%BND_free%

direct dynamic pressure boundary conditions at free surface

BCON($BCindex$,%ind_p_dyn%) = ( %BND_free% ) BCON($BCindex$,%ind_p_dyn%) = ( %BND_free%, OuterDynamicPressure ) BCON($BCindex$,%ind_p_dyn%) = ( %BND_free%, OuterDynamicPressure, RelaxationFactor )
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.