Algebraic Topology Metheds on Graph Coloring

, M.Sc. Thesis Sharif University of Technology Pouria Omidi (Author) ; Jafari, Amir (Supervisor)

Abstract

The aim of this thesis is to introduce some algebraic topologies methods and apply them on fining the chromatic number of some famous graphs and also hypergraphs. In the first part, we will use a mixture of two well-known technics, Tucker lemma and Discrete Morse theory to find an upper bound for the chromatic number of s-stable Kneser for some specific vector s. to find the sharper upper bound, we will deviate our strategy and use another approach by finding an edge-labeling and apply some theorems in POSET algebraic topology. In this way, we also find a connection between Young diagrams and the numbers of spheres in the box complex related to Kneser graphs and hypergraph. Actually, we can...

Examination of indirect responses of helicopters using a refined inflow model

, Article Aircraft Engineering and Aerospace Technology ; Volume 81, Issue 1 , 2009 , Pages 25-37 ; 00022667 (ISSN) Shahmiri, F ; Saghafi, F ; Sharif University of Technology

2009

Abstract

Purpose - The purpose of this paper is to examine the cross-coupled responses of a coupled rotor-fuselage flight dynamic simulation model, including a finite-state inflow aerodynamics and a coupled flap-lag and torsion flexible blade structure. Design/methodology/approach - The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and finite-state inflow formulation. The finite-state inflow formulation is based on a 3D unsteady Euler-based concepts presented in the time domain. The most advantages of the model are the capability of modeling dynamic wake effects, tip losses and skewed wake aerodynamics. This is,...

Improvement of dynamic response prediction of helicopters

, Article Aircraft Engineering and Aerospace Technology ; Volume 79, Issue 6 , 2007 , Pages 579-592 ; 00022667 (ISSN) Shahmiri, F ; Saghafi, F ; Sharif University of Technology

2007

Abstract

Purpose – This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters. Design/methodology/approach – The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and state-space represented indicial-based unsteady aerodynamics. The model is represented by a set of nonlinear partial differential equations for the main rotor within a state-space representation for all other parts of helicopter dynamics. The coupled rotor and fuselage formulation enforces the use of numerical solution techniques for trim and linearization...

Modeling and Solving On-line Ride Sharing Problem with Modified Dial-a-Ride Model

, M.Sc. Thesis Sharif University of Technology Shahmiri, Pouria (Author) ; Eshghi, Koorosh (Supervisor)

Abstract

Today, considering the challenges that have been raised around fossil fuels and energy consumption in recent years, efforts have been made to reduce as much as possible the number of vehicles that are personal or single-passenger on the streets. For this purpose, a concept called travel sharing has been proposed in online platforms and businesses, where travelers can travel part or all of their journey with other travelers, but pay less money. The purpose of this research is to solve the problem of allocation and accessibility of passengers and cars in travel-sharing systems. To move in this direction, we have used mathematical programming tools and designed online algorithms to solve this...

Friction stir lap joining of aluminium alloy to polypropylene sheets

, Article Science and Technology of Welding and Joining ; Volume 22, Issue 2 , 2017 , Pages 120-126 ; 13621718 (ISSN) Shahmiri, H ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology

Taylor and Francis Ltd 2017

Abstract

Joining feasibility of aluminium alloy to polypropylene sheets via friction stir lap joining was examined. Effects of heat-input on microstructure and mechanical behaviour of the joints were investigated. A covering plate was used to confine flow of molten polymer. The results showed a distinctive interaction layer at polymer/aluminium interface, consisted mainly of C, O and Al. Shear strength of the joints decreased by enhancement of the heat-input due to increase in the thickness of the interaction layer as well as the gap width between this layer and both aluminium and polymer matrices. Maximum shear-tensile strength of 5.1MPa (∼20% of polymer shear strength) was obtained, which was...

Performance Assessment of PEM Fuel Cell in Extreme Conditions (Sub- Freezing Temperatures)

, M.Sc. Thesis Sharif University of Technology Shirazi, Peimaneh (Author) ; Rajabi Qhahnuyeh, Abbas (Supervisor) ; Ahmadi, Pouria (Supervisor)

Abstract

Fossil fuels provide the most needs of the world's energy, however, continues to lead to two key problems. The first problem is their limitation, and the second problem is the creation of serious environmental issues. Therefore, the need for renewable energy sources is felt more than ever.As an energy source, hydrogen is the lightest, most efficient and cleanest fuel. One of its unique properties is efficiency, the production of electricity by fuel cells through the electrochemical process, has far greater efficiency than of mechanical energy production from fossil fuels in internal combustion engines or energy production in thermal power plants. A fuel cell is a device that converts...

Joining of AA5052 Aluminum to C30S Polypropylene Sheets Using Friction Stir Welding

, M.Sc. Thesis Sharif University of Technology Shahmiri, Hamid Reza (Author) ; Movahhedi, Mojtaba (Supervisor) ; Kokabi, Amir Hossein (Supervisor)

Abstract

Joining metals to polymers is an increasing demand in industry mainly due to weight savings. Polymer-metal hybrid structures are widely used in aerospace and automotive industries. However, dissimilar joining of polymer to metal is very difficult due to large mechanical and physical properties differences. Since conventional methods for joining polymers to metals have various limitations, it is necessary to employ new practical and environmental friendly joining processes. In this study, the feasibility of joining an aluminum alloy (AA5052) to polypropylene (C30S) sheets via friction stir welding was examined. Lap joint configuration was determined as the optimized configuration by analyzing...

Multi-objective Design and Optimization of a Delta Robot and its Pareto-Optimal Solution and its Robust Control with Sliding Mode Method

, M.Sc. Thesis Sharif University of Technology Esmaeili Shahmiri, Yussuf Reza (Author) ; Vossoughi, Gholamreza (Supervisor) ; Moradi, Hamed (Supervisor)

Abstract

Nowadays, Automation and Robots have many industrial and non-industrial applications. One of the most important of Robotic applications in industries for speed increasing, is utilizing them for packing procedures on production lines. Speed and accuracy enhancement, low-error repeatability, and cost reduction are benefits if using robots. Delta robot, is one of the parallel robots which is consists of three arms each connected to universal joints at the base and can reach high speeds.Delta robot can be optimized in 1. Performance speed, 2.accuracy, 3. Maximum payload, 4. Workspace and dexterious workspace and 5. Costs reduction. Since it’s not possible to fully optimize all goals...