Figure 7.

Contact model with solid boundaries. Obstacles and surfaces (grey) are modelled as soft boundaries allowing for the interpenetration ϵ=r−d with the elements of the filament (blue) characterized by radius r and distance d from the substrate. The surface normal u^w_⊥ determines the direction of the wall’s response F^w_⊥ to contact. We note that F^w_⊥ balances the sum of all forces F_⊥ that push the rod against the wall, and is complemented by the other two components, which allow it to amend to possible interpenetration due to numerics. These components are an elastic one (k_wϵ) and a dissipative one (γ_wv⋅u^w_⊥), where k_w and γ_w are, respectively, the wall stiffness and dissipation coefficients.