“…We consider (1.1)-(1.3) in a convex polygon Ω ⊂ R 2 up to a given time , with the following boundary and initial conditions: u = 0 on Ω × [0, ], = 0 and u = u 0 at = 0, (1.4) where 0 and u 0 are given functions, and Ω the boundary of the domain Ω. For given smooth initial data 0 and u 0 with positive density, i.e., min the existence and uniqueness of smooth solutions of (1.1)-(1.4) have been proved in [14,32,44]. In particular, this hyperbolic-parabolic system does not generate shock wave (at least in 2D).…”