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arXiv 2008.04725math.AP
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Using periodic boundary conditions to approximate the Navier-Stokes equations on $\mathbb{R}^3$ and the transfer of regularity

James C. Robinson

英文摘要:

This paper considers solutions $u_α$ of the three-dimensional Navier--Stokes equations on the periodic domains $Q_α:=(-α,α)^3$ as the domain size $α\to\infty$, and compares them to solutions of the same equations on the whole space. For compactly-supported initial data $u_α^0\in H^1(Q_α)$, an appropriate extension of $u_α$ converges to a solution $u$ of the equations on ${\mathbb R}^3$, strongly in $L^r(0,T;H^1({\mathbb R}^3))$, $r\in[1,\infty)$. The same also holds when $u_α^0$ is the velocity corresponding to a fixed, compactly-supported vorticity. A consequence is that if an initial compactly-supported velocity $u_0\in H^1({\mathbb R}^3)$ or an initial compactly-supported vorticity $ω_0\in H^1({\mathbb R}^3)$ gives rise to a smooth solution on $[0,T^*]$ for the equations posed on ${\mathbb R}^3$, a smooth solution will also exist on $[0,T^*]$ for the same initial data for the periodic problem posed on ${Q_α}$ for $α$ sufficiently large; this illustrates a `transfer of regularity' from the whole space to the periodic case.

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