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April 23, 2009, 19:09 |
Logarithmic velocity profile
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#1 |
New Member
Join Date: Apr 2009
Posts: 14
Rep Power: 17 |
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 tried to use the C_WALL_DIST(c,thread) macro to resolve this issue (this macro estimate the distance from any cell to the nearest WALL, which is the terrain), like this: #include "udf.h" DEFINE_PROFILE(log_velocity,thread,index) { real z; face_t f; cell_t c; begin_f_loop(f,thread) { z = C_WALL_DIST(c,thread); F_PROFILE(f,thread,index) =3*log(z/0.01)/log((10)/0.01); } end_f_loop(f,thread) } But when i selected the udf in velocity inlet in boundary condition, fluent gave me this message: Error: FLUENT received fatal signal (ACCESS_VIOLATION) 1. Note exact events leading to error. 2. Save case/data under new name. 3. Exit program and restart to continue. 4. Report error to your distributor. Error Object: () I think the problem is that the boundary condition that I set is to a face and I use a macro for cells in the udf. I don’t know how to use this macro for my situation. Can anyone help me with this issue ? I would appreciate any suggestions. PS: Sorry for repeat the thread of fluent forum but only now I noticed that there is a sub-forum dedicated to udf Last edited by cfdworker; April 23, 2009 at 20:38. |
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