W = 1/6 [pi] d^3 x (i - f^3) [sigma], (20)
d²
Wk1² = 1/6 [pi] d^3 x -- (1 - f^5) [sigma], (21)
10
l² + d²
Wk2² = 1/6 [pi] d^3 x ------- (1 - f^5) [sigma]. (22)
20
Encyclopaedia Britannica, 11th Edition, "Hydromechanics" to "Ichnography" Volume 14, Slice 2 · 第 80 / 120 题