In industrial drives market, speed and position estimation are one of the most important subjects for accurate motor drives. Vector controlled drives has the best dynamic performance among AC motor drives. Sensorless vector control is one of the most studied one. However, sensorless drive systems fail at low or zero speeds and may not have enough accuracy. For better accuracy and speed range speed sensors or position encoders are usually essential. However, coupling of sensor and sensor prices introduces extra cost on the drive. Thus in order to reduce the cost of the drive a cheap and easy to mount speed sensor is essential. Throughout this study, a speed and position sensor using an external search coil placed between cooling fins on the frame of an induction machine is proposed. The search coil utilizes the fringing flux outside the frame of induction motor. Using the induced voltage on the external search coil, a new method that estimates the flux and rotor position is proposed. In this study, the induced voltage on the search coils are investigated with different types of search coils placed on various positions. The frequency domain and time domain analysis are performed in order to build a model that can estimate machine flux, rotor speed and rotor position. As a result of this study, a low cost, easy to mount speed and position sensor is designed and implemented. Experiment results are presented.

In the thesis, automatic flight control system is designed for Tilt Duct Unmanned Aerial Vehicle (UAV). The vehicle is a Vertical Take-Off Landing (VTOL) type with two symmetric rotors on the wings, one aft rotor on the aft body. It behaves like a helicopter but with higher speeds in forward flight. Transition flight of the aircraft from hover to cruise or take-off to forward flight is the primary concern of the thesis study with the nonlinearities and instabilities encountered, together with the over-actuated controls in this mode. A nonlinear simulation code is developed including nonlinear equations of motion together with the nonlinear aerodynamics, environmental eects, and rotor dynamics. Trim and linearization codes are also developed. Trim conditions for the transition flight phase are calculated for two different transition scenarios. Linear controllers are developed and nonlinear controller is designed for the transition mode. Nonlinear controller uses the state dependent Ricatti equation SDRE approach by using extended linearization. Two loop approach is used in order to increase controllability. In the inner loop, attitude rates are fed back and SDRE approach is used to calculate the feedback gain matrix online. In the outer loop, vehicle attitude is controlled using the eigenvalue assignment. Blended inverse algorithm based control allocation method is used in control of the over-actuated transition phase. This algorithm is shown to be quite effective among different methods in not only generating necessary forces needed for the control, but also allocating with more control authority on the desired actuator.

In this thesis analysis and design of helicopter rotor blades were discussed for reduced vibrational level. For this purpose an optimization procedure was developed which involves coupling of the comprehensive rotorcraft analysis tool CAMRAD JA and the gradient based optimization algorithm. The main goal was to achieve favorable blade structural dynamics characteristics that would lead to reduction in vibrational level. For this purpose blade stiffness and mass distributions were considered as the design variables. In order to avoid likely occurrences of unrealistic results, the analyses were subjected to constraints which were sensitive to the design variables. The optimization procedure was applied on two isolated rotor blades and a full helicopter with main rotor, tail rotor and fuselage by using natural frequency separation and hub load minimization respectively. While the former approach relied on the blade natural frequencies, the latter approach involved higher harmonic aerodynamic and blade motion calculations. For both approaches, the improvement in vibration characteristics and blade mass and stiffness distributions of the initial design and the design after optimization analyses were compared and discussed.

Ceramics can highly withstand the environments of high temperature and serious erosion, it completely substitutes for alloys which reach their specific limitations. Turbine rotor operates in the compressed stage with temperature over thousand Celsius degrees; it must rely on excellent properties of ceramics to elevate the durability and lifetime. To manufacture complex ceramic component before, industry usually uses near net shaping or rapid prototyping (RP) processes. A manufacturing process based on machining green ceramic turbine component is presented here. Initially, formulating a series of machining experiments for green ceramics to verify the idea of thesis, and analyzing the probability of Al2O3 ceramic as a turbine material. Firstly, it needs to check the machinability of green ceramic by face milling. Secondly, point milling the normal plate of green compact and the plate with analogical blade geometry to find a set of usable machining parameters (such as revolution speed, feed rate, step over and cutting depth); meanwhile, addressing machining amendment by observing the final conditions of specific geometric characteristics on workpiece. Finally, try to machining green ceramic turbine successfully applying the above parameters.

The concept of applying several disciplines to the design and optimization processes may not be new, but it does not currently seem to be widely accepted in industry. The reason for this might be the lack of well-known tools for realizing a complete multidisciplinary design and analysis of a product. This study aims to propose a method that enables engineers in some design disciplines to perform a fairly detailed analysis and optimization of a design using commercially available software as well as codes developed at Georgia Tech. The ultimate goal is when the system is set up properly, the CAD model of the design, including all subsystems, will be automatically updated as soon as a new part or assembly is added to the design; or it will be updated when an analysis and/or an optimization is performed and the geometry needs to be modified. Such a design process takes dramatically less time to complete; therefore, it should reduce development time and costs. The optimization method is demonstrated on an existing helicopter rotor originally designed in the 1960's. The rotor is already an effective design with novel features. However, application of the optimization principles together with high-speed computing resulted in an even better design. The objective function to be minimized is related to the vibrations of the rotor system under gusty wind conditions. The design parameters are all continuous variables. Optimization is performed in a number of steps. First, the most crucial design variables of the objective function are identified. With these variables, Latin Hypercube Sampling method is used to probe the design space of several local minima and maxima. After analysis of numerous samples, an optimum configuration of the design that is more stable than that of the initial design is reached. The process requires several software tools: CATIA as the CAD tool, ANSYS as the FEA tool, VABS for obtaining the cross-sectional structural properties, and DYMORE for the frequency and dynamic analysis of the rotor. MATLAB codes are also employed to generate input files and read output files of DYMORE. All these tools are connected using ModelCenter.

Measuring the farfield noise levels of full-scale rotor systems is not trivial and can be costly. Researchers prefer to perform small-scale experiments in the laboratory so that they can extrapolate the model scaled results to the larger scale. Typically Inverse Square Law (ISL) is used to extrapolate the sound pressure levels (SPL), obtained from model-scale experiments at relatively small distances to predict noise at much larger distances for larger scale systems. The assumption underlying this extrapolation is that the source itself can be treated as a point sound source. At what distance from a rotor system it can be treated as a point source has never been established. Likewise, many theoretical models of shielding by hard surfaces assume the source to be a point monopole source. If one is interested in shielding the noise of a rotor system by interposing a hard surface between the rotor and the observer, can the rotor system really be considered to be a monopole? If rotating noise sources are under consideration what is the effect of configuration and design parameters? Exploring the validity of point source assumption alluded to above for a rotor for farfield acoustic measurements with and without shielding form the backbone of the present work.

Zugl.: München, Universiẗat der Bundeswehr, Diss., 2009.

In this work, the time varying stresses in a Howden axial flow fan are obtained by finite element analyses. Dynamic substructuring is used to obtain accurate values of the stresses in the threads of the blade shaft, the component which connects the blade with the hub. Three different global models are used to compare the influence of neglecting the fan shaft and the stiffness influence of the centrifugal force. The relative displacements, which are obtained from the global models, have been used as boundary condition in the detailed models. The detailed models are used to obtain the Von Mises stresses in the root of the threads of the blade shaft. Finally the results of the three global models are compared with experimental measured data provided by Howden. The experimental data results in the highest Von Mises stresses. The model with the fan shaft and the stiffness influence of the centrifugal force gives values for the Von Mises stresses which are approximately twenty percent lower. The model without the fan shaft results in the lowest stresses which are approximately forty percent lower than the stresses obtained using the measured data.

Offshore wind power production is an attractive clean energy option, but the difficulty of access can lead to expensive and rare opportunities for maintenance. Smart loads management (controls) are investigated for their potential to increase the fatigue life of damaged offshore wind turbine rotor blades. This study will consider two commonly encountered damage types for wind turbine blades, the trailing edge disbond (bond line failure) and shear web disbond, and show how 3D finite element modeling can be used to quantify the effect of operations and control strategies designed to extend the fatigue life of damaged blades. Modern wind turbine blades are advanced composite structures, and blade optimization problems can be complex with many structural design variables and a wide variety of aeroelastic design requirements. The multi-level design method is an aeroelastic structural design technique for beam-like structures in which the general design problem is divided into a 1D beam optimization and a 2D section optimization. As a demonstration of aeroelastic design, the multi-level design method is demonstrated for the internal structural design of a modern composite rotor blade. Aeroelastic design involves optimization of system geometry features as well as internal features, and this is demonstrated in the design of a flying wing aircraft. Control methods such as feedback control also have the capability alleviate aeroelastic design requirements and this is also demonstrated in the flying wing aircraft example. In the case of damaged wind turbine blades, load mitigation control strategies have the potential to mitigate the effects of damage, and allow partial operation to avoid shutdown. The load mitigation strategies will be demonstrated for a representative state-of-the-art wind turbine (126m rotor diameter). An economic incentive will be provided for the proposed operations strategies, in terms of weighing the cost and risk of implementation against the benefits of increased revenue due to operation of damaged turbines. The industry trend in wind turbine design is moving towards very large blades, causing the basic design criterion to change as aeroelastic effects become more important. An ongoing 100 m blade (205 m rotor diameter) design effort intends to investigate these design challenges. As a part of that effort, this thesis will investigate damage tolerant design strategies to ensure next-generation blades are more reliable.

This work considers formulation of new classes of adaptive controllers for double-integrator type systems where the underlying system parameters are uncertain and the complete state-vector is not available for feedback. Given the parameter uncertainty within the system model, a "separation principle" cannot generally be invoked towards an observer geared towards reconstruction of the full state vector using only measured variables. In this report, controllers are designed for some important sub-classes of Euler-Lagrange type mechanical systems, where states are physically interpreted as position and velocity variables, and only the position part of the state vector is available as measured output. The typical approach to obtain velocity estimates using position interpolation (also known as dirty differentiation), is known to be strongly susceptible to measurement noise and therefore does not usually represent a robust option for feedback control implementation. The proposed control scheme achieves global asymptotic stability for system dynamics subject to the condition that velocity states appear within the governing dynamics in a linear fashion. This arguably restrictive condition is loosened for the special case of scalar system with friction non-linearity as is typical within hardware implementations. The objective is to study prototypical mechanical systems with non-linearity appearing in the velocity rate equations with the eventual applications envisioned towards the attitude control problem accounting for the gyroscopic non-linearity in the Euler rotational dynamics. Based on classical certainty equivalence approaches for adaptive control, one cannot readily deal with cross terms associated with parameter estimates and unmeasured states in the Lyapunov function derivative in order to make the Lyapunov function negative definite or negative semi-definite. However, employing a new approach, this obstacle is shown in this report to be circumvented for scalar systems. In order to generalize the methodology for higher-order dynamics, a filtered state approach is used. Specifically, an auxiliary variable is introduced which plays an important role in determining restrictions on the control parameters and analyzing the stability. The proposed approach helps to overcome the uniform detectability obstacle. Additionally, this work can be applied to uncertain linear systems where independent control inputs are applied on each of the velocity state dynamics. Lastly, the solution for the scalar is applied to the rotor speed control system and is extended to the case where Coulomb friction is considered in addition to viscous friction. Since a sign function can be approximated as a hyperbolic tangent, the tanh model is used for the Coulomb friction. A controller is developed with the assumption that the coefficients of these frictions are unknown. The proposed control is then verified with Educational Control Product Model 750 Control Moment Gyroscope, and the simulation and actual test results are compared. / text