Estimation of the Natural Roll Frequency of a Ship in a Confused Sea.

摘要

The natural roll frequency of a ship in a confused sea has been estimated from analysis of the roll history. The estimator was defined, the sources of error were identified, and the parameters of the analysis were selected to minimize the variance of the estimator. The probability distribution was derived for the estimator of the natural roll frequency assuming a Pierson-Moskowitz spectral form for the sea. Bias in the estimator resulting from the steepness of the wave-slope spectrum in the vicinity of resonance and from the finite bandwidth and sidelobe structure of the spectral window was examined. The results of the theoretical analysis were confirmed by cumulative distribution functions computed from three 4-hr records from the roll history of a light cruiser. Correlations are presented of the estimated natural roll frequency with linear dimension and displacement for a variety of American naval vessels. (Author)