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Does NX use splines to draw elliptical curves?

Valued Contributor
Valued Contributor

Does anyone know if NX uses splines to draw ellipses (or elliptical curves)?  I ask because solid bodies I create from extruded or revolved ellipical curves are getting distorted when imported into my FEA code.  Apparently there is a known issue with spline geometry doing this, and the developer was asking if that is what NX uses to construct ellipical curves.  Does anyone know?

 

Thanks!

9 REPLIES

Re: Does NX use splines to draw elliptical curves?

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

How is the FEA code accessing the NX geomerty?

- directly opening the NX part?

- going thru a translator (STEP/Parasolid/Other)?

Ken Akerboom Sr CAx Systems Engr, Moog, Inc.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled


Re: Does NX use splines to draw elliptical curves?

Siemens Phenom Siemens Phenom
Siemens Phenom

Ellipses, as well as other conic curves in NX, are created as and stored using their Conical form, not as Splines.  However, if an application is not able to use Conic curves directly then they will be converted, by the application code, to a form that can be utilized.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

Re: Does NX use splines to draw elliptical curves?

Valued Contributor
Valued Contributor

Thanks for the responses.

 

The FEA code uses a third party package (CAPRI CAE Gateway by CADNexus) to bring NX model geometry into the code.  Most likely that is where the problem is.  It's probably as John described, where CAPRI can't handle the conic curve and so is converting it to a spline (which the FEA can't handle!).  

 

I'll let the developer know.  Thanks again.

Re: Does NX use splines to draw elliptical curves?

Valued Contributor
Valued Contributor

@JohnRBaker wrote:

Ellipses, as well as other conic curves in NX, are created as and stored using their Conical form, not as Splines.  


Is this true even if the ellipse is cut into a segment?  The part is not using a full ellipse, but just a quarter section (see below). Just a thought that occurred to me.

 

040617_ellipse.png

 

Re: Does NX use splines to draw elliptical curves?

Siemens Phenom Siemens Phenom
Siemens Phenom

That should not make a difference.  Now it is possible that the curve might be stored as an 'Intersection Curve' which again is technically not a spline, but I suspect that there is less of a chance that downstream applications, at least not those based on Parasolid, will be able to directly handle an intersection curve so they will of course have to be converted into a spline, again, by the application.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

Re: Does NX use splines to draw elliptical curves?

Siemens Legend Siemens Legend
Siemens Legend

I think you have to create extremely simple models to avoid spline/ intersection curves . 
  ( - all edges circular or linear, does not leave much room for advanced shapes.)

 

In the initial post, you say that "solid bodies I create from extruded or revolved ellipical curves are getting distorted when imported into my FEA"

Is it the extruded / revolved surfaces/faces giving you the problem or the curve ?

Go back to the supplier of that software and ask for a patch.

Re: Does NX use splines to draw elliptical curves?

Valued Contributor
Valued Contributor

@1u7obd wrote:


Is it the extruded / revolved surfaces/faces giving you the problem or the curve ?

Go back to the supplier of that software and ask for a patch.


Yes, the revolved part is being distorted (flattened) when imported in to the FEA code (see below).

 

040717_part_distorted_after_import_into_JMAG.png

Re: Does NX use splines to draw elliptical curves?

Siemens Phenom Siemens Phenom
Siemens Phenom

From your image, it appears that the 'curves' are coming across OK, but that it's the faces that are not.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

Re: Does NX use splines to draw elliptical curves?

Valued Contributor
Valued Contributor

@JohnRBaker wrote:

From your image, it appears that the 'curves' are coming across OK, but that it's the faces that are not.


Yes, you're right about that. It is the revolved face that is getting flattened, not the parent curve.

 

I passed this info on to the developer and will let them sort it out.

 

Thanks for the feedback.  It was very helpful.