[Gmsh] lower limit for characteristic length
Christophe Geuzaine
cgeuzaine at ulg.ac.be
Wed Jan 7 07:49:41 CET 2009
Zenker, Dr. Matthias wrote:
> Hi,
>
> (just returned from holidays...)
> thank you for the hint with the fields, I will try it that way.
> I have examined demos/fields.geo. Seems like I have to enter all that
> field-related stuff by hand. I don't mind to do so, but is there a more
> elegant way, using the GUI? And can I visualize the defined fields
> before starting the meshing?
Yes: download the latest nightly snapshot, and in the Mesh module click
on "Define", then "Fields".
>
> Best regards,
>
> Matthias
>
>> -----Original Message-----
>> From: Christophe Geuzaine [mailto:cgeuzaine at ulg.ac.be]
>> Sent: Tuesday, December 16, 2008 9:41 AM
>> To: Zenker, Dr. Matthias
>> Cc: gmsh at geuz.org
>> Subject: Re: [Gmsh] lower limit for characteristic length
>>
>> Zenker, Dr. Matthias wrote:
>>> Of course. Here it is.
>>>
>>> BTW, I use gmsh 2.2.6 on a WIN XP SP 2, Pentium 4, 3.2 GHz,
>> 1.5 GB RAM
>>> computer.
>>>
>> The default random perturbation factor seems to be a bit
>> small in your case. The following (increased "-rand" from
>> "1.e-9" to "1.e-7")
>>
>> gmsh small_cl.geo -2 -rand 1.e-7
>>
>> seems to work just fine, but I had to stop it before the end
>> due to insufficient memory on my laptop. Multiplying all the
>> element sizes by 3 and using the faster del2d algorithm
>>
>> gmsh small_cl.geo -2 -rand 1.e-7 -clscale 3 -algo del2d
>>
>> produced a nice mesh with about 23 million triangles.
>>
>>
>>> If I could force gmsh not to ignore the cl of the spline control
>>> points, it would probably be faster for such a case (if it wouldn't
>>> crash). Is there a trick to do that? Would it help to put isolated
>>> points with the desired cl at the desired location?
>> You should probably use Fields to fine-tune the element
>> sizes. There are some examples on the mailing list, as well
>> as in demos/fields.geo.
>>
>>
>>
>>> Thank you and best regards,
>>>
>>> Matthias
>>>
>>>> -----Original Message-----
>>>> From: Christophe Geuzaine [mailto:cgeuzaine at ulg.ac.be]
>>>> Sent: Monday, December 15, 2008 1:07 PM
>>>> To: Zenker, Dr. Matthias
>>>> Cc: gmsh at geuz.org
>>>> Subject: Re: [Gmsh] lower limit for characteristic length
>>>>
>>>> Zenker, Dr. Matthias wrote:
>>>>> Hi there,
>>>>>
>>>>> the question remains: is there a lower limit for the
>> characteristic
>>>>> length cl, and why does gmsh crash when some points have
>> a small cl?
>>>> It shouldn't crash, except when "cl" divided by the overall
>>>> size of model is getting close to machine accuracy (or more
>>>> accurately, close to the value of the random pertutbation
>>>> used in the meshing algorithms, which is 1e-9 by default).
>>>>
>>>> Could you send a file that shows the problem?
>>>>
>>>>
>>>>> I would like to add another one: Is it possible that gmsh
>>>> ignores the
>>>>> cl of the control points of a spline except for the first
>> and last
>>>>> one? If
>>>> That's what Gmsh does: the cls of the control points are ignored.
>>>>
>>>>
>>>>
>>>>> so, is there a way to force gmsh to take into account the
>> cl of the
>>>>> intermediate points also?
>>>>>
>>>>> Best regards,
>>>>>
>>>>> Matthias
>>>>>
>>>>>
>>>> --------------------------------------------------------------
>>>> ----------
>>>>> *From:* gmsh-bounces at geuz.org
>> [mailto:gmsh-bounces at geuz.org] *On
>>>>> Behalf Of *Zenker, Dr. Matthias
>>>>> *Sent:* Monday, November 17, 2008 10:49 AM
>>>>> *To:* gmsh at geuz.org
>>>>> *Subject:* Re: [Gmsh] lower limit for characteristic length
>>>>>
>>>>> I was wrong, it crashes also for cl=0.0005 (but after a
>>>> looong time,
>>>>> and with a runtime error).
>>>>>
>>>>>
>>>> --------------------------------------------------------------
>>>> ----------
>>>>> *From:* gmsh-bounces at geuz.org
>>>> [mailto:gmsh-bounces at geuz.org] *On
>>>>> Behalf Of *Zenker, Dr. Matthias
>>>>> *Sent:* Monday, November 17, 2008 10:16 AM
>>>>> *To:* gmsh at geuz.org
>>>>> *Subject:* [Gmsh] lower limit for characteristic length
>>>>>
>>>>> Hi,
>>>>>
>>>>> I wonder if there is a lower limit for the characteristic
>>>>> length. I have a rather simple 2D geometry, and if
>>>> I set the cl
>>>>> for just two points to 0.0001, gmsh crashes during
>>>> the meshing
>>>>> after having given the error message "3 identical
>> points in
>>>>> Qtest". The .gmsh-errors file is not written. With
>>>> cl=0.0005,
>>>>> this does not happen (but it takes veeery long to
>>>> compute the mesh).
>>>>> Best regards,
>>>>>
>>>>> Matthias
>>>>>
>>>>>
>>>> ----------------------------------------------------------------
>>>>> ERBE Elektromedizin GmbH
>>>>> Dr.rer.nat. Matthias Zenker
>>>>> Dipl. Phys.
>>>>> Grundlagenentwicklung Technologie
>>>>> Waldhoernlestrasse 17
>>>>> D-72072 Tuebingen
>>>>> Tel.: + 49 (0) 7071 - 755 226
>>>>> Fax: + 49 (0) 7071 - 755 5226
>>>>> E-Mail: <_mailto:Matthias.Zenker at ERBE-med.de_>
>>>>> URL: _http://www.ERBE-med.de_
>>>>>
>>>>> ----------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ERBE Elektromedizin GmbH
>>>>> Firmensitz: 72072 Tuebingen
>>>>> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>>>>> Registergericht: Stuttgart HRB 380137
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ERBE Elektromedizin GmbH
>>>>> Firmensitz: 72072 Tuebingen
>>>>> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>>>>> Registergericht: Stuttgart HRB 380137
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ERBE Elektromedizin GmbH
>>>>> Firmensitz: 72072 Tuebingen
>>>>> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>>>>> Registergericht: Stuttgart HRB 380137
>>>>>
>>>>>
>>>>>
>>>>>
>> ----------------------------------------------------------------------
>>>>> --
>>>>>
>>>>> _______________________________________________
>>>>> gmsh mailing list
>>>>> gmsh at geuz.org
>>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>> --
>>>> Prof. Christophe Geuzaine
>>>> University of Liege, Electrical Engineering and Computer
>>>> Science http://www.montefiore.ulg.ac.be/~geuzaine
>>>>
>>>
>> _____________________________________________________________________
>>> ERBE Elektromedizin GmbH
>>> Firmensitz: 72072 Tuebingen
>>> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
>>> Registergericht: Stuttgart HRB 380137
>>>
>>>
>>>
>>>
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>> ----------
>>> _______________________________________________
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>>
>> --
>> Prof. Christophe Geuzaine
>> University of Liege, Electrical Engineering and Computer Science
>> http://www.montefiore.ulg.ac.be/~geuzaine
>>
>>
>>
>
> _____________________________________________________________________
> ERBE Elektromedizin GmbH
> Firmensitz: 72072 Tuebingen
> Geschaeftsfuehrer: Christian O. Erbe, Reiner Thede
> Registergericht: Stuttgart HRB 380137
>
>
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> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh
>
>
--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine