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Subject: Re: Tet meshing in FLOTRAN
Author: Chris Kennedy
Date: 1999-09-01 10:45:00

I have a function called 'Offset Specified Dir' in the Midsurface Compression
Tool that allows the user to pick a surface or set of surfaces and then also a
'target keypoint' along with an offset distance. It then processes the selected
areas and generates offset surfaces in the direction of the target keypoint.
Thus if you have a pressure vessel type geometry, you could put a keypoint at
it's center then select all the internal surfaces and this target keypoint,
specify the offset and have ANSYS generate the surfaces in the proper location.

Now the process of taking the newly offset surface and forming a volume is
something that I could include in the 'Offset Specified Dir' function, but
making it brick meshable is another task....

David J Power wrote:

> From: David J Power

> Brad,

> Perhaps a reasonable approach, assuming you are using CAD geometry, would be
> to use an "offset surfaces" utility to generate a extra layer of surfaces
> within the fluid domain near the bounding surfaces that can be brick meshed,
> with the rest of the domain being tet meshed - assuming accuracy is not
> required in this area of the model. Unfortunately you would still have to
> get your hands on 5.6 beta 1 to do this !

> Regards,

> David

> > -----Original Message-----
> > From: blamirand@t... [mailto:blamirand@t...]
> > Sent: Wednesday, September 01, 1999 10:20 AM
> > To: 'xansys@o...'
> > Subject: RE: [xansys] Tet meshing in FLOTRAN

> > Janet,

> > Thank you for the update. My best to all back there.

> > Brad

> > -----Original Message-----
> > From: Janet Wolf [SMTP:janet.wolf@a...]
> > Sent: Wednesday, September 01, 1999 9:49 AM
> > To: xansys@o...
> > Subject: RE: [xansys] Tet meshing in FLOTRAN

> > Brad--

> > 5.6 will have tet to hex mesh capabilities, and I've already
> > tested it on the beta version. The only problem was, I got a warning that
> > pyramid elements shouldn't be used at a wall; I haven't gone far enough to
> > see if it REALLY is a problem.

> > Janet Wolf
> > ANSYS/Houston

> > > -----Original Message-----
> > > From: Brad Lamirand [mailto:blamirand@t...]
> > > Sent: Wednesday, September 01, 1999 6:35 AM
> > > To: 'xansys@o...'
> > > Subject: RE: [xansys] Tet meshing in FLOTRAN

> > > Stefano,

> > > I've run several FLUID142 tet meshed problems with varying

> > > success, although sometimes I was more interested in
> > "trending"
> > > results to see what happens between differing geometry
> > than
> > > getting the exact answer. When I NEEDED to get the best
> > answer
> > > I could, I would take the extra time (sometimes a
> > considerable
> > > amount of time) to brick mesh. When I needed to do just a

> > > "quickie", I would try to get away with a tet mesh.

> > > The real trick to getting a tet mesh to work in Flotran is

> > > controlling your mesh density and change in aspect ration
> > as the
> > > mesh transitions away from the walls. This can be almost
> > near
> > > impossible. The first thing that I always recommended was
> > to mix
> > > and match your ESIZE,value with your SMRTSIZ,value to get
> > fine
> > > mesh where it matters and a courser mesh where it don't.
> > Also,
> > > the layer meshing in 5.5 goes a long way to helping,
> > although it
> > > makes LOTS of elements.

> > > The other problem, probably even tougher to overcome, is
> > how many
> > > more elements a tet meshed problem will take to converge
> > to a
> > > decent solution compared to a brick mesh. Although
> > Flotran only
> > > solves for one DOF at a time instead of all seven, it is
> > still
> > > very easy to get over a million nodes/DOF problem which is
> > of a
> > > degree of nonlinearity that even the contact analysis pros
> > would
> > > shudder at. The general rule of thumb that I like to use
> > as a
> > > first guess is that a tet meshed problem will take about
> > (7)
> > > times more elements than a brick element meshed problem,
> > although
> > > this is very dependant on how many boundaries are in your
> > problem.

> > > Lastly, I have been having very good luck with "sweep"
> > meshing
> > > volumes; i.e.- quad meshing an area and sweeping that into
> > a
> > > volume. Areas can almost always be entirely quad meshed
> > (99% of
> > > the time), and then the real trick is how to project that
> > 2D mesh into 3D.

> > > ON A SIDE NOTE - HAS ANYONE HEARD IF 5.6 WILL HAVE TET TO
> > HEX
> > > TRANSITION OF FLUID142 ELEMENTS?

> > > Hope this helps,

> > > Brad Lamirand
> > > Cooper Turbocompressor, Inc.
> > > Sr. Analytical Engineer
> > > 3101 Broadway St.
> > > Buffalo, NY 14225
> > > Phone: (716) 891-3764
> > > FAX: (716) 896-1233
> > > EMAIL: blamirand@t...

> > > -----Original Message-----
> > > From: Lucarelli, Stefano
> > [SMTP:stefano.lucarelli@d...]
> > > Sent: Wednesday, September 01, 1999 5:29 AM
> > > To: 'xansys@o...'
> > > Subject: [xansys] Tet meshing in FLOTRAN

> > > From: "Lucarelli, Stefano"
> >

> > > Hi group.

> > > We have to perform an air cooling problem with
> > Flotran but we have little
> > > experience in CFD. Geometry is quite complex and
> > brick meshing is not
> > > feasible. Has someone experience with tets in such
> > a case? Results we have
> > > got seem meaningless.
> > > We performed some benchmarks on simpler
> > geometries, and we found that
> > > results coming from tet meshes are very bad; brick
> > meshes, even
> > > if coarser,
> > > perform better.
> > > Any suggestion would be appreciated.

> > > Thanks in advance,
> > > Stefano

> > > Stefano Lucarelli
> > > Mannesmann VDO AG
> > > Entwicklung Informationssysteme NFZ
> > > IC43LE/S
> > > Tel.: 07721-67-2214
> > > email: stefano.lucarelli@d...

Chris Kennedy Email: ckennedy@t...
Offering THINK3 CAD products, see http://www.think3.com
Providing design, analysis, training and implementation services.
Customized productivity plug-ins for ANSYS software.
IBM Intellistations, Thinkpads and Netfinity servers.
Research Triangle Park, NC Ph: 919-387-8822 Fax: 919-363-4300
"for your solutions" http://www.thinkpeak.com
(formerly http://www.peaktechnology.com)

Posts possibly associated with message #4373AuthorDateScore
4364Tet meshing in FLOTRANStefano Lucarelli1999/09/01 
4365Re: Tet meshing in FLOTRANBrad Lamirand1999/09/01 
4367Re: Tet meshing in FLOTRANRoger Yang1999/09/01 
4369Re: Tet meshing in FLOTRANJanet Wolf1999/09/01 
4371Re: Tet meshing in FLOTRANBrad Lamirand1999/09/01 
4372Re: Tet meshing in FLOTRANDavid Power1999/09/01 
4373Re: Tet meshing in FLOTRANChris Kennedy1999/09/01 
4382Re: Tet meshing in FLOTRANBill Bulat1999/09/01 
4388Re: Tet meshing in FLOTRANRick Morgans1999/09/01