Hi Andy and John,
Andy already expressed my point perfectly. I would just like to add one point regarding CFD/FE as this often comes up in the discussion and is given as an example where the use of CAD models works easily. Actually it doesn’t – at least not without human intervention when it comes to halfway complex 3D models. Often FE calculations are done in 2D where the meshing is numerically much more forgiving and in 3D people spend a lot of time cleaning up meshes. So they suffer from the same problems but the code packages usually come with cleanup tools.
In addition there are also mesh free FE approaches based on compact smoothing kernels. They avoid the issue already from the start but the mathematical foundation is completely different and much more complex.
So at the end of the day, there is no such thing as a free lunch. But I’m certainly looking forward to seeing DAGMC in combination with FLUKA, which I think is very good initiative.
Cheers
Chris
From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Andrew Davis
Sent: 04 February 2016 07:48
To: cary_at_colorado.edu
Cc: fluka-discuss_at_fluka.org
Subject: Re: [fluka-discuss]: geometry import from cad file
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<mailto: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<tel:%2B%2055%20%2819%29%203512-2490>
>> >>
>> >>
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Received on Thu Feb 04 2016 - 11:36:59 CET