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

Problems with Dynamic Mesh: DEFINE_GRID_MOTION

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 2, 2006, 08:31
Default Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #1
Claudia
Guest
 
Posts: n/a
Hi everybody,

I'm trying to work with dynamic meshes with a DEFINE_GRID_MOTION UDF. The UDF does work, so the boundary for which it is defined does move, but the fluid-mesh stays the same so that I get after some iterations problems with negative cells. So does someone know this kind of problem and can tell me what I forgot to enable so that the interior-nodes will also change their places so that I will not get negative cells

Thanks
  Reply With Quote

Old   November 2, 2006, 11:04
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #2
qincz
Guest
 
Posts: n/a
maybe your time step is too large. in one step the boundary moved so big distance that u got the negative cells
  Reply With Quote

Old   November 3, 2006, 02:45
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #3
Claudia
Guest
 
Posts: n/a
I don't think that is the problem, because I can run 6 timesteps till the distance the boundary moves is so big that I get negative Volume cells. The problem is the surrounding cells do not react on the slowly motion of the boundary....
  Reply With Quote

Old   November 3, 2006, 03:57
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #4
cfdxue
Guest
 
Posts: n/a
1) pay attention to collaps factor,... ur mesh is not going to collaps,.. chang it,..

2) decrease ur time step,.. it could work, if ur collapse factor is little bit wrong,...

if its not work,.. inform me ur grid size,.. and time step,..

  Reply With Quote

Old   November 3, 2006, 05:02
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #5
Claudia
Guest
 
Posts: n/a
20 minutes ago I got it. Now it works. The mistake was the I took no trinangular cells. I took rectangular cells. But its for me a little bit strange that it doesn't work because of rectangular cells.... does somebody know how I can get it work with rectangular cells?

Thanks for the response. What is a collapse factor and where can I check and change it? Maybe this problem will appear someday and it would be good to know the answer...

Thanks a lot!
  Reply With Quote

Old   November 3, 2006, 05:47
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #6
cfdxue
Guest
 
Posts: n/a
It should work with both mesh,..

if u like, u could send me case file and udf at cfdxue@yahoo.com,..

best luck

  Reply With Quote

Old   November 3, 2006, 12:59
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #7
Eirik
Guest
 
Posts: n/a
Deformation of hex-meshes is initially swithced off in Fluent. You can turn this feature on through the TUI command 'def mod dmc sp soas', alternative set the scheme variable dynamesh/spring/all-element-type? to #t

Regards,

Eirik
  Reply With Quote

Old   November 3, 2006, 14:22
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #8
Claudia
Guest
 
Posts: n/a
That would explain why it doesn't work with rectangular mesh. Unfortunatly I don't know how to use both of them... can you tell me how and where I have to make the changes, please?

Thanks a lot!

  Reply With Quote

Old   November 3, 2006, 15:25
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #9
Eirik
Guest
 
Posts: n/a
In Fluent's Text User Interface (TUI - perhaps main window is a better phrase), just type the command I gave you. Typing return after each word will bring you to the next menu-level, like it's written brings you all the way down in one step. You'll then be prompted whether or not to turn the feature on, just answer yes.

- Eirik
  Reply With Quote

Old   November 3, 2006, 16:34
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #10
Claudia
Guest
 
Posts: n/a
Tanks a lot! I will try it on Monday morning first! (Here it is 22:40 at the moment Friday evening....) have a nice weekend!
  Reply With Quote

Old   November 6, 2006, 03:28
Default Re: Problems with Dynamic Mesh: DEFINE_GRID_MOTION
  #11
C. H.
Guest
 
Posts: n/a
Thanks a lot!

It does work!

Claudia
  Reply With Quote

Old   September 25, 2013, 14:23
Default
  #12
New Member
 
Alexandre Felipe Medina Correa
Join Date: Aug 2013
Posts: 3
Rep Power: 4
LexMedina is on a distinguished road
Dear Eirik,

I am having the same problem as Claudia. I tried to set the command you gave on TUI, but it didn't recognize the comand dmc...

I tried part by part, first with def, then mod, works fine. But the 'dmc so soas' does not work that well. Could it be a version problem? I am using 14.5 here in university.

Thanks,
Alex
LexMedina 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
Mesh motion with Translation & Rotation Doginal CFX 2 January 12, 2014 07:21
pls help. mesh collapsed with dynamic mesh. wlt_1985 FLUENT 1 July 28, 2011 01:53
snappyHexMesh won't work - zeros everywhere! sc298 OpenFOAM Native Meshers: snappyHexMesh and Others 2 March 27, 2011 21:11
Several problems with the mesh conversion utility when converting the meshes from Gridgen su_junwei OpenFOAM Meshing & Mesh Conversion 2 July 26, 2008 23:58
Can Fidap solve dynamic mesh problems? Sandy FLUENT 0 September 29, 2003 00:45


All times are GMT -4. The time now is 15:32.