none Water Strider Locomotion

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/43881

Title:	none Water Strider Locomotion
Authors:	王郁雯;Yu-wen Wang
Contributors:	物理研究所
Keywords:	水黽;推進;漩渦;黏滯力;剪應力;water strider;propulsion;vortex;viscous force;shear stress
Date:	2010-08-12
Issue Date:	2010-12-08 14:24:05 (UTC+8)
Publisher:	國立中央大學
Abstract:	水黽是一種生活在靜水流域的昆蟲，特徵體長約 1-2 cm ,體重約 10-50 mg，水黽的體重是由水的表面張力支撐，而且水黽可以用超疏水且細長的腳在水面快速移動而幾乎不會沾濕，現在的研究學者推論水黽在水面移動的機制，是藉著漩渦尾流轉移向後的動量，這個假設認為向後移動的半球漩渦攜帶著跟移動的水黽相近的動量。在我們的實驗中，我們改變水深去影響半球漩渦的形狀，不過結果顯示，水黽在不同水深移動的平均距離沒有明顯的改變，但在淺水中漩渦卻變得較小而且幾乎靜止不動，因此我們認為水黽移動的流體力學推進，並不是直接依賴漩渦的動量轉移。我們用理論計算證明，當水黽腳下的水面凹陷隨著腳划過水面時，產生的剪流提供了足夠的黏滯剪應力去推動水黽向前，而且產生的剪流深度只有 0.2 mm，這可以解釋為什麼當實驗水深下降到 0.5 mm 時，水黽的平均移動距離依舊不變。而接著這個剪流在深水中會發展成漩渦，但是在淺水中則會直接傳到底板，因此形成的漩渦很小且幾乎不動。在這個特別的生物流體例子中顯示，即使在雷諾數高達數千，黏滯力也有可能主宰水生生物的移動。 Abstract Water striders, Aqyarius elongatus, are insects living on the water surface like ponds, slow streams, marshes, and other quiet waters, and their body range typically 1-2 cm in length and 10-50 dynes in weight. Their weights are supported by the surface tension force and they can move over the water surface very quickly by their hydrophobic elongated legs and rarely get wet. The recent investigate inferred that the mechanism of water strider motion on water surface relies on the vortices transferring momentum backward. The assumption describes that the moving hemispherical vortices carry the momentum of walking water strider approximately. In our experiments we change the depth of water from deep to thin to influence the hemispherical vortex shape. However the results show that the average distance for one stroke of water strider doesn’t vary apparently and the vortices become smaller and almost stationary at shallow water as well as. Therefore we think the hydrodynamic propulsion of water strider locomotion does not directly rely on the momentum transfer by the vortices shed. Through theoretical calculation, we show that the shear flow during the water strider stroking on the water surface provides enough viscous shear stress to drive the water strider moving forward. Furthermore the depth of shear flow is just 0.2 mm, and that explains our results, the water striders move unrestrictedly even the water depth decreases to 0.5 mm. After water strider stroking, the shear flow develops into the vortices in deep water, however at shallow water the momentum transfer to the bottom of tank to cause the vortices small and staying behind nearly. This case shows that the viscous force dominate the locomotion of an aquatic creature even the Reynolds number is thousands.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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