Self-Sustained Swimming of a Thick-Walled Ring on a Hot Liquid Surface

TL;DR: Self-sustained swimming of a thick-walled ring on a hot liquid surface is achieved by utilizing thermal energy as fuel. The ring exhibits two motion modes: static and self-swimming. The threshold value and the quantitative effect of various parameters on the flip angular velocity and translation velocity are investigated. The findings have promising applications in soft robotics, micro-machines, and energy harvesters.

Abstract: Thermally responsive machines utilize thermal energy from the environment as a source of power, and have many unique advantages including no electronic equipment, self-supplementary energy, and self-adaptation to their surroundings, and they are closer to biological motion in form and function. In this study, a thick-walled ring with a paddle structure is innovatively proposed, which uses thermal energy as fuel to self-sustained flip and horizontal movement on hot liquid surface. Based on the theoretical model and the well-established temperature field equations, the temperature distribution of the cross-section of the ring is given. Subsequently, the driving torque of the ring self-swimming is deduced, and the flip angular velocity and translation velocity of the ring are obtained. The findings reveal two motion modes of the ring on the hot liquid surface: the static mode and the self-swimming mode, which arises from the competition between the thermally-induced driving torque and the friction torque. Moreover, the threshold value that distinguishes the static mode from the self-swimming mode is investigated, and the quantitative effect of each parameter on the flip angular velocity and translation velocity is analyzed. Notably, there exists an optimum dimensionless heat transfer coefficient, inside-outside radius ratio, and dimensionless density that maximize the flip angular velocity and the translation velocity. The thick-walled ring self-swimming system has promising applications in the design and manufacture of soft robots, micro-machines, and energy harvesters.