A WEIBULL DISTRIBUTION-BASED PARAMETRIZATION FOR ENCOUNTER WAVE SPECTRA

The continuous monitoring of sea states is important for many activities, from gathering oceanographic data to the planning of ship operations. There are several means to infer sea conditions, with variable levels of accuracy. Among these, the methods based on on-board measurements of vessel motions have been addressed by many researchers, attracted mainly by its practicality regarding installation and maintenance issues. However, the idea of using vessels as wave sensor also brings restrictions, mainly associated with the filtering of short waves that causes no significant motions of the hull, and, furthermore, the vessel speed introduces considerable complexity in the mathematical inference procedure. A significant part of this complexity is associated with the triple-value problem related to stern wave conditions. In the context of a research that addresses an alternative method for the parametric estimation of sea waves based on vessels with forward speed, this article deals with the problem of devising a proper parametric representation of the wave energy distribution as seen in the ship's reference frame, i.e., the encounter wave spectrum. A Weibull-distribution parametrization is proposed, for its ability to handle the significant variations of encounter wave spectrum shapes. Analyses performed for several combinations of wave directions, peak frequencies and vessel's speed show that this approach is indeed capable of providing proper representation of the spectral shapes based on few parameters, both for bow and stern waves.