[Gmsh] lower limit for characteristic length

Zenker, Dr. Matthias Matthias.Zenker at erbe-med.de
Mon Jan 5 16:32:21 CET 2009


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?

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
> > 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