Re: [fluka-discuss]: Area of a complicated surface

From: Alessandro Calamida <alex.calamida2_at_tiscalinet.it>
Date: Tue, 24 Mar 2020 16:33:11 +0100

I tried again with your method for larger and more complicate suface and
unfortunately it leads to big inconsistency with the results. The
differences with the expected results arrive to more tha 40%.
Unfortunately I do not think that this could be a good method to measure
the area of the surface after this results.

Best regards, Alessandro Calamida.

Il 18/03/2020 18:15, Alessandro Calamida ha scritto:
> After your correction I obtained a good results. The theorical Area
> was 312.59 cm^2 and the real one 314.16 cm^2.
>
> I run 10^6 particle for the simulation. An increase in statistics
> maybe could decrease the difference between the two valus. But the
> methods could be a good alternative to measure tha area of complicated
> surface.
>
> Best regards and thank you for your time, Alessandro Calamida.
>
> Il 18/03/2020 15:34, Answers ha scritto:
>> Hello
>> the USRBDX scoring should be FLUENCE, not current (what(1)=111 , not 11)
>> ( in an isotropic field, there is a factor two between fluence and
>> current, that is exactly what you find)
>> Regards
>>
>> On Wed, 18 Mar 2020, Alessandro Calamida wrote:
>>
>>> Dear FLUKA experts,
>>>
>>> I tried with differents bodys and test surface. Unfortunately the
>>> method that you suggested seems to not work for me.
>>>
>>> The last attempt was with a sphere and it leads the results of
>>> At=624.86 cm^2 instead of an Ar=314.16 cm^2 as it should be. The
>>> sphere has a radius of 5 cm.
>>>
>>> Maybe I made some mistakes. What is the correct value given by the
>>> usrbdx scoring that I have to use?
>>>
>>> I attach on the email the input and the scoring file.
>>>
>>> Best regards and thank you for your time, Alessandro Calamida.
>>>
>>> Il 16/03/2020 10:27, Answers ha scritto:
>>>> Dear Alessandro
>>>>
>>>> there is no obvious way for computing the surface of a complicated
>>>> region.
>>>>
>>>> However there could be a possibility (never tested... ) using the
>>>> FLOOD
>>>> option in the BEAMPOS card.
>>>>
>>>> This possibility works perfcetly when computing volumes for
>>>> complicated regions, on paper it could work for surfaces as well
>>>> (no guarantee).
>>>>
>>>> Let me explain the logic (see also the manual for the BEAMPOS card):
>>>>
>>>> a) your problem should have for this purpose all regions (apart
>>>> blackhole)
>>>> filled with vacuum;
>>>> b) you define a beam (whichever particle, say PHOTON's) and put a
>>>> BEAMPOS card with SDUM=FLOOD;
>>>> c) this will generate an isotropic and uniform fluence inside the
>>>> sphere
>>>> with radius = WHAT(1) of the BEAMPOS card, be sure such radius
>>>> contains wholly your region;
>>>> d) the fluence so generated will be equal to 1/(pi R^2), this is an
>>>> exact analytical result;
>>>> e) you define a USRBDX, fluence-like, two-ways, estimator between the
>>>> region you want to know the surface of and the surrounding, with
>>>> normalization surface=1. It would be highly preferable/simple if
>>>> the
>>>> surrounding is made of a single region (you could make an ad hoc
>>>> run/geometry for this purpose);
>>>> f) you run Fluka for sufficient primaries/cycles in order to get
>>>> a negligible statistical error on the USRBDX result (let's call
>>>> its result F);
>>>> g) since you know that F/Area should be equal to 1/(pi R^2) you
>>>> can easily derive Area
>>>>
>>>> Normally this method is used in order to compute volumes using
>>>> a tracklength estimator instead of a USRBDX, and using the
>>>> equation F_track_length/Volume = 1/(pi R^2). This works perfectly
>>>> and it is sure to give the exact answer within the statistical
>>>> errors. On paper I do not see an obvious reason why it should not
>>>> work for computing an area as well, there will be numerical precision
>>>> issues since for grazing incidence a fluence boundary crossing
>>>> estimator would result into an infinite (or better a division by
>>>> zero). This
>>>> is protected in the code and the influence of the necessarily
>>>> approximate protection should be small, however as I said before we
>>>> never tried this method.
>>>>
>>>> Let us know if it works!
>>>>
>>>> On Fri, 13 Mar 2020, Alessandro Calamida wrote:
>>>>
>>>>> Dear FLUKA experts,
>>>>>
>>>>> In my geometry I have a regione that is the union of different
>>>>> bodies.
>>>>> Calculating the surface of it is quite complicated and so I cannot
>>>>> put
>>>>> the normalization factor in the USRBDX scoring.
>>>>>
>>>>> There is a FLUKA or Flair tool that allows to evaluate surfaces.
>>>>>
>>>>> I attach in the email the input of the file. The region from wich
>>>>> I need
>>>>> the surface is the SUPP_TRG.
>>>>>
>>>>> Best regards and thank you for your time, Alessandro Calamida.
>>>>>
>>>>>
>>>>>
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Received on Tue Mar 24 2020 - 18:34:33 CET

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