[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
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> >>> Fax: + 49 (0) 7071 - 755 5226
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> >>>
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> >>>
> >>>
> >>>
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> >>> ERBE Elektromedizin GmbH
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> >>>
> >>>
> >>>
> >>>
> >>> 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
> >>>
> >>>
> >>>
> >>>
> >>
> ----------------------------------------------------------------------
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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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> >
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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