[ANSYS Meshing] How to get rid of skewed elements while meshing a pipe with many interfacing surfaces

everdimension · June 2, 2012, 12:18

Hello!

Here is an object that i want to perform analysis on: http://dl.dropbox.com/u/55240438/ima...so_section.png

Here is the geometry i made in design modeler. I had to slice it many times to be able to create 'sweeped method' mesh at those sections. I also made round corners where the fluid makes sharp turns. Then i applied virtual topology onto those corners so that the inflation is not interrupted there.

For some reason i get smooth and even inflation when i use "total thickness" method. Here is what you get: pic1 and pic2
It looks like a good mesh, but it has some bad elements. After playing with the inflation layers number and total thickness size the mesh was improved. After that i tried to raise the "Relevance" value. For some reason its effect cannot be predicted. I got best results at the relevance "20", "21" and "23" and other values just worsened the mesh severely. Also the result on one and the same value is not always the same after regenerating the mesh a few times.
The best parameters i got were
Min Orthgonal Quality: 0,152
Max Skewness: 0.9251

After improving skewness i was able to finally reach convergence in FLUENT but only at k-e turbulence model.

So I wish to improve the mesh more and i need help and advice.
Please, help

You may download my project here http://dl.dropbox.com/u/55240438/ima...ipemeshing.rar

Gweher · June 4, 2012, 02:29

Hi,

I had a quick look at your geometry, first do you have access to ICEM? If yes I should proceed with this meshing software as it allows you to create easily O-grids and permits more "control" than Ansys Meshing.

You can still create O-grid with AM, just split your inner pipe and assign mapped faces (I generate a coarse mesh just to show you the principle). You will have a far better mesh. I would also assign "sweep" methods to your parts, using source and target face in order to "help" the meshing software. I quickly split your geometry and created 2 O-grids. If you spend more time splitting your geometry you could improve your mesh metrics

everdimension · June 4, 2012, 04:51

Thank you for the reply!

Well, that looks very good, i didn't know about this method.
But how will the mesh behave at the 'branches' and at the 'turn' when the inflation is added? And as I understand you still cannot avoid tetra cells, and the parts where hexa cells transform to tetra are the most problematic ones.

And, hmm, how did you 'quickly' split the geometry like that? I can think of one way but it's really not quick...))

And I do not have ICEM, unfortunately.

Gweher · June 4, 2012, 20:17

Well for the splitting it took me 10-15min, but once you know how to do it it's quite easy and quick. You just need to split it like I showed it previously. I'm more familiar with ICEM but I use AM for simple geometries, and then use multizone to mesh more "complex" one with ICEM.

For the inflation layers I'm not sure how it will "behave" with AM, I should first assign sweep methods to your parts and then right click on that method and use "inflate this method". And as I said before, for me it's way easier to mesh your geometry with ICEM, but as you don't have it you should continue splitting your geometry into easier "meshable" sub-parts.

If I have some time, I'll try to find a way to mesh your geometry within AM.

everdimension · June 5, 2012, 15:41

Turns out i do have ICEM CFD! That was very pleasant to find out.

So i installed it, but obviously it is going to take some time learning how to use it. I really hope that in the end I would be able to mesh this model with high quality elements. I would be grateful for any kind of further tips.
Thank you, Gwenael, for looking into my model.

By the way, i was able to improve the mesh in Ansys Meshing even a little more just by adding same 'edge sizing' for all of the sweepable elements.The max skewness is now 0.899, min orthogonal quality is 0.159, but... The simple 'element quality' property is as low as 0.043. Do I understand correctly that this property is also important and it shouldn't be that low at all?

hwet · October 2, 2014, 23:45

minimum orthogonal quality of as low as 0.1 is acceptable

hwet · October 2, 2014, 23:45

you can also improve your mesh further in fluent by just a few clicks

Ata.tavakkoli · September 13, 2016, 12:01

Dear every body

i need help in meshing complex geometry
i have tried many options but still my calculation not converge
how i can send my geometry file to you ?

Kapi · September 13, 2016, 18:59

post pic of your geometry and settings u r using!

Ata.tavakkoli · September 14, 2016, 03:28

Dear Sir

please check picture i attached . the picture is taken from meching window , you can see setting which i made to . and skewness quality bars exist in bottom .

thanks

Kapi · September 15, 2016, 02:22

click on the bar to see which places have high skewness
then pick those faces/edges and give sizing on them. Make sure you use behavior as "Hard" in your sizing function

Ata.tavakkoli · September 15, 2016, 02:55

when i click on the skewness bars it does not show anything on geometry .
may i have to enable any option in setting ?

Kapi · September 15, 2016, 18:54

it should show, no settings for that
when you click on it, what does it show? can u take pic?

June 2, 2012, 12:18	How to get rid of skewed elements while meshing a pipe with many interfacing surfaces	#1
everdimension New Member Join Date: May 2012 Location: Moscow Posts: 27 Rep Power: 13	Hello! Here is an object that i want to perform analysis on: http://dl.dropbox.com/u/55240438/ima...so_section.png Here is the geometry i made in design modeler. I had to slice it many times to be able to create 'sweeped method' mesh at those sections. I also made round corners where the fluid makes sharp turns. Then i applied virtual topology onto those corners so that the inflation is not interrupted there. For some reason i get smooth and even inflation when i use "total thickness" method. Here is what you get: pic1 and pic2 It looks like a good mesh, but it has some bad elements. After playing with the inflation layers number and total thickness size the mesh was improved. After that i tried to raise the "Relevance" value. For some reason its effect cannot be predicted. I got best results at the relevance "20", "21" and "23" and other values just worsened the mesh severely. Also the result on one and the same value is not always the same after regenerating the mesh a few times. The best parameters i got were Min Orthgonal Quality: 0,152 Max Skewness: 0.9251 After improving skewness i was able to finally reach convergence in FLUENT but only at k-e turbulence model. So I wish to improve the mesh more and i need help and advice. Please, help You may download my project here http://dl.dropbox.com/u/55240438/ima...ipemeshing.rar

September 13, 2016, 12:01	Meshing Complex Geometry	#8
Ata.tavakkoli New Member Ata Join Date: Sep 2016 Posts: 3 Rep Power: 9	Dear every body i need help in meshing complex geometry i have tried many options but still my calculation not converge how i can send my geometry file to you ?

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June 4, 2012, 04:51		#3
everdimension New Member Join Date: May 2012 Location: Moscow Posts: 27 Rep Power: 13	Thank you for the reply! Well, that looks very good, i didn't know about this method. But how will the mesh behave at the 'branches' and at the 'turn' when the inflation is added? And as I understand you still cannot avoid tetra cells, and the parts where hexa cells transform to tetra are the most problematic ones. And, hmm, how did you 'quickly' split the geometry like that? I can think of one way but it's really not quick...)) And I do not have ICEM, unfortunately.

June 4, 2012, 20:17		#4
Gweher Senior Member Gwenael H. Join Date: Mar 2011 Location: Switzerland Posts: 392 Rep Power: 20	Well for the splitting it took me 10-15min, but once you know how to do it it's quite easy and quick. You just need to split it like I showed it previously. I'm more familiar with ICEM but I use AM for simple geometries, and then use multizone to mesh more "complex" one with ICEM. For the inflation layers I'm not sure how it will "behave" with AM, I should first assign sweep methods to your parts and then right click on that method and use "inflate this method". And as I said before, for me it's way easier to mesh your geometry with ICEM, but as you don't have it you should continue splitting your geometry into easier "meshable" sub-parts. If I have some time, I'll try to find a way to mesh your geometry within AM.

June 5, 2012, 15:41		#5
everdimension New Member Join Date: May 2012 Location: Moscow Posts: 27 Rep Power: 13	Turns out i do have ICEM CFD! That was very pleasant to find out. So i installed it, but obviously it is going to take some time learning how to use it. I really hope that in the end I would be able to mesh this model with high quality elements. I would be grateful for any kind of further tips. Thank you, Gwenael, for looking into my model. By the way, i was able to improve the mesh in Ansys Meshing even a little more just by adding same 'edge sizing' for all of the sweepable elements.The max skewness is now 0.899, min orthogonal quality is 0.159, but... The simple 'element quality' property is as low as 0.043. Do I understand correctly that this property is also important and it shouldn't be that low at all?

October 2, 2014, 23:45		#6
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	minimum orthogonal quality of as low as 0.1 is acceptable

September 13, 2016, 18:59		#9
Kapi Senior Member Join Date: Apr 2014 Location: Melbourne Posts: 584 Rep Power: 14	post pic of your geometry and settings u r using!

September 15, 2016, 02:22		#11
Kapi Senior Member Join Date: Apr 2014 Location: Melbourne Posts: 584 Rep Power: 14	click on the bar to see which places have high skewness then pick those faces/edges and give sizing on them. Make sure you use behavior as "Hard" in your sizing function

September 15, 2016, 02:55		#12
Ata.tavakkoli New Member Ata Join Date: Sep 2016 Posts: 3 Rep Power: 9	when i click on the skewness bars it does not show anything on geometry . may i have to enable any option in setting ?

September 15, 2016, 18:54		#13
Kapi Senior Member Join Date: Apr 2014 Location: Melbourne Posts: 584 Rep Power: 14	it should show, no settings for that when you click on it, what does it show? can u take pic?