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

How to compute UDS fourth order gradient

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

Reply
 
LinkBack Thread Tools Display Modes
Old   December 23, 2009, 04:32
Default How to compute UDS fourth order gradient
  #1
New Member
 
emma
Join Date: Dec 2009
Posts: 4
Rep Power: 7
Emma66 is on a distinguished road
Hi! Guys!
I computate fourth order derivative with UDS through Gauss's divergence theorem.

We can obtain second order derivative of Φ through integrating Laplacian of Φ at cell c0.
For computing fourth order derivative, the idea is that using Gauss's divergence theorem again and let the second order derivative to be the UDS.

i was confusing that seconder order gradient is a vector here, and not like the original Φ, which is a scalar.

how to solve this problem?

I directly use C_face_loop to present second order derivative first.
c_face_loop(c,t,n)
{

F_AREA(A,C_FACE(c,t,n), C_FACE_THREAD(c,t,n));
At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);

NV_DS(Grad2, +=, C_UDSI_G(c,t,GRAD_1)[0], C_UDSI_G(c,t,GRAD_1)[1], C_UDSI_G(c,t,GRAD_1)[2],*,Aterm);
}

For computing fourth order derivative, I use magnitude of second order gradient to define a UDS.
C_UDSI(c,t,GRAD_1) =NV_MAG(Grad2)

The fourth gradient is then be,
c_face_loop(c,t,n)
{
F_AREA(A,C_FACE(c,t,n), C_FACE_THREAD(c,t,n));
At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);

NV_DS(Grad4, +=, C_UDSI_G(c,t,GRAD_1)[0], C_UDSI_G(c,t,GRAD_1)[1], C_UDSI_G(c,t,GRAD_1)[2],*,Aterm);
}


I was wondering if this is correct to slove it.

Could you please give me some advise?

Expecting your early reply!!

Many thanks,
Emma66 is offline   Reply With Quote

Old   April 27, 2010, 05:44
Smile Gradients
  #2
New Member
 
A
Join Date: Sep 2009
Posts: 14
Rep Power: 7
Ronnfors is on a distinguished road
Hi Emma,

I read your post but I cannot help you, sorry. But maybe you can help me with a problem that I had for months.

I program a UDF and I need the second order gradient of temperature or any UDSI. I see that you caluculate it by: "integrating Laplacian of Φ at cell c0" The code is:

"c_face_loop(c,t,n)
{
F_AREA(A,C_FACE(c,t,n), C_FACE_THREAD(c,t,n));
At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);
NV_DS(Grad2, +=, C_UDSI_G(c,t,GRAD_1)[0], C_UDSI_G(c,t,GRAD_1)[1], C_UDSI_G(c,t,GRAD_1)[2],*,Aterm);
}
"


The problem is that I dont fully understand the operation. Is there any reference to this operation?

I would be very happy if you could help me, this problem starts to be hopeless!
Thank you!
/Andreas
Ronnfors 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
Gradient of UDS gemini Fluent UDF and Scheme Programming 2 December 24, 2013 01:24
reconstruction gradient of a UDS gemini Fluent UDF and Scheme Programming 0 June 7, 2009 16:03
Fourth order surface normal gradient interpolation adona058 OpenFOAM Running, Solving & CFD 8 September 24, 2007 15:12
Gradient UDS tom FLUENT 1 April 28, 2006 03:46
How to compute gradient for non-orthogonal grids? Paul Hsieh Main CFD Forum 3 November 11, 2003 05:52


All times are GMT -4. The time now is 19:50.