(21)
Here, Γ e represents the θr or zrside surface of the element region shown in Figure 2.n θ and n z are the inward
unit normal vectors concerning the side surface andS e is an element surface (θz surface).
Coefficients such as S θ,S z, and D θ are given by
the following equations using Eq. (12) evaluated by the screw diameter
at the element position and the barrel diameter, respectively.