Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008phdt.........5u&link_type=abstract
Ph.D. Thesis, University of Edinburgh
Mathematics
Logic
N-Body, Chaos, Lyapunov Time
Scientific paper
Despite the wide acceptance that errors incurred in numerical solutions to N-body systems grow exponentially, most research assumes that the statistical results of these systems are reliable. However, if one is to accept that the statistical results of N-body solutions are reliable, it is important to determine if there are any systematic statistical errors resulting from the incurred growth of errors in individual solutions. In this thesis we consider numerical solutions to the 3-body problem in which one of the bodies escapes the system. It is shown for a particular 3-body configuration, known as the Sitnikov problem, that the mean lifetime of the system is dependent on the accuracy of the numerical integration. To provide a theoretical explanation of the phenomenon, an approximate Poincaré map is developed whose dynamics on a particular surface of section is shown to be similar to the dynamics of the Sitnikov Problem. In fact there is a set on which the approximate Poincaré map is topologically equivalent, like the Sitnikov Problem, to the shift map on the set of bi-infinite sequences. The structure of the escape regions on the surface of section form a cantor set-like structure whose boundary can more easily be delineated using the approximate Poincaré map than for the Sitnikov problem. Further it is shown that numerical errors destroy escape regions and can cause orbits to migrate to a region in which escape is faster. Finally, a relationship between the Lyapunov time, tl, and the lifetime, td, of the 3-body problem is discussed. First, the Sitnikov problem and the approximate Poincaré map of the Sitnikov problem both exhibit a two-part power law relationship beween tl and td like that for a particular case of the general 3-body problem. Further, it is demonstrated that large perturbations to the energy of the escaping body influences the relationship between tl and td for small tl. Finally, it is shown that the approximate Poincaré map yields a theoretical explanation of the phenomenon based on the structure of the escape regions the orbits traverse before escape.
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