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

Abstract

The growing usage of permanently moored floating production storage and offloadings (FPSO) in harsh environment regions increases the frequency and severity of the green water problem. Many numerical researches on green water prediction for FPSOs have been carried out. Most of the past researches chose to neglect or consider only part of the effects by appendages and attachments, such as bilge keel, mooring lines, and risers. The influences of these appendages on green water prediction have not been thoroughly studied. This paper presents a practical numerical approach of green water prediction for FPSOs in irregular waves. The calculation of relative wave elevation is conducted in frequency domain, including linear and nonlinear effects of bilge keels, spread mooring system, and asymmetrically arranged risers. Numerical approach was applied to calculate the statistical distribution of relative wave elevation for an FPSO. Comparison with experimental results showed that the accuracy of relative wave motion prediction is significantly improved by incorporating the linear and nonlinear effects of bilge keels, mooring, and risers. Analysis of the results by different numerical models further indicated that the relative wave elevation at sides of the FPSO in oblique waves was strongly affected by bilge keel, mooring, and risers.

3D Numerical Simulations of Green Water Impact on Forward-Speed Wigley Hull Using Open Source Codes

“…Over the years the development of non linear numerical methods for the assessment of risks associated with impact of green water on decks has been challenging. Measuring freeboard exceedance or free surface elevation relative to the deck using 3D linear diffraction theory has been extensively applied for the prediction and statistical analysis of green water risk due to its relative simplicity [3][4][5]. In reality, a green water event is highly nonlinear.…”

A Simplified Numerical Method for the Design and Analysis of FPSO Platform Brackets Subjected to Operational Conditions

“…In addition to the previously mentioned studies, significant contributions have been made to improving the mooring system's interaction and ship displacement in the ocean using realistic approaches considering dynamic loads [9][10][11][12][13][14]. Moreover, an interesting review of the modeling and control of thruster-assisted position mooring systems was presented in Skjetne and Zhengru [15].…”

Effects of the asymmetric riser and bilge keel arrangements on FPSO green water assessment

“…Besides, the understanding on the combined effect of the one-side riser arrangement with truncated bilge keel design seems to be insufficient, and a frequency domain approach for practical application appears to be uncompleted. In our recent work, we have proposed a practical numerical approach for short-term and long-term green water prediction [10][11][12][13]. By applying stochastic linearization to the quadratic damping and including off-diagonal terms for asymmetric riser arrangement, the nonlinear effects due to bilge keel, mooring and riser are included in frequency domain analysis, without sacrificing on the computational efficiency.…”