Probability Analysis of Wave Run-Ups and Air Gap Response of a Deepwater Semisubmersible Platform Using LH-Moments Estimation Method

Abstract

This version is available at https://strathprints.strath.ac.uk/62977/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the AbstractThe air gap response in harsh environments, a critical design issue for offshore platforms, is related to the wave run-ups due to wave-platform interactions and potentially results in serious wave impacts. Therefore, the reliable prediction of wave run-ups and air gap response in harsh environments is a challenging task and needs further study. In this study, probability analysis of the wave run-up data from an experimental study of a deepwater semi-submersible platform is conducted based on the three-parameter Weibull distribution model using the LH-moments method for parameter estimation.One of the highlights in the present study is that the explicit relationships between the first three LH-moments at arbitrary levels and the parameters of the Weibull distribution are established analytically. The accuracy of LH-kurtosis estimation is proposed to determine the appropriate level for probability analysis. The air gap response is more serious in quartering and beam seas than in head seas.In front of the columns along the wave incoming direction, especially the aft one, the wave run-ups show higher probability distributions leading to higher likeliness of suffering from negative air gap and wave impact accidents than the other platform areas. At the platform center, the wave run-up is significantly lower than the incident wave. The probability distributions based on LH-moments at the appropriate level can well represent large wave run-ups, except for that beyond the still-water air gap, where both measurement methods and probability analyses warrant further research.

LH-moment estimation for statistical analysis on the wave crest distributions of a deepwater spar platform model test

“…For large extreme values with a small probability of exceedance, such as wave crests and wave run-ups, in practice the method of LH-moments tends to be more appropriate than the method of L-moments for the parameter estimation of the probability distributions. Xiao et al [34] established a methodology based on the method of LH-moments and the three-parameter Weibull distribution model. Generalised formulae for any level of LH-moment were derived from the first four LH-moments and their explicit relationships with the parameters of the Weibull distribution.…”