Hydrodynamic Loads on Marine Propellers Subject to Ventilation and Out of Water Condition
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- Institutt for marin teknikk 
Traditionally ships and propulsion units have been optimised for operation in calm water. Consideration of hydrodynamic loads in calm water might not be enough since the propeller always operate in heavy seas subject to intermittent ventilation and out of water effects. There is a need for more knowledge in order to provide understanding and if possible computational methods to estimate dynamic forces to develop the control system that shall reduce the mechanical loads and increase the efficiency of the propeller operating in extreme sea conditions. The main objective of the thesis is to provide understanding and computational methods to estimate dynamic forces (especially propeller thrust and torque) on propeller operating in heavy seas subject to intermittent ventilation and out of water effect. Seven different experimental campaigns are presented and analysed in the thesis. Model tests were performed with both open pulling and ducted pushing propeller. Propeller immersion ratios, carriage speed, propeller rate of revolutions, period of heave oscillations and oscillation amplitude were varied during experiments. The analysis of the results shows the influence of the mentioned parameters on thrust loss, and the relation between ventilation and thrust losses. A calculation model, able to predict thrust loss due to ventilation is presented in the thesis. The model can be applied to estimate the thrust loss for a wide range of propeller submergence ratios and at different advance ratios. The calculation model is static in the sense that it is assuming that the response is quasi steady. The time domain simulation model PropSim (2018) for propeller forces due to ventilation is also presented in the thesis. The propeller simulation model is a further development of Dalheim’s model, which was updated by including a physical model for estimating ventilated blade area ratio based on propeller loading. It is also discussed how the dynamic effects i.e. hysteresis effect and blade frequency dynamics can be included in the simulation model PropSim (2018). In addition the propeller blade slamming hypothesis is discussed, together with experimental results by the author by Mork (2007). It is concluded that it cannot be confirmed that propeller blade slamming is a likely cause of TIFF type gear wheel damages.