The carbon fork developed for this thesis is a lightweight fork intended for the road racing athletes and amateurs. The work performed for this thesis includes geometrical and structural design of the fork but also concentrates on developing and optimizing a manufacturing process to create a complete solution for composite fabrication using vacuum assisted resin transfer moulding (VARTM). In the past many research projects concentrated on structural design and finite element analysis but failed to show satisfactory practical results due to poor manufacturing method for prototypes. This thesis emphasizes the development of the fabrication process. The stages for this thesis consist of analyzing previous work done on a carbon fibre fork and, from there, creating and developing a new fork whose weight will be reduced and performance increased. Using this new design, a new custom manufacturing process is implemented for VARTM. The final stage consists of producing prototypes and evaluating their performance and resistance under static and fatigue loadings.

An analytical and experimental investigation was conducted to study the design of three different types of aerobars for a composite bicycle. / A Finite Element Analysis software was used for the analysis of the aerobars. Maximum tensile and compression stresses were found in the aerobars that were subjected to three kinds of static load. / A laboratory fabrication method for the aerobar bar-ends was developed, and some sample aerobar bar-ends were made for experimental verification of the analytical results. / The Bicycle Components Test Device was used to perform static tests on the sample aerobar bar-ends under two static load conditions. / Combining the analytical and experimental results, a better understanding of the design and critical problems in the aerobars was obtained.

Renewed interest in pulse detonation engines has focused attention on the problem of deflagration to detonation transition (DDT) in fuel-air mixtures. A prohibitively large deposition of energy is required for direct initiation of higher-hydrocarbon fuels in air. Consequently, methods are being sought to reduce the run-up distance required for DDT. It has been proposed that the addition of a very sensitive fuel, or of nitrate-based sensitizers typically used in diesel fuels, could increase the sensitivity of hydrocarbon fuel-air mixtures by increasing the chemical kinetic rates. Studies have indicated that the effect of nitrates on diesel fuels occurs through the action of nitrogen dioxide (NO2) abstracted from the nitrate molecule. / Experiments were therefore carried out in order to evaluate the effect of acetylene (C2H2) and NO2 addition to propane (C3H8)---oxygen (O2)---nitrogen (N 2) mixtures at ambient conditions. The run-up distance for mixtures of C3H8/C2H2-O2-N 2 was first investigated for varying proportions of C3H 8 and C2H2 in the fuel. Then, the run-up distance and detonation cell size were established for C3H8-O 2-N2 mixtures without NO2 and with NO2 added as a 10% to 50% fuel additive. The results show that the effect of C 2H2 is a very gradual reduction in run-up distance with increasing C2H2 concentration, making it an ineffective additive. The addition of NO2 causes no change in either the run-up distance or the cell width, indicating that the kinetic changes brought about by the NO2 are not significant to the initiation of detonation. This result is shown to agree with kinetic models that suggest that NO2 is not very effective at promoting ignition at very high temperatures such as that characteristic of detonations.

<p> Current robots lack the precise relative positioning necessary to complete automatic assembly tasks. Several solutions have been proposed. Some approaches use complex vision and force sensing systems to generate corrective motion if misalignment is present in the assembly task. Other solutions rely on generating elastic behavior, known as compliance, between the end eector and the held movable part. This compliant mechanism helps guide the movable part of the assembly into its proper position. The project focuses on designing a process by which passive compliant systems can achieve successful assembly for a range of misalignment and generate errorreducing motion that is considered of high quality. This is accomplished by using a velocity metric as the goal of a constrained optimization. The metric uses the average discrepancy of all the particle motion from an established "best motion". This motion minimizes the discrepancy in the velocity of all particles motion from their ideal motion towards their proper position. This procedure identies the best worst case scenario for a representative set of congurations. The results obtained for optimization over polygonal geometries of 3, 4, and 5 vertices, demonstrate the eectiveness of the procedure in designing passive compliant behavior resulting in high quality error-reducing motion. Results also show that high quality motion is not only achieved for a set of nite congurations but also for all intermediate ones.</p>

<p> Applications for energy absorption materials range from athletic equipment, to vehicle crumple zones, to blast protection for military vehicles and personnel. Many energy absorption structures employ stochastic foams because of their plateau-like stress-strain response that allows for the absorption of large amounts of energy at relatively low stresses over large compressive strains. Periodic lattice structures, when properly designed, provide the same capabilities as stochastic systems, but with a more tailorable response that provides potential for improved specific strength and energy absorption. The present dissertation provides an in-depth study of the pyramidal lattice: one particular periodic structure that strikes a good compromise between performance and manufacturability. Through finite element and analytical modeling, this study identifies key parameters of the geometry, boundary conditions, and parent material properties that determine the compressive stress-strain response of the structure. In conjunction with experimental investigations, these models are used to understand and determine the potential for improving the response of the as-manufactured polymeric pyramidal lattice structures through additional heat treatment and filling the lattice void-space with stochastic foam. Finally, additional models are developed to understand and predict the structural rate effects that arise from inertial stabilization of strut buckling during dynamic loading. Particular emphasis is given to the effects of yield strain and density of the parent material on failure modes and dynamic response. In addition to providing a strong basis for the design of pyramidal lattice materials, this work provides useful insight into the design of energy absorption materials in general. </p>

<p> Many Small Unmanned Aerial Vehicles (SUAV) are driven by small scale, fixed blade propellers. The flow produced by the propeller, known as the propeller slipstream, can have significant impact on SUAV aerodynamics. In the design and analysis process for SUAVs, numerous Computational Fluid Dynamic (CFD) simulations of the coupled aircraft and propeller are often conducted which require a time-averaged, steady-state approximation of the propeller for computational efficiency. Most steady-state propeller models apply an actuator disk of momentum sources to model the thrust and swirl imparted to the flow field by a propeller. These momentum source models are based on simplified theories which lack accuracy. Currently, the most common momentum source models are based on blade element theory. Blade element theory discretizes the propeller blade into airfoil sections and assumes them to behave as two-dimensional (2D) airfoils. Blade element theory neglects many 3D flow effects that can greatly affect propeller performance limiting its accuracy and range of application. </p><p> The research work in this dissertation uses a surrogate modeling method to develop a more accurate momentum source propeller model. Surrogate models for the time averaged thrust and swirl produced by each blade element are trained from a database of time-accurate, high-fidelity 3D CFD propeller simulations. Since the surrogate models are trained from these high-fidelity CFD simulations, various 3D effects on propellers are inherently accounted for such as tip loss, hub loss, post stall effect, and element interaction. These efficient polynomial response surface surrogate models are functions of local flow properties at the blade elements and are embedded into 3D CFD simulations as locally adaptive momentum source terms. Results of the radial distribution of thrust and swirl for the steady-state surrogate propeller model are compared to that of time-dependent, high-fidelity 3D CFD propeller simulations for various aircraft-propeller coupled situations. This surrogate propeller model which is dependent on local flow field properties simulates the time-averaged flow field produced by the propeller at a momentum source term level of detail. Due to the nature of the training cases, it also captures the accuracy of time dependent 3D CFD propeller simulations but at a much lower cost.</p>

<p> In the past decade, the level of autonomy of unmanned vehicles has been rising rapidly from remote-controlled towards fully autonomous. Without human operators on board, teams of autonomous vehicles are the best candidates for high risk applications such as search and rescue after disasters and information gathering in hostile environments. For a team of autonomous vehicles to operate effectively in these scenarios, it must be able to respond promptly to environmental hazards and/or hostile entities. In this dissertation, a collaborative team evasion framework is proposed to maximize the survival time of a team of autonomous vehicles against a faster and more agile hostile agent. The proposed framework is based on an open-loop formulation of the single-pursuer-multiple-evader pursuit-evasion game that is conservative to the evaders and provides guarantees on team survival time in the worst-case scenario. An iterative open-loop approach that repeatedly solves the open-loop problem corresponding to the most current state of the game is developed to relax the conservatism of the open-loop formulation and enhance the survival time performance. Extensions to the framework make it possible to take into account the turning rate constraints of the evaders and uncertainties in the position of the pursuer. Numerical approximations are also proposed to reduced the required computation time. Through extensive simulations, the proposed framework is shown to produce reliable strategies for the evaders that result in significantly longer team survival time than previous work in the literature.</p>

<p> Discovering the key-features of how aquatic swimmers such as stingrays propel themselves in nature can inspire the next generation of underwater vehicles with improved maneuverability and decreased noise signatures. To discover the key-features of stingrays swimming, fluid-structure interaction simulations of a self-propelled virtual stingray, modeled closely after the freshwater stingray, <i>Potamotrygon orbignyi,</i> are performed. The first closed-form kinematics description of the stingray's body motion was developed from three-dimensional experimental measurements of undulatory body motion of the fresh water stingray, <i>Potamotrygon orbignyi,</i> which is prescribed in our simulations. The self-propelled simulations produce a high-resolution view of the three-dimensional flow field and quantifiable forces created from the stingray's swimming unobtainable by other experimental means. A leading edge vortex (LEV) was discovered to be present on the pectoral disc of the stingray, which drastically affects the hydrodynamic forces and the pressure distribution on its disc. The LEV was found to stays attached to the stingray's body until its swimming cycle reverses direction at which time the vortex detaches to travels along with the stingray's swimming undulations, creating pressure differentials across the surfaces of the stingray which promotes thrust. At the time instance of highest thrust generation during its swimming cycle, three separate vortices present on the stingrays body, all of which were formed on the leading edge, are creating a pressure distribution promoting thrust. This finding can inspire new propulsive fins that generate LEV instead of mitigating separation.</p>

<p> A Hybrid Projectile (HP) is a munition that transforms into an unmanned aerial vehicle (UAV) after being launched from a tube. In many situations it is desirable for this type of projectile to change its point of impact and depart from its current ballistic trajectory similar to a UAV following a path. A method was created to utilize deflectable control surfaces in conjunction with a guidance system to ensure the HP was statically and dynamically stable and to maneuver the HP to a desired point of impact. Methods were devised to control heading and pitch using vertical and horizontal tail surfaces. Testing and tuning these control methods were done using the Six Degree of Freedom (6DoF) system in Simulink. A cruciform tail section was utilized so that the HP could be statically and dynamically stable. The simulation showed that the method devised was able to guide a 40 mm HP up to 6250 projectile diameters off of the line of fire and increase range by 25.8% while landing within 125 projectile diameters of the desired impact point.</p>

<p> High performance motion trajectory tracking can be achieved on a piezoelectric stack actuator stage by the combination of a new hysteresis model, judicious modeling of the dominant dynamics, and adaptive robust control design. </p><p> A new hysteresis model for piezoelectric actuators is proposed. Inspired by the similarity between pre-sliding friction and piezoelectric hysteresis, the Dahl friction model is extended with non-local memory to model piezoelectric hysteresis. Asymmetry in hysteresis loops is accommodated with a shaping function, which eliminates the need for having different parameters for different branches of the hysteresis loops. All parameters of the hysteresis model can be identified from the outer-loop alone, and the identified model reduces hysteresis nonlinearity from 14 percent of the actuator range to less than 1 percent. </p><p> A low-order dynamic model is developed by recognizing the domain switching dynamics of the actuator as the dominant dynamics when the resonant frequency of the stage is far beyond the application bandwidth. The piezoelectric dynamics is well approximated by a feed-through gain and a first-order nonlinear dynamics driven by the input with hysteretic disturbances. </p><p> Based on the parameterized model, an adaptive robust controller is designed to achieve (a) guaranteed transient error under the assumption of bounded uncertainties and disturbances; and (b) asymptotic tracking in the presence of parametric uncertainties only. Good tracking performance is achieved for large amplitude trajectories up to 100 Hz even when the hysteresis is entirely attenuated as an unknown disturbance. With additional model compensation from the hysteresis model, the final tracking errors are more than two orders of magnitude smaller than previously reported in literature on an identical actuator. </p><p> For single-loop periodic trajectories, performance can be improved without using an explicit hysteresis model. By approximating the unknown but periodic uncertainty with harmonic basis functions and adapting their amplitudes online, non-parametric uncertainty from unknown hysteresis is significantly reduced. Experimental results demonstrate tracking error down to the sensor noise level for sinusoidal trajectories up to 100 Hz with moderate amplitudes and less than one percent for large amplitudes.</p>