| dc.description.abstract | This master thesis is written with the goal to analyse air lubrication at high speed catamarans. It continues where the authors project thesis written during the autumn of 2017
ended, and includes available full scale results from MS Brage, as well as published test
data from earlier tested vessels as MS Rygerfonn, MS Sognekongen and MS Fjordprins.
Within this thesis is a thorough study of interceptors and air lubrication presented. This
part of the thesis introduces forces induced on interceptor blades, a connection between
interceptors and steps and boundary layer theory. Feasible solutions are at an early
stage presented and discussed to introduce practical concerns regarding implementation
on existing vessels. Further are several studies and air lubrication techniques introduced,
including definitions of two phase and multiphase flows. Flat plates and a hull is tested
with numerical methods as described in chapter 6. Results from full scale testing, numerical methods and a regression analysis are provided in chapter 7. The latter to estimate
the percentage savings at a similar high speed catamaran in the future.
All of the work done within this thesis is based on the set-up at MS Brage. This vessel
was refitted in December 2017 with mid ship mounted interceptors and air lubrication
outlets downstream. Data collected during sea trials are provided by Ingebjørn Aasheim,
and used to compare full scale results with computational fluid dynamics (CFD) in the
software Star CCM+ by Siemens. Three flat plates with the dimensions 12m · 0.5m are
tested at five velocities each, respectively 9, 12, 14, 15 and 16m/s. The hull testing in
CFD is done with four different set ups, a clean hull, interceptors only, and 6 and 8 holes
at each side of the centre line. The results shows that the current implemented solver in
CFD provides a total drag reduction of 17% at 14m/s. It is not possible to differentiate
between 6 and 8 holes at the hull, but plate testing favours the 8 hole edition. Full
scale results shows a 16% drag reduction at the same velocity, and the regression analysis
provided 13.8%. These results are discussed and connected to what is believed to be one
of the largest uncertainties, which is hull roughness.
The thesis ends in a conclusion and a section of recommended further work. Within the
latter lays testing in a cavitation tunnel, use of an advanced Lagrange solver in CFD and
a long term goal with a regression line which counts in air lubrication. The conclusion
is that air lubrication is working, and may be crucial for a vessel to be able to serve a
given contract. An estimate for the next vessel to be retted is to increase the number
of outlets and increase the spreading by fushing them in the vessels forward direction
towards the interceptor blade. | en |
