projects. In order to identify the causes of delay and propose recommendations to minimize it in Mashhad, Iran, a comprehensive literature review and interview with experts were conducted. One hundred and eight factors were identified and categorized into nine main groups. Based on the identified factors, a questionnaire survey was prepared, developed and distributed among the people who were active in the residential construction...