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

Lumped mass on triangular unstructured mesh

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 4, 2011, 23:08
Default Lumped mass on triangular unstructured mesh
  #1
New Member
 
Felipe Hernandez
Join Date: Apr 2011
Posts: 13
Rep Power: 5
Petrov is on a distinguished road
I was wondering what method is used for lumped mass matrices on a triangular mesh. Guass-Lobatto integration rules fail (in my experience) because the jacobian of the transformation from the bi-unit square to the triangle goes to zero on one corner. Therefore, zeros sometimes appear on the diagonals. (I'm not sure if I was clear in that explanation!)

I've been using a row-sum technique because I haven't had much luck with the "special lumping technique". Is that what is usually done?

Thanks!
Petrov is offline   Reply With Quote

Old   August 5, 2011, 03:09
Default
  #2
Senior Member
 
cfdnewbie
Join Date: Mar 2010
Posts: 546
Rep Power: 10
cfdnewbie is on a distinguished road
Petrov,
the transformation as you would describe it would indeed give a singularity when two nodes are projected onto one. Usually, what's done to prevent this is to define the transformation in another way:

A
|\
| \D
|__ \
B C

So D is chosen as the midpoint of the side. The Jacobi in that case behaves well, no singular point. You might read the book by Karniadakis about spectral methods for more on this!

Hope this helps!
cfdnewbie is offline   Reply With Quote

Old   August 5, 2011, 12:49
Default
  #3
New Member
 
Felipe Hernandez
Join Date: Apr 2011
Posts: 13
Rep Power: 5
Petrov is on a distinguished road
Great!

One more question:
Is this the correct generalization to a quadratic element?

Code:
D--G--C                  A
|       |                   | H
H   J  F         ==>   E   D
|       |                   |    G
A--E--B                  B-F--C
(With J in the middle of the triangle)
Petrov 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
2D Mesh Generation Tutorial for GMSH aeroslacker Open Source Meshers: Gmsh, Netgen, CGNS, ... 12 January 19, 2012 03:52
snappyHexMesh won't work - zeros everywhere! sc298 OpenFOAM Native Meshers: snappyHexMesh and Others 2 March 27, 2011 21:11
2d irregular grid Remy Main CFD Forum 1 December 22, 2008 04:49
Moving unstructured mesh with changing topology meaton OpenFOAM Running, Solving & CFD 6 April 27, 2008 07:56
unstructured vs. structured grids Frank Muldoon Main CFD Forum 1 January 5, 1999 10:09


All times are GMT -4. The time now is 13:14.