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Old   May 9, 2011, 10:47
Default vortex induced vibration
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Wang Xiaosong
Join Date: May 2011
Posts: 1
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Hi, everybody
I'am do a numerical simulation of vortex induced vibration use fluent 6.3.But I met some very stange problems, if I use boundary layer in mesh, the cylinder amplitude is much too high and fore exerted on cylinder is also larger than normal level. If I don't use boundary layer in my mesh, the mesh near to the cylinder became very bad in simulation.
So is there anybody can help me, I have been stuck by this problem for months.

Here is the full text of my UDF.
#include <stdio.h>
#include "udf.h"
# define UDF_FILENAME "udf_loc_velo_acc"
# define Temp_File "mytemp"

/* read current location,velocity and accelerator from file */
static void
read_loc_vel_acc_file (real *loc1, real *vel1,real *acc1)
{
FILE *fp = fopen(Temp_File, "r");
if (fp != NULL)
{
float read_loc1, read_vel1, read_acc1;
fscanf (fp, "%e %e %e", &read_loc1, &read_vel1, &read_acc1);
fclose (fp);
*loc1 = (real) read_loc1;
*vel1 = (real) read_vel1;
*acc1=(real) read_acc1;
Message ("\nUDF read viv: y_vel = %f, acc = %f, loc(m)= %f\n",
*vel1, *acc1, *loc1);
}
else
{
*loc1 = 0.0;
*vel1 = 0.0;
*acc1 = 0.0;
Message("\nThe first reading of udf_loc_vel_acc_file\n");
}
}
/* write current location, velocity and acceleration into file */
static void
write_loc_vel_acc_file (real loc, real vel, real acc)
{
FILE *fp = fopen(UDF_FILENAME, "a");
if (fp != NULL)
{
fprintf (fp, "%e %e %e\n", loc, vel, acc);
fclose (fp);
}
else
Message ("\nWarning: cannot write %s file", UDF_FILENAME);
}
/* write current location,velocity and acceleration into temp_file */
static void
write_loc_vel_acc_file2 (real loc, real vel, real acc)
{
FILE *fp = fopen(Temp_File, "w");
if (fp != NULL)
{
fprintf (fp, "%e %e %e\n", loc, vel, acc);
fclose (fp);
}
else
Message ("\nWarning: cannot write %s file", Temp_File);
}
DEFINE_CG_MOTION(viv, dt, cg_vel, cg_omega, time, dtime)
{
#define DELTA 0.5
#define BETA 0.25
#define K_SPRING 22.406
#define MASS 4.864
#define xi 0.0054
real wn=sqrt(K_SPRING/MASS);
real CC=2*xi*wn*MASS;
/*fn=2.92745*/
/*mass ratio equaul 2.4*/
real loc,vel,acc,loc1,vel1,acc1;
real a0,a1,a2,a3,a4,a5,a6,a7,keff,reff;
static int id1=5; /* Face ID of the cylinder */
static real f_glob[3]; /* Total forces (global) */
static real m_glob[3]; /* Moment (global) */
static real x_cg[3]; /* CG location */
static real force[3];
int i=0;
Thread *tf1;
Domain *domain = Get_Domain(1);
tf1 = Lookup_Thread(domain, id1);
a0=1/(BETA*dtime*dtime);
a1=DELTA/(BETA*dtime);
a2=1/(BETA*dtime);
a3=0.5/BETA-1;
a4=DELTA/BETA-1;
a5=0.5*dtime*(DELTA/BETA-2);
a6=dtime*(1-DELTA);
a7=DELTA*dtime;
keff=a0*MASS+a1*CC+K_SPRING;
/* reset velocities */
NV_S (cg_vel, =, 0.0);
NV_S (cg_omega, =, 0.0);
if (!Data_Valid_P ())
return;

/* Get CG position */
for (i=0; i<ND_ND; i++) x_cg[i] = DT_CG(dt)[i];
/* compute force on cylinder */
force[1] = 0.0;
Compute_Force_And_Moment(domain, tf1, x_cg, f_glob, m_glob, TRUE);
for (i=0; i<ND_ND; i++)
{
force[i] = f_glob[i];
}

/*read data calculated in the former step*/
read_loc_vel_acc_file (&loc1, &vel1, &acc1);
/* compute response of cylinder by newmark method*/

reff=force[1]+MASS*(a0*loc1+a2*vel1+a3*acc1)+CC*(a1*loc1+a4*vel 1+a5*acc1);
loc=reff/keff;
acc=a0*(loc-loc1)-a2*vel1-a3*acc1;
vel=vel1+a6*acc1+a7*acc;

Message ("\nUDF of viv: time = %f, y_vel = %f, acc = %f, loc(m)= %f\n",
time, vel, acc, loc);
write_loc_vel_acc_file (loc, vel, acc);
write_loc_vel_acc_file2 (loc, vel, acc);
cg_vel[1] = vel;
}
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Old   May 31, 2011, 02:18
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  #2
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hisham
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Could you describe your error in more detail. What do you actually mena by BL here? Also how do you assign the UDF to your dynamic mesh?
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Old   October 11, 2011, 03:17
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Quote:
Originally Posted by Simon Wang View Post
Hi, everybody
I'am do a numerical simulation of vortex induced vibration use fluent 6.3.But I met some very stange problems, if I use boundary layer in mesh, the cylinder amplitude is much too high and fore exerted on cylinder is also larger than normal level. If I don't use boundary layer in my mesh, the mesh near to the cylinder became very bad in simulation.
So is there anybody can help me, I have been stuck by this problem for months.

Here is the full text of my UDF.
#include <stdio.h>
#include "udf.h"
# define UDF_FILENAME "udf_loc_velo_acc"
# define Temp_File "mytemp"

/* read current location,velocity and accelerator from file */
static void
read_loc_vel_acc_file (real *loc1, real *vel1,real *acc1)
{
FILE *fp = fopen(Temp_File, "r");
if (fp != NULL)
{
float read_loc1, read_vel1, read_acc1;
fscanf (fp, "%e %e %e", &read_loc1, &read_vel1, &read_acc1);
fclose (fp);
*loc1 = (real) read_loc1;
*vel1 = (real) read_vel1;
*acc1=(real) read_acc1;
Message ("\nUDF read viv: y_vel = %f, acc = %f, loc(m)= %f\n",
*vel1, *acc1, *loc1);
}
else
{
*loc1 = 0.0;
*vel1 = 0.0;
*acc1 = 0.0;
Message("\nThe first reading of udf_loc_vel_acc_file\n");
}
}
/* write current location, velocity and acceleration into file */
static void
write_loc_vel_acc_file (real loc, real vel, real acc)
{
FILE *fp = fopen(UDF_FILENAME, "a");
if (fp != NULL)
{
fprintf (fp, "%e %e %e\n", loc, vel, acc);
fclose (fp);
}
else
Message ("\nWarning: cannot write %s file", UDF_FILENAME);
}
/* write current location,velocity and acceleration into temp_file */
static void
write_loc_vel_acc_file2 (real loc, real vel, real acc)
{
FILE *fp = fopen(Temp_File, "w");
if (fp != NULL)
{
fprintf (fp, "%e %e %e\n", loc, vel, acc);
fclose (fp);
}
else
Message ("\nWarning: cannot write %s file", Temp_File);
}
DEFINE_CG_MOTION(viv, dt, cg_vel, cg_omega, time, dtime)
{
#define DELTA 0.5
#define BETA 0.25
#define K_SPRING 22.406
#define MASS 4.864
#define xi 0.0054
real wn=sqrt(K_SPRING/MASS);
real CC=2*xi*wn*MASS;
/*fn=2.92745*/
/*mass ratio equaul 2.4*/
real loc,vel,acc,loc1,vel1,acc1;
real a0,a1,a2,a3,a4,a5,a6,a7,keff,reff;
static int id1=5; /* Face ID of the cylinder */
static real f_glob[3]; /* Total forces (global) */
static real m_glob[3]; /* Moment (global) */
static real x_cg[3]; /* CG location */
static real force[3];
int i=0;
Thread *tf1;
Domain *domain = Get_Domain(1);
tf1 = Lookup_Thread(domain, id1);
a0=1/(BETA*dtime*dtime);
a1=DELTA/(BETA*dtime);
a2=1/(BETA*dtime);
a3=0.5/BETA-1;
a4=DELTA/BETA-1;
a5=0.5*dtime*(DELTA/BETA-2);
a6=dtime*(1-DELTA);
a7=DELTA*dtime;
keff=a0*MASS+a1*CC+K_SPRING;
/* reset velocities */
NV_S (cg_vel, =, 0.0);
NV_S (cg_omega, =, 0.0);
if (!Data_Valid_P ())
return;

/* Get CG position */
for (i=0; i<ND_ND; i++) x_cg[i] = DT_CG(dt)[i];
/* compute force on cylinder */
force[1] = 0.0;
Compute_Force_And_Moment(domain, tf1, x_cg, f_glob, m_glob, TRUE);
for (i=0; i<ND_ND; i++)
{
force[i] = f_glob[i];
}

/*read data calculated in the former step*/
read_loc_vel_acc_file (&loc1, &vel1, &acc1);
/* compute response of cylinder by newmark method*/

reff=force[1]+MASS*(a0*loc1+a2*vel1+a3*acc1)+CC*(a1*loc1+a4*vel 1+a5*acc1);
loc=reff/keff;
acc=a0*(loc-loc1)-a2*vel1-a3*acc1;
vel=vel1+a6*acc1+a7*acc;

Message ("\nUDF of viv: time = %f, y_vel = %f, acc = %f, loc(m)= %f\n",
time, vel, acc, loc);
write_loc_vel_acc_file (loc, vel, acc);
write_loc_vel_acc_file2 (loc, vel, acc);
cg_vel[1] = vel;
}
Did you solve your problems of udf file?
Please let me know the solution of your problem.

Thanks
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Old   June 17, 2012, 05:22
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  #4
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zhang guoqing
Join Date: May 2011
Posts: 10
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Hi Simon Wang:
Have you already solved your problem, I am currently doing some simulation like yours. Could you exchange with me through email? My email address is zhangguoqing@ntu.edu.sg
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