One of the first things I tried to do was make a 2D mesh generator and maintain
a specific
relationship between nodes and (rectangular lol ) boundary. It looked like
nodes on the boundary created
some issues and I could deal with special elements at the interfaces. I tried
to do this using rational numbers to describe the node locations.
The rational number locations may sound a bit odd but it seemed to help avoid
fp rounding problems
although as my first shot I don't have a lot of perspective.
Curious if anyone cares to point to a link or keywords for search describing
the issues in more detail.
I then diverted to some issues with Fick's Law and found that more interesting
for now :)
Thanks.
________________________________________
From: Joa Ljungvall <libm...@joa.me.uk>
Sent: Tuesday, June 6, 2017 8:05 AM
To: Paul T. Bauman
Cc: libmesh-users
Subject: Re: [Libmesh-users] Meshrefinment snapping nodes to surface of geometry
Hi,
thank you for your input. I will think a bit... If I come up with something
useful I'll let you know
Joa
On Tue, May 30, 2017 at 11:14:10AM -0400, Paul T. Bauman wrote:
> Just FYI, this is something Roy and I have funding to work on over the next
> 2.5 years. We will keep the community posted as this capability comes
> online.
>
> On Tue, May 30, 2017 at 10:59 AM, John Peterson <jwpeter...@gmail.com>
> wrote:
>
> > On Tue, May 30, 2017 at 3:29 AM, Joa Ljungvall <libm...@joa.me.uk> wrote:
> >
> > > Dear all,
> > >
> > > I'm revisting an old problem involving solving laplace and poision for a
> > > moderatly complicated geometry. Here I would like to start with a 3D mesh
> > > with
> > > few nodes and refine based on a kerry estimator. I've tried this before
> > > (2009-2010) with libmesh and ran into the problem that I could not figure
> > > out a good way to snap new nodes to the boundary of my geometry. Last
> > time
> > > around I gave up since I created meshes that had all types of problems.
> > >
> > > Now my question, If I make my own MeshRefinment class and rewrite the
> > >
> > > Node * libMesh::MeshRefinement::add_node ( Elem & parent,
> > > unsigned int child,
> > > unsigned int node,
> > > processor_id_type proc_id
> > > )
> > > {
> > >
> > > ....
> > > }
> > >
> > > method, more in particular the lines
> > >
> > > 135 // Otherwise we need to add a new node, with a default id and the
> > > 136 // requested processor_id. Figure out where to add the point:
> > > 137
> > > 138 Point p; // defaults to 0,0,0
> > > 139
> > > 140 for (unsigned int n=0; n != parent.n_nodes(); ++n)
> > > 141 {
> > > 142 // The value from the embedding matrix
> > > 143 const float em_val = parent.embedding_matrix(child,node,n);
> > > 144
> > > 145 if (em_val != 0.)
> > > 146 {
> > > 147 p.add_scaled (parent.point(n), em_val);
> > > 148
> > > 149 // If we'd already found the node we shouldn't be here
> > > 150 libmesh_assert_not_equal_to (em_val, 1);
> > > 151 }
> > > 152 }
> > >
> > > so that if the created node is on a surface I snap it to the boundary
> > > by moving it along the normal of the surface of the parent element. Could
> > > that
> > > work without any strange side effects? This is the old thread of
> > > discussion we
> > > had at the time
> > >
> > > https://sourceforge.net/p/libmesh/mailman/libmesh-users/
> > > thread/20091014130140.GM20082%40joa.me.uk/#msg23751829
> >
> >
> >
> > I don't think deriving your own MeshRefinement object is the right
> > approach... not saying that it couldn't be made to work, just that the
> > class was not really written with that use case in mind, so you would
> > probably run into a lot of gotchas.
> >
> > If it's possible for you to use quadrilateral/hexahedral elements, I think
> > you might have better luck doing what you are trying to do using deal.II.
> >
> > Since the 2009 email thread, they have added support for linking deal.II
> > with OpenCascade [0], including IIRC the ability to snap adaptively refined
> > elements' nodes to the underlying "true" geometry.
> >
> > [0]: https://www.dealii.org/8.5.0/external-libs/opencascade.html
> >
> > --
> > John
> > ------------------------------------------------------------
> > ------------------
> > Check out the vibrant tech community on one of the world's most
> > engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> > _______________________________________________
> > Libmesh-users mailing list
> > Libmesh-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/libmesh-users
> >
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