Green Sea and Water Impact on FPSO in Steep Random Waves

TLDR: In this paper, the authors present results from 1:55 scaled model tests with an FPSO in irregular waves and investigate the interactions leading to green sea events in steep random waves and the resulting impact loads.

Abstract: Publisher Summary This chapter presents results from 1:55 scaled model tests with an FPSO in irregular waves. Interactions leading to green sea events in steep random waves and the resulting impact loads are investigated. This includes water on deck as well as bow slamming. In particular, storm sea states with moderate wavelengths are considered. The measuring equipment include wave probes in a grid at the bow and on the front deck, vessel motions, as well as load and pressure cells on the deck house and on the bow. High-resolution video recordings are also included. One main experience from this experimental case study is that the most critical green sea and impact events observed in steep random wave conditions are mostly generated by steep and energetic waves or wave groups. Nonlinear effects in the incoming waves, including the kinematics, play an important role. The ship motion is also important. Thus, relative short and steep waves are more critical than longer waves due to the phase lag of the pitch motion. Large pitch amplitudes can worsen the problem. It has been observed that the most critical impact load events, with average pressures above 200 kPa over areas more than 5 m2, occur as very rare events, and it is a challenge to become able to predict their probability.