孔隙率＝孔隙体积/总体积圆筒直径D，高H，小球直径d民，数量为n总体积V0＝Hπ（D/2）^2小球体积V1＝n(4/3)π（d/2）^3孔隙体积V2＝Hπ（D/2）^2－n(4/3)π（d/2）^3孔隙率η＝V2/V0＝1－(2nd^3)/(3HD^2)
