intel and outel in teh same boundary
 

hello,

I have a cavity with a single enter.
So this enter is inlet and outel. I want to input a function field on the pressure, like Pinlet=cos(time), Poutlet=-cos(time).
But how can set these conditions on the same boundary?

I hope that my english is not so bad, and that you can understand me;)

Thanks for your help.

Either you split up the boundary (strongly recommended), or you can modify your field function (NOT recommended) to something like

$$Position[0]>=-0.1&&$$Position[0]<=0.1?-cos(time):cos(time)

You can also add some more conditions like $$Position[0] (x-direction), $$Position[1] (y-direction) etc.
When you need a circular split up, you might think about using $$Position[] in a cylindrical coordinate system. See the field function programming reference.