Hi,
Trying to implement a Neumann condition at the upper boundary of a 1D
transient problem, I am facing an interesting case. In fact, changing
the size of the domain, modifying the value Xmax of the upper
boundary, alters the result.
//-------------------------------------------------------//
for (unsigned int i=0; i<phi_face.size(); i++)
{
Number valueNeumann= 1.0;
Fe(i) += JxW_face[qp]*valueNeumann*phi_face[i][qp];
}
//-------------------------------------------------------//
To illustrate, the value of the first derivative at the boundary is
effectively 1.0 only when the value of Xmax is 133.3333. Elsewhere,
the derivative is too small when Xmax > 133.33 and to big when Xmax <
133.33.
Using a second order Lagrange element, I may forget a correction term
to evaluate the surface integral.
Any ideas are welcome,
Maxime
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