CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent UDF and Scheme Programming

6DOF for spring valve motion problem

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 19, 2015, 02:08
Thumbs down 6DOF for spring valve motion problem
  #1
New Member
 
JEONGWOO2
Join Date: Aug 2015
Posts: 1
Rep Power: 0
ahehuhehuh is on a distinguished road
Dear all~
I want solve the problem that 6DOF constant spring motion in 2-D
Using DEFINE_SDOF_PROPERTIES

But it's results weird.. something likes function of sine..
How can i write 6DOF function?

Here are some attachment.
first, using the 6DOF


#include "udf.h"
#define spring_constant 1.5 /*idonknow*/
#define original_pin_cg_y 3.25e-4

DEFINE_SDOF_PROPERTIES(Pinconst_1_5, prop, dt, time, dtime)
{

real pin_movement_y;
prop[SDOF_MASS] = 6.792e-6;
prop[SDOF_IXX] = 6.4059e-11;
prop[SDOF_IYY] = 6.28e-13;
prop[SDOF_IZZ] = 6.4676e-11;
prop[SDOF_ZERO_TRANS_X] = TRUE;
prop[SDOF_ZERO_TRANS_Z] = TRUE;
prop[SDOF_ZERO_ROT_X] = TRUE;
prop[SDOF_ZERO_ROT_Y] = TRUE;
prop[SDOF_ZERO_ROT_Z] = TRUE;

pin_movement_y = (DT_CG(dt)[1] - original_pin_cg_y);
Message("DT_CG = %e, %e, %e\n",DT_CG(dt)[0], DT_CG(dt)[1], DT_CG(dt)[2]);
prop[SDOF_LOAD_F_Y] = - spring_constant * pin_movement_y;
Message("spring force = %e\n",prop[SDOF_LOAD_F_Y]);
}


model and mesh for simulation,
results of coordinate for <Time vs 'wall box positions'>

Thanks
Attached Images
File Type: jpg im1.jpg (33.6 KB, 77 views)
File Type: jpg im2.jpg (28.2 KB, 45 views)
ahehuhehuh is offline   Reply With Quote

Old   February 26, 2018, 13:36
Default
  #2
New Member
 
Lucas Gasparino
Join Date: Feb 2018
Posts: 3
Rep Power: 4
LucasGasparino3110 is on a distinguished road
Hi there mate!!

Did you get any closure in your case? For me, the sine-like motion doesn't seem wrong, tbh. Is your UDF used as interpret or compiled? I'm having a similar case but with the addition of torsion, so I'm willing to try your solution, as it is the only reference I got that uses a spring...

Thank you very much!
LucasGasparino3110 is offline   Reply With Quote

Old   April 18, 2018, 15:39
Talking
  #3
New Member
 
Flavio Martins
Join Date: Mar 2018
Posts: 2
Rep Power: 0
PRIDEmartins is on a distinguished road
It is not wrong what you have done.
In my opinion, there are only two things missing in here:

I. a damping coeficient. Something like: -c*DT_VEL_GD(dt), on the force equation, in order to make the system more stable.

II. Descrease the time step.

For I: try using: zeta = c/2*sqrt(M*K), for correctly determing your damping coeficient, c.

For II, a good start point is: dt = fn/50 (fn = system's natural frequency, given by: fn = sqrt(k/m)/2*pi.

For me, in II, the frequency of vortex sheeding is also a good idea. Use the Strouhal nunber, St=0.2, to guess f_vortex e try doing the same.

Sorry for the bad English. I'm in a hurry in here.
PRIDEmartins is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Modelling an initially closed valve which a fluid opens siw CFX 1 April 26, 2014 06:32
please help valve motion UDF g-wagon Fluent UDF and Scheme Programming 0 December 28, 2011 22:21
problem in writing CEL expressions for mesh motion hasan56 CFX 2 October 20, 2011 12:55
3D valve motion but no mesh motion with smoothing slaol2 FLUENT 1 September 22, 2011 18:06
Large Valve Flow Analysis - Inflation Problem sercan85 ANSYS Meshing & Geometry 2 June 1, 2010 14:02


All times are GMT -4. The time now is 01:11.