A priori error estimates of a diffusion equation with Ventcel boundary conditions on curved meshes
Résumé
In this work is considered an elliptic problem, referred to as the Ventcel problem, involving
a second order term on the domain boundary (the Laplace-Beltrami operator). A variational
formulation of the Ventcel problem is studied, leading to a finite element discretization. The
focus is on the construction of high order curved meshes for the discretization of the physical
domain and on the definition of the lift operator, which is aimed to transform a function
defined on the mesh domain into a function defined on the physical one. This lift is defined
in a way as to satisfy adapted properties on the boundary, relatively to the trace operator.
The Ventcel problem approximation is investigated both in terms of geometrical error and of
finite element approximation error. Error estimates are obtained both in terms of the mesh
order r ≥ 1 and to the finite element degree k ≥ 1, whereas such estimates usually have been
considered in the isoparametric case so far, involving a single parameter k = r. The numerical
experiments we led, both in dimension 2 and 3, allow us to validate the results obtained and
proved on the a priori error estimates depending on the two parameters k and r. A numerical
comparison is made between the errors using the former lift definition and the lift defined in
this work establishing an improvement in the convergence rate of the error in the latter case.
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