Diffusion du champ électromagnétique dans une sphère ferromagnétique conductrice avec hystérésis

This paper deals with the numerical simulation of a hard steel sphere magnetization under a pulsed current through a solenoid. We could show that the association of the induced current and the magnetic hysteresis leads to a permanent trapped flux loop. We could also confirm the existence of this phenomenon by means of experiment.Cet article concerne la simulation numérique de l'aimantation d'une sphère en acier dur par une brève impulsion de courant dans un soléndide. On montre que les courants induits et l'hystérésis magnétique conduisent à un flux d'induction rémanent piégé d'une façon permanente dans cette sphère. On donne également une mise en évidence expérimentale de ce phénomène

Simulation numérique globale de la décharge impulsionnelle d'une génératrice asynchrone sans fer

The authors have done a numerical analysis of a high pulse energy generation system which consists of an asynchronous, iron-free solid rotor generator with a resonating load (power factor correction capacitors plus a full wave diode bridge and an inductive load). The automatic simulation program for the analysis of the static converters (SACSO) was modified by the introduction of resistive coupling terms in the network matrices. Results have been obtained for a complete discharge (200 periods) using two distinct models of the machine and are accurate to within 20 % of the practical system tested.Les auteurs effectuent une analyse numérique d'une source d'énergie électrique impulsionnelle constituée par une génératrice asynchrone sans fer à rotor discoïde massif et à charge accordée (capacité de compensation de facteur de puissance, pont redresseur, inductance de stockage). Le programme de simulation automatique de convertisseurs statiques sur ordinateur (SACSO) a été modifié à cet effet par l'introduction de couplages résistifs. Les résultats ainsi obtenus pour une décharge complète (200 périodes) au moyen de deux modélisations de la machine asynchrone sont en accord avec l'expérience, les écarts maximums étant inférieurs à 20 %

Development and Modification of Yield Line Patterns in Thin Slabs Subjected to Tensile Membrane Action

It is widely recognized that composite floor slabs experiencing large displacement develop a central zone of hydrostatic membrane tension, surrounded and equilibrated by a ring of membrane compression around the periphery. This mechanism, known as tensile membrane action, can greatly enhance the load-bearing capacity of a slab compared with that defined by yield line analysis. This is a very useful effect in cases where large deflections can be accepted, particularly in fire-resistance design of composite slabs, since the strength enhancement permits some beams to be left unprotected. Studies of tensile membrane action in the 1960s led to the development of several methods to define slab load capacity under large displacement. The method due to Hayes [5] has become the most widely accepted, and was adopted by Bailey [1, 2] in developing the BRE method for fire-safe design of composite floors. Based on observations from the Cardington fire tests and on assumptions concerning yield line patterns and membrane stresses, it calculates the load-carrying enhancement of a slab as a function of its deflection [2]. It also postulates a deflection limit at which the maximum acceptable strain in the rebar is reached. On close examination, however, several hypotheses, such as the assumed failure mechanisms, seem illogical. The BRE method assumes that a common observation, of a through-depth crack forming across the central short-span of the slab, represents the limit state for such slabs. However, it has been observed that similar cracks can also appear at the intersections of the yield lines, or even not appear at all [3]. This paper proposes a simple way to define the deflection at which the through-depth crack forms, and where on the slab it appears. Based on consistent kinematic assumptions, it calculates the tensile stresses at key points of the slab [4], and predicts the position and displacement at which through-depth cracking occurs

Modélisation magnétique et numérique par éléments finis de feuilletages ferromagnétiques

Stacked iron sheets magnetics circuits are frequently used in electrical engines, but the calculation of the field distribution is difficult by the anisotropy in the iron. We propose in this paper a bidimensional modelisation of these structures using a finite elements variational method which is adapted to such anisotropic saturable magnetic problems.Les circuits magnétiques constitués par des empilements de tôles de fer sont fréquemment utilisés en électrotechnique. Nous proposons ici une modélisation bidimensionnelle de telles structures associée à une méthode variationnelle par éléments finis adaptée aux problèmes pour lesquels il faut tenir compte à la fois de l'anisotropie et de la saturation magnétique