Nicolae Marinescu

A new improved method for computation of radial stiffness of permanent magnet bearings

The new method for the computation of the radial stiffness is based on the perturbative treatment of the deviation from the cylindrical symmetry of the magnetic field due to the small displacements of the rotor. It turns out that the partial differential equations of the vector potential are 2D and can be easily solved by means of appropriately adapted FEM programs. The present method is more general than the exact Coulomb integral method which can be applied only for force calculation in bearings without iron parts and is more exact and needs less computation effort than the method based on Cartesian development of the system. >

New permanent magnetic separator with NdFeB meets theoretical predictions

A permanent magnet drum separator was designed, assembled, and tested, which uses high-energy magnets made of NdFeB-type VACODYM. The separator called PERMOS is of the medium-field-type, with >0.4-T flux density at the drum surface. Calculations and measurements of the field strength and the magnetic forces are in good agreement. Preliminary tests with the separator gave promising results. >

Magnetic leakage fields from extended inhomogeneities in ferromagnetic plates

The computation of the leakage fields is a very important problem for the magnetostatic detection method of defects in ferromagnetic materials. The computation method which we propose is based on the experimentally very well confirmed assumption, that the leakage flux is negligible compared to the main flux in the ferromagnetic plate. Then the computation of the flux distribution in the plate can be reduced to a 2D problem. The leakage field can be calculated subsequently by using a Dirichlet-Greens integral. The method allows the determination of the size and permeability of extended defects in plane parallel plates from leakage field measurement data. >

Optimization of magnetic circuits for loudspeakers 1970 and now

One of the largest volume applications of permanent magnet materials are loudspeaker systems. High performant loudspeakers can be obtained by using rare earth permanent magnets with a high residual flux density, as for instance NdFeB. Because such devices are produced in a very large quantity and because the rare earth permanent magnets are quite expensive, it is very important for the manufacturer to keep the volume of the magnetic material used as low as possible. This aim can be achieved by using design methods to optimize the magnetic circuit of the loudspeaker, i. e. to obtain a given flux density in the air gap with a minimum volume of magnetic material. Prof. A. Timotin has done in this respect pioneering work. He and one of the authors of the present work have calculated the magnetic flux in the air gap as well the leakage fluxes of a loudspeaker system by solving analytically the magnetic potential equation with given boundary conditions. Also they have formulated certain constraints on the geometrical parameters of the system to be optimized. However the analytical solution could be obtained only under simplifying assumptions which practically are fulfilled only approximately. Such limitations can be avoided by using numerical methods for computation of the magnetic field. In this work we present the optimization of a large class of magnetic circuits for loudspeaker systems by using high precision numeric finite-elements-method computations.

Lineare Netzwerke bei nichtsinusförmiger Erregung

Sind die Schaltungen linear (d.h. hier: sie enthalten keine Spulen mit Eisenkern), so kann man, zur Bestimmung aller Strome bei Vorgabe der Quellenspannungen (oder -strome) und aller Schaltelemente R,L,C, das Superpositionsprinzip anwenden.

Berechnung von Ausgleichsvorgängen im Zeitbereich mithilfe von Differentialgleichungen

Seit dem Anfang des 21. Jahrhunderts haben umwalzende Veranderungen bei der Erzeugung und Ubertragung der elektrischen Energie stattgefunden: Die sogenannte „Energiewende“ wird uberall auf der Welt intensiv eingefuhrt.

Berechnung von Ausgleichsvorgängen mithilfe der Laplace-Transformation

Erinnerung an die Berechnung von Netzwerken bei sinusformiger Erregung also bei Wechselstrom, im stationaren Zustand.

Nichtsinusförmige periodische Vorgänge (Fourier-Analyse)

Bisher wurde davon ausgegangen, dass alle Strome und Spannungen in Wechselstromnetzwerken sinusformige Grosen mit derselben Frequenz f sind. Diese Annahme erleichtert die Berechnung der stationaren Vorgange in linearen Netzwerken (durch komplexe Rechnung oder Zeigerdiagramme).