A computationally efficient method of determining vibration characteristics of marine propellers in drift conditions

Abstract

The unsteady, non-uniform inflow to marine propellers causes a time dependent load and response of the propeller blades. Although techniques exist to model the fluid structure interaction of marine propellers operating behind a hull wake, these are often computationally expensive. The ability to predict the response of the propeller blades at the design phase is desirable as it will enable a propeller designer to obtain a more optimal design with a smaller time investment. This Thesis aims to develop a computationally efficient and validated numeric tool for computing the vibration characteristics of marine propeller designs. This can be achieved by use of a numerically efficient hydrodynamic model and coupling it to a reduced degree of freedom structural model. The hydrodynamic model used to obtain the performance of the propeller and load distributions along and across the blades is Blade Element Momentum Theory. This includes a database of 2D foil CFD simulations to calculate pressure on each blade section. This hydrodynamic model is validated using high fidelity CFD simulations and found to agree well.
To obtain an unsteady, non-uniform inflow to the propeller CFD has been utilized to obtain the flow field at the propeller plane of the KVLCC2 hull form. This has been validated against experimental data available. To obtain the structural characteristics of the propeller blades a plate model has been implemented. This is shown to give reasonably good accuracy compared to a full 3-D model but at an order of magnitude computationally cheaper. An algorithm has been developed to couple the hydrodynamic and structural models. This is compared to a high-fidelity CFD-FEA coupled simulation. The computationally efficient model compares reasonably well to the high fidelity model. However the Plate-BEMT model achieves the deflection in a fraction of the time of the high fidelity model. The method developed can assist the propeller designer generate geometries which have optimal vibration properties for the given hull form and can perform well in manoeuvring configurations.

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Identifiers

ORCID for Stephen Turnock: orcid.org/0000-0001-6288-0400

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