5.7 Computational Timestep
5.7.2 Description
The computational timestep defines how frequently TUFLOW FV updates the model state during a simulation. It directly influences model stability, accuracy, and model run times.
TUFLOW FV uses an adaptive computational timestep that changes during a simulation in response to flow and scalar concentration stability constraints. Timestep selection and timestep science is described in Appendix B.4.3 and Appendix B.4.5.2. The computational timestep model implementation is summarised in Table 5.10, with a link to the relevant implementation section below. The commands affecting TUFLOW FV’s computational timestep are provided in Table 5.11.
| Model Implementation | Description |
|---|---|
| Computational Timestep | Sets timestep limit and timestep stability constraints. |
| Command | Description |
|---|---|
| Timestep Limits | Required - Sets the limiting value for the lower and upper timestep for the simulation. |
| CFL | Optional - Assigns the global computational stability constraints. |
| CFL Internal | Optional - Command to override the global CFL stability constraint for internal mode calculations. |
| CFL External | Optional - Command to override the global CFL stability constraint for external mode calculations. |
5.7.3 Computational Timestep
The following example is a typical setup for a 2D HD simulation where a single CFL constraint is used.
This example shows the use of differing internal and external model CFL numbers. This can be of use to improve model stability and speed when internal model processes are constraining the overall model timestep.