Environmental contours of sea states by the I-FORM approach derived with the Burr-Lognormal statistical model

Abstract

Environmental contours are constructed using the Inverse-First Order Reliability Method based on return periods of one and twenty years. The paper proposes the use of the Burr distribution to model the marginal distribution of long-term significant wave heights and uses the conditional approach, by combining this marginal with conditional log-normal distributions of peak wave periods. The resulting environmental contours constructed based on the implementation of the Burr-Lognormal model are compared with the contours constructed with the commonly applied Weibull-Lognormal model considered as the baseline. Statistical tests of fit are used, and they do not reject any of the two models being compared, indicating that both approaches are acceptable. The environmental contours from the newly implemented scheme are different from the ones of the reference approach, as expected. Return values obtained with both marginal distributions of significant wave heights show differences comparable to the ones reported in other comparisons of methods reported in the literature.