The dynamic characteristics of harvesting energy from mechanical vibration via piezoelectric conversion

As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping （i.e., the decrease in the energy removed from the mechanical vibration）. This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.

Experimental Investigation of Multi-Mode Vortex-Induced Vibration of Flexible Risers with Different Mass Ratios

Experiments were conducted on risers with different mass ratios to study the effect of mode conversion and spanwise correlation. The slenderness ratio of the riser model was set as 169, and the Reynolds numbers are 1600-14400. The dynamic responses of riser models versus reduced velocity were analyzed, and the spanwise displacement, frequency,and trajectory of the mode conversion from the lower to the higher mode were explored. The results revealed that the riser model with a higher mass ratio excites a higher number of modes. The conversion region of multi-mode competition exists and narrows with the increasing mass ratio. Mode conversion is continuous and manifests as the transmission of peaks and troughs in mode shape: the peaks and troughs of mode shape move up in the mode stable development region and move down in the mode conversion region. The single-mode dominating vibration exhibits a standing wave feature, and the traveling wave feature is significant in the mode conversion region. Furthermore, the frequency jump is always transmitted from the trough to the peak of the mode shape, and finally, all the axial positions vibrate at the same frequency. The trajectory in the mode conversion region deviates from the 8-shape and recovers the standard8-shape at the middle and late stages of the mode stable development region.

Dynamic Properties and Energy Conversion Efficiency of A Floating Multi-Body Wave Energy Converter

The present study proposed a floating multi-body wave energy converter composed of a floating central platform,multiple oscillating bodies and multiple actuating arms. The relative motions between the oscillating bodies and the floating central platform capture multi-point wave energy simultaneously. The converter was simplified as a forced vibration system with three degrees of freedom, namely two heave motions and one rotational motion. The expressions of the amplitude-frequency response and the wave energy capture width were deduced from the motion equations of the converter. Based on the built mathematical model, the effects of the PTO damping coefficient, the PTO elastic coefficient, the connection length between the oscillating body and central platform, and the total number of oscillating bodies on the performance of the wave energy converter were investigated. Numerical results indicate that the dynamical properties and the energy conversion efficiency are related not only to the incident wave circle frequency but also to the converter’s physical parameters and interior PTO coefficients. By adjusting the connection length, higher wave energy absorption efficiencies can be obtained. More oscillating bodies installed result in more stable floating central platform and higher wave energy conversion efficiency.

Effect of scratch on corrosion resistance of calcium phosphate conversion coated AZ80 magnesium alloy

In order to analyze the effect of scratch on the corrosion behaviour of a calcium phosphate conversion coating(CPCC)on AZ80,the electrochemical testing,scanning vibrating electrode technique(SVET),immersion test and hydrogen evolution experiment were performed to study the corrosion resistance of AZ80,AZ80 with CPCC and coated AZ80 with scratch.The results show that the coating improves the corrosion resistance of the AZ80 from a current density of(85±4)to(4±1)μA/cm^(2).When the coating was damaged,its protection on substrate would be reduced.The scratch with a length of around 12 mm on the coating reduced the corrosion resistance to a current density of(39±1)μA/cm^(2).In addition,the corrosion occurred initially in the scratch area and the corrosion site first occurred at the junction of the scratch and the coating.Besides,the micro corrosion mechanism of the specimen containing scratch was clarified.

Application of Piezoelectric Materials in a Novel Linear Ultrasonic Motor based on Shear-induced Vibration Mode

A novel linear ultrasonic motor based on d15 effect of piezoelectric materials was presented. The design idea aimed at the direct utilization of the shear-induced vibration modes of piezoelectric material. Firstly, the inherent electromechanical coupling mechanism of piezoelectric material was investigated, and shear vibration modes of a piezoelectric shear block was specially designed. A driving point’s elliptical trajectory induced by shear vibration modes was discussed. Then a dynamic model for the piezoelectric shear stator was established with finite element（FE） method to conduct the parametric optimal design. Finally, a prototype based on d15 converse piezoelectric effect is manufactured, and the modal experiment of piezoelectric stator was conducted with laser doppler vibrometer. The experimental results show that the calculated shear-induced vibration modes can be excited completely, and the new linear ultrasonic motor reaches a speed 118 mm/s at noload, and maximal thrust 12.8 N.

模式转换型超声扭转焊接振子的研究

基于超声振动的模式转换理论,结合有限元方法设计了谐振频率为20 kHz的超声扭转焊接振子。该振子主要由夹心式压电换能器与模式转换变幅杆组成,模式转换变幅杆的互推杆和传振杆通过螺栓连接。为减少振子的漏波,设计了一种特殊结构的减振型法兰,并保证模式转换变幅杆输出端产生扭转振动。利用有限元分析软件进行模态分析和谐响应分析,仿真出振子的扭转频率为19.877 kHz,得到振子的频率响应曲线,通过模式转换变幅杆处完成振动模式的转换。最后,通过阻抗分析仪测得研制的振子谐振频率为19.69 kHz,与理论值和仿真值相差较小。激光测振仪测量振子互推杆端面处的纵向振幅为10.2μm,与仿真值接近,验证了设计方法的可行性,可为设计其他超声扭转焊接振子提供参考。

面向新型电力传感器的能量收集技术

电力传感器作为能源互联网的关键基础设施,其持续稳定的电力供应是保证能源互联网高效运行的前提。然而,传统供电方式存在诸多局限。全面梳理了面向新型电力传感器的能量收集技术,包括振动能量收集、温差能量收集、光伏能量收集和电磁能量收集等,这些技术利用环境中的分布式能源,通过不同的转换机理为传感器提供电力,有望解决供电难题。阐述了各种能量收集技术的应用现状,分析了目前所面临的关键技术挑战,如能量转换效率低、工作条件要求苛刻、器件可靠性和集成度有待提高等;探讨了未来能量收集技术的创新方向,包括开发新型高性能材料、优化器件结构设计、使用复合式收集技术等,以期实现更高的能量利用效率,满足新型电力传感器的实际需求,推动智能电网等相关领域的技术创新。

基于FPGA的高精度振动采集传输系统

为了满足某飞行器飞行过程中不同部位振动监测的需求,完成多路振动信号实时采集,论文提出一种基于FPGA的高精度振动采集传输系统设计方案。首先设计调理电路,将传感器输出的电荷信号调理至采集范围内。其次,使用模拟开关对14路采集通道进行切换,使用16bit高精度ADC实现模数转换。最后,利用FPGA控制整个采集传输过程,将数字量编帧、打包、缓存,并通过以太网接口将采集数据发送至防护存储器进行数据存储。测试表明,数据可靠性高,在单路采样率为20kSPS、测量范围为±2000g时,振动信号的采集精度可达到±0.5%。

炸药性能对爆破地震波传播与能量衰减规律影响研究

为探究炸药性能对爆破地震波传播与能量衰减规律的影响,以便更好地控制爆破振动,提高炸药能量利用率,开展了岩石粉状乳化炸药、改性铵油炸药两种不同性能炸药条件下爆破振动对比试验。结合某露天矿现场采集的爆破振动相关数据,从爆破振动峰值质点速度及爆破地震波能量两个角度,利用萨道夫斯基公式及小波包分析方法对比分析了岩石粉状乳化炸药、改性铵油炸药两种不同性能炸药条件下爆破地震波传播及能量衰减规律。结果表明:在同一岩石介质中,两种炸药所产生的爆破振动峰值质点速度及爆破地震波能量衰减系数均相差不大;波阻抗较高的岩石粉状乳化炸药所产生的爆破振动峰值质点速度相对较低,爆破地震波能量相对较高;两种性能炸药总能量转化为爆破振动能量的百分比分别为6.701%、5.079%,高性能的岩石粉状乳化炸药能量利用率相对较低。研究结果对矿山生产爆破炸药选型具有一定的指导意义,丰富了工程实践中的降振手段及途径。

微半球陀螺交直流混合电压切换驱动方法研究

微半球谐振陀螺的标度因数受阻尼不均匀程度和幅值控制精度影响,保证陀螺结构高度对称性的同时,驱动模态幅值控制精度也尤为重要。针对常见一倍频、1/2倍频电压驱动方式存在同频驱动噪声干扰和补偿相位延时导致微半球谐振陀螺驱动模态幅值控制精度较低,标度因数稳定性不足等问题,由于起振后陀螺等效驱动形式变化,基于微谐振子电压驱动原理构建了稳幅阶段微谐振子动态振动模型,提出了一种用于稳幅阶段的同相位二倍频电压驱动方式,设计了一种用于陀螺模态控制的交直流混合电压切换驱动方法,避免了相位补偿和同频驱动引起的幅值波动干扰。最后经力平衡模式仿真试验对比验证,混合电压切换驱动方法下驱动模态幅值控制精度提升5.882%,陀螺仪标度因数稳定性提高6.625%。

振荡浮子式波能装置的功率计算分析及参数设计

波浪能是重要的可再生资源之一,提高波浪能装置的能量捕获率是波浪能规模化利用的关键。本文对波浪能的能量转换装置进行了研究,针对装置于不同摇荡条件下的最大平均输出功率、最优阻尼系数及相关参数进行演化分析及求解。利用牛顿定律及质心系、转动惯量等建立二自由度、四自由度波浪能转换装置耦合运动模型,基于时间离散化的差分原理求解,同时采用模拟退火算法降低时间复杂度,提出了改良的粒子群算法,得到较为准确的结果,为实际工程中波浪能的高效采集提供思路和途径。

基于传感信号采集的电控发动机振动故障监测方法

通过调理振动信号可以更高效地监测振动故障。为此,提出基于传感信号采集的电控发动机振动故障监测方法。首先,搭建电控发电机传感信号采集与处理架构,通过放大传感信号增益、滤波和转换信号模数的方式处理待监测信号,为提高监测准确性奠定可靠的数据基础。通过小波包分解与重构,获取信号的时域参数和小波能谱熵,并构建三维特征量。然后,利用“一对一”分解策略优化孪生支持向量机,构造多元分类器,使其更适用于振动故障监测这一多类别分类问题,再输入待监测信号的特征量,通过确定故障类别实现持续性监测。仿真结果表明:该方法训练耗时的最大值仅为897 ms,对于转子摩擦振动、不平衡振动等5种类型故障的监测准确率始终在97%以上,在缩减训练样本后准确率仍保持在90%以上。

基于单线振动台的角振动试验系统研究

目的 考核陀螺类产品在角振动环境下的适应性。方法 开发基于单线振动台的角振动试验系统,该系统以线角转换原理为依据,设计铰接机械结构,将线振动台的平动自由度转换为转动自由度。以角振动控制原理为依据,设计控制流程,实现闭环控制。结果 开展了角定频试验和角扫频试验,对系统的控制效果进行了验证。对比了线参数控制和角参数控制2种方法,结果表明,角参数控制法具有更高的控制精度。由于闭环控制的作用,角参数控制法可通过驱动电压的调整直接影响角参数值,从而抵消了部分由于系统连接、解耦或振动引入的误差。结论 该角振动试验系统解决了双台角振动旋转半径受限、线能力受限等问题,克服了摇摆台频带过窄的问题,为角振动试验提供一种新的实施方法。

基于Fe-Co-V合金的逆磁致伸缩效应高性能振动发电

旨在探讨和研究磁致伸缩振动发电技术的设计方案。磁致伸缩振动发电是一种利用磁致伸缩材料将振动能转化为电能的技术。该技术具有体积小、重量轻、能量转换效率高等优点,适用于微型能量收集和无线传感器网络等领域。目前磁致伸缩振动发电技术仍面临一些挑战,例如低效率和能量输出不稳定。因此,研究的目标是设计和优化一种磁致伸缩振动发电装置,以提高能量转换效率和稳定性。将采用优化的材料选择、结构设计和电路调整,通过实验研究不同设计参数对发电效果的影响,并对实验结果进行分析和评估。预期结果将为磁致伸缩振动发电技术的进一步发展和应用提供有益的参考和指导。

基于STFT的织构涂层硬质合金表面振动解析方法

针对织构涂层复合工艺对硬质合金表面改性时存在消极振动的问题,提出一种基于织构涂层表面摩擦振动行为的解析方法来探索织构涂层复合工艺改性效果。因此,搭建了微织构AlSiTiN涂层硬质合金-钛合金磨盘摩擦磨损试验平台,基于短时傅里叶变换(STFT)与灰度算法对摩擦振动变化规律性映射和振动行为平稳时段进行了获取,进而分析了微织构AlSiTiN涂层工艺参数对硬质合金的改性效果。试验研究得出了微织构及AlSiTiN涂层对硬质合金表面耐磨改性效果最为积极的时间段,即自接触摩擦起第5~25 min的稳定作用时期,得出微织构及AlSiTiN涂层参数对硬质合金表面改性的影响机理,优选该复合改性方法抑制硬质合金表面消极摩擦振动的工艺参数,为提升硬质合金表面性能研究提供新思路。

设置分段式声屏障桥梁的涡振幅值反演方法

大跨桥梁的涡激共振常采用节段模型风洞试验进行测量,但节段模型试验建立在二维理论上,当桥梁由于分段式声屏障导致沿跨向存在多种气动外形时,涡振响应难以通过节段试验直接测量.本文基于线性涡激力模型提出考虑多气动外形影响的节段-实桥涡振幅值反演方法.首先,分别对带屏障与无屏障段截面进行节段模型风洞试验;然后,通过ANSYS谐响应分析,反演全跨布置与不布置屏障两种工况的实桥涡振幅值,获得对应的涡激荷载幅值;最后,根据声屏障实际布置位置分段施加涡激荷载,得到设置分段式声屏障桥梁的实桥涡振响应,并基于本文方法对不同声屏障布置方案进行了参数分析与讨论.试验结果表明:全封闭声屏障会显著降低主梁抗风性能,屏障的分段布置对整体涡振影响较大;本文方法可通过节段模型试验结果直接估算多气动外形桥梁的全桥涡振响应,声屏障布置应在满足降噪条件下尽量布置于边跨,若布置长度超过桥塔位置,须尽量缩短布置长度以减小涡振响应.

波浪锥型风力俘能结构能量转换效率

为提高风力俘能结构能量收集效率,提出一种新型的波浪锥型无叶片风力俘能结构,建立了波浪锥型风力俘能结构能量转换数学模型,采用雷诺平均N-S方程结合SST k-ω湍流模型对俘能结构涡激振动响应过程进行了数值模拟,分析了质量比、阻尼比对波浪锥型风力俘能结构涡激振动响应和风能转换效率的影响.结果表明:质量比m^(*)=2,阻尼比ζ=0.05的波浪锥型俘能结构可获得更宽的锁频区间,能量转换效率更高.同时发现质量阻尼比m^(*)ζ直接影响能量转换效率,合适的m^(*)ζ组合可以提高能量转换效率,m^(*)ζ=0.10的情况下平均能量转换效率较m^(*)ζ=0.05提高近31%.研究结果可为无叶片风力发电机能量转换效率的提升提供理论支持.

不等直径双圆柱流致振动能量转换特性研究

为研究不等直径双圆柱在风力振动发电领域的应用前景和能量俘获特征,该文在L/D=1.5条件下,对不等直径双圆柱流致振动响应和能量转换特性进行研究,其中上游圆柱固定,下游圆柱仅做横流向振动。研究结果表明:下游圆柱会呈现涡激振动与尾流驰振两种响应,且直径比对下游圆柱的振动响应、受力特性和锁定区范围都有影响。对于获能功率驰振响应为涡激振动的2倍,但对于能量转换效率在涡激振动区间可达约30%,但在驰振区间仅有10%。从分析结果来看,在低折合速度下,d/D=0.8时能量俘获优势较明显,但在高折合速度下,d/D=0.6时能量俘获优势更加显著。

光电法受迫振动实验的研究与应用

以常见的玻璃杯为对象,研究通过声波使其受迫振动。利用光杠杆放大法及图形分析法测量反射光斑的振动频率及宽度,即玻璃杯受迫振动的频率及振幅,从而取得不同玻璃杯受迫振动的幅频特性曲线、峰值及对应玻璃杯的共振频率,并依据受迫振动理论模型计算出玻璃杯的固有频率,结果表明实测玻璃杯受迫振动的频率与理论模型计算的固有频率二者相符。将不同体积、不同种类的液体加入玻璃杯后会改变玻璃杯的共振频率,测量得到的玻璃杯共振频率与理论计算结果一致;测量加入不同浓度液体玻璃杯的共振频率,将之与浓度进行拟合,根据拟合方程可以计算该溶液的浓度,结果误差较小。