On 04/01/2013 07:50 AM, Kirk, Benjamin (JSC-EG311) wrote:
> On Mar 31, 2013, at 11:35 PM, "Manav Bhatia" <[email protected]> wrote:
>
>> Thanks, Derek.
>>
>> A related question about libMesh:
>>
>> If I need to output the solution values on the boundary nodes, can I use
>> BoundaryMesh along with the IO classes for that?
>>
>> Meaning, if I do the following
>>
>> BoundaryMesh b_mesh(mesh.mesh_dimension()-1);
>> mesh.boundary_info->sync(b_mesh);
>> VTKIO(b_mesh).write_equation_systems("boundary_output.pvtu",
>> equation_systems);
>>
>>
>> Would this write the solution values on the boundary nodes?
> Almost. Unfortunately it is a little more manual than this, but that's the
> right idea. In your example the equation systems object can only be
> associated with one mesh, so it won't work. The fix is to create a second
> equation systems object that lives on the boundary and then extract the trace
> values.
>
> This is not automated because in general the user will want physics-dependent
> things like shear stress, heat flux, whatever...
>
> I suppose we could automate the values-only case though.
>
> -Ben
To get the "boundary only values" I first make a "boundary_dofmap", as
in the code below. Then copying the solution values over from system to
boundary_system is easy.
void create_disp_boundary_dofmap(System& system,
System& boundary_system,
std::vector<unsigned int>&
boundary_dofmap)
{
boundary_dofmap.resize(boundary_system.n_dofs());
// make a point locator for system
AutoPtr<PointLocatorBase> point_locator =
system.get_mesh().sub_point_locator();
// loop over the boundary nodes and locate them
// then fill in boundary_dofmap
MeshBase::node_iterator node_it =
boundary_system.get_mesh().nodes_begin();
const MeshBase::node_iterator node_end =
boundary_system.get_mesh().nodes_end();
for( ; node_it != node_end; node_it++)
{
Node* node = *node_it;
// get an element in the full mesh that contains node
const Elem* element = point_locator->operator()(*node);
// loop over the nodes of element until we find the one that
matches node
for(unsigned int node_id=0; node_id<element->n_nodes(); node_id++)
{
Node* new_node = element->get_node(node_id);
Real dist = std::sqrt(
pow(node->operator()(0)-new_node->operator()(0),2.) +
pow(node->operator()(1)-new_node->operator()(1),2.) +
pow(node->operator()(2)-new_node->operator()(2),2.) );
if(dist < TOLERANCE)
{
for(unsigned int var=0; var<system.n_vars(); var++)
{
unsigned int index1 =
node->dof_number(boundary_system.number(), var, 0);
unsigned int index2 = new_node->dof_number(system.number(),
var, 0);
boundary_dofmap[index1] = index2;
}
continue;
}
}
}
}
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