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Smoothness properties of solutions to the nonlinear Stokes problem with nonautonomous potentials. (English) Zbl 1313.76079

The author presents some regularity results concerning local minimizers of variational integrals with nonautonomous integrands like \[ \int _{\Omega }\left \{ F\left (\cdot ,\varepsilon (w)\right) -f\cdot w\right \} dx \; \text{ in the class } \left \{ w\in W_{\mathrm{loc}}^{1,p}\left (\Omega ,\mathbb {R}^{n}\right) :\operatorname {div}w=0\right \}. \] A \(\left (p,q\right) \)-elliptic growth condition for the potential \(F\left (x,\varepsilon \right) =g\left (x,\left | \varepsilon \right | \right) \) is assumed. The author proves, under some assumptions, that for a local minimizer \(u:\mathbb {R}^{n}\supset \Omega \rightarrow \mathbb {R}^{n}\) there is an open subset \(\Omega _{0}\) (\(\Omega _{0}=\Omega \) for \(n=2\)) with full Lebesgue-measure such that \(u\) belongs to the space \(C^{1,\alpha }\left (\Omega _{0},\mathbb {R}^{n}\right) \) for any \(\alpha \in \left (0,1\right)\). The result may be applied to weak solutions of the nonlinear Stokes type system \(\operatorname {div} \left \{ \nabla F\left (\varepsilon \left (v\right) \right) \right \} =\nabla \pi -f\) in \(\Omega \).

MSC:

76M30 Variational methods applied to problems in fluid mechanics
76D07 Stokes and related (Oseen, etc.) flows
49N60 Regularity of solutions in optimal control
35J50 Variational methods for elliptic systems