Magnetic Damping Effects in Forced-Oscillation Vibrating-Wire Viscometers |
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Authors: | Peter Lloyd Woodfield Andrew Seagar Wayne Hall |
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Affiliation: | 1. School of Engineering, Griffith University, Gold Coast Campus, QLD, 4222, Australia
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Abstract: | Vibrating wire viscometers rely on the principle that the viscosity of the fluid surrounding the wire provides the dominant
damping action on the motion of the wire. However, some residual damping is always present due to other effects such as internal
friction of the wire (anelastic relaxation), losses through the wire supports, and magnetic damping. Magnetic damping is a
physical mechanism that has received relatively less attention than internal friction in the context of viscometers. The phenomenon
arises because the current induced by the motion of the wire contributes to the magnetic field in such a way as to oppose
its own motion. For a test circuit using a 40 μm diameter tungsten wire in a 0.3 T magnetic field, surprisingly, the effect
of magnetic damping was found to be of a similar order of magnitude to other non-viscous damping effects. The effect can be
accounted for by including the internal impedance of the oscillating voltage source in the model and it disappears completely
for a perfect oscillating current source. |
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