CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Laplacian of a TensorField ?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 23, 2010, 07:11
Post Laplacian of a TensorField ?
  #1
Senior Member
 
Join Date: Sep 2010
Location: France
Posts: 193
Rep Power: 6
T.D. is on a distinguished road
Hi,

How to calculate laplacian of A*T
if A is a scalar function of another scalar Main field c and , T is a 2nd order tensor

example

when i put

"
solve
(
fvm::ddt(c) + fvm::div(phi,c) == fvm::laplacian(A,T)
);

A=2*pow(c,2)+5;
"

it doesnot work!!!!?

Help lease??
T.D. is offline   Reply With Quote

Old   September 23, 2010, 07:18
Default
  #2
Super Moderator
 
niklas's Avatar
 
Niklas Nordin
Join Date: Mar 2009
Location: Stockholm, Sweden
Posts: 693
Rep Power: 19
niklas will become famous soon enough
Quote:
Originally Posted by T.D. View Post
solve
(
fvm::ddt(c) + fvm::div(phi,c) == fvm::laplacian(A,T)
);
so what you are saying is
Code:
scalar + scalar == tensor
I hope you see the mistake here
niklas is offline   Reply With Quote

Old   September 23, 2010, 08:02
Smile Hi
  #3
Senior Member
 
Join Date: Sep 2010
Location: France
Posts: 193
Rep Power: 6
T.D. is on a distinguished road
Execuse me,
In another words
the last term to the write is

∇(A*(∇.T)) which must be a scalar ok to go on with the c equation.


where A is a scalar and T is a second order tensor


so ∇T is div(T) and it is a vector ok (since divergence of a tensor) ??

and V=A*∇T is a vector then

so ∇(A*(∇.T)) must be written something like div(A,V) ?? knowing that A is always a function of c.


helpme
Thanks
T.D. is offline   Reply With Quote

Old   September 23, 2010, 08:14
Default
  #4
Super Moderator
 
niklas's Avatar
 
Niklas Nordin
Join Date: Mar 2009
Location: Stockholm, Sweden
Posts: 693
Rep Power: 19
niklas will become famous soon enough
Quote:
Originally Posted by T.D. View Post
∇(A*(∇.T))
ah ok, so its 2 div operations...
∇(A*(∇.T)) = fvc::div(A*fvc::div(T))

but this will make this term fully explicit.
I think it will be hard to treat it fully implicit.
If you run into stability problems you should try to split it up into implicit/explicit parts.
niklas is offline   Reply With Quote

Old   September 23, 2010, 09:43
Post HI
  #5
Senior Member
 
Join Date: Sep 2010
Location: France
Posts: 193
Rep Power: 6
T.D. is on a distinguished road
Hi Niklas thanks,


BUT A is a function of the scalar field c.

so it stays like that ∇(A*(∇.T)) = fvc::div(A*fvc::div(T)) ??


another thing please: do you know how to turn off all dimensions?

thank you so much
T.D. is offline   Reply With Quote

Old   September 23, 2010, 09:54
Default
  #6
Super Moderator
 
niklas's Avatar
 
Niklas Nordin
Join Date: Mar 2009
Location: Stockholm, Sweden
Posts: 693
Rep Power: 19
niklas will become famous soon enough
yes of course it does.

and why do you want to turn off dimensions,
it has saved me on numerous occasions.

but ok, I can see that the exp-function can give you problems.

if you are using 1.7.1 it is in
OpenFoam-1.7.1/etc/controlDict

lookup the line
dimensionSet 1;

and change the 1 to 0.
niklas is offline   Reply With Quote

Old   September 23, 2010, 12:40
Default Thanks
  #7
Senior Member
 
Join Date: Sep 2010
Location: France
Posts: 193
Rep Power: 6
T.D. is on a distinguished road
Thanks a lot Niklas
T.D. 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
Modifying the laplacian operator mlawson OpenFOAM Running, Solving & CFD 11 September 7, 2011 12:30
why laplacian() failed OFCrash OpenFOAM Running, Solving & CFD 1 February 1, 2010 08:32
Probable bug with laplacian steady state novyno OpenFOAM 1 November 23, 2009 20:31
Laplacian operator and nuSgs for heat equation Bedotto OpenFOAM Programming & Development 4 September 7, 2009 15:08
Implementation of div, laplacian, etc and variables sven OpenFOAM 3 July 19, 2009 18:18


All times are GMT -4. The time now is 16:40.