Validation of CFD for a deterministic breaking wave impact on a semi submersible

For structural design, prediction of run-up, green water and impact loads have to be taken into accoun t, to assure the integrity and safety of structures of f h re. For predicting these highly non-linear phenomena, most of the offshore industry relies on detailed model testing. In the last couple of years , however, CFD simulations have shown more and more p romising results in predicting these events (Iwanowski (2014), Pakozdi (2015), Veldman (2015)). For the offshore industry to have sufficient confidence in the accuracy of CFD simulations in th e c allenging field of extreme wave impacts, it is essential that a proper verification and validation study of such CFD tools is performed. In this paper, two CFD simulation tools, i.e. ComFL OW and ReFRESCO will be considered. In Bandringa et al. (2016), these two CFD tools wer e successfully validated for a regular wave impact on a fixed semi submersible. To increase the comple xity of the validation, in the present paper we focus on simulating a deterministic breaking wave impact on a fixed semi submersible, for which results will again be validated against experiments carried out by MARIN. Details on the two CFD tools can be found in Bandringa et al. (2016) and t he references therein. Considering the topic at han d, the most relevant differences between the two CFD t ools can be summarized as follows: ComFLOW explicitly reconstructs the free surface on a struc tured grid and integrates the free surface explicit ly in time, using a variable time step. In ReFRESCO the f re surface is implicitly reconstructed on an unstructured grid and implicitly integrated in time with a fixed time step. ComFLOW has the option to run in single-phase mode, whereas ReFRESCO alway s solves in two-phase mode. ComFLOW was specifically developed to simulate inertia driven f ree-surface flows (Luppes (2013)). ReFRESCO (Vaz (2009)) was developed to simulate viscous flow s ith complex geometries (Koop (2011), Kerkvliet (2014)).