putting on a perturbation in a 2phase problem
 

hi everyone
I wanna make a velocity correction head file, for this task i must define a certain time and fixed position, but I don't know how i can do this.
for example i must define t=10s & x=5 & y=5, and in this time and position i have to add a perturbation in velocity, for instance U=U+10e-1.
I can't do it in c++
Is there anyone who can help me? :(