Figure 2: Complete ship+propeller+rudder flow analysis using sliding grids


exclusively for maritime applications; thus no compromises need to be made for different application fields. Additionally, all verification and validation work addresses relevant hydrodynamic cases. Further development is being carried out by MARIN in collabora- tion with Instituto Superior Tecnico (Lisbon), University of Sao Paulo (Brazil), Technical Universities of Delft and Twente (The Neth- erlands), the University of Southampton (UK), and recently, Chalmers University (Sweden).


Developing a dedicated code has the advan- tage that it makes it possible to focus on the issues that are essential for the reliable and accurate application for the problems it must address. Full access to all the informa- tion enables developers to make detailed improvements. An ‘own code’ also facilitates unlimited deployment on many processors without any licence costs; a significant asset in view of the large computing clusters now available at MARIN.


Flexibility and accuracy The develop- ment at MARIN was initiated in 2005, in cooperation with TUHH and HSVA in


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Hamburg. From 2009, separate development lines have followed. From the start, a strong emphasis was put on flexibility and robust- ness but also on accuracy and computing speed. The code was formulated for unstruc- tured grids in order to deal with all kinds of complex structures, such as fully appended ships or highly detailed offshore platforms. In principle, all kinds of geometry and all types of grids and cells can be dealt with, including local refinement.


Proven technology methods are largely used, for robustness and to minimise the risk of the development. Well-known, finite-volume formulation and discretizations are used, similar to commercial or open-source CFD packages. A widely used sub-domain decomposition and MPI parallelisation are deployed, making the code suited for multi-core processors. From this solid basis specific new algorithms have been devel- oped by the team at MARIN and its partners, as just incorporating known techniques was not considered sufficient. Specific features include: - Coupled solvers to decrease the computa- tional time;


- Corrections for poor quality grids to increase the code’s robustness and accuracy;


- Turbulence model implementation details to make them easy to converge and more accurate;


- Improved free-surface and cavitation models and their discretization schemes, offering substantial advantages compared to existing CFD tools. A complex code like this, with developers at different locations, needs a tight code versioning and testing control framework. Therefore a large database of test cases is automatically run periodically to check the accuracy and performance of the code on different hardware. Additionally, for each new class of applications modern verifica- tion and validation studies are done.


State-of-the-art CFD To further extend the applicability of the code, state-of-the- art CFD features are being incorporated in ReFRESCO and introduced in practical applications. These include: - Sliding grids: With this technique parts of the grid can slide along others. This permits a calculation for a ship with a


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