Validation of an Open-Source CFD Tool to Support Efficient Design of Offshore Gravity-Based Structures Exposed to Extreme Waves

Babaei, Hossein (National Research Council Canada) | Baker, Scott (National Research Council Canada) | Cornett, Andrew (National Research Council Canada)

OnePetro 

ABSTRACT

Computational Fluid Dynamics (CFD) could be an inexpensive complement and even an alternative to physical modelling for investigating the interaction of ocean waves with offshore structures. CFD models however cannot be relied on unless they are well validated. We validated the OpenFOAM® CFD toolbox, a publically available open-source model, for modelling the interaction of extreme regular and irregular waves with offshore gravity-based structures. CFD results including water levels, pressures and forces generally compared well with results for a physical model test program previously conducted by the National Research Council Canada (NRC).

INTRODUCTION

For optimal and safe design of offshore structures subjected to waves, accurate estimation of forces and water levels are needed. This estimation is usually obtained either by physical or numerical modelling approaches. Each approach has pros and cons: physical modelling usually involves smaller-than-reality model structures where the wave-structure interaction processes are subject to scale effects, and the study outputs are uncertain as a result. Physical modelling requires test facilities, model fabrication and instrumentation and hence can be expensive. Physical modelling however reveals many details of wave-structure interaction. Numerical modelling on the other hand is a relatively inexpensive approach without the model size limitation. If numerical models are based on correct physics and well validated, they are a reliable complement and perhaps even an alternative to physical modelling.

The literature on the validation of Computational Fluid Dynamics (CFD) models for studying wave-structure interaction is fast expanding and not fully developed. This is particularly true for the application of publically available open-source CFD models. Some of the most relevant recent literature is (Ong et al., 2017; Hu et al., 2016; Palomares, 2015; Chen et al., 2014; Paulsen et al., 2014; Palemón-Arcos et al., 2014; Lambert, 2012; Thanyamanta et al., 2011; Afshar, 2010).

We have previously examined (Babaei et al., 2016) the applicability of the OpenFOAM CFD Toolbox, freely available and open source, for estimating the interaction of extreme regular waves with a four-column offshore gravity-based structure. Therein, it was shown that OpenFOAM results are very similar to results of an equivalent physical model test program conducted previously at the National Research Council Canada (NRC). A summary of the physical model test program is given in the next section.