Sharif Digital Repository

Wind turbines have been the subject of many researches in recent decades. Optimization and continuous improvement of these systems play a decisive role in the development and exploitation of wind farms. Wind turbines can be studied from several aspects such as structure, dynamics, aerodynamics, electricity and control. In this research, robust power control of the wind turbine has been studied with emphasis on accurate 2 DOF mechanical and aerodynamic modeling. Aerodynamic coefficients of the turbine have been calculated using the numerical methods and the effect of this numerical modeling has been studied in comparison with the analytical methods on the turbine power control. Several new... 

The present study focus is on finding a new solution to control laminar separation bubble phenomenon by combustion actuators in micro scale, which is investigated in flows with low Reynolds number surface effect and free flows. The main parameters in this problem are classified in three groups of formation location of laminar separation bubble, its length, and transition from laminar to turbulent around airfoil SD8020 in attack angle of 5 and 8 degree. Following that, the new combustion actuators in micro scale method the comparison it with cold (and hot) air jet injection is introduced to control boundary layer flow with separation bubble point of view. Some mechanisms are identified in... 

To make it easier to transition and increase the number of missiles on the launcher, many missiles consider the fins are designed to be foldable. Also, these types of fins can be opened during the flight and therefore reduce the drag force in the initial phase of the flight. One of the disadvantages of this type of design is that the fins may not open during the flight. Moreover, locking the actuator, breaking or destroying some part or all of the control surface of supersonic aircraft due to high speed and temperature and loss of thermal insulation is very probable. This thesis considers the locking, not opening, or even breaking the control surfaces, as well as the destruction of some part... 

The present thesis follows two aims in the phenomenon of vibration and control of cable of cable-stayed bridge under rain-wind induced vibration (RWIV). The first one is to study the response of the cable and consequently the second one aims to control these vibrations that occurred in the cable. The assumed continuous cable has lateral, in plane bending (IP), out of plane bending (OOP) and torsion mode. The effect of rainfall on the cable has been modeled with mobile upper rivulet on the cable surface and the effect and shape of lower rivulet have been neglected. RWIV is not vortex-induced vibration (VIV), nor wake galloping, because the dominant frequency of RWIV is lower than VIV and... 

The physics of the flow around the wing in the oscillatory motion of the wing has various patterns, including the leading edge vortex, the tip vortex and trailing edge vortex escape. The interaction of these vortices forms a complex flow structure around the wing, which will have a direct effect on the aerodynamic performance of the wing. Therefore, controlling these structures can be considered as a way to improve the performance of the flapping wing. One of the passive flow control techniques that has recently been taken into consideration is a leading-edge protuberance method. Another type of passive flow control is geometric correction, using corrugation method. According to studies, two... 

Integrated guidance and control (IGC) as a new approach to guidance and control methods has been studied in this thesis. A new approach to nonlinear aerodynamic formulation with backstepping controller has been proposed in order to improve interception. Various curve fitting techniques like Gram-schmidt method has been tested. But finally a planar aerodynamic formulation was used which only varies with angle of attack. Results showed that the proposed method requests smaller control input than the linear IGC formulation and conventional G&C methods, because of more precise knowledge of normal force coefficient. Thus the vehicle experiences smaller angle of attack and normal acceleration.... 

In the present work, dynamic behavior of submerged slender bodies under external hydrodynamic forces with internal sloshing tanks is studied. The main application of this thesis is in submarines. For this purpose slender body theory is used for hydrodyanamics of body and unsteady hydrodynamics is used for the vehicle control fins. In submarines there are some water tanks that control the buoyancy, so that sloshing can be importatnt. An equivalent mechanical model is developed for simulating the dynamics of sloshing tanks. Assuming that a submarine is a slender body, elastic deformation of submarine body can affect dynamics of the whole system. Elastic behavior of the main body is simulated... 

Using flapping motions, birds produce aerodynamic forces required to fly. Flapping wing aerodynamics is one of the most complicated problems in unsteady aerodynamic field. Experimental study on the structure, the way of production and growth and the feasibility of controlling the leading edge vortex are the main goals of this research in order to improve the aerodynamic performance of flapping wings. Since leading edge vortex structure appears in both upstroke and downstroke of a complete storke in flapping motion, controlling the structure in one of the half-storkes can provide the possibility of having a better aerodynamic performance. In this research, the wing is designed and... 

This study aims to evaluate aerodynamic coefficients of an airplane with air breathing engine experimentally. In these experiments, an ejector is used to better simulate flying conditions and aerodynamic interferences generated in inlet and exhaust engine. Therefore, at first, an ejector was designed for simultaneous simulation of exit cold flow and inlet flow of engine. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85, angles of -4 to 6 deg. and for various amounts of pressure ejector and control surfaces angles. Finally, for the Mach number of 0.5, effect of roughness on the aerodynamic coefficients was examined. The results showed that, drag... 

In adaptation with nature, Flapping Wing Arial Robots (FWARs) are flying vehicles that use wing flapping motion to produce lift and thrust forces simultaneously. Wing oscillating motion of FWARs in turn creates an unsteady and turbulent flow field around them that makes their aerodynamic modeling and analysis a complex and formidable task. As a result, experimental aerodynamic investigation of FWARs has been the focus of many researchers in the last few years. Inspired by nature, Bird-like FWARs utilize a tail as an augmented aerodynamic surface during their flight motion. In turn the tail aerodynamics that in general plays an important role in flight stability and control is adversely... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

Flapping wing vehicles produce aerodynamic lift and thrust through the flapping motion of their wings. The dynamic performance of a flexible membrane flapping wing is experimentally investigated here. To investigate aeroelastic effects of flexible wings (specifically, wing’s twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion for different flapping frequencies, angles of attack, various wind tunnel velocities up to 12 m/s and for various wings with different chordwise... 

In this study, a model for the optimal routes for the recovery of space debris is expressed. The dynamic model using a binary system consisting of satellites and orbital debris containment space is extracted. Trastrhay available on satellite and aerodynamic drag on the system circuit changes the whole system and the entry of debris into the thick atmosphere began to burn.This circuit must be optimized. The thrusters are assumed as variable optimization problem. After simulation of optimization, it follows that by changing the initial value thrusters, Trastrhay the optimal cost function changes. Also, indicating the final height of system affects on parameters, thrusters and the cost... 

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 study, the two rigid body modelling of a Coanda air vehicle (one rigid includes rotor and propeller and the second rigid includes the other parts of it) has been developed using Newton’s and Euler’s laws, and its motion was simulated in climb and forward flight conditions. Air vehicle propulsion force and moment have been modelled by employing the blade element momentum theory. In order to model the forces acting on the air vehicle, the drag force has been estimated by the results of analytical and computational fluid dynamics methods for the case of climb flight and by using experimental data of a cylindrical body for the forward flight. For modelling the control surfaces of this... 

Dynamical behavior of a dragonfly-like with rigid flapping wings considering aerodynamic forces has been modelled and simulated. At first, the dragonfly with its unique flying capabilities and the reasons for choosing it has been introduced. Then, modelling process is started with preliminary definitions including frames, coordinates and equations of motion, continued by applying initial conditions and ended with verification tests. After that, aerodynamic effects in a quasi-steady sense is added to dynamical model resulting in an 18 DOF model developed to be used for nonlinear simulation or controller designing. At the end, the results are validated in comparison to an experimental study.... 

Millions of people are exposed to noise every day in their work and life, and their physical and mental health is at risk due to this issue. Hence, the issue of noise and vibration has become an important factor in car quality. One of the sources of noise and vibration in the vehicle is the engine. The engine is the heart of the car and its most important part. Therefore, reducing Engine noise can have a significant effect on the noise emitted by the vehicle. Engine noise can be divided into three categories: 1 - combustion noise 2 - mechanical noise 3 - aerodynamic noise. This project is in line with a project defined between the university and industry aimed at improving all sources of... 

This thesis is focused on flight dynamics modeling and analysis of an articulated Flapping Micro Air Vehicle (FMAV), where the articulating joint is placed near the wing mid chord span. The articulation modeling, its results and verification due to added degrees of freedom are considered the key motivation and novelties of this project. Initial analyses indicated that a simple articulation device such as joint is not appropriate and will not be efficient for flying FMAV. As a corrective action, a spring-damper mechanism was utilized beside the articulation. Subsequently, the kinematics’ equations are developed and verified using the MSC Automated Dynamic Analysis of Mechanical Systems... 

A complete 6DOF flight dynamic model of an elastic flapping wing (EFW), integrated with unsteady aerodynamic theory is developed. In this respect, initially efficient high fidelity modules for EFW structural dynamics (SD) as well as unsteady aerodynamics loadings (UAL) to be coupled with its flight dynamics are prepared. A modal approach is followed to model structural dynamics of plain and 3D EFWs. This is in contrast with the Euler-Bernoulli beam theory that is mostly utilized for SD in the existing literature. In addition, due to the possibility of large wing deformations as well as the existence of non-linear displacement regime for realistic EFW flights, non-linear modal approaches such... 

Properly adjusting the trim angle during the craft speed up will be extremely important in special cases as in sport competitions or military missions. In such applications, the goal of trim adjustment is to reach final speed in a minimum possible time which is an advantage to just passing the resistance hump. Present study tries to provide insight into how the concerned control variables such as angles of the drive system and trim tab of a planing craft should be changed during acceleration mode so as to minimize the time needed to reach the final speed. This is a time-optimal control problem. Optimal control theory has been used previously for the motion control of marine vessels in...