## [Libmesh-users] Orientation of LibMesh Elements

 [Libmesh-users] Orientation of LibMesh Elements From: Rahul Sampath - 2010-02-16 20:53:07 ```Hi: In your online documentation, you have shown the local node numbering scheme for each element type. For example, HEX8: 7 6 o--------o /: /| / : / | 4 / : 5 / | o--------o | | o....|...o 2 | .3 | / | . | / |. |/ o--------o 0 1 TET4: 3 o /|\ / | \ / | \ 0 o...|...o 2 \ | / \ | / \|/ o 1 However, you have not shown the coordinate axes. I need to know the following: 1) The relationship between the local coordinate system and the local node numbering scheme. For example, In Hex8 whether the edge 0-1 is parallel to the local xi or eta axes. 2) The relationship between the physical global coordinate system and the local coordinate system. I believe you must already be using some convention for both to be able to compute the Jacobian of the transformation. It would be very helpful if you could tell me where I can find this information. Thank you. Best Regards, Rahul ```

 [Libmesh-users] Orientation of LibMesh Elements From: Rahul Sampath - 2010-02-16 20:53:07 ```Hi: In your online documentation, you have shown the local node numbering scheme for each element type. For example, HEX8: 7 6 o--------o /: /| / : / | 4 / : 5 / | o--------o | | o....|...o 2 | .3 | / | . | / |. |/ o--------o 0 1 TET4: 3 o /|\ / | \ / | \ 0 o...|...o 2 \ | / \ | / \|/ o 1 However, you have not shown the coordinate axes. I need to know the following: 1) The relationship between the local coordinate system and the local node numbering scheme. For example, In Hex8 whether the edge 0-1 is parallel to the local xi or eta axes. 2) The relationship between the physical global coordinate system and the local coordinate system. I believe you must already be using some convention for both to be able to compute the Jacobian of the transformation. It would be very helpful if you could tell me where I can find this information. Thank you. Best Regards, Rahul ```
 Re: [Libmesh-users] Orientation of LibMesh Elements From: Roy Stogner - 2010-02-16 21:04:45 ```On Tue, 16 Feb 2010, Rahul Sampath wrote: > HEX8: 7 6 > o--------o > /: /| > / : / | > 4 / : 5 / | > o--------o | > | o....|...o 2 > | .3 | / > | . | / > |. |/ > o--------o > 0 1 > > TET4: > 3 > o > /|\ > / | \ > / | \ > 0 o...|...o 2 > \ | / > \ | / > \|/ > o > 1 > > However, you have not shown the coordinate axes. I need to know the following: > 1) The relationship between the local coordinate system and the local > node numbering scheme. For example, In Hex8 whether the edge 0-1 is > parallel to the local xi or eta axes. > > 2) The relationship between the physical global coordinate system and > the local coordinate system. > > I believe you must already be using some convention for both to be > able to compute the Jacobian of the transformation. It would be very > helpful if you could tell me where I can find this information. To the best of my recollection: For triangles and tets, the nodes are at (0,0,0), (1,0,0), (0,1,0), (0,0,1) in master coordinates For tensor product elements, the geometry is [-1,1]^d and the edges are 0-1:xi, 0-3:eta, 0-4:zeta For pyramids, the peak is at (0,0,1) and the base is the same as a quad. Prisms are the tensor product of a triangle and an edge, with the triangle at zeta=-1 given the lower local node numbers. I'm afraid that the only place where you can find this information solidly may be implicitly in the fe_lagrange*.C code, though; I'm not sure we've got it cleanly documented. If you'd like to add such documentation, a patch (in ASCII so we can put it in the headers) would be appreciated. --- Roy ```
 Re: [Libmesh-users] Orientation of LibMesh Elements From: Kirk, Benjamin (JSC-EG311) - 2010-02-16 21:09:05 ```You can infer this from the 2d numbering. For example, for the HEX8, the base is oriented wrt (xi,eta) according to the QUAD4, and zeta is the vertical direction. On 2/16/10 3:04 PM, "Roy Stogner" wrote: > > > On Tue, 16 Feb 2010, Rahul Sampath wrote: > >> HEX8: 7 6 >> o--------o >> /: /| >> / : / | >> 4 / : 5 / | >> o--------o | >> | o....|...o 2 >> | .3 | / >> | . | / >> |. |/ >> o--------o >> 0 1 >> >> TET4: >> 3 >> o >> /|\ >> / | \ >> / | \ >> 0 o...|...o 2 >> \ | / >> \ | / >> \|/ >> o >> 1 >> >> However, you have not shown the coordinate axes. I need to know the >> following: >> 1) The relationship between the local coordinate system and the local >> node numbering scheme. For example, In Hex8 whether the edge 0-1 is >> parallel to the local xi or eta axes. >> >> 2) The relationship between the physical global coordinate system and >> the local coordinate system. >> >> I believe you must already be using some convention for both to be >> able to compute the Jacobian of the transformation. It would be very >> helpful if you could tell me where I can find this information. > > To the best of my recollection: > > For triangles and tets, the nodes are at (0,0,0), (1,0,0), (0,1,0), > (0,0,1) in master coordinates > > For tensor product elements, the geometry is [-1,1]^d and the edges > are 0-1:xi, 0-3:eta, 0-4:zeta > > For pyramids, the peak is at (0,0,1) and the base is the same as a > quad. > > Prisms are the tensor product of a triangle and an edge, with the > triangle at zeta=-1 given the lower local node numbers. > > I'm afraid that the only place where you can find this information > solidly may be implicitly in the fe_lagrange*.C code, though; I'm not > sure we've got it cleanly documented. If you'd like to add such > documentation, a patch (in ASCII so we can put it in the headers) > would be appreciated. > --- > Roy > > ------------------------------------------------------------------------------ > SOLARIS 10 is the OS for Data Centers - provides features such as DTrace, > Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW > http://p.sf.net/sfu/solaris-dev2dev > _______________________________________________ > Libmesh-users mailing list > Libmesh-users@... > https://lists.sourceforge.net/lists/listinfo/libmesh-users ```