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Effects of hysteresis of static contact angle (HSCA) and boundary slip on the hydrodynamics of water striders

Acta Mechanica Sinica 2017年第1期33卷 40-61页

作者： J. Zheng B. S. Wang W. Q. Chen X. Y. Han C. F. Li J. Z. Zhang K. P. Yu School of Energy and Power Engineering Jiangsu UniversityZhenjiang 212013 China China Ship Scientific Research Center Wuxi 200482 China School of Astronautics Harbin Institute of TechnologyHarbin 150001 China

It is known that contact lines keep relatively still on solids until static contact angles exceed an interval of hysteresis of static contact angle (HSCA), and contact angles keep changing as contact lines relatively slide on the solid. Here, the effects of HSCA and boundary slip were first distinguished on the micro-curvature force (MCF) on the seta. Hence, the total MCF is partitioned into static and dynamic MCFs correspondingly. The static MCF was found proportional to the HSCA and related with the asymmetry of the micro-meniscus near the seta. The dynamic MCF, exerting on the relatively sliding contact line, is aroused by the boundary slip. Based on the Blake-Haynes mechanism, the dynamic MCF was proved important for water walking insects with legs slower than the minimum wave speed . As insects brush the water by laterally swinging legs backwards, setae on the front side of the leg are pulled and the ones on the back side are pushed to cooperatively propel bodies forward. If they pierce the water surface by vertically swinging legs downwards, setae on the upside of the legs are pulled, and the ones on the downside are pushed to cooperatively obtain a jumping force. Based on the dependency between the slip length and shear rate, the dynamic MCF was found correlated with the leg speed U, as , where and are determined by the dimple depth. Discrete points on this curve could give fitted relations as (Suter et al., J. Exp. Biol. 200, 2523-2538, 1997). Finally, the axial torque on the inclined and partially submerged seta was found determined by the surface tension, contact angle, HSCA, seta width, and tilt angle. The torque direction coincides with the orientation of the spiral grooves of the seta, which encourages us to surmise it is a mechanical incentive for the formation of the spiral morphology of the setae of water striders.

关键词： seta Water strider Hysteresis of static contact angle (HSCA) Boundary slip

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Restudies on Body Surface of Dung Beetle and Application of Its Bionics Flexible Technique

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Journal of Bionic Engineering 2004年第1期1卷 53-60页

作者： Jiurong Sun 1, Jianqiao Li 2, Hong Cheng 1, Zhendong Dai 3, Luquan Ren 2 1.College of Life Sciences, Peking University, Beijing, 100871,P.R. China 2.Key Laboratory of Terrain-Machine Bionics Engineering (Ministry of Education,China), Jilin University at Nanling Campus, Changchun, 130022,P.R.China 3.College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016,P.R.China College of Life Sciences Peking University Beijing 100871P.R. China Key Laboratory of Terrain-Machine Bionics Engineering Ministry of Education China Jilin University at Nanling Campus Changchun 130022 P. R. China College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and Astronautics Nanjing 210016 P. R. China

A scanning electron microscope was used to observe the structures of the setae on the surface of a dung beetle Copris ochus, Motschulsky. There are lots of setae on the body surface, especially on the ventral part surface and lateral to the legs which are different in size, arrangement and shape. These setae have different lengths and many thorns on the whole seta. The top ends of these setae stand up without furcations which direct uprightly towards the surface of the touched soil. By the method of removing these setae, getting the insect weight before and after digging into the dung we affirm farther that the setae on the beetle body surface form the anti-stick and non-adherent gentle interface. The soil machines and components made by imitating the gentle body surface of beetles have favorable non-adherent results.

关键词： dung beetle seta flexible surface scanning electron microscopy bionics soil adhesion

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