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Ocean Engineering

Analysis Methodology for Vortex-Induced Motion (VIM) of a Monocolumn Platform Applying the Hilbert–Huang Transform Method

[+] Author and Article Information
Rodolfo T. Gonçalves

TPN-Numerical Offshore Tank, Department of Naval Architecture and Ocean Engineering, Escola Politécnica-University of São Paulo, Avenida Professor Mello Moraes, 2231 Cidade Universitária, São Paulo, SP 05508-900, Brazilrodolfo_tg@tpn.usp.br

Guilherme R. Franzini

TPN-Numerical Offshore Tank, Department of Naval Architecture and Ocean Engineering, Escola Politécnica-University of São Paulo, Avenida Professor Mello Moraes, 2231 Cidade Universitária, São Paulo, SP 05508-900, Brazilgfranzini@usp.br

Guilherme F. Rosetti

TPN-Numerical Offshore Tank, Department of Naval Architecture and Ocean Engineering, Escola Politécnica-University of São Paulo, Avenida Professor Mello Moraes, 2231 Cidade Universitária, São Paulo, SP 05508-900, Brazilguilherme.feitosa@tpn.usp.br

André L. C. Fujarra

TPN-Numerical Offshore Tank, Department of Naval Architecture and Ocean Engineering, Escola Politécnica-University of São Paulo, Avenida Professor Mello Moraes, 2231 Cidade Universitária, São Paulo, SP 05508-900, Brazilafujarra@usp.br

Kazuo Nishimoto

TPN-Numerical Offshore Tank, Department of Naval Architecture and Ocean Engineering, Escola Politécnica-University of São Paulo, Avenida Professor Mello Moraes, 2231 Cidade Universitária, São Paulo, SP 05508-900, Brazilknishimo@usp.br

J. Offshore Mech. Arct. Eng 134(1), 011103 (Oct 12, 2011) (7 pages) doi:10.1115/1.4003493 History: Received February 05, 2010; Revised December 20, 2010; Published October 12, 2011; Online October 12, 2011

Vortex-induced motion (VIM) is a highly nonlinear dynamic phenomenon. Usual spectral analysis methods, using the Fourier transform, rely on the hypotheses of linear and stationary dynamics. A method to treat nonstationary signals that emerge from nonlinear systems is denoted Hilbert–Huang transform (HHT) method. The development of an analysis methodology to study the VIM of a monocolumn production, storage, and offloading system using HHT is presented. The purposes of the present methodology are to improve the statistics analysis of VIM. The results showed to be comparable to results obtained from a traditional analysis (mean of the 10% highest peaks) particularly for the motions in the transverse direction, although the difference between the results from the traditional analysis for the motions in the in-line direction showed a difference of around 25%. The results from the HHT analysis are more reliable than the traditional ones, owing to the larger number of points to calculate the statistics characteristics. These results may be used to design risers and mooring lines, as well as to obtain VIM parameters to calibrate numerical predictions.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Motions in the in-line direction (x) and transverse direction (y)

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Figure 2

Example of a time history of a typical VIM signal in the transverse direction

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Figure 3

Example of a time history of a typical VIM signal in the in-line direction

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Figure 4

IMFs generated by the signals for the motion in the transverse direction. Scales are distinct for different IMFs and trend.

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Figure 5

IMFs generated by the signal of the motion in the in-line direction

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Figure 6

Hilbert spectrum for the motions in the transverse direction

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Figure 7

Hilbert spectrum for the motions in the in-line direction

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Figure 8

Marginal spectrum for the motion in the transverse direction

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Figure 9

Marginal spectrum for the motion in the in-line direction

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Figure 10

Instantaneous energy level for the motion in the transverse direction

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Figure 11

Instantaneous energy level for the motion in the in-line direction

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Figure 12

Comparison between characteristic amplitude results from traditional analysis and HHT analysis for the motions in the transverse direction

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Figure 13

Comparison between results from traditional analysis and HHT analysis for the motions in the in-line direction

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Figure 14

Comparison between oscillation period results from traditional and HHT analysis for the motions in the in-line direction, 0 deg incidence

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Figure 15

Comparison between oscillation period results from traditional and HHT analysis for the motions in the transverse direction, 0 deg incidence

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Figure 16

Percentage difference between characteristic amplitude results from traditional and HHT analysis for the motions in both directions

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Figure 17

Example of a typical VIM time history in the in-line direction for a cylinder with L/D=2.00 and Vr0=9.5 with different sample sizes: (a) 100, (b) 50, (c) 33, (d) 25, and (e) 20 peaks

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Figure 18

Sensitivity study on the number of sample points sufficient for convergence between traditional and HHT analysis

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