# Starter

## Only Keyword

Only /AMS must be present in order to apply the AMS to either a
designated group of parts, or the entire model, if followed by a blank line (Radioss Starter Input).

CAUTION: /DT/AMS
is mandatory in Radioss Engine Input followed by the scale
factor and the targeted increased time step to activate AMS (Radioss Engine Input). Without /DT/AMS in the
Engine file, /AMS in the Starter file is ignored.

## HMPP / SPMD

If `DOMDEC` is set to 0, the Starter points to 3 (Multi-level Kway
decomposition) by default. Up until version 11.0.230, if /AMS is applied,
DOMDEC must be manually switched to 5 (DOF-based Multi-level Kway
decomposition). As of version 11.0.240, the Starter automatically sets
DOMDEC to 5, if it is set to 0 and if /AMS is
present, otherwise, DOMDEC will be set to 3, if /AMS
is absent.

## Interfaces

- It is recommended to use Interface stiffness flag
`I`_{stf}= 4 $K=\mathrm{max}\left[S{t}_{\mathrm{min}},\mathrm{min}\left(S{t}_{\mathrm{max}},{K}_{n}\right)\right]$ with ${K}_{n}=\mathrm{min}\left({K}_{m},{K}_{s}\right)$ and Stiffness scale factor`Stfac`= 1 (default value) for contact interfaces TYPE7, TYPE11, and TYPE19. - If friction is involved, it is advised to set the friction penalty formulation type,
`I`_{form}to 2 (incremental stiffness for Coulomb friction), whenever this option is available (/INTER/TYPE7, and /TYPE19. - For AMS, like in standard mass scaling, it is recommended to not have friction in a
TYPE11 contact, if a TYPE7 (already handling
friction) contact is already defined for the same parts. This avoids drops of time step
and helps model convergence. This recommendation becomes obsolete, if
TYPE11 friction is using
`I`_{form}=2 for edge-to-edge contacts, as of version 13.0. - With contact interfaces TYPE7, TYPE11, and TYPE19 using nonlinear penalty stiffness for contact, it might be necessary to use the /DT/INTER/DEL option in the Radioss Engine input deck. Otherwise, AMS may slowly converge, or may diverge.
- Using /DT/INTER/AMS is meaningless when using /DT/AMS, but /DT/INTER/AMS can be used, instead of /DT/NODA/CST when contacts highly affect the time step.
- Initial intersections and penetrations should be removed, as much as possible (as well
as in traditional mass scaling, notably if it is used for comparison with the AMS
results).CAUTION: Barriers, other impactors, and more particularly dummies contain a lot of interfaces that must NOT be modified since their validation is based on their original /INTER options (if modified, their validation is not guaranteed).

## Rigid Bodies

- Small rigid bodies inertia should rather be spherical with
`I`_{spher}set to 1.CAUTION: Dummies contain a lot of small rigid bodies that must NOT be modified since their validation is based on their original /RBODY options (if modified, their validation is not guaranteed). - Flying nodes: are not a limitation but they should be removed, as well as unconnected small rigid bodies that are not needed.
- Rayleigh damping: in few cases where the elastic domain remains large along the
simulation, poor AMS performances with noisy time history curves (example, force-time) and
Harlequin patterns in contour plots (example, von Mises) may be observed. A significant
improvement should occur by inserting a Rayleigh damping card (/DAMP in
the Starter file) affecting the parts subject to AMS using these parameters:
$\alpha =0$ and $\beta =0.05\text{\Delta}{t}_{AMS}$

(with $\text{\Delta}{t}_{AMS}$ is AMS target time step, so $\beta $ is 5% times the AMS target time step). Such a modification may allow to increase the AMS target time step for much better AMS performances.Note: It is not advised to use numerical damping (dm or Navier-Stokes), instead of Rayleigh damping, here.