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Measuring the deformations of a composite propeller at full scale

Nicola Grasso, I

mportant measurement data was gathered at full scale to facilitate the design of shape-adaptive propellers.

Ship propellers are generally constructed using metallic materials such as bronze alloys, while fibre-reinforced composites are mainly seen on smaller recreational craft and yachts. These composite materials are lower in weight, have good fatigue properties and possibly geometric flexibility, which are important drivers for the improvement of ship performance. In particular, the possibility to adapt the geometry of the propeller blades through structural flexibility may enable improvements in fuel efficiency, underwater-radiated noise and onboard comfort.

The design of an effective, flexible propeller requires the development and validation of methods able to predict its complex hydro- elastic behaviour. This is the aim of the Greenprop research project, which is chaired by Delft University of Technology and funded by the Netherlands Organisation for Scientific Research (NWO). MARIN, the Dutch Ministry of Defence, Solico and Wärtsilä are partners in the project. One of the key tasks is to collect high quality experimental data to be used as validation material for numerical prediction tools. In this regard, three test campaigns were carried out respectively at model scale in uniform and

16 report

non-uniform flow at the cavitation tunnel, and at full scale on a sailing vessel, including the measurement of the blade deformations.

Optical measurement of deformation Measuring how the propeller geometry

adapts to the varying hydrodynamic loads through blade flexibility is key in the validation of numerical prediction tools for flexible propellers. For this reason, MARIN developed an optical method based on Digital Image Correlation (DIC) able to measure deformations in highly dynamic

Composite propeller after installation in dry-dock

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