/DT/NODA/Keyword3/Iflag

Engine Keyword Activates the nodal time step control method with the option to apply mass scaling to increase a model’s time step.

Format

/DT/NODA/Keyword3/Iflag: $Δ T_{s c a}$ $Δ T_{\min}$
If Iflag=1, insert the next line: grnd_ID

Definitions

Data	Description	SI Unit Example
`Keyword3`	Time step control type. 1 `CST` Use default constant time step method, /DT/NODA/CST2. 5 6 `CST1` Nodal mass is increased to maintain the constant time step $Δ T_{\min}$ . Recommend $Δ T_{s c a}$ =0.67 `CST2` (Default) Nodal mass is increased to maintain the constant time step $Δ T_{\min}$ . Improved formulation. `SET` Reduce the equivalent nodal stiffness to maintain the constant time step, $Δ T_{\min}$ `STOP` The simulation will stop if the time step reaches $Δ T_{\min}$ and a restart file will be written. If `Keyword3` is not specified, as in /DT/NODA/`Iflag`, then the computation will use the nodal time step and $Δ T_{\min}$ is not used.
`Iflag`	Node group flag. =0 or blank All nodes use the nodal time step method. =1 The nodal time step method is only applied to the nodes in node group `grnd_ID`.
$Δ T_{s c a}$	Scale factor on critical nodal time step. Default = 0.9
$Δ T_{\min}$	Minimum time step
`grnd_ID`	The nodal time step method is only applied to the nodes in this node group, read only if `Iflag`=1.

Comments

For all Keyword3 options, the time step control will be activated when the time step of the node controlling the time step of the simulation becomes less than:
$\frac{Δ T_{\min}}{Δ T_{s c a}}$
Only one /DT/NODA/Keyword3 option can be used in a simulation.
When using Nodal time step, the computation of each cycle is slightly more expensive but the time step can be higher especially for low quality meshes.
When /DT/NODA/Iflag is used, the computation will use the nodal time step method and $Δ T_{\min}$ is not used.
To determine how much mass will be added to a model, Radioss calculates a target time step for different amounts of percent mass increase and prints this information as a table and a graph in the Starter output file.
/DT/NODA/Keyword3 is compatible with all options of /DT/Eltyp/Keyword3.
/DT/NODA and /DT/NODA/CST* are compatible with /DT/INTER/AMS from version 2017.2.3.
/DT/NODA/CTS* is compatible with advanced mass scaling, /DT/AMS. If used with /DT/AMS, AMS will be applied to the part group defined in Starter /AMS card and /DT/NODA/CST* applied to nodes not belonging to the AMS part group.
For example:
- /DT/AMS/1
- $Δ T_{s c a 1}$ $Δ T_{\min 1}$
- Tol_AMS
- /DT/NODA/CST, /DT/NODA/CST1, /DT/NODA/CST2
- $Δ T_{s c a 1}$ $Δ T_{\min 1}$
This is even advised in order to minimize computing time in models where AMS only applies to selected parts.
Note: It is pointless to use a higher time step in AMS than the one used in classic mass scaling since the smaller time step limits the performance.