Hi Roy,
Below is how I create mesh, nodes, and elements:
ReplicatedMesh mesh(*comm);
// create list of nodes and segments
std::vector<unsigned int> nodes;
std::vector<unsigned int> elems;
// create two nodes at point (0,0,0) and (1,1,1) and element between these
// nodes
{
auto add_node = mesh.add_point(Point(0., 0., 0.));
nodes.push_back(add_node->id());
add_node = mesh.add_point(Point(1., 1., 1.));
nodes.push_back(add_node->id());
auto elem = Elem::build(EDGE2).release();
elem->set_node(0) = mesh.node_ptr(nodes[0]);
elem->set_node(1) = mesh.node_ptr(nodes[1]);
auto add_elem = mesh.add_elem(elem);
elems.push_back(add_elem->id());
// finish adding nodes and elements
mesh.prepare_for_use();
}
// add equation system for pressure
EquationSystems eq_sys(mesh);
auto &flow = eq_sys.add_system<TransientLinearImplicitSystem>("Flow");
flow.add_variable("pressure", FIRST);
flow.time = 0.0;
// attach initial condition
flow.attach_init_function(initial_condition);
// attach assembly function
flow.attach_assemble_function(assemble_net);
// fix value of first node (Dirichlet boundary condition)
{
// auto elem_0 = mesh.elem(elems[0]);
// flow.get_dof_map().constrain_p_dofs(0, elem_0, 0, elem_0->level());
std::set<boundary_id_type> boundary_ids;
boundary_ids.insert(0);
std::vector<unsigned int> variables = {0};
ConstFunction<Number> df(2);
DirichletBoundary diri_bc(boundary_ids, variables, &df);
flow.get_dof_map().add_dirichlet_boundary(diri_bc);
}
eq_sys.init();
I am not setting boundary id of the element (can we set them?).
For Dirichlet boundary condition on 1 dof, I am not sure how to put a
constraint row.
Regards,
Prashant
On Thu, Dec 5, 2019 at 12:52 PM Stogner, Roy H <royst...@ices.utexas.edu>
wrote:
>
> On Thu, 5 Dec 2019, Prashant Kumar Jha wrote:
>
> > I can create a network mesh consisting of edge elements in 3D space. This
> > is non-standard mesh in the sense that I start with empty mesh, add
> couple
> > of nodes, add edge element between nodes. Each node has 1 pressure dof.
> On
> > this network, I am now trying to solve 1D pde for pressure. For boundary
> > conditions, I want to fix the two ends of the network (i.e. the first dof
> > and the last dof) to a specific value.
> >
> > DirichletBoundary with boundary id 0 and 1 result in error possibly due
> to
> > mesh in 3D where as elements are of 1D nature.
>
> That shouldn't be the case. What exactly is the error? Did you set
> the boundary ids when you created the mesh?
>
> > To get around this, I was wondering if I could fix the individual dof to
> a
> > specific value. Any suggestions to make above work is appreciated.
>
> You can manually add a constraint row for each boundary dof, or you
> can use a penalty method.
> ---
> Roy
>
--
Regards,
Prashant
https://www.math.lsu.edu/~jha/
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