Luciano Misici

Three-dimensional inverse obstacle scattering for time harmonic acoustic waves: a numerical method

A numerical method for a three-dimensional inverse acoustic scattering problem is considered. From the knowledge of several far fields patterns of the Helmholtz equation a closed surface

An inverse problem for the three dimensional vector Helmholtz equation for a perfectly conducting obstacle

\partial D

A new formalism for wave scattering from a bounded obstacle

representing the boundary of an unknown obstacle D is reconstructed. The obstacle D is supposed to be acoustically soft or acoustically hard or characterized by a given acoustic impedance.

Explicit finite-difference simulation of a dropping mercury electrode utilizing an exponentially expanded space grid

Abstract A numerical algorithm for a three-dimensional inverse electromagnetic scattering problem is considered. For time-harmonic waves the Maxwells equations are reduced to the vector Helmholtz equation. From the knowledge of several far fields generated by an obstacle D when hit by incoming linearly polarized plane waves the boundary ∂D of the obstacle is reconstructed. The obstacle D is supposed to be bounded, connected, with smooth boundary and perfectly conducting. The reconstruction procedure proposed here generalizes the “Herglotz function method” introduced by Colton and Monk [1] for the acoustic problem and is effective in the so-called resonance region.

Three dimensional time harmonic inverse electromagnetic scattering

Let Ω⊂R3 be an obstacle that is a simply connected bounded domain. The exterior Dirichlet problem for the Helmholtz equation in R3\Ω with the Sommerfeld radiation condition at infinity is considered. Based on an integral representation formula, a new method to compute the solution of the exterior boundary value problem mentioned above is proposed. This method generalizes the formalism introduced for an unbounded obstacle by Milder [J. Acoust. Soc. Am. 89, 529–541 (1991)] and consists in computing a perturbation series whose coefficients are integrals. These integrals are independent one from the other so that the computation of the series is fully parallelizable. Finally, some numerical results obtained on test problems are shown. In particular, numerical experiments for obstacles with nonsmooth boundaries such as polyhedra and obstacles with multiscale corrugations are shown.

The inverse gravimetry problem: an application to the Northern San Francisco Craton Granite

Abstract An exponentially expanded space grid has been applied in the explicit finite-difference computer simulation of a dropping mercury electrode (DME). The simulator has been proved to be considerably faster than previously described models using uniform grids (S.W. Feldberg, J. Electroanal. Chem., 109 (1980) 69) and easily adaptable to different electrode reaction stoichiometries and forms of excitation potential.

Original article: A three-dimensional model for the study of the cooling system of submersible electric pumps

A numerical method for the three dimensional inverse electromagnetic time harmonic scattering is presented. We consider an obstacle D that is a bounded, simply connected domain with smooth boundary ∂D contained in the three dimensional euclidean space IR3. The far field patterns of the vector Helmholtz equation generated by a known electromagnetic wave incident on the obstacle D are used as data. From these data the boundary of the obstacle ∂D is reconstructed. The reconstruction procedure proposed here generalizes the “Herglotz function method” introduced by Colton and Monk [1] in the acoustic problem and is effective in theso called resonance region.

PolyFront: an algorithm for fast generation of high quality triangular mesh

From the knowledge of the anomalies of the gravitational field, we reconstruct the mass density distribution in a large region of the state of Bahia (Brazil). This inverse gravimetry problem has been translated into a linear programming problem and solved using the simplex method. Both two-dimensional and three-dimensional models have been considered.

The Use of Optimization and Multiresolution Techniques for the Numerical Solution of First Kind Fredholm Equations

We study the cooling system for submersible electric pumps. This study aims to provide some guidelines to improve the existing cooling system of these electric pumps when they work partially or totally not immersed in the service fluid. Note that inefficient cooling systems cannot prevent the rise in temperature of the alternating current (AC) motor of the pump, and the consequent reduction of the service factor. We propose a three-dimensional model to describe the fluid flow in the cooling circuit and the heat transfer among the engine of the electric pump, the cooling system and the external environment. This model is discretized by using a finite element method, and the resulting algorithm has been implemented in a FORTRAN code. We show some preliminary results obtained by this code using two different geometries for the cooling circuit, and we compare these results with experimental data and with other numerical results obtained in a previous work, by using a two-dimensional model.

A regular perturbation approach to the problem of diffusion towards a growing mercury drop electrode

In this article the authors present PolyFront, a new triangulation algorithm for two dimensional domains with holes. PolyFront is based on a normal offsetting technique, where a domain is triangulated starting from a discretization of its boundary and constructing the mesh layer by layer going toward the interior of the domain. The authors propose some numerical experiments to compare this algorithm with other four mesh generators. This comparison shows that the algorithm gives good quality meshes with reduced computational time.