Long term analyses of wave characteristics

Abstract

The focus in this master’s thesis was to describe and compare the two long-term analysis methods: All Sea States and Peak-Over-Threshold. Both methods are equitable and commonly approved methods to estimate extreme waves. Hence, the motivation of this study was to compare and discuss similarities and differences between the extreme waves estimated by these two long-term analysis methods. The analysis aimed for the estimation of the extreme wave crest heights and wave heights. The extreme waves within this study are defined as waves corresponding to an annual exceedance probability of, respectively, 𝑞 = 10−2 and 𝑞 = 10−4. In this thesis the metocean contour line method is also introduced. This method is useful to establish preliminary estimates of the extreme waves during initial phases of design. Then at a later stage, estimates from the metocean contour line method can typically be verified by a long-term analysis using one of the two methods stated above. A general conclusion of this thesis is that the extreme wave crest heights obtained with the Peak-Over-Threshold are less conservative than those estimated using the All Sea States approach. The practical implication is a more optimized design of offshore structures without compromising the safety aspect.