[zhixin]

Hi,
I'm doing dynamic mesh on a 3D model, and the model is like below. Basically the inner wall rotates along the Y-axis.

http://thumbsnap.com/i/nX4AHkBt.png
http://thumbsnap.com/CSWQ3Ph2
http://www.dumpt.com/img/links.php?f...cxkg2uyxcs.png

I used the Compute_Force-And_Moment macro,and the udf is shown below
while in FLUENT i use the smoothing and remeshing methods, and set the inner walls as rigid body

#include "udf.h"
#include "f_wall.h"
#include "mem.h"
#include "math.h"
#include "dynamesh_tools.h"
static real axis_rotor1[3]={0.0,1.0,0.0};
real omega_y1=0.0,omega_y2=0.0;
double angle1=25.000000000000000,angle2=25.00000000000000 0;
real domega_y1,dangle1,domega_y2,dangle2;
real timestep,total_time;
real torque_rotor1,torque_rotor2;
real moment_rotor1[3],moment_rotor2[3];

DEFINE_CG_MOTION(leaflet1,dt,vel1,omega1,time,dtim e)
{
NV_S(vel1,=,0.0);
NV_S(omega1,=,0.0);
omega1[1]=omega_y1;
timestep=dtime;
total_time=time;
}

DEFINE_CG_MOTION(leaflet2,dt,vel2,omega2,time,dtim e)
{
NV_S(vel2,=,0.0);
NV_S(omega2,=,0.0);
omega2[1]=omega_y2;
}

DEFINE_EXECUTE_AT_END(rot1)
{
#if !RP_HOST
Domain *domain=Get_Domain(1);
Thread *rotor1,*rotor2;
face_t f;
real force_rotor1[3];
real force_rotor2[3];
real point_rotor1[3]={0.0027,0.0,0.0};/*point at rotor of leaflet1*/
real point_rotor2[3]={-0.0027,0.0,0.0};

rotor1=Lookup_Thread(domain,23);/*leaflet 1*/
Compute_Force_And_Moment(domain,rotor1,point_rotor 1,force_rotor1,moment_rotor1,0);/*ture seriel, false parallel?*/
torque_rotor1=NV_DOT(moment_rotor1,axis_rotor1);

rotor2=Lookup_Thread(domain,24);/*leaflet 2*/
Compute_Force_And_Moment(domain,rotor2,point_rotor 2,force_rotor2,moment_rotor2,0);/*ture seriel, false parallel?*/
torque_rotor2=NV_DOT(moment_rotor2,axis_rotor1);
#endif
node_to_host_real_1(torque_rotor1);
node_to_host_real_1(torque_rotor2);
}

DEFINE_EXECUTE_AT_END(move1)
{
dangle1=-omega_y1*timestep;
angle1+=dangle1;
domega_y1=timestep*torque_rotor1/2/pow(10,-9);/*moment of inertia*/

if((angle1-(omega_y1+domega_y1)*timestep)>85.000000000000000)
{
omega_y1=0.0;
angle1=85.000000000000000;
}
else if((angle1-(omega_y1+domega_y1)*timestep)<25.000000000000000)
{
omega_y1=0.0;
angle1=25.000000000000000;
}
else
{
omega_y1+=domega_y1;
}

dangle2=omega_y2*timestep;
angle2+=dangle2;
domega_y2=timestep*torque_rotor2/2/pow(10,-9);/*moment of inertia*/
if((angle2+(omega_y2+domega_y2)*timestep)>85.00000 0000000000)
{
omega_y2=0.0;
angle2=85.000000000000000;
}
else if((angle2+(omega_y2+domega_y2)*timestep)<25.00000 0000000000)
{
omega_y2=0.0;
angle2=25.000000000000000;
}
else
{
omega_y2+=domega_y2;
}
}

The problem I met is when the wall begins to rotate, the omega fluctuate like below then leads to negative volume

-0.208
4.01
-4.7
103.7

But when i restrict the omega to be negative, the cas can be run and omega and domega are like below

-0.11 -0.11
-0.11 0
-0.49 -0.37
-0.49 0

so how can i make the cas run without restrict the omega value? please help me.

[zhixin]

I use the 6DOF method today, but the omega still fluctuate

[jmex]

Use six DOF. and what's your timestep size. Use as small as possible. Also look for CG you've kept.

[zhixin]

Originally Posted by jmex

Use six DOF. and what's your timestep size. Use as small as possible. Also look for CG you've kept.

I've tried the six DOF, and the smallest timestep I tried is 0.000001s. as can be seen from the autosave file, the theta has a big fluctuate and leads to negative volume.(the negative theta is right)

# Fluent dynamic mesh motion history
#
# Location (meters) Orientation (degrees)
# time CG_X CG_Y CG_Z THETA_X THETA_Y THETA_Z
#
1.12010e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 4.88853e-08 0.00000e+00
1.12020e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 2.17892e-06 0.00000e+00
1.12030e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -4.89625e-07 0.00000e+00
1.12040e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 3.26834e-06 0.00000e+00
1.12050e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 1.24606e-05 0.00000e+00
1.12060e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -4.29631e-05 0.00000e+00
1.12070e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 1.27735e-04 0.00000e+00
1.12080e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -1.93768e-04 0.00000e+00
1.12090e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -1.48239e-05 0.00000e+00
1.12100e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 1.41311e-03 0.00000e+00
1.12110e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -5.62079e-03 0.00000e+00
1.12120e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 1.38875e-02 0.00000e+00
1.12130e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -2.15875e-02 0.00000e+00
1.12140e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -4.62013e-03 0.00000e+00
1.12150e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 1.73618e-01 0.00000e+00
1.12160e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 -8.53320e-01 0.00000e+00
1.12170e-02 2.70000e-03 0.00000e+00 0.00000e+00 0.00000e+00 3.55020e+00 0.00000e+00

[litzj]

neg. vol is probably coming from geometry change is too quick to remeshing

try smaller rotating or moving speed of body, and remesh for each time step

[zhixin]

Originally Posted by litzj

neg. vol is probably coming from geometry change is too quick to remeshing

try smaller rotating or moving speed of body, and remesh for each time step

but how can i use smaller speed since the speed is calculated from the flow field.