Re: [fluka-discuss]: geometry import from cad file

From: Andrew Davis <andrew.davis_at_wisc.edu>
Date: Thu, 04 Feb 2016 00:48:15 -0600

Hi John

Just to expand some of what Chris is saying, there are a number of things
that limit using CAD immediately.

1) overlaps - there can be very slight overlaps in geometry, imagine a
cylinder sliced through the circular cross section. The two surfaces should
be topological equivalent and usually are at the point of creation.
Sometimes going through a save and import these can drift from equivalence.

2) surface representation - CAD can operate with non analytic surfaces,
which require some form of simplification in order to be translated to use
the CSG geometry of the MC code

Both 1 and 2 hinder an automatic transfer from CAD to MC, in our experience
most time is spent fixing that CAD before it can be translated to MC or
used in DAGMC for example. However, for the models of the complexity that
would warrant the use of CAD, we find that we can turn around analysis 2 or
3 times faster than the translation route with something like McCAD or MCAM.

Furthermore, there are tools like Ansys-Spaceclaim which make fixing the
CAD very intuitive and straightforward.

The FE approaches (including Attila) require dramatic simplifications and
cleaning in order to be able to mesh (which is not the case for Dagmc),
which are often the show stoppers that Chris is speaking of.

Chris, appologies for putting words in your mouth, feel free to correct if
I've misspoken on your behalf.

Thanks

Andy

################

Hi Chris,

I am very interested to learn more about your thoughts on this.

There is a big CAE industry for fluid dynamics, electromagnetics,
and structural mechanics, all of which do seem to integrate CAD,
at least well enough so that companies buy their stuff. Do you
have an idea of what distinguishes MC?

There are also commercial radiation modeling products, like
FastRad (Geant4 based I

On 2/3/16 1:19 PM, Chris Theis wrote:

>
> >
> > Dear Marlon,
> >
> > The complex geometries which you seem to be referring to have been
built "manually" without CAD import. CAD import is a widely discussed topic
but the technical difficulties discussed in the thread that you're
referring to still stand. Additionally, in the more than 11 years that I've
been working computer graphics industry I have not come across one single
CAD file in an exchange format which was numerically 100% robust and
correct so that it would not require substantial manual corrections. Often
the problems are visually not apparent but as soon as you do some
mathematical modeling with the geometry (Monte Carlo, FEM, etc.) presumably
small errors can become show-stoppers.
> >
> > It is not impossible to use CAD with MC but, depending on the
application, it can be a rather laborious and non-trivial process.
> >

>>
>> >> Currently, Is using SimpleGeo and creating bodies from a 2D
background image still the best way to generate complex geometries for
Fluka?


>
>
> >
> >
> > This is one possible way and there is also the option in SG to use 3D
CAD files for verification of the model built by the user. But there are
several tools out there (e.g. GeoViewer, manual input via Boolean algebra),
each with its advantages and disadvantages. In the end it depends on the
user which tool suits him best.
> >
> > Cheers Chris
> >
> > On 03 Feb 2016, at 20:42, Marlon Saveri Silva <marlon.saveri_at_lnls.br>
wrote:
> >

>>
>> >> Dear experts,
>> >>
>> >>
>> >>
>> >> I would like an update regarding this 2010 discussion:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/2726.html
>> >>
>> >>
>> >>
>> >> I’ve seen some of yours studies with entire sites simulated at Fluka,
I wonder if they have been drawn without importing from a CAD file.
>> >>
>> >>
>> >>
>> >> Currently, Is using SimpleGeo and creating bodies from a 2D
background image still the best way to generate complex geometries for
Fluka?
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> Att.
>> >>
>> >>
>> >>
>> >> Marlon Saveri Silva
>> >>
>> >> Mechanical Engineer
>> >> Beamlines Instrumentation and Support Group – SIL
>> >> Brazilian Synchrotron Light Laboratory– LNLS – CNPEM
>> >> + 55 (19) 3512-2490 <%2B%2055%20%2819%29%203512-2490>
>> >>
>> >>


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Received on Thu Feb 04 2016 - 09:00:22 CET

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