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Offshore Technology

Response of a Large Spar Platform to Monochromatic Input Wave Excitation

[+] Author and Article Information
A. E. Altenberg

Laboratorio de Procesamiento de Señales, Universidad Argentina de la Empresa, Lima 717, Buenos Aires, C1073AAO, Argentina; Unidad de Investigación de la Facultad de Ingeniería, Universidad de la Marina Mercante, Avenida Rivadavia 2258, Buenos Aires, C1034ACO, Argentinaaaltenberg@uade.edu.ar

J. Offshore Mech. Arct. Eng 133(3), 031301 (Mar 31, 2011) (8 pages) doi:10.1115/1.4001952 History: Received July 10, 2008; Revised May 17, 2010; Published March 31, 2011; Online March 31, 2011

A wavelet analysis of the behavior of a large spar platform model undergoing a monochromatic input wave excitation is presented. Two techniques are involved in this analysis. First, a continuous wavelet transform (CWT) with complex Morlet wavelets is performed. For this transform, special attention is given to the treatment of the signals ends by mean of stating adequate hypotheses on the behavior of the time series at their boundaries. Second, to validate the hypotheses on the boundary extensions made for the CWT analysis and to provide additional insight on the system behavior, a cubic B-spline discrete wavelet transform representation on a bounded interval is performed. This transform relies only on the interval data, giving in this way a truly semi-orthogonal representation of the energy density of the system on a bounded interval. In this manner, it becomes possible the analysis of wave tank experiments with spar platforms in which it is not possible to conduct tests involving long spans of data and making extrapolation assumptions can pose a question on the validity of the analysis.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 3

Peak to peak amplitude envelope of the surge response

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Figure 4

Close-up of the peak to peak amplitude envelope of the surge response

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Figure 5

Peak to peak amplitude envelope for the monochromatic input wave and spar surge response at scale a=25.6

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Figure 6

Close-up of the peak to peak amplitude envelope for the surge response with new boundary treatment

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Figure 7

DWT representation of the input wave up to level 8 (scale 28)

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Figure 8

DWT representation of the spar platform surge response up to level 8 (scale 28)

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Figure 9

DWT representation of the wavelet coefficients at levels 4 and 5 (scales 24, and 25) of the input wave and surge response of the spar platform

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Figure 10

DWT representation of the wavelet coefficients at levels 6 and 7 (scales 26 and 27) of the input wave and surge response of the spar platform

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Figure 11

DWT representation of the wavelet and approximation coefficients at level 8 (scale 28) of the input wave and surge response of the spar platform

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Figure 1

Monochromatic input wave and spar surge response

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Figure 2

Peak to peak wave amplitude envelope for the monochromatic input wave

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