[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
>>>
>>>
>>>
>>>
>> --------------------------------------------------------------
>> ----------
>>> _______________________________________________
>>> gmsh mailing list
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>>> 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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> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine