  We numerically study the tidal instability of accretion discs in close binary
systems using a two-dimensional SPH code. We find that the precession rate of
tidally unstable, eccentric discs does not only depend upon the binary mass
ratio q. Although the (prograde) disc precession rate increases with the
strength of the tidal potential, it also increases with the shear viscosity.
Increasing the disc temperature has a retrograde impact upon the precession
rate.
  We find that motion relative to the binary potential results in
superhump-like, periodic luminosity variations in the outer reaches of an
eccentric disc. The nature and location of the luminosity modulation is a
function of the shear viscosity, nu. Light curves most similar to observations
are obtained for nu values appropriate for a dwarf nova in outburst.
  We investigate the thermal-tidal instability model for superoutburst. A dwarf
nova outburst is simulated by instantaneously increasing nu, which causes a
rapid radial expansion of the disc. Should the disc encounter the 3:1 eccentric
inner Lindblad resonance and become tidally unstable, then tidal torques become
much more efficient at removing angular momentum from the disc. The disc then
shrinks and mass flux through the disc increases. The resulting increase in
disc luminosity is found to be consistent with the excess luminosity of a
superoutburst.
