| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 102 === The propulsion efficiency of a commercial vessel is usually related to the tangential energy loss in the wake zone of the propeller. In order to elevate the efficiency practically, we can either pre-swirl the fluid in front of the propeller or transform the energy loss into thrust through the appendages behind propellers. Asymmetric stern ship is an example for the first concept. The asymmetric stern is modeled parametrically by the program named Grasshopper in this research and simulated by Star-CCM+ to analyze the wake zone behind stern and the efficiency of propeller.
The prototype of this research is the container ship developed by KRISO with also its related propeller. We first simulate the resistance and self-propulsion test of this prototype, and then compare the result with the experimental data for verification. And then we construct a parametric model that can be applied to any stern. We use four parameters including rotation strength, longitudinal distribution weighting, sectional rotation distribution bandwidth and sectional rotation position, to transform arbitrary hull form to asymmetric stern while keeping the smoothness of lines. Also for analyzing the effect of asymmetric stern, we establish rotational wake coefficient. To discuss the relation between the four parameters and the axial/tangential velocity distribution in the wake zone, we calculate various types of asymmetric stern with design speed of 24 knots, and analyze the wake in propeller plane. The simulation results show that longitudinal distribution has insignificant effect on rotational wake coefficient while radial distribution has positive correlation. We choose three types which have significant effects to simulate the self-propulsion test. The results show that the propulsion efficiency can increase 2.96% at self-propulsion point and can increase 4.02% at the same propeller loading. Besides, with the analysis of wake zone in self-propulsion test and the propulsion efficiency factor, we consider that the effect of asymmetric stern on propulsion efficiency mainly comes from the difference of effective wake coefficient.
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