I want to create an expression used to define a boundary condition.

The expression needs to be able to calculate the specified boundary condition at different time(s).

For example, the inlet velocity for one of my boundary conditions is defined as:

(3*t+5), for t<2

(11), for t>2

(-12t+14), for t>5

I tried messing aronud with the step function, but I don't believe this is the right approach. Any help would be greatly appreciated.

Hi,

Either use the step function or an interpolation function. There are no other options.

In CFX V12 you will be able to use an if function.

Glenn Horrocks

(3*t+5)*step(2-t)+11*step(t-2)*step(5-t)+(14-12*t)*step(t-5) Becouse Step is dimensionless function you should use t/1[s] insted of t (if t=time, of course). All parts of expression must have Velosity units. So, finally expression is ((3*t+5[s])*step(2-t/1[s])+11[s]*step(t/1[s]-2)*step(5-t/1[s])+(14[s]-12*t)*step(t/1[s]-5))*1[m/s^2] Not so camfortable as "if" "else" but it works. I hope it help you.

Thank you very very much!!!