<p> Within the field of Guidance, Navigation, and Control, the navigation process refers to accurately determining one's position in space. The quest of accurate navigation has shaped human history. Early navigation techniques involved dead reckoning with infrequent measurement updates from line-of-sights to stars or landmarks on the shore. The first practical inertial navigation system (INS) attributed to the German V-2 missile in 1942. In the early 1960's the Kalman filter was developed to aid in the merging of mathematical models and measurement updating. Throughout the space age and continuing into today's remote systems the hardware has made vast improvements; however, the navigation filtering theory has remained mostly stagnant with the multiplicative Extended Kalman Filter (MEKF) still being the workhorse of most modern INS applications. </p><p> In most INS applications, the state vector usually consists of the attitude, position, velocity, and Inertial Measurement Unit (IMU) calibration parameters such as biases and scale factors. Because position-type measurements are usually only given, such as pseudoranges to GPS satellites, the observability of the attitude and gyroscope calibration parameters is weak. Since the early days of employing the MEKF for INS applications, and even modern-day applications, the state errors are defined as a simple algebraic difference between the truth and the estimate. </p><p> It has been argued that a new state-error definition is required in which state-error quantities are defined using elements expressed in a common frame. This provides a realistic framework to describe the actual errors. In previous work, the errors were put into a common frame using the estimated attitude error, which led to the ``geometric EKF'' (GEKF). The GEKF provides extra transport terms, due to error-attitude coupling with the states, in the filter. This previous work focused strictly on attitude estimation, which incorporated only ``body-frame" errors. In this work the GEKF is extended to the INS formulation. Here, errors are considered for both the body frame and the filter's navigation frame. </p><p> In this work, it is shown how these body-frame and navigation-frame errors are related through a similarity transformation. The body-frame error, and the navigation-frame error through this similarity transformation, are first examined in a Planar Inertial Navigation (PIN) problem. For the PIN problem, the MEKF and GEKF algorithms are derived using the same kinematic and measurement models. These algorithms are then studied for a single simulation test case; these results were then verified via Monte Carlo analysis. For this example, it was shown that the body-frame errors had a faster convergence for the GEKF; however, the navigation-frame states showed slower convergence. It is argued here that the direct comparison of these results is inconclusive since both filters employ different error definitions; therefore, the errors being examined utilize a different error metric. It can be stated that the errors realized by the GEKF are more representative of the real errors experienced by the system. </p><p> The body-frame and navigation-frame errors are also used to derive the GEKF for three navigation filters. Specifically, this work examines the absolute Earth-Centered-Earth-Fixed (ECEF) navigation, relative ECEF navigation, and North-East-Down (NED) navigation filters. The counterpart MEKF filters are also derived in this work to illustrate the differences seen in the state matrices due to the additional coupling terms. These filters are also studied via simulation studies. However, now the body-framed vectors do not show faster convergence for the GEKF. This is because the measurement update for this specific example is unaffected by the new error definition. The measurements are not affected by the new error definition because these filters only utilize pseudo-GPS position measurements, and it is shown that the position error still utilizes the old error definition due to its kinematic relation to the velocity error. </p><p> Finally, this work conducts a linearize analysis of a simplified INS where the GEKF in the NED frame is considered. It is shown via a stationary analysis that the fundamental frequencies of the GEKF are the same as those of the MEKF. This is because during the stationary analysis all of the additional coupling terms seen in the state error matrix are neglected due to assumptions made about the vehicle's motion.</p><p>

<p> This thesis studies the feasibility of using neural networks to ''learn" the vortex panel method. This study is motivated by the desire for the rapid and accurate prediction of fluid flows during the preliminary design of engineering systems, where traditional computational fluid dynamics (CFD) are too computationally costly. The results show that a two-layer neural network can estimate the pressure coefficient and elements in the vortex-panel influence-coefficient matrix. However, when the neural-network-predicted influence-coefficient matrix is used to estimate the pressure coefficients, the results are in poor agreement with the baseline prediction, although general trends are captured. </p><p>

<p> The variable pitch quadrotor is not a new concept but has been largely ignored in small unmanned aircraft, unlike the fixed pitch quadcopter which is controlled only by changing the RPM of the motors and only has about 30 minutes of total flight time. The variable pitch quadrotor can be controlled either by the change of the motor RPM or rotor blade pitch angle or by the combination of both. This gives the variable pitch quadrotor potential advantages in payload, maneuverability and long endurance flight. This research is focused on the design methodology for a variable pitch quadrotor using a single motor with potential applications for a long endurance flight. This variable pitch quadcopter uses a single power plant to power all four rotors through a power transmission system. All four rotors have the same rpm but vary the blade pitch angle to control its attitude in the air. A proof of concept variable pitch quadcopter is developed for testing the drivetrain mechanism on the vehicle and evaluating performance of the vehicle through numbers of testing. </p><p>

<p> In today&rsquo;s space industry, satellite formation flying has become a cost-efficient alternative solution for science, on-orbit repair and military time-critical missions. While in orbit, the satellites are exposed to the space environment and unpredictable spacecraft on-board disturbances that negatively affect the attitude control system&rsquo;s ability to reduce relative position and velocity error. Satellites utilizing a PID or adaptive controller are typically tune to reduce the error induced by space environment disturbances. However, in the case of an unforeseen spacecraft disturbance, such as a fault in an IMU, the PID based attitude control system effectiveness will deteriorate and will not be able to reduce the error to an acceptable magnitude. </p><p> In order to address the shortcomings a PID-Extended Memory RNN (EMRNN) adaptive controller is proposed. A PID-EMRNN with a short memory of multiple time steps is capable of producing a control input that improves the translational position and velocity error transient response compared to a PID. The results demonstrate the PID-EMRNN controller ability to generate a faster settling and rise time for control signal curves. The PID-EMRNN also produced similar results for an altitude range of 400 km to 1000 km and inclination range of 40 to 65 degrees angles of inclination. The proposed PID-EMRNN adaptive controller has demonstrated the capability of yielding a faster position error and control signal transient response in satellite formation flying scenario. </p><p>

<p> Carbon-Fiber Reinforced Polymers (CFRPs) provides superior mechanical properties and low weight, enabling their extensive use in the aerospace industry. Susceptibility to internal damage due to out-of-plane loads and poor electrical properties are some of their major challenges that require to be addressed in order to increase the utilization of composites in further aerospace structures. Lightning strikes can lead to catastrophic damage, inflicting high repair and certification costs. Lightning Strike Protection (LSP) solutions such as integration of metallic meshes or foils into the composite structures, even though effective, impose extra costs and hinders the aircraft performance due to the increased weight of the aircraft. </p><p> This research aims at the development of a different LSP solution, by enhancing the electrical conductivity of composite, while maintaining a sufficient degree of mechanical properties. The use of non-woven conductive interlayers was proposed for manufacturing of conductive composites. Highly-conductive, low-aerial-weight carbon veil was utilized to manufacture prepreg-based CF/Epoxy laminates, which are generally toughened, in order to improve their conductivity using vacuum bag only (VBO) and heat-pressing techniques. Further, a bi-functional interlayer of graphene coated Polyamide (PA) was developed using interfacial trapping method. This conductive thermoplastic interlayer was then utilized for manufacturing Benzoxazine (BZ) infused carbon fabric laminate with Vacuum-assisted resin transfer molding (VARTM) method, which acted as a conductive toughener and improves the Inter-laminar Fracture Toughness (ILFT) as well as to increase the electrical conductivity. </p><p> The effects of the incorporation of non-woven interlayers on the electrical conductivity, thermal behavior of composites, and mechanical properties such as shear strength, compressive strength, and the ILFT (Mode-I and Mode-II) were investigated in this study. In both types of composites, an increase in electrical properties, as well as mechanical properties, were observed. The only exception was in the Mode-I ILFT of the CF/Epoxy prepregs, which decreased with the increase of the areal weight of the interleaved carbon veils. The mechanical properties increased in the range of 9%&ndash;138% with the only decrement observed in Mode-I ILFT of CF/Epoxy with carbon veils of 25%. The volume resistivity of the CF/Epoxy samples decreased significantly by approximately 50% due to the incorporation of the conductive interlayer. This added feature was used to develop a structural health monitoring (SHM) procedure. The conductive composite showed an increased sensitivity in detecting the pre-identified damage location in the composites.</p><p>

A linear model of the shock cell structure of a slightly imperfectly expanded supersonic jet is constructed by the method of multiple scales. The model takes into account the gradual spatial change of the mean flow, and includes the effect of turbulence in the mixing layer. Computational procedures are established which yield numerical results from the model. Extensive comparisons are made with data obtained from NASA Langley Research Center. The graphs of the calculations are shown to agree quite favorably with experimental measurements in overall spacing and amplitude of the shocks. In addition, the model reproduces many of the fine scale features that exist within the region close to the nozzle exit. The study indicates that, beyond this region, the shocks are adequately described by a fundamental mode alone. The appropriate turbulent Reynolds number for shock cell calculations is investigated, and shown to be related to scales pertaining to the mean flow. An expression is developed to represent the acoustic radiation from a proposed source form of shock associated noise. The numerical evaluation of this expression is then used to produce a sound pressure level contour map which demonstrates the source location and directivity patterns of shock associated noise. / Source: Dissertation Abstracts International, Volume: 46-08, Section: B, page: 2687. / Thesis (Ph.D.)--The Florida State University, 1985.

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Prevailing Torque Locking Feature Wear-out

Acoustoelasticity is the study of the dynamic interaction between elastic structures and acoustic enclosures. In this dissertation, acoustoelasticity is considered in the context of liquid rocket engine design. The techniques presented here can be used to determine which forcing frequencies are important in acoustoelastic systems. With a knowledge of these frequencies, an analyst can either find ways to attenuate the excitation at these frequencies or alter the system in such a way that the prescribed excitations do result in a resonant condition. The end result is a structural component that is less susceptible to failure. The research scope is divided into three parts. In the first part, the dynamics of cylindrical shells submerged in liquid hydrogen (LH₂) and liquid oxygen (LOX) are considered. The shells are bounded by rigid outer cylinders. This configuration gives rise to two fluid-filled cavities: an inner cylindrical cavity and an outer annular cavity. Such geometries are common in rocket engine design. The natural frequencies and modes of the fluid-structure system are computed by combining the rigid wall acoustic cavity modes and the <em>in vacuo</em> structural modes into a system of coupled ordinary differential equations. Eigenvalue veering is observed near the intersections of the curves representing natural frequencies of the rigid wall acoustic and the <em>in vacuo</em> structural modes. In the case of a shell submerged in LH₂, system frequencies near these intersections are as much as 30% lower than the corresponding <em>in vacuo</em> structural frequencies. Due to its high density, the frequency reductions in the presence of LOX are even more dramatic. The forced responses of a shell submerged in LH₂ and LOX while subject to a harmonic point excitation are also presented. The responses in the presence of fluid are found to be quite distinct from those of the structure <em>in vacuo</em>. In the second part, coupled mode theory is used to explore the fundamental features of acoustoelastic systems. The result is the development of relatively simple techniques that allow analysts to make informed decisions concerning the importance of acoustic-structure coupling without resorting to more time consuming and complex methods. In this part, a new nondimensional parameter is derived to quantify the fundamental strength of a particular acoustic-structure interaction irrespective of material and fluid properties or cavity size. It is be shown that, in some cases, reasonable approximations of the coupled acoustic-structure frequencies can be calculated without explicit knowledge of the uncoupled component mode shapes. Monte Carlo simulations are performed to determine the parameter values over which the approximate coupled frequency expressions are accurate. General observations concerning the forced response of acoustoelastic systems are then made by investigating the response of a simplified two mode system. The third part of this research discusses the implementation of a component mode synthesis (CMS) technique for use with geometrically complex acoustoelastic systems. The feasibility of conceptually similar techniques was first demonstrated over 30 years ago. Since that time there have been remarkable advancements in computational methods. It is therefore reasonable to question the extent to which CMS remains a computationally advantageous approach for acoustoelastic systems of practical interest. This work demonstrates that relative to the most recent release of the popular finite element software package, ANSYS, CMS techniques have a significant computational advantage when the forced response of an acoustoelastic system is of interest. However, recent improvements to the unsymmetric eigensolver available in ANSYS have rendered CMS a less efficient option when calculating system frequencies and modes. The CMS technique is then used to generate new results related to geometrically complex acoustoelastic systems. / Dissertation