Determination
of aerodynamic admittance functions and flutter derivatives
The research is conducted in order to determine through the computational approach:
- the aerodynamic admittance functions necessary for the evaluation of the structural responses of bridge decks to gusty wind (buffeting or gust response);
- the flutter derivatives required to determine the self-induced forces due to structure motion and to evaluate the aeroelastic stability of bridge decks (flutter instability).
These aerodynamic and aeroelastic
coefficients should first of all be determined by experimental or computational
means with good accuracy and reduced effort. The unified identification method
is based on a modified indicial approach adapted to the solution of the
Navier-Stokes equations in Eulerian (aerodynamic admittance function) or
Arbitrary Lagrangian Eulerian formulation (flutter derivatives). The variation
of a component of the flow velocity or of the structure motion is imposed in
the computation domain and the flow field around the structure and in its wake
is computationally simulated. The evaluation of the time histories of the
forces acting on the structure, their transformation in the frequency domain
and their relationship with the frequency content of the input quantity (wind
gust or structure motion) allow an accurate transfer function identification
for each reduced velocity with exceptionally reduced computational costs
compared to other methods proposed in literature. These characteristics of the
method have made it possible to carry out an extensive analysis of the Reynolds
number effects on the flow field and on the flutter derivatives and to
establish relationships between the variation of the Reynolds number, the
physical phenomena induced in the flow and the flutter derivatives, thus
demonstrating the exceptional sensitivity of the latter to the parameter.
