title: Nonlinear Flutter Analysis of Curved Panels Under Yawed Supersonic Flow and at Elevated Temperatures Using Finite Elements
Creators: name: Ghoman, Satyajit Sudhir
Publisher: name: Old Dominion University
publisherIdentifier: https://ror.org/04zjtrb98
publisherIdentifierScheme: ROR
Year: 2008

description: There are large number of papers dedicated toward the investigation of flutter analysis of flat plates in supersonic flow regime, but very few papers address the problem of flutter of curved panels. Furthermore, many of the panel flutter investigations including thermal effects, have dealt with liat plates. Scarce literature exists regarding the flutter of curved panels with thermal effects. Hence, the objective of this thesis is to develop, for the first time in the literature, a consistent finite element formulation and an efficient solution procedure to investigate nonlinear flutter of curved panels at yawed supersonic flow at elevated temperatures.

Panel flutter phenomenon can be described as aeroelastically induced self-excited and self-sustained oscillations of the external skin of a flight vehicle exposed on one side to high-speed airflow. Study of panel flutter, addressed in this thesis, falls in the domain of 'aero-thermo-elasticity', as it results from the interactions among aerodynamic, thermostatic and elastic forces. The Marguerre curved plate theory, the von Karman large deflection theory, the quasi-steady first-order piston theory, and quasi-static thermoelasticity theory are used in the formulation. The principle of virtual work is applied to develop the equations of motion of the fluttering system in the structural degrees of freedom. In the frequency domain, the Newton-Raphson method is used to determine the panel deflection under the Static Thermo-Aerodynamic Loading, and the Eigen-value solution is employed for the prediction of flutter critical dynamic pressure for curved panels of different height-rises and at different flow yaw angles. Flutter coalescence frequencies, and damping rates of the fluttering curved system are thoroughly investigated for three-dimensional (3-D) curved panels under increasing dynamic pressure and uniform or linearly varying temperature gradient loading. Critical buckling temperatures are found out for 3-D flat plates of the same geometry, and used to define non-dimensionalized thermal loading. Effects of uniform and linear thermal gradient loadings across the panel thickness, as well as effects of increasing panel curvature are studied. It was observed that application of thermal loading tends to prepone the flutter.

In time domain, the system equations of motion are transformed into modal coordinates, and solved by a fourth-order Runge-Kutta numerical scheme. Time history responses, phase plots, power spectrum density plots, and bifurcation diagram are used for better understanding of the pre/post flutter responses of cylindrical panels. The results demonstrated that the flutter dynamic behavior, characterized by a motion map, moved directly to chaos skipping the limit cycle oscillations region.

In general, it was observed that pre/post-flutter panel behavior and flutter onset alter significantly when temperature effects come into the picture.