Effective Transmission Conditions Research Articles

Hamilton-Jacobi Equations on Networks as Limits of Singularly Perturbed Problems in Optimal Control: Dimension Reduction

We consider a family of star-shaped planar domains Ωϵ, made of N non intersecting semi-infinite strips of thickness ϵ and of a central region whose diameter is proportional to ϵ. As ϵ → 0, Ωϵ tends to a network 𝒢 made of half-lines sharing an endpoint O. We study infinite horizon optimal control problems in which the state is constrained to remain in . We prove that the value function tends to the solution of a Hamilton-Jacobi equation on 𝒢, with an effective transmission condition at O. The effective equation is linked to an optimal control problem.

Effective transmission conditions for domain decomposition methods applied to the time-harmonic curl–curl Maxwell's equations

The time-harmonic Maxwell equations describe the propagation of electromagnetic waves and are therefore fundamental for the simulation of many modern devices we have become used to in everyday life. The numerical solution of these equations is hampered by two fundamental problems: first, in the high frequency regime, very fine meshes need to be used in order to avoid the pollution effect well known for the Helmholtz equation, and second the large scale systems obtained from the vector valued equations in three spatial dimensions need to be solved by iterative methods, since direct factorizations are not feasible any more at that scale. As for the Helmholtz equation, classical iterative methods applied to discretized Maxwell equations have severe convergence problems.We explain in this paper a family of domain decomposition methods based on well chosen transmission conditions. We show that all transmission conditions proposed so far in the literature, both for the first and second order formulation of Maxwell's equations, can be written and optimized in the common framework of optimized Schwarz methods, independently of the first or second order formulation one uses, and the performance of the corresponding algorithms is identical. We use a decomposition into transverse electric and transverse magnetic fields to describe these algorithms, which greatly simplifies the convergence analysis of the methods. We illustrate the performance of our algorithms with large scale numerical simulations.

Multiscale analysis and simulation of a reaction–diffusion problem with transmission conditions

This paper considers a transmission problem for partial differential equations obtained in the recent paper [M. Neuss-Radu, W. Jäger, Effective transmission conditions for reaction-diffusion processes in domains separated by an interface, SIAM J. Math. Anal. 39 (2007) 687–720] as the effective system modeling a reaction–diffusion process in two domains separated by a membrane. For the analysis of this problem an appropriate function space, which includes the coupling conditions for the concentrations on the interface, is introduced. The transmission conditions for the flux are included in the variational formulation with respect to this function space. The solution of the transmission problem is approximated by using the Galerkin method. Numerically the problem is reduced to a system of ordinary differential equations, where the coupling of the micro- and macro-variables leads to a special structure, distinguishing the variables relevant for the transmission. Results of numerical simulations are illustrating the effect of the microscopic process in the membrane on the macroscopic reaction–diffusion process in the bulk domains.

A thermoelastic junction problem in a thin-walled structure: asymptotic analysis

The two-dimensional model for a thin-walled structure in the plane strain time-harmonic case is discussed. A model of a surface crack defect subjected to oscillatory thermal loading in the middle part of the thin-walled bridges is presented. As a first part of the asymptotic model, the effective transmission condition in the vicinity of a deep surface-breaking crack in a thin-walled bridge is discussed. Then, the two-term boundary layer model determining the asymptotic behaviour of the field near the tip of the crack is constructed.

Asymptotic model of fields in a thin-walled structure with crack-like defects

The transition from two-dimensional (2D) wave propagation through the square periodic structure in anti-plane shear time-harmonic case to a discretised model of a 2D lattice with masses connected by springs is considered. A model of a defect in the middle part of the thin-walled bridges is presented. As a first part of the asymptotic model, the effective transmission condition in the vicinity of the transverse cut of the thin-walled bridges is discussed. Then, a boundary layer determining the asymptotic expansion of the field near the tip of the crack is constructed. Stress intensity factors are evaluated for deep cracks in the junction regions. The corresponding boundary layer analysis is non-trivial and has not been attempted elsewhere.

Optimized Schwarz Methods for Maxwell's Equations

Over the last two decades, classical Schwarz methods have been extended to systems of hyperbolic partial differential equations, using characteristic transmission conditions, and it has been observed that the classical Schwarz method can be convergent even without overlap in certain cases. This is in strong contrast to the behavior of classical Schwarz methods applied to elliptic problems, for which overlap is essential for convergence. More recently, optimized Schwarz methods have been developed for elliptic partial differential equations. These methods use more effective transmission conditions between subdomains than the classical Dirichlet conditions, and optimized Schwarz methods can be used both with and without overlap for elliptic problems. We show here why the classical Schwarz method applied to both the time harmonic and time discretized Maxwell's equations converges without overlap: the method has the same convergence factor as a simple optimized Schwarz method for a scalar elliptic equation. Based on this insight, we develop an entire new hierarchy of optimized overlapping and nonoverlapping Schwarz methods for Maxwell's equations with greatly enhanced performance compared to the classical Schwarz method. We also derive for each algorithm asymptotic formulas for the optimized transmission conditions, which can easily be used in implementations of the algorithms for problems with variable coefficients. We illustrate our findings with numerical experiments.

Effective Transmission Conditions for Reaction-Diffusion Processes in Domains Separated by an Interface

In this paper, we develop multiscale methods appropriate for the homogenization of processes in domains containing thin heterogeneous layers. Our model problem consists of a nonlinear reaction-diffusion system defined in such a domain, and properly scaled in the layer region. Both the period of the heterogeneities and the thickness of the layer are of order $\varepsilon.$ By performing an asymptotic analysis with respect to the scale parameter $\varepsilon$ we derive an effective model which consists of the reaction-diffusion equations on two domains separated by an interface together with appropriate transmission conditions across this interface. These conditions are determined by solving local problems on the standard periodicity cell in the layer. Our asymptotic analysis is based on weak and strong two-scale convergence results for sequences of functions defined on thin heterogeneous layers. For the derivation of the transmission conditions, we develop a new method based on test functions of boundary l...