How sea lions swim
September 13, 2016 -
3:00pm to 4:00pm
The George Washington University
Soft Condensed Matter and Physics of Living Systems: Prof. Megan Leftwich, The George Washington University
We are interested in fluid dynamical systems that arise in nature. There are many, highly diverse, systems that fit this description: plankton in the ocean, branches on trees and shrubs, a pumping heart, or a sneeze. In this talk, I will present a specific problem that is appropriately described as a biological-flow—the swimming California sea lion.
California Sea Lions are highly maneuverable swimmers, capable of generating high thrust and agile turns. Their main propulsive surfaces, the fore flippers, feature multiple degrees of freedom, allowing their use for thrust production (through a downward, sweeping motion referred to as a “clap”), turning, stability and station holding (underwater “hovering”). To determine the two-dimensional kinematics of the California sea lion fore flipper during thrust generation, digital, high definition video is obtained using the specimen at the Smithsonian National Zoo in Washington, DC. Single camera videos are analyzed to digitize the flipper during the motions, using 10 points spanning root to tip in each frame. Digitized shapes were then fitted with an empirical function that quantitatively allows for both comparison between different claps and for extracting kinematic data. The resulting function shows a high degree of curvature (with a camber of up to 32%). Analysis of sea lion acceleration from rest shows thrust production in the range of 150-680 N and maximum flipper angular velocity (for rotation about the shoulder joint) as high as 20 rad/s. Analysis of turning maneuvers indicate extreme agility and precision of movement driven by the fore flipper surfaces. This work is being extended to three-dimensions via the addition of a second camera and a sophisticated calibration scheme to create a set of camera-intrinsic properties. Simultaneously, we have developed a robotic sea lion foreflipper to investigate the resulting fluid dynamic structures in a controlled, laboratory setting.