Sharif Digital Repository

Turbofan engines are widely employed as the propulsion unit in commercial aircrafts. Turbofan engines may experience inlet flow distortion during their operation which may alter the performance magnitude and stability of the engines. In this research, an object-oriented (modular) model for turbofan engine components is developed by using Simulink/Matlab. Through the integration of the 1D models and the related thermodynamic equations for the engine components, the engine design point is determined. The off-design performance matching across the different components is established by scaling the characteristics and incorporating matrix iteration method. The spool dynamics is used to simulate... 

Climate conditions are one of the key factors influencing railway infrastructure, and future climate changes and the occurrence of extreme weather events increase the risks to the sustainability and performance of these infrastructures. In this study, the relationship between climate conditions and geometric degradation of railway tracks in Iran is investigated using deep learning models. Geometric data of railway tracks from the EM120 track recording machine over a 14-year period were combined with meteorological data including temperature, humidity, precipitation, and wind speed for all 19 railway regions in Iran (covering approximately 14,000 kilometers of track and 180 GB of data).... 

In this study we consider a two-level supply chain, with a supplier and a number of identical retailers, demand process is Poisson with random rate. All retailers apply (R,Q) policy with backorder case for their inventory control supplier fulfills the orders of retailers according to FIFO discipline. At any point of time the supplier has online information about inventory position of all retailers.
Whenever the inventory position of a retailer reaches to a fixed value (s) above its reorder point, the supplier orders a batch of size Q to an outside source with infinite capacity. Lead-time of each retailer is equal to the sum of a constant transportation time and a delay time which is... 

In this study, Al-20Si-5Fe ribbons produced by melt-spinning method. Nanostructure and growth morphology of rapidly solidified products explored using optical microscope, scanning electron microscope and x-ray diffraction. Microstructural investigations depicted two distinctive zones of featureless (faceted morphology) and dendritic. In addition, no intermetallic phases could be observed in the rapidly solidified ribbons in comparison with coarsed and needle shaped intermetallic phases of as cast alloys which it demonstrates the extension of solid solubility of Si and Fe in the matrix and consequently intermetallics formation was hindered by higher cooling rates. Subsequently, ribbons... 

n the present study, the optimal design of feeding system in steel sand-mold castings is considered. The first part of this research includes fundamental studies on the physics of shrinkage defect formation during the casting process. The results of these studies lead to new findings on the mechanism of shrinkage defect formation, effect of melt quality on the distribution of defects within the castings and the connection between shrinkage and gases defects. The theoretical analysis of thermal criterion functions for the prediction of shrinkage defects in castings and introducing new criterion function with fewer shortcomings can be accounted as the other finding of this part. A new model... 

Grobner bases were introduced by Bruno Buchberger in 1965. The terminology acknowledges the influence of Wolfgang Grobner on Buchberger’s work. He introduced a specific generator for ideals in the ring of polynomials over a field and then gave an algorithm for computing of that generator. It leads to solutions to a large number of algorithmic problems that are related to polynomials in several variables. Most notably, algorithms that involve Grobner basis computations allow exact conclusions on the solutions of systems of nonlinear equations, such as the (geometric) dimension of the solution set,the exact number of solutions in case there are finitely many, and their actual computation with... 

In this research ,Al-20Si-5Fe-3Cu-1Mg-XMn alloys were produced by gas atomizing and melt spinning processes. Microstructure and growth morphology of powder and ribbons were investigated using optical microscopy , scanning electron microscopy. powders were hot pressed at 400ºC/250Mpa and microstractural variations, mechanical properties were evaluated after consolidation. Results show that relatively high cooling rate in gas-atomized powders lead to refinement of microstructure and formation of semi-equilibrium δ intermetallic phase . As the powder particle size decrease , the growth morphology changes from primary silicon + euthectic to euthectic + primary dendritic aluminum . Mn changed the... 

Cyclones are efficient devices in order to separate suspended particles and droplets from gas media and this effieciency is mainely because of spiral flow nature affecting the particles and droplets and taking them towards the wall. Therefore, particles and droplets move downwards toward down outlet by the gravity force. In consequence, they are being separated of the gas flow and relatively pure gas flow exits the cyclone. In this project, GAMBIT software has been used to produce three dimensional meshes including coarse, medium and fine sizes for two different geometries of cyclone. After simulation, little differences between the obtained results were revealed, showing that modeling is... 

Gray Cast Irons are the most important engineering Cast Irons. Gray color of fracture surface and morphology of graphite flakes are the reasons of this naming. Gray iron is relatively cheap with easy production; because of wide chemical composition range rather other cast irons. Furthermore, shrinkage and feeding in the casts from gray iron, besides surface finishing by machining are easy. The other properties of gray iron are resistance against sliding wear, high thermal conduction coefficient, low module of elasticity and thermally shock resistance. In this research, the effects of added nitrogen as an alloying element and cooling rate on microstructure, hardness and tensile properties of... 

In this study, the recovery mechanism of nickel oxide by carbon dissolved in molten iron with the study of reaction kinetics were investigated. Nickel oxide pellets into molten iron containing graphite were added in the neutral atmosphere and the release of CO gas as a function of reaction time was measured until the end. The volume of gas produced at different times shows the number of moles of Ni metal was revived. Reaction by a) the following decomposition reaction under 1475 °C ; and b) carbon diffusion rate at temperatures over ° C1475 is controlled. The main reaction mechanism in order to a) decomposition of NiO; b) penetration of oxygen atoms in the melt, and c) reaction between... 

AS5U3G and AS7U3G are two prevalent types of alloy which are used in producing cylinder head. In this research AS5U3G alloy is studied. Gravity casting is one of the method of producing this part. Produced porosities in cylinder head casting process, cause leakage in this part. In order to solve this problem, some actions have been taken that we can divide them into quality operations improvement of melt and making changes in casts. The sampling is done in four levels to evaluate the gas porosity and shrinkage. In these levels, pressure and degassing duration and strontium's modifying in a 745℃ fixed temperature have been evaluated. Based on reports by comparing density of relative samples,... 

Since mechanical properties of cast Al-Si-Mg alloys are directly influenced by microstructural defects, understanding the characteristics of these defects and any interaction between them is important for improving the properties of castings. This study investigated the effect of the most common defects normally found in cast aluminium alloys namely, double oxide films, Fe-rich phases and prosity. A different level of each defect was introduced into castings to investigate their effects on tensile properties of A356 Alloy. Differents casting condition experiment produced different entrained oxide film, Fe-rich phases and porosity caused by shrinkage content, from low to high, were tested...