基本沒深入，因為目前還用不到這里。

OpenFOAM 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 3 of the License, or
??? (at your option) any later version.

??? OpenFOAM 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.