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May 20, 2005, 11:25 
UDF for slip and moving wall

#1 
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Dear all:
I am trying to put a slip and moving boundary condition at the wall. so I write a UDF as the followed. But the FLUENT said there is a fatal problem "Segmentation violation". I select moving wall and nonslip at Fluent, maybe that is the reason? But if I select slip wall, I can not specify the wall velocity. Anybody has some experience to put a slip moving wall boundary? please give some suggestion. Thanks a lot #include "udf.h" DEFINE_PROFILE(wall_velocity,t,i) { face_t f; cell_t c; real cellnumber = 0; /*the number of the cells on the boundary*/ real A = 0.002; /*the amplitude of the oscillation*/ real omega = 100; /*the frequency of the oscillation*/ real dudy; /*the y derivative of the horizontal velocity*/ real sumdudy = 0; /*the sum of the velocity derivative*/ real avgdudy; /*the average of the velocity derivative*/ real beta = 0.2; /*the slippy coefficient*/ Thread *tc; tc = THREAD_T0(t); if (NULL != C_DUDY(c,tc)) { begin_c_loop(c,tc) { cellnumber = cellnumber + 1; dudy = C_DUDY(c,tc); sumdudy = sumdudy + dudy; } end_c_loop(c,tc) avgdudy = sumdudy/cellnumber; begin_f_loop(f,t) { real tempt = RP_Get_Real("flowtime"); F_PROFILE(f,t,i) = omega*A*cos(omega*tempt)  beta*avgdudy; } end_f_loop(f,t) } else { begin_f_loop(f,t) { real tempt = RP_Get_Real("flowtime"); F_PROFILE(f,t,i) = omega*A*cos(omega*tempt)  beta*avgdudy; } end_f_loop(f,t) } } 

May 21, 2005, 21:55 
How to access variables in Fluent

#2 
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Posts: n/a

Dear all:
This seems a hard question. I checked that once I try to access the variables, the "Segmentation violation" appears. So what is the trick to access the varibles in Fluent? I attached my UDF again. #include "udf.h" DEFINE_PROFILE(wall_velocity, t, i) { face_t f; cell_t c; real cellnumber = 0; /*the number of the cells on the boundary*/ real A; /*the amplitude of the oscillation*/ real omega; /*the frequency of the oscillation*/ real dudy; /*the y derivative of the horizontal velocity */ real sumdudy = 0; /*the sum of the velocity derivative */ real avgdudy; /*the average of the velocity derivative */ real beta; /*the slippry coeeficient*/ if (NULL != C_DUDY(c,t)) { begin_c_loop(c, t) { cellnumber++; dudy = C_DUDY(c,t); sumdudy =+ dudy; } end_f_loop(f,t); avgdudy = sumdudy/cellnumber; begin_f_loop(f, t) { real t = RP_Get_Real("flowtime"); F_PROFILE(f,t,i) = omega*A*cos(omega*t)  beta*avgdudy; } end_f_loop(f,t); } else { begin_f_loop(f, t) { real t = RP_Get_Real("flowtime"); F_PROFILE(f,t,i) = omega*A*cos(omega*t); } end_f_loop(f,t); } } 

May 30, 2005, 14:24 
Re: UDF for slip and moving wall

#3 
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Hi, DEFINE_PROFILE takes input the boundary face not the cell. So when u are running a loop on the faces u cant access the particular cell directly. Because the thread for face is different from thread for cells. If u want to access the cell of the partciular boundary face use F_C0(f,tf). I hope this should solve the problem


March 26, 2014, 05:37 
moving wall slip

#4 
New Member
elaf
Join Date: May 2013
Posts: 14
Rep Power: 6 
Hi all
I was wondering if any body can help me? I am using flow around cylinder, the shear stresses at the wall need to be specified to constant value. In this option, there are 3 components for the shear stresses, i.e. x direction components and so on. Does anyone know for example how can set these values for cylinder surface Regard. 

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