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arXiv 1202.2071math.AP
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粘性Burgers方程中的拟能增长

Enstrophy growth in the viscous Burgers equation

Dmitry Pelinovsky

摘要:

研究了粘性Burgers方程在单位圆上解的涡度拟能增长的界。利用Lu和Doering的变分公式,我们证明了对于平均为零的1-周期函数,涡度拟能变化率的最大值在大涡度拟能的极限下是尖锐的,但不饱和Poincaré不等式.利用动力系统方法,给出了线性稀疏波背景下粘性激波在大涡度拟能极限下极大值的渐近表示。这种渐近结构被用来证明,一个更大的增长的涡度拟能可以实现时,初始数据的粘性Burgers方程饱和的庞加莱不等式的数值常数。本文构造了Burgers方程的精确自相似解,用以描述线性稀疏波背景下亚稳态粘性激波的形成。当我们考虑无限直线上的Burgers方程受非零(激波型)边界条件时,我们证明了在时间演化中达到的最大拟能的尺度为$\mathcal{E}^{3/2}$,其中$\mathcal{E}$是大的初始拟能,而达到最大拟能所需的时间的尺度为$\mathcal{E}^{-1/2} \log(\mathcal{E})$ .在单位圆上证明了相似但较慢的速率。

英文摘要:

We study bounds on the enstrophy growth for solutions of the viscous Burgers equation on the unit circle. Using the variational formulation of Lu and Doering, we prove that the maximizer of the enstrophy's rate of change is sharp in the limit of large enstrophy up to a numerical constant but does not saturate the Poincaré inequality for mean-zero 1-periodic functions. Using the dynamical system methods, we give an asymptotic representation of the maximizer in the limit of large enstrophy as a viscous shock on the background of a linear rarefactive wave. This asymptotic construction is used to prove that a larger growth of enstrophy can be achieved when the initial data to the viscous Burgers equation saturates the Poincaré inequality up to a numerical constant. An exact self-similar solution of the Burgers equation is constructed to describe formation of a metastable viscous shock on the background of a linear rarefactive wave. When we consider the Burgers equation on an infinite line subject to the nonzero (shock-type) boundary conditions, we prove that the maximum enstrophy achieved in the time evolution is scaled as $\mathcal{E}^{3/2}$, where $\mathcal{E}$ is the large initial enstrophy, whereas the time needed for reaching the maximal enstrophy is scaled as $\mathcal{E}^{-1/2} \log(\mathcal{E})$. Similar but slower rates are proved on the unit circle.

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