[Gmsh] R: R: R: Newbie question

Karen Pease meme at eaku.net
Fri May 27 04:18:59 CEST 2016

Okay, so I've made a little progress, although it's taken all evening
(half spent trying to get ccx and its dependencies to compile  :Þ). 
 Concerning gmsh, I found that I can see how it's supposed to look with
surface faces, as suggested; that I can:

1) go to modules->geometry->elementary entities->add->volume
2) link it to the mesh, and get a geo file with a volume defined
3)save that as an inp file
4) make small changes in the inp file (as per a video I found)
5) hand-write another inp, "modal.inp", which defines material
properties as well as a couple other things I don't understand
6) Process it modal.inp in ccx 
7) load the output in gcx
8) select the dataset and view displacement.

However, that result seems meaningless as I haven't defined any forces,
or anyway for it to be resisting forces, so I can't see how it would
have any stress or deflection at all (I haven't yet done any attempts
to measure peak deflection or stresses from the results, either).

Clearly I should have to define attachment points some how.  Maybe by
placing nodes in gmsh?  Not sure exactly how to use them in ccx to
define an attachment point, but it seems like something that might be
needed.  But if I just arbitrarily place nodes then I can't see how
they would be "connected" to the volume I got by clicking on the mesh
in step #2.

Once the volume (from step #2) is "anchored" to something I'll also
somehow need to define uniform forces on the volume.  And then somehow
from the output extract the peak deflection and stress...

Am I moving in the right direction here?
 - kv, Karen

On fim, 2016-05-26 at 08:33 +0000, Alessandro Vicini wrote:
> Yes, that’s from gmsh. Probably you only see it as a wireframe
> because you don’t have the option “surface faces” turned on. You can
> find it in Tools->Options->Mesh.
> From the same Tools->Options panel, if you turn off visualization of
> all mesh elements (surface edges, surface faces), and turn on the
> geometry (Tools->Options->Geometry), you don’t see anything. So gmsh
> does not have any geometry, but only mesh elements. 3d model geometry
> and surface mesh are not the same thing. The first is composed by
> points, lines, curves, surfaces and so on; the second by nodes,
> edges, surface and volume elements. Generally what you want to do is
> import a geometry, and use gmsh (or whatever) to build your mesh.
> A.
> Da: Karen Pease [mailto:karenpease at gmail.com] Per conto di Karen
> Pease
> Inviato: giovedì 26 maggio 2016 10.27
> A: Alessandro Vicini
> Oggetto: RE: R: R: [Gmsh] Newbie question
> I'm confused is that screenshot from within gmsh? Because on my side
> gmsh draws it as wireframe.
> Perhaps its just me that's the problem, but when you write that
> "there's only a surface mesh in the file, and no geometry elements",
> to me, "surface mesh" and "3d model geometry" are synonymous.
> - Kv, Karen
> ---- Alessandro Vicini wrote ----
> Hi Karen,
> in the attached picture you can see what I get from Gmsh (I'm using
> version 2.8.5 on windows).
> It seems that there's only a surface mesh in the file, and no
> geometry elements.
> A.
> -----Messaggio originale-----
> Da: Karen Pease [mailto:karenpease at gmail.com] Per conto di Karen
> Pease
> Inviato: giovedì 26 maggio 2016 9.32
> A: Alessandro Vicini
> Oggetto: Re: R: [Gmsh] Newbie question
> Thank you for the reply! I'm attaching a test model I made as an
> example.  It loads fine in Blender, with faces.
> - kv, Karen
> On fim, 2016-05-26 at 07:20 +0000, Alessandro Vicini wrote:
> > 
> > Hi Karen,
> > 
> > does your STL file contain surfaces, besides lines and points?
> Would 
> > it be possible for you to send it to me?
> > 
> > A.
> > 
> > 
> > 
> > -----Messaggio originale-----
> > Da: gmsh [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] Per conto
> di 
> > Karen Pease
> > Inviato: giovedì 26 maggio 2016 2.13
> > A: gmsh at onelab.info
> > Oggetto: [Gmsh] Newbie question
> > 
> > Hi all.  I've spent all evening trying out different meshing and
> FEA 
> > software and gotten precisely nowhere... so I decided it's time to 
> > ask. Where is a good place to start?  All I'm wanting to do is:
> > 
> > 1) Take an existing model (say, exported as STL)
> > 2) Import it
> > 3) Assign material properties, anchor points, and assign forces
> > 4) Run a FEA simulation
> > 5) See the stresses and deflections
> > 
> > Seems like a pretty basic workflow, but I can hardly get past the 
> > first step.  GMSH got me the furthest - at least I could actually
> see 
> > it.  But it's just a wireframe, I can't do anything more with it
> than 
> > pan around it, there's no interactive points.  The model is just 
> > window decor as far as I can tell.  I see nothing in the visibility
> > options that makes it any more interactive.
> > 
> > (At least this is further than I got with other tools... netgen
> might 
> > as well have had the interface in Swahili).
> > 
> > I've tried reading the documentation, but what's called a
> "tutorial"
> > (http://gmsh.info/doc/texinfo/gmsh.html#Tutorial) is practically an
> > API manual.  I've tried watching videos on Youtube, but one, not
> only 
> > do they rarely deal with importing geometry like STLs, but for most
> > programs the interface in the videos looks different from what I
> see 
> > because I use Linux and they use Windows.  And the Windows versions
> > usually seem to have more user friendly versions (at least gmsh is 
> > better than calculix in this regard, with calculix it's like half
> the 
> > interface is missing....)
> > 
> > What do I do?  How can I get my bearings here?
> > 
> > Any feedback at all would be greatly appreciated... thanks, all.
> > 
> >  - kv, Karen
> > 
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> > gmsh at onelab.info
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