Negative volume in moving mesh

mvee · September 17, 2011, 03:05

Hi to all

Can you shed light on How to locate negative volume in moving mesh problem?
In my case there are more than 10 dynamic zones. When I simplified the geometry to 2 dynamics zones, it works well. But with actual geometry, it shows negative volume and it is difficult to locate negative volumes.
My concern is to move the mesh not to find out negative volumes. But i think finding negative volumes I can attack on that component.

Thank you
mvee

m2montazari · September 18, 2011, 16:10

hi,
I didnt ever had negative volume problem, but I think you can simply use contour of cell volume to check the negative ones. and if when this error occurs the contour displaying is disabled, interrupt the iteration just before the timestep that a volume goes to negative value. then minimum value of cell volume is more volunteer to become neg. hope it helps.
yours,
mohammad

mvee · September 19, 2011, 00:51

Thanks for your reply.

I believe this is not the problem of smoothing, remeshing and skewness size. But still I will see the suggestion given by you.
Presently i am trying with moving zones which i think is improperly defined.

Thank you
mvee

3DmaniacSLDWRKS · September 29, 2011, 19:50

Negative volume happens when your geometry is moving large distances in small time-steps so that fluent can not re-mesh or smooth the grid well enough and therefor you get a negative volume error.
To fix that you need to make sure your time-steps are small enough, also try to change the settings for dynamic mesh zones, spring coefficient and so on.

Also remember that there should always be atleast one row of cells in between to geometries assuming there is flow in between them.

mvee · September 30, 2011, 00:04

Thanks 3DmaniacSLDWRKS.

You are right that body is moving large distances. Due to this only negative volume exists. I will try with reducing time stepping.
Can you please tell me when there is moving and stationary body exist in fluid domain, How should I adopt the modelling and meshing strategy? Bodies are solid and are present in fluid. This is just like you are modeling road (as stationary solid), vehicle (as moving solid) and fluid (as air). Am I clear?

Can you suggest in this regard?

3DmaniacSLDWRKS · September 30, 2011, 13:56

Settings and methods used are very case dependent, I would suggest you take a look at advanced tutorials Ansys has provided for their licensed, registered users. you can find them on their costumer portal. that would help you better understand dynamic mesh capabilities of FLUENT and give you some idea what to do next.

Also just as a reminder always preview your dynamic mesh to make sure everything works smooth and then move on to the iteration

September 17, 2011, 03:05	Negative volume in moving mesh	#1
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17	Hi to all Can you shed light on How to locate negative volume in moving mesh problem? In my case there are more than 10 dynamic zones. When I simplified the geometry to 2 dynamics zones, it works well. But with actual geometry, it shows negative volume and it is difficult to locate negative volumes. My concern is to move the mesh not to find out negative volumes. But i think finding negative volumes I can attack on that component. Thank you mvee

September 19, 2011, 00:51	Negative volume in moving mesh	#3
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17	Thanks for your reply. I believe this is not the problem of smoothing, remeshing and skewness size. But still I will see the suggestion given by you. Presently i am trying with moving zones which i think is improperly defined. Thank you mvee

September 29, 2011, 19:50		#4
3DmaniacSLDWRKS New Member Jack cosby Join Date: Jul 2011 Posts: 15 Rep Power: 15	Negative volume happens when your geometry is moving large distances in small time-steps so that fluent can not re-mesh or smooth the grid well enough and therefor you get a negative volume error. To fix that you need to make sure your time-steps are small enough, also try to change the settings for dynamic mesh zones, spring coefficient and so on. Also remember that there should always be atleast one row of cells in between to geometries assuming there is flow in between them. mvee and amin_ghaemian like this.

September 30, 2011, 00:04	Negative volume in moving mesh	#5
mvee Senior Member Vaze Join Date: Jun 2009 Posts: 172 Rep Power: 17	Thanks 3DmaniacSLDWRKS. You are right that body is moving large distances. Due to this only negative volume exists. I will try with reducing time stepping. Can you please tell me when there is moving and stationary body exist in fluid domain, How should I adopt the modelling and meshing strategy? Bodies are solid and are present in fluid. This is just like you are modeling road (as stationary solid), vehicle (as moving solid) and fluid (as air). Am I clear? Can you suggest in this regard?

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September 18, 2011, 16:10		#2
m2montazari Senior Member Mohammad Join Date: Feb 2010 Location: Shiraz, Iran Posts: 108 Rep Power: 16	hi, I didnt ever had negative volume problem, but I think you can simply use contour of cell volume to check the negative ones. and if when this error occurs the contour displaying is disabled, interrupt the iteration just before the timestep that a volume goes to negative value. then minimum value of cell volume is more volunteer to become neg. hope it helps. yours, mohammad

September 30, 2011, 13:56		#6
3DmaniacSLDWRKS New Member Jack cosby Join Date: Jul 2011 Posts: 15 Rep Power: 15	Settings and methods used are very case dependent, I would suggest you take a look at advanced tutorials Ansys has provided for their licensed, registered users. you can find them on their costumer portal. that would help you better understand dynamic mesh capabilities of FLUENT and give you some idea what to do next. Also just as a reminder always preview your dynamic mesh to make sure everything works smooth and then move on to the iteration