Nonlinear dynamics and performance analysis of modified snap-through vibration energy harvester with time-varying potential function

Vibration energy harvesting has emerged as a promising method to harvest energy for small-scale applications. Enhancing the performance of a vibration energy harvester(VEH) incorporating nonlinear techniques, for example, the snap-through VEH with geometric non-linearity, has gained attention in recent years. A conventional snap-through VEH is a bi-stable system with a time-invariant potential function, which was investigated extensively in the past. In this work, a modified snap-through VEH wit...     

Dynamics in two nonsmooth predator–prey models with threshold harvesting

Considering a good pest control program should reduce the pest to levels acceptable to the public, we investigate the threshold harvesting policy on pests in two predator–prey models. Both models are nonsmooth and the aim of this paper is to provide how threshold harvesting affects the dynamics of the two systems. When the harvesting threshold is larger than some positive level, the harvesting does not affect the ecosystem; when the harvesting threshold is less than the level, the model has complex dynamics with multiple coexistence equilibria, limit cycle, bistability, homoclinic orbit, saddle-node bifurcation, transcritical bifurcation, subcritical and supercritical Hopf bifurcation, Bogdanov–Takens bifurcation, and discontinuous Hopf bifurcation. Firstly, we provide the complete stability analysis and bifurcation analysis for the two models. Furthermore, some numerical simulations are given to illustrate our results. Finally, it is found that harvesting lowers the level of both species for natural enemy–pest system while raises the densities of both species for the pest–crop system. It is seen that the threshold harvesting policy of the enemy system is more effective than the crop system.     

Investigation on Savonius turbine technology as harvesting instrument of non-fossil energy: Technical development and potential implementation

Environmental risk due to excessive residual emission is rising. Greenhouse effect, ice melting in the Arctic, reduction of air quality are several concerns which need immediate development and change. Energy harvesting equipment is one of the key solutions. Environment potential, e.g. water resource can be collaborated with mechanical equipment to harvest clean energy. Savonius turbine has been proposed and studied for this purpose and can be placed on several energy resources, i.e. water and wind. Still, real-world implementation of this technology is lacking,especially in tropical archipelago countries which have abundant water resources. In this work,assessment of Savonius turbine technology as instrument to harvest clean energy is conducted. A series of development on the turbine performance and technical modification is considered as reference to implement the technology in water and open air environments. It is noted that rotor design, operation depth and nozzle attachment are several key influencing factors.     

Terrain trafficability analysis and soil mechanical property identification for planetary rovers: A survey

The advances in the field of robotics enabled successful exploration of the Moon and Mars. Over the years, rover missions have demonstrated deployment of various scientific payloads for robotic field geology on these extra-terrestrial bodies. The success of these missions clearly emphasises the need to further advance rover technology in order to maximise scientific return. The success of future robotic surface exploration missions will depend on two key factors – autonomy and mobility on soft sandy and unstructured terrains. The main contribution of this paper is that it brings together vital information pertaining to various terrain characterisation techniques into a single article. Special care is taken in structuring the paper so that all the relevant terrain characterisation methods that have been used in past planetary exploration missions and those under consideration for future space exploration missions are covered. This paper will not only lists advantages and disadvantages of various terrain characterisation techniques but also presents the methodology for evaluating and comparing terrain characterisation techniques and provides a trade-off study of existing and potential approaches that could improve the mobility of future planetary exploration rovers. This survey shows that further advances in currently deployed technology are required in order to develop intelligent, on-board sensing systems which will detect and identify near surface and sub-surface terrain properties to enhance the mobility of rovers.     

Circuit implementation of a piezoelectric buckled beam and its response under fractional components considerations

In this paper, an analog testing circuit and determinist averaging method for a vibration energy harvesting system with fractional derivative and nonlinear damping under a sinusoidal vibration source is proposed in order to predict the system response and its stability. The objective of this paper is to show that there is a possibility to make a pre-experimental design of the structure by using analog circuit and discussing the performance of a system with fractional derivative. Bifurcation diagram, poincaré maps and power spectral density are provided to deeply characterize the dynamic of the system. These results are corroborated by using 0–1 test. By using the Melnikov method, we find the necessary condition for which homoclinic bifurcation occurs. Understanding and predicting this bifurcation is very judicious in the energy harvesting field because it may lead to different types of motion in the perturbed system. The appearance of chaotic vibrations increases the frequency’s bandwidth of the harvester thereby, allowing to harvest more energy. The pre-experimental investigation is carried out through appropriate software electronic circuit (Multisim^®). The corresponding electronic circuit is designed exhibiting transient to chaos in accord with numerical simulations. The impact of fractional derivatives is presented upon the power generated by the system. In addition, by combining the harmonic force and a random excitation, the stochastic resonance appears, giving rise to large amplitude of vibration and consequently, enhancing the performance of the system. The results obtained in this work show the interest of using the electronic circuit to make the experiment analysis of the physical structure and also, the effects of the use of piezoelectric material exhibiting fractional properties in this research field.     

A comparison of novel chassis suspended machines for sustainable forestry

Cut-to-length logging (CTL) is a mechanized harvesting process where trees are delimbed and cut to length directly at the stump. The main challenges for the manufacturers of forestry machines for CTL logging are to address new customer demands and tougher health and environmental legislations by finding means that: (1) further increase the harvesting and log transportation productivity, e.g. by enabling operation on eco-soils, (2) reduce the damage to the soil, e.g. by controlling the ruts depth and preserving the root layer, (3) reduce exhaust emissions, e.g. by reducing the rolling resistance, and (4) reducing the daily vibration dosage for the machine operators, e.g. by active chassis and cabin damping.This paper presents of a number of passive forwarder chassis suspension concepts and compares their performance from three perspectives: their gentleness to terrain and operator, as well as their potential for improved fuel efficiency. Based on multi-body dynamics simulations, it is shown that a passive pendulum arm suspension can reduce the lateral accelerations in a passively suspended cabin with 50% compared to traditional bogie machines when travelling in rough hard terrain.     

Predictability of boreal forest soil bearing capacity by machine learning

In forest harvesting, terrain trafficability is the key parameter needed for route planning. Advance knowledge of the soil bearing capacity is crucial for heavy machinery operations. Especially peatland areas can cause severe problems for harvesting operations and can result in increased costs. In addition to avoiding potential damage to the soil, route planning must also take into consideration the root damage to the remaining trees. In this paper we study the predictability of boreal soil load bearing capacity by using remote sensing data and field measurement data. We conduct our research by using both linear and nonlinear methods of machine learning. With the best prediction method, ridge regression, the results are promising with a C-index value higher than 0.68 up to 200 m prediction range from the closest point with known bearing capacity, the baseline value being 0.5. The load bearing classification of the soil resulted in 76% accuracy up to 60 m by using a multilayer perceptron method. The results indicate that there is a potential for production applications and that there is a great need for automatic real-time sensoring in order to produce applicable predictions.     

面内压电振动能量采集动力学设计与性能研究

压电振动能量采集将环境中普遍存在的机械能转换为电能,可以实现自供能传感、控制与驱动,具备灵活、节能环保、可持续的优势,具有广阔的应用前景.为了促进压电振动能量采集器件的集成与融合,提出面内压电振动能量采集,将压电振动能量采集器进行扁平化设计,使其在二维平面内采集振动能量,在保证较大功率输出下能够显著减小器件所需三维空间.为了提高输出功率与工作频宽,设计了具有双稳态与力放大机制的面内压电振动能量采集器.考虑弯张小变形,通过能量法建立了面内压电振动能量采集器的机电耦合动力学模型.分析了关键设计参数对面内压电振动能量采集器性能的影响.数值仿真了面内压电振动能量采集器在简谐激励下的俘能性能,结果表明,通过合理的设计,面内压电振动能量采集器可以低频、宽频弱激励下有效俘获能量.面内压电振动能量采集设计方法有利于推动便携式、可穿戴式自供能等方面的应用和产业化.     

基于卷积神经网络的涵洞式直立堤波浪透射预测

涵洞式直立堤是一种具有特殊用途的海岸工程结构物,对其透浪特性的研究具有重要工程意义.然而,目前众多学者对于涵洞式直立堤波浪透射问题的研究主要以理论分析、实验模拟及数值计算为主.随着机器学习技术的发展,传统水动力学问题迎来了新的求解理念.机器学习算法可根据训练数据集自主学习相应的规律,以数据映射的方式建立水动力学特征预测...     

非线性振动能量俘获技术的若干进展

随着工程中低功耗电子设备和自供能无线传感网络的迅速发展, 使得振动能量俘获在航空航天工程、机械工程、生物医学工程和可持续能源工程等领域得到了广泛地应用. 振动能量俘获不仅可以将振动能转化为可用的电能为微电子设备供电, 还能减少有害振动保护仪器设备. 根据振动能量不同转换机制, 可以将振动能量俘获系统分为静电式、电磁式、压电式、磁致伸缩式、摩擦起电式以及它们的混合式. 其中压电和电磁振动能量转化机制由于结构简单、容易组装、能量转换性能高等优点, 已被广泛应用于各种工程领域中. 受极端环境干扰, 工程中容易出现宽带、低频等振动, 迫使振动能量俘获技术向非线性方向迅猛发展, 进一步吸引了诸多学者对振动能量俘获系统的结构和电路进行优化设计研究. 本文首先综述了非线性振动能量俘获技术近十年来的研究进展, 主要包括设计技术基础、非线性结构设计、动力学分析等方面的研究现状. 其次, 重点阐述了振动能量俘获与振动抑制一体化的主要研究成果, 包括非线性准零刚度和非线性能量汇在振动能量俘获领域的应用. 最后, 总结了振动能量俘获外接电路和主动控制策略的优化设计, 分析了进一步提升非线性振动能量俘获效能的有效方法.      

Flutter of spring-mounted flexible plates in uniform flow

A fluid–structure interaction (FSI) system is studied wherein a cantilevered flexible plate aligned with a uniform flow has its upstream end attached to a spring mounting. This allows the entire system to oscillate in a direction perpendicular to that of the flow as a result of the mounting׳s dynamic interaction with the flow-induced oscillations, or flutter, of the flexible plate. We also study a hinged-free rotational-spring attachment as a comparison for the heaving system. This variation on classical plate flutter is motivated by its potential as an energy-harvesting system in which the reciprocating motion of the support system would be tapped for energy production. We formulate and deploy a hybrid of theoretical and computational modelling for the two systems and comprehensively map out their linear-stability characteristics at low mass ratio. Relative to a fixed cantilever, the introduction of the dynamic support in both systems yields lower flutter-onset flow speeds; this is desirable for energy-harvesting applications. We further study the effect of adding an inlet surface upstream of the mount as a means of changing the destabilising mechanism from single-mode flutter to modal-coalescence flutter which is a more powerful instability more suited to energy harvesting. This strategy is seen to be effective in the heaving system. However, divergence occurs in the rotational system for low spring natural frequencies and this would lead to its failure for energy production. Finally, we determine the power-output characteristics for both systems by introducing dashpot damping at the mount. The introduction of damping increases the critical speeds and its variation permits optimal values to be found that maximise the power output for each system. The addition of an inlet surface is then shown to increase significantly the power output of the heaving system whereas this design strategy is not equally beneficial for the rotational system.     

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为了提高舰船及其设备的抗冲击能力,满足最新抗冲击标准的要求,同时提高传统冲击试验 机的最大测试能力,提出了一套全液压驱动的新型重载舰船设备抗冲击试验系统模型, 以解决系统高能量存储及瞬间释放和避免二次撞击的关键问题. 构建了系统非线性 动力学模型,并利用数值计算方法考察了在不同冲击速度测试条件下冲击机系统所能达到的 预期性能. 结果表明: 该系统可以产生与最新抗冲击标准BV043/85和MIL-S-901D相吻合的 冲击加速度波形,同时可根据不断提高的抗冲击标准以及测试能力要求进行相应的扩展.     

Mode change in the dynamics of exploited limited population with age structure

This study focuses on the dynamics of exploited limited population with age structure and compares dynamic modes of population models with and without exploitation while considering age-specific harvesting. Transcritical, period-doubling, and Neimark–Sacker bifurcations occur in the population models. In the case of juvenile harvest, the way of stability loss does not depend on the harvest rate. However, in the case of adult harvest, the hydra effect occurs, which is an increase in harvest rate that subsequently increases the stationary size of the young group. As a rule, harvesting leads to dynamics stabilization. However, the models reveal multistability. Hence, in the case of exploitation, different dynamic modes can occur with their attraction basins at the same population parameter values. Irregular harvesting or a changing harvest rate may also result in fluctuations in exploited population size because the current population size can shift from one attraction basin to another. Controlling exploited population dynamics is sufficient to shift and retain the population number to within the attraction basin of the dynamic mode selected.     

Flexible Wiper System Dynamic Instabilities: Modelling and Experimental Validation

The optimization of wiper systems under various conditions and the creation of a product which is as robust as possible are the main objectives for an equipment supplier. However, in certain conditions, instabilities can appear and generate wiping defects due to the rubber-glass contact. To improve wiping quality and to reduce the number of test stages for design, this study proposes a wiper system modeling method. The wiper system is represented by a rigid blade holder on which a rubber blade is fitted. This rigid blade system is used on a flat test bench at constant wiping velocity. The model is based on modal synthesis methods and will be validated through comparison with experimental tests under various conditions. The right correlation obtained allows the same modelling method to be applied to the new generation of flexible wiper blades which take account of the degree of freedom of the wiper blade flexions. So, a new computation tool will be developed and validated through experimentation on a specific test bench.     

Coupled Hydraulic System for Tensile Testing in Compression-only Machines

Fracture theory for normal strength concrete has thoroughly been studied over the past decades. Through indirect and direct tensile testing techniques, the post-peak softening response of conventional concrete has been established and utilized in analysis and design. However, for more recently developed concrete materials (e.g. fiber reinforced, high performance) under complex loading conditions, the required fracture properties to predict response are extremely limited. Considering this lack of knowledge, the objective of this research was to develop a uni-axial tensile testing technique to attain the post-peak softening response for ultra-high performance concrete for ultimate use in conjunction with an applied confining pressure system. Specifically, this research was conducted for implementation into an existing, large compression-only machine at the US Army Engineer Research and Development Center (ERDC). The new methodology enabled the existing testing frame to apply a stiffening force, while an external hydraulic plunger cylinder performed the tensile test. The scheme enables tensile testing under confining pressures in the compression-only machine.     

压电与摩擦电复合型旋转能量采集动力学协同调控机制研究

低转速激励下能量采集性能差是目前制约旋转能量采集技术应用的瓶颈问题. 本文提出了动力学协同调控机制, 并用于调控系统的动力学行为, 可以使器件在低转速激励下有效工作, 提高了旋转能量采集系统的电学性能. 旋转刚度软化、非线性磁力、几何边界的协同调控既可以增加系统在低速下的振动位移以及压电材料的形变, 也可调控系统的最大位移, 使其振动可控并限制位移过大提高可靠性. 此外, 几何边界可以方便地集成摩擦纳米发电机, 实现压电与摩擦两种机电转换机制在振动和碰撞过程中协同发电, 有效利用空间和提高输出电能. 基于哈密顿原理建立了系统的机电耦合动力学模型并进行了实验验证. 实验结果表明系统能够在0~250 r/min的低转速范围内有效工作, 在转速为250 r/min时, 压电单元和摩擦纳米发电机的最大峰峰值电压分别为132 V和1128 V, 总平均功率为1426 μW. 本文提出的动力学协同调控机制为能量采集系统动力学和电学性能改进提供新的途径, 有益于促进自供能物联网技术的发展与应用.      

Nonlinear energy harvesting with dual resonant zones based on rotating system

An electromagnetic nonlinear energy harvester(NEH) based on a rotating system is proposed, of which the host system rotates at a constant speed and vibrates harmonically in the vertical direction. This kind of device exhibits several resonant phenomena due to the combinations of the rotating and the vibration frequencies of the host system as well as the cubic nonlinearity of the NEH. The governing equation of motion for the NEH is derived, and the dynamic responses and output power are investig...     

Experiments on tension measurement in manufacturing processes

Today's demand to preserve energy, to optimally utilize limited resources and to still increase quality calls for more-precise measurements in virtually all manufacturing processes. One such field is the measurement of tension in, for instance, paper machines, printing presses, machines for the manufacturing of rubber, plastics, fabrics, etc. Newspaper-printing presses produce today an impressive number of paper breaks. Measurement of the web tension at critical positions could give an early warning when the tension in the paper is growing to dangerous values. In a paper macnine, it is necessary to introduce webtension measurements at many positions to optimize quality, to prevent paper breaks and to reduce wear. Measurements have been carried out with a particular force transducer that can be easily built into an existing, as well as a new machine. Several installations, mainly in paper machines and newspaper-printing presses, show that

- the number of paper breaks are drastically reduced

- a more-uniform quality of the paper can be achieved

- the lifetime of machine parts, such as wires and felts, can be increased.

     

Optimal harvesting of a two species competition model with imprecise biological parameters

In this paper a two competing species harvesting model with imprecise biological parameters has been developed. We have developed a method to handle these imprecise parameters and discuss the dynamical behaviour of the model. We have discussed the existence of various equilibrium points and stability of the system at these equilibrium points. Also the bionomic equilibrium of the harvesting model has been analysed. Next the equilibrium solution of the control problem has been derived, and then dynamical optimization of the harvest policy is carried out taking combined harvesting effort as a dynamic variable by invoking Pontryagin’s Maximum Principle. Our important analytical findings are illustrated through computer simulation using MATLAB followed by discussions and conclusions.     

一种具有新型动力放大器压电悬臂梁俘能器计算模型和解析解

为了提高压电振动能量俘获的效率,提出了一种新型的压电悬臂梁俘能器。新的压电俘能器在悬臂梁固定端安装一个新型动力放大器系统,另一端带有一个有限尺寸的质量块。新型动力放大器由平移及转动约束的弹簧-质量块系统组成。考虑有限尺寸质量块的质量分布效应和平移及转动约束的弹簧刚度等结构参数的影响,利用广义Hamilton原理,针对带有新型动力放大器的压电式悬臂梁俘能器,建立了分布参数型运动微分方程,获得了相应的特征函数,分析了自振频率和能量俘获效果。分析结果表明,考虑质量块偏心距和转动惯量可提高能量俘获效率的预测精度;合理选择动力放大器的平移及转动弹簧刚度可提高能量俘获的效率,降低俘能器的共振频率。