[cfdworker]

Hello, I have a problem with the definition of a boundary condition with UDF to simulation of the wind in a terrain. I have to define a velocity inlet in a 3d domain; this condition is a logarithmic velocity profile. I can define the logarithmic velocity profile with UDF, like this:



#include "udf.h"

DEFINE_PROFILE(log_velocity,thread,index)
{
real x[ND_ND];
real z;
face_t f;

begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
z = x[2];
F_PROFILE(f,thread,index) = 3*log(z/0.01)/log(10/0.01);
}
end_f_loop(f,thread)
}


My domain is this:



I have to impose the logarithmic profile in the front face that is shown in figure.
My question is how I define in the UDF so that the velocity in bottom of the face is equal 0.
My problem is the coordinates that I use in UDF are absolute and I don’t know how to define relative coordinates, in order to the z in the equation that defines the velocity profile, is the height relatively to the bottom of the face and not the absolute height.

I would appreciate any suggestions.