Date: 12/05/08

Speaker: Sankha Banerjee

Title: Flapping Dynamics of a Three dimensional Flag

Abstract:
We investigate the flapping instability and response of a three  dimensional flag of high
extensional rigidity and low bending rigidity  in a uniform and incompressible flow.
The relevant non-dimensional para-meters governing the problem are  identified. The soft
cloth of a flag is represented by very low  bending rigidity and the subsequent dominance
of flow-induced tension  as the main structural restoring force.
The flutter modes are calculated in three dimensions for different  values of aspect
ratio of the flag, assuming that the fluid viscosity  and the plate viscoelastic damping
to be negligible. We compute the  linear stability domain which agrees with previous
approximate models. To study the nonlinear stability and response, we develop a
fluid-structure direct  simulation (FSDS) capability,
coupling a direct numerical simulation of the Navier-Stokes equations to a solver for
thin-membrane dynamics of arbitrarily large motion. The fully-nonlinear dynamics are
solved numerically with the flow grid fitted to the structural boundary.
Span-wise periodicity is used and external forcing to the structure is
calculated from the boundary fluid dynamics.