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Research Papers

Magnetic Damper Consisting of a Combined Hollow Cylinder Magnet and Conducting Disks

[+] Author and Article Information
Yoshihisa Takayama

e-mail: takayama@mech.kyushu-u.ac.jp

Takahiro Kondou

Department of Mechanical Engineering,
Kyushu University,
744 Moto-oka, Nishi-ku,
Fukuoka 819-0395, Japan

Contributed by the Design Engineering Division of ASME for publication in the Journal of VIBRATION AND ACOUSTICS. Manuscript received August 28, 2011; final manuscript received March 15, 2013; published online June 18, 2013. Assoc. Editor: Paul C.-P. Chao.

J. Vib. Acoust 135(5), 051007 (Jun 18, 2013) (11 pages) Paper No: VIB-11-1188; doi: 10.1115/1.4024094 History: Received August 28, 2011; Revised March 15, 2013

It is recognized that unstable vibration occurs at a rotating speed above the major critical speed by a rotating-conducting-disk type magnetic damper, but not by a rotating-circular-magnet type magnetic damper. In addition, magnetic dampers generally have relatively poor damping performance. In the present work, two new rotating-circular-magnet type magnetic dampers, (which consist of a combined hollow cylinder magnet with alternating directional magnetic poles), are introduced and their design method is presented. Applying the modeling method that the authors have been studying, a prototype magnetic damper with a combined magnet is fabricated and the damping ratios from the analytical results agree well with those from the experimental results. Rotating tests are performed and it is confirmed that unstable vibration does not occur at a rotating speed of more than twice the major critical speed. Based on these findings, an optimally designed magnetic damper with a combined magnet is developed and a damping ratio of 0.25 (damping coefficient of 215 Ns/m) is achieved.

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References

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Takayama, Y., Sueoka, A., and Kondou, T., 2004, “Vibration Reduction of a Rotating Machinery by Magnetic Damper With Rotating Circular Magnet (Nonoccurrence of an Unstable Vibration Caused by Magnetic Damping Force),” Trans. Jpn. Soc. Mech. Eng., 70(696), pp. 2195–2202 (in Japanese). [CrossRef]
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Figures

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Fig. 1

Coordinate systems and rotating-circular-magnet type magnetic damper

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Fig. 2

Layout of the experimental setup of the rotating-circular-magnet type magnetic damper. (a) Prototype magnetic damper composed of two conducting plates and a combined magnet. (b) Vertical Jeffcott rotor with a combined magnet consisting of a small hollow cylinder magnet (Magnet I) and a large magnet (Magnet II).

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Fig. 3

Detailed drawing of the prototype magnetic damper

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Fig. 4

Comparison of static magnetic field distributions. (a) Static magnetic field distribution of Magnet I only. (b) Static magnetic field distribution of Magnet II only. (c) Static magnetic field distribution of the combined magnet with alternating directional magnetic poles. (d) Static magnetic field distribution of the combined magnet with unidirectional magnetic poles.

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Fig. 5

Measurement example of the damping waveform without a magnetic damper and the yn − yn+1 chart: (a) the damping waveform without the two conducting plates (see Fig. 2(b)), and (b) the yn − yn+1 chart

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Fig. 6

Measurement example of the damping waveform of the prototype magnetic damper and the yn − yn+1 chart at d = 7 mm: (a) the damping waveform, and (b) the yn − yn+1 chart

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Fig. 7

Measurement example of the damping waveform of the prototype magnetic damper and the yn − yn+1 chart at d = 1 mm: (a) the damping waveform, and (b) the yn − yn+1 chart

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Fig. 8

Experimental and analytical magnetic damping ratios as a function of the distance between the magnet and the conducting plate

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Fig. 9

Simulation results for the magnetic damping ratios between the ALT, UNI, and SGL magnetic dampers

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Fig. 10

Distribution of the integrand in Eq. (4) at d = 1 mm at the middle of the disk in the thickness direction

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Fig. 11

Distribution of the integrand in Eq. (4) at d = 10 mm at the middle of the disk in the thickness direction

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Fig. 12

Amplitude of the rotor with the prototype magnetic damper as a function of the rotational speed at d = 1 and 5 mm

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Fig. 13

Simulation results for the relationship between the magnet damping coefficients and the spacer radius

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Fig. 14

Simulation results for the magnetic damping coefficients as a function of the spacer radius for the design of an optimally designed magnetic damper

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Fig. 15

Measurement example of the damping waveform without a magnetic damper and the yn − yn+1 chart: (a) the damping waveform without the two conducting plates, and (b) the yn − yn+1 chart

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Fig. 16

Measurement example of the damping waveform of the optimally designed magnetic damper and the yn − yn+1 chart at d = 7 mm: (a) the damping waveform, and (b) the yn − yn+1 chart

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Fig. 17

Measurement example of the damping waveform of the optimally designed magnetic damper and the yn − yn+1 chart at d = 1 mm: (a) the damping waveform, and (b) the yn − yn+1 chart

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Fig. 18

Experimental and analytical magnetic damping ratios of the optimally designed magnetic damper

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Fig. 19

Coordinate systems and wire coil

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Fig. 20

Simple modeling of a hollow cylinder magnet

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Fig. 21

Modeling example of a hollow cylinder magnet with five pairs of coils

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Fig. 22

Discrete model of a conducting disk for the calculation of the magnetic damping force

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Fig. 24

The yn − yn+1 chart

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Fig. 23

Vibration decay with viscous damping

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