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arXiv 1904.03337math.FA
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Lebesgue和Sobolev范数在特征空间上的同时逼近

Simultaneous approximation in Lebesgue and Sobolev norms via eigenspaces

Charles L. Fefferman, Karol W. Hajduk, James C. Robinson

摘要:

我们近似函数定义在光滑有界域的拉普拉斯算子或斯托克斯算子的特征空间的元素,在这样一种方式,近似是有界的,并在索伯列夫和勒贝格空间收敛。证明了希尔伯特空间上正的、自伴的、紧的逆算子的分数次幂空间的一个抽象结果,然后利用Dirichlet Laplacian算子和Stokes算子的分数次幂空间的显式形式得到了我们的主要结果.作为一个简单的应用,我们证明了${\mathbb R}^3$中有界区域上的不可压对流Brinkman-Forchheimer方程的所有弱解满足能量等式.

英文摘要:

We approximate functions defined on smooth bounded domains by elements of the eigenspaces of the Laplacian or the Stokes operator in such a way that the approximations are bounded and converge in both Sobolev and Lebesgue spaces. We prove an abstract result referred to fractional power spaces of positive, self-adjoint, compact-inverse operators on Hilbert spaces, and then obtain our main result by using the explicit form of these fractional power spaces for the Dirichlet Laplacian and Stokes operators. As a simple application, we prove that all weak solutions of the incompressible convective Brinkman--Forchheimer equations posed on a bounded domain in ${\mathbb R}^3$ satisfy the energy equality.

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