Numerical study of the steady/unsteady multibody interaction in ship propulsion systems

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2018-05

Authors

Su, Yiran, Ph. D.

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Abstract

The goal of this research is to reduce the computational cost of a fully unsteady RANS simulation for the multibody interaction problems in the ship propulsion system. To achieve this, the boundary element method (BEM) can be coupled with a RANS solver. The rapid-changing propeller-induced flow is first decoupled from the slow-changing or steady total flow. While RANS can be used to calculate the total flow, BEM is applied to the propeller-induced flow. By representing the propeller blades by a body force field and a mass source field, it becomes possible for RANS to use a larger time step size (or even run as a steady problem) and a smaller number of cells. The use of BEM to handle the propeller-induced flow improves the numerical efficiency and also provides a framework for sheet cavitation predictions. Depending on the level of simplifications, the coupled BEM/RANS scheme can be implemented by three different approaches: the unsteady approach, the time-averaged non-axisymmetric approach, and the time-averaged axisymmetric approach. All of the three approaches are described in this dissertation, as well as some numerical studies on different body force distribution models, mass source models, effective wake calculation models, etc. Then, the scheme is validated by several simple cases in which the propeller’s interaction with upstream bodies is not considered. Finally, the scheme is applied to a hull-propeller-rudder interaction problem and a contra-rotating propeller problem.

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