Aerodynamic Control of Bridge Deck Flutter by Active Surfaces

Abstract

An active aerodynamic control method of suppressing flutter of a very-long-span bridge is presented in this paper. The control system consists of additional control surfaces attached to the bridge deck; their torsional movement, commanded via feedback control law, is used to generate stabilizing aerodynamic forces. The frequency independent formulation of unsteady aerodynamic forces acting on the bridge deck as well as the control surfaces is derived through rational function approximation. The high precision of approximation is ensured by multilevel linear and nonlinear constrained optimization. Although the proposed mathematical model of aeroservoelastic system is augmented by new aerodynamic states, it is in the form of a set of constant coefficient differential equations that are particularly convenient for control law synthesis. The obtained equations of motion are functions of mean wind speed so the efficiency of application of the conventional constant gain optimal feedback control is limited. To cope with the system dependence on wind speed, a variable-gain control is proposed. The static output variable-gain approach is formulated in terms of a mathematical optimization problem and the necessary conditions are derived. Application of the variable-gain control provides variation of control strategies in different wind velocities and is found to be efficient for the studied aerodynamic active control of bridge deck flutter.