The "P-RAY", A Mechanical Fish

The ability to produce a mechanical fish has been limited by the ability to simply produce a traveling wave on a mechanical body. Tradition systems have consisted of complex hydraulic and pneumatic activation technology. A much simpler system consists of a flat plate, activated to produce Euler buckling modes. Activation of the first two modes are achieved via a system of cables. These two modes are shown in the images below. Individually these standing waves are inefficient thrust production devices, however if the modes are activated out of phase it is possible to produce a traveling wave on the membrane. The thruster has been mounted in a water channel for controlled investigation of the wake development and also under a boat to demonstrate the thrust production capability. Play the movies below. Future work will concentrate on variation of the membranes aspect ratio and the development of artificial muscles as activation components. The P-RAY will form the mechanical test bed to reveal and diagnose the complex behavior of the flow around a lamprey for example. 
Click for movie showing the coherent wake forming behind the thruster
Click for a movie of the thruster powering a small boat

---

The following images show PIV (Particle Image Velocimetry) measurements of the wake of the mechanical fish.
 

Flow field of the wake at a convective velocity equal 0.07U.