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Nonlinear flutter of a cantilever wing including the influence of structure uncertainties

Domenii publicaţii > Stiinte ingineresti + Tipuri publicaţii > Tezã de doctorat (nepublicatã)

Autori: Castravete, S. C.

Editorial: 2007.

Rezumat:

The present work deals with the effect of parametric excitation and uncertainties on the flutter characteristics of an aeroelastic wing. The work is structured in two parts. First part explores the possibility of suppressing wing flutter via parametric excitation along the plane of highest rigidity in the neighborhood of combination resonance. The aerodynamics of the wing is modeled using Theodorsen’s theory and the equations are obtained using Hamilton’s principle. The domains of attraction and bifurcation diagrams are obtained to reveal the conditions under which the parametric excitation can provide stabilizing effect. The basins of attraction for different values of excitation amplitude reveal the stabilizing effect that takes place above a critical excitation level. Below that level, the response experiences limit cycle oscillations, cascade of period doubling, and chaos. For flow speed slightly higher than the critical flutter speed, the response experiences a train of spikes, known as ” firing ,” a term that is borrowed from neuroscience, followed by ” refractory ” or recovery effect, up to an excitation level above which the wing is stabilized.

The second part of the paper investigates the influence of stiffness uncertainties on the flutter behavior of an aeroelastic wing using a stochastic finite element approach. A numerical algorithm to simulate unsteady, nonlinear, incompressible flow (based on the unsteady vortex lattice method) interacting with linear aeroelastic wing in the presence of uncertainties was developed. The air flow and the wing structure are treated as elements of a single dynamical system. In order to implement this algorithm in the presence of uncertainties, a random field representing bending or torsion stiffness parameters is introduced using a truncated Karhunen-Love expansion. Both perturbation technique and Monte Carlo simulation are used to establish the boundary of stiffness uncertainty level at which the wing exhibits LCO and above which the wing experiences dynamic instability. The analysis also includes the limitation of perturbation solution for a relatively large level of stiffness uncertainty. It was found that the presence of the uncertainties in bending and torsion stiffness can lower the flutter speed and the effect of torsion stiffness uncertainty induce greater disturbance in the system.

Cuvinte cheie: Wing flutter, vortex-lattice method, stochastic finite element, aeroelasticity