TimeStepCriteria

In a DROPLETPHASE chamber, MESHFREE, computes the local, time step size by \begin{align} dt^{local}_i = \min \left( \text{COEFFdt} \cdot \frac{h_i}{\|{\bf v}_i\|}, C_{d30} \cdot \frac{D_i}{2} \frac{1}{ \|{\bf v}_i\| } , C_{coll} \cdot \sqrt{\frac{m_i}{k_i}} \right) \end{align}

• Remarks on the first term
  • If subcycling (see COMP_DropletphaseSubcycles) gets activated the first term maybe reduced by a factor equal to the ratio of the sum of all substeps to the local time step \( \Sigma \Delta t_{sub} / \Delta t_{global}\).
  • The smoothing length \( h_i\) maybe be decreased by up to the factor given in H:MIN_FACTOR if to many neighbours collect at the same place, for performance reasons.
  • The first term is dependent by the smoothing length. In this sense the user can always take control of this criteria by the definition the smoothing length in the corresponding chamber. However, in LiquidLayer approximations the quality of the results may be affected by an excessive increase of the time step. If H:MIN_FACTOR is chosen to large an increase of smoothing length may also lead to many neighbours and therefore lead to a poor performance.
• The second term corresponds to the time step criteria depending on the droplet diameter %ind_d30%. This is only active if COEFF_dt_d30 > 0 . See COEFF_dt_d30
• The third term corresponds to the time step criteria for the collision modell. This is only active if COEFF_dt_coll > 0 . See COEFF_dt_coll

Remarks:

Additional criteria may be defined by DELT_dt_AddCond

If a LIQUID chamber is present, and COMP_dt_indep = 0, then additional time step criteria from this chamber are described in COEFF_dt