Green Water and Wave Impact on FPSOs in Santos Basin: Challenges and Prediction Tools

Abstract

Green water (water-on-deck) and subsequent wave impact is a strongly non-linear, random and complex phenomenon that represents an important factor to be considered in the design of moored vessels and vessels in transit. The Santos Basin, in southeast Brazil, is a new frontier for deep water oil production, where FPSO green water issues are expected to be more important. In this paper, we investigate new green water challenges associated with the Santos Basin. We employ an engineering prediction tool, KINEMA, designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in early design load analysis. We perform a sensitivity study to arbitrary wave directions and present preliminary results from a case study that would be illustrating for the Santos Basin. Firstly, a comparison between numerical green water predictions and a set of earlier model test data for a Campos Basin case shows satisfactory agreement. A sensitivity study suggests that an empirical tuning factor, which is related to wave amplification and wave-structure interaction, should decrease with increasing wave heading. Then, a preliminary numerical investigation of the green water problem in Santos Basin wave conditions demonstrates that although the wave impact from the largest waves (S-SW) may be avoided by heading the vessel towards S-SW, other wave directions have to be taken into consideration. The results presented herein confirm that multi-directional wave heading is a green water challenge in the Santos Basin. Further studies that address this problem in detail, in special variations in the wave-structure interactions due to wave heading, and for actual particular Santos Basin FPSO’s, are recommended.

Study on green water prediction for FPSOs by a practical numerical approach

“…The simulation was further corrected by some semi-empirical approaches for nonlinearities due to bulwark and limit water volume before the velocity and impact load of green water on deck was calculated. The software Kinema was further developed to extend applicable wave directions and was used to study green water on FPSOs in Santos Basin (Schiller et al, 2014). In Pakozdi et al (2014), the selected relative wave elevation and freeboard exceedance (corrected by Kinema3) were used to setup local CFD simulation for critical green water event by using VOF-based software Star-CCM+.…”