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UDF Airfoil SHM flapping motion not executing, rather rotating 360degs

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Old   December 4, 2020, 00:59
Exclamation UDF Airfoil SHM flapping motion not executing, rather rotating 360degs
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AfreedFaizan
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I'm working on oscillating airfoils based on flapping wings. In order to do so, I took a simple airfoil and made the geometry. I had no issues while building the "udflib" and the code which I used given below. Once I set the CG location and preview the motion. It is rotating 360 degs at a very fast rpm rather than executing slow shm. I'm pretty sure it's something to do with the software rather than the code. Please help me because this is my uni project.

#include "udf.h"
#define Freq 5 % defining flapping frequency i.e 5, 6, 7, 8, 9 and 10Hz
#define PI 22/7
#define angular_freq 2.0*PI*Freq % defining angular frequency
#define tetmax 30.0*PI/180 % defining angular amplitude
DEFINE_CG_MOTION (shm, dt, cg_vel, cg_omega, time, dtime)
{
real omega;
omega = tetmax *angular_freq* cos (angular_freq *time);
cg_vel[0] = 0.0;
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;
cg_omega[0] = 0.0;
cg_omega[1] = 0.0;
cg_omega[2] = omega;
}
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Old   February 18, 2024, 07:11
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johnny simson
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hey any fixes? im facing the exact same issue.
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Old   February 18, 2024, 09:06
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Quote:
#define PI 22/7
#define angular_freq 2.0*PI*Freq % defining angular frequency
#define tetmax 30.0*PI/180 % defining angular amplitude
You could try the following things:
1) change the PI macro definition, instead of that you invoke M_PI instead
2) the reason it rotates instead of executing a simple harmonic motion is because the angles are inconsistent.

so here's the fixed code:
Code:
#define angular_freq 2.0*Freq*M_PI/180
#define tetmax 30.0*PI/180
Hope this fixed your code!
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airfoil pitching 2d, fluent - udf, fluent - udf - parallel, shm not snapping, udf cg motion

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