TimeControl

The possible commands for initial time, final time, and time step control are described below. As Meshfree performs a transient simulation, the simulation time interval must be specified in any setting. Optionally, the simulation can be performed for a maximum of TimeIntegration_N_final timesteps. The simulation will stop if either TimeIntegration_N_final timesteps have been performed or the simulation time has reached Tend.

Non-adaptive Timestep size

The Ucv-parameter

indicates that the timestep size does not automatically adapt to the flow characteristics. (e.g. CFL-conditions)

Meshfree steadily increases the timestep size from DELT_dt_start until DELT_dt is reached. The cv-parameter time_step_gain limits the change rate of the timestep size. If DELT_dt is smaller than DELT_dt_start, then the timestep size is constant DELT_dt_start.

Adaptive timestep size (recommended)

The Ucv-parameter

indicates that the timestep size automatically adapts to the flow characteristics in the simulation such that CFL conditions are met, see parameter COEFF_dt.

Also here, the cv-parameters time_step_loss and time_step_gain limit the change rate of the timestep size. Additional USER defined timestep size criterions can be defined per material with the DELT_dt_AddCond.

For EULERIMPL, additionally the criterions defined by TOL_T, TOL_v and TOL_keps are considered for the choice the timestep size.

Good to know:

• Apart from DELT_dt_AddCond, all parameters are read exactly once at the beginning of the simulation and can thus only contain scalar values (not equations!)
• The local proposed timestep size is calculated per point and is available in the index %ind_dt_local%.