Fluent Dynamic Mehsing Help

Rhyno466 · April 8, 2012, 11:55

I am doing an analysis on tandem oscillating airfoils and I have the UDFs written to drive the motion, but I am struggling to get good re-meshing settings and would appreciate any input anyone might be able to give me. the main problem is that as the simulation progresses, the mesh seems to degrade significantly. The base mesh (shown below) has around 80k cells. I only end up with, depending on the settings, 17k to 32k cells. I cannot for the life of me seem to be able to find the appropriate settings that provide a high quality mesh throughout the simulation. I use the spring based smoothing and re-meshing methods. I am more focused on the re-meshing settings. I have tried the sizing function but have had little success. If anyone would like me to upload the udf library and the case I can do so.

Thanks,

Ryne

mvee · April 9, 2012, 06:49

Hi Rhyno466

You may try two options:
1) use small time step.
2) use the min and max cell size according to you mesh quality (this will be shown by min and max size in use default)

I believe reducing the time step size will solve your issue.

Best regards
mvee

Rhyno466 · April 9, 2012, 10:04

Thanks for your help! I have been using a dt of .02 (and sometimes .002) but I will try going smaller today. Can I ask how the time step size affects the re-meshing?

So just using the default settings should be sufficient? Is that the case with the sizing function as well?

mvee · April 10, 2012, 04:36

Hi

You can think by considering two dx - one small and another large with one velocity (rigid body). For the smaller dt and specified velocity, you require almost same dx which was defined during meshing. Otherwise this dx will increase with dt for the specified velocity.

Best wishes
mvee

Rhyno466 · April 10, 2012, 16:05

I have halved my time step (.001 down from .002), it made zero difference when using the default settings for both the re-meshing and sizing function. Do you think going lower with the time step will make any difference? If so, how small would you recommend?

mvee · April 11, 2012, 05:07

Hi

Use time step = ratio of (dx)minimum to velocity or use less than this. This might work, if there is a problem with coarseness of the mesh.

Regards
mvee

fsifsi · July 4, 2012, 03:16

can you try with diffusion- option instead of spring- based smoothing

Vidit Sharma · December 16, 2012, 09:38

Hi All..

Sir,
I am trying to rotate a 2D box or a 2D cup structure in Fluent using smoothing and remeshing. I am using tri mesh and as mentioned in Fluent Manual I am using smoothing and remeshing and also set the remeshing parameters from mesh info tab given in the remeshing menu. But the problem is that when i start simulation and it goes to first time step Fluent display "Updating mesh at time level N..." and here it stops and it happened alot of time and even waiting after a whole day it didnt worked. I also tried time step size from 0.01 to 0.000001 but it still show this problem.

Can you plz help in this case?

Thank u in advance

April 9, 2012, 06:49	Small dt and optimize remeshing settings	#2
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 16	Hi Rhyno466 You may try two options: 1) use small time step. 2) use the min and max cell size according to you mesh quality (this will be shown by min and max size in use default) I believe reducing the time step size will solve your issue. Best regards mvee

April 10, 2012, 04:36	effect of delta t	#4
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 16	Hi You can think by considering two dx - one small and another large with one velocity (rigid body). For the smaller dt and specified velocity, you require almost same dx which was defined during meshing. Otherwise this dx will increase with dt for the specified velocity. Best wishes mvee

April 11, 2012, 05:07	time step	#6
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 16	Hi Use time step = ratio of (dx)minimum to velocity or use less than this. This might work, if there is a problem with coarseness of the mesh. Regards mvee

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April 9, 2012, 10:04		#3
Rhyno466 Member Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 16	Thanks for your help! I have been using a dt of .02 (and sometimes .002) but I will try going smaller today. Can I ask how the time step size affects the re-meshing? So just using the default settings should be sufficient? Is that the case with the sizing function as well?

April 10, 2012, 16:05		#5
Rhyno466 Member Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 16	I have halved my time step (.001 down from .002), it made zero difference when using the default settings for both the re-meshing and sizing function. Do you think going lower with the time step will make any difference? If so, how small would you recommend?

July 4, 2012, 03:16		#7
fsifsi Member le Join Date: Nov 2009 Location: seoul Posts: 34 Rep Power: 16	can you try with diffusion- option instead of spring- based smoothing

December 16, 2012, 09:38		#8
Vidit Sharma Member Vidit Sharma Join Date: Aug 2012 Location: Delhi, India Posts: 32 Rep Power: 13	Hi All.. Sir, I am trying to rotate a 2D box or a 2D cup structure in Fluent using smoothing and remeshing. I am using tri mesh and as mentioned in Fluent Manual I am using smoothing and remeshing and also set the remeshing parameters from mesh info tab given in the remeshing menu. But the problem is that when i start simulation and it goes to first time step Fluent display "Updating mesh at time level N..." and here it stops and it happened alot of time and even waiting after a whole day it didnt worked. I also tried time step size from 0.01 to 0.000001 but it still show this problem. Can you plz help in this case? Thank u in advance