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collage_experiments

 

The Robo-Scallop

underwater windmill

Here is some further info on the working principle and thought applications of our so called aocustic scallop or robo-scallop. The manuscript can be found here. It is an acoustic only powered device. Therefore, it does not need wires or a battery as an energy source, but picks up the energy from the sound field and transforms it into a translational motion. If you fix it, the device can act as a pump.

Working principle:

A bubble in a tube closed at one end is driven into resonant pulsations with an acoustic field. When the pressure increases the bubble compresses and when the pressure decreases the bubble expands.
working principle
During the compression of the gas bubble, liquid is sucked under a large angle into the tube. However, at expansion the liquid leaves the tube as a jet. The repulsive force on the tube is different for the suction and the jetting, thereby a net force is generated acting towards the left.

The Acoustic Scallop in motion

Some still images of the device propelling from left to right. The length of the device is approximately 3mm.
swim1swim2swim3
or watch the movie.

Fish Designs

design 1
Tapered mouth to increase the acceptance angle.

design 2
Acoustic scallop with fins.

Other applications:

Attaching six individual scallops on spikes and connecting them to a bearing makes a motor, or call it an acoustic underwater windmill :-).

windmill
or watch the movie.

History of the name:

Initially, the device was called acoustic fish. However, one of the referees mentioned that typically a fish propells by shedding vorticies and not by jet propulsion. He is right and as most fishes use low Reynolds number (visocisty dominated flow) we followed his adivse and named it acousctis scallop. The scallop is a moussle that propells with the help of little jets.

People involved:

Prof. Dr. Andrea Prosperetti: Had the original idea and did most of the calculations/dimensioning
Ir. Rory Dijkink: Did the initial experiments and measured the force during his Master thesis. He is now working on a different subject as PhD student in the group.
Ir. Johan van der Dennen: Made the experiments on the moving scallop, two headed scallop, and many other cute things during his Master project.
Dr. Claus-Dieter Ohl: Supervising the experiments.

Web links