Invariants and chaos in the Volterra gyrostat without energy conservation

Abstract

The model of the Volterra gyrostat (VG) has not only played an important role in rigid body dynamics but also served as the foundation of low-order models of many naturally occurring systems. It is well known that VG possesses two invariants, or constants of motion, corresponding to kinetic energy and squared angular momentum, giving oscillatory solutions to its equations of motion. Nine distinct subclasses of the VG have been identified, two of which the Euler gyroscope and Lorenz gyrostat are each known to have two constants. This paper characterizes quadratic invariants of the VG and each of its subclasses, showing how these enjoy two invariants even when rendered in terms of a non-invertible transformation of parameters, leading to a transformed Volterra gyrostat (TVG). If the quadratic coefficients of the TVG sum to zero, as they do for the VG, the system conserves energy. In all of these cases, the flows preserve volume. However, physical models where the quadratic coefficients do not sum to zero are ubiquitous, and characterization of invariants and the resulting dynamics for this more general class of models with volume conservation but without energy conservation is lacking. This paper provides the first such characterization for each of the subclasses of the VG in the absence of energy conservation, showing how the number of invariants depends on the number of linear feedback terms. It is shown that the gyrostat with three linear feedback terms has no invariants. The number of invariants circumscribes the possible dynamics for these three-dimensional flows, and those without any invariants are shown to admit rich dynamics including chaos. This gives rise to a broad class of three-dimensional volume conserving chaotic flows, arising naturally from model reduction techniques.