I am working on a simple explicit-integration lumped-mass elastic FEM code which implements CST+DKT triangles (plate+shell) and constant-strain tetrahedra (http://woodem.eu/doc/theory/membrane-element.html, http://woodem.eu/doc/theory/tet4-element.html). The code focuses on contact dynamics, so FEM is there only to model flexible boundaries. I would like to add some kind of viscous damping to the model, and I am looking for some resource which is not overly complicated.I independently thought I could use the elastic stiffness matrix $\mathbf{K}$ (as in $f=\mathbf{K}u$), scaled by some viscosity factor $\eta'$ (that would be computed from material's $E$ and $\eta$), to compute viscous resisting force as $f_v=-\eta'\mathbf{K}\dot u$. It this formulation something known in literature? Or is it plain wrong?Thanks for pointers.
Resources for viscous behavior in simple FEM
finite element;stiffness;explicit methods