# UDF for slip and moving wall

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 May 20, 2005, 12:25 UDF for slip and moving wall #1 lichun Dong Guest   Posts: n/a 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 non-slip 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("flow-time"); 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("flow-time"); F_PROFILE(f,t,i) = omega*A*cos(omega*tempt) - beta*avgdudy; } end_f_loop(f,t) } }

 May 21, 2005, 22:55 How to access variables in Fluent #2 lichun Dong Guest   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("flow-time"); 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("flow-time"); F_PROFILE(f,t,i) = omega*A*cos(omega*t); } end_f_loop(f,t); } }

 May 30, 2005, 15:24 Re: UDF for slip and moving wall #3 ramesh Guest   Posts: n/a 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: 15 Rep Power: 11 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.