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Feature 3 | CFD & HYDRODYNAMICS


• a tool to help the engineer to convert his model into an efficient optimisation


of detail and sets up a design search space that is large enough to find significant improvements, yet small enough to allow efficient exploration


process. Care is needed when changes in


CFD prediction of rudder cavitation (left) and observed erosion at actual ship (right).


candidate designs are small, as then the required accuracy in turn is high. Fortunately, oſten the task is to find the design that is optimum, rather than an accurate determination of the object function (e.g. required power) for this design. Thus if the relative ranking is right independent of (similar or constant) errors in objective function the task can be solved even with usual discretisation or model errors. Optimisation soſtware is available to guide an automated simulation process towards a (near) optimum design, combining automatic generation of parameterised geometry, automatic mesh generation, automatic CFD simulation and analysis, and subsequent automatic determination of new parameters.


CFD simulations for ships in waves capturing slamming and green water on deck are by now widely applied in industry projects.


Simulation of experiments CFD can be used to generate data sets for subsequent fast evaluation in design and operation. One example are ship simulators, used to train ship crews in the handling of ships. Te manoeuvring coefficients for these simulators used to come from dedicated model basin tests. More recently, Voith has replaced model tests by CFD simulations to determine the manoeuvring coefficients.


Model tests to determine hydrodynamic coefficients (left) are now replaced by CFD (right).


ship design and coupling CFD in simulators for training and assessment purposes.


Design optimisation In optimisation, the main difficulty lies in the expressing all objectives and constraints


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in mathematical functions of sufficient accuracy and numerical efficiency. Tis task requires.


• a smart engineer, who is able to model the problem at hand with just the right level


Final remarks No matter what the soſtware can do, it remains just a tool. How quickly and well problems get solved depends on the craſtsman using the tool – the engineer remains indispensable. In the end, the engineer is paid for his modelling skills, choosing the model that offers reliable and sufficiently accurate answers obtained with minimum cost (in terms of time and money). NA


PERIC, M.; BERTRAM, V. (2011), Trends in industry applications of CFD for maritime flows, 11th COMPIT Conf., Berlin.


The Naval Architect July/August 2011


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