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L'étude du comportement d'un réservoir de gaz en nappe aquifère réclame une connaissance aussi précise que possible des caractéristiques géométriques et pétrophysiques des couches réservoirs. Les moyens d'investigation sont de deux natures : - forages permettant une connaissance locale des roches réservoirs ; - mesures sismiques conduisant à une estimation approximative des cotes de certains repères stratigraphiques, en des points situés le long de profils. Les données recueillies sont donc, par nature, fragmentaires et discrètes : là où elles sont absentes, il y a lieu d'estimer les grandeurs étudiées en tenant compte au mieux de notre connaissance de leur variabilité spatiale. Ce problème d'interpolation optimale a donné lieu, depuis une vingtaine d'années, à l'élaboration et la mise en pratique d'un outil théorique particulièrement bien adapté aux besoins exprimés par les techniciens des sciences de la terre : la théorie des variables régionalisées due à G. Matheron. Des programmes informatiques mettant en oeuvre cette théorie sont actuellement opérationnels. Des exemples d'application en sont donnés : - tracé automatique de cartes structurales à partir des données de forages et des mesures sismiques ; - estimation des incertitudes de prévision sur les profondeurs ; - tracé de plusieurs variantes de carte compatibles avec les données ; - établissement d'éléments statistiques relatifs à une grandeur caractéristique d'un stockage : volume stockable par exemple ; - génération automatique des données nécessaires à la mise en oeuvre d'un modèle maillé de réservoir. Predicting and monitoring the behavior of an aquifer gas-storage reservoir requires as precise a knowledge as possible of the geometric and petrophysical properties of the reservoir layer. Two ways of obtaining this information can be given: (a) Boreholes which provide local knowledge of the reservoir, and (b) Seismic measurements which lead to more or less accurate depth estimates for some stratigraphic markers at points located along profiles. Therefore, the data are inherently fragmentary. At points where they are lacking, we have to make the most of available information in order to estimate the unknown values. This problem of optimum interpolation has led to a new theoretical approach which is particularly suited to the earth sciences. This theory is called the theory of regionalized variablesby its author, G. Matheron. It has given rise to effective computer programs, and developments are still being made. Examples of possible applications are: (a) Computer-drawn structural maps based on borehole data and seismic measurements; assessment of the prediction uncertainty for the depth of the top-layer; alternative top-layer maps all of which are consistent with the data. (b) Probabilistic evaluation of the storage volume available. (c) Gridded input to reservoir models.

A coupling of the partial element equivalent circuit method with the finite element method for solving magneto-harmonic electromagnetic problems is proposed. The new formulation, which combines the main advantages of the previous methods, is particularly well suited for modeling electromagnetic complex devices including a large number of conductors. Index Terms--Finite element method, mutual matrix, partial element equivalent circuit, [T.sub.0]--[phi] formulation.

In order to improve the finite-element modeling of macroscopic eddy currents (associated with motion and/or a time- varying electrical excitation), an original error criterion for adaptive meshing, based on a local power conservation, is proposed. Then, the importance of the order element in the error computation is investigated. Finally, the criterion is coupled to a 'bubble' mesh generator, and an adaptive meshing of a 2-D induction heating case is performed. Index Terms--Adaptive meshing, eddy currents, error criterion, power conservation.

The aim of this paper is to propose and argue specific electromagnetic formulations including dynamic electric and magnetic properties of soft materials, working with transient signals and time harmonics within the quasi-static approximation. Special attention will be paid to origin, nature, and relevance of these so-called dynamic properties, which will act on both the diffusion process and coupling between regions. Nonlinear transient experimental identifications of a homogenized dynamic magnetic property are also carried out and discussed. It can provide useful experimental data of soft magnetic materials for simulation and conception purposes. Index Terms--Dynamic hysteresis and properties, eddy currents, experimental characterization, fields coupling, magnetization reversal processes, materials modeling.

Thermal constraint is one of the major cause of capacitor failures. In this paper, a loss model, based on electrode current distribution, is first established to determine, by numerical simulation, a temperature mapping of capacitor. This mapping is successfully compared to measurements. Then a shape optimization, coupling losses computing and finite-element method, is led in order to find parameters that give the best lifespan and the larger reactive power provided. Very interesting new geometries have been found out; they allow an increase in reactive power greater than the increase in volume. Index Terms--Capacitor lifespan, capacitor losses, metallized film capacitors, shape optimization.

In this paper, we consider taking both microscopic excess and macroscopic classical induced losses and damping, occurring within bulk and laminated soft magnetic materials, into account. We will not detail actual eddy currents distributions but use homogenizing techniques and variational principles to derive a dedicated formulation with respect to the reduced magnetic vector potential AM, and still including specific material dynamic properties. At last, some 2-D computations are carried out and first results are discussed. Index Terms--Dynamic hysteresis and eddy currents, homogenization of bulk and laminated materials, quasi-static electromagnetic fields formulations.

This paper investigates a new approach to face the problem of dynamic hysteresis and extra-losses in soft magnetic materials. Thanks to a spatial averaging technique and a variational principle, a dedicated formulation is derived. It takes microscopic magnetization mechanisms and domain wall motion-induced Joule losses into account. Implementation with the finite element method is dicussed and first simple two dimensions and three dimensions calculations are carried out. The method is shown to be suitable whithin the linear dynamic approximation and far from saturation, which only requires additional non linear properties and numerical methods. Index Terms--Dynamic hysteresis, eddy currents, magnetic materials, sensors, transformers, transient formulations.

High frequency electrical machine modeling based on lumped parameter equivalent circuit requires that eddy currents effects be taken into account for R and L coefficient derivation. Substituting hysteretic materials (complex permeability) to conductive materials makes it possible to accurately approximate proximity losses and shielding effect while considering realistic meshes for finite element methods computation. Three-dimensional magnetodynamic simulations of transformer test-cases using anisotropie complex permeability for magnetic core and windings have shown a good agreement with the standard models results. Index Terms--Eddy currents, electromagnetic transient analysis, finite element methods (FEMs), hysteresis, losses.

This paper deals with the modeling of eddy currents generated by are motion during opening phases of low voltage circuit breakers. Two kinds of modeling are tested. While the first one consists in determining eddy currents in splitter plates, the second one is devoted to the calculation of eddy currents in electrodes. All simulations are carried out with a T--[PHI] finite-element method formulation and no new mesh at each time step is required. Index Terms--Circuit breakers, eddy currents, finite-element method, magnetic forces.

A new approach to lace the problem of dynamic hysteresis and assess extra losses in soft magnetic materials is investigated. Thanks to a spatial averaging technique and a variational principle, a dedicated formulation is derived. It takes into account microscopic magnetization mechanisms and domain wall motion-induced Joule losses. Implementation within the finite element method is discussed, and calculations are carried out for a 2-D geometry. The model provides first-order low-pass filtering properties. Index Terms--Dynamic hysteresis, eddy currents, magnetic materials, transient formulations.

Two new different integral equation methods for the study of axisymmetric harmonic electromagnetic problems are presented. Both proposed formulations allow the modeling of conductive and magnetic media, and inhomogeneous media can be considered as well. Thanks to the use of low-rank approximation techniques, a drastic reduction in the required memory and computational cost is achieved with a truly negligible loss of accuracy. The numerical features of the two proposed integral methods are widely discussed and compared. Moreover, most of the considerations hold for the case of 3-D integral methods. Sample implementations of the two formulations are made publicly available. [ABSTRACT FROM AUTHOR]

This paper deals with the use of the volume integral method to compute the magnetic anomaly created by a non-conductive ferromagnetic thin shell placed in a static inductor field. An original facet integral formulation considering the magnetic induction as unknowns is presented. The use of thin shell element assumption leads to a surface mesh decreasing highly the number of elements so the computation cost. The method is very performing in terms of speed and accuracy. [ABSTRACT FROM AUTHOR]

An extension of the unstructured partial element equivalent circuit (PEEC) method to magnetic media is proposed. Linear inhomogeneous conductive, dielectric, and magnetic media are considered. By formulating PEEC in terms of div-free currents, an efficient circuit algorithm based on the independent loop search or basis reduction scheme can be used to solve the electromagnetic problem. In such a way, a limited number of unknowns can be used and non-simply connected domains can be treated as well. The formulation is validated on a real integrated inductor, capacitor, and transformer ($L$ – $C$ –T) component against measurements and numerical results from commercial software based on integral equation method and finite element method. [ABSTRACT FROM AUTHOR]

Presents a study which obtained results with the two-dimensional finite-element method including hysteretic behavior in magnetostatic-field computation. Advantage of using the finite-element method in computing electromagnetic fields in devices; Computation of the magnetization change in devices; Details on the Gauss-Seidel process; Results of the study.

Presents a study that examined two-dimensional finite-element and analytic calculation of eddy-current losses in thin linear conductors. Eddy-current losses for thick conductors; Comparison between the analytic and the finite-element-method; Conclusion.

Develops a means of modeling an induction machine with a nonlinear step-by-step method. Basis of the method; Comparison of the curves obtained by the method with those by the magnetodynamic model for different types of induction machine; Motion of the rotor in the modeling of a polyphase induction machine.

Presents a study which proposed a comparison between results predicted by mathematical models of magnetic hysteresis and experimental data. Summary of the principles; Properties of the models; Comparison of the experimental behavior of a hard magnetic material to those predicted by the models.

Presents a study that employed two methods involved in adaptive mesh generation in conjunction. Error criteria used to test the strategy; Computation of the forces on permanent magnets; Reason that adaptive refinement is to be commended; Approaches that are possible in improving the trial function; Advantages of each approach.