Friday, January 30, 2004
1:30pm Ð 2:30pm
Professor Earl Dowell
Duke University
ÒNONLINEAR
DYNAMICS OF FLUID-STRUCTURE INTERACTION
OF
VERY HIGH DIMENSIONAL SYSTEMSÓ
Abstract:
Fluid-structural systems are often of very high dimension. The structure may be described in terms of a finite element model with several thousand degrees of freedom and, even when the eigenmodes (or other modal basis functions) are used to describe the structure, the degrees of freedom may be several tenfold. For the fluid the models are typically much larger, in significant part because the fluid extends over one higher spatial dimension than the structure. An airplane wing may be modeled as a two-dimensional plate or a one dimensional beam, but the fluid must be described in three or at least two spatial dimensions. When using a finite difference or finite element or finite volume model of the fluid, the number of degrees of freedom can range from tens of thousands to a million or more. Interestingly it has recently been shown that it is feasible to find a set of global basis functions that allow a reduction in the number of degrees of freedom for the fluid to less than one hundred without any essential loss of physical information. This has made fluid-structural modeling much more attractive for both linear and nonlinear systems.
In this presentation
representative results drawn from the recent literature are presented from both
theory and experiment. Good correlation is shown and the principal physical
phenomena arising from several distinct physical systems including airfoils
with freeplay, delta wings with plate-like behavior and very high aspect ratio
wings with substantial flexibility are described. Fluid nonlinearities arising
from shock wave motion and separated flow are given special emphasis drawing on
very recent results for the F-16 aircraft, turbomachinery cascades, and for
oscillating flows in the wakes behind a bluff body.