Time Step Output from a Model

The time step of the initial model is output to the Starter output file. Whereas the time step of a running model can be output to the animation files.

Initial Model Time Step

Various methods are available to find the time step of a model. Some preprocessors can calculate and display the time step of a mesh. When the Radioss Starter is executed, the time step, based on element types and nodes is written in the Starter output file runame_0000.out. These time step values are calculated using the formulas above and do not include the time step scale factor.

A histogram showing the distribution of the nodal time step in the model is also printed in the Starter output file.

Running Model Time Step

When the Radioss Engine is running, the nodal time step can also be written to the animation output files using the output option /ANIM/NODA/DT or /H3D/NODA/DT. The element time step is available using /ANIM/ELEM/DT or /H3D/ELEM/DT. The animation file can then be contour plotted in HyperView to observe the time step of the elements in a simulation.

The time step can also be viewed in the Engine output file. The frequency can be set using the /PRINT/#, where the time step is written every # cycles, or the time step information of the current cycle can be output using the /INFO command in a Control File (C-File).

If element time step is being used, the element type and ID of the element with the minimum time step will be printed in the Engine output file. If there is a contact interface in the model, a node or interface can be listed as having the minimum time step and described in Time Step Control Methods.

Time Step Controlled by an Element

  CYCLE    TIME      TIME-STEP  ELEMENT          ERROR  
     0   0.000      0.2043E-03 SHELL        202   0.0% 
  1000  0.2043      0.2043E-03 SHELL        201   0.0% 
  2000  0.4086      0.2043E-03 SHELL        201   0.0% 
  3000  0.6129      0.2043E-03 SHELL        201   0.0% 
  4000  0.8171      0.2043E-03 SHELL        201   0.0%

If nodal time step control is being used, the Engine output file will typically say that a NODE is controlling the time step and list the node ID. How is it possible that the time step is controlled by a node even while using elementary time step (i.e did not specify /DT/NODA)? describes a situation where the time step, based on the contact stiffness is the minimum time step in a simulation based on: (1)

Δ t_{i n t e r n o d a l} = \sqrt{\frac{2 M_{n o d a l}}{\sum (K_{i n t e r f a c e} + K_{e l e m e n t})}}

Time Step Controlled by a Node

 CYCLE     TIME      TIME-STEP  ELEMENT          ERROR
     0   0.000      0.5317E-06 NODE       20404   0.0% 
  1000  0.5317E-03  0.5317E-06 NODE       20404   0.0% 
  2000  0.1063E-02  0.5317E-06 NODE       20404  -0.4% 
  3000  0.1595E-02  0.5317E-06 NODE       20404  -1.0%    
  4000  0.2127E-02  0.5317E-06 NODE       20404  -0.9%

If the kinematic time step of a contact interface has the minimum time step in the model, the Engine output file will say that INTER is controlling the time step and list the contact interface ID. When this happens, secondary node(s) of a contact interface are moving so fast that they will pass through the main contact surface in one time step cycle and thus to prevent this from happening the time step of the simulation is reduced. Using /DT/INTER/DEL in Radioss Engine file (Runname_0001.rad). How is it possible that the time step is given in the output file (Runname_0001.out) by an interface, and is lower than the minimum value given in /DT/INTER/DEL? provides more details.

Time Step Controlled by a Contact Interface

  CYCLE    TIME      TIME-STEP  ELEMENT          ERROR  
     0   0.000      0.1093E-04 INTER         35   0.0% 
  1000  0.1093E-4   0.1093E-04 INTER         35   0.0% 
  2000  0.2186E-4   0.1093E-04 INTER         35   0.0% 
  3000  0.3279E-4   0.1093E-04 INTER         35   0.0% 
  4000  0.4372E-4   0.1093E-04 INTER         35   0.0% %