Preprint A409/2005
Neumann problems for quasilinear parabolic systems modelling polydisperse suspensions

Hermano Frid | Berres, Stefan | Bürger, Raimund

**Keywords: **
Quasilinear parabolic system | boundary value problem | polydisperse suspensions

We discuss the well-posedness of a class of Neumann problems
for $n\X n$ quasilinear parabolic systems arising from models of sedimentation of polydisperse suspensions
in engineering applications. This class of initial-boundary value problems includes the standard (zero-flux) Neumann
condition, in the limit as a positive perturbation
parameter $\te$ goes to 0. We call, in general, the problem associated with $\te\ge0$, the $\te$-flux Neumann problem. The Neumann boundary conditions, although natural and usually convenient for integration by parts,
are nonlinear and couple the different components of the system. An important aspect of our analysis is a time stepping procedure that considers linear boundary conditions for each time step in order to circumvent the difficulties arising from the nonlinear coupling in the original boundary conditions. We prove the well-posedness of the $\te$-flux Neumann problems for $\te>0$ and obtain a solution of the standard (zero-flux) Neumann problem as the limit for $\te\to0$ of solutions of the $\te$-flux Neumann problems.
Concerning applications, the analysis developed here supports a new model for the settling of polydisperse suspensions forming compressible sediments.