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-   -   Problem with function Compute_Force_And_Moment (https://www.cfd-online.com/Forums/fluent/71027-problem-function-compute_force_and_moment.html)

 zedas December 12, 2009 17:23

Problem with function Compute_Force_And_Moment

Hi, Im not very good in english, but I will try to explain my problem.

My work problem is aeroelastic instability in bridge deck which modeled in 2D. Im wrote UDF wich include function Compute_Force_And_Moment. So, problem is that, this function in my udf return same force value like from return>forces in fluent, but moment value from this function is very very lower than report (moment from udf isnt realistic). Center of gravity I set center of profile. Maybe someone had same broblem or know how this function works? Is there another way to get moment of proflie in UDF? Any advise is welcome.

First part of my UDF.

include"udf.h"
#include"f_wall.h"
#include"dynamesh_tools.h"
static real v_y=0.0,omega_z=0.0;
real dy,da;
DEFINE_CG_MOTION(profilis,dt,vel,omega,time,dtime)
{
face_t f;
cell_t c;
real f_glob[ND_ND],m_glob[2],x_cg[ND_ND],theta[ND_ND],dv_y,domega_z;
Domain *domain=Get_Domain(1);
int i;

NV_S(vel, =, 0.0);
NV_S(omega, =, 0.0);
if (!Data_Valid_P())
return;

for(i=0;i<=ND_ND;i++)
{
f_glob[i]=0.0;
m_glob[i]=0.0;
}

for(i=0;i<ND_ND;i++)
{
x_cg[i]=DT_CG(dt)[i];
theta[i]=DT_THETA(dt)[i];
}

Compute_Force_And_Moment (domain, tf1, x_cg, f_glob, m_glob, TRUE);

Message (
"\ntime=%f ,x=%.1f ,y=%.10lf ,theta=%.10lf ,force_y=%.5f ,moment_z=%.10lf ,Vy=%.10lf ,omega_z=%.10lf ,moment_x=%.10lf, moment_y=%.10lf\n",time ,x_cg[0] ,x_cg[1] ,theta[2] ,f_glob[1] ,m_glob[2] ,v_y ,omega_z ,m_glob[0] ,m_glob[1]);

 Dorit October 15, 2012 00:36

Hello zedas,

I know it's a long time ago that you sent your post but did you find a solution to your problem? I'm having a very similar problem. My Compute_Force_And_Moment doesn't work.

Thanks,
Dorit

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