Mesh problems

DesmoR · February 6, 2018, 08:05

Hi guys.

I have some problem with my simulations of an open-wheel car.
I am doing a 3D steady analysis, but I get these errors:

-Conjugate-Gradient solver did not converge !
A floating point exception has occurred: floating point exception [Divide by zero]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide.
Context: star.segregatedflow.SegregatedFlowSolver

-WARNING: Ap = 0 on multigrid level 6, nRows = 4203, blockSize = 1
AMG coarsening halted.

I don't understand where and what are the problems
Can you explain me why I get these two errors?

Thanks.

ashokac7 · February 6, 2018, 08:09

Quote:

Originally Posted by DesmoR

Hi guys.

I have some problem with my simulations of an open-wheel car.
I am doing a 3D steady analysis, but I get these errors:

-Conjugate-Gradient solver did not converge !
A floating point exception has occurred: floating point exception [Divide by zero]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide.
Context: star.segregatedflow.SegregatedFlowSolver

-WARNING: Ap = 0 on multigrid level 6, nRows = 4203, blockSize = 1
AMG coarsening halted.

I don't understand where and what are the problems
Can you explain me why I get these two errors?

Thanks.

Check your set up first. You have to narrow down the possible problem. Like check your mesh quality and parameters. Check physics. Then try reducing urf of pressure velocity etc. What is your physics set up?

DesmoR · February 6, 2018, 08:16

I am using K-omega SST with Segregated flow and second order convection. I left all the default values for the urf.
For example the problems appear if I just add a volumetric control for the wake.

ashokac7 · February 7, 2018, 00:42

Quote:

Originally Posted by DesmoR

I am using K-omega SST with Segregated flow and second order convection. I left all the default values for the urf.
For example the problems appear if I just add a volumetric control for the wake.

ok so the problem may be with the mesh right!! May be there is sudden change in element sizes. Instead of using volumetric refinement we can use wake refinement. But it is available only with Automated mesh. You can refer CCM user guide.

me3840 · February 7, 2018, 19:49

This error is a pretty common problem for wrapped cases, is it wrapped?

DesmoR · February 8, 2018, 04:25

No, it's not wrapped. I import the geometry files from rhino using .step or .iges format and then I use directly the subtract operation.

me3840 · February 8, 2018, 17:21

If you try to split the region by non-contiguous, does it result in more than one volume?

slesar85 · February 9, 2018, 03:27

Quote:

Originally Posted by me3840

If you try to split the region by non-contiguous, does it result in more than one volume?

Yes, it's 100% solution. Each closed area must be a separate region

DesmoR · February 9, 2018, 04:37

Quote:

Originally Posted by me3840

If you try to split the region by non-contiguous, does it result in more than one volume?

I obtain only two more regions made of one cell each.
Should i get one more region for each part or just one?

ashokac7 · February 9, 2018, 04:42

Quote:

Originally Posted by DesmoR

I obtain only two more regions made of one cell each.
Should i get one more region for each part or just one?

There should be only one region. You should get message like no region would be created. If there are more then split them. You may decide if you want to keep them and then physics will be solved fro them otherwise delete them if they are unnecessary.

DesmoR · February 9, 2018, 04:47

Ok thank you. I will try to delete them and run again the simulation.
I will let you know.

Omel · November 6, 2018, 08:50

Quote:

Originally Posted by ashokac7

There should be only one region. You should get message like no region would be created. If there are more then split them. You may decide if you want to keep them and then physics will be solved fro them otherwise delete them if they are unnecessary.

Worked for me. Thanks a lot

SoAero · November 16, 2018, 09:56

Quote:

Originally Posted by me3840

This error is a pretty common problem for wrapped cases, is it wrapped?

Are you saying that floating point errors are common when using the wrapper?

me3840 · November 16, 2018, 10:10

Quote:

Originally Posted by SoAero

Are you saying that floating point errors are common when using the wrapper?

Not when used correctly. Floating point errors are very rarely the actual error in the simulation, they're usually a symptom of some other error, which includes user error.

The error I was referring to is the message from the AMG algorithm.

February 6, 2018, 08:05	Mesh problems	#1
DesmoR New Member Join Date: Feb 2018 Posts: 5 Rep Power: 8	Hi guys. I have some problem with my simulations of an open-wheel car. I am doing a 3D steady analysis, but I get these errors: -Conjugate-Gradient solver did not converge ! A floating point exception has occurred: floating point exception [Divide by zero]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide. Context: star.segregatedflow.SegregatedFlowSolver -WARNING: Ap = 0 on multigrid level 6, nRows = 4203, blockSize = 1 AMG coarsening halted. I don't understand where and what are the problems Can you explain me why I get these two errors? Thanks.

February 7, 2018, 19:49		#5
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	This error is a pretty common problem for wrapped cases, is it wrapped? ashokac7 likes this.

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February 6, 2018, 08:16		#3
DesmoR New Member Join Date: Feb 2018 Posts: 5 Rep Power: 8	I am using K-omega SST with Segregated flow and second order convection. I left all the default values for the urf. For example the problems appear if I just add a volumetric control for the wake.

February 8, 2018, 04:25		#6
DesmoR New Member Join Date: Feb 2018 Posts: 5 Rep Power: 8	No, it's not wrapped. I import the geometry files from rhino using .step or .iges format and then I use directly the subtract operation.

February 8, 2018, 17:21		#7
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	If you try to split the region by non-contiguous, does it result in more than one volume?

February 9, 2018, 04:47		#11
DesmoR New Member Join Date: Feb 2018 Posts: 5 Rep Power: 8	Ok thank you. I will try to delete them and run again the simulation. I will let you know.