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On a canonical extension of Korn's first and Poincaré's inequality to $\mathsf H(\operatorname{Curl})$
P. Neff,
D. Pauly,
K.-J. Witsch Universität Duisburg-Essen, Fakultät für Mathematik, Essen, Germany
Abstract:
We prove a Korn-type inequality in $\overset\circ{\mathsf H}(\operatorname{Curl};\Omega,\mathbb R^{3\times3})$ for tensor fields
$P$ mapping
$\Omega$ to
$\mathbb R^{3\times3}$. More precisely, let
$\Omega\subset\mathbb R^3$ be a bounded domain with connected Lipschitz boundary
$\partial\Omega$. Then, there exists a constant
$c>0$ such that
\begin{equation}
c\|P\|_{\mathsf L^2(\Omega,\mathbb R^{3\times3})}\leq\|\operatorname{sym}P\|_{\mathsf L^2(\Omega,\mathbb R^{3\times3})} +\|\operatorname{Curl}P\|_{\mathsf L^2(\Omega,\mathbb R^{3\times3})}
\tag{0.1}
\end{equation}
holds for all tensor fields $P\in\overset\circ{\mathsf H}(\operatorname{Curl};\Omega,\mathbb R^{3\times3})$, i.e., all
$$
P\in\mathsf H(\operatorname{Curl};\Omega,\mathbb R^{3\times3})
$$
with vanishing tangential trace on
$\partial\Omega$. Here, rotation and tangential trace are defined row-wise. For compatible
$P$ (i.e.,
$P=\nabla v$),
$\operatorname{Curl}P=0$, where
$v\in\mathsf H^1(\Omega,\mathbb R^3)$ a vector field having components
$v_n$, for which
$\nabla v_n$ are normal at
$\partial\Omega$, the estimate
$(0.1)$ is reduced to a non-standard variant of the Korn's first inequality:
$$
c\|\nabla v\|_{\mathsf L^2(\Omega,\mathbb R^{3\times3})}\le \|\operatorname{sym}\nabla v\|_{\mathsf L^2(\Omega,\mathbb R^{3\times3})}.
$$
For skew-symmetric
$P$ (
$\operatorname{sym}P=0$) the estimate
$(0.1)$ generates a non-standard version of the Poincaré. Therefore, the estimateis a generalization of two classical inequalities of Poincaré and Korn.
Key words and phrases:
Korn's inequality, gradient plasticity, theory of Maxwell's equations, Helmholtz' decomposition, Poincaré/Friedrichs type estimate.
UDC:
517 Received: 14.12.2011
Language: English