Flutter derivatives identification through full bridge aeroelastic model transfer function analysis

摘要

A full bridge 1: 250 scale 13 m long aeroelastic model of the proposed Messina Suspension Bridge has been built and tested at the Danish Maritime Institute wind tunnel. This experimental exercise was undertaken as a check at the conclusion of the design, having already defined the optimised deck section and measured its aerodynamic characteristics through 1: 87 and 1: 30 section model tests. In addition to the usual tests always performed on a full bridge aeroelastic model (i.e. static and dynamic response to smooth and turbulent flow excitation and flutter speed limit), a specific measure set-up and test program has been realised, aimed at defining the modal characteristics of the structure and their modifications due to the wind effects. In the present paper a modal approach for identifying the aerodynamic terms, usually mentioned as flutter derivatives, from the measure of the aeroelastically modified full bridge transfer functions is presented. The analytical formulation of the transfer functions for a two mode structure description have been obtained as a function of all the modal and aerodynamic parameters. A least squares iterative procedure was then applied allowing to evaluate a best estimate of the parameters minimising the distance between the experimental and the numerical transfer :functions. Given the generality of the identification method, both the structural and aerodynamic parameters can be addressed, and due to the two DoF approach also the coupling terms can be taken into account. The opportunity of extending the method at least to a three mode structure description was clearly suggested by this first experience.