/DT1/BRICK/Keyword3/Iflag

Engine Keyword Alternative time step calculation method for /TETRA4 using /PROP/SOLID I_tetra4=1000 solid elements.

It results in a lower but more accurate time step than the default calculation method. The result will be more robust and stable. Otherwise, this option is identical to /DT/BRICK/Keyword3/Iflag.

Format

/DT1/BRICK/Keyword3/Iflag

$Δ T_{s c a}$ $Δ T_{\min}$

If using /DT1/BRICK/CST/1, insert the next line

ASP_min VDEF_min

Definitions

Field	Contents	SI Unit Example
`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 certain values of `I`_smstr as defined in element properties. 4 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, /DT1/BRICK, then the default STOP option is used.
$Δ T_{s c a}$	Scale factor on critical time step. 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. 5 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. 5 Default = 0

Comments

The time step control will be activated when the time step of the element controlling the time step of the simulation becomes less than:
$\frac{Δ T_{\min}}{Δ T_{s c a}}$
/DT1/BRICK/Keyword3 can be used with /DT/NODA/Keyword3. It will also result in a more robust calculation of the time step, and a more stable computation.
This time step calculation is actually the same as default one, except for /TETRA4 using I_tetra4=1000.
/DT1/BRICK/CST is only active when I_smstr=2 or 12 is defined in /PROP/SOLID. It is compatible with /TETRA4 with I_tetra4=1000, /TETRA10, and /BRICK solid elements with I_solid=1, 2, 14, 17, or 24.
When using /DT1/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.