Test and theory of electrodynamic bearings coupled to active magnetic dampers
Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means. Such a feature would make this type of bearing a viable alternative to active and permanent magnet bearings. Although electrodynamic bearings do not violate Earnshaw’s theorem, the open issue remains the stabilization system that is needed to make the rotating body stable, due to the low rotational speeds. Stabilizing solutions proposed in the literature are partially effective and not totally convincing. This limits real industrial applications. The present paper proposes a combination of electrodynamic and active magnetic bearings. At low speed the active part behaves as a conventional active magnetic bearing, while at high speed it provides damping. The readiness of the proposed solution is demonstrated by experimental results obtained using a dedicate test rig.
DESIGN METHODOLOGY OF ELECTRODYNAMIC BEARINGS
Sommario I cuscinetti elettrodinamici (EDBs) costituiscono una nuova tipologia di supporti utilizzabili per la sospensione in assenza di contatto di alberi rotanti. Rispetto ai cuscinetti attivi, la natura passiva dei cuscinetti eletrodinamici consente la costruzione di sistemi piu semplici, affidabili ed economici, aprendo cosi il campo di applicazione ad apparecchi di largo consumo. In questo articolo sono presentati gli strumenti necessari alla caratterizzazione meccanica dei cuscinetti elettrodinamici, focalizzando l’attenzione sulla relazione tra le caratteristiche in condizioni quasi stazionarie e la simulazione ad elementi finiti di conduttori in moto, in modo da stabilire una metodologia per determinare le caratteristiche meccaniche degli EDBs. Alcune analisi di sensitivita sono state condotte per evidenziare l’influenza delle caratteristiche geometriche di un cuscinetto elettrodinamico rispetto alle sue proprieta meccaniche.
Flow in a branching open channel: a review
Branching channel flow refers to any side water withdrawals from rivers or main channels. Branching channels have wide application in many practical projects, such as irrigation and drainage network systems, water and waste water treatment plants, and many water resources projects. In the last decades, extensive theoretical and experimental investigations of the branching open channels have been carried out to understand the characteristics of this branching flow, varying from case studies to theoretical and experimental investigations. The objectives of this paper are to review and summarise the relevant literatures regarding branching channel flow. These literatures were reviewed based on flow characteristics, physical characteristics, and modeling of the branching flow. Investigations of the flow into branching channel show that the branching discharge depends on many interlinked parameters. It increases with the decreasing of the main channel flow velocity and Froude number at the upstream of the branch channel junction. Also it increases with the increasing of the branch channel bed slope. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to an increase of water depth at the downstream of the main channel. From the review, it is important to highlight that most of the study concentrated on flow characteristics in a right angle branch channel with a rigid boundary. Investigations on different branching angles with movable bed have still to be explored.