/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:

COL_min Vdef_min

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

COL_min Vdef_min ASP_max Vdef_max

Definition

Field	Contents	SI Unit Example
`Eltyp`	Entity selection: `BRICK` Brick elements `QUAD` Quad elements `SHELL` Shell elements. 8 `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, that is, /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 or /DT/BRICK/DEL/1. = 0 or blank Only one card for $Δ T_{s c a}$ and $Δ T_{\min}$ is read. = 1 An additional card for `COL_min`, `Vdef_min`, `ASP_max` and `Vdef_max` are read.
`COL_min`	Minimum collapse ratio to switch solid element to small strain formulation (to keep constant time step) or to deleted solid element. If `Ndir` ≥ 1, the element is deleted and SPH elements are activated. 6 7 Default = 0
`Vdef_min`	Minimum volume ratio (V/Vo) to switch solid element to small strain formulation (to keep constant time step) or to deleted solid element. If `Ndir` ≥ 1, the element is deleted and SPH elements are activated. 6 7 Default = 0
`ASP_max`	Maximum aspect ratio to deleted solid element. If `Ndir` ≥ 1, the element is deleted and SPH elements are activated. 7 Used only if different from 0. Default = 0
`Vdef_max`	Maximum volume ratio (V/Vo) to deleted solid element. If `Ndir` ≥ 1, the element is deleted and SPH elements are activated. 7 Used only if different from 0. 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.
With /DT/BRICK/CST/1, solid elements will be switched to small strain formulation when criteria for COL_min or Vdef_min is reached.
- COL_min uses the same collapse ratio calculation as in HyperMesh element quality check.
- Elements failing the COL_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.
With /DT/BRICK/DEL/1, solid elements will be deleted, or switched to SPH elements if Ndir ≥ 1 in the solid property, when criteria COL_min, Vdef_min, ASP_max or Vdef_max is reached.
- COL_min and ASP_max use the same collapse ratio and very similar aspect ratio calculation as in HyperMesh element quality check. For thickshell, thickness direction is not taken into account, then aspect ratio 2D and collapse ratio 2D (L_min/L_max) are used to compute COL_min and ASP_max.
- Elements failing the COL_min or ASP_max criteria will be used to delete or switch to SPH elements (if Ndir ≥ 1 in the solid property) at the beginning or during a simulation.
- Vdef_min or Vdef_max can be used to delete or switch to SPH elements (if Ndir ≥ 1 in the solid property) when the solid element is highly deformed.
A more conservative and thus lower time step calculation for shell elements can be activated by using, /DT1/SHELL.
A more conservative and thus lower time step calculation for solid elements can be activated by using, /DT1/BRICK.