The time step tool is intended to assist in the selection of a time step for a numerical simulation that is based on the Courant number calculation. This tool can be thought of as the inverse of the Advective Courant Number tool. Refer to that documentation of the Adventive Courant Number tool for clarification. The objective of this tool is to compute the time step that would result in the specified Courant number for the given mesh and velocity field. The user would then select a time step for analysis that is at least as large as the maximum value in the resulting times step dataset. The tool computes the time step at each node in the selected geometry

${\displaystyle {\displaystyle TimeStep=CourantNumber*NodalSpacing/Velocity}}$

If the input velocity dataset is transient, the time step tool will create a transient dataset.

Typically, the Courant number specified for this computation is <= 1.0 for Courant limited solvers. Some solvers maintain stability for Courant numbers up to 2 or some solver specific threshold. Specifying a Courant number below the maximum threshold can increase stability since the computation is approximate.

#### Input Parameters

• Input dataset – Specify which velocity dataset will be used to represent particle velocity magnitude.
• Use courant number – Enter the threshold Courant value (or a number lower than the threshold for additional stability).

#### Output Parameters

• Advective time step dataset – Enter the name for the new dataset which will represent the maximum time step. (Suggestion: specify a name that references the input. Typically this would include the Courant number used in the calculation. The velocity dataset used could be referenced. The geometry is not necessary because the dataset resides on that geometry.)