Using 2D- Nodal velocity (line) and Strain type

[kuailebozai]

Hi all，
I am using 2D- Nodal velocity (line) to simulate a sinking boundary, however, there are a few material points at the boundary that are displaced more than the rest, what do I need to do so that the material points at the boundary keep falling at the same rate.
The strain output by ParaView is plastic strain or shear strain, how should I understand this. What is the maximum shear strain output in 2D plane strain and how should I choose it?