Extreme response estimation of umbilical on very deep water

Abstract

The scope of study is an umbilical arranged in a lazy wave con guration at 1300 m depth in Brazilian waters. The surface vessel is a ship, about 300 m long and 55 m wide. The wave environment is given by a wave scatter diagram and a 100-year contour curve and is acting in the beam sea direction of the ship. The long term extremes of important top end excitation parameters have been determined using frequency domain methods. This includes the wave elevation, the top end umbilical axial motion and velocity as well as the vessel roll angle. Long term extremes of important umbilical response parameters as bend stiener angle and tension have been estimated in addition to the sag tension through time domain simulations considering the entire wave scatter diagram. The long term extremes have been compared to results from simulations of sea states on the 100-year wave contour curve. A selected 100-year sea state have been investigated using full non-linear time domain analysis. Extreme value estimates from ten three hour realizations have been established for top and sag tension including top angle. The relation between the top end axial velocity and the sag tension have been investigated. The results demonstrates that the extreme top axial velocity is well correlated to the sag tension and show that the the axial velocity extreme occurs practically at the same time as the sag tension extreme.