Multi-layer quasi-zero-stiffness meta-structure for high-efficiency vibration isolation at low frequency

An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is used to design the unit cel,i.e.,the single-layer QZS(SL-QZS)meta-structure.Second,the stiffness feature of the unit cell is investigated and verified through static experiments.Third,the unit cells are stacked one by one along the direction of vibration isolation,and thus the ML-QZS meta-structure is constructed.Fourth,the dynamic modeling of the ML-QZS vibration isolation metastructure is conducted,and the dynamic responses are obtained from the equations of motion,and verified by finite element(FE)simulations.Finally,a prototype of the ML-QZS vibration isolation meta-structure is fabricated by additive manufacturing,and the vibration isolation performance is evaluated experimentally.The results show that the vibration isolation performance substantially enhances when the number of unit cells increases.More importantly,the ML-QZS meta-structure can be easily extended in the direction of vibration isolation when the unit cells are properly stacked.Hence,the ML-FQZS vibration isolation meta-structure should be a fascinating solution for highly efficient vibration isolation performance at low frequency.

Active Low-frequency Vertical Vibration Isolation System for Precision Measurements

Low-fi＇equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been developed. However, few researches focus on how to optimize the test mass install position in order to improve the vibration transmissibility. An active low-frequency vertical vibration isolation system based on an earlier instrument, the Super Spring, is designed and implemented. The system, which is simple and compact, consists of two stages： a parallelogram-shaped linkage to ensure vertical motion, and a simple spring-mass system. The theoretical analysis of the vibration isolation system is presented, including terms erroneously ignored before. By carefully choosing the mechanical parameters according to the above analysis and using feedback control, the resonance frequency of the system is reduced from 2.3 to 0.03 Hz, a reduction by a factor of more than 75. The vibration isolation system is installed as an inertial reference in an absolute gravimeter, where it improved the scatter of the absolute gravity values by a factor of 5. The experimental results verifies the improved performance of the isolation system, making it particularly suitable for precision experiments. The improved vertical vibration isolation system can be used as a prototype for designing high-performance active vertical isolation systems. An improved theoretical model of this active vibration isolation system with beam-pivot configuration is proposed, providing fundamental guidelines for vibration isolator design and assembling.

Low-frequency and broadband vibration energy harvester driven by mechanical impact based on layer-separated piezoelectric beam

Vibration energy harvesting is to transform the ambient mechanical energy to electricity. How to reduce the resonance frequency and improve the conversion efficiency is very important. In this paper, a layer-separated piezoelectric cantilever beam is proposed for the vibration energy harvester(VEH) for low-frequency and wide-bandwidth operation, which can transform the mechanical impact energy to electric energy. First,the electromechanical coupling equation is obtained by the Euler-Bernoulli beam theory.Based on the average method, the approximate analytical solution is derived and the voltage response is obtained. Furthermore, the physical prototype is fabricated, and the vibration experiment is conducted to validate the theoretical principle. The experimental results show that the maximum power of 0.445 μW of the layer-separated VEH is about3.11 times higher than that of the non-impact harvester when the excitation acceleration is 0.2 g. The operating frequency bandwidth can be widened by increasing the stiffness of the fundamental layer and decreasing the gap distance of the system. But the increasing of operating frequency bandwidth comes at the cost of reducing peak voltage. The theoretical simulation and the experimental results demonstrate good agreement which indicates that the proposed impact-driving VEH device has advantages for low-frequency and wide-bandwidth. The high performance provides great prospect to scavenge the vibration energy in environment.

Low-frequency characteristics extension for vibration sensors

Traditional magneto-electric vibration sensors and servo accelerometers have severe shortcomings when used to measure vibration where low frequency components predominate.A low frequency characteristic extension for velocity vibration sensors is presented in this paper.The passive circuit technology,active compensation technology and the closed- cycle pole compensation technology are used to extend the measurable range and to improve low frequency characteristics of sensors.Thses three types of low frequency velocity vibration sensors have been developed and widely adopted in China.

Analysis and compensation of low frequency characteristics of sensors for vibration testing

In view of the influence and harm of low frequency vibration environment on the structure of spaceflight products,a low frequency dynamic study method for piezoelectric sensor based on the dynamic system of sinusoidal pressure is proposed.This method uses a sinusoidal pressure dynamic system with two-way dual channel import and export synchronization technology to study the low frequency characteristics of a piezoelectric sensor of PCB company,and its lower cut-off frequency is 0.26 Hz.It is also studied that when the frequency of the measured vibration or shock signal is 1-200 kHz,the error range of signal positive pressure action time is 4.87%-0.03%.The dynamic compensation for the low frequency of the vibration sensor is carried out,and the compensation effect is good.

DESIGN AND ANALYSIS OF NOVEL ACTIVE ACTUATOR TO CONTROL LOW FREQUENCY VIBRATIONS OF SHAFT SYSTEM

Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.

Vibration energy harvesting for low frequency using auto-tuning parametric rolling pendulum under exogenous multi-frequency excitations

An electromagnetic parametrically excited rolling pendulum energy harvester with self-tuning mechanisms subject to multi-frequency excitation is proposed and investigated in this paper.The system consists of two uncoupled rolling pendulum.The resonance frequency of each the rolling pendulum can be automatically tuned by adjusting its geometric parameters to access parametric resonance.This harvester can be used to harvest the energy at low frequency.A prototype is developed and evaluated.Its mathematical model is derived.A cam with rolling follower mechanism is employed to generate multi-frequency excitation.An experimental study is conducted to validate the proposed concept.The experimental results are confirmed by the numerical results.The harvester is successfully tuned when the angular velocity of the cam is changed from 1.149 to 1.236 Hz.

Tracking coherent low frequency vibrational information of Rh101 in ground and excited electronic states by broadband transient grating spectroscopy

Time-and frequency-resolved broadband transient grating(BB-TG) spectroscopy is used to distinguish between ground-and excite-electronic state vibrational coherence at different wavelengths. Qualitative theoretical analysis using double-sided Feynman diagrams indicates that a superposition of ground and excited state vibrational coherence are contained in the ground state absorption(GSA) and stimulated emission(SE) overlap band, while only the excited state is contained in the excited state absorption(ESA) band. The TG experiment, in which a white light continuum(WLC) is adopted as a probe, is conducted with rhodamine101(Rh101~+) as the target molecule. Fourier analysis of TG dynamics in a positive delay time range at specific wavelengths enables us to distinguish the low-frequency vibrational modes of Rh101 in ground-and excite-electronic states.

Low-Frequency Vibrations of Indole Derivatives by Terahertz Time-Domain Spectroscopy

Several indole derivatives with different ＇3-＇ substituents have been investigated by terahertz （THz） time-domain spectroscopy. The low-frequency absorption spectra and refractive indices were obtained in the range of 0.2 THz to 2.5 THz （7 cm-1 to 83 cm-1）. These derivatives with different substituents present distinct features, which suggests that THz spectroscopy is sensitive to different structures and components of these chemicals. The density functional theory was employed to calculate the low-frequency vibrational properties of indole-3-carboxylic acid and indole-3-propionic acid based on their crystal structures, and the intermolecular interactions were involved. Meanwhile, the temperature dependence of the spectra agreed with the calculated results. The quantitative analysis of a ternary mixture was studied by taking the THz fingerprints into account, and the results demonstrate THz spectroscopy has great potential for the practical applications in biochemistry and pharmaceutics.

Frequency Features Based Fuzzy System for Rotating Machinery Vibration Analysis Using Smartphones Low-Cost MEMS Sensors

Smart devices have become an important entity for many applications in daily life activities. These devices have witnessed a rapid improvement in its technology to fulfill the increasingly diverse usage demands. In the meanwhile, rotating machinery vibration analysis based on low-cost sensors has gained a considerable attraction over the last few years. For a long time, the vibration analysis of machines has been accepted as an effective solution to detect and prevent failures in complex systems to avoid the sudden malfunction. The objective of this work is to use MEMS accelerometer measurements to monitor the different level of vibration of a machine. This work presents a new technique for rotating machinery vibration analysis. It uses Fast Fourier Transformation as a feature extraction algorithm and Fuzzy Logic System (FLS) as the classifier algorithm. A smartphone accelerometer is used to collect the data from the vibrating machine. The performance of the proposed technique is tested using data from different vibration resources at a different speed of operations. The results are discussed to illustrate the various vibration levels.

A vibration isolator with a controllable quasi-zero stiffness region based on nonlinear force design

To achieve stability optimization in low-frequency vibration control for precision instruments,this paper presents a quasi-zero stiffness(QZS)vibration isolator with adjustable nonlinear stiffness.Additionally,the stress-magnetism coupling model is established through meticulous theoretical derivation.The controllable QZS interval is constructed via parameter design and magnetic control,effectively segregating the high static stiffness bearing section from the QZS vibration isolation section.Furthermore,a displacement control scheme utilizing a magnetic force is proposed to regulate entry into the QZS working range for the vibration isolation platform.Experimental results demonstrate that the operation within this QZS region reduces the peak-to-peak acceleration signal by approximately 66.7%compared with the operation outside this region,thereby significantly improving the low frequency performance of the QZS vibration isolator.

Study on System of Low Frequency Signal′s Measurement and Extraction of its Characteristic Quantity

The essay mainly studies a system of low frequency signal′s measurement and the extraction of its characteristic quantity,introduces how matlab analyzes and extracts low frequency signal.MATLAB,a visual programming software,designs testing program for mechanic vibration signal,analyzes and identifies vibration signal.The collected data shows the effectiveness of the system.Based on XM121 modules,the testing system collects and analyzes single channel signal.

仿生肢状准零刚度隔振系统的振动特性研究

在低频隔振领域,针对线性系统存在承载能力不足及传统准零刚度隔振系统存在刚度硬化,非线性跳跃导致系统失稳的问题,以仿生肢状结构作为负刚度元件与正刚度弹簧并联建立了仿生肢状准零刚度隔振系统的力学模型,分析了系统的静力学特性;基于拉格朗日方程建立动力学模型,采用谐波平衡法进行解析求解;通过理论分析和试验研究对比分析了线性、传统准零刚度隔振系统和仿生肢状准零刚度隔振系统隔振特性,以及激励幅值对系统隔振性能和稳定特性的影响规律。结果表明:相比线性系统和传统准零刚度隔振系统,仿生肢状准零刚度隔振系统不仅保证了系统具有较高的承载能力,而且通过结构参数设计有效降低了位移传递率,拓展了隔振频宽,提高了系统在复杂激励环境中的稳定性和隔振性能。

惯容器元件对轨道车辆横向低频振动的影响研究

惯容器是新型的隔振元件,探究其低频减振效果,可为轨道车辆横向低频晃动研究提供新思路和理论借鉴。建立包含惯容器元件的车辆系统动力学模型,研究车辆横向低频晃动的机理及惯容器元件对低频减振效果,借助欧式贴近度,定义整个车辆系统所有模态之间的耦合度,该指标能有效表征转向架蛇行频率被车体固有频率俘获的程度。以降低车辆整体耦合度为目标,对惯容器参数进行优化。计算结果表明:转向架蛇行频率被车体某些固有频率俘获,此时两者的固有频率非常接近,并且振型极为相似,引起车辆横向低频晃动。对于二系横向悬挂采用“惯容-弹簧-阻尼”减振结构,能有效降低车辆系统模态间的耦合程度,该减振结构具有良好的低频隔振性能。

地铁诱发近轨建筑楼板差异振动

为研究地铁对近轨建筑物楼板整体及局部振动的影响,依托成都某工程,研究地铁诱发的建筑物楼板振动特性和传播规律。首先,基于列车-轨道耦合动力学理论和有限元技术,引入黏弹性人工边界,建立列车-轨道-隧道-土体-建筑物耦合动力学模型;其次,实测地铁诱发的土体振动并对数值模型进行验证;然后,研究楼板振动的衰减特性及不同位置楼板的振动差异;最后,研究楼板厚度、建筑总高度对楼板振动的影响。研究表明:楼板振动主频为40Hz;第一层楼板的振动最大;承重柱附近的楼板振动大于楼板中心处的振动;近轨侧楼板振动大于远轨侧;沿楼层高度方向,楼板Z振级先减再增;随着楼板厚度增加,楼板Z振级减小,每增加2 cm的厚度,振动最大可减小2~3 dB;当总楼层数减小时,每减少4层,楼板振动增加1~3 dB。研究思路可为地铁环境振动测试和分析提供参考。

Kagome点阵夹芯超材料的汽车前围板隔振特性研究

为高效控制汽车前围板振动噪声,弥补传统材料抑制低频振动性能的不足及易燃、环保性能低的缺陷,设计一种基于Kagome点阵的局域共振型夹芯超材料,建立单胞结构的有限元模型,计算并分析其能带结构、带隙产生机理和弹性波传播特性,以及关键几何参数对带隙频段的影响,利用正交实验极差分析法(Statistical Product and Service Software Automatically,SPSSAU)对关键几何参数进行优化,同时开展基于该材料的汽车前围板隔振性能的研究。研究表明,所设计的Kagome点阵夹芯超材料能够实现低频带隙;增加圆块厚度和半径会使带隙频段整体向低频方向移动,且拓宽低频带隙;减小韧带宽度会使带隙频段向低频区域移动,且使带隙宽度减小。将优化后的Kagome点阵夹芯超材料应用于汽车前围板,可明显提高其隔振性能。

Vibration stimuli and the differentiation of musculoskeletal progenitor cells: Review of results in vitro and in vivo

Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact onquality of life and result in hundreds of hours of hospital time and resources. There is growing interest in the use of low magnitude, high frequency vibration(LMHFV) to improve bone structure and muscle performance in a variety of different patient groups. The technique has shown promise in a number of different diseases, but is poorly understood in terms of the mechanism of action. Scientific papers concerning both the in vivo and in vitro use of LMHFV are growing fast, but they cover a wide range of study types, outcomes measured and regimens tested. This paper aims to provide an overview of some effects of LMHFV found during in vivo studies. Furthermore we will review research concerning the effects of vibration on the cellular responses, in particular for cells within the musculoskeletal system. This includes both osteogenesis and adipogenesis, as well as the interaction between MSCs and other cell types within bone tissue.

沙漏型声子晶体的中低频隔声减振性能研究

针对机械工业装备上难以解决的低频振动与噪声问题,提出一种小尺寸、轻量化的新型声子晶体结构,研究其隔声减振特性,通过有限元仿真计算该声子晶体无限周期排列时的隔声量、能带结构以及有限周期排列时的振动响应,分析该结构的隔声机理及减振特性,并研究了关键几何参数、散射体材料和声波入射角度对该结构的隔声特性的影响规律,以及板结构减振频带的拓宽方法.结果表明:该声子晶体结构在1 000 Hz以下频率范围内具有优越的隔声减振性能,通过将不同参数的结构进行组合的方法可以拓宽声子晶体板的减振频带,为工程结构的中低频隔声减振及声子晶体的应用提供了新的思路与可行性参考.

低频大幅隔振器设计及实验

为了突破传统隔振器刚度和承载能力之间的矛盾,需要隔振器具有高的静态刚度,低动态刚度的特性.如今的准零刚度隔振器技术可以实现低频微幅隔振,但是对于大幅振动,隔振效果并不明显甚至失效,因此突破宽幅隔振成为隔振领域亟待解决的问题.为此,我们利用多稳态折纸通过并联装配的方式,构造具有宽幅零刚度区间的折纸型隔振器,以解决传统隔振器振动抑制幅值较低的问题.本文建立了宽零刚度隔振器模型,提出宽幅零刚度的设计方法,并通过动力学分析分析了模型的隔振效果.最后搭建试验样机,验证了理论的正确性.这种设计打破了传统准零刚度隔振器单点准零的设计准则,能够在一个大幅范围内保证稳定性,同时实现零刚度,极大拓宽了隔振器的适用范围.这种设计理念能够被用在新隔振材料设计和航空、船舶等大幅低频动态环境中.