# /DT/NODA/Keyword3/Iflag (Obsolete)

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
 $\text{Δ}{T}_{sca}$ $\text{Δ}{T}_{\mathrm{min}}$ initial_mass_ratio
If Iflag=1, insert the next line
grnd_ID

## Definition

Field Contents SI Unit Example
Keyword3 Time step control type. 1
CST1
Nodal mass is increased to maintain a constant time step $\text{Δ}{T}_{\mathrm{min}}$ . 5 6
Recommend $\text{Δ}{T}_{sca}$ =0.67.
CST2
Nodal mass is increased to maintain the constant time step $\text{Δ}{T}_{\mathrm{min}}$ . Improved formulation. 5 6
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.
initial_mass_ratio Mass ratio increases at the beginning of the computation is used to increase the minimum time step. This value is entered as a ratio, so a 5% increase in mass is entered as 0.05.

Default = blank or 0

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 the defined timestep divided by $\text{Δ}{T}_{sca}$ .
4. For constant nodal time step options, the time step used at the beginning of the simulation is the maximum of $\text{Δ}{T}_{\mathrm{min}}$ or, time step calculated with mass added by initial_mass_ratio. The initial time step will then be maintained during the simulation by adding additional mass, if needed.
 /DT/NODA/Keyword30 $\text{Δ}{T}_{\mathrm{min}}$ The computation is done with minimum nodal time step of $\text{Δ}{T}_{\mathrm{min}}$ value. Mass will be added to maintain this timestep. /DT/NODA/Keyword30 $\text{Δ}{T}_{\mathrm{min}}$ 0 /DT/NODA/Keyword30 $\text{Δ}{T}_{\mathrm{min}}$ 0.05 Radioss calculates a nodal time step to give 0% of initial mass increase and uses the maximum value of this calculated time step and defined $\text{Δ}{T}_{\mathrm{min}}$ .