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

solidDisplacementFoam linear? nonlinear?

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 6, 2016, 09:24
Default solidDisplacementFoam linear? nonlinear?
  #1
New Member
 
Xiaoxue Shen
Join Date: Aug 2016
Posts: 8
Rep Power: 9
xiaoxue is on a distinguished road
Hi everyone,

I applied the solidDisplacementFoam to analyse a simple case, a plate (1m*1m*3mm) with four edges fixed ,and put a constant 10 Pa force on one of the remainder face, the other with 0 Pa(using tractionDisplacement BC). The geometry is in like picture "Selection_016.png". and I set the d2dt2Schemes under the fvSchemes dictionary Euler. The displacement of the point at center of the plate is like the "Selection_017.png". It seems that there is nonlinear factors in it.

But the solidDisplacementFoam solver is a linear solver, I was really confused about this. Anybody can help me with this... I would appreciate it very much.

Wishes,

Xiaoxue


The D dictionary is

FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object D;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 0 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
consoleFixed
{
type fixedValue;
value uniform (0 0 0);
}
consoleSolid1
{
type tractionDisplacement;
traction uniform (0 0 0);
pressure uniform 0;
value uniform (0 0 0);
}
consoleSolid2
{
type tractionDisplacement;
traction uniform (0 0 0);
pressure uniform 10;
value uniform (0 0 0);
}
}

// ************************************************** *********************** //
Attached Images
File Type: png Selection_016.png (55.9 KB, 20 views)
File Type: png Selection_017.png (37.1 KB, 18 views)
xiaoxue is offline   Reply With Quote

Old   November 30, 2016, 14:02
Default
  #2
Super Moderator
 
bigphil's Avatar
 
Philip Cardiff
Join Date: Mar 2009
Location: Dublin, Ireland
Posts: 1,086
Rep Power: 34
bigphil will become famous soon enoughbigphil will become famous soon enough
Hi Xiaoxue Shen,

You are correct, solidDisplacementFoam assumes a linear analysis:
  • Linear geometry: small strains and rotations
  • Linear material: stress is linearly proportional to strain
  • Linear loading conditions: the standard boundary conditions are linear functions of displacement

Why do you think you are getting nonlinear results?

From your results for the displacement vs. time at the centre of the plate, the decay in the displacement amplitude suggests numerical dissipation: this is consistent with the use of a 1st order time integration scheme (backward Euler).

If you would like to reduce this numerical dissipation, you can try the following:
  • a smaller time-step
  • a higher order time differencing scheme e.g. "backward" is second order; though finite element methods typically use Newmark-beta schemes.

Philip
bigphil is offline   Reply With Quote

Old   December 4, 2016, 21:37
Default
  #3
New Member
 
Xiaoxue Shen
Join Date: Aug 2016
Posts: 8
Rep Power: 9
xiaoxue is on a distinguished road
Hi Philip,

Sorry to say thanks to you so late. Yes, as you say, after changing a smaller time-step,the dissipation disappeared. And I have to learn more about theories and methods, thanks for your work of solid mechanics and your helpful papers.

Best wishes,

Xiaoxue Shen
xiaoxue is offline   Reply With Quote

Reply

Tags
soliddisplacementfoam

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
2nd Order Convergence Problem for 3D Airfoil turkmengokce OpenFOAM Running, Solving & CFD 1 September 10, 2015 08:20
A turbulent test case for rhoCentralFoam immortality OpenFOAM Running, Solving & CFD 13 April 20, 2014 07:32
suitable boundary condition for scavenging process? immortality OpenFOAM Running, Solving & CFD 3 January 25, 2013 20:10
how to modify fvScheme to converge? immortality OpenFOAM Running, Solving & CFD 15 January 16, 2013 14:06
solution diverges when linear upwind interpolation scheme is used subash OpenFOAM 0 May 29, 2010 02:23


All times are GMT -4. The time now is 15:17.