Measurement of swimming ability of moon jellyfish using a Particle Imaging Velocimetry

The swimming behavior and biomimetics of marine organisms have been recently investigated to understand the interrelation between the organism and the fluid in the fluid dynamics by using a variety of digital optic instrument technologies. Unlike the terrestrial animals, the marine organisms were biologically evolved and developed in hydrodynamic so that they have a linear structure suitable to high pressures and strong tidal currents as well as propulsion feature for moving. It has been known that the jellyfish would have a swimming ability to utilize the kinetic energy effectively during swimming. This study is aimed to investigate and analyze characteristics of vortex wave formation and vorticity structure of both side of moon jellyfish's bell with oblate-shaped which was changed by width-to-height ratio rowing in swimming by using 2 dimensional analysis in PIV (Particle Image Velocimetry) method. Results showed that the ratio of height-to-width (W/H) was ranged in 0.3 similar to 0.6 and the swimming speed was estimated to be slow at 0.5 of W/H. When it turns, the 2D bell of a moon jellyfish was shown in rowing at 0.5 similar to 0.6 and there is no propulsion without rowing under 0.5 at W/H ratio. Also this result has shown that the jellyfish moved to the left side from the central axis, the right side of the vortical structure of the bell had a faster speed, and its propulsion was obtained from the movement of the central axis resulting from the difference between the speeds of the left and right sides of the bell.