Modeling, analysis, and control of a hypersonic vehicle with significant aero-thermo-elastic-propulsion interactions, and propulsive uncertainty

This thesis examines the modeling, analysis, and control system design issues for scramjet powered hypersonic vehicles. A nonlinear three degrees of freedom longitudinal model which includes aero-propulsion-elasticity effects was used for all analysis. This model is based upon classical compressible flow and Euler-Bernouli structural concepts. Higher fidelity computational fluid dynamics and finite elementmethods are needed formore precise intermediate and final evaluations. The methods presented within this thesis were shown to be useful for guiding initial control relevant design. The model was used to examine the vehicles static and dynamic characteristics over the vehicles trimmable region. The vehicle has significant longitudinal coupling between the fuel equivalency ratio (FER) and the flight path angle (FPA). For control system design, a two-input two-output plant (FER - elevator to speed-FPA) with 11 states (including 3 flexible modes) was used. Velocity, FPA, and pitch were assumed to be available for feedback. Propulsion system design issues were given special consideration. The impact of engine characteristics (design) and plume model on control system design were addressed.Various engine designs were considered for comparison purpose. With accurate plume modeling, effective coupling from the FER to the FPA was increased, which made the peak frequency-dependent (singular value) conditioning of the two-input two-output plant (FER-elevator to speed-FPA) worse. This forced the control designer to trade off desirable (performance/robustness) properties between the plant input and output. For the vehicle under consideration (with a very aggressive engine and significant coupling), it has been observed that a large FPA settling time is needed in order to obtain reasonable (performance/ robustness) properties at the plant input. Ideas for alleviating this fundamental tradeoff were presented. Plume modeling was also found to be particularly significant. Controllers based on plants with insufficient plume fidelity did not work well with the higher fidelity plants. Given the above, the thesismakes significant contributions to control relevant hypersonic vehicle modeling, analysis, and design.