%BND_free%
direct dynamic pressure boundary conditions at free surface
The pressure at the free surface is given by the dynamic, viscous stretch of the free surface. The general condition is:
\begin{align} p_\text{hyd} + p_\text{dyn} = p^{outer}_\text{dyn} + p^{outer}_\text{hyd} + p_{\sigma} + {\bf n}^T ( {\bf S}_\text{v} + {\bf S}_s ) {\bf n}\end{align}
Again, the hydrostatic part is already taken care of (see
%BND_free%), such that the remaining part for the dynamic pressure is (
OuterDynamicPressure =\( p^{outer}_\text{dyn}\)):
\begin{align} p_\text{dyn} = {\bf n}^T {\bf S}_\text{v} {\bf n} + p^{outer}_\text{dyn}\end{align}
If the
RelaxationFactor is used, we have the constraint (RelaxationFactor=\( \alpha\)):
\begin{align} p^{n+1}_\text{dyn} = p^{outer}_\text{dyn} + \alpha ( {\bf n}^T {\bf S}_\text{v} {\bf n} ) + (1-\alpha) p^{n}_\text{dyn}\end{align}
This will only be applied, if the
v-- solver is active for the present boundary point.
In order to detect free surfaces, the parameter
compute_FS must be set to 'YES' for the chamber, where the boundary condition shall be applied.