Extreme Value Statistics of Whipping Response for Large Ships

摘要

This paper describes a method for prediction of extreme stresses measured in deck amidships of a container vessel during operation in harsh weather. The nonlinear structural response known as "whipping" is studied. It refers to transient vibration response of the hull girder due to wave impacts mainly in the bow area. For the safety of crew and cargo it is essential to assess all aspects of the wave loading to ensure that ships are built to endure such extreme storm events. Due to non-stationarity and complicated nonlinearities of both the waves and the ship response, there are no reliable numerical simulation tools available for predicting the extreme response including whipping. Moreover, lab tests may not fully reproduce the critical conditions that may occur in reality. Therefore measurements on real ships during their voyages in harsh weather provide unique insight into statistics of the measured responses. The aim of the work is to develop a specific method which makes it possible to extract the necessary information about the extreme response from relatively short time series. The method proposed in this paper opens up for the possibility to predict simply and efficiently both short-term and long-term extreme response statistics.