/DT/Eltyp/Keyword3/Iflag

Engine Keyword Element time step control.

Format

/DT/Eltyp/Keyword3/Iflag

$Δ T_{s c a}$ $Δ T_{\min}$

If using /DT/BRICK/CST/1, insert the next line:

ASP_min VDEF_min

Definitions

Data	Description	SI Unit Example
`Eltyp`	Entity selection: `BRICK` Brick elements `QUAD` Quad elements `SHELL` Shell elements. 7 `SH_3N` Triangular shell elements `TRUSS` Truss elements `BEAM` Beam elements `SPRING` Spring elements
`Keyword3`	Time step control type. 1 `CST` Elements are switched to small strain formulation to maintain the constant time step $Δ T_{\min}$ . Only valid for `Eltyp`=`BRICK` or `SHELL` and certain values of `I`_smstr as defined in element properties. 5 `DEL` The element which is controlling the time step is removed so that the constant time step $Δ T_{\min}$ can be maintained. `STOP` The run will stop if the time step reaches $Δ T_{\min}$ and a restart file will be written. If `Keyword3` is not specified, i.e. /DT/Eltyp, then the default `Keyword3` option for each `Eltyp` is used. 2
$Δ T_{s c a}$	Scale factor on critical time step for the option defined by `Eltyp`. Default = 0.9
$Δ T_{\min}$	Minimum time step
`Iflag`	Number of additional (optional) cards. Only used for /DT/BRICK/CST/1. = 0 or blank Only one card for $Δ T_{s c a}$ and $Δ T_{\min}$ is read. = 1 An additional card for `ASP_min` and `VDEF_min` are read.
`ASP_min`	Minimum Aspect ratio (Tet collapse); Solid elements for which aspect ratio ≤ `ASP_min` will be switched to small strain formulation to keep constant time step. 6 Default = 0
`VDEF_min`	Minimum Volume ratio (V/Vo); Solid element for which Volume change ≤ `VDEF_min` will be switched to small strain formulation to keep constant time step. 6 Default = 0

Comments

For all Keyword3 options, the time step control will be activated when the time step of the element controlling the time step of the simulation becomes less than:
$\frac{Δ T_{\min}}{Δ T_{s c a}}$

The table below lists the different available combinations of Eltyp and Keyword3. The default options are used when Keyword3 is not specified such as /DT/BRICK or /DT/SHELL.

	STOP	DEL	CST
`QUAD`	Default	Optional
`BRICK`	Default	Optional	Optional
`SHELL`, `SH_3N`	Optional	Default	Optional
`BEAM`, `TRUSS`, `SPRING`	Optional	Optional

For each Eltyp value, only one /DT/Eltyp/Keyword3 option can be used in a simulation.
/DT/Eltyp/Keyword3 can be used with /DT/NODA/Keyword3.
/DT/BRICK/CST is only active when I_smstr=2 or 12 is defined in /PROP/SOLID. It is compatible with /TETRA4 with I_tetra=0, /TETRA10, and /BRICK solid elements with I_solid=1, 2, 14, 17, or 24.
When using /DT/BRICK/CST/1, elements will be switched to small strain formulation when one of the two minimum values for ASP_min or VDEF_min have been reached. ASP_min uses the same tet collapse calculation as HyperMesh element quality check. Elements failing the ASP_min criteria will be switched to the small strain formulation at the beginning or during a simulation. VDEF_min can be used to switch highly deformed or compressed elements to the small strain formulation during the simulation thus avoiding negative volume issues that can arise.
A more conservative and thus lower time step calculation for shell elements can be activated by using, /DT1/SHELL.