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TECHNICAL PAPERS

Nonlinear Model for Sub- and Superharmonic Motions of a MDOF Moored Structure, Part 1—System Identification

[+] Author and Article Information
S. Raman

 Skillings-Connolly, Inc., 5016 Lacey Boulevard S.E., Lacey, WA 98503

S. C. Yim

Coastal and Ocean Engineering Program, Department of Civil Engineering, Oregon State University, Corvallis, OR 97331

P. A. Palo

 Naval Facilities Engineering Service Center, 1100 23rd Avenue, Port Hueneme, CA 93043

J. Offshore Mech. Arct. Eng 127(4), 283-290 (Mar 24, 2005) (8 pages) doi:10.1115/1.2073208 History: Received September 26, 2004; Revised March 24, 2005

In this first part of a two-part study, the general nonlinear system identification methodology developed earlier by the authors for a single-degree-of-freedom (SDOF) system using the reverse-multi-input/single-output (R-MI/SO) technique is extended to a multi-degree-of-freedom (MDOF), sub-merged, moored structure with surge and heave motions. The physical nonlinear MDOF system model and the formulation of the R-MI/SO system-identification technique are presented. The corresponding numerical algorithm is then developed and applied to the experimental data of the MDOF system using only the subharmonic motion responses to identify the system parameters. The resulting model is then employed in Part 2 for a detailed analysis of both the sub and superharmonic dynamic behavior of the MDOF experimental system and a comparison of the MDOF response results and observations with those of the corresponding SDOF system examined earlier by the authors.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 2

Schematic diagram OF the MDOF system: (a) system diagram for the calculation of wave velocity and acceleration, (b) surge, (c) heave

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Figure 3

The nonlinear-structure nonlinearly damped (NSND) model: (a) with feedback, (b) without feedback

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Figure 4

MDOF experimental data, ML1 and ML2: (a) wave time series, (b) wave spectra, (c) heave time series, (d) heave spectra, (e) surge time series, (f) surge spectra

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Figure 5

MDOF experimental data, MH: (a) wave time series, (b) wave spectra, (c) heave time series, (d) heave spectra, (e) surge time series, (f) surge spectra

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Figure 1

MDOF experimental setup: (a) plan, (b) profile view

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Figure 6

A comparison between the identified and experimental response for ML: (a) (first) heave time series, (b) (second) heave spectra, (c) (third) surge time series, (d) (fourth) surge spectra

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