arXiv subjects

Klas Pettersson

Publications and source records attributed to Klas Pettersson.

8 recordsLinked to original sources

arXiv2021

A feedforward neural network for modelling of average pressure frequency response

The Helmholtz equation has been used for modelling the sound pressure field under a harmonic load. Computing harmonic sound pressure fields by means of solving Helmholtz equation can quickly become unfeasible if one wants to study many different geometries for ranges of frequencies. We propose a machine learning approach, namely a feedforward dense neural network, for computing the average sound pressure over a frequency range. The data is generated with finite elements, by numerically computing the response of the average sound pressure, by an eigenmode decomposition of the pressure. We analyze the accuracy of the approximation and determine how much training data is needed in order to reach a certain accuracy in the predictions of the average pressure response.

cs.LG↗

arXiv2021

Localization of eigenfunctions in a thin domain with locally periodic oscillating boundary

We study a Dirichlet spectral problem for a second-order elliptic operator with locally periodic coefficients in a thin domain. The boundary of the domain is assumed to be locally periodic. When the thickness of the domain $\varepsilon$ tends to zero, the eigenvalues are of order $\varepsilon^{-2}$ and described in terms of the first eigenvalue $μ(x_1)$ of an auxiliary spectral cell problem parametrized by $x_1$, while the eigenfunctions localize with rate $\sqrt{\varepsilon}$.

math.AP↗

arXiv2021

Homogenization of a locally periodic oscillating boundary

This paper deals with the homogenization of a mixed boundary value problem for the Laplace operator in a domain with locally periodic oscillating boundary. The Neumann condition is prescribed on the oscillating part of the boundary, and the Dirichlet condition on a separate part. It is shown that the homogenization result holds in the sense of weak $L^2$ convergence of the solutions and their flows, under natural hypothesis on the regularity of the domain. The strong $L^2$ convergence of average preserving extensions of the solutions and their flows is also considered.

math.AP↗

arXiv2016

Subcritical perturbation of a locally periodic elliptic operator

We consider a singularly perturbed Dirichlet spectral problem for an elliptic operator of second order. The coefficients of the operator are assumed to be locally periodic and oscillating in the scale $\varepsilon$. We describe the leading terms of the asymptotics of the eigenvalues and the eigenfunctions to the problem, as the parameter $\varepsilon$ tends to zero, under structural assumptions on the potential. More precisely, we assume that the local average of the potential has a unique global minimum point in the interior of the domain and its Hessian is non-degenerate at this point.

math.AP↗

arXiv2015

A local-effective relation in planar linear elasticity

We give an example of a relation between local and effective properties for elastic structures, up to geometric constants. The model considered is a periodic structure with isotropic and homogeneous local elasticity tensor in planar linear elasticity. The corresponding physical model is a flat two dimensional body with holes as, for example, a perforated plate.

math.AP↗

arXiv2015

Spectral asymptotics for a singularly perturbed fourth order locally periodic self-adjoint elliptic operator

We consider the homogenization of a singularly perturbed self-adjoint fourth order elliptic equation with locally periodic coefficients, stated in a bounded domain. We impose Dirichlet boundary conditions on the boundary of the domain. The presence of large parameters in the lower order terms and the dependence of the coefficients on the slow variable give rise to the effect of localization of the eigenfunctions. We show that the $j$th eigenfunction can be approximated by a rescaled function that is constructed in terms of the $j$th eigenfunction of fourth or second order order effective operators with constant coefficients, depending on the large parameters.

math.AP↗

arXiv2014

Concentration of eigenfunctions of a locally periodic elliptic operator with large potential in a perforated cylinder

We consider the homogenization of an elliptic spectral problem with a large potential stated in a thin cylinder with a locally periodic perforation. The size of the perforation gradually varies from point to point. We impose homogeneous Neumann boundary conditions on the boundary of perforation and on the lateral boundary of the cylinder. The presence of a large parameter $1/\varepsilon$ in front of the potential and the dependence of the perforation on the slow variable give rise to the effect of localization of the eigenfunctions. We show that the $j$th eigenfunction can be approximated by a scaled exponentially decaying function that is constructed in terms of the $j$th eigenfunction of a one-dimensional harmonic oscillator operator.

math.AP↗

arXiv2012

An elementary proof of the Vigdergauz equations for a class of square symmetric structures

For a periodically perforated structure, for which homogenization takes place in the linear theory of elasticity, the components of the effective elasticity tensor depend in general on the geometry of the holes as well as on the local elastic properties. These dependencies were shown by Vigdergauz in [7] to be separated in an elementary way for one particular class of structures. The original proof of this relation made use of the lattice approach to describe periodic functions using complex variables. In this paper we present a proof of the so-called Vigdergauz equations for a related class of square symmetric structures. Our proof relies solely on the fundamental theorem of real variable calculus. The differences between the two mentioned classes of structures are nontrivial which makes our result a partial generalization as well.

math.AP↗