the drill rotation怎么理解？

smilew

在能量输出里面有ALLAE:“Artificial” strain energy associated with constraints used to remove singular modes (such as hourglass control) and with constraints used to make the drill rotation follow the in-plane rotation of the shell elements.不怎么理解，其中那个the drill rotation 更不知道是什么啦？怎么理解呢？请指点一下,感谢！