UDF Wall functions conundrum
 

Can anybody please tell me what DUPLUS is the the following UDF file?
http://my.fit.edu/itresources/manual...udf/node52.htm

I am trying to model my wall function such that in the log-law region,
u+=(1/kappa)*log(y+/y0+)
where y0+ is z0*utau/viscosity.
z0 is just some value i will input.
Can anybody help me program this macro? or at least guide me how to do it? i have read the UDF manual and i'm still clueless.

Please advice

thank you