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Research Papers

Nonlinear Vibrations and Chaos in Floating Roofs

[+] Author and Article Information
R. Shabani1

Mechanical Engineering Department,  Urmia University, Urmia 15311-57561, Iranr.shabani@urmia.ac.ir

S. Tariverdilo

Civil Engineering Department,  Urmia University, Urmia 15311-57561, Irans.tariverdilo@urmia.ac.ir

H. Salarieh

Mechanical Engineering Department,  Sharif University of Technology, Tehran 11155-9567, Iransalarieh@sharif.edu

1

Corresponding author.

J. Comput. Nonlinear Dynam 7(2), 021012 (Jan 10, 2012) (13 pages) doi:10.1115/1.4005437 History: Received May 16, 2011; Revised October 24, 2011; Accepted October 25, 2011; Published January 10, 2012; Online January 10, 2012

Variational principle is used to derive the nonlinear response of the floating roof of cylindrical liquid storage tanks due to harmonic base excitations. The formulation accounts for nonlinearity due to large deflections of the floating roof. The derived nonlinear governing equation for the sloshing response of the floating roof has a cubic nonlinear stiffness term similar to the well known Duffing equation. It is shown that accounting for large deflections could substantially reduce the wave elevation for near resonance harmonic excitations. Evaluating the response of the nonlinear model for increasing amplitudes of near resonance harmonic excitations gives rise to the appearance of sub and super harmonics in the response. The broadband structure of the frequency spectrum, the fractal structure of the Poincare maps, and the bifurcation diagram as qualitative criteria and Lyapunov exponent evolution as quantitative criterion are used to investigate the emergence of chaotic response.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical liquid storage tank with single deck floating roof

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Figure 2

Response of a linear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 0.6 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 3

Response of a nonlinear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 0.6 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 4

Response of a linear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 0.4 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 5

Response of a nonlinear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 0.4 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 6

Response of a linear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 3 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 7

Response of a nonlinear model for a ground motion acceleration amplitude of 1.42 m/s2 and an excitation frequency of 3 Hz. (a) Time history of wave elevation at roof edge, (b) time history of pressure at roof edge, and (c) FFT of wave elevation at roof edge.

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Figure 8

Response of a nonlinear model for a ground motion acceleration amplitude of 2.84 m/s2 and an excitation frequency of 0.6 Hz. (a) Phase plane, (b) Poincare map, and (c) spectrum.

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Figure 9

Response of a nonlinear model for a ground motion acceleration amplitude of 5.26 m/s2 and an excitation frequency of 0.6 Hz. (a) Phase plane, (b) Poincare map (50000 points), and (c) spectrum.

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Figure 10

Response of a nonlinear model for a ground motion acceleration amplitude of 11.65 m/s2 and anexcitation frequency of 0.6 Hz. (a) Phase plane, (b) Poincare map (50000 points), and (c) spectrum.

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Figure 11

Response of a nonlinear model for a ground motion acceleration amplitude of 12.08 m/s2 and an excitation frequency of 0.6 Hz. (a) Phase plane, (b) Poincare map (50000 points), and (c) spectrum.

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Figure 12

Bifurcation diagram of the roof edge displacement for increasing ground accelerations and an excitation frequency of 0.6 Hz

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Figure 13

Largest Lyapunov exponent associated to the bifurcation diagram (Fig. 1) for an excitation frequency of 0.6 Hz

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Figure 14

Bifurcation diagram of the roof edge displacement for increasing ground accelerations and an excitation frequency of 0.5 Hz

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Figure 15

Largest Lyapunov exponent associated to the bifurcation diagram (Fig. 1) for an excitation frequency of 0.5 Hz

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Figure 16

Response of a nonlinear model for a ground motion acceleration amplitude of 1.77 m/s2 and an excitation frequency of 0.5 Hz. (a) Phase plane, (b) Poincare map, and (c) spectrum.

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Figure 17

Response of a nonlinear model for a ground motion acceleration amplitude of 7.10 m/s2 and an excitation frequency of 0.5 Hz. (a) Phase plane, (b) Poincare map (50000 points), and (c) spectrum.

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