Nonlinear vibration energy harvesting with adjustable stiffness,damping and inertia

A novel nonlinear structure with adjustable stiffness, damping and inertia is proposed and studied for vibration energy harvesting. The system consists of an adjustable-inertia system and X-shaped supporting structures. The novelty of the adjustable-inertia design is to enhance the mode coupling property between two orthogonal motion directions, i.e., the translational and rotational directions, which is very helpful for the improvement of the vibration energy harvesting performance. Weakly nonlinear stiffness and damping characteristics can be introduced by the X-shaped supporting structures. Combining the mode coupling effect above and the nonlinear stiffness and damping characteristics of the X-shaped structures, the vibration energy harvesting performance can be significantly enhanced, in both the low frequency range and broadband spectrum. The proposed 2-DOF nonlinear vibration energy harvesting structure can outperform the corresponding 2-DOF linear system and the existing nonlinear harvesting systems. The results in this study provide a novel and effective method for passive structure design of vibration energy harvesting systems to improve efficiency in the low frequency range.     

Enhancing the performance of a bistable energy harvesting device via the cross-entropy method

Nonlinear Dynamics - This work deals with the solution of a non-convex optimization problem to enhance the performance of an energy harvesting device, which involves a nonlinear objective function...     

等效刚度对非线性压电俘能系统性能影响研究

基于Hamilton原理,考虑几何非线性和梁的不可伸长条件,建立了五层压电双晶片叠合梁俘能器在直接和参数激励作用下的运动微分方程。利用Galerkin法和谐波平衡法获得了俘能器的位移、输出电压和输出功率的解析解。引入随时间变化的扰动,提出了非线性方程解的稳定性条件。为了对压电俘能器的结构-性能关系进行综合分析,研究了被动层的配置形式、被动层与主动层的厚度比和弹性模量对压电俘能系统性能的影响。结果表明,在叠合梁厚度不变的情况下,采用五层的压电双晶片叠合结构,选择合理的被动层与主动层厚度比、被动层弹性模量、被动层厚度比和负载电阻,可以有效提高能量俘获的效率。     

Optimal quasi-circular motion of a spacecraft with an energy storage device

The problem of using an energy storage device in spacecraft low-thrust propulsion systems with a constant-power thruster is considered and solved for optimal quasi-circular maneuvers in the near-Earth space. The maximum payload is the optimality criterion. The optimal control as a function of time and the optimal mass parameters of the spacecraft were determined. Domains of the mass parameters where the use of an energy storage device makes sense are shown. T. G. Shevchenko University, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 10, pp. 93–100, October, 1999.     

Dynamics of an electromagnetic vibro-impact nonlinear energy sink,applications in energy harvesting and vibration absorption

Nonlinear Dynamics - The dynamics of an electromagnetic vibro-impact nonlinear energy sink (VINES) is investigated. The system consists of a linear oscillator equipped with multiple turns of coil,...     

Damping in a parametric pendulum with a view on energy harvesting

The present article addresses the quantification of damping in a parametric pendulum, with a view on further applications in the design of energy harvesting devices. Detailed new experimental data is obtained for such purpose, and a novel mathematical model is presented. Linear and quadratic viscous damping and also dry friction are taken into account. To introduce the dry friction component, the pendulum axis is mounted on ball bearings. This is considered as a very realistic situation of a harvester. Damping parameters are determined by minimizing the difference between numerical and experimental time histories. It is shown that the damping model here presented is more adequate to replicate experiments than commonly used linear models, which consider only a linear viscous damping term characterized by means of free decay tests. It is also pointed that linear models are not adequate for refined studies, since they can lead to erroneous predictions of rotation zones, and consequently to wrong considerations in the design of pendulum harvesters.     

Dynamic non-linear behavior and stability of a ventricular assist device

This paper investigates the non-linear dynamic behavior and stability of the internal membrane of a ventricular assist device (VAD). This membrane separates the blood chamber from the pneumatic chamber, transmitting the driving cyclic pneumatic loading to blood flowing from the left ventricle into the aorta. The membrane is a thin, nearly spherical axi-symmetric shallow cap made of polyurethane and reinforced with a cotton mesh. Experimental evidence shows that the reinforced membrane behaves as an isotropic elastic material and exhibits both membrane and flexural stiffness. So, the membrane is modeled as an isotropic pressure loaded shallow spherical shell and its dynamic behavior and snap-through buckling considering different types of dynamic excitation relevant to the understanding of the VAD behavior is investigated. Based on Marguerre kinematical assumptions, the governing partial differential equations of motion are presented in the form of a compatibility equation and a transverse motion equation. The results show that the shell, when subjected to compressive pressure loading, may loose its stability at a limit point, jumping to an inverted position. If the compressive load is removed, the shell jumps back to its original configuration. This non-linear behavior is the key feature in the VAD behavior.     

Stochastic averaging of energy harvesting systems

A stochastic averaging method is proposed for nonlinear energy harvesters subjected to external white Gaussian noise and parametric excitations. The Fokker–Planck–Kolmogorov equation of the coupled electromechanical system of energy harvesting is a three variables nonlinear parabolic partial differential equation whose exact stationary solutions are generally hard to find. In order to overcome difficulties in solving higher dimensional nonlinear partial differential equations, a transformation scheme is applied to decouple the electromechanical equations. The averaged Itô equations are derived via the standard stochastic averaging method, then the FPK equations of the decoupled system are obtained. The exact stationary solution of the averaged FPK equation is used to determine the probability densities of the displacement, the velocity, the amplitude, the joint probability densities of the displacement and velocity, and the power of the stationary response. The effects of the system parameters on the output power are examined. The approximate analytical outcomes are qualitatively and quantitatively supported by the Monte Carlo simulations.     

Energy harvesting in a nonlinear energy sink absorber using delayed resonators

Nonlinear Dynamics - This paper examines periodic and quasi-periodic (QP) vibration-based energy harvesting (EH) in a nonlinear energy sink (NES) absorber that is coupled to an electric circuit...     

Wide spectrum solar energy harvesting through an integrated photovoltaic and thermoelectric system

This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splitting＇ technique, short wavelength solar radiation is converted directly into electricity in the PV cells, while the long wavelength segment of the spectrum is used to produce moderate to high temperature thermal energy, which then generates electricity in the TE device. To overcome the intermittent nature of solar radiation, the system is also coupled to a thermal energy storage unit. A systematic analysis of the integrated system is carried out, encompassing the system configuration, material properties, thermal management, and energy storage aspects. We have also attempted to optimize the integrated system. The results indicate that the system configuration and optimization are the most important factors for high overall efficiency.     

The force transmissibility of MDOF structures with a non-linear viscous damping device

In the present study, the concept of the Output Frequency Response Function (OFRF), recently proposed by the authors, is applied to theoretically investigate the force transmissibility of MDOF structures with a cubic non-linear viscous damping device. The results analytically show that the introduction of cubic non-linear damping can significantly reduce the transmissibility over all resonance regions for a Multiple Degree of Freedom (MDOF) structure and at the same time leave the transmissibility over the isolation region virtually unaffected. The analysis also indicates that a strong linear damping may shift the system resonances and compromise the beneficial effects of cubic non-linear viscous damping on the force transmissibility of MDOF structures. This suggests that a less significant linear damping together with a strong cubic non-linear damping can be used in MDOF structures to achieve a desired vibration isolation performance. This research work has a significant implication for the design of viscously damped MDOF structures for a wide range of practical applications.     

Clearance-type nonlinear energy sinks for enhancing performance in electroacoustic wave energy harvesting

This paper explores a clearance-type nonlinear energy sink (NES) for increasing electrical energy harvested from non-stationary mechanical waves, such as those encountered during impact and intermittent events. The key idea is to trap energy in the NES such that it can be harvested over a time period longer than that afforded by the passing disturbance itself. Analytical, computational, and experimental techniques are employed to optimize the energy sink, explore qualitative behavior (to include bifurcations), and verify enhanced performance. Unlike traditionally studied single-DOF NESs, both subdomains of the NES (i.e., on either side of the clearance) contain displaceable degrees of freedom, increasing the complexity of the analytical solution approach. However, closed-form solutions are found which quantify the relationship between the impact amplitude and the energy produced, parameterized by system properties such as the harvester effective resistance, the clearance gap, and the domain mass and stiffness. Bifurcation diagrams and trends therein provide insight into the number and state of impact events at the NES as excitation amplitude increases. Moreover, a closed-form Poincaré map is derived which maps one NES impact location to the next, greatly simplifying the analysis while providing an important tool for follow-on bifurcation studies. Finally, a series of representative experiments are carried out to realize the benefits of using clearance-type nonlinearities to trap wave energy and increase the net harvested energy.     

Wake of a cylinder: a paradigm for energy harvesting with piezoelectric materials

Short-length piezoelectric beams were placed in the wake of a circular cylinder at high Reynolds numbers to evaluate their performance as energy generators. The coherent vortical structures present in this flow generate a periodic forcing on the beam which when tuned to its resonant frequency produces maximum output voltage. There are two mechanisms that contribute to the driving forcing of the beam. The first mechanism is the impingement of induced flow by the passing vortices on one side of the beam, and the second is the low pressure core region of the vortices which is present at the opposite side of the beam. The sequence of these two mechanisms combined with the resonating conditions of the beam generated maximum energy output which was also found to vary with the location in the wake. The maximum power output was measured when the tip of the beam is about two diameters downstream of the cylinder. This power drops off the center line of the wake and decays with downstream distance as (x/D)^−3/2.     

六边形桥墩柔性抗船撞装置抗弯刚度

针对中国自主研发的桥梁柔性抗船撞装置,构建该装置模型:由两个相似的六边形梁为内外钢围以及均布且垂直于六边形各边的防撞圈构成。分析该模型得到在冲击载荷作用下六边形梁的控制方程及相应的初边值条件。利用Laplace变换和数值Laplace逆变换对该方程进行求解,揭示六边形梁在冲击载荷作用下的动态响应。并进一步分析外钢围等效抗弯刚度对抗船撞装置动态响应的影响,发现外刚围结构在冲击载荷作用下存在临界等效抗弯刚度。当外钢围等效抗弯刚度达到该临界值后,该外钢围在冲击载荷作用下可以近似为刚性。     

Complementary energy theorem in geometrically non-linear structural problems

The principle of stationary complementary energy for geometrically non-linear problems of beams and trusses is considered. The functional of complementary energy is formulated in terms of force quantities. The stationary conditions describe the conditions of compatibility of the structure. The applications include the problem of elastica, a truss, and a bending problem by use of beam elements.     

Vibration energy harvesting from impulsive excitations via a bistable nonlinear attachment

A vibration-based bistable electromagnetic energy harvester coupled to a directly excited primary system is examined numerically. The primary goal of the study is to investigate the potential benefit of the bistable element for harvesting broadband and low-amplitude vibration energy. The considered system consists of a grounded, weakly damped, linear oscillator (LO) coupled to a light-weight, weakly damped oscillator by means of an element which provides both cubic nonlinear and negative linear stiffness components and electromechanical coupling elements. Single and repeated impulses with varying amplitude applied to the LO are the vibration energy sources considered. A thorough sensitivity analysis of the system's key parameters provides design insights for a bistable nonlinear energy harvesting (BNEH) device able to achieve robust harvesting efficiency. This is achieved through the exploitation of three BNEH main dynamical regimes; namely, periodic cross-well, aperiodic (chaotic) cross-well, and in-well oscillations.