synchronized motion while Fig. 9b corresponds to a chaotic attractor. The dominant Lyapunov exponents calculated
for these responses are k1 ¼ 0:1625 (Fig. 9a) and k1 ¼ 0:03540 (Fig. 9b). Note, the chaotic attractor
is very similar to that studied by Thompson [33] where the harmonic potential has been supplemented by a
nonlinear term with displacement to the power 3 (z3). Fig. 9 also shows the time histories for the two cases:
A ¼ 0:31 m (Fig. 9c) and A ¼ 0:41 m (Fig. 9d). In this figure the difference between the periodic and chaotic
responses is clear.