Change of type in three-phase flow: A simple analogue (Q910945)

Here the Riemann problem is solved for a model equation having a similar structure to systems employed in analysing three-phase porous medium flow, such as Stone's saturation equations. The equation has hyperbolic and elliptic regimes, and is solved analytically for data in or near the elliptic region, then compared with numerical results of Bell, Trangenstein and Shubin. For left and right states close together there is a unique solution, obtained by generalizing the Lax admissibility criterion.