Improving the Flexibility of Ship Propellers Additively Manufactured from High-Density Polyethylene/Long Carbon Fiber Composites by Prepreg Coating.

In efforts to achieve the goal of reducing ship emissions in the fight against climate change, reducing fuel consumption by making ships lighter is stated as one of the solutions. In this study, the possibilities of making composite equivalents of propellers, which are the most complex ship elements and traditionally produced from metal materials, are investigated with the advantages of additive manufacturing, which offers a rapid production opportunity for such forms. In this way, a lighter composite propeller and, therefore, a lighter ship will be achieved, and negative environmental impacts, especially harmful emissions, will be reduced. In the study, a 1/14-scale ship propeller was produced through the material extrusion method of additive manufacturing using an HDPE composite containing long carbon fiber with a 15% weight fraction. An attempt to reduce flexibility with an epoxy-carbon fabric prepreg coating was made, as the flexibility has negative effects on the performance of the produced propeller. The propeller tunnel test showed that the applied carbon fabric epoxy prepreg helped to improve the propeller's performance by decreasing the flexibility of the propeller and reducing the deformation at the tips. At the same time, the propeller weight was decreased by 60% compared to its metal counterparts.

Frictional drag measurements of large-scale plates in an enhanced plane channel flowcell.

This paper describes the design of an enhanced, plane channel, flowcell and its use for testing large-scale coated plates (0.6 m × 0.22 m) in fully developed flow, over a wide range of Reynolds numbers, with low uncertainty. Two identical, hydraulically smooth plates were experimentally tested. Uniform biofilms were grown on clean surfaces to test skin friction changes resulting from different biofilm thickness and densities. A velocity survey of the flowcell measurement section, using laser Doppler anemometry, showed a consistent velocity profile and low turbulence intensity in the central flow channel. The skin friction coefficient was experimentally determined using a pressure drop method. Results correlate closely to previously published regression data, particularly at higher speeds. Repeated measurements indicated very low uncertainty. This study demonstrates this flowcell's applicability for representing consistent frictional drag of ship hull surfaces, enabling comparability of hydrodynamic drag caused by surface roughness to the reference surface measurements.