Kronecker flow

Thus, the orbits in the domain Q x Tn of phase space lie on invariant tori parameterized by the action variables h,..., /n, and the motion on each torus is a Kronecker flow with frequencies wi(/),..., ojn(I). 

To arrive at these results, we have noted that the time-average of the leading partial time derivative in Eq. 2 is zero and that, since the velocity field is already a first-order quantity (with the base state being one of zero flow), the acoustic stress is correct to secrnid order as written on the far right-hand side of Eq. 17. Here, S denotes the unit isotropic tensor of rank two whose components in a Cartesian system are given by the Kronecker delta symbol 8 ,. That is, in component form, riy = - (p po) ij - poiviVj). 

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