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arXiv 1504.01580math.APphysics.class-ph
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真空中可压缩气体的膨胀

Expansion of a compressible gas in vacuum

Denis Serre

摘要:

刘太平\cite{Liu\_JJ}介绍了气体被真空包围时等熵欧拉系统的“物理解”概念。这个概念可以解释为,波前是由声速的霍德尔奇点产生的力驱动的。我们要解决的问题是,这种加速度何时出现,或者何时锋面只是以恒定速度运动。我们从\cite{Gra,SerAIF}知道,对于适当的初始数据,具有非加速锋的光滑等熵流在时间上是全局存在的。在偶数空间维中,这些解对所有的$t\in\R$都是存在的,我们称它们是{ \em eternal}。我们得到了一个关于初值的充分条件,在此条件下,边界奇异性必然出现。因此,我们表明,在偶数维的情况下,永恒的流动与非加速前不存在于奇数空间维度。在一维空间中,我们给出了物理解的精确定义。我们表明,对于无激波流动,它们的渐近两端$t\rightarrow\pm\infty$是密切相关的。

英文摘要:

Tai-Ping Liu \cite{Liu\_JJ} introduced the notion of "physical solution' of the isentropic Euler system when the gas is surrounded by vacuum. This notion can be interpreted by saying that the front is driven by a force resulting from a Hölder singularity of the sound speed. We address the question of when this acceleration appears or when the front just move at constant velocity. We know from \cite{Gra,SerAIF} that smooth isentropic flows with a non-accelerated front exist globally in time, for suitable initial data. In even space dimension, these solutions may persist for all $t\in\R$ ; we say that they are {\em eternal}. We derive a sufficient condition in terms of the initial data, under which the boundary singularity must appear. As a consequence, we show that, in contrast to the even-dimensional case, eternal flows with a non-accelerated front don't exist in odd space dimension. In one space dimension, we give a refined definition of physical solutions. We show that for a shock-free flow, their asymptotics as both ends $t\rightarrow\pm\infty$ are intimately related to each other.

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