/DT/CST_AMS

Engine Keyword This option is a combination of nodal time step (/DT/NODA/CST) and advanced mass scaling (/DT/AMS) with the same target time step.

All elements having an initial elementary time step lower than specified criteria are automatically selected for AMS. Classical constant nodal time step is applied on the rest of the model.

Format

DT/CST_AMS/Iflag

$Δ T_{s c a}$ $Δ T_{\min}$ $Δ T_{s c a_a m s}$

If Iflag =1 or 2, insert the next line

Tol_AMS

If Iflag =2, insert the next line

Niter Nprint

Definition

Field	Contents	SI Unit Example
`Iflag`	Number of additional (optional) lines. = 0 or blank Only one card for $Δ T_{s c a}$ and $Δ T_{\min}$ is read. =1 `Tol_AMS` are read from input. =2 `Tol_AMS`, `Niter`, and `Nprint` are read from input.
$Δ T_{s c a}$	Scale factor on critical time step. Default = 0.9
$Δ T_{s c a_a m s}$	Scale factor on critical time step for AMS (optional). Default = 0.67
$Δ T_{\min}$	Minimum time step. 2
`Tol_AMS`	Tolerance for AMS convergence. Default = 10^-3
`Niter`	Maximum number of iterations in conjugate gradient. Default = 1000
`Nprint`	Frequency (number of cycles) for writing additional output about the number of iterations before convergence in the conjugate gradient. Default = 0

Comments

The Starter keyword /AMS must be defined in the Starter input file.
The AMS is applied on an element when the initial elementary time step is less than:
$\frac{Δ T_{\min}}{Δ T_{s c a}}$
. If the element is not selected, then /DT/NODA/CST is applied.
The automatic element selection is performed in the Starter if the keyword /DT/CST_AMS is detected in the Engine input file. The element selection can be checked in the Starter output file.
The AMS element selection can also be visualized in animation files using the keyword /ANIM/ELEM/AMS.
For the AMS, if Iflag =0, the default values for Tol_AMS, Niter, and Nprint are used.
For the AMS, if Iflag =2, the maximum number of iterations in conjugate gradient Niter, and the frequency for additional output Nprint, must be entered. Otherwise, the maximum number of iterations in conjugate gradient is set to its default value (1000), and no additional output is provided.
For the AMS, if more than Niter iterations have been performed before convergence of the conjugate gradient, the following error message is output and the computation stops:
```
“** ERROR: AMS IS LIKELY DIVERGING”
```
For the AMS, if Nprint is specified, then at each Nprint cycle an additional output is provided including:
- the number of iterations before convergence of the conjugate gradient at this cycle
- the final residual norm, and the force vector norm
It is also possible to combine the automatic element selection with manual element selection based on a group of parts. The part group must then be specified in Radioss Starter Input deck (/AMS).
For additional information, refer to /DT/NODA/CST for constant nodal time step, /DT/AMS for the AMS and “Capabilities and Limitations and Limitations (may coexist, but out of the selected AMS part group) in Advanced Mass Scaling (AMS)” in the User Guide.