“…The singular level Δ × S 1 × {0} of K is, viewed as an orbit cylinder, trivially foliated by closed orbits of system (4)-(6) carrying a periodic motion with frequencies ω(s). To be completely integrable, Hamiltonian system (4)-(6) needs an additional integral of motion, functionally independent of H and K. Finding the integrability conditions for systems of such a type is a difficult task even in the case of the "quadratic" Hamiltonian H [2,5,11]. We are interested in the qualitative behavior of the Euler dynamics around the orbit cylinder in the context of the KAM results on the persistence of quasi-periodic tori and the excitation of normal modes [3,4,7,10,14,15].…”