5 research outputs found
Catastrophic Transitions and Unpredictability in Nonchaotic Dynamics of Nonlinear Aeroelastic Systems
No full text
A first-order Green's function approach to supersonic oscillatory flow: A mixed analytic and numeric treatment
No full textA frequency domain Green's Function Method for unsteady supersonic potential flow around complex aircraft configurations is presented. The focus is on the supersonic range wherein the linear potential flow assumption is valid. In this range the effects of the nonlinear terms in the unsteady supersonic compressible velocity potential equation are negligible and therefore these terms will be omitted. The Green's function method is employed in order to convert the potential flow differential equation into an integral one. This integral equation is then discretized, through standard finite element technique, to yield a linear algebraic system of equations relating the unknown potential to its prescribed co-normalwash (boundary condition) on the surface of the aircraft. The arbitrary complex aircraft configuration (e.g., finite-thickness wing, wing-body-tail) is discretized into hyperboloidal (twisted quadrilateral) panels. The potential and co-normalwash are assumed to vary linearly within each panel. The long range goal is to develop a comprehensive theory for unsteady supersonic potential aerodynamic which is capable of yielding accurate results even in the low supersonic (i.e., high transonic) range
Chaotic rotation of a towed elliptical cylinder
No full textIn this paper I consider the self-excited rotation of an elliptical cylinder towed in a viscous fluid as a canonical model of nonlinear fluid–structure interactions with possible applications in the design of sensors and energy extraction devices. First, the self-excited ellipse system is shown to be analogous to the forced bistable oscillators studied in classic chaos theory. A single variable, the distance between the pivot and the centroid, governs the system bifurcation into bistability. Next, fully coupled computational fluid dynamics simulations of the motion of the cylinder demonstrate limit cycle, period doubling, intermittently chaotic and fully chaotic dynamics as the distance is further adjusted. The viscous wake behind the cylinder is presented for the limit-cycle cases and new types of stable wakes are characterized for each. In contrast, a chaotic case demonstrates an independence of the wake and structural states. The rotational kinetic energy is quantified and correlated to the vortex shedding and the trajectory periodicity. Chaotic and high-period system responses are found to persist when structural damping is applied and for Reynolds numbers as low as 20
