Session: 02-05-02 Extreme Loads and Responses 2

Paper Number: 120738

120738 - An Evaluation of Design Wave Selection Methods for Floating Offshore Structure Design 

For floating offshore structures, the structure design should consider site-specific loads with a target return period, typically 100-year. The equivalent design wave approach based on response based analysis (RBA) has been a popular method to represent long-term extreme responses in a site-specific environment. Although the method is convenient and efficient, the design wave method is a great simplification to represent extreme responses. Therefore, the design waves have to be chosen with great care. In this study, several design wave selection methods are reviewed and evaluated for rational design of floating offshore units.

The conventional method to choose equivalent design waves are based on the heading angles and the wave crest locations at the peak of the response amplitude operators (RAOs). This approach works well for trading vessels but have drawbacks for offshore applications that do not have equal wave heading probabilities. The conventional method may choose the wave parameters where there is very little wave energy in the hindcasted metocean data. Another method choosing the wave parameters from the greatest contribution to the long-term responses also has a potential issue as the wave parameters may be chosen where there is very small RAO, hence, the design wave amplitude (=long-term response/RAO) could become excessive. Such cases from actual projects will be presented and discussed in this study. A new method will be discussed that can reflect both responses and wave energy is proposed and evaluated. The mixed of above method can also be a good alternative. For the evaluation, the four methods are applied to actual projects with metocean data of a multi-wave system, and the results will be compared for discussion.

There is no or very little study on the design wave selection methods showing the resultant responses with the associated responses based on actual projects. A new method that can reflect both responses and wave energy is also proposed and discussed. The case study uses metocean data of a multi-wave system, hence, the various cases can be covered.

Presenting Author: Youngkook Kim Lloyd's Register

Presenting Author Biography: Youngkook Kim is currently a senior specialist in hydrodynamics and offshore technology at Lloyd's Register. Youngkook worked as a team leader of Floating Offshore research team in LR Singapore Global Technology Centre and moved to North Asia Technology Centre in Korea in 2019 where he is responsible for offshore technology development, Rules & procedure, consultancy, etc. Youngkook has extensive experience in various areas of naval architecture especially in hydrodynamics, structures and mooring analysis. He is also a member of IEC committee to develop the design requirements for floating offshore wind turbines.
He obtained his degree in Naval Architecture & Ocean Engineering from Pusan National University and M.Eng in Mechanical & Aerospace Engineering from Nanyang Technological University.

Authors:

Youngkook Kim Lloyd's Register
Lei Yu Lloyd's Register