Bio-mimicking 3D Printed Hull Coating—Friction Hovering Technology
Did you know the ‘black marlin’ can swim a 80 mph? It can do so because its skin has a drag-reducing microstructure. The principle that microscopic riblets reduce friction in water and air is better known as ‘sharkskin’, as sharks have a similar special skin. When riblets are applied on ships, airplanes or cars, the friction is reduced up to 8%. This results in a higher top speed, higher optimal cruise speed or reduced fuel consumption. In 1987, the sailing team ‘Stars and Stripes’ won an Olympic medal and the America’s Cup with a sharkskin coating developed at NASA Langley. More recently, aircraft manufacturers have observed a 3% reduction in fuel consumption when testing a riblet structure. Although the idea is more than 50 years old, there are a few issues that have made large-scale adaptation impossible.
The main reason why riblets are not widely applied, is the lack of a scalable application method. Templating does not allow for local optimization of the microstructure and can’t treat double curved surfaces effectively. Lithography is very effective in creating small structures on chips, but can’t be scaled up and uses nasty chemicals. Using a customized riblet sticker also can’t handle double curved surfaces and is hard to remove or repair.
Two other reasons that riblet coatings are not applied, are fears over increased fouling and wear. Although fouling strongly depends on the local fauna, microstructures have been very effective in reducing the settlement of zoospores. The design of the printed microstructures is optimized for wear resistance. The actual wear resistance will become apparent from full-scale tests in the near future. For now, try not to crash too often!
The innovative printing technique, developed by qlayers, avoids all of these issues. A special printing head is mounted on an autonomous robot arm that scans the surface. It locally optimizes the microstructure and uses existing topcoats that have been applied extensively. Due to the use of a robot, the whole painting process can be made greener, healthier, more efficient and cheaper.
Qlayers was started by students from the Novel Aerospace Materials group at the TU Delft in 2016. The team has built a first prototype printer that can produce the desired structure on small scale. The first real-life test will be done on the TU Delft Solar Boat Team (link to www.solarboatteam.nl), to validate the drag reduction, fouling and durability. In the summer of 2017, qlayers aims to start a full scale pilot together with a shipyard.
Sharkskin under a scanning electron microscope
The TU Delft Solar Boat Team
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