Research On Nonlinear Energy Capture Mechanism Of Parametric Excited Pendulum

With the energy crisis and environment issues becoming increasingly prominent,research on clean and renewable wave energy has drawn more attention of the public.The point absorber wave energy converters prove to be more efficient on energy capture performance.While the energy conversion mechanism is always focused on the linear mechanism,which has a narrow resonance frequency near the intrinsic frequency of the floater.Thus,to widen the resonance frequency and improve the energy capture performance,the nonlinear parametric pendulum is applied in wave energy converters(WECs).Chapter 2 illustrates the nonlinear characteristics of nonlinear pendulum through theoretical analysis.It reveals that the pendulum will experience a series of nonlinear behaviors,including oscillations,rotations,and chaos.In chapter 3,the energy extracted from ambient vibrations is studied.The relationship between the nonlinear dynamic behavior and the energy absorption is built through numerical simulation.It is found that in the primary resonance zone which is twice the natural frequency of the pendulum,it captures the most energy when it is rotating.However,the natural frequency of the pendulum is too high for the wave frequency to match with.Hence,a novel concept of the submerged pendulum is proposed in Chapter 4.The pendulum is kept submerged in water which can reduce the intrinsic frequency to a desired state by adjusting the mass ratio of the pendulum.Compared with the traditional pendulum in the air,it has wider resonance spectrum width in the low-frequency ocean environment.Approximately solutions for period-1 rotation are also analyzed through the multi-scale method in Chapter 5.When the pendulum is coupled with a floater,the motion response and energy capture properties are discussed in Chapter 6.The numerical result shows that the submerged pendulum can harvest more wave energy than the pendulum swinging in the air,especially under lower excitation.In addition,the large natural frequency of the floater amplifies the response as the natural frequency affects the amplitude of oscillations.