/SHSUB

Engine Keyword Enables you to activate new sub-cycling option, for which I_subcycle =2 in the /ANALY Radioss Starter option should be specified.

Format

/SHSUB/NSH print/NSH ctrl

Definitions

Data	Description	SI Unit Example
`NSH print`	Defines the output frequency (in the output file or .out file in new extension) for the shell elements, over sub-cycles (that is to say over the only cycles for which internal forces of shell elements are computed).
`NSH ctrl`	In some cases where the sub-cycling time step falls down, shells may need to be computed each cycle and this process may require to be more CPU time-consuming than deactivating sub-cycling. Default = 1000

Comments

It is possible to make a run with sub-cycling and to switch after restart to a non sub-cycling (standard) computation, and reciprocally.
NSH print defines the output frequency (in the output file .out in new extension) for the shell elements, over subcycles (that is to say over the only cycles for which internal forces of shell elements are computed).
With a negative value, the printing is also done to the standard output.

This additional output to the .out file for Radioss Engine will be written with frequency NSH_print over subcycles:
in case of /DT/SHNOD (nodal time step for SHELL and SH3N elements sub-cycling):
```
NC T DTSUB NODE SUBCYCLE
```
Where,

NC

Current cycle number

T

Current time

DTSUB

Time step for sub-cycling

NODE

SUBCYCLE

node_ID

Sub-cycle number

At this time, the node_ID gives the time step for sub-cycling.
else:
```
NC T DTSUB SHELL or SH3N SUBCYCLE
```
Where,

NC

Current cycle number

T

Current time

DTSUB

Time step for sub-cycling

SHELL or SH3N

shell_ID or sh3n_ID

SUBCYCLE

Sub-cycle number

At this time, the shell_ID or sh3n_ID gives the time step for sub-cycling.
NSH ctrl has been introduced with the /SHSUB keyword, since in case of the sub-cycling time step falls down, shells may need to be computed each cycle and this process may become some more CPU time consuming than deactivating sub-cycling.
Indeed, shells and 3-nodes shell elements are computed each $D t$ time step, corresponding to the $D t$ stability time step for shells: sub-cycling time step is a stability time step related to shells.

NSH ctrl: if NSH ctrl cycles are computed without sub-cycling, that is to say if shell elements are computed each cycle during NSH ctrl consecutive cycles, the sub-cycling method will be deactivated by Radioss Engine.
Shells and 3-nodes shell elements are computed each $D t$ time step, corresponding to the $D t$ stability time step for shells: sub-cycling time step is a stability time step related to shells.
In case of element time step (/DT/NODA is not specified in the Radioss Engine Input deck):
$D t = Δ T_{s c a} \cdot \min_{o v e r _ s h e l l s _ a n d_3 - n o d e s _ s h e l l s} (l c / c)$

Where,

$l_{c}$

Characteristic length

c

Sound speed of the related material

Parameters of /DT/SHELL will be considered, especially for the value of $Δ T_{s c a}$ (default value is 0.9). Parameters of the sub-options /DT/SHELL will be normally considered.
In case of nodal time step (/DT/NODA is specified in the Radioss Engine Input deck).
$D t = Δ T_{s c a} \cdot \min_{o v e r _ n o d e s _ c o n n e c t e d _t o _ s h e l l s} s q r t (2 \cdot m / K s h)$

Where,

m

Nodal mass

Ksh

Stiffness corresponding to the connected shells

$Δ T_{s c a}$

The value given in /DT/NODA; but may be changed by using /DT/SHNOD