Sharif Digital Repository

In the era of artificial intelligence, achieving high accuracy in machine learning models is crucial for their practical applications. This thesis presents a novel approach to improve the accuracy of machine learning models by learning to defer to a team of human experts. The primary goal of this work is to build upon and extend previous research, proposing a model that outperforms existing models in the literature. Inspired by the "Mixture of Experts" framework, we introduce a neural network-based allocation system responsible for assigning cases to each member of the team, which consists of a machine learning model and multiple human experts. The allocation system intelligently determines... 

Nowadays, vertical take-off and landing (VTOL) UAVs are widely used in various commercial and military applications due to its high flying capabilities. RMIT VTOL is a special design of this family. This bird has a small size and low weight and along with the vertical takeoff and landing capabilities, it also has the ability to fly at high speed Cruise.
The overall objective of this project is to design and evaluate the efficiency of the proposed three control methods that are linear, predictive and adaptive on the dynamic model of this bird. Thus, the first part of the project is obtaining a dynamic model with sufficient detail for the dedicated bird. This model consists of different... 

Steel shear wall system has been used in recent years as the lateral-load resisting system in the design and retrofit of high-rise buildings. This system consists of infill shear panel is framed by surrounding steel frames. Infill shear panel can be applied in two types: stiffened or unstiffened. Considering to the previous studies, the stiffened type is more convenient in the seismic performance and utility condition. However, in the stiffened system, the construction cost is considerably higher because of the complicated construction details. This dissertation concentrates on the experimental and analytical studies of trapezoidally corrugated steel shear walls as an option for removing the... 

In recent years, Rheological behavior and heat transfer of nanofluid studies have been increasing considerably and results show significant progress in this area. In this study we analyze the laboratory examination of the influence of parameters of volume fraction and temperature on thermal conductivity coefficient, dynamic viscosity of new and useful nanofluid carbon nanotube in engine oil. Most of fluid comparing to solid has lower thermal conductivity coefficient therefore solid particles increase thermal conductivity coefficient. On the other hand by adding particles, the dynamic viscosity of nanofluid also increases. Since nanoparticles have high volume ratio to surface (SSA) they have... 

During the past decade the ever increasing volume of greenhouse gases due to fossil fuels consumption have made humans to seek for alternative, non-polluting fuels as an effective strategy to reduce pollution and prevent environmental issues thereof. Electric cars are today known as one of the most effective solutions for this purpose. Of course, transition from gasoline-powered cars to electric cars in a wide scale is not technically possible in short term due to technological and infrastructural limitations. As a result, this lengthy process would lead to emergence of a combinational transportation system including both gas and electric-powered vehicles. The major differences between these... 

In the current study, shape-memory alloys are analysed analytically under mechanical loading. Due to the special properties of these materials, their usage in various applications is rapidly increasing. However, mostly, the numerical methods such as finite-elements methods are employed to model the thermo-mechanical behavior of these materials. Also, due to the complexity of their behavior, there are few analytical solutions for them in the literature. In this research, an analytical approach is proposed to investigate the response of these materials under mechanical loading using a fundamental model which is suitable for modelling their crystalline structure. Given the impact of multiple... 

Nonholonomic constraints are a vast portion of constraints that happen in variety of dynamics applications such as robotics and control. In this project we present a new form of D’Alembert’s principle and employ it to generalize classical methods of Analytical Dynamics. It results in a new formulations which can be implemented to solve constrained dynamical systems either holonomic or nonholonomic. These formulations do not have any restrictions on the order of the nonholonomic constraints and can analyze high order nonholonomic constraints (HONCs) as well as first order constraints. In addition using these formulation one can find equations of motion of nonholonomic systems without... 

In this research a copper- diamond nanocomposite coating prepared by electrodeposition from a sulfate bath in order to increase the hardness and erosion resistance of cooper without disturbing cooper's specific physical properties as like as electrical and thermal conductivity. The mechanism of electrodeposition was analyzed with the technique of Cyclic Voltammetry, Chronopotentiometry and Chronoamperometry. The morphology, hardness, scratch resistance, elastic modulus and friction factor of coating were investigated by using a scanning electron microscope (SEM) and atomic force microscope(AFM) also the mechanism of co- deposition of diamond particles with copper was corresponded with... 

Peer-to-peer streaming has developed as a popular application in today’s Internetinfrastructure. In a typical peer-to-peer live streaming system, publishers provide the streaming content and the interested peers receive and deliver data in a distributed manner and also apeer structure is created by forming an overlay inside the network. In reality, peers are strategic and there is no motivation to contribute any of their upload bandwidth toward other peers. To address this issue, we proposed a simple arcade algorithm that makes an arcade based mechanism for peers to facilitate adjacent peers with more bandwidth to achieve a higher bandwidth themselves.Commensurate with our algorithm, if... 

The purpose of this thesis is to control altitude and attitude of a Tilt Tri-Rotor UAV in rotorcraft mode and control of altitude, attitude and forward velocity in transition mode (from rotorcraft mode to cruise) by using model predictive control. First, the detailed mathematical model is obtained by the Newton-Euler equations of motion, in both rotorcraft and transition modes. In the next step, a MIMO model predictive controller has been designed, considering input constraints. Then, since, robustness of the model-based control approach is an important challenge, the performance of the controller is presented in the presence of model uncertainties and wind disturbances. The results indicate... 

The steering system is very important in controlling the car. This requires to turning wheels at certain angles. These angles ideally follow the Ackerman geometry. But there is a difference between the real steering angle and the ideal geometry, which caused to steering error. This error depends on two factors, the steering mechanism and the vehicle suspension. Reducing steering error causes to reducing tire wear and increasing vehicle maneuverability at low speeds. In addition, the stability of the vehicle increases when crossing straight line and uneven roads. So far, mechanisms have been designed in accordance with the Ackerman geometry, but in these mechanisms used cam profile. Also... 

In this thesis, hemodynamic parameters of flow and deposition of low density lipoproteins (LDL) on wall of coronary arteries with taking into account their curvature on the heart are studied. At first, numerical solution of the blood flow by assumption of blood as incompressible and Newtonian fluid for steady and pulsatile inlet is done. Then by assuming LDL particles as dilute solute in the blood, LDL transport from artery lumen into arterial wall is studied. LDL accumulation and penetration into the vessel wall cause thickening of the walls and eventually eclipse it and its known as the first stage of atherosclerosis disease. The results show that low shear region occurs on inner wall... 

Increasing the application of elastomeric structures in industries has caused an interest in the researchers for nonlinear elasticity and viscoelasticity of solids. Such materials which show large deformation and rate dependent behavior are treated by visco-hyperelastic constitutive equations. Based on visco-hyperelastic constitutive equations, total stress is divided into two parts: quasi-static and viscous stress. The method for determining the visco-hyperelastic constitutive equation is strictly dependent on the chosen rheological model. In this project, a new visco-hyperelasic constitutive equation in the integral form was introduced based on the Zener model. Also, based on the internal...