/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
$\text{\Delta}{T}_{sca}$ $\text{\Delta}{T}_{\mathrm{min}}$
If using /DT1/BRICK/CST/1, insert the next line
COL_min Vdef_min
If using /DT1/BRICK/DEL/1, insert the next line:
COL_min Vdef_min ASP_max Vdef_maxDefinition
Field  Contents  SI Unit Example 

Keyword3  Time step control
type. 1
If Keyword3 is not specified, that is, /DT1/BRICK, then the default STOP option is used. 

$\text{\Delta}{T}_{sca}$  Scale factor on
critical time step. Default = 0.9 

$\text{\Delta}{T}_{\mathrm{min}}$  Minimum time step.  
Iflag  Number of additional
(optional) cards. Only required for
/DT1/BRICK/CST/Iflag or
/DT/BRICK/DEL/1.


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. 5
6
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. 5
6
Default = 0 

ASP_max  Maximum aspect ratio
to deleted solid element. If Ndir ≥
1, the element is deleted and SPH elements
are activated. 6
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. 6 Used only if different from 0. 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:
$\frac{\text{\Delta}{T}_{\mathrm{min}}}{\text{\Delta}{T}_{sca}}$
 /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.
 With
/DT/BRICK/CST/1, solid elements will be switched to small
strain formulation when criteria COL_min,
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
switch 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.