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UDF resulting in negative volume..

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Old   February 22, 2012, 15:13
Unhappy UDF resulting in negative volume..
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Hi, im using the following udf to bend a 3D beam as though having a parabolic loading in fluent. But it shows negative volume when i try to preview the mesh motion. I m using very small smoothing and remeshing numbers anyway. So I would be grateful if someone could point out my error. Thank you.

#include "udf.h"
DEFINE_GRID_MOTION(wing, domain, dt, time, dtime)
{
Thread *tf = DT_THREAD (dt);
face_t f;
Node *v;
real dispy;
real NV_VEC (position);
int n;

SET_DEFORMING_THREAD_FLAG(THREAD_T0(tf));

begin_f_loop (f, tf)
{
f_node_loop (f, tf, n)
{
v=F_NODE (f, tf, n);
if (NODE_POS_NEED_UPDATE (v))
{
NODE_POS_UPDATED (v);
position[0]=NODE_X(v);
position[1]=NODE_Y(v);
position[2]=NODE_Z(v);
dispy=NODE_Z(v)*NODE_Z(v)*0.0271+0.2496*NODE_Z(v)+ 0.1396;// y displacement based on the present z position
NODE_Y(v)=+dispy; // new y position is equal to the present y position + displacement
}
}
}
end_f_loop (f, tf)
}
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