%BND_free%

free surface boundary condition for velocities

For mathematical reference, see section 1.2 in DOCUMATH_LIQUID_BoundaryConditions.pdf Syntax:
BC_v($xyz$) = (%BND_free%) BC_v($xyz$) = (%BND_free%, \( S_{n_x}\), \( S_{n_y}\), \( S_{n_z}\), Thickness, RegularizationParameter),
where
  • (\( S_{n_x}, S_{n_y}, S_{n_z}\)) is the stress in normal direction with the normal pointing outwards, (optional, default 0,0,0 )
  • Thickness is the thickness of the control element, (optional, default is 0.0). In the pdf-document mentioned above, the control thickness is \( \delta h = \text{Thickness} \cdot H\)
  • RegularizationParameter is a numerical regularization parameter for the \( \frac{\partial}{\partial n}\)-operator. (optional, default 0.0 )
These parameters are optional! If not set, they are using the default value of 0. Good to know:
  • Make sure to set the Thickness to ZERO if using EULER, EULERIMPL or EULEREXPL!, i.e.
    BC_v($xyz$) = (%BND_free%, \( S_{n_x}\), \( S_{n_y}\), \( S_{n_z}\), 0.0 , RegularizationParameter),
  • 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.