Passive aerodynamic control of wind induced instabilities in long span bridges

The aim of the study is derivation of mathematical models of the proposed passive aerodynamic control systems and estimation of their effectiveness in the improvement of stability of long-span suspension bridges exposed to action of wind. The analyzed wind actions on bridge structure are limited to wind induced instabilities of the bridge structure e.g., flutter and divergence. The influence of the turbulence on the unsteady aerodynamic forces is neglected [103]. The bridge is assumed to undergo small amplitude oscillations around the equilibrium position and therefore the linear model of the bridge structure is applied. Two types of control systems are proposed. The first one, uses the control surfaces at- tached beneath the bridge deck. The motion of the surfaces is governed by a pendulum attached to the center of gravity of the bridge. The control surfaces are connected to pendu- lum, and thus, rotation of the surfaces is induced by motion of the bridge girder. This con- trol system is referred to as the bridge-surfaces system. The second considered passive system consists of control surfaces directly attached to the edges of the bridge girder. This system is called bridge-flaps control system. The motion of the flaps is induced by addi- tional cables connecting the flaps with the main cables is such a way that the rotation and horizontal deformation of the bridge induce rotations of the flaps. The first part of the study is devoted to derivation of the mathematical models of the sections of the passive control systems. The time domain formulation of the unsteady aero- dynamic forces, acting of the bridge equipped with control surfaces or flaps, is obtained through rational function approximation. The preliminary parametric study is conducted to select the configuration of the systems which are the most effective in stabilizing bridge structure exposed to actions of wind. The second part, presents the experimental study conducted in the wind tunnel on sec- tional models of the system. The study of the bridge-surfaces system was designed and conducted by K. Wilde (former Associate Professor at the Bridge and Structure Lab., Uni- versity of Tokyo, Japan). The aim of the experiment was the estimation of the critical wind speeds of the bridge-surfaces control system. The experimental tests on the bridge-flaps system were conducted by T. Sato (former Master student of the Bridge and Structure Lab., University of Tokyo, Japan). The experiment was devoted to measurements of the unsteady aerodynamic forces acting on the moving bridge with rotating flaps. The experimental results were compared with the analytical results obtained from the sectional mathematical models of the control systems. The third part of the work presents the derivation of the full three dimensional FEM models of the bridge and control systems. The models are obtained through the Finite Ele- ment Method. Then the dynamic analysis on FEM models of the control systems with the selected configurations is conducted. The efficiency of the studied systems as well as their advantages and disadvantages are discussed.