[2018-Vol.15-Issue 3]Operculum of a Water Snail is a Hydrodynamic Lubrication Sheet
Time: 2018-05-12 21:20  Click:374
Journal of Bionic Engineering
 
Volume 15, Issue 3, May  2018, Pages 471-480.
 
Xiaoyan Xu1, Jianing Wu2,3, Yunqiang Yang1*, Rengao Zhu1, Shaoze Yan2,3*
1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China
2. Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
3. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
 
Abstract  Water snails developed a distinct appendage, the operculum, to better protect the body against predators. When the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum. We observed the water snails (Pomacea ca-naliculata) spend ~3 hours per day foraging, and the relative angular velocity between the shell and operculum can reach up to 10 ?•s−1, which might inevitably lead to abrasion on the shell and operculum interface. However, by electron microscopy images, we found that the underside of the shell and outer surface of the operculum is not severely worn, which indicates that this animal might have a strategy to reduce wear. We discovered the superimposed rings distributed concentrically on the surface, which can generate micro-grooves for a hydrodynamic lubrication. We theoretically and experimentally revealed the mechanism of drag reduction combing the groove geometry and hydrodynamics. This textured operculum surface might provide a friction coefficient up to 0.012 as a stability-resilience, which protects the structure of the snail’s shell and operculum. This mechanism might open up new paths for studies of micro-anti-wear struc-tures used in liquid media.
 
Key words: water snails      operculum      micro-grooves      friction reduction      biomaterial     
 
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