Hydrodynamic Analysis and Optimization of Interceptor based Air Lubrication for High Speed Vessels
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- Institutt for marin teknikk 
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 2017ended, and includes available full scale results from MS Brage, as well as published testdata 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. Thispart of the thesis introduces forces induced on interceptor blades, a connection betweeninterceptors and steps and boundary layer theory. Feasible solutions are at an earlystage presented and discussed to introduce practical concerns regarding implementationon 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 testedwith 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 estimatethe 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 vesselwas refitted in December 2017 with mid ship mounted interceptors and air lubricationoutlets downstream. Data collected during sea trials are provided by Ingebjørn Aasheim,and used to compare full scale results with computational fluid dynamics (CFD) in thesoftware Star CCM+ by Siemens. Three flat plates with the dimensions 12m · 0.5m aretested at five velocities each, respectively 9, 12, 14, 15 and 16m/s. The hull testing inCFD is done with four different set ups, a clean hull, interceptors only, and 6 and 8 holesat each side of the centre line. The results shows that the current implemented solver inCFD provides a total drag reduction of 17% at 14m/s. It is not possible to differentiatebetween 6 and 8 holes at the hull, but plate testing favours the 8 hole edition. Fullscale results shows a 16% drag reduction at the same velocity, and the regression analysisprovided 13.8%. These results are discussed and connected to what is believed to be oneof the largest uncertainties, which is hull roughness. The thesis ends in a conclusion and a section of recommended further work. Within thelatter lays testing in a cavitation tunnel, use of an advanced Lagrange solver in CFD anda long term goal with a regression line which counts in air lubrication. The conclusionis that air lubrication is working, and may be crucial for a vessel to be able to serve agiven contract. An estimate for the next vessel to be retted is to increase the numberof outlets and increase the spreading by fushing them in the vessels forward directiontowards the interceptor blade.