Sharif Digital Repository

In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,... 

There are experimental observations that show material response in micro-scale is dependent on some other parameters rather than Lame parameters. Strain gradient elasticity has been recently developed to take into account this characteristic of materials response. In strain gradient elasticity, characteristic length parameters enter the constitutive equations through the elastic strain energy density function. The elastic strain energy density function is assumed to be a function of the gradient of strain tensor in addition to the strain tensor. In this way, new material constant (characteristic length parameters) are introduced and entered into the constitutive equations. In recent years,... 

Flows in porous media exist in many practical and research fields including water flow in soil, transport of pollution in soil, oil recovery engineering, and etc. Studying the multi-phase flows seems being too complex due to the interactions between fluids or between fluid and media in the porous media, wetting tendency of fluids, intrinsic permeability of the porous media, tortuosity of the flow’s path and etc. Hence, the field and laboratory studies of multi-phase flows is difficult, if not impossible. While numerical methods can handle many of these complexities, many of them are unable to simulate the micro-scale flows. On contrary, Lattice Boltzmann has no such shortcomings and even is... 

A numerical framework is proposed to estimate the liquefaction-induced settlement of the fully saturated sandy layers in the free fields due to earthquake excitation and the results of the proposed method are compared with those of the empirical or probabilistic methods suggested by the previous researchers. Liquefaction is a sudden transformation of saturated sandy soil into a viscous fluid which is caused by the increase in the pore pressure and decrease in the effective stress and results in the reduction of the shear strength of the soil. One of the most important consequences of liquefaction is the liquefaction induced settlement which has caused severe damages in many places in the... 

Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using... 

Despite major environmental and economic benefits of cold recycled asphalt mixtures, many agencies have not yet made widespread use of this technology due to its so-called poor field performance and lack of accurate information on mechanical properties of cold recycled mixtures. Fiber is one the additives that is sometimes used to enhance asphalt mixture properties. Using fibers to improve the performance of cold recycled asphalt mixture has been studied by a few researchers with somehow contradictory results. In this research, the effects of adding four synthetic fibers (Polypropylene, A-glass, Para-Aramid, and Polyester) and two waste fibers (Waste Polyester and Waste Nylon) with different... 

In this thesis the steady state convective heat transfer for turbulent, two-dimensional, incompressible gas flow in a circular microchannel under slip flow and temperature jump conditions is numerically investigated by means of finite volume scheme. The low Reynolds number k-ε turbulence model is employed using a new boundary condition for turbulent kinetic energy at solid surface. To calculate variables at control volume surfaces in the axial direction upwind differencing scheme and in the radial direction central differencing scheme are used. Rhie-Chow interpolation technique is used to prevent pressure field oscillations. The set of discrete equations are solved using SIMPLE Algorithm. In... 

Because of deregulation and economic issues, power systems operate closer to their stability limits than before. So, security assessment of power system has gained a lot of attention in power system studies. Transient stability and its real time assessment is a great concern in power system security. Among all different methods for transient stability assessment, Automatic Learning methods are used the most in real time assessment problems. These methods can provide fast assessment of transient stability, sensitivity analysis and means of control of the transient stability phenomena. In this paper Adaboost algorithm is used as a brand new method in transient stability assessment of a medium... 

In recent years, advances have been made in the field of miniaturization of the devices (in order to increase their efficiency, lessen the materials needed for the constructions and experiments, reduce costs and energy usage) resulting in the dramatic increase of surface to volume ratio in these devices. This progress has led to the dominance of surface forces which can be used to control very important interface phenomena having a special application such as electrokinetic. Using today’s manufacturing technology; it is possible to construct micro-nanochannels made from different materials such as silicon, glass, quartz, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA) whose... 

This paper studies a multi-product, multi-period, multi-allocation hub location problem based on real case in domestic automotive industry. As 3PL companies spread, using dynamic hubs in a contractual manner becomes passible; So in this paper the hub set is the combination of both static and dynamic hubs. The nodes are suppliers, sites and dealers of a supply chain that have certain demand of each product in each period. In this problem backlogging is allowable and causes penalty. Different transportation modes like road and railroad are usable just in hub network. Direct transmission is possible and candidate hubs are capacitated with multi suggested capacities. A mixed integer programming... 

Reviewing trends of energy consumption in the world reveals that sooner or later energy resources will be depleted. This concerning rate of consumption has brought about more greenhouse gases (GHG) emission influencing deleteriously on environment and climate. Human has continued energy consumption to maintain and improve the quality of his life through industrial production. Industry as a significant energy user owns considerable contribution to this consumption. Several attempts have been carried out to develop energy management systems in order to improve the energy efficiency of industrial sectors. Whilst they are comprehensive and could be applied to any sector, there is lack of... 

In this research, the effect of organizational Bureaucracy on the integration of technical knowledge and market knowledge in the process of developing new products, along with other factors mentioned in previous literature, has been studied. To this purpose, a questionnaire was prepared which measured both the degree of integrity and the effect of bureaucracy on integrity. This questionnaire was completed by marketing and research and development managers of 39 innovative companies in the field of information and communication technology (ICT). Regression analysis was used for data analysis. The results of this research show that bureaucracy as an organizational factor, along with other... 

A microwave transceiver system requires an array of amplifiers. Low-noise amplifiers (LNAs) are integral parts of receivers while transmitters are based on several stages of power amplifiers (PAs). In modern communication standards, power amplifiers have to achieve high efficiencies over increasingly larger dynamic ranges and banwidths, while maintaining tight linearity requirements. In these systems, PAs must be highly efficient to simplify the thermal management and to reduce dc power requirements. Recently, the use of monolithic microwave integrated circuit (MMIC) for commercial and military applications have been paid more attention to, given the fact that the possibility of building... 

Todays, given the existence of a strong competitive environment in the industry, supply chains should be quick and reactive, in addition to keeping their costs down. Transit warehouses and warehousing issues are one of the most efficient techniques that reduce inventory costs, while increasing the flow of goods and shorter transport cycles. Regardless of how a warehouse system is designed, the allocation and sequencing of input and output trucks to platforms is considered necessary. The inappropriate sequence of input and output trucks on the platforms increases the completion time of the operation. Also, the uncertainty and unpredictable circumstances of the real world make planning and...