Sharif Digital Repository

Because of advancing fractional calculus and modeling physical phenomena by using fractional calculus more accurately than that by using integer calculus, and also existing uncertainties in models of real world systems, robust stability and performance analysis of fractional order systems are necessary. This thesis deals with the robust -stability analysis of LTI fractional order systems from kind of uncertain typical fractional order systems (UTFOS) and the robust stability analysis of LTI fractional order systems with delays from kind of uncertain retarded type systems (URTS) and uncertain neutral type systems (UNTS) with interval uncertainties. The coefficients of the numerator and the... 

The importance of aircraft mass properties, including mass, center of gravity position and moments of inertia, and the effect of these parameters on the aircraft performance, stability and control is clearly bright for aviation science specialists. The ability to in-flight estimation of the aircraft mass properties in all flight conditions is a powerful technology for improving conditioned based maintenance systems, automatic flight control systems, flight safety, airplane performance, flight path planning, air traffic management, cooperative and formation flight management, facilitating investigation of aerial accidents caused by uncertainty of the mass properties, and increasing... 

Due to the large application of electro-sprays in various industries, the study of the stability of electro-hydrodynamic flows is important. This thesis examines the stability of cylindrical liquid jets in the presence of an axial electric field. The definition of this jet is a simplified model of electrospray, electrospinning. In this model, the stability of a free incompressible cylindrical flow with surface tensile strength, conductivity, polarization, viscosity, and dielectric constant is determined, irrespective of the solubility of the jet and the surrounding fluid (air), in the presence of uniform axial electric field has taken. This will be done by adding the forces generated by the... 

This thesis is focused on development, modeling and simulation of a complete 6DOF elastic flapping air vehicle (FAV). In this respect the aerodynamic modeling is performed using a recent experimentally validated generalized modified strip theory (GMST) that considers the unsteady effect of wake and leading edge vortices via the Theodorsen function and Polhamus analogy respectively. The FAV wing structure is modeled using an elastic plate whose dynamic behavior is determined via a modal approach that is also verified with experimentation. The resulting novel integrated aerodynamic and structure (IAS) equations of motion are simulated for case study of FAV flight. Subsequently, since the IAS... 

Direct steam generation (DSG) process using linear FRESNEL collectors has been developed widely in recent years and is one of the most promising solar technologies for thermal power generation, Industrial processes and domestic usage. In this process water as heat transfer fluid (HTF) is heated through a solar field. Continuous breakthroughs are being achieved on improvement of these collectors. A multi-phase CFD model is developed to calculate the wall temperature of linear Fresnel absorber tubes and fluid properties including temperature, velocity, and pressure. In order to design the collector field and identify the critical condition such as overheating of the absorber tubes, modeling of... 

In this research a novel intelligent back-stepping control method is developed. This method is robust to sensor noise and external disturbances. In addition, the controller is robust under model uncertainty. This controller does not need precise knowledge of system parameters. This method is based on three methods of: back-stepping control, least squares estimation and a fuzzy compensator. This controller is used to control quadrotor stand witch is like an inverse pendulum. In quadrotor stand modeling, the inverse pendulum effect is considered too, witch is one of the innovations of the research. By doing various simulations, the validity of controller is tested. Also the performance of the... 

Today, a lot of efforts have been done in order to commercialize space travels. Spacecrafts have a lot of components and producing each of them spends high costs. Components such as propellant tanks and boosters are multi segment and are released simultaneously and therefore it is economically feasible to recover them. Due to Parafoil ability in low-cost, soft (no damage to the cargo) and accurate landing, it is gradually replacing parachute. Parafoil can fly long distances after being released, so its landing point could be determined. The aim of the study is to evaluate this scenario in which some segments of launch vehicle (e.g. booster) that are equipped with Parafoil expand their... 

The problem of spacecraft rendezvous on periodic orbits around the L_1Lagrange point of the Earth-Moon system is investigated. For this purpose, the nonlinear relative equations of motion are drived within the contex of the Circular Restricted Three Body (CRTB) problem. Subsequently, several types of rendezvous missionas well as control teqniques are considered for analysis and simulation. Application of different control approaches allows for partial verification as well as comparison of results achieved with various teqniques. The considered control approaches include optimal closed loop Linear Quadratic Regulator (LQR), nonlinear Feedback Linearazation (FL) as well as the nonlinear... 

In the present thesis, a high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied for an accurate and efficient numerical simulation of liquid-vapor two-phase flows. At first, the stability of the fourth-order CFDLBM is performed by using the von Neumann stability analysis for the D2Q7 and D2Q9 lattices. The stability analysis indicates that the CFDLBM proposed is stable and thus suitable for the simulation of high Reynolds number flows. The high-order CFDLBM is then developed and applied to accurately compute 2-D and 3-D incompressible flows in the Cartesian coordinates. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized... 

In this thesis, multi-body modeling of a monocopter air vehicle is developed based on the Newton-Euler approach along with nonlinear simulation in vertical flight phases consist of climb, hover and descent. Aerodynamic and thrust forces and moments are modeled utilizing blade element momentum theory. The sole control surface is modeled like a conventional flap on a wing. Free flight simulation is implemented in MATLAB Simulink environment to appraise the behavior of the monocopter dynamic and to show the efficiency and productivity of the suggested model. Simulation results present harmonic oscillations in Euler angles, linear and angular velocities that are compatible with the physics and... 

In this thesis the problem of spacecrafts formation control for halo orbit around the second libration point (L2) of the Sun-Earth Three Body (TB) system is investigated. Station keeping, reconfiguration and precision formation control of spacecrafts on halo orbits are performed via the use of the nonlinear Integral Sliding Mode (ISM) method, optimal closed loop Linear Quadratic regulator (LQR) approach as well as the Model Prodective Control (MPC). In this regard the nonlinear relative dynamics of deputy-chief spacecrafts are derived within the concept of both circular and elliptical three body problem; as well the perturbation model of the Moon and the linear model of restricted three... 

In this thesis a novel non-rotating space tethered configuration is introduced which its relative positions are controlled using electromagnetic forces. The attitude dynamics is controlled by three reaction wheels in the body axes. The nonlinear coupled orbital dynamics of a dumbbell tethered satellite formation flight are derived through a constrained Lagrangian approach. These equations are presented in the leader satellite orbital frame. The advantage of using equations in the Cartesian coordinate system over presenting the equations of satellite formation plane angles is the appearance of gravity gradient and Earth’s magnetic field effects. The tether is assumed to be mass-less and... 

In this thesis, single channel control of a rotating flying vehicle by using an INS is designed based on a nonlinear model simulation. Despite the widespread use of single channel guidance and control systems in some homing missiles, they have not been utilized in rotating rockets due to absence of stabilized seeker in this kind of rockets. The idea proposed in this thesis is to make it possible to use single channel control system by means of a stable platform in the flying vehicle which is completely isolated from body rolling motion. The INS is located on the stable platform and an appropriate guidance algorithm is presented in the stable platform coordinate system.
In this... 

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... 

Identification of dynamic behavior and extraction of mathematical model for aerial vehicle is important in design, test and evaluation processes. Due to explosion of unmanned vehicles industry in recent years, many innovative aerial concepts is introduced. Coanda-effect air vehicle is one of these novel ideas which is similar to flying saucers. In this study, an experimental scale model of this air vehicle is designed, built and tested with purpose of identifying the linear dynamic model of the vehicle, using the frequency domain identification methods. Performing the system Identification in hover requires a stable hovering capability in the vehicle. Given the inherent instabilities of... 

In the study, the simulation of two-dimensional cavitating flows is performed by applying a high-order accurate numerical method to the preconditioned, homogenous, multiphase Navier-Stokes equations. The baseline differential equations system is comprised of the mixture volume, mixture momentum and constituent volume fraction equations. A coordinate transformation is applied and the resulting system of governing equations in curvilinear coordinates is discretized using a fourth-order compact finite-difference scheme. The high-order accurate numerical scheme employing the suitable linear and nonlinear filters to account for density jumps across the cavity interface is shown to yield an... 

In comparison to attitude control of a satellite which is widely used in practical missions, orbit control (espescialy autonomous orbit control) has been only recently paid attention. Autonomous, on-board orbit control, also called autonomous stationkeeping, means the automatic maintenance of all of orbital elements by the satellite itself. In this thesis, an autonomous absolute orbit control strategy for a single Low Earth Orbit (LEO) satellite is presented. When the satellite violates the control trigger error limits, then the controller is activated and calculates a sequence of orbital maneuvers that move the satellite towards its desired states. The absolute orbit control of the... 

In this research, the design of control system has been studied for a special flying vehicle at whole of flight time. This flying vehicle is vertically launched and few time after launch its attitude changes to the desired attitude by a reaction jet control system, then the acceleration commands are tracked when the aerodynamic is activated. Design process includes attitude control system design in launch phase and aerodynamic control system design. Because of the existence of nonlinear and multi-variable dynamics in the flying vehicle and the presence of uncertainty and disturbance, combination of nonlinear, robust and adaptive methods are used in controller design process. Design of... 

The first project ,paid to review and analysis types of crack and agents Also, was referred methods to control them in rail industry .
The wheel of Alestom train and UIC60 rail were simulated and stress analysis by software FEM (ANSYS and ABAQUS) , and effect of various parameters such as applied forces , train wheel diameter , contact position and rail inclination on stress values was studied . For comparision of results has been used analytic Hertz theory .
By using experimental data on the subsurface crack , those cracks were created in the wheel . For load on the modeling wheel and rail, ,assuming contact on the wheel rolling point , were used vertical load of wagon weight ( with... 

Scientific collaboration and the resulting outputs have been always of interest to the scientific community. Specifically, drawing and understanding the elements of scientific collaboration network and identifying its determinants are important step in prescribing and implementing policies in various fields and disciplines of science. Focusing on the Iran context, this study examines the scientific collaborations of faculty members in selected Iranian universities (Sharif University of Technology, University of Tehran, Iran University of Science and Technology, Amirkabir University of Technology, Isfahan University of Technology, and Ferdowsi University of Mashhad). We have drawn the...