Time Step Control Methods
The time step can often be increased using some of these time step control methods.
Ignoring contact stiffness, the minimum time step of a simulation is a function of the mesh size, material stiffness, and density. Therefore, the first way to increase the time step of a model is to improve the mesh quality by modifying elements with small edge lengths relative to the average element length of the mesh.
Once the mesh is improved, another common problem is a reduction in time step, due to deformation of the mesh. As mentioned earlier, the minimum time step is calculated during each cycle of a simulation and as deformation occurs the elements size may reduce which cause a reduction in time step. If there is a large reduction in time step, there will be a large increase in simulation time. There are various methods to deal with the reduction in time step.
- /DT/option/Keyword3/Iflag
- $\text{\Delta}{T}_{sca}$ $\text{\Delta}{T}_{\mathrm{min}}$
- $\text{\Delta}{T}_{sca}$
- Scale factor for the critical nodal time step
- $\text{\Delta}{T}_{\mathrm{min}}$
- Minimum model time step that activates the time step control
For all options, the time step control is activated when $\text{\Delta}{T}_{\mathrm{min}}\ge \text{\Delta}{T}_{sca}*\text{\Delta}{t}_{option}$ ; where, $\text{\Delta}{t}_{option}$ is the time step calculation, based on the option being used such as nodal, element, or interface.
Element Type and Formulation | Strain Formulation | Negative Volume Handling Method |
---|---|---|
/BRICK, I_{solid} =1, 2, 14, 17, 24 /TETRA4, I_{tetra} = 0 /TETRA10 |
Full geometric nonlinearities I_{smstr} = 2, 4 |
Switch to small strain using element shape from cycle before negative volume |
Lagrange type total strain I_{smstr} = 10, 12 |
Lagrange type total strain with element shape at time=0.0 |
The automatic switch to small strain can be disabled by setting Keyword2 to STOP in /NEGVOL.