running propeller for instance, but can also facilitate simulations for multiple, independently moving objects.


- Deforming grids: For other types of relative body motions (e.g. a buoy close to an FPSO, or a ship rolling in shallow water), simulations on deforming grids are now possible. The grid deformation methods implemented maintain good grid quality for a robust and accurate solution.


- Adaptive grids: With this technique the code is automatically refining the grid during the computation in areas where large flow variations or important flow features are detected; and coarsening the grid where no large resolution is needed. This can be used to decrease discretization errors or to better capture flow details e.g. to track the location of separation areas, shear-layers, free surfaces, bilge-keel vortices or propeller-tip vortices.


- Equations of motion: By solving the body dynamics equations in conjunction with the flow equations, freely moving objects can be simulated, e.g. ship motions in waves or VIV/VIM behaviour of an offshore platform.


- Free surface and waves: For computing free-surface flows around ships and off- shore structures, issues such as problem start-up, numerical damping and disper- sion, wave generation and absorption at the boundaries are being addressed.


- Coupling with potential-flow tools: Re- FRESCO has been coupled with the pro- peller code PROCAL for modelling a propeller in a ship wake, and with the acoustics code EXCALIBUR in order to model radiated pressure fluctuations and noise. These methods make it possible to tackle several problems with different levels of fidelity and therefore to perform optimisation studies.


Enabling innovation Problems to be tackled with CFD are quickly becoming more complex, with more complicated geometries, needing finer levels of physical resolution and consequently, higher compu- tational power. Additionally, the hardware will evolve and CFD codes have to change accordingly in order to use them efficiently. Therefore, besides the further extension and refinement planned for direct application,


Figure 3: Vortex-Induced Motion (VIM) simulation for a semi-submersible using coupling with structural Equations-of-Motion


longer-term developments are already going on. These include finer turbulence modelling by using scale-resolving methods such as SAS/DES/PANS and LES; fluid- structure-interaction, including elastic deformation of the structures; and improving the scalability of the code for future many- core hardware architectures (CPUs, GPUs, coprocessors). Future plans include address- ing overlapping grids and combining all grid techniques to simulate an arbitrary number of freely moving bodies.


In this way, a comprehensive development of a tailor-made CFD code for the maritime world is taking shape. With the future in sharing, a ReFRESCO community of devel- opers and users is there to take up this challenge. The large capabilities of modern CFD techniques will thus be exploited for solving maritime problems in a precise and responsible fashion; contributing to MARIN’s objective of spearheading design improve- ments, increased efficiency and innovation in the maritime industry.


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