Investigation into new non-linear energy harvesters

Abstract

Energy harvesting from ambient vibration has arose ever-increasing research interests in recent decades. Using non-linear mechanism for vibration energy harvesting has shown considerable effectiveness due to its capability of generating non-linear responses without the requirement of additional external tuning techniques thus it can harvest energy over broader band of frequencies. In this thesis, a non-linear Smooth and Discontinuous (SD) oscillator is investigated as a new type of SD nonlinear energy harvester to explore the potential of energy harvesting and develop an effective energy harvesting system. The findings of this research are examined to enhance the performance of the energy harvesting efficiency.

The nonlinear dynamical properties of SD oscillator are firstly studied. The study shows that the oscillation can be local or global depending on the level of input power and geometric parameters, due to the double well potential mechanism. A harmonic external base excitation is then introduced to investigate the dynamic response and power flow behaviour of a single degree-of-freedom (DOF) SD oscillation system. Both analytical and numerical methods are applied. It has been shown that the existence of bifurcation is sensitive to the nonlinearity and excitation level. The single DOF SD energy harvester is developed by attaching electromagnetic induction system to convert kinetic energy into electrical energy. Moreover, power flow variables, especially the consumed energy by electrical resistor, are calculated to examine the effects of damping and electromechanical coupling coefficients. It is seen that the system is sensitive to both the parameters. The response can be chaotic, periodic or quasi-periodic with a small change of these two values. With the full use of analysis results of the studied single DOF SD system, a two-DOF SD oscillation system is then established. The mass and frequency ratios indicate energy exchange between the two masses. An integrated two-DOF SD vibrational energy harvester is then developed, coupling with the electrical energy extraction system. Parameters in the electrical conversion system are also investigated. It is found that the electrical coupling coefficients have significant influence on power transmission from mechanical to electrical system. Numerical simulation is performed to validate the energy generation efficiency by changing significant system parameters. It shows 50 watts of generated power for the SD energy harvester under harmonic excitation. The results demonstrate improved benefits particularly in terms of broadband vibrational energy harvesting, especially in the frequency region below the resonance frequency, under harmonic external base excitation. In addition, random excitations of both Gaussian white noise and random ocean wave, e.g. JONSWAP wave spectrum to the SD system are studied in detail. The investigations on dynamic behaviours and power flow properties indicate the considerable advantages of SD system in terms of broad band vibrational energy harvesting.

The research provides a new insight into the SD vibrational energy harvesting method from both harmonic and stochastic ambient vibrations points of view. The new knowledge base through this study and explored advantages of the new type of nonlinear SD energy harvesting from ambient vibrations lays the theoretical foundation for the future design of SD energy harvester for applications in engineering.

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ORCID for Yeping Xiong: orcid.org/0000-0002-0135-8464

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