We investigate the nonlinear stability of the icosahedral relative equilibrium configuration of point vortices on a sphere. The relative equilibrium problem is formulated as a problem of finding the nullspace of the configuration matrix that encodes the geometry of the icosahedron, as in Jamaloodeen and Newton (Proc. Royal Soc. A, Math. Phys. Eng. Sci. 462(2075):3277, 2006). The seven-dimensional nullspace of the configuration matrix, A, associated with the icosahedral geometry gives rise to a basis set of vortex strengths for which the icosahedron stays in relative formation, and we use these values to form the augmented Hamiltonian governing the stability. We choose the basis set made up of (i) one element with equal strength vortices on every vertex of the icosahedron (the uniform icosahedron); (ii) six elements made up of equal and opposite antipodal pairs. We start by proving nonlinear stability of the antipodal vortex pair (by direct methods). Following the methods laid out in Simo et al. (Arch. Ration. Mech. Anal. 115(1):15–59, 1991) and Pekarsky and Marsden (J. Math. Phys. 39(11):5894–5907, 1998) and more generally in Marsden and Ratiu (Introduction to Mechanics and Symmetry, 1999), we then combine our knowledge of the nullspace structure of A with the structure of the underlying Hamiltonian, and analyze the stability of the icosahedron using the energy-momentum method. Because the parameter space is large, we focus on the physically motivated and important case obtained by combining the basis elements into (i) the uniform icosahedron; (ii) a von Kármán vortex street configuration of equal and opposite staggered, evenly spaced latitudinal rows equidistant from the equator (Chamoun et al. in Phys. Fluids 21:116603, 2009), and (iii) the North Pole–South Pole equal and opposite vortex pair. Stability boundaries in a three-parameter space are calculated for linear combinations of these grouped basis configurations.
Stability of point vortices Relative equilibria Point vortex equilibria Energy-momentum method
Mathematics Subject Classification
76B47 70H14 70E50 37N10 37J25
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We dedicate this paper to the memory of Jerry Marsden, whose work in Hamiltonian mechanics and stability theory laid the groundwork for much that is described in this paper. Support from the National Science Foundation, grant NSF-DMS-0804629, is greatly appreciated.
Humphreys, T., Marcus, P.S.: Vortex street dynamics: the selection mechanism for the areas and locations of Jupiter’s vortices. J. Atmos. Sci. 64, 1318–1333 (2008)
Jamaloodeen, M.I., Newton, P.K.: The N-vortex problem on a rotating sphere. II. Heterogeneous Platonic solid equilibria. Proc. R. Soc. A, Math. Phys. Eng. Sci. 462(2075), 3277 (2006)
Patrick, G.: Relative equilibria in Hamiltonian systems: the dynamic interpretation of nonlinear stability on a reduced phase space. J. Geom. Phys. 9, 111–119 (1992)