Problem with skewed elements

s7evin · January 6, 2012, 01:51

Hi everyone. I'm meshing a ship hull on Gambit and having skewed elements on 6 faces of the hull. I have applied a curvature sizing function on the hull side and have tried various ways(eg. refining the curvature sizing function, splitted the faces with skewed elements) but they do not work so far. I have the screenshot of the mesh here. Suggestions/ reasons would be most welcome.

Thank you in advance!

Terence

-mAx- · January 6, 2012, 04:41

try to reduce the max size (in size function panel)

shk12345 · January 6, 2012, 12:21

Just try to mesh different volumes differently with smaller mesh size.
And try to use use different schemes in areas where skewness is high.

s7evin · January 10, 2012, 02:09

Thanks mAx and shk12345! Reducing the max size for size function works!

s7evin · January 16, 2012, 12:16

I have another problem here. I'm trying to create the flow volume by subtracting the ship hull from a brick and the flow volume is multiphase, the top for the air and bottom one for water. I have persistently encountered the following errors:
1. ERROR: ACIS error 8032: inconsistent edge-face relationship
2. ERROR: ACIS error 30001: coincident face_face_ints with different body vertices.

I have done the volume checks and there are no errors detected. Funnily enough, I didn't encounter this problems when I did a scaled up version of the exact same model. Sorry for the numerous questions, I am very new to Gambit. I can also send the .dbs if you think you want to have a closer look.

Suggestions/ reasons are very welcome! Thanks!

-mAx- · January 17, 2012, 01:16

substracting will only work, if you do it with 2 volumes, or 2 surfaces.
But not with a volume and a surface.
In your case, your need to split your volume, with the surface.
Once your split is done, you can do your other split for multiphase.

s7evin · January 17, 2012, 03:14

Yeah, all were in volume form when I attempted the subtraction. I have already split the volume with surface as well. Could there be other reasons?

-mAx- · January 17, 2012, 03:21

hull volume should be fully in your outer volume (not just one half for instance), and both volume should be real

shk12345 · January 17, 2012, 08:04

hi
just try to make the two volume geometry in some cad model as gambit is too old now.
then import in gambit and do meshing and bc there and then import in fluent.
means make two real volume one your ship hull as a single volume and then make the outer two boxes and then substract them when they are 2 volumes.
Or try to do that in gambit whatever suits you.

Hope that will help you
Regards
Shk

s7evin · January 17, 2012, 12:49

Hi max, the hull volume is fully in their outer volumes and I have aligned to ensure it is as such. Also both volumes are real. I still could not subtract to obtain the flow volume.

Hi shk12345, what cad model do you recommend? I have tried to do it on Solidworks but there was so much cleanup to be done that it was more economical to do it on gambit.

Many thanks for your patience!

shk12345 · January 17, 2012, 12:51

Quote:

Originally Posted by s7evin

Hi max, the hull volume is fully in their outer volumes and I have aligned to ensure it is as such. Also both volumes are real. I still could not subtract to obtain the flow volume.

Hi shk12345, what cad model do you recommend? I have tried to do it on Solidworks but there was so much cleanup to be done that it was more economical to do it on gambit.

Many thanks for your patience!

try to make the solid ship hulk in solid works and make the outer portion in ansys workbench
i hope that will make the work easier

regards
shk

-mAx- · January 18, 2012, 07:37

ok I checked your geometry (half).
You have a problem at edges 1-2-6-143-12
You may fix this issue.
But I tried on the full geometry, and it is ok if you unite first both outer domains, and if you have only one hull volume. For that unite doesn t work, and you need to delete both hull volumes (lower geometry disabled). Then delete the common surface (face.81), and recreate volume from all hull surfaces.
Then substract is ok.
But attempting to split on the middle will fail.

s7evin · January 18, 2012, 11:15

Pardon my ignorance, but do I have to keep the flow volume split for multiphase?

-mAx- · January 19, 2012, 01:07

Yes you can, but you should do the split, after substract is successful

s7evin · January 28, 2012, 09:38

Thank you for the advice mAx!

January 6, 2012, 04:41		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	try to reduce the max size (in size function panel) s7evin likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider

January 17, 2012, 01:16		#6
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	substracting will only work, if you do it with 2 volumes, or 2 surfaces. But not with a volume and a surface. In your case, your need to split your volume, with the surface. Once your split is done, you can do your other split for multiphase. __________________ In memory of my friend Hervé: CFD engineer & freerider

January 17, 2012, 03:21		#8
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	hull volume should be fully in your outer volume (not just one half for instance), and both volume should be real __________________ In memory of my friend Hervé: CFD engineer & freerider

January 18, 2012, 07:37		#12
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	ok I checked your geometry (half). You have a problem at edges 1-2-6-143-12 You may fix this issue. But I tried on the full geometry, and it is ok if you unite first both outer domains, and if you have only one hull volume. For that unite doesn t work, and you need to delete both hull volumes (lower geometry disabled). Then delete the common surface (face.81), and recreate volume from all hull surfaces. Then substract is ok. But attempting to split on the middle will fail. __________________ In memory of my friend Hervé: CFD engineer & freerider

January 19, 2012, 01:07		#14
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	Yes you can, but you should do the split, after substract is successful s7evin likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider

January 6, 2012, 12:21	hi	#3
shk12345 Senior Member shoeb khan Join Date: Nov 2011 Posts: 179 Rep Power: 14	Just try to mesh different volumes differently with smaller mesh size. And try to use use different schemes in areas where skewness is high.

January 10, 2012, 02:09		#4
s7evin New Member Terence Chung Join Date: Dec 2011 Posts: 9 Rep Power: 14	Thanks mAx and shk12345! Reducing the max size for size function works!

January 17, 2012, 03:14		#7
s7evin New Member Terence Chung Join Date: Dec 2011 Posts: 9 Rep Power: 14	Yeah, all were in volume form when I attempted the subtraction. I have already split the volume with surface as well. Could there be other reasons?

January 17, 2012, 08:04	hi	#9
shk12345 Senior Member shoeb khan Join Date: Nov 2011 Posts: 179 Rep Power: 14	hi just try to make the two volume geometry in some cad model as gambit is too old now. then import in gambit and do meshing and bc there and then import in fluent. means make two real volume one your ship hull as a single volume and then make the outer two boxes and then substract them when they are 2 volumes. Or try to do that in gambit whatever suits you. Hope that will help you Regards Shk

January 17, 2012, 12:49		#10
s7evin New Member Terence Chung Join Date: Dec 2011 Posts: 9 Rep Power: 14	Hi max, the hull volume is fully in their outer volumes and I have aligned to ensure it is as such. Also both volumes are real. I still could not subtract to obtain the flow volume. Hi shk12345, what cad model do you recommend? I have tried to do it on Solidworks but there was so much cleanup to be done that it was more economical to do it on gambit. Many thanks for your patience!

January 18, 2012, 11:15		#13
s7evin New Member Terence Chung Join Date: Dec 2011 Posts: 9 Rep Power: 14	Pardon my ignorance, but do I have to keep the flow volume split for multiphase?

January 28, 2012, 09:38		#15
s7evin New Member Terence Chung Join Date: Dec 2011 Posts: 9 Rep Power: 14	Thank you for the advice mAx!

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