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arXiv 1508.04337math.AP
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一维可压缩Euler方程经典解的最佳时间依赖密度下界

Optimal time-dependent lower bound on density for classical solutions of 1-D compressible Euler equations

Geng Chen

摘要:

对于可压缩Euler方程,即使初始值一致远离真空,解也可以在无限时间内逼近真空。在欧拉方程的研究中,获得精确的密度下界是至关重要的。本文对一维等熵和全Euler方程的初值问题,假设初始密度有正下界,证明了对于任意的$\textstyle 0<δ\ll 1$,经典解中的密度函数分别有$\textstyle O(1+t)^{-1}$和$\textstyle O(1+t)^{-1-δ}$阶的正下界,其中$t$是时间.这些界限的顺序分别是最优或几乎最优的。此外,对于欧拉坐标系$(y,t)\in\mathbb{R}\times[0,T)$中的经典解,我们证明了速度$u$满足$u_{y}(y,t)$从上到下一致有界于一个与$T$无关的常数,尽管当梯度爆破发生时,即激波形成时,$u_{y}(y,t)$趋于负无穷大.

英文摘要:

For the compressible Euler equations, even when the initial data are uniformly away from vacuum, solution can approach vacuum in infinite time. Achieving sharp lower bounds of density is crucial in the study of Euler equations. In this paper, for the initial value problems of isentropic and full Euler equations in one space dimension, assuming initial density has positive lower bound, we prove that density functions in classical solutions have positive lower bounds in the order of $\textstyle O(1+t)^{-1}$ and $\textstyle O(1+t)^{-1-δ}$ for any $\textstyle 0<δ\ll 1$, respectively, where $t$ is time. The orders of these bounds are optimal or almost optimal, respectively. Furthermore, for classical solutions in Eulerian coordinates $(y,t)\in\mathbb{R}\times[0,T)$, we show velocity $u$ satisfies that $u_{y}(y,t)$ is uniformly bounded from above by a constant independent of $T$, although $u_{y}(y,t)$ tends to negative infinity when gradient blowup happens, i.e. when shock forms, in finite time.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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