## Line theory: Interaction with seabed and shapes |

Nodes are subjected to reaction forces from the seabed and any elastic solids with which they come into contact. The contact occurs at the outer edge of the line, as specified by the outer contact diameter. The penetration reaction force $\vec{f}_\mathrm{R}$ takes the form \begin{equation} \vec{f}_\mathrm{R} = r(d)\ a\ \vec{n} \end{equation} where

$d=$ depth of penetration, allowing for the outer contact diameter

$r(d)=$ reaction force per unit contact area at penetration $d$

$a=$ contact area = outer contact diameter multiplied by the length of line represented by the node

$\vec{n}=$ unit vector in the reaction force direction for seabed or shapes.

If explicit integration is used in the dynamic analysis, nodes may also experience a damping force. For details of both the reaction force and the damping force, see seabed theory and shape theory.

Frictional forces are also modelled when contact occurs, using the seabed friction coefficient and friction coefficient data, and following the model described in friction theory.