Engine Keyword Element time step control.



Δ T sca Δ T min

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

ASP_min VDEF_min


Data Description SI Unit Example
Eltyp Entity selection:
Brick elements
Quad elements
Shell elements. 7
Triangular shell elements
Truss elements
Beam elements
Spring elements
Keyword3 Time step control type. 1
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 Ismstr as defined in element properties. 5
The element which is controlling the time step is removed so that the constant time step Δ T min can be maintained.
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 sca 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 sca 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



  1. 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:

    Δ T min Δ T s c a

  2. 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.
    QUAD Default Optional  
    BRICK Default Optional Optional
    SHELL, SH_3N Optional Default Optional
    BEAM, TRUSS, SPRING Optional Optional  
  3. For each Eltyp value, only one /DT/Eltyp/Keyword3 option can be used in a simulation.
  4. /DT/Eltyp/Keyword3 can be used with /DT/NODA/Keyword3.
  5. /DT/BRICK/CST is only active when Ismstr=2 or 12 is defined in /PROP/SOLID. It is compatible with /TETRA4 with Itetra=0, /TETRA10, and /BRICK solid elements with Isolid=1, 2, 14, 17, or 24.
  6. 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.
  7. A more conservative and thus lower time step calculation for shell elements can be activated by using, /DT1/SHELL.