  A numerical study of nonlinear r-modes in isentropic, rapidly rotating
relativistic stars, via 3-D general-relativistic hydrodynamical evolutions, is
presented. On dynamical timescales, we find no evidence for strong coupling of
r-modes to other modes at amplitudes of order one or larger. Therefore, unless
nonlinear saturation sets in on longer timescales, the maximum r-mode amplitude
is of order one. An absolute upper limit on the amplitude is set by causality.
Our simulations also show that r-modes and inertial modes in isentropic stars
are discrete modes, with no evidence for the existence of a continuous part in
the spectrum.
