Fish are thought to adjust their tail stiffness to swim efficiently over a wide range of speeds, but how they tune stiffness has been a mystery. We derived a model that combines fluid dynamics and bio-mechanics to reveal that muscle tension should scale with swimming speed squared. By applying our strategy to a fish-like robot, we were able to nearly double its efficiency.
Animals and bio-inspired robots can swim/fly faster near solid surfaces like the seafloor. In the past, researchers had quantified how strong these effects were for two-dimensional airfoils. We studied how these results extend to the three-dimensional fins. We found that lowering the aspect ratio weakens the effect of the surface: thrust enhancements become less noticeable, stable equilibrium altitudes shift lower and become weaker, and wake asymmetries become less pronounced. (This work was done in collaboration with the Biofluids Research Lab at Lehigh University.)
We developed a model that estimates how thrust and efficiency change as a pitching hydrofoil gets closer to a planar boundary. Our model predicts that the modified forces are caused by an increasing amount of virtual mass and an increasingly distorted wake. We validated the model by comparing with water channel experiments and inviscid flow simulations. (This work was done in collaboration with the Biofluids Research Lab at Lehigh University.)
Because of their small size and agility, quadrotors could revolutionize search-and-rescue or terrain-mapping missions. However, to do so, they have to operate in confined spaces such as rubble corridors or glacial crevasses. Existing models for how quadrotors behave near obstacles are based on helicopter theories, which are inaccurate at the smaller scales of quadrotors. We therefore built a flow-mapping arena to study how micro-scale quadrotors interact with nearby boundaries. We discovered, for example, that dueling vortices appear beneath micro-quadrotors as they land at an angle.
Cyber Physical Systems (CPS) is an emerging field. Existing CPS Education Programs typically have just a couple classes, and they often consist of previously offered classes. Along with others in the UVA Link Lab, we are creating a stand-alone graduate curriculum for CPS that consists of teaching core classes, in-depth classes, and professional development skills. New classes focus on the intersection of the physical and cyber and explicitly relate the technical material in the classes to CPS applications. (This work came out of the CPS National Research Traineeship at UVA, directed by Jack Stankovic).