Block Format Keyword Describes the part group on which the advanced mass scaling is applied.


(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)


Field Contents SI Unit Example
grpart_ID Part group identifier.

(Integer, maximum 10 digits)



  1. Advanced Mass Scaling (AMS) allows setting the time step to a higher value than the usual elementary or nodal time step to the whole model or a group of its parts. /AMS allows specifying a group parts on which AMS is applied. To minimize computing time, it is advised to also apply classical mass scaling to the parts not belonging to /AMS part group, otherwise; no AMS processed parts are, by default, computed in natural Elementary time step. If no part group is specified (blank line) or is equal to 0, then AMS is applied to the model in its whole.
  2. AMS does not modify the global mass so that the global momentum of the related nodes is conserved. Engine keyword /DT/NODA/CST (or /DT/INTER/CST) can coexist with /DT/AMS for optimized computing time performances when /AMS is applied to only a group of parts.
  3. In order to activate /AMS on the part group or the entire model, keyword /DT/AMS (invoking AMS elementary time step) must be present in Engine Input. It should appear only once in the Starter input deck.
  4. If /DT/AMS is present in Radioss Engine Input, option /AMS is mandatory in Radioss Starter Input. It should appear only once in the Starter input deck.
  5. Rigid bodies, involving nodes where AMS applies, can be activated and deactivated with Engine keywords /RBODY/ON and /OFF, but not with sensors /SENSOR from Starter.
    • When using AMS, it is recommended to set Istf to 4 and stiffness scale factor set to its default value for interfaces TYPE7, TYPE11 and TYPE19. It is also recommended to set Iform to 2 (incremental stiffness formulation for Coulomb friction) whenever this formulation is available (for example: interfaces TYPE7, and TYPE19)
    • When using AMS and the interfaces TYPE7, TYPE11, and TYPE19 with a nonlinear penalty stiffness for contact, it may be necessary to use /DT/INTER/DEL in Radioss Engine input deck; otherwise, AMS may slowly converge, or possibly diverge.
  6. When using AMS, it is recommended to set the inertia to spherical (Ispher set to 1) for small rigid bodies.
  7. When using AMS, it is advised to set DOMDEC to 5 in option /SPMD (for versions 11.0.230 and above, set it to 0 and Radioss automatically applies the relevant DOMDEC option).
  8. For information about limitations related to AMS, refer to Capabilities and Limitations (AMS) in the User Guide.
  9. Automatic element selection for AMS can be activated if /DT/CST_AMS is present in Engine Input (Refer to /DT/CST_AMS for more information concerning automatic selection). If a group of part is specified alongside with automatic selection then the total element selection for AMS is the sum of the two selections.