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 account, to assure the integrity and safety of structures offshore. 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 promising 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 the challenging 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. ComFLOW and ReFRESCO will be considered. In Bandringa et al. (2016), these two CFD tools were successfully validated for a regular wave impact on a fixed semi submersible. To increase the complexity 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 the references therein. Considering the topic at hand, the most relevant differences between the two CFD tools can be summarized as follows: ComFLOW explicitly reconstructs the free surface on a structured grid and integrates the free surface explicitly in time, using a variable time step. In ReFRESCO the free 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 always solves in two-phase mode. ComFLOW was specifically developed to simulate inertia driven free-surface flows (Luppes (2013)). ReFRESCO (Vaz (2009)) was developed to simulate viscous flows with complex geometries (Koop (2011), Kerkvliet (2014)).