On the lifespan of and the blowup mechanism for smooth solutions to a class of 2-D nonlinear wave equations with small initial data

Abstract

This paper is concerned with the lifespan and the blowup mechanism for smooth solutions to the 2-D nonlinear wave equation $\p_t^2u-\ds\sum_{i=1}^2\p_i(c_i^2(u)\p_iu)$ $=0$, where $c_i(u)\in C^{\infty }({\mathbb{R}}^n)$, $c_i(0)\ne 0$, and $(c_1^{\prime }(0){)}^2+(c_2^{\prime }(0){)}^2\ne 0$. This equation has an interesting physics background as it arises from the pressure-gradient model in compressible fluid dynamics and also in nonlinear variational wave equations. Under the initial condition $(u(0,x), \p_tu(0,x))=(\ve u_0(x), \ve u_1(x))$ with $u_0(x),u_1(x)\in C_0^{\infty }({\mathbb{R}}^2)$, and $\ve>0$ is small, we will show that the classical solution $u(t,x)$ stops to be smooth at some finite time $T_{\ve}$. Moreover, blowup occurs due to the formation of a singularity of the first-order derivatives $\na_{t,x}u(t,x)$, while $u(t,x)$ itself is continuous up to the blowup time $T_{\ve}$.

22 pages

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