Robust modelling of flow induced oscillations of bluff bodies

In mechanical engineering and in the engineering literature dealing with flow induced oscillations of bluff bodies frequently a non-robust model with non-linear terms of third order and two parameters is used. By means of the methods of bifurcation theory it can be shown that this system corresponds to a degenerate system with a double zero eigenvalue with Codimension 3. Therefore 3 parameters are needed to obtain a robust model. A physical interpretation of the third parameter and its influence on the bifurcation diagram are given.