Surfing on Free Surfaces by Undulating Propulsion

forthcoming

Wave-driven propulsion (WDP) is a little-known type of locomotion in which a floating body generates surface waves to push itself forwards. Some animals have evolved to use WDP when moving on the water surface, such as water striders and water snakes. Meanwhile, WDP technologies have the potential to revolutionise engineering applications, such as the cleanup oil spills, the automation of hydroponic agriculture, and the reduction of fuel consumption of ships. Despite the great potential of WDP, it remains in a state of scientific and technological infancy. The only examples in the literature are ad hoc, untested and un-optimised. The challenge is that WDP is not fully understood i.e. the dominant controls on the propulsion force and the efficiency have not yet been determined. Without addressing this challenge, the powerful technologies mentioned above cannot be developed. In this proposal we seek to rectify the knowledge gap with a suite of work packages that will ultimately open up a new paradigm in the field where surface waves are thought of as a means of propulsion in their own right rather than just a consequence of motion. Our research design is centred on 3 aspects of WDP: Acceleration (how the WDP mechanism changes with velocity), Vorticity (the ratio of vortex- & wave-driven propulsion), and Optimisation (maximising the efficiency of WDP towards useful application). We will explore three canonical “surfer” geometries via experiments in a purpose-built hydrodynamics tank fitted with high-speed cameras to measure the 3D velocities and free surface. A modelling campaign will run in tandem, using a combination of hi-fidelity simulations, simple models to gain physical insight, and numerical optimisation to maximise WDP efficiency. By doing so, we will uncover breakthrough knowledge on the propulsive power of waves, critical resonances, and wave-vortex interactions - knowledge that will unlock applications across Transport, Sustainability and the Environment.