A numerical and experimental study of codimension-2 points in a parametrically excited double pendulum

The results of a study of parametric excitation of a double pendulum are pr esented. In particular, we focus on the bifurcation set which gives rise to swinging motion including low-dimensional chaos. The interaction of the di stinct modes of the system is organized in codimension-2 points when the un derlying modes have different symmetry properties. Qualitatively different organizing centres exist for the planar and orthogonal geometries in discon nected regions of parameter space. The surprising result we have uncovered is that there is a critical angle which divides the qualitatively different types of dynamical motion found in the respective limits.