Abstract
Abstract State of the art ULS/ALS mooring analysis is based on potential flow calculated wave drift forces. However, it is acknowledged that higher order effects in steep sea states increase the wave drift forces as compared to the potential flow 2nd order models. This is the background for the EXWAVE 2 JIP where semi-empirical methods to correct wave drift forces were implemented and checked, which shows the significance of this problem to the industry. This publication aims at applying CFD simulations to better understand the physics of wave drift loads in steep sea states and to identify higher than 2nd order effects. Calculations are performed with a RANSE-VOF based CFD code and with a linear potential flow code for a floating production storage and offloading (FPSO) unit in deep water regular waves with three periods and three wave steepnesses. The vessel is restrained from moving to make a simple and a consistent comparison between the results from the two approaches. Comparisons for small amplitude waves provide an assessment of the quality of the CFD simulations, while increasing wave steepness conditions are used to identify higher than second order effects on the wave drift forces. CFD simulation resulting force time series are decomposed into mean value and harmonics by means of a Fourier analysis and compared against potential theory estimated mean and first order forces. The comparisons for small wave amplitudes show a good agreement, which proofs the correctness of the applied CFD setup. Further, the CFD results show an increasing trend of the mean wave forces normalized by the wave amplitude squared with increasing wave steepness for the two shorter wave periods. The trend is unclear for the longer wave period.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call