Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Michael Athans. / "September 1980" "Proceedings 19th IEEE Decision and Control Conference, Albuquerque, N.M., December 1980." / Bibliography: leaf 5. / "Office of Naval Research ... contract ONR/N00014-77-C-0532" "Air Force Office of Scientific Research ... contract AFOSR-80-0229"

Numerical models of insect flapping flight have previously been developed and used to simulate the performance of insect flight. These models were commonly developed via Blade Element Theory, offering efficient computation, thus allowing them to be coupled with optimisation procedures for predicting optimal flight. However, the models have only been used for simulating hover flight, and often neglect the presence of the induced flow effect. Although some models account for the induced flow effect, the rapid changes of this effect on each local wing element have not been modelled. Crucially, this effect appears in both axial and radial directions, which influences the direction and magnitude of the incoming air, and hence the resulting aerodynamic forces. This thesis describes the development of flapping wing models aimed at advancing theoretical tools for simulating the optimum performance of insect flight. Two models are presented: single and tandem wing configurations for hawk moth and dragonfly, respectively. These models are designed by integrating a numerical design procedure to account for the induced flow effects. This approach facilitates the determination of the instantaneous relative velocity at any given spanwise location on the wing, following the changes of the axial and radial induced flow effects on the wing. For the dragonfly, both wings are coupled to account for the interaction of the flow, particularly the fact that the hindwing operates in the slipstream of the forewing. A heuristic optimisation procedure (particle swarming) is used to optimise the stroke or the wing kinematics at all flight conditions (hover, level, and accelerating flight). The cost function is the propulsive efficiency coupled with constraints for flight stability. The vector of the kinematic variables consists of up to 28 independent parameters (14 per wing for a dragonfly), each with a constrained range derived from the maximum available power, the flight muscle ratio, and the kinematics of real insects; this will prevent physically-unrealistic solutions of the wing motion. The model developed in this thesis accounts for the induced flow, and eliminates the dependency on the empirical translation lift coefficient. Validations are shown with numerical simulations for the hover case, and with experimental results for the forward flight case. From the results obtained, the effect of the induced velocity is found to be greatest in the middle of the stroke. The use of an optimisation process is shown to greatly improve the flapping kinematics, resulting in low power consumption in all flight conditions. In addition, a study on dragonfly flight has shown that the maximum acceleration is dependent on the size of the flight muscle.

The thesis traces the history of missile aerodynamic prediction methods and defines the aerodynamic requirements for the subsonic free-flight projectiles configurations under consideration. Different types of trajectory model are described with the aerodynamic input requirement being analysed. Methods of generating the required aerodynamic data for the trajectory models are discussed emphasising the aerodynamic models capabilities, weaknesses and ease of use. The method of masses aerodynamic prediction method is defined, highlighting the adaptations to the method that were carried out to generate the aerodynamic stability data required for subsequent projectile trajectory analysis. An assessment of the sensitivity and accuracy of the simulated data is carried out using experimental flight trial data on different projectile configurations. Finally, using the simulation models developed in previous chapters, a parametric analysis is carried out on different projectile configurations to optimise the trajectory performance.

abstract: One hypothesis for the small size of insects relative to vertebrates, and the existence of giant fossil insects, is that atmospheric oxygen levels have constrained body sizes because oxygen delivery would be unable to match the needs of metabolically active tissues in larger insects. This study tested whether oxygen delivery becomes more challenging for larger insects by measuring the oxygen-sensitivity of flight metabolic rates and behavior during hovering for 11 different species of dragonflies that range in mass by an order of magnitude. Animals were flown in 7 different oxygen concentrations ranging from 30% to 2.5% to assess the sensitivity of their behavior and flight metabolic rates to oxygen. I also assessed the oxygen-sensitivity of flight in low-density air (nitrogen replaced with helium), to increase the metabolic demands of hovering flight. Lowered atmosphere densities did induce higher metabolic rates. Flight behaviors but not flight metabolic rates were highly oxygen-sensitive. A significant interaction between oxygen and mass was found for total flight time, with larger dragonflies varying flight time more in response to atmospheric oxygen. This study provides some support for the hypothesis that larger insects are more challenged in oxygen delivery, as predicted by the oxygen limitation hypothesis for insect gigantism in the Paleozoic. / Dissertation/Thesis / M.S. Biology 2011

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Small Unmanned Aerial Vehicles (UAVs) have seen continual growth in both research and commercial applications. Attractive features such as their small size, light weight and low cost are a strong driver of this growth. However, these factors also bring about some drawbacks. The light weight and small size means that small UAVs are far more susceptible to performance degradation from factors such as wind gusts. Due to the generally low cost, available sensors are somewhat limited in both quality and available measurements. For example, it is very unlikely that angle of attack is sensed by a small UAV. These aircraft are usually constructed by the end user, so a tangible amount of variation will exist between different aircraft of the same type. Depending on application, additional variation between flights from factors such as battery placement or additional sensors may exist. This makes the application of optimal model based control methods difficult. Research literature on the topic of small UAV control is very rich in regard to high level control, such as path planning in wind. A common assumption in such literature is the existence of a low level control method which is able to track demanded aircraft attitudes to complete a task. Design of such controllers in the presence of significant wind or modelling errors (factors collectively addressed as lumped disturbances herein) is rarely considered. Disturbance Observer Based Control (DOBC) is a means of improving the robustness of a baseline feedback control scheme in the presence of lumped disturbances. The method allows for the rejection of the influence of unmeasurable disturbances much more quickly than traditional integral control, while also enabling recovery of nominal feedback con- trol performance. The separation principle of DOBC allows for the design of a nominal feedback controller, which does not need to be robust against disturbances. A DOBC augmentation can then be applied to ensure this nominal performance is maintained even in the presence of disturbances. This method offers highly attractive properties for control design, and has seen a large rise in popularity in recent years. Current literature on this subject is very often conducted purely in simulation. Ad- ditionally, very advanced versions of DOBC control are now being researched. To make the method attractive to small UAV operators, it would be beneficial if a simple DOBC design could be used to realise the benefits of this method, as it would be more accessible and applicable by many. This thesis investigates the application of a linear state space disturbance observer to low level flight control of a small UAV, along with developments of the method needed to achieve good performance in flight testing. Had this work been conducted purely in simulation, it is likely many of the difficulties encountered would not have been addressed or discovered. This thesis presents four main contributions. An anti-windup method has been devel- oped which is able to alleviate the effect of control saturation on the disturbance observer dynamics. An observer is designed which explicitly considers actuator dynamics. This development was shown to enable faster observer estimation dynamics, yielding better disturbance rejection performance. During initial flight testing, a significant aeroelastic oscillation mode was discovered. This issue was studied in detail theoretically, with a pro- posed solution developed and applied. The solution was able to fully alleviate the effect in flight. Finally, design and development of an over-actuated DOBC method is presented. A method for design of DOBC for over actuated systems was developed and studied. The majority of results in this thesis are demonstrated with flight test data.

A study has been conducted of reaction controls for VSTOL aircraft using thrust augmenting ejector techniques. Rapid mixing nozzles have been developed for high pressure ejectors. Mass flow increases for sonic nozzles of up to 50\ at x/D=8 were recorded, compared with plain circular nozzles. Their use was found to improve the thrust performance of a simple ejector by 9\, and larger increases are believed possible. Results from an ejector performance prediction model were successfully compared with experimental data. The use of rapid mixing nozzles in a practical ejector design has been assessed. It is predicted that a maximum thrust increment of 20\ ·could be achieved, compared with a simple fully expanded jet flow.

Integrated Modular Avionics standardises hardware and software platforms of Line Replaceable Modules (LRMs) and other system components in order to reduce the overall cost of system development. operation and maintenance. Several identical processing units within a cabinet. and fast communication media in the form of a backplane bus introduces further possibility of reconfiguring the system in terms of changing the applications performed by particular core LRMs. In this thesis a study into Reconfigurable Integrated Modular Avionics is presented. The main objectives of the project were to investigate the benefits, and feasibility of, employing autonomous dynamic in-tlight reconfiguration of the system as a means for providing fault-tolerance. In this approach, allowing processing modules to change their function permits the system to share the redundant modules as well as sacrificing less important avionics functions to sustain the more critical applications. Various architecture examples are reviewed in order to establish a system design that would support reconfiguration at a minimal cost. Two modified ARINC 651 architecture examples are proposed for implementation of dynamic in-flight reconfiguration. The benefits of reconfiguration are identified with the use of Markov state space analysis, and are found to be substantial with respect to the reduced number of redundant processing modules required to implement the system functions within the safety requirements. Suitable reconfiguration schemes are identified, and the most promising one is formally specified with the use of the Vienna Development Method. The safety properties of the scheme are shown based on the specification. In order to study the feasibility of autonomous dynamic reconfiguration, the scheme is implemented into two distinct systems, and the results of the practical observation of the system behaviour are presented and discussed. As the project was sponsored by the UK Civil Aviation Authority, a number of certification issues related to reconfigurable avionics systems are identified and discussed based on the practical implementation and previous theoretical analysis. It is concluded that dynamic in-flight reconfiguration of avionics systems can lead to substantial savings in terms of the reduced number of required core LRMs, and greater fault-tolerance than traditional non-reconfigurable systems

A paper submitted to The University of Arizona College of Medicine - Phoenix, History of Medicine course.