Figure 6: Validation: Tanker Hull: FreSCo+
Results (right) vs. experimental data (left).
more detail for example in the region of the forward shoulder and especially behind the transom stern.
Wake field predictions Wake analysis and propulsion optimisation are among the most important elements during ship design as propulsive efficiency largely determines the commercial viability of any new design. It is hence of great importance for all RANS solvers applied in wake predictions to validate results on approved experimental data. FreSCo+
underwent a
series of validation exercises on standard cases such as the KVLCC2 tanker and other hulls before being finally released. Having gained confidence in the
numerical results obtained from FreSCo+ predictions, the more challenging tasks of optimising a hullform for improved wake flow was addressed in different in-house projects. The first one was
aimed at the optimisation of the aſt body of a tanker hull where first comparisons of the wake alone were performed. In a more thorough exercise performed in a second project a full optimisation of the hullform of a bulk carrier was performed, accounting for wake quality and all relevant resistance components. This was based on a parametric CAD model allowing for quick modifications of the hull form and subsequent analysis. Tis was the first example for an integrated process chain in which FreSCo+
could
be used within a complete design environment comprising CAD, RANS analysis and optimisation. Another big issue in this context is the
application of Propulsion Improvement Devices (PID) to increase propulsive performance and efficiency of existing ships. Retrofitting such devices to today’s cargo vessels is expected to give a substantial contribution to reduced
Figure 7.1 & 7.2: Wake optimisation: tanker hull (left), bulk carrier (right), each showing the baseline design on the left and the optimised hull on the right.
Figure 8: Wake development under the influence of fins mounted ahead of the propeller.
emissions from maritime transportation. FreSCo+
has been applied in a number of
projects already to analyse the effects of different types of PIDs, flow alignment fins or ducts. Te detailed flow results obtained from the computations, typically combined with a numerical propulsion test described above, allow for dedicated design optimisation and customised PIDs to be selected for a given case.
Manoeuvring simulations Forecasting manoeuvring performance is another important area of hydrodynamic ship design. Again in the context of the VIRTUE project, FreSCo+
has been
applied to the prediction of manoeuvring coefficients for a large range of standard manoeuvres which could be validated with experimental data obtained from model tests in HSVA’s large towing tank.
The Naval Architect July/August 2010 41
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