/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 sca 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 sca =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 sca 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

  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:

    Δ T min Δ T s c a

  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 Δ T 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
    • Δ T sca1 Δ T min1
    • Tol_AMS
    • /DT/NODA/CST, /DT/NODA/CST1, /DT/NODA/CST2
    • Δ T sca1 Δ T min1
    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.