Comparative analysis of closed-form expressions and other commonly used seakeeping methods

Abstract

Closed-form expressions (CFE) are semi-analytical transfer functions for ship wave-induced responses based only on main ship particulars. They are useful in an early stage of ship design and situations when hull lines for seakeeping analysis are not available. As the accuracy of CFE remains an open subject, the aim of the present study is to quantify the frequency independent model error (FIME) of CFE. Measured transfer functions of the heave, pitch, and vertical wave bending moment at midship for 13 ships are acquired from literature, together with calculated transfer functions using the strip theory and the 3D panel method, where several speeds and heading angles are available. FIME is determined by comparing transfer functions calculated by CFE, strip theory, and 3D panel codes with model-scale experiments. Multivariate linear regression analysis is performed for three seakeeping methods to indicate a dependence of FIME on the main parameters of the analysis. Dispersion of the FIME around the regression line is determined, enabling a relative comparison of the uncertainty of seakeeping methods of different complexity. The results of this study may improve the practical applicability of CFE and provide an uncertainty quantification of commonly used seakeeping methods, which is important for probability-based applications.