# /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
$\text{Δ}{T}_{sca}$ $\text{Δ}{T}_{\mathrm{min}}$
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 $\text{Δ}{T}_{\mathrm{min}}$ .
Recommend $\text{Δ}{T}_{sca}$ =0.67
CST2 (Default)
Nodal mass is increased to maintain the constant time step $\text{Δ}{T}_{\mathrm{min}}$ . Improved formulation.
SET
Reduce the equivalent nodal stiffness to maintain the constant time step, $\text{Δ}{T}_{\mathrm{min}}$
STOP
The simulation will stop if the time step reaches $\text{Δ}{T}_{\mathrm{min}}$ 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 $\text{Δ}{T}_{\mathrm{min}}$ 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.

$\text{Δ}{T}_{sca}$ Scale factor on critical nodal time step.

Default = 0.9

$\text{Δ}{T}_{\mathrm{min}}$ 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.

1. 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:

$\frac{\text{Δ}{T}_{\mathrm{min}}}{\text{Δ}{T}_{sca}}$

2. Only one /DT/NODA/Keyword3 option can be used in a simulation.
3. 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.
4. When /DT/NODA/Iflag is used, the computation will use the nodal time step method and $\text{Δ}{T}_{\mathrm{min}}$ is not used.
5. 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.
6. /DT/NODA/Keyword3 is compatible with all options of /DT/Eltyp/Keyword3.
7. /DT/NODA and /DT/NODA/CST* are compatible with /DT/INTER/AMS from version 2017.2.3.
8. /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
• $\text{Δ}{T}_{sca1}$ $\text{Δ}{T}_{\mathrm{min}1}$
• Tol_AMS
• /DT/NODA/CST, /DT/NODA/CST1, /DT/NODA/CST2
• $\text{Δ}{T}_{sca1}$ $\text{Δ}{T}_{\mathrm{min}1}$
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.