说明：  下列被集成在UDF 中的语句在求解过程中说明一个相的体积分数。它在求解过程的开始执行。这个函数建立一个中心在0.5, 0.5, 0.5，半径为 0.25的球形体。第二个相的体积分数1 被补充说明到球形体内的单元中，但是第二个相在其他单元中的体积分数为0
(The following statement is integrated in the UDF in the description of a phase volume fraction in the solution process. It performed at the beginning of the solution process. This function sets up a central spherical body in 0.5, 0.5, 0.5, with a radius of 0.25. The second phase volume fraction of a supplementary explanation to the spherical body unit, but the second phase in the other unit in the volume fraction of 0)