A layered heat flux gauge, which can withstand a high temperature environment for applications such as for use on thermal protection shields on aeroentry vehicles, is analyzed, designed, fabricated, and tested. The heat flux gauge consists of two resistance temperature detectors on the top and bottom faces of a thin ceramic substrate. The heat flux is calculated from temperature measurements of the two temperature detectors. An analytical model is used to simulate the gauge response. Several numerical methods to calculate the heat flux are investigated to improve the time response of the gauge. The error due to gauge intrusiveness and the validity of one-dimensional heat transfer within the gauge is studied by solving a steady state two-dimensional composite problem using a semi-analytical approach. Gauge fabrication techniques and measurement devices are discussed. Testing apparatus, including a "close-to-entry" condition apparatus using an arcjet at low pressure and a conduction calibration furnace, are explained. Experimental data showing qualitative gauge response is presented.

An experimental investigation into the characteristics of the unsteady laminar shear layer developed over a wall-mounted cavity was conducted, and the effects of the addition of a flush-mounted rotating cylinder to the leading edge or trailing edge of the cavity were quantified through extensive velocity and frequency measurements. It is shown that the injection of circulation resulting from the rotation of the leading edge cylinder caused the shear layer deflect into the cavity and re-attach to the cavity floor at greater cavity depths; also, the additional momentum caused a delay of the formation of shear-layer vortices, interrupting the cavity vortex formation-impingement feedback phenomenon. Higher leading-edge cylinder rotation speeds induced rapid laminar-to-turbulent transition, precluding any of the periodicity associated with laminar shear-layer flow. Furthermore, though the trailing-edge is the source of the feedback information for the self-sustained vortex formation, rotation of a cylinder at the trailing edge had little effect on the flow fields. Experiments were carried out with a ratio of separating boundary layer momentum thickness to impingement length of 6.07 x 10-3 .

An experimental study of the process of shock initiation of detonation in liquid nitromethane sensitized with diethylenetriamine (DETA) was conducted. In particular, the effect of the lateral boundary conditions on the sensitivity of the explosive to shock stimuli was investigated. The explosive was tested in a "gap test" arrangement. Various charge diameters and different materials for the capsule that contained the test explosive were used. The arrival time of the shock front was recorded at different locations along the test charge and the light emitted in the cases where detonation was initiated in the test explosive was monitored. / It is found that the minimum shock strength necessary to initiate detonation in the explosive test mixture is greater if the test charge diameter is small. It is also found that for a given shock strength, the minimum charge radius that permits initiation corresponds to the distance necessary to establish detonation. / In charges with small diameters, interactions between the input shock and the charge capsule walls permit initiation for input shock strengths that would normally not be sufficient to cause initiation. The nature of these interactions is complex and the outcome of a shock initiation experiment cannot be predicted from mere knowledge of the impedance of the capsule material or the shock speed within it.

In this thesis, an analytical investigation of the dynamics of three-body tethered satellite systems is presented. The analysis is performed for two cases: two-dimensional and three-dimensional motion. At first, the equations governing the motion of such systems are obtained assuming that the system center of mass moves in a circular orbit around the Earth. Then, the various equilibrium configurations are obtained. The equilibrium configurations are classified in eleven groups. Three of these groups are collinear configurations, and the others are triangular configurations. A stability analysis is performed for each equilibrium configuration. It is found that two of the collinear configurations are marginally stable. These are configurations with the three masses on the local vertical. The other collinear configurations are unstable. The triangular configurations are unstable except for some systems with a small middle mass. The results for two-dimensional motion are consistent with those for three-dimensional motion.

This work investigates fluid mechanical processes involving movement of shock waves inside channels. In particular, the prediction and control of shock motion in intakes is of great importance to high-speed flight and future spacecraft engines--it is a fundamental problem whose solution currently enjoys a high degree of interest. In the first part of the thesis, an analytical, numerical, and experimental study is performed in two-dimensions to assess the quasi-steady flow starting characteristics in an external-compression ramp-type intake. Using the popular model based on common understanding in the field and consistent with well-cited literature, it is shown that the traditional model based on one-dimensional flow across a planar shock is inaccurate. To remedy this, a novel analytical model is presented to predict off-design self-starting behaviour using a curved shock wave. The analytical results are supported by the numerical evidence from CFD simulations as well as by the experimental evidence; taken together, these results constitute overwhelming evidence supporting the arguments presented. In the second part of the thesis, an analytical and numerical study is performed in the unsteady, quasi-one-dimensional setting to assess the feasibility of predicting shock dynamics inside an intake using a simple, approximate, yet representative model. There is very little widely-available knowledge on impulsive flow starting in the literature, and there is no existing theory for analytically predicting impulsive flow starting phenomena discussed here. The well-known Chester-Chisnell-Whitham formulation is extended using a novel model (labelled lifting isentrope); it is effectively a provision for non-uniform, unsteady flow upstream of the shock wave. It is found that a singularity exists in the CCW model, which prevents its application to problems in impulsive flow starting. There is little or no literature on this singularity. To resolve these issues, a novel for / Ce travail examine des processus de la mécanique des fluides impliquant le mouvement des ondes de choc a travers des chaînes. En particulier, la prédiction et le contrôle de mouvement du choc dans les entrées d'air ont une grande importance pour le vol ultra-rapide et pour les moteurs des vaisseau spatiaux futurs--c'est un problème fondamental dont la solution attire présentement un haut degré d'intérêt. Même si les processus de démarrage et non-démarrage d’entrées d’air sont considérés bien compris au niveau conceptuel, d'importants détails restent à régler.Dans la première partie de la thèse une étude analytique, numérique et expérimentale est réalisée. L'étude est bidimensionnelle dans le but d’évaluer les caractéristiques de l'écoulement quasi-stationnaire dans une entrée d’air de type rampe avec compression externe. À l'aide d’un modèle bien-connu basé sur la compréhension commune dans le monde scientifique et selon la littérature de spécialité on montre que le model traditionnel basé sur l'écoulement unidimensionnel sur un plan de choc est inexact. Pour corriger cette situation un nouveau modèle analytique est présenté pour montrer le démarrage d’entrées d’air en utilisant une onde de choc courbe. Les résultats analytiques sont bases sur des preuves numériques obtenus des simulations CFD ainsi que par éléments expérimentales. Mises ensemble ces résultats constituent des preuves écrasantes à l'appui les arguments présentés.Dans la deuxième partie de la thèse une étude analytique et numérique est réalisée sur le sujet de l'écoulement instable, quasi-unidimensionnel. Le but est d’évaluer la faisabilité de la prédiction de la dynamique des chocs dans une entrées d’air en utilisant un modèle e simple, approximatif mais représentative.Il n’y a pas beaucoup des études et connaissances sur le démarrage impulsive d’entrées d’air disponibles et il n’existe pas une théori

The unsteady flows generated by the harmonically variable inflow velocities are studied in this thesis by using a numerical method for the time-accurate solution of the Navier-Stokes equations. This method, which has been developed by Mateescu and Venditti, uses an implicit three-point-backward scheme for the real time discretization, and a pseudo-time discretization based on a relaxation procedure using artificial compressibility. A special decoupling procedure is used to eliminate the pressure from the momentum equations with the aid of the continuity equation in pseudo-time, in order to reduce the problem to the efficient solution of scalar tridiagonal systems of equations. The method uses a finite difference formulation on a stretched staggered grid, which was validated for the steady incompressible flows in a duct with a downstream-facing step, by comparison with previous computational and experimental results. / This thesis first presents the solutions obtained for the unsteady flows with multiple separation regions in a duct with fixed geometry, which are generated by the variation in time of the inflow velocities. Then, the solutions for the unsteady flows generated by both an oscillating wall and the variation in time of the inflow velocity are also presented. The influence of the Reynolds number, of the inflow velocity amplitudes, and of the phase difference is also thoroughly studied.

Computations of transonic viscous flows are very challenging. The major difficulty comes from the discontinuity in the solution across a shock wave, causing undesired oscillations in the solution. In this work we focus on minimizing the oscillations by the use of a limiter to control the amount of diffusivity. This limiter provides the right amount of viscosity to capture a sharp shock and an accurate solution in high gradient regions. The limiter employs changes in pressure and entropy and has been implemented into the Streamline Upwind Finite Element Method. A mesh adaptation strategy has been employed to further enhance the accuracy of the solution. Results of simulations over RAE 2822 airfoil and ONERA M6 wing indicate significant improvements to the solution with this implementation.

This thesis examines a new method of detecting the presence of structural cracks in wing-like structures at an incipient stage. This method is based on the analysis of the dynamics of damaged structures with bonded piezoelectric strips executing flexural oscillations. Such oscillations can be generated by mechanical loads, piezoelectric actuators, or unsteady aerodynamic loads in certain flight conditions of the aircraft. The proposed method of crack detection uses pairs of piezoelectric strip sensors bonded on the opposite sides of the structure and is based on the fact that the presence of a crack causes a difference between the strains measured by the two sensors of a given pair. The structural analysis presented in this thesis uses a nonlinear model for the cracks and a finite element formulation for the piezoelectric strips coupled with the structure. A 3D panel method is used to determine the unsteady aerodynamic loads acting on the oscillating wing. This study includes the dynamic analysis in time domain of cracked wing-like structures undergoing forced flexural vibrations in a range of frequencies generated by a pair of piezoelectric actuators, as well as the analysis of the oscillating wings with piezoelectric strips subjected to unsteady aerodynamic loads. The numerical simulations have shown that the presence of a crack in wing-like structures can be efficiently detected at an early stage by monitoring the response of the piezoelectric sensor pairs. / Cette thèse étudie une nouvelle méthode de détection de la présence de fissures structurelles à un stade précoce dans une structure de type aile. Cette méthode est basée sur l'analyse des oscillations en flexion des structures endommagées munies de bandes piézoélectriques collées. Ces oscillations peuvent être générées par des charges mécaniques, des actionneurs piézoélectriques, ou des charges aérodynamiques instationnaires dans certaines conditions de vol de l'avion. La méthode de détection des fissures proposée utilise des paires de capteurs piézoélectriques collés sur les côtés opposés de la structure et est basée sur le fait que la présence d'une fissure entraîne une différence entre les déformations mesurées par les deux capteurs d'une paire donnée. L'analyse structurale présentée dans cette thèse utilise un modèle non linéaire pour les fissures et une formulation par éléments finis pour les bandes piézoélectriques couplées avec la structure. Une méthode de panneau tridimensionnelle est utilisée pour déterminer les charges aérodynamiques instationnaires agissant sur l'aile oscillante. Cette étude comprend l'analyse dynamique dans le domaine temporel de structure de type aile fissurée subissant des vibrations en flexion forcées dans une gamme de fréquences générées par une paire d'actionneurs piézoélectriques, ainsi que l'analyse des ailes oscillantes équipées de bandes piézoélectriques soumises à des charges aérodynamiques instationnaires. Les simulations numériques ont montré que la présence d'une fissure dans ces structures peut être efficacement détectée à un stade précoce en surveillant la réponse des capteurs piézoélectriques.

This thesis deals with mathematical programming problems of flight mechanics of a jet aircraft. The aircraft is assumed to be in quasi-steady flight. Different flight phases are considered here; they cover rectilinear level flight, climbing flight, gliding flight, and curvilinear level flight. In this thesis, the problems studied include feasibility and optimization. These problems are solved via the modified quasilinearization algorithm for mathematical programming problems. Results for the different flight phases are presented here. They illustrate the performances of a jet aircraft in rectilinear level flight, climbing flight, gliding flight, and curvilinear level flight.

<p> One of the main research focus areas of the WVU Flight Control Systems Laboratory (FCSL) is the increase of flight safety through the implementation of fault tolerant control laws. For some fault tolerant flight control approaches with adaptive control laws, the availability of accurate post failure aircraft models improves performance. While look-up tables of aircraft models can be created for failure conditions, they may fail to account for all possible failure scenarios. Thus, a real-time parameter identification program eliminates the need to have predefined models for all potential failure scenarios. The goal of this research was to identify the dimensional stability and control derivatives of the WVU Phastball UAV in flight using a frequency domain based real-time parameter identification (PID) approach.</p><p> The data necessary for this project was gathered using the WVU Phastball UAV, a radio-controlled aircraft designed and built by the FCSL for fault tolerant control research. Maneuvers designed to excite the natural dynamics of the aircraft were implemented by the pilot or onboard computer during the steady state portions of flights. The data from these maneuvers was used for this project.</p><p> The project was divided into three main parts: 1) off-line time domain PID, 2) off-line frequency domain PID, and 3) an onboard frequency domain PID. The off-line parameter estimation programs, in both frequency domain and time domain, utilized the well known Maximum Likelihood Estimator with Newton-Raphson minimization with starting values estimated from a Least-Squares Estimate of the non-dimensional stability and control derivatives. For the frequency domain approach, both the states and inputs were first converted to the frequency domain using a Fourier integral over the frequency range in which the rigid body aircraft dynamics are found. The final phase of the project was a real-time parameter estimation program to estimate the dimensional stability and control derivatives onboard the Phastball aircraft. A frequency domain formulation of the least-squares estimation process was used because of its low computational and memory requirements and robustness to measurement noise and sensor information dropouts. Most of the onboard parameter estimates obtained converge to the values determined using the off-line parameter estimation programs (though a few typically show a bias) within four to six seconds for longitudinal estimates and four to eight seconds for the later estimates. For the experiments conducted, the real-time parameter estimates did not diverge after the conclusion of the maneuver.</p>