Re: [Libmesh-users] 1D/2D elements in 3D space

[Roy Stogner]

On Mon, 12 Feb 2018, Manav Bhatia wrote:


So, would the shape function derivatives account the orientation of the element?

For instance, a 1D element oriented along:   x-axis   vs   y-axis   vs   x=y 
line.

In all cases, there is only one shape function defined along the
element coordinate. But its derivative wrt x and y will vary. Is
this handled for both 1st order and 2nd order Lagrange (for
instance)?


IIRC it's handled properly for all scalar-valued elements, where by
"properly" I mean that the derivative is returned as a directional
gradient in LIBMESH_DIM-dimensional space.  E.g. If you have an EDGE2
element with a value of 1 at the origin and 0 at the other end, then
if the other end is at (x,y,z) the gradient in physical space we
return should be (-x, -y, -z).

That means that if you're solving e.g. a Laplacian problem, then you
want to be integrating grad(u)*grad(v) as a dot product of 2 vectors,
not just assuming that you can still ignore the m>>n indexed
components for an n-dimensional element.

I'm actually not sure if anybody ever made sure we support embedded
vector-valued elements.  Cc'ing Paul Bauman; if he didn't do it then
nobody did.
---
Roy

--
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

Re: [Libmesh-users] 1D/2D elements in 3D space

[Manav Bhatia]

Thanks! 

So, would the shape function derivatives account the orientation of the 
element? 

For instance, a 1D element oriented along:   x-axis   vs   y-axis   vs   x=y 
line. 

In all cases, there is only one shape function defined along the element 
coordinate. But its derivative wrt x and y will vary. Is this handled for both 
1st order and 2nd order Lagrange (for instance)?

-Manav

> On Feb 12, 2018, at 5:06 PM, Roy Stogner  wrote:
> 
> 
> On Mon, 12 Feb 2018, Manav Bhatia wrote:
> 
>>  I was looking through some code in FE and noticed some comments
>>  about 1D/2D elements in 3D space. What is the extent of support
>>  for this?
> 
> IIRC:
> 
> If you're using just one or just the other, then the support should be
> complete.
> 
> If you're connecting one to the other (or connecting either/both to 3D
> elements), then you don't get neighbor links for those connections.
> 
> If you're overlapping one on or within the other (e.g. elements which
> occupy the sides of higher dimensional elements) and you want them to
> share DoFs consistently then I think you're limited to LAGRANGE
> variables for those DoFs.
> ---
> Roy


--
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

Re: [Libmesh-users] 1D/2D elements in 3D space

[Roy Stogner]

On Mon, 12 Feb 2018, Manav Bhatia wrote:


  I was looking through some code in FE and noticed some comments
  about 1D/2D elements in 3D space. What is the extent of support
  for this?


IIRC:

If you're using just one or just the other, then the support should be
complete.

If you're connecting one to the other (or connecting either/both to 3D
elements), then you don't get neighbor links for those connections.

If you're overlapping one on or within the other (e.g. elements which
occupy the sides of higher dimensional elements) and you want them to
share DoFs consistently then I think you're limited to LAGRANGE
variables for those DoFs.
---
Roy

--
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