|
[Sponsors] |
September 25, 2014, 05:45 |
Immersed Solid Problem
|
#1 |
New Member
Peter
Join Date: Sep 2014
Posts: 5
Rep Power: 12 |
Hello dear forum !
I have a problem concerning the immersed solid method in CFX. What i am trying to do: I want to simulate the opening/closing of a valve. I build up a quasi 2-D model (2D- 5 degree wedge) and defined the fluid and immersed solid regions. During the simulation the valve is closing and therefor the valve cone is moving 2 mm. Everything is working fine for the first 0,8 mm. Then the results diverge and the massflow becomes high/unlimited. When i inspect the results short before the divergence i can see strange singularities in pressure/velocity right behind the moving valve cone. (see attached image). What i tried sofar: variation of: mesh sizes / time steps size / momentum scaling factor I set up a very similar simulation just with another cone angle (45° instead of 38°) and it runs without any problems. After days of trial and even more errors i have no clue what i could try. I would be very thankful for any advice what i could try now. Many thanks Peter |
|
September 25, 2014, 07:22 |
|
#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144 |
This shows your simulation has borderline numerical stability, so you need to make it more stable. Try:
* Improve mesh quality (this is the most important one - and I can see your inflation layers are not too good) * Double precision numerics * Smaller time step size |
|
September 25, 2014, 09:35 |
|
#3 |
New Member
Peter
Join Date: Sep 2014
Posts: 5
Rep Power: 12 |
Many thanks for your fast reply.
* Double precision numerics * Smaller time step size already tried this without success (even very very small timestep has no influence) Improve mesh quality: What i wonder about is that the Immersed Solid moves for 0,8mm through the mesh with the "same bad quality" without problems. I have also tried a finer mesh in the region where the immersed solid moves. I will try an even finer mesh and report you if this solves the problem. Many thanks sofar. Peter |
|
September 26, 2014, 05:52 |
|
#4 |
New Member
Peter
Join Date: Sep 2014
Posts: 5
Rep Power: 12 |
Hello !
I refined the mesh in the region where the valve cone is moving. The same problem occurs - at another timestep and another position of the cone but the problem still exists. Do you think its still a problem of mesh size/quality ? As i mentioned before a very similar modelsetup run without any problems with a much much coarser mesh. Many thanks Peter |
|
September 26, 2014, 07:01 |
|
#5 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144 |
Your problem is numerical instability.
Refining a mesh makes it less stable, so problems with a finer mesh are to be expected. The suggestions I made (mesh quality, double precision, smaller time steps, better initial condition) are the usual suspects for improving numerical stability. You can always improve mesh quality - and it will make the biggest difference if you do. In this case as this is a 2D simulation I would recommend trying hex elements as they are often more stable then tets/prisms. There are a few settings specific to immersed solids - I am not too familiar with them so cannot make a suggestion but I would try some of them. |
|
September 29, 2014, 06:09 |
|
#6 |
Senior Member
Marcin
Join Date: May 2014
Location: Poland, Swiebodzin
Posts: 313
Rep Power: 13 |
can You copy of error information which You have in solver ??
|
|
September 29, 2014, 07:32 |
|
#7 |
New Member
Peter
Join Date: Sep 2014
Posts: 5
Rep Power: 12 |
Hello !
I tried a pure hex mesh in the region, where the valve cone is moving. Same error ..... Error message: Parallel run: Received message from slave ----------------------------------------- Slave partition : 6 Slave routine : ErrAction Master location : RCVBUF,MSGTAG=1214 Message label : 001100279 Message follows below - : +--------------------------------------------------------------------+ | ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Floating point exception: Overflow | | | | | | | | | | | +--------------------------------------------------------------------+ Parallel run: Received message from slave ----------------------------------------- Slave partition : 6 Slave routine : ErrAction Master location : RCVBUF,MSGTAG=1214 Message label : 001100279 Message follows below - : +--------------------------------------------------------------------+ | ERROR #001100279 has occurred in subroutine ErrAction. | | Message: | | Stopped in routine FPX: C_FPX_HANDLER What i am confused about: If i change the cone angle from 37° to 45° the simulation run without error with nearly any meshes. This might be an annoying coincidence. |
|
September 30, 2014, 04:55 |
|
#8 |
Senior Member
Marcin
Join Date: May 2014
Location: Poland, Swiebodzin
Posts: 313
Rep Power: 13 |
You can try to change turbulence model to SST if You have k-epsilon
next way - on the domain turn on mesh deformation What do You have on outlet - opening or outlet ?? Best regards |
|
October 1, 2014, 13:20 |
|
#9 |
New Member
Peter
Join Date: Sep 2014
Posts: 5
Rep Power: 12 |
Hey,
many thanks for your advices !! I already use the SST-model. The outlet is defined as outlet / no message about back flow occurs. I will try an opening and report you if this solves my problem. Mesh deformation: I did not tried this sofar. I have to read a bit about this topic and will also report if i could solve the problem. Offtopic: I am still everytime amazed about the possibilities of the internet - within a second its possible to get in touch with persons - perhaps 10000 km away - and ask for an advise GREAT !! Many thanks sofar Stephan |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
problem in exporting stl files from solid work to openfoam | reza1980 | OpenFOAM | 2 | April 25, 2013 18:37 |
help on Immersed Solid approach | anori | ANSYS | 6 | May 25, 2012 07:02 |
Immersed Solid no flow! | exocubedesign | CFX | 3 | May 25, 2010 02:57 |
convergency problem with Solid Pressure Model | commonyue | Main CFD Forum | 0 | March 30, 2010 06:18 |
Rigid Body State Variables in Solid Immersed Simulation | Hamidreza | CFX | 1 | October 19, 2009 07:14 |