Identification Of Flutter Derivatives And Its Accuracy Research Based On Free Vibration Method

Flutter of long span bridges in natural wind is a self-excited divergent oscillation. In order to evaluate the flutter stability of bridges, the flutter derivatives, as the essential parameters, have to be studied carefully. Typically, obtaining of the flutter derivatives can be conducted by wind tunnel testing of two dimensional section model of bridge decks. For the sectional model, two wind tunnel testing methods are available in present, i.e. forced vibration method and free vibration method. In this dissertation, the focus is on the free vibration testing method and the main work is as follows:1) The development of bridge wind engineering for cable supported bridges are reviewed and various methods for determine the bridge deck flutter derivatives are introduced;2) The physical significance of the bridge deck flutter derivatives is discussed and the free vibration method of bridge deck sectional model for the identification of the flutter derivatives is described in detail;3) The theory of Eigensystem Realization Algorithm (ERA) on the basis of state space theory is investigated circumstantially. As a method of identification of system modal parameters, the ERA method is employed combined with numerical simulation so as to identify the parameters of a two DOF free vibration system. The simulation suggests that though the identification results testify the availability of the ERA method, there are some shortcomings regarding the identification accuracy.4) In terms of the error issues of adopting free vibration time domain method, research attention is forced on the following aspects:advancement of the ERA method, noise source analysis, and optimizing of testing parameters. The research show that:compared with the ERA method, the advanced data correlation ERA method (ERA/DC) reveals superior quality in the identification accuracy; the vibration instability of the sectional model has side effect on the flutter derivatives identification accuracy thus it should be considered in the testing; identification accuracy will be improved in relative high wind speed if the model mass and mass moment of inertia are increased.5) Sectional model wind tunnel tests of two typical bridge deck cross sections are conducted to obtain the corresponding flutter derivatives based upon the above research fruits.