Interest-inspired
We explore any interesting problems which are multi-disciplinary fluid dynamics problems including interesting nature problems, e.g. how a flat-fish hide under a sand bed?, how often a flower releases an order, any fun problem from ordinary life, mimicking nature systems to clean environments, spreading of human and plant diseases, and mimicking natural structures. From the questions, we try to apply new physic-chemical ideas for industrial applications and commercialization.
We show how often a flower releases their floral scent through optical interferometry measurements by detecting the refractive index difference of vapors. Most of flowering plants have own floral fragrance that triggers and induces dynamical interactions between plant and insect, which are important to understand the pollination process. Therefore, it is crucial to investigate volatile organic compounds of floral fragrance. To date, typically, volatile organic compounds of floral fragrance have been investigated by various spectrometry methods. Unfortunately, those methods could not confirm how often the flower emits floral scents. In this study, we report that a lily discontinuously releases fragrance in time. Using the interferometry method, we find spectro-temporal power spectrums of lilies, which mean that each flower has own flux profiles of floral scents. The emission rate is typically less than 1 hr. We believe that the current measurement results can provide a new insight to understand and to further explore the biosynthesis and emission mechanism of floral volatiles.
Related publication:
H. Kim, G. Lee, J. Song, and S.-G. Kim, "Real-time visualization of scent accumulation reveals the frequency of floral scent emissions," accepted in Frontiers in Plant Science.
To understand how quickly a flat fish hide under a sand bed, we explore the hiding mechanism of this. To do this, we simplify the flapping system that is inspired by the flat fish. We made a vibrating disk model to investigate the basic mechanics of burying motion. The results show that burial motion cannot begin until there is enough kinetic energy to cause fluidization in the granular bed; pressure differences at the model's bottom are insufficient to trigger this process. Particle transportation and burial motion are made possible by the movement of the flapping model, which creates an outward-pointing counterclockwise vortex from the center. According to the analysis, when the flexural stiffness reduces, so does the kinetic energy causing the movement. A soft robot designed to resemble a flatfish was created in order to investigate these mechanisms in greater detail. This allowed for a thorough analysis of the basic mechanisms underlying the burial motion.
Related information:
Investigation on hiding skill in the sand of bio-inspired soft robotic flatfish, URP research program by Song Hyeon Chung
During cooking, we can easily find the droplet explosion on a very hot plate. There is a critical condition to avoid this explosion, which enhance cooling. On the other hand, there is a Leidenfrost effect. If evaporation by heating creates an air cushion under the droplet, the droplet can self-levitate, which suppress heat transfer so that the cooling effect may not occur.
We experimentally study a gravity-driven liquid flow on a flexible beam. The elastic material bends due to the weight of the liquid. The relationship between hydrodynamics and elasticity is investigated by varying an applied flow rate, the bending stiffness of the beam, and the beam length. Surface tension effects are negligible for these experiments. We compare our results with a model that predicts the beam deformation in terms of two dimensionless parameters, one representing a dimensionless beam length and the other representing a dimensionless beam stiffness. The results span both small deformations as well as large deformations of the cantilever.
Related publication:
1) P.D. Howell, J. Robinson, and H.A. Stone "Gravity-driven thin-film flow on a.flexible substrate," J. Fluid Mech. 732, 190-213 (2013)
2) P.D. Howell*, H. Kim*, M. Popov, H.A. Stone, "Rivulet flow along a flexible substrate," J. Fluid Mech. 796, 285 (2016) *Equivalent 1st co-author.
The small water droplets (the diameter is typically around 1-10 μm) falls down to the ground and the jet was applied to the horizontal direction (right to left). The dispersion pattern of droplets is taken by high-speed camera, Photron SA-X @ 50,000 fps.
Some butterfly has a beautiful flap color that is created by a well-ordered nano structure. The reflected color depends on a typical structure size and the inter distance between particles. It is so-called "photonic crystal structures". This structure can be used as counterfeit technologies. The color changes depending on the viewing direction, which is iridescence. Inspired by nature materials, we explore the nano materials' packing mechanism and furthermore we are interested in controlling packing structures by using physico-chemical hydrodynamic effects.