Navier-Stokes systems with quasimonotone viscosity tensor Pierre Dreyfuss, Norbert Hungerbuhler Mathematics Department, University of Fribourg, Perolles, CH-1700 Fribourg (Switzerland) Abstract: In [1] we investigated a class of Navier-Stokes systems which is motivated by models for electrorheological fluids. We obtained an existence result for a weak solution under mild monotonicity assumptions for the viscosity tensor. In this article, we continue the analysis of such systems, but with various notions of quasimonotonicity instead of classical pointwise monotonicity assumptions. Moreover we allow the external force to be of a more general form. 1 Introduction 1.1 Retrospect of former results In this paragraph we introduce some notations, and we recall the main results es- tablished in [1] in order to relate them later on with the new results which we derive below. Let ? ? IRn be a bounded open domain with Lipschitz boundary. In [1] we consid- ered the following Navier-Stokes system for the velocity u : ? ? [0, T ) ? IRn and the pressure P : ? ? [0, T ) ? IR ∂u ∂t ? div ?(x, t, u, Du) + (u · ?)u = f ? gradP on ? ? (0, T ) (1) div u = 0 on ? ? (0, T ) (2) u = 0 on ∂? ? (0, T ) (3) u(·, 0) = u0 on ? (4) Here, f ?
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