Full-order and multimode flutter analysis using ANSYS

This paper presents the full-order and multimode methods for analyzing coupled flutter of long-span bridges using commercial finite element (FE) package ANSYS. In the full-order method of flutter analysis, a novel FE model is developed to model the coupled wind-bridge system, in which a specific user-defined Matrix27 element in ANSYS is adapted to model the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. Variation of complex eigenvalues of the coupled system with wind velocity is then depicted by using this model together with complex eigenvalue analysis, and flutter instability can be determined from the variation diagram. In the multimode method, equations of motion for the coupled wind-bridge system are first represented using a modal superposition technique. This formulation leads to a single-parameter searching technique without iteration to determine the conditions of flutter instability when structural damping is not considered in solution. The contribution of participating modes to flutter instability is given in terms of modal amplitude and modal energy in the multimode method. Numerical studies are provided to validate the developed methods as well as to demonstrate both the procedures for flutter analysis using ANSYS. The proposed methods enable the bridge designers and engineering practitioners to analyze bridge flutter in commercial FE package ANSYS.