Self-oscillation of a liquid crystal elastomer string-mass system under constant gradient temperature

Recent experiments have found that a fiber-mass system can self-oscillate along the vertical direction under a non-uniform temperature field, which necessitates significant vertical space. To address the challenge in adapting to situations with limited vertical space, the current work introduces a self-oscillating string-mass system, comprising of a mass ball and a thermos-responsive liquid crystal elastomer string exposed to a constant gradient temperature. By employing theoretical modeling and numerical simulation, we've identified two motion regimes of the system, namely, the static regime and the self-oscillation regime, and elucidated the mechanism of self-oscillation. Utilizing the analytical method, we derived the expressions for bifurcation point, amplitude and frequency of the self-oscillation, and investigated the impact of system parameters on these aspects, which were verified by numerical solutions. Compared to a fiber-mass system, the string-mass system has superior stability to deal with small horizontal disturbances, can amplify its amplitude and frequency limited by small thermal deformation of material, and saves a significant amount of vertical space. Given these attributes, such self-oscillating string-mass system presents novel possibilities for designing energy harvesters, active machinery and soft robots.