XANSYS Message: 16518 [Go back to message list] [bookmark on del.icio.us]
No rating yet Subject: Re: IGES import with subsequent creation of a Solid model Author: Sheldon Imaoka Date: 2000-10-11 21:09:00Hi Mitch, I believe that what you mentioned is correct about the faceted surface representation ('MicroTopology', if I recall correctly). The "fineness" (is that a real word? My dictionary says so, but it sounds kinda funny.) is controlled via the GMFACE command. [I think that prior to the introduction of the GMFACE command somewhere around 5.5, this was controlled via IOPTN,GTOLER, which, of course, also controlled merge tolerances at 5.4.] The Shapes (XOX) modeler still has different geometry representation than the standard ANSYS modeler. Shapes uses MicroTopology which has surfaces as a set of triangular (or rectangular) facets [for lack of a better explanation], the resolution of which is controlled via GMFACE as noted above. On the other hand, the standard ANSYS modeler uses NURBS representation for surfaces, etc., so instead of chopping up a surface into triangular and rectangular facets, there are equations (NURBS) representing the surfaces (then, you get into the whole thing about trimmed surfaces, boundaries, etc., which I won't bore you with).
One point of confusion myself and others have had is when the Shapes (XOX) modeler really comes into play. I had heard from others that, as Mark mentioned below, during *any* boolean operations, the Shapes modeler is used. [unless I misread Mark's statements since I don't want to put words into anyone's mouths] I am under the impression that the Shapes and ANSYS standard modelers are completely different. In other words, Shapes has its own Boolean operations, and so does ANSYS standard modeler. Hence, if a user imports a model that uses Shapes modeler, it remains in the Shapes modeler. Likewise, if a user imports a model that is in the ANSYS standard modeler, it never uses Shapes (XOX), but it only uses ANSYS standard modeler operations. That is why the Shapes (XOX) modeler has limited Boolean capabilities (if all Booleans were done by Shapes modeler, I couldn't imagine why the XOX method would be limited). Also, that is why geometry repair and simplification tools are available. That also may explain why the standard (ANSYS) modeler has all Boolean operations available as well as geometry creation tools, but it lacks the simplification and repair tools Shapes has.
I think most people are familiar with the points below, but to digress and cover something else: 1) Shapes (XOX) modeler is used when default IGES import is done *or* any Connection Kit product with "Allow defeaturing" is turned on. (For CK, you get an *.aaa file) 2) Standard (ANSYS) modeler is used when the alternative IGES method is used or the default "no defeaturing" for Connection Products is used. (For CK, you get an *.anf file)
Anyways, I hope I didn't beat this topic to death. I also hope the above info is correct, so anyone, please feel free to correct any points I might've missed. [I don't want to disseminate misinformation as I am so often inclined to do]
:)
Laters, Sheldon CSI
http://www.csi-ansys.com/ Collaborative Solutions, Inc. http://www.ansys.net/ (no affiliation with ANSYS, Inc.)
P.S. DesignSpace is NURBS-based, like ANSYS standard modeler, from what I heard from folks at ANSYS. AGM is Parasolids-based.
----- Original Message ----- To: Sent: Wednesday, October 11, 2000 5:01 PM
> Thanks for the clarification.
> Still I have one question. I seem to recall having read that the "new" > geometry and topology repair tools work using a triangular mesh > representing the surfaces of the structure. I thought that I read this > in the update seminar notes for the software release at which this > capability was introduced (5.4?). Unfortunately, that was some time ago > and I no longer have a copy of the notes around. Can you enlighten me > as to whether this understanding is (somewhat) correct, or whether the > geometry/topology repair is done directly using whatever native geometry > representation is used by XOX?
> Thanks for your help.
> Mark Rodamaker wrote:
> > The conclusions from this are correct but some of the details are not. > Ansys > > does not really want to tell you what is going on here so they have > invented > > some new terms. My understanding is as follows. When you do a Boolean > > operation in Ansys, the entities are transferred from the Ansys > database to > > XOX, the operation is performed in XOX and the result is then sent > back to > > the Ansys database. The "traditional" Ansys database is not the XOX > > database. When you do an alternate IGES import, the model is stored in > the > > Ansys database. You can perform Booleans on this database . Ansys > doesn't > > care and doesn't really know it was imported. However, if you use the > > default import, the model is read and stored in the XOX database. It > is > > never saved in the Ansys database so many operations you might like to > > perform are not possible. Examples are keypoint and line creation > since the > > results of these opeations are normally stored in the Ansys database. > The > > thought was that the XOX database would be more robust than the Ansys > > database. In practice , we very seldom use the default because it is > not > > noticeably more reliable and it precludes subsequent work.
> > ----- Original Message ----- > > From: "Mitch Voehl" > > To: > > Sent: Wednesday, October 11, 2000 9:48 PM > > Subject: Re: [xansys] IGES import with subsequent creation of a Solid > model
> > > The "default" and "alternate" IGES import options use two different > > > underlying solid modeling engines for storing the imported geometry. > > > (See section 6.2 of the Modeling and Meshing Guide.) The > "alternate" > > > method uses the traditional ANSYS (XOX) solid modeling engine, and > > > therefore allows you to perform any of the standard ANSYS solid > modeling > > > operations after the IGES geometry has been imported.
> > > The "default" option uses a different method of representing the > > > geometry -- I believe that it basically approximates the surfaces > > > (areas) of the object with a mesh of triangles. The mesh is coarse > in > > > flat regions and fine in regions of high curvature. This surface > > > representation method facilitates the capabilities of the geometry > and > > > topological repair tools since most of these operations can be done > by > > > creating, merging, or deleting sets of adjacent triangles, rather > than > > > trying to work with the mathematics of the NURBS used by the > "standard" > > > ANSYS geometry engine.
> > > Unfortunately, one cannot use the features of both geometry engines > at > > > the same time. If you import your geometry using the "default" > method, > > > you have access to the "new" geometry and topology repair tools, but > do > > > not have access to most of the standard geometry creation and > boolean > > > operations. If you choose to import your geometry using the > "alternate" > > > method, you have access to all of the ansys geometry creation and > > > boolean operations (OK, so sometimes they have trouble operating on > > > imported geometry), but do not have access to the new geometry and > > > topology repair tools.
> > > Unfortunately, I believe if you import your geometry using the > "default" > > > method, which stores the geometry surfaces as a mesh of triangles, > that > > > you cannot then CDWRITE out your solid model, as there is yet no way > to > > > convert the surface mesh back into the type of mathematical surfaces > > > (NURBS, BSPLINES ?) used in the IGES specification.
> > > Section 6.2 in the Modeling and Meshing Guide states:
> > > ANSYS provides the following two options for importing IGES > files:
> > > DEFAULT--This option uses an enhanced geometry database and > > > should, in almost all cases, be your choice...
> > > ALTERNATE--This option uses the standard ANSYS geometry > > > database, and is provided largely for backward compatibility with > the > > > previous RV52 import option.
> > > which clearly promotes the use of the new "default" import option. > > > Unfortunately, I have found I almost always have to manipulate the > > > geometry after I import it, and therefore I have encountered very > FEW > > > situations where I can use the "default" option. For me, the > > > "alternate" method is, in almost all cases, my choice.
> > > Bottom line, if you want to create or manipulate the geometry after > > > importing an IGES file, use the "alternate" method.
> > > JPatterson@h... wrote:
> > > > Karol,
> > > > Will CDREAD and CDWRITE help you? Perhaps import your iges > geometry, > > > do a > > > > CD WRITE, then run your APDL and then CDREAD.
> > > > Karol Galik > > > > > xansys > > > > .pitt.edu> cc: > > > > Subject: [xansys] > IGES > > > import with subsequent creation of a Solid model > > > > 10/11/00 > > > > 01:07 PM
> > > > Hi everybody,
> > > > I got an IGES file from a company ( an implant) that has to be > > > combined > > > > with my > > > > model (bones). My model is created in APDL and it will > automatically > > > offset > > > > entity numbers if there are any entities to start with. The > problem is > > > that > > > > ones > > > > I transfer the IGES file with "default defeaturing" (transfer > works > > > > perfect, > > > > Booleans work) a cannot create any additional entities. > > > > If I transfer it with ALTERNATE I have to recreate volumes.
> > > > Is there any way that you can create additional solid models (from > new > > > > keypoints, lines...) after the "default defeaturing"?
> > > > Karol Galik > > > > PhD student at ME department > > > > University of Pittsburgh, PA > > > > 412 624 9776 Phone > > > > kagst34@i...