Abstract

Nature has evolved structural materials along millions of years of incremental changes to fulfil functional requirements of very different situations. Let´s take as an example the sharks, one of the best adapted species for swimming across the oceans, and their smooth skin that is composed of millions of small scales (denticles), with complex geometries formed by sharp spines and micro-grooves aligned with flow direction, varying in size and shape at different locations of the sharkskin. The purpose of this microstructure is to reduce the viscous drag produced by the water when it adheres to the hull forming the fluid boundary layer, which can stick out the added mass to the weight of the fish and increase dramatically its peak speed. Inspired by this natural solution, we have started the design of a bioinspired new material, to be incorporated to the hull wet surface, reducing the viscous drag and increasing the velocity and the efficiency (less fuel consumption) of the ship. In this way, it will be easier to control the green effect gas emissions while sailing. We present the development of this new bioinspired, hybrid material with scales obtained by additive manufacturing using polymeric materials. To control the orientation of the denticles respect to flow direction, the scales have been mounted on a substrate of hydrogel, who interact with the fluid field of pressures to adapt the angle of the moving scales as the velocity increases. No mechanical devices are needed, as the hydrogel act as a nonlinear spring accommodating the movements of the scales. CFD code helps in the development of the most efficient shape and coating design. A water channel has been developed to measure the actual forces acting on the surface of coated panels.