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arXiv 1709.04778math.AP
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一类具有导数二次非线性项的拟线性wave equations方程的稳定ODE型爆破

Stable ODE-type blowup for some quasilinear wave equations with derivative-quadratic nonlinearities

Jared Speck

摘要:

我们证明了一个建设性的稳定的ODE型爆破结果的开放集的解决方案,一个家庭的拟线性波动方程在三维空间具有Riccati型导数二次半线性项。奇点比激波更严重,因为解本身会像距离到爆破时间的对数那样爆破。我们假设准线性项满足一定的结构假设,这特别确保了波算子的“椭圆部分”精确地在奇点处消失。在$L^{\infty}$中,初始数据是完全支持的,可以是小的或大的,但是空间导数必须首先满足与时间导数相比非线性的小条件。证明的第一个主要思想是构造一个准线性的积分因子,它允许我们将波动方程重新表述为一个系统,其解保持正则,一直到奇点。这等价于构造适应于非线性流的拟线性向量场。第二个主要思想是利用各种估计中的一些重要单调项,特别是能量估计,其特征在于积分因子。单调性的可用性与我们对数据和拟线性项结构的假设有关。第三个主要思想是将空间导数的相对小性一直传播到奇点,使得解在许多方面表现得像常微分方程解。作为我们的主要结果的推论,我们表明,有准线性波动方程表现出两种不同的爆破:形成一个非平凡的数据集的冲击,和ODE型爆破的另一个非平凡的设置。

英文摘要:

We prove a constructive stable ODE-type blowup result for open sets of solutions to a family of quasilinear wave equations in three spatial dimensions featuring a Riccati-type derivative-quadratic semilinear term. The singularity is more severe than a shock in that the solution itself blows up like the log of the distance to the blowup-time. We assume that the quasilinear terms satisfy certain structural assumptions, which in particular ensure that the "elliptic part" of the wave operator vanishes precisely at the singular points. The initial data are compactly supported and can be small or large in $L^{\infty}$, but the spatial derivatives must initially satisfy a nonlinear smallness condition compared to the time derivative. The first main idea of the proof is to construct a quasilinear integrating factor, which allows us to reformulate the wave equation as a system whose solutions remain regular, all the way up to the singularity. This is equivalent to constructing quasilinear vectorfields adapted to the nonlinear flow. The second main idea is to exploit some crucial monotonic terms in various estimates, especially the energy estimates, that feature the integrating factor. The availability of the monotonicity is tied to our assumptions on the data and on the structure of the quasilinear terms. The third main idea is to propagate the relative smallness of the spatial derivatives all the way up to the singularity so that the solution behaves, in many ways, like an ODE solution. As a corollary of our main results, we show that there are quasilinear wave equations that exhibit two distinct kinds of blowup: the formation of shocks for one non-trivial set of data, and ODE-type blowup for another non-trivial set.

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