Now, if we try to simulate this effect with traditional techniques on a coarse grid, we'll encounter a weird phenomenon: namely, the longer our simulation runs, the larger the volume of the sand becomes.

现在，如果我们尝试用传统方法在粗糙的网格上模拟这个效果，我们将会遇到一个奇怪现象：模拟的时间越长，沙子的体积就会变得越大。