Uncertainty Propagation in Integrated Airframe Propulsion System Analysis for Hypersonic Vehicles
Air{breathing hypersonic vehicles are based on airframe{integrated SCRAMjet engine. The elongated forebody which serves as the inlet of the engine is subject to harsh aerothermodynamic loading which causes it to deform. Unpredicted deformations may produce unstart, combustor chocking or structural failure due to increased loads. This study presents a framework allowing one to assess the impact of aerothermoelastic deformations on the engine performance prediction. Aerothermoelastic deformations are calculated for trajectories and angle of attack and transferred to a SCRAMjet engine analysis. Uncertainty associated with deformation prediction is propagated to the engine performance analysis. The importance of modeling the aerodynamic heating and aerothermoelastic deformations at the cowl of the inlet is noted. The cowl deformation is the main contributor to uncertainty and sensitivity of the propulsion system analysis.
Materials and structures for hypersonic vehicles
Hypersonic vehicles are envisioned to require, in addition to carbon-carbon and ceramic-matrix composities for leading edges heated to above 2000 F, such 600 to 1800 F operating temperature materials as advanced Ti alloys, nickel aluminides, and metal-matrix composited; These possess the necessary low density and high strength and stiffness. The primary design drivers are maximum vehicle heating rate, total heat load, flight envelope, propulsion system type, mission life requirements and liquid hydrogen containment systems. Attention is presently given to aspects of these materials and structures requiring more intensive development.
A switching controller for multivariable LTI systems with known and unknown parameters
The design of adaptive controllers for multi-input multi-output (MIMO) linear time invariant (LTI) systems is challenging due to the high dimension and parameterization issues associated with MIMO systems. In this paper we design and analyze a nonlinear control scheme for a general MIMO system to overcome some of the traditional parameterization issues. The design is based on switching and the theory of control Lyapunov functions. The new scheme guarantees stability and convergence of the output to a residual set by output-feedback if the plant parameters are known and by state-feedback if the plant. parameters are unknown. The size of the residual set depends on some of the design parameters and can be made arbitrarily small.