Self-propelling, self-navigating water surface vehicles
Rolling spinners on the water surfaceJB Gorce, K.Y. Bliokh, H. Xia, N. Francois, H. Punzmann and M. Shats
Rolling spinners on the water surface, Science Advances 7, eabd4632 (2021) (link) This paper reports a remarkable behaviour of fast-spinning objects on the surface of water. The new effect opens numerous possibilities to create self-propelling water surface vehicles capable of self-navigating themselves along boundaries of any shape.
The key ingredient in this phenomenon is the Magnus effect, known in many areas of physics, from quantum elementary particles to planets and stars. The Magnus force acts on spinning objects, and it is widely used in sports, for example by tennis players who employ spin to control the ball trajectory. A spinning ball creates a vortex around it which bends the balls trajectory.
Vortex formed around spinning tennis ball
Flettner rotor-ship (1924)
The idea of using the Magnus force to propel water surface vehicles was first implemented by a German engineer Anton Flettner last century in so-called ‘rotor ships’, where large rotors mounted vertically on a vessel and driven by the ship’s engine, create the Magnus propulsion force pushing the ship in the direction orthogonal to the wind, thus acting as a sail. This idea was resurrected in recent years since it leads to an economic increase in the ships fuel efficiency.
But what happens if there is no wind? In this work we study the motion of fast-spinning disks on the water surface. In our experiments, we found that above a certain spin rate the disks start to self-propel themselves. When such a disk approaches a solid boundary, its stops accelerating and travels at constant speed and at a fixed distance along the boundary. The experiments show it can follow boundaries of practically any shape:
Example trajectories of a self-propelling spinners guided by solid boundaries
in the shape of a triangle, star or the outline of Australia.
The new discovery opens paths to a variety of applications related to autonomous water surface vehicles. Such vehicles could be useful in marine robotics, inspection of the ship hulls, or they can be used in chemical and biological reactors for monitoring conditions in sterile and hazardous environments, to name just a few.
Reference:
J.B. Gorce, K.Y. Bliokh, H. Xia, N. Francois, H. Punzmann, and M. Shats.
Rolling spinners on the water surface, Science Advances 7, eabd4632 (2021) (link)