The Identification Of Flutter Derivatives For Long-span Bridges Applying The Forced Vibration Method

The identification of flutter derivatives for bridge sectional model has long been a key issue in long-span bridge flutter and buffeting analysis. As to the current problems existing in the identification for these flutter derivatives, the dissertation tries to trace the development in the identification for the past unsteady aerodynamic forces of long-span bridges. It also investigates the method for flutter and buffeting analysis and the flutter derivatives. Based on the present methods used in obtaining the unsteady aerodynamic forces and flutter derivatives, and co-funded by a natural scientific fund from the Nation and a key project fund from the Railway Ministry, the current research has attempted to develop a device which can be employed in the wind tunnel to test flutter derivative through a forced vibration method. Major contents of the dissertation includes the following:1. As the first successful experiment which has been conducted in China to test the unsteady aerodynamic forces in wind tunnel, the feasibility of the method is proved through numerous tests and abundant practice. The result of the experiment shows that the proposed forced vibration method device has the quality of stability and repetitiveness of the data, the wide range of the testable reduced velocity, the exactness of coupled and direct flutter derivatives. And it does not need to employ any complicated identification system to check it further.2. A systematic test has been carried out to observe how the model actuating frequencies and amplitudes affect the flutter derivatives, and the effect is found to be quite minor. The researcher also concludes that in the range of reduced velocity, the flutter derivatives equal to the function of it.3. A test has been carried out on three typical bridges sectional models of flutter derivatives to find the general rules with the change of flutter derivatives of thebridges sectional model. And it has been discovered that this change depend on the torsional damping, an element closely relating to the H*2 and A*24. A study on the proposed Scanlan linearity has discovered that if the self-excited loads and movement of the model and velocity constitute a linear relationship, and the model vibration accounts for a sine function of the frequency, the rate of the high-order harmonic waves should be quite small. And the result shows that the self-excited loads and the flutter derivatives satisfying the linear relationship as to the streamline section-like thin plate. While the flutter self-excited loads of a bluff section has a quality of obvious nonlinearity. And the application of flutter derivatives to self-excited loads of the bluff section is close to a linear relationship.5. Based on a identification device of forced vibration mthod for 2-DOF flutter derivatives of bridges sectional model, the researcher, cooperated with some others from the National University of Defense Technology and Tongji University, has developed a set of identification device for a 3-DOF flutter derivatives of bridges sectional model, and further research is being conducted.