title: Effect of ship motions on propeller-hull interaction
Creators: name: Ali, Md Ashim
Publisher: name: Memorial University of Newfoundland
Year: 2020

description: It is important to consider the detailed hydrodynamics of the propeller, the associated
 flow conditions and the hull interaction with effective wake distribution for developing
 the best ship propulsion system design. Model experiments are conventionally used
 to assess propeller flow and performance but are subject to scale effect and difficulties
 in flow measurement. Computational Fluid Dynamics (CFD), using a viscous flow
 solver, provides an alternate way to simulate propeller flow conditions. Although
 simplified propeller flow models are currently available, this thesis extends the CFD
 approach to develop a more comprehensive model that includes detailed propeller
 geometry, ship motions and wave action.
 Numerical self-propulsion simulations with propeller action and ship motions are
 performed using a newly developed dynamic motion class based on the sliding mesh
 method in OpenFOAM. Validation and verification are carried out in a step by
 step manner. As a first step, a model incorporating bare hull resistance, wave
 elevation on the hull surface, free surface wave contour, and axial velocity distribution
 at several transverse planes for a fixed ship condition and dynamic ship condition
 was developed and validated using available experimental data, and the comparison
 between the simulations and the experiments showed good agreement. Propeller open
 water simulations with detailed propeller geometry and using the body-force method
 were developed and validated with experimental data in the second step. Because of the highly non-linear and rotational nature of the flow near to the propeller region,
 curvature correction was implemented to the standard k − ω SST turbulence model
 to improve the numerical predictions.
 Prior to the third stage self-propulsion simulation, which combined the stage 1 and
 2 simulations, a numerical wave tank was developed and validated. Numerical
 self-propulsion simulations were performed for a ship at an even keel condition
 with constant propeller rotational speed. The numerical calculation of the
 skin friction correction, thrust coefficient, torque coefficient, and axial velocity
 distribution downstream of the propeller, confirmed good accuracy against the
 available experimental data. Then the developed dynamic motion class was extended
 to models with ship sinkage and trim. Comparison with available data showed a
 excellent agreement for all self-propulsion parameters. An expected increase in total
 resistance and decrease in propeller thrust was observed due to ship motion.
 As an alternative of detailed propeller geometry modelling, two body-force models
 were developed for self-propulsion simulation when detailed flow features are not
 required. The effective local velocity body-force model showed better numerical
 predictions than nominal average velocity body-force method. The self-propulsion
 simulation was performed in waves with forward speed using the developed dynamic
 motion class and it was able to incorporate the rotating propeller with large ship
 motions. The thrust generated by a propeller varied with encounter wave period and
 was reduced compared to the even keel condition.