Question about "if" function

Hello,

I want to add a volume force to NS equation with a special condition.
The volume force is like this: H/Re
Re is reynolds number.
u2 is calculated from convection-diffusion equation and I want to limit the values of u2 like this.

if (u2>=0 or u2<=1) then H=u2
if (u2>1) set it to 1 and then H=u2
if (u2<0) set it to 0 and then H=u2


Would you please help me?
Thanks,
Hooman