Strange Nonchaotic Attractors PDF Download

Attractors which are not chaotic but nevertheless display strange geometric properties have been the subject of a number of studies since they were studied in certain quasiperiodically forced maps, by Grebogi et al. (Physica 13D, 26 (1984)). The attractors, as defined by these authors, are nonchaotic, since they are characterized by Lyapunov exponents which are smaller than zero; but are, however, strange since they display geometric properties unlike either limit cycles or quasiperiodic attractors. The attractors are produced by dissipative, nonlinear systems which are driven by two periodic external forces whose frequences are incommensurate. Strange nonchaotic attractors have been observed in numerical experiments with a variety of bistable and monostable nonlinear oscillators as well as in one ingenious experiment, designed by Ditto et al. (Phys. Rev. Lett. 65, 533 (1990)), using a forced, free standing beam whose mechanical properties could be externally controlled by magnetic fields. We study here a nonlinear oscillator with a multistable potential both numerically and with an analog simulator. The dynamics mimics that of the internal magnetic flux through an under damped, multistable, superconducting quantum interference device which is quasiperiodically forced. We report measurements and numerical computations of the power spectra, invariant density, and Poincare sections Precision numerical computations were used to study the Lyapunov exponents and to observe the destruction of a chaotic attractor and its replacement by a strange nonchaotic one.