Electromagnetic damping and energy harvesting devices in civil structures

Abstract

Energy harvesting is an emerging technique that extracts green energy from ambient environment to power electronics. For example, it can provide sustainable power to autonomous wireless sensors, thus enabling long-term wireless monitoring. Structural control is a traditional research area aiming to protect primary structures against excessive vibrations induced by traffic, wind, waves and earthquakes. This work presents a novel integration of these two techniques. An electromagnetic damping and energy-harvesting (EMDEH) device, consisting of an electromagnetic device and an energy harvesting circuit, is proposed to fulfil vibration-damping and energy-harvesting functions simultaneously. When subjected to external excitation, the kinetic energy of a structure is converted into electrical energy through the electromagnetic device. The electrical energy is then stored in a rechargeable battery, while a reaction force is imposed on the structure to suppress relative motion. Another advantage of EMDEH device is that energy is extracted outside the device rather than being dissipated inside, consequently limiting device overheating. Mathematical modeling of the EMDEH device connected to various energy harvesting circuits has been established in terms of the damping coefficient and energy harvesting efficiency. The optimal load resistance required to achieve the maximum harvesting efficiency was derived. An energy harvesting circuit that emulates a constant resistor was used to maximize the energy harvesting efficiency and achieve target damping coefficient without any feedback loop and external power supply. The modeling of EMDEH devices was successfully verified by experiments. An analysis of coupled structure-EMDEH systems was then performed, in which the structure was assumed to respond within the elastic range. Based on random vibration theory, closed-form output power expressions for EMDEH devices installed in single-degree-of-freedom and multi-degree-of-freedom structures have been derived considering band-limited white noise input. The consistency between vibration control and energy harvesting in the presence of inherent structural damping was first demonstrated. A simple design procedure for EMDEH devices (including the energy harvesting circuit) was established to optimize both vibration damping and energy harvesting. Two applications, namely, a regenerative TMD for high-rise buildings and EMDEH devices for bridge stay cables, were investigated through laboratory tests and numerical simulation. A series of tests, including a shaking table test of a single-story steel frame and a dynamic test of a scaled stay cable, have illustrated the effectiveness of the proposed EMDEH device to provide optimal vibration damping and efficient energy harvesting simultaneously. Numerical simulation was conducted to evaluate the performance of EMDEH devices when applied to full-scale high-rise buildings or full-scale bridge stay cables considering wind excitation. Through a combination of theoretical, numerical and experimental studies, this work clearly demonstrates the promise of applying the proposed dual-function EMDEH device to full-scale civil structures. Some challenges are also discussed based on the outcome of this work.