Experimental drag minimization of a morphing soft silicone-shell robot.

Despite the overwhelming dominance of bilateral symmetries in animal morphologies, examples of Radial Symmetries (RS) are not uncommon in aquatic environments. Some RS animals have developed exceptional abilities to survive repeated exposure to extreme fluid flow events. Species living in intertidal regions, for example, must be able to withstand wave velocities up to 8m/s. These animals have developed inspiring strategies to survive these loads. The sea star, Pisaster Ochraceus, produces passive downforce due to their pentaradial pyramid-like geometry, which may serve to enhance attachment to surfaces during wave exposure. These sea stars are also known to exhibit morphological plasticity in response to fluid flow intensity. Inspired by these observations, we developed a soft silicone-shell 7 degree-of-freedom (5 arm extensors, 1 height extensor, 1 volume inflator) robot that changes its shape to minimize drag and lift forces. We applied a Bayesian Optimization algorithm with a coarse grid search initial dataset to rapidly converge to an optimal shape configuration. This work shows that emerging soft robotic technologies can be used to advance hydrodynamic shape optimization and such systems could tune fluid-structure interactions for performance gain.