Direction-adaptive Flow Velocity Sensing and Energy Harvesting Design Under Vortex Induced Vibration


Student thesis: Doctoral Thesis

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Awarding Institution
  • Tao Xie (External person) (External Supervisor)
  • Zhengbao YANG (Supervisor)
Award date13 Jun 2022


The oceans, which occupy more than 70% of the Earth’s surface, regulate global temperatures and absorb and process pollution worldwide. To closely monitor changes in marine environments, many ocean monitors and sensors placed in deep-ocean areas are required to gather information on velocity, temperature, and other quantities.

Energy is essential for the sensors. However, batteries easily leak in high electrolyte environment, causing further pollution and the failure of equipment. While, the power consumption of sensors is relatively low, permitting the use of energy harvesters. Marine environments provide a rich source of mechanical energy, solar energy and osmotic energy etc. The use of energy harvesting rather than batteries reduces the risk of further pollution, lowers recall costs caused by frequent recycling, and prolongs equipment life. Among the types of marine energy, fluid mechanical energy is important due to its extensiveness and continuousness.

Based on the marine micro kinetic energy harvester, here puts forward a systematic research on combined system taking ocean current direction and velocity sensing into account. According to the variability of ocean flow direction, a variety of flow direction adaptive structural forms are designed and their advantages and disadvantages are analyzed.

Firstly, aiming at the flow direction adaptation function, the L-shaped straight elastomer system based on traditional transverse vibration and the arc (C/S-shaped) elastomer system based on torsional vibration are proposed. The structural analysis and theoretical research of two forms of systems are carried out. L-shaped system applies theoretical mechanics and hydrodynamics to analyze the three motion states of rotation, transverse vibration and lodging in the process of flow direction adaptation. We analyze its starting conditions, its vibration equilibrium angle as the critical value of rotation and transverse vibration and its rotation stall angle as the critical value of rotation and lodging based on the principle of minimum action. Finally, the direction adaptive angle is comprehensively analyzed. Design and analysis of curved (C/S) elastomer system is based on the progress of solid trajectory study vortex induced vibration, combined with the boundary layer theory and vibration theory in hydrodynamics. The torsional vibration of structural coupling superposition is analyzed. The mathematical model of flow direction adaptation is established and analyzed through the first-order rigid body model.

Secondly, according to the velocity sensing principle and method, the frequency equation based on vortex shedding and size parameters is established for the L-shaped elastomer system. A two degree of freedom mechanical model of torsional vibration for C/S-shaped elastomer system is established. Through the relationship between torsional amplitude and vortex shedding frequency, the relationship between size parameters and velocity measurement resolution and the relationship between velocity and frequency are analyzed.

Thirdly, based on the realization of velocity sensing and flow direction adaptation, the modeling and analysis of the two systems combined with piezoelectric material for energy harvesting are further carried out. For L-shaped elastomer system, the position parameters of piezoelectric materials are simulated and the energy capture experiment is prepared. The three degree of freedom model of C/S-shaped elastomer system is established, and the influence of important parameters on energy harvesting effect is analyzed, including the structural parameters of the cylinder bluff and the arc elastomer, bearing friction coefficient and so on.

Finally, the flow direction adaptation, speed sensing and energy harvesting are verified and analyzed by experiments. The effects of important parameters on the performance of the three functions are further verified, and the data linearity of velocity sensing is studied. By comparing the experimental data and mathematical model, the correctness of the flow direction adaptation model, velocity sensing model, velocity sensing resolution model and energy harvesting model are verified.