UDF for subtract velocity component
 

Hi everybody, I'm a beginner in writing UDF....
My basic problem is that i'm making an object moving.With the object is also moving the boundary layer,so i don't have to remesh that zone..now,in the boundary layer there is a component of that velocity(that i know because i know the velocity the object have at every time step) that i wont to subtract,so the simulation is phisically correct.
What kind of macros i have to use?the define_adjust or a define_profile?
If anyone have some idea about this I would be very grateful!!!

Paul