  We apply Maxwell and Cattaneo's relaxation approaches to the analysis of
strong shockwaves in a two-dimensional viscous heat-conducting fluid. Good
agreement results for reasonable values of Maxwell's relaxation times.
Instability results if the viscous relaxation time is too large. These
relaxation terms have negligible effects on slower-paced subsonic problems, as
is shown here for two-roll and four-roll Rayleigh-Benard flows.
