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At the time of the numerical analysis, the experimental data—measured sinkage, trim and resistance—was only available for one of the hulls. The simulations of the hulls, including keel, bulb and rudder and involving about 2 million control volumes, were performed on a simple multi-core workstation and delivered, in addition to trim, sinkage and resistance, detailed information about local variation of pressure and velocity in the flow. The latter is vital for the optimization of performance, since integral data alone does not give any indication of why one design would be better than the other.
The STAR-CCM+ results showed that the relative trim at different boat
speeds was computed within an accuracy of 0.01°, translating into an
accuracy in the resistance predictions of the order of 1% for the hull
with its appendages – against 10% for the bare hull ten years ago. This
level of accuracy is especially meaningful when compared with the
uncertainty of the towing tank tests, which is also of the order of 1%,
and makes STAR-CCM+ the tool of predilection for design and analysis in
the marine industry: "STAR-CCM+ is the most advanced code for simulating hull performance and it represents the state-of-the-art for
the America’s Cup community" says Dr. Viola.
The next America’s Cup will probably be sailed in much rougher conditions than recent editions and seakeeping will be fundamental for a successful design. This raises a new question: how will we measure in the towing tank differences in the hydrodynamic drag smaller than 1% when we have to model 20-plus-knots of boat speed in waves caused by a 30-knot wind? When this happens it may very well be that STAR-CCM+ predictions will be "too" accurate to be validated against experimental measurements!
For more information on Dr. Ignazio Maria Viola, who is currently Lecturer in Naval Architecture at the School of Marine Science and Technology of the Newcastle University, please visit his personal homepage.
For more information on STAR-CCM+ in the Marine Industry, please visit our Marine Resource Center.
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