单相流体，在迭代的步骤里加入了源项，这样，加速度得以显现。适合周期性边界条件(This program is free software; you can redistribute it and/or　　*
*　　 modify it under the terms of the GNU General Public License as　 *
*　　 published by the Free Software Foundation; either version 2 of　 *
*　　 the License, or (at your option) any later version.　　　　　　　*
*　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　*
*　　 This program is distributed in the hope that it will be useful,　*
*　　 but WITHOUT ANY WARRANTY; without even the implied warranty of　 *
*　　 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.　See the　　*
*　　 GNU General Public License for more details.)