Formulas are one possibility, besides tables, that allow to specify a variable or parameter (velocity, temperature, etc) as a function of other independent variables ( e.g time or distance). You can add mathematical operations involving different variables, what gives you the chance to easily implement any distribution with no need to add a great number of discrete values in a table.
As for tables, not every variable is allowed to be defined as a function of another variables. If formulas are allowed, you can find the icon of a graph next to the variable you want to define.
Once you click on the icon, a dialogue box appears to define the table. You can click on the ‘Formula’ tab and access the interface where you can input your data as shown below.
Formula input interface for a velocity boundary condition.It is an example of formula input for a velocity boundary condition. Three velocity components can be defined in this case either as a single value or a formula. different units are available next to each component.
In grey, it appears the variables that can be included in the formula. In blue, all the numbers and operators available to create the formula, included trigonometric, exponential and logarithmic operations.
It is also possible to add conditional statements (<,>,=), useful for piecewise functions.