Development of a spined underwater biomimetic vehicle with SMA actuators

We present here our progress towards the development of a type of biomimetic active hydrofoil that utilizes Shape Memory Alloy (SMA) actuator technology. The actuation is presently applied to the control of hydrodynamic forces and moments, including thrust generation, on a 2-D hydrofoil. The SMA actuation elements are two sets of thin wires (0.015'" to 0.027") on either side of an elastomer element that provides the main structural support. Controlled heating and cooling of the two wire sets generates bi-directional bending of the elastomer, which in turn deflects (for quasi-static control) or oscillates (for thrust generation) the trailing edge of the hydrofoil. The aquatic environment of the hydrofoil lends itself to cooling schemes that utilize the excellent heat transfer properties of water. The SMA actuator was able to deflect the trailing edge by +/- 5 degrees at rates as high as 2 Hz. FEM modeling of hydrofoil response to thermoelectric heating has been carried out using a thermomechanical constitutive model far SMAs. FEM predictions are compared with experimental measurements.