From 9978ba7355d05ac09f5002706479ae996de2c114 Mon Sep 17 00:00:00 2001 From: Timo Heister Date: Wed, 28 Aug 2019 11:56:16 -0400 Subject: [PATCH] address comments --- examples/step-49/doc/results.dox | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) diff --git a/examples/step-49/doc/results.dox b/examples/step-49/doc/results.dox index 870823510d..638b320545 100644 --- a/examples/step-49/doc/results.dox +++ b/examples/step-49/doc/results.dox @@ -332,17 +332,30 @@ the nice detail of the boundary fitted mesh if we refine two more times:

Possible extensions

-

Modify a mesh

+

Assigning different boundary ids

-Similar to the operations in step-1, iterate over a mesh and change boundary -indicators. +It is often useful to assign different boundary ids to a mesh that is +generated in one form or another as described in this tutorial to apply +different boundary conditions. + +For example, you might want to apply a different boundary condition for the +right boundary of the first grid in this program. To do this, iterate over the +cells and their faces and identify the correct faces (for example using +cell->center() or cell->get_boundary_id()). You can then use +cell->set_boundary_id() to set the boundary id to something different. You can +take a look back at step-1 how iteration over the meshes is done there.

Extracting a boundary mesh

-To compute on surfaces on manifolds, you can use the function -GridTools::extract_boundary_mesh() to extract the surface elements of a -mesh. For example, using the function on a 3d mesh (a Triangulation<3,3>), -this will return a Triangulation<2,3> that you can use in step-38 for example. +Computations on manifolds, like they are done in step-38, require a surface +mesh embedded into a higher dimensional space. While some can be constructed +using the GridGenerator namespace or loaded from a file, it is sometimes +useful to extract a surface mesh from a volume mesh. + +Use the function GridTools::extract_boundary_mesh() to extract the surface +elements of a mesh. Using the function on a 3d mesh (a Triangulation<3,3>, for +example from grid_4()), this will return a Triangulation<2,3> that you can use +in step-38. Also try extracting the boundary mesh of a Triangulation<2,2>.