XANSYS Message: 16508 [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: Mark Rodamaker Date: 2000-10-11 09:10:00The 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.
Mark Rodamaker MCR Associates Sunnyvale,California voice: 408-736-1636
----- Original Message ----- To: Sent: Wednesday, October 11, 2000 9:48 PM
> 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 > > > > .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...