CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > ANSYS Meshing & Geometry

ICEM: setting tolerance

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 28, 2009, 06:32
Question ICEM: setting tolerance
  #1
Senior Member
 
Join Date: Apr 2009
Posts: 118
Rep Power: 8
lost.identity is on a distinguished road
Hi,

When creating a surface using ICEM it asks for a tolerance and I'm not sure what value to enter.

Lets say I have a cuboid with the following dimensions, l=1 m, b=0.00017 m and h=0.07 m. If I were to create surfaces on each of the six side what would I set the tolerance to be? Would it be a value less than 0.00017m?

Thanks.
lost.identity is offline   Reply With Quote

Old   April 29, 2009, 11:08
Default Tolerance
  #2
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
The tolerance you are talking about is to connect adjacent curve ends within in this tolerance. This function automatically closes gaps between boundary edges using a best fit approximation. For best results, just connect the curves end to end to form a closed loop that doesn’t need the tolerance to close gaps… In your case, the default setting of 0.01 is fine.

One other thing… For creating this geometry, you will save time by creating it using Create/Modify Surfaces => Standard Shapes => Box… You just need to enter the three dimensions and it will create the connected box for you.
PSYMN is offline   Reply With Quote

Old   May 9, 2009, 10:21
Unhappy
  #3
Senior Member
 
Join Date: Apr 2009
Posts: 118
Rep Power: 8
lost.identity is on a distinguished road
Hi,
Thanks for the reply.

My real geometry is actually an angular segment as I'm trying to do an axisymetric geometry. The problem is the CFD code I'm using can't deal with a true angular segment where the two side surfaces meet on the axis. So I'm having to create a surface with a finite size as the 'bottomwall'.

This finite surface has a width of 2e-5 m and length 1.2m. I created the geometry in ICEM with the tolerance set at the default 0.01. Then I clicked repair geometry and it highlighted the curves on the bottomwall as yellow (shown below). I don't know how I could fix this.

Thanks.

lost.identity is offline   Reply With Quote

Old   May 9, 2009, 22:04
Default Create a Surface
  #4
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
If using the Repair geometry option, you want to choose "fill"...

But I would probably just use the "create surface" from "2 to 4 curves" tool. In that case, since the curves actually connect at corner points, this tolerance won't even come into play. I would just leave it at the default. You can also create the surface from the 4 corner points if that suits you, in which case, there is no tolerance needed.
PSYMN is offline   Reply With Quote

Old   May 11, 2009, 07:02
Default
  #5
Senior Member
 
Join Date: Apr 2009
Posts: 118
Rep Power: 8
lost.identity is on a distinguished road
Cheers mate. I'm creating the surfaces from 2-4 curves. I just thought that it's a bit strange to leave the tolerance at default (esp. when my smallest dimension is smaller than the default tolerance). But I'm gonna take your word for it.

Also I thought that I always have to use the Repair Geometry tool every time I make a geometry so that it fixes the geometry? Or for such a simple geometry as mine would it suffice just to make the surfaces?
lost.identity is offline   Reply With Quote

Old   May 11, 2009, 09:26
Default These tools evolve over time.
  #6
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
These tools evolve over time.

For instance, that tolerance setting was added to support some customers with sloppy data who wanted the geometry to handle gaps between the ends of the curves. It is to allow the curves to extend by that much to make the loop. In your case, they don’t need to extend and the tolerance won’t even come into play. Before responding to you the first time, I tested it on a few cases to make sure.

The suite of surface creation and repair tools also evolved. The surface create tools were originally in DDN, but were brought over when that tool died. Once in ICEM CFD, the connectivity code was improved so that when you create a surface it automatically establishes the connectivity and you don’t need to go into the repair menu…

ICEM CFD is not a CAD tool, but it has a lot of ways to get something done. If one doesn’t work, try another…

Moving forward, the ANSYS Design Modeler tool will become the primary geometry creation and repair tool for ICEM CFD (in addition to the CAD interfaces). You should tray that out if you want to do more advanced things including adding or removing fillets, parameterizing geometry, etc.
PSYMN is offline   Reply With Quote

Old   May 11, 2009, 12:22
Default
  #7
Senior Member
 
Join Date: Apr 2009
Posts: 118
Rep Power: 8
lost.identity is on a distinguished road
Thanks for the detailed explanation.

I still have a few doubts on ICEM. Sometimes I feel that ICEM creates curves over the curves I've already drawn. I'm saying this because when I delete a curve, there's another curve, on the exact same location as the one I deleted. This also happens with points. I'm certain that I didn't create extra curves. I know it doesn't affect my mesh or anything but just thought that it's a bit strange.
lost.identity is offline   Reply With Quote

Old   May 13, 2009, 10:16
Default Color by count...
  #8
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
For the curves, turn on color by count... If you see yellow curves between two surfaces, then they are each single edge curves and you probably have two... Build topology will remove the duplicate if your tolerance is sufficient. This will also change the curve color by count to red, meaning a single curve is between those surfaces.

As for deleting curves, it really just makes them dormant. When you recreate a curve in the same location later, it first tries to restore the dormant curve. This has the effect of keeping your hopefully highest quality CAD curves. Not sure if that is what you are seeing, but I thought it was a good feature.

Good luck with ICEM CFD.
PSYMN is offline   Reply With Quote

Reply

Tags
icem tolerance

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
ICEM working directory setting Bogesz CFX 2 October 8, 2008 07:45
Tri Tolerance in ICEM Hexa Mohammad Faridul Alam CFX 1 November 21, 2007 11:55
ICEM Default Setting Customization Amod Kumar CFX 0 September 17, 2007 03:57
About Mesh size setting in ICEM Eric CFX 2 July 11, 2006 08:16
Warning 097- AB CD-adapco 6 November 15, 2004 05:41


All times are GMT -4. The time now is 13:09.