Estimating directional wave spectrum based on stationary ship motion measurements

Autor(es)

Tannuri‚ E.A. ; Sparano‚ J.V. ; Simos‚ A.N. ; Da Cruz‚ J.J.

• Tipo de documento: Artigo Científico
• Fonte: APPLIED OCEAN RESEARCH; v. 25, n. 5, p. 243-261, 2003.

Resumo

Useful information can be derived from on-board estimation of the directional wave spectrum of the sea, especially concerning feed forward control of dynamically positioned systems. This work discusses the feasibility of using stationary ship motion measurements for in-site directional wave spectrum estimation, focusing on the particular problems that may arise in the application of adapted estimation methods to this kind of system. Load variations, operational trim and other disturbances frequently occur, modifying the ship response to incident waves. Since the methodology depends on previous knowledge about the amplitude response operators, these errors may cause some degradation in the estimated spectrum. Furthermore, due to the large inertia of the ship, high frequency wave components are filtered, reducing the frequency range of the spectrum that can be estimated. These drawbacks are analyzed and their influence in final estimation is quantified. Roll motion of the ship presents non-linear and resonant behavior and is extremely sensitive to load variations. For this reason, sway motion was used instead of roll one, differently from common directional buoys algorithms that take into account the three motions in the vertical plane (heave, roll and pitch). A parametric estimation method, normally used for directional buoys measurements, was adapted to the case and tested. Exhaustive numerical trials were carried out using a tanker in two loading conditions (full and ballasted) and a pipe-laying barge, under typical wave spectra of Brazil's Campos Basin, either in unimodal or bimodal cases. Small-scale towing-tank results were also used as a first experimental validation concerning unimodal unidirectional sea states. Spectral estimations based on experimental results were also compared to those obtained by means of a Bayesian estimation method presented in literature, for the sake of comparison. Parametric Method presented best accuracy in all tested cases. (C) 2004 Elsevier Ltd. All rights reserved. (AU)

• Processo FAPESP: 97/04668-1 - Controle de sistemas com dinâmica sujeita a incertezas
• Beneficiário: Oswaldo Luiz Do Valle Costa
• Modalidade de apoio: Auxílio à Pesquisa - Temático