Uncertainty Quantification of Sea Waves - An Improved Approach

Sea waves are important dynamic loadings for the design of offshore structures. Casual observations will indicate that the sea waves are very unpredictable and may not be modeled deterministically. To capture the unpredictable nature of the sea waves, they are generally expressed in terms of a joint probability density function of mean zero crossing period Tz and the significant wave height Hs. Estimation of parameters of the joint distribution can be very challenging, particularly considering the scarcity of data. The joint probability density function (PDF) of Tz and Hs is generally represented as the multiplication of a conditional distribution for Tz given Hs and the marginal distribution of Hs. The estimation of parameters of the joint PDF is addressed in this paper. The available information on North Atlantic, as reported by Det Norske Veritas (DNV), is considered to document its applicability. DNV reported values for all the required parameters. They are considered as the reference values. Using the Maximum Likelihood Method (MLM), the three parameters of the Weibull distribution for the marginal distribution of Hs are estimated. Assuming Hs can be represented by a two-parameter Weibull distribution, they are also estimated. To compare different alternatives, their Root-Mean-Square-Error values are also estimated. It can be observed that the proposed MLM to estimate the parameters of Hs is superior to that of proposed by DNV.