Investigation On Flutter Active Control Of Bridges With Aerodynamic Flaps

Flutter is the main constraint on the designing and development of super-long-span bridges.Therefore,it is necessary to seek for control measures in order to increase the aerodynamic stability.Compared to traditional passive control measures,active control can significantly increase flutter critical speed,thus it is expected to be the technical solution for the flutter stability of super-long-span bridges.Based on the modern control theory and computational fluid dynamic approach,this dissertation focuses on a suspension bridge of streamlined box girder with aerodynamic flaps and establishes a theoretical framework for active control of bridge flutter.Modeling and identification of the self-excited forces,designing of control law,suppression mechanism and the control potential are the main researches conducted in the dissertation.The entire work is aimed to develop a more adaptive theoretical framework for active control of bridge flutter,and pave the way to the construction of super-long-span bridges.The main works and contributions done in this dissertation are as follows:1)The theoretical framework for active control of bridge flutter is established.By introducing Hansen's expression of motion-induced forces,the identification method,which can be applied in both numerical and physical wind tunnel tests,is proposed based on the principle of single-degree-of-freedom forced vibration approach.Combined with the modern control theory,state-space equations under feedback control strategy is derived;and examination of the wing-aileron case indicates the accuracy and good performance of the theoretical framework in flutter control2)Numerical approach based on the proposed forced vibration method is developed to identify the motion-induced forces for deck-flap system.Experiments of the deck-flap system under different amplitudes and phases were firstly carried out,in order to validate the linear superposition of the motion-induced forces and provide the application scope of the presented identification method.Then,a wing-aileron system was investigated,and comparison of the flutter derivatives between numerical approach and theoretical one highlights the accuracy and the performance of the identification method.Finally,flutter derivatives of the deck-flap system were identified through the same approach.3)Based on the secondary development of ANSYS FLUENT software,the fluid solid interaction and feedback control are combined to simulate the aeroelastic behavior of the deck-flap system under desired wind speeds.The deck-flap system can achieve notable increase of the critical speed with the appliance of suitable control law.Explanation on the suppression mechanism of the deck-flap system is made in terms of system aerodynamic damping and stiffness.Influence of flap configuration parameters is investigated through theoretical and numerical approaches.An iterative method for the control potential is suggested,and its control stability is discussed as well.4)Based on the principles of finite element and the flutter analysis of multimodal superposition,the three dimensional feedback control model for the deck-flap system is developed.By introducing a long-span suspension bridge,numerical calculation of the three dimensional active control is conducted,as well as the investigation on the influence of the spanwise flap pattern on the flutter suppression.