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No rating yet Subject: Re: IGES import with subsequent creation of a Solid model Author: Mitch Voehl Date: 2000-10-11 20:01:00Thanks 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.
> > > Hope it sparks an idea,
> > > Jim P.
> > > James J. Patterson > > > Engineering Analyst > > > Hendrickson Trailer Suspension Systems > > > 2070 Industrial Place SE > > > Canton, OH 44707 > > > Tele: 330-489-0095 > > > Fax: 330-489-0450 > > > email: jpatterson@h...
> > > 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...
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