Speed losses of ships due to steering and other controls have become increasingly important with the ever increasing cost of energy. Direct measurement of the losses is difficult due to the small relative magnitudes of the quantities involved, and it is often necessary to use indirect methods to assess the magnitude of losses. Determination of the actual parameters in the ship speed equation is therefore needed. As the loss terms in the speed equation are inherently nonlinear, identification of the parameters is a nontrivial task. The paper addresses the identification of parameters in the nonlinear ship speed equation from experiments at sea. The choice of input signals is treated, and deterministic, harmonic excitation is shown to be advantageous by providing easy separation between linear and nonlinear kernels in the system response. The application of the cross-bispectrum technique for analysis of the responses is discussed, and particular emphasis is given to the case when only short records from experiments are available. The problem of expressing confidence levels for the spectral estimates is further treated for the particular case at hand, where time records can not be considered stationary random processes. As an example, the application of the cross-bispectrum technique to identify the speed dynamics of a super tanker is described.
Cross-bispectrum technique identification of nonlinear ship speed dynamics
Kreuz-Doppelspektrums-Technik-Identifikation von nichtlinearem Verhalten der Schiffsgeschwindigkeits-Dynamik
Control and Computers ; 14 , 2 ; 54-62
1986
9 Seiten, 21 Quellen
Aufsatz (Zeitschrift)
Englisch
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