Fluid mechanics of bubble capture by the diving bell spider

Abstract

The water spider, a unique member of its species, is used as inspiration for a bubble capture mechanism. Bubble mechanics are studied in the pursuit of a biomimetic solution for transporting air bubbles underwater. Careful experimentation is performed to understand the mechanics of bubble formation and capture. Investigation of bubble formation through an underwater nozzle shows that bubble volume increases by 15% when parallel rods are spaced above the nozzle at the same width as the inner diameter of the nozzle. Bubble volume decreases linearly with increasing air injection rate. Decreasing surface tension by approximately 40% decreases bubble volume by approximately 20%. Changing the angle the nozzle from parallel to perpendicular with the bottom of the tank increases bubble volume 40%. Based on trends observed in the nozzle experiments and using the spider's mechanisms for bubble capture as inspiration, a bubble capture device is manufactured. Decreasing the surface tension of the fluid by 25% decreases captured bubble volume by 50%. Below a device submersion speed of approximately 2.4 mm/s, bubble formation was at a maximum for the device, regardless of fluid surface tension. This research elucidates the limitations on bubble capture by the water spider. For future applications, these limitations can be pinpointed and adjusted for more efficient bubble capture and plastron maintenance.