COEFF_dt

Default: COEFF_dt = 0.2 In MESHFREE, each point computes his own local, time step size for the temporal discretization by \begin{align} dt^\text{local}_i = \text{COEFF\_dt} \cdot \min \left( \frac{h_i}{\|{\bf v}_i\|} , \sqrt{ \frac{h_i}{ \|{\bf g}_i\| } } , \sqrt{ \frac{1}{\sigma_i \cdot \nu } \cdot \rho h_i^{3} } \right) \end{align}

• The first term is the typical CFL condition (MESHFREE points should not move more than \( \text{COEFF\_dt} \cdot h_i\) per time step.
• The second term comes from gravity waves.
• The third term is motivated by surface waves due to surface tension. The complete derivation of this term is to be found in DOCUMATH_TimeStepCriterionSurfaceTension.pdf.

The global time step size is finally computed by \begin{align} dt^\text{global} = \min \limits_{i=1...N} \left( dt^\text{local}_i \right) \end{align} The time step restrictions come due to the fact, that the point movement in MESHFREE is explicit. For steering of the time step size in USER_common_variables, see TimeControl. Note: This parameter can also be set chamberwise for multiphase simulations (see also KindOfProblem, CHAMBER), e.g. If it is not set for specific chambers, it is automatically set according to the non-chamberwise definition for all chambers.