CFD Online Logo CFD Online URL
Home > Forums > STAR-CCM+

High residual for extruder mesh

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

LinkBack Thread Tools Display Modes
Old   March 28, 2013, 11:27
Default High residual for extruder mesh
Arun Krishnan.L.H
Join Date: Jan 2013
Posts: 75
Rep Power: 4
arun7328 is on a distinguished road
Dear All,

My problem is a cylinder oscillating(swaying) on free surface. I am comparing the horizontal force from star ccm+ with experimental values.
I am have tried to use 3 different motions to simulate the same problem. The motions used were translation(overset), morphing and rigid body(overset). My inital cell size was about 5.7 lacs. I got a good agreement with experimental and CFD values. I had used trimmer for all the 3 cases.

Now i was trying to simulate the same problem with just about 50-70k cells and using morpher. In this case i used extruder mesh. I had used fine cells even at areas(the first time) far away from the cylinder. Increasing the sizes of these cells helped me to decrease the total cell count.

When i run this mesh using morpher, i am facing a problem with residual levels. I do understand residuals are not the final say for a solution to have converged. When i check the horizontal force, it is again similar to my previous results, agreeing well with the experiments. I have attached the screen shot of the force, residuals and my mesh.

1. The residuals settle to a high value but they remain constant there.The solution is not diverging i guess. I believe this is because the cells far away from the domain have a very high aspect ratio and hence there is something going wrong with the numerical calculation in those cells. How do i ascertain this in STAR CCM+? Is it possible to plot individual cell residual for me to see if they are high in the cells which are of interest to me? Ya and when i simulated it previously i was getting residuals of order of 10^-5(the first time for all 3 motions).

2. How should i improve my mesh to get a lower value of residuals?

There is no flow, cylinder is on calm water and i have wall boundary all around.

Please guide if you know the answer

Attached Images
File Type: jpg mesh.jpg (23.8 KB, 13 views)
File Type: jpg mesh1.jpg (49.6 KB, 9 views)
File Type: jpg residual.jpg (45.6 KB, 22 views)
File Type: jpg horizontal force.jpg (59.2 KB, 12 views)
arun7328 is offline   Reply With Quote


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
Velocity blows up suddenly after 30,000+ iterations lordvon OpenFOAM Running, Solving & CFD 15 October 19, 2015 13:52
pimpleFoam: turbulence->correct(); is not executed when using residualControl hfs OpenFOAM Running, Solving & CFD 3 October 29, 2013 09:35
calculation stops after few time steps sivakumar OpenFOAM Running, Solving & CFD 7 March 17, 2013 07:37
Floating point exception error Alan OpenFOAM Running, Solving & CFD 10 April 6, 2012 14:02
lift and drag on ship superstructures vaina74 OpenFOAM Running, Solving & CFD 3 June 8, 2010 12:30

All times are GMT -4. The time now is 09:44.