Hello Isa,
I would propose to use the FEValues::Extractors class to access the
single solution components U and V. You can find more about this
approach in the module on vector-valued problems.
Best Regards,
Markus
Am 18.02.11 18:52, schrieb [email protected]:
Hello,
I'd like to assemble the "complete" diffusion matrix in the 2D
Navier-Stokes equation:
for component U: d/dx(nu*d/dx(U))+d/dy(nu*d/dy(U)) +
d/dx(nu*d/dx(U))+d/dy(nu*d/dx(V))
for component V: d/dx(nu*d/dx(V))+d/dy(nu*d/dy(V)) +
d/dy(nu*d/dy(V))+d/dx(nu*d/dy(U))
nu is the viscosity and it isn't constant, so I do:
So, I do:
/////////////////////////////////////////////////////
for (; cell!=endc; ++cell)
{
cell_matrix=0.0;
cell_rhs=0.0;
fe_values.reinit (cell);
.
.
.
for (unsigned int i=0; i<dofs_per_cell; ++i)
{
//0=U,1=V,2=P
const unsigned int comp_i=fe_total.system_to_component_index(i).first;
for (unsigned int j=0; j<dofs_per_cell; ++j)
{
const unsigned int comp_j=fe_total.system_to_component_index(j).first;
for (unsigned int q_point=0; q_point<n_q_points; ++q_point)
{
if (comp_i == comp_j)
{
//To assemble d/dx(nu*d/dx(U))+d/dy(nu*d/dy(U)) for component U
//To assemble d/dx(nu*d/dx(V))+d/dy(nu*d/dy(V)) for component V:
if (comp_i != DIMENSION)
cell_matrix(i,j)+=(fe_values.JxW(q_point)*
(
(nu*fe_values.shape_grad(i,q_point)
*
fe_values.shape_grad(j,q_point))
)
);
//To assemble d/dx(nu*d/dx(U)) for component U:
else if (comp_i == 0)
cell_matrix(i,j)+=(fe_values.JxW(q_point)*
(
(nu*fe_values.shape_grad(i,q_point)[comp_i]
*
fe_values.shape_grad(j,q_point))[comp_i]
)
);
//To assemble d/dy(nu*d/dy(V)) for component V:
else if (comp_i == 1)
cell_matrix(i,j)+=(fe_values.JxW(q_point)*
(
(nu*fe_values.shape_grad(i,q_point[comp_i]
*
fe_values.shape_grad(j,q_point))[comp_i]
)
);
}
if ((comp_i != comp_j)&& (comp_i != DIMENSION)&&(comp_j!=DIMENSION))
{
//To assemble d/dy(nu*d/dx(V)) for component U
//To assemble d/dx(nu*d/dy(U)) for component V
cell_matrix(i,j)+=(fe_values.JxW(q_point)*
(
(nu*fe_values.shape_grad(i,q_point)[comp_j]
*
fe_values.shape_grad(j,q_point))[comp_i]
)
);
}
}
}
}
.
.
.
}
/////////////////////////////////////////////////////
Is it the way to create this complete diffusion matrix?
Thanks in advance.
Best regards.
Isa
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