110 research outputs found
Test and Theory of Electrodynamic Bearings Coupled to Active Magnetic Dampers
Electrodynamic bearings (EDBs) are passive magnetic bearings that exploit the interaction between eddy currents developed in a rotating conductor and a static magnetic field to generate forces. Similar to other types of magnetic suspensions, EDBs provide contactless support, thus avoiding problems with lubrication, friction and wear. Electrodynamic bearings have also drawbacks such as the difficulty in insuring a stable levitation in a wide speed range. The paper presents a solution where the EDBs are coupled with active magnetic dampers (AMDs) to guarantee a stable levitation
Non-dimensional design approach for electrodynamic bearings
Electrodynamic bearings (EDBs) are passive magnetic bearings that exploit the interaction between eddy
currents developed in a rotating conductor and a static magnetic field to generate forces. Similar to other types of
magnetic suspensions, EDBs provide contactless support, thus avoiding problems with lubrication, friction and
wear. The most interesting aspect of EDBs is that levitation can be obtained by passive means, hence, no electronic
equipment, such as power electronics or sensors, are necessary.
Despite their promising characteristics, rotors running on EDBs are still lacking a design procedure; furthermore, at
present the static behavior of a bearing can only be defined by means of finite element analyses. The aim of the
present paper is to present a methodology that allows performing a first approximation design without resorting to
detailed FE analyses. The methodology is based on the use of non-dimensional parameters, similar to the analysis of
fluid bearings (Sommerfeld number). The non-dimensional quantities are derived using dimensional analysis, and
contain the main geometrical and physical parameters determining the EDBs' performance. The relation between the
non-dimensional quantities characterizing the static performance of the EDB is derived using FE simulations and is
presented in the form of graphs
Stability of a 4 degree of freedom rotor on electrodynamic passive magnetic bearings
Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means without violating the Earnshaw stability criterion. This remarkable characteristic makes this type of bearing a suitable alternative to active magnetic bearings in fields such as kinetic energy storage flywheels, turbo pumps, high speed compressors, among others. However, the suspension can become unstable due to rotating damping. To obtain deeper understanding of this instability phenomenon this paper presents the analysis of stability of a four degree of freedom (4dof) rotor supported by electrodynamic bearings. The 4dof rotor model is coupled to the dynamic model of the eddy current forces generated by the electrodynamic bearing and the stability of the complete system is analyzed. This model is used to study the stability of both cylindrical and conical whirling motion of the rotor. In addition to the well known cylindrical whirl instability the possible occurrence of conical instability is demonstrated. Finally the effects of two stabilization strategies are analyze
Octahedral molybdenum cluster complexes with aromatic sulfonate ligands
This article describes the synthesis, structures and systematic study of the spectroscopic and redox properties of a series of octahedral molybdenum metal cluster complexes with aromatic sulfonate ligands (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] (where X- is Cl-, Br- or I-; OTs- is p-toluenesulfonate and PhSO3 - is benzenesulfonate). All the complexes demonstrated photoluminescence in the red region and an ability to generate singlet oxygen. Notably, the highest quantum yields (>0.6) and narrowest emission bands were found for complexes with a {Mo6I8}4+ cluster core. Moreover, cyclic voltammetric studies revealed that (nBu4N)2[{Mo6X8}(OTs)6] and (nBu4N)2[{Mo6X8}(PhSO3)6] confer enhanced stability towards electrochemical oxidation relative to corresponding starting complexes (nBu4N)2[{Mo6X8}X6]
Produtividade e qualidade da uva 'Cabernet Sauvignon'produzida sob cobertura de plástico em cultivo orgânico
Medida da convergência de prioridades em planejamento participativo: Indicador de Sustentabilidade em Sistemas de Interesses - ISSI
Sistema de condução em Y com e sem cobertura plástica: microclima, produção, qualidade do cacho e ocorrência de doenças fúngicas na videira 'Niagara Rosada'
Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N<sub>2</sub> fixation
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