Sharif Digital Repository

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... 

Electroless coating is a chemical reduction process which depends on the catalytic reduction. In this study, the influences of different concentrations, stirring rate, pH and heat treatment of Al2O3 and SiO2 Nano sized particles in the bath on deposition rate, hardness, wear resistant, surface morphology and corrosion behavior of the Ni-P-Al2O3-SiO2 composite coatings have been investigated. The microstructure was investigated by field emission scanning electron microscopy (FESEM) and among the nanoparticles SiO2 and Al2O3 have drawn attention due to their high hardness, availability, particles distribution and reduced cost. The amount of Al2O3 and SiO2 was examined by Energy Dispersive... 

Friction stir welding (FSW) is considered a significant manufacturing process for joining of different metals and alloys and usage of this process has been developed in different industries. Accordingly, extensive works have been done on FSW of different engineering materials. However many ambiguous problems related to thermo-mechanical behavior of this process have not been solved yet. This research investigates FSW behavior of a hardenable aluminum alloy, AA2017. Firstly, thermo-mechanical response of the material has been predicted using a three-dimensional finite element analysis performed in ABAQUS software. Then, microstructural events such as grain size, distribution of second phase... 

The main objective of this project is to take the first steps in designing power plants governor in Iran. In this work, we obtain a realistic model of a hydro-power plant including hydraulic characteristics from the dam to the outlet tail water, mechanically including: the turbine, the gates and all mechanical and dynamic parts, and electrically including generators, transformers and the consumption network. The model is used to simulate different working modes of turbine operation. The Bond Graph method is used for deriving the system equations and MATLAB software for simulations. A conceptual design of the governor is done and the governor model is combined with the turbine model. Using... 

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).... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

Recently, Aluminum alloys have been the materials of choice for both military aircraft and automotive industries due to their high strength-to-weight ratio, high electrical and thermal conductivities and excellent corrosive resistance. However, their applications have been limited due to the low yield stress and wear resistance. In order to improve the surface wear resistance, structural and chemical surface modifications such as producing composite coatings could be applied. Gas Tungsten Arc welding (GTAW) process can be used to produce alloy and composite surface layers on different substrates. In this research, GTAW process and aluminum cored wires were used for coating of Al/Al3Ti... 

Estimation of demand, for example, for transportation is an important issue for the planning and programming of various systems. Thus, enhancing the predictability power of such models is of high value. Demand stems from choices of individuals, and choice is subject to uncertainty and fuzziness. Uncertainty comes from many factors including incomplete information of decision-maker, and fuzziness comes from many other factors including personal perception regarding the value of the variables affecting choice. This study tries to introduce a new approach in building choice models, in which variables are transformed into another variable by the help of a global wisdom. This wisdom shows the... 

As the crowded cities require public transportation and because of lack of space on the ground, Subway and boring underground tunnels encountered. In this thesis the interaction of boring the line 7 of Tehran metro with the existing station of line 1 of Tehran metro (Molavi station) is studied. By changing the soil specification, The surface settlement is significant so the soil specification is one of the important parameters of the interaction. For comparinf the effect of these parameters, the soil settlement and bending moments is investigated in different parts of station while the lower tunnel is passing beneath it. The 3D Abaqus software is used for modeling this interaction. In... 

In Persian language, there are some special uncertainties and complexities regarding the extraction of phonemes due to its flexible structure. In this work, we try to solve two problems caused by this issue, homographs disambiguation and Ezafe recognition in Persian text to speech systems.
In this work, two methods are presented for solving the two problems. The first one is a pattern recognition method based on Aho-Corasick algorithm that has the best performance according to the execution time. The second method is a hidden Markov model tagger based on Viterbi algorithm that uses bigram and trigram statistics. These methods are run on 10 million word corpus and the results are compared... 

Airplanes usually experience minor position change and height loss during cruise flight, but under normal circumstances the aircraft total energy is adequately acceptable to maintain the trajectory and the desired performance without severe oscillations. On the other hand, if the airplane encounters a wind-shear or microburst during take-off or landing phases, it would be a dangerous situation, as the aircraft kinetic and potential energy levels are not as high.
In this research, a model predictive controller is designed and investigated to allow a transport category aircraft to either escape or penetrate the microburst. In this regard, initially a DMC controller is designed for 6-DoF... 

Safely navigating complex urban environments presents a critical challenge in autonomous driving perception tasks. This challenge necessitates the ability to consider interaction with traffic scene agents while accurately predicting the behavior of vulnerable road users (VRUs) like pedestrians. This thesis aims to enhance AV perception by focusing on scene interaction awareness from two key perspectives: vehicle-vehicle and vehicle-pedestrian interactions. For vehicle-vehicle interactions, monocular depth estimation, a low-cost, data-driven approach, is employed to approximate inter-vehicle distance from an RGB image. First, vehicles and their lights are detected using the YOLOv7 algorithm... 

Recently, Needs for construction of rock structures and underground ones such as tunnels, dam foundations, power plants and caverns built to keep oil, gas and nuclear waste has increased dramatically. In order to design, construct and excavate these underground structures safely and economically, full understanding of rock mass properties, suitable tools and practical techniques of drilling are necessary. Because of existing this discontinuities, including joints and layered rock masses and their effects on mechanical behavior of rock mass, it is necessary for the geomechanical profile, shear strength and failure mechanism of rock mass to be accurately indentified. Shear strength criterions...