/DT/GLOB/Iflag

Engine Keyword Global time step estimation, enables setting the time step to a higher value than the usual elementary or nodal time step.

Format

/DT/GLOB/Iflag

Δ T sca

If Iflag =1, insert the next line

Tol_GTS Ncycles

Definitions

Data Description SI Unit Example
Iflag Number of additional (optional) cards.
= 0 or blank
Only one card for Δ T sca is read.
=1
Tol_GTS and Ncycles are read from input. 2
  
Δ T sca Scale factor on critical time stop.

Default = 0.9

  
Tol_GTS Tolerance for GTS convergence.

Default = 10-3

  
Ncycles Frequency (number of cycles) for global time step estimation.

Default = 20

  

Comments

  1. If /DT/GLOB is used with /DT/NODA, the simulation begins with nodal time step and global time step follows.

    If /DT/GLOB is used alone or with /DT, the starting time step is element type step followed by global time step.

  2. If Iflag =1, the tolerance for GTS convergence, Tol_GTS and the frequency Ncycles for global time step must be entered.

    If Iflag =0 or is blank, default values for Tol_GTS and Ncycles are used.

  3. The Global Time Step option is available for the following features:
    • Solid elements: /TETRA4, /TETRA10, hexa with the flags below
    • /PROP/SOLID: Isolid = 1 (Belytschko), 14 (HA8), 17 (H8C), 24 (HEPH) and 16 (20-noded)
    • Shell elements: Ishell = 1 (Belytschko-Tsay), 12 (Batoz), and 24 (HEPH)
    • Truss element
    • Beam element
    • Contact interfaces: TYPE7, TYPE24 (without edge-to-edge option), and TYPE2 with Spotflag= 25 and 27.
  4. In most cases, default values are sufficient to ensure a stable run, however in cases where the global stiffness varies frequently due to oscillating contact conditions, it is recommended to increase the convergence tolerance, Tol_GTS= 0.05 and reduce the scale factor on time step, Δ T sca = 0.8.