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Research Papers: Design and Analysis

Vibration Reduction of a Floating Roof by Dynamic Vibration Absorbers

[+] Author and Article Information
M. Utsumi

Machine Element Department, Technical Research Laboratory, IHI Corporation, 1 Shinnakaharacho, Isogo-ku, Yokohama, Kanagawa Prefecture 235-8501, Japan

J. Pressure Vessel Technol 133(4), 041204 (May 16, 2011) (11 pages) doi:10.1115/1.4002923 History: Received November 09, 2009; Revised October 26, 2010; Published May 16, 2011; Online May 16, 2011

This paper investigates the use of dynamic vibration absorbers as a means to reduce the vibration of a floating roof due to sloshing caused by long-period earthquakes. It is shown that the damping ratio of the primary system caused by the dynamic vibration absorbers increases with rising filling level, hence increasing the probability of liquid overspilling, although the ratio of the vibration absorbers’ mass to the liquid mass decreases as the filling level rises. We also study dynamic vibration absorbers that can be more easily tuned to the filling-level dependent sloshing frequency. A feature of these vibration absorbers is that they use time-integral feedback of the primary structure’s displacement near the tuning frequency unlike ordinary vibration absorbers. Computer simulation is carried out using a sinusoidal wave function and an actual earthquake ground motion record as the excitation applied to the tank.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Computational model

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Figure 2

Tunable vibration absorbers

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Figure 3

Geometry of floating roof used for numerical example

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Figure 4

Responses of floating roof displacement −u¯∣(r,φ)=(b,0) to sinusoidal excitation; (a) h=20 m, ωpr/2π=ωa/2π=0.122 Hz; (b) h=10 m, ωpr/2π=ωa/2π=0.1 Hz

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Figure 5

Actual earthquake ground motion record used for numerical examples

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Figure 6

Responses of (a) floating roof displacement −u¯∣(r,φ)=(b,0) and (b) liquid surface elevation η∣φ=0; h=20 m, ωpr/2π=ωa/2π=0.122 Hz

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Figure 7

Responses for the case where the vibration absorbers’ eigenfrequency is kept constant ωa/2π=0.111 Hz; (a) h=20 m, (ωpr/2π=0.122 Hz); (b) h=10 m, (ωpr/2π=0.1 Hz)

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Figure 8

Responses for the case where the liquid density is increased to 980 kg/m3 (h=20 m, ωpr/2π=ωa/2π=0.122 Hz)

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Figure 9

Numerical results for the tunable vibration absorbers shown in Fig. 2; ωa/2π=(g/la0)1/2/2π=0.1 Hz; (a) h=10 m, (ωpr/2π=0.1 Hz), θ0=0 deg; (b) h=20 m, (ωpr/2π=0.122 Hz), θ0=2 deg

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Figure 10

Numerical results that are compared with Fig. 9; h=20 m, (ωpr/2π=0.122 Hz), θ0=0; (a) ωa/2π=(g/la0)1/2/2π=0.1 Hz; (b) ωa/2π=(g/la0)1/2/2π=0.122 Hz

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Figure 11

Absorber mass displacement for the cases of Figs.  99

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Figure 12

Amplitude magnification curves of the tunable vibration absorbers

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Figure 13

Calculation of buoyancy force

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Figure 14

Buoyancy and gravity forces

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