CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

UDF divergence of a vector

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 26, 2006, 12:21
Default UDF divergence of a vector
  #1
cris
Guest
 
Posts: n/a
i am working with the eulerian model and I would like to add a new term in the dispersed phase momentum equation. I can add easy terms using the macro DEFINE_SOURCE but i need the divergence of a vector. I made some easy probes to calculate the divergence of vector but i didn't suceed. Is there any macro to calculate the divergence of a vector? Is there anyone who has made a udf to calculate the divergence? I created some udf that use the divergence theorema to calculate the volume of a cell and the result is good, but when i tried to probe the udf in the steady state continuity equation the udf failed. If theres is someone interested i would send him my udfs. Sorry I am a spanish girl and i explain the best i could.

  Reply With Quote

Old   April 15, 2010, 15:32
Default
  #2
Member
 
Casey
Join Date: Jun 2009
Posts: 96
Rep Power: 8
meangreen is on a distinguished road
Did you ever get this? I am working on the same thing. I just submitted a support question to FLUENT, I will post the result.

Casey
meangreen is offline   Reply With Quote

Old   June 8, 2010, 11:55
Default
  #3
Member
 
Casey
Join Date: Jun 2009
Posts: 96
Rep Power: 8
meangreen is on a distinguished road
Yeah, I did. I cant get the simulation to converge at first. I opened up a service request with fluent, but they said the UDF is running fine and that the problem must be somewhere else. I am not happy with the fact that the simulation does not converge for the first few time steps, so I am going to keep looking into it, but below is the divergence part of the UDF I wrote.
Casey

/* Include statements */

#include "udf.h"

/************************************************** *********************
UDF for specifying frictional pressure
************************************************** **********************/

DEFINE_PROPERTY(pf_cfifteen, cp, tp)
{
real np = 5.;
real nn = 2.;
real esmax = 0.63;
real esmin = 0.5;
real bp = 0.6237;
real sm_val = 1.0e-12;
real P[ND_ND];
real delt, pfr, nc, fric, Smag, vfrac, dudx, dudy, dvdx, dvdy, r, radv, DIV;

/* Retrieve volume fraction and magnitude of the deviatoric Smag tensor */
/*x direction is axial direction, y direction is radial so dvdy = d(radialvelocity)/dradial */

vfrac = C_VOF(cp,tp);
dudx = C_U_G(cp,tp)[0];
dudy = C_U_G(cp,tp)[1];
dvdx = C_V_G(cp,tp)[0];
dvdy = C_V_G(cp,tp)[1];
radv = C_V(cp,tp);
C_CENTROID(P,cp,tp);
r = P[1];
DIV = dvdy + radv/r + dudx;
Smag = sqrt(pow((dvdy-(1./3.)*DIV),2.)+2.*pow((0.5*(dudy-dvdx)),2.)+pow((dudx-(1./3.)*DIV),2.));

__________________________________________________ ____

I had to leave out the rest of the UDF because it pertains to my research and I have not published yet. Below here it just uses the DIV in "if" statements, so any user that wants to use the above DIV part of the code you just need the folowing:
__________________________________________________ __________
dudx = C_U_G(cp,tp)[0];
dudy = C_U_G(cp,tp)[1];
dvdx = C_V_G(cp,tp)[0];
dvdy = C_V_G(cp,tp)[1];
radv = C_V(cp,tp);
C_CENTROID(P,cp,tp);
r = P[1];
DIV = dvdy + radv/r + dudx;
Smag = sqrt(pow((dvdy-(1./3.)*DIV),2.)+2.*pow((0.5*(dudy-dvdx)),2.)+pow((dudx-(1./3.)*DIV),2.));

__________________________________________________ _________

Hope this helps everyone!

Casey
meangreen is offline   Reply With Quote

Old   September 4, 2014, 18:06
Default
  #4
Senior Member
 
rkhr
Join Date: May 2011
Posts: 211
Rep Power: 7
Kanarya is on a distinguished road
Hi Casey,
if the case is 2D than we should divide the DIV by 2 right?
thanks in advance!
Quote:
Originally Posted by meangreen View Post
Yeah, I did. I cant get the simulation to converge at first. I opened up a service request with fluent, but they said the UDF is running fine and that the problem must be somewhere else. I am not happy with the fact that the simulation does not converge for the first few time steps, so I am going to keep looking into it, but below is the divergence part of the UDF I wrote.
Casey

/* Include statements */

#include "udf.h"

/************************************************** *********************
UDF for specifying frictional pressure
************************************************** **********************/

DEFINE_PROPERTY(pf_cfifteen, cp, tp)
{
real np = 5.;
real nn = 2.;
real esmax = 0.63;
real esmin = 0.5;
real bp = 0.6237;
real sm_val = 1.0e-12;
real P[ND_ND];
real delt, pfr, nc, fric, Smag, vfrac, dudx, dudy, dvdx, dvdy, r, radv, DIV;

/* Retrieve volume fraction and magnitude of the deviatoric Smag tensor */
/*x direction is axial direction, y direction is radial so dvdy = d(radialvelocity)/dradial */

vfrac = C_VOF(cp,tp);
dudx = C_U_G(cp,tp)[0];
dudy = C_U_G(cp,tp)[1];
dvdx = C_V_G(cp,tp)[0];
dvdy = C_V_G(cp,tp)[1];
radv = C_V(cp,tp);
C_CENTROID(P,cp,tp);
r = P[1];
DIV = dvdy + radv/r + dudx;
Smag = sqrt(pow((dvdy-(1./3.)*DIV),2.)+2.*pow((0.5*(dudy-dvdx)),2.)+pow((dudx-(1./3.)*DIV),2.));

__________________________________________________ ____

I had to leave out the rest of the UDF because it pertains to my research and I have not published yet. Below here it just uses the DIV in "if" statements, so any user that wants to use the above DIV part of the code you just need the folowing:
__________________________________________________ __________
dudx = C_U_G(cp,tp)[0];
dudy = C_U_G(cp,tp)[1];
dvdx = C_V_G(cp,tp)[0];
dvdy = C_V_G(cp,tp)[1];
radv = C_V(cp,tp);
C_CENTROID(P,cp,tp);
r = P[1];
DIV = dvdy + radv/r + dudx;
Smag = sqrt(pow((dvdy-(1./3.)*DIV),2.)+2.*pow((0.5*(dudy-dvdx)),2.)+pow((dudx-(1./3.)*DIV),2.));

__________________________________________________ _________

Hope this helps everyone!

Casey
Kanarya is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
how to set periodic boundary conditions Ganesh FLUENT 13 January 22, 2014 05:11
UDF for wall slipping HFLUENT Fluent UDF and Scheme Programming 0 April 27, 2011 12:03
64bit error compiling UDF : divergence detected UtoS_99 FLUENT 7 March 29, 2011 03:19
UDF: Density Cell Gradient Vector Macros matteo FLUENT 0 December 1, 2007 13:14
changing gravity vector direction using UDF Nico FLUENT 0 September 7, 2006 12:00


All times are GMT -4. The time now is 06:12.