圆锥漏斗的底面半径 r = Rφ/(2π),高 h = √(R^2-r^2) = R√(4π^2-φ^2)/(2π),容积 V = πhr^2/3= (π/3) [Rφ/(2π)]^2 [R√(4π^2-φ^2)/(2π)]= [R^3/(24π^2)] φ^2√(4π^2-φ^2)
