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Safety and Reliability

Stability Analysis of TLP Tethers Under Vortex-Induced Oscillations

[+] Author and Article Information
A. K. Banik1

Department of Civil Engineering, National Institute of Technology, Durgapur, M.G. Avenue, Durgapur 713209, Indiaakbanik@gmail.com

T. K. Datta

Department of Civil Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India

1

Corresponding author.

J. Offshore Mech. Arct. Eng 131(1), 011601 (Oct 15, 2008) (7 pages) doi:10.1115/1.2948946 History: Received January 15, 2007; Revised April 05, 2008; Published October 15, 2008

The vortex-induced oscillation of TLP tether is investigated in the vicinity of lock-in condition. The vortex shedding is caused purely due to current, which may vary across the depth of the sea. The vibration of TLP is modeled as a SDOF problem by assuming that the first mode response of the tether dominates the motion. Nonlinearity in the equation of motion is produced due to the relative velocity squared drag force. In order to trace different branches of the response curve and investigate different instability phenomena that may exist, an arc-length continuation technique along with the incremental harmonic balance method (IHBC) is employed. A procedure for treating the nonlinear term using distribution theory is presented so that the equation of motion is transformed to a form amenable to the application of IHBC. The stability of the solution is investigated by the Floquet theory using Hsu’s scheme.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

TLP and tether systems

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Figure 2

Variation of amplitude of response with detuning parameter (Period 1 solution; CD=0.1, CL=0.6)

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Figure 3

Phase plot for detuning parameter γ=0 (Period 1 solution; CD=0.1, CL=0.6)

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Figure 4

Variation of amplitude of response with detuning parameter (Period 2 solution; forward sweep; CD=0.1, CL=0.6)

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Figure 5

Phase plot at γ=−0.011 (Unstable 2T solution; forward sweep; CD=0.1, CL=0.6)

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Figure 6

Phase plot at γ=0.0483 (Stable 2T solution; forward sweep; CD=0.1, CL=0.6)

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Figure 7

Variation of amplitude of response with detuning parameter (Period 2 solution; backward sweep; CD=0.1, CL=0.6)

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Figure 8

Variation of amplitude of response with vortex shedding frequency (γ=0; Period 1 solution; both sweep; CD=0.1, CL=0.6)

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Figure 9

Variation of amplitude response with amplitude of excitation (Period 1 solution; both sweep; CD=0.1)

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Figure 10

Variation of amplitude with forcing amplitude (Period 2 solution; both sweep; CD=0.1)

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Figure 11

Variation of amplitude of response with detuning parameter (Period 1 solution; Case I: CD=0.1, CL=0.6; Case II: CD=0.6, CL=0.1)

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