Engine Keyword Interface time step control.



Δ T sca Δ T min

If using /DT/INTER/AMS/1, insert the next line.



Field Contents SI Unit Example
Keyword3 Time step control type. 1:
Use default constant time step method, /DT/INTER/CST2.
Nodal mass of interface secondary node is increased to maintain the constant time step Δ T min .
CST2 (Default)
Nodal mass of interface secondary node is increased to maintain the constant time step Δ T min . Improved formulation.
The impacting secondary node is deleted from the contact interface so that constant time step Δ T min can be maintained.
The run will stop if the time step reaches Δ T min and a restart file will be written.
Advanced Mass Scaling is used on the interface secondary nodes to maintain the constant time step Δ T min .

If Keyword3 is not specified, that is, /DT/INTER, then Δ T min is not used and Δ T sca is used for TYPE7 contacts only.

Iflag Number of additional (optional) cards. Only used when Keyword3=AMS.
= 0 or blank
Only Δ T sca and Δ T min is read.
= 1
Additional card for Tol_AMS is read.
Δ T sca Scale factor on critical time step for interface.

Default = 0.9

Δ T min Minimum time step.  
Tol_AMS Tolerance for AMS convergence - only used for /DT/INTER/AMS/1.

Default = 10-3



  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. All Keyword3 options are only applicable for TYPE7, TYPE10, TYPE11, and TYPE19 interfaces.
  3. Keyword3= STOP also applies to TYPE21 interfaces.
  4. Both /DT/INTER/CST and /DT/INTER/AMS can be used at the same time as /DT/INTER/DEL or /DT/INTER/STOP.
  5. /DT/INTER/Keyword3 can be combined with /DT/NODA or /DT/NODA/CST.
  6. For Keyword3=AMS
    • Advanced Mass Scaling does not modify the global mass, so that the global momentum of the related nodes is conserved. Therefore, /DT/INTER/AMS is more accurate than /DT/INTER/CST, /DT/INTER/CST1 and /DT/INTER/CST2.
    • /DT/INTER/AMS is compatible with the following kinematic conditions: boundary conditions, imposed velocities, imposed displacements, imposed accelerations, tied interfaces (/INTER/TYPE2), rigid bodies, fixed rigid walls, rigid links and cylindrical joints.
    • /DT/INTER/AMS is compatible with dynamic relaxation (/DAMP) and Rayleigh damping (/DAMP).
    • /DT/INTER/AMS will not work if applied to nodes involving rivets (/RIVET) or Lagrange multipliers (for example, /MPC and /GJOINT). In such cases, an error is output by the Radioss Engine.
    • The rigid bodies which are connected to nodes where AMS applies can be activated/deactivated during Radioss Engine run through /RBODY/ON and /RBODY/OFF, but not with sensors.
    • /DT/INTER/AMS always applies to the whole model, except that it is possible to use Elementary time step for AMS (/DT/AMS) on a part group and to use /DT/INTER/AMS at the same time: /DT/INTER/AMS will then apply to nodes which are not belonging to the part group.
      For example:
      • /DT/AMS/1
      • Δ T sca Δ T min
      • Tol_AMS
      • /DT/INTER/AMS
      • Δ T sca Δ T min
    • Elementary time step for Advanced Mass Scaling will apply on the part group declared in /AMS of the Radioss Starter Input deck, but /DT/INTER/AMS will apply to nodes which do not belong to the part group.