Roughness effect on Neumann boundary condition

Article type: Research Article

Authors: Chupin, Laurent

Affiliations: Laboratoire de Mathématiques, UMR 6620, Université Blaise Pascal, Campus des Cézeaux, F-63177 Aubière Cedex, France. E-mail: [email protected]

Abstract: We study the effect of a periodic roughness on a Neumann boundary condition. We show that, as in the case of a Dirichlet boundary condition, it is possible to approach this condition by a more complex law on a domain without rugosity, called wall law. This approach is however different from that usually used in Dirichlet case. In particular, we show that this wall law can be explicitly written using an energy developed in the roughness boundary layer. The first part deals with the case of a Laplace operator in a simple domain but many more general results are next given: when the domain or the operator are more complex or with Robin–Fourier boundary conditions. Some numerical illustrations are used to obtain magnitudes for the coefficients appearing in the new wall laws. Finally, these wall laws can be interpreted using a fictive boundary without rugosity. That allows to give an application to the water waves equation.

Keywords: Neumann or Robin–Fourier boundary conditions, asymptotic development, rough boundaries, hight order approximation, wall laws, Laplace equation, water wave, Dirichlet–Neumann operator

DOI: 10.3233/ASY-2011-1086

Journal: Asymptotic Analysis, vol. 78, no. 1-2, pp. 85-121, 2012