Simple Tool for Prediction of Green Water and Bow Flare Slamming on FPSO

Abstract

A practical method for prediction of green water and wave impact on FPSO’s in steep irregular waves is described. The relative wave elevation and kinematics are found from combining ship motions, wave diffraction and nonlinear irregular waves. Water heights on deck and related velocities are estimated by simple analytical formulas originally derived from dam-breaking theory but modified in this work to take into account a non-zero water velocity input and the effects from a dynamic and finite wave-determined water reservoir. A bulwark is also included. Deckhouse slamming and bow flare slamming loads are computed by simple formulas from the local velocities and, in the latter case, also the relative angle between the water surface and the flare. Verification against more advanced models and to model test data show promising results. The method is being implemented into a simple research-type software tool.

Extreme runup events around a ship-shaped floating production, storage and offloading vessel in transient wave groups

“…Ship motion must be included but a linear representation of this appears to be adequate. This is consistent with the observations in Stansberg & Berget (2009) and Schiller et al (2014).…”

“…For a freely floating structure, Stansberg & Karlsen (2001) found that the largest relative wave-vessel motions in their dataset are close to Rayleigh distributed because the pitch motion is overpredicted, which cancels out the underprediction of the free surface elevation. Stansberg & Berget (2009) and Schiller et al (2014) concluded that the nonlinearities in the relative wave kinematics mainly result from the nonlinear asymmetry of the incident wave elevation and the nonlinearity associated with local waves diffracted/radiated from a floating FPSO. The vertical vessel motion (mainly due to the pitch motion), however, is found to be well predicted by linear analysis, except for waves that are clearly longer than the vessel.…”

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

“…The on-deck green water may be modeled by dam-break theory (Goda et al, 1979;Vermeer, 1980) or shallow-water theory (Dillingham, 1981;Greco, Lugni and Faltinsen, 2014;Greco et al, 2015). Based on this approach, many efforts have been made to derive analytical and empirical formulas to predict hydrodynamic loads caused by green water flow, which can be found in Buchner (1995Buchner ( , 2002, Hamoudi and Varyani (1994), Ogawa (2003), Greco (2001), Kapsenberg and de Kat (2000), and Stansberg and Berget (2009). Alternatively, there have also been researches that used CFD methods for the local interaction between green water flow and structures, including Pham and Varyani (2005), Shibata and Koshizuka (2007), and Pakozdi et al (2014).…”

“…Applications of this method can also be found in HSE UK ( 2001) and Fyfe and Ballard (2003). Stansberg and Berget (2009) used 3D potential flow software (WAMIT) to analyze relative wave elevation RAOs from solved ship motion and disturbed wave profile. Based on the frequency domain results, an in-house code Waveland/Kinema was then used to generate the timedomain simulation, including adjustment for second-order wave component and local wave particle kinematics.…”