global shell的用法和樣例：
例句
- The compatible boundary conditions are evidently uniform tractions applied on the inner and outer surfaces of the shell.
可相容的邊值條件顯然是作用在球殼的內表面和外表面上的均勻曳力。 - A particle inside the shell is drawn equally in all directions and experiences no force at all.
在球殼內部的質(zhì)點(diǎn)，因被對等地吸引向各個(gè)方向，所以完全沒(méi)有感受到力。
