## Here is an assortment of research topics which are currently being investigated in our group. We are constantly seeking interesting phenomena or problems to solve, and collaboration with talented researchers and interdisciplinary group.## Capillary attraction between floating objects (Andong He, Michael J Miller, Khoi Nguyen)We seek to fully determine the interaction forces of objects of varying geometries floating on a fluid surface. This is accomplished utilizing various optical techniques to accurately map the liquid surface deformed by the effects of surface tension. From the full three-dimensional map of the fluid surface, a net force can be calculated acting upon each floating object. Alongside this experimental procedure is a rigorous theoretical analysis to corroborate the forces for any geometry. Our objective is to characterize the interaction force when the objects are very close to each other. The framework of multipole expansion becomes less useful when distance between the objects is comparable to or smaller than the objects themselves. The details of the object shape become important in such instances. For examples, the force of attraction appears to be focused at the sharp points on edge of the floating triangles, as can be seen in the adjoining movie. ## Foot in motion (in collaboration with Madhusudhan Venkadesan, Mahesh Bandi)We hypothesize that the elasticity of the foot is actively tuned while running to reject perturbations from an uneven ground. The duration the foot is in contact with the ground during running is shorter than the timescale for neural feedback, hence material response and open loop neural control are the only possible stabilizing mechanisms. To test this hypothesis, we devise techniques to measure spatio-temporally resolved traction forces exerted by the foot on the ground while running. These measurements inform a model of the foot based on thin elastic shell theory. ## Synchronous waving of marine grass (Ravi Singh, in collaboration with Amala Mahadevan and L. Mahadevan, and with assistance from Mahesh Bandi)Synchronized waving of grass in aquatic and terrestrial setting and its impact on environmental transport have been well known. The waving affects hydrodynamics of flow, which in turn influence transport and mixing of fluid, nutrients etc above and below grass, hence can affect the ecological function of aquatic and terrestrial systems. Common feature of these waving is generation and flow of vortices in stream wise direction at top of canopy(grass). The generation of these vortices is manifested due to presence of a hydrodynamic instability of flow experiencing different resistance within and above the grass canopy, similar to classical Kelvin Helmholtz instability. To understand the mechanism of this waving, we use theoretical analysis of a mathematical models, numerical simulations and a simple experiment on a flowing soap film with nylon filaments inserted in to film (see adjoining movie). In the experiment nylon filaments mimic the role of grass and flow in the film mimic flow or air/water in terrestrial/aquatic setting. ## Fluid structure interaction boundary layer (Xinjun Guo, in collaboration with Kenneth Breuer)Our goal is to develop simplified theoretical and computational models of the interaction of airfoils/hydrofoils with their surrounding fluid. A conceptually simple and physically accurate method is provided to account for the vortex shedding from structures at high Reynolds numbers, which plays a key role in determining the mechanical and dynamical properties of the fluid-structure system. In the outer region far from the structure, the vortex methods are applied, which reduces the computational cost a lot compared to CFD in the whole domain. In order to describe accurately the location and strength of vortex shedding, we solve the simplified Navier-Stokes equations in the thin inner region close to the structure, rather than impose the Kutta condition. ## Tidal in-stream energy harvesting (in collaboration with Kenneth Breuer and Heather Leslie)The kinetic energy from tidal currents, termed tidal in-stream energy, estimated to be a 50 GW resource in the US. Since tides are predictable, this source of renewable energy is easier to integrate within the existing infrastructure. We are developing a cyber-physical system to extract the kinetic energy from the flow. The cyber-physical device consists of a hydrofoil with two degrees of freedom for its motion, pitching and heaving. An optimization algorithm controls these degrees of freedom to maximize the power extracted from the flow. The commercialization component of this project is supported by Advanced Research Projects Agency - Energy. |

### Research

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Capillary attraction between floating objects