表面四电极含金属芯压电纤维的冲击振动传感特性研究

模仿昆虫毛发感受器的结构和功能,设计制备了一种能测量外部振动的表面四电极含金属芯压电纤维(FMPF)冲击振动传感器.采用干压成型法制备了含铂金芯的压电陶瓷纤维胚体,经过高温烧结、涂镀表面电极、高温极化后,制成FMPF传感器.基于压电方程和振动理论,建立了悬臂梁结构的FMPF冲击振动传感器的理论模型,分析了传感信号与冲击振动角度和幅值的关系.把FMPF固定在基体上,搭建了实验系统,测试了FMPF对冲击振动的响应,验证了理论模型.结果表明,FMPF的传感信号和冲击振动的幅值成线性关系,和方向成"8"字形关系.得出了FMPF传感器能够测量冲击振动幅值和方向的结论.     

Plastic collapse of circular conical shells under uniform external pressure

The article reports on two theoretical investigations and an experimental investigation into the collapse of six circular conical shells under uniform external pressure. Four of the vessels collapsed through plastic non-symmetric bifurcation buckling and one vessel collapsed through plastic axisymmetric buckling. A sixth vessel failed in a mixed mode of plastic non-symmetric bifurcation buckling, combined with plastic axisymmetric buckling. The theoretical and experimental investigations appeared to indicate that there was a link between plastic non-symmetric bifurcation buckling and plastic axisymmetric buckling. The theoretical investigations were via the finite element method and were used to provide a design chart for these vessels.     

Laplace transform finite volume modeling of water hammer along fluid–structure interaction

Water hammer or propagation of pressure waves generates profound forces through pipelines of industrial high pressure processes which causes structural vibration of the pipe in both radial and axial directions. To model the sudden rupture of a pipeline system the fluid–structure interaction, FSI, is taken into account by coupling the structural vibration equations to the fluid dynamic equation. In this paper, Laplace transform finite volume, LTFV, which is a new technique along the finite element method is developed to treat fluid transient and the structural vibration equations respectively.To evaluate the numerical results, a Thermal Hydraulic Test Loop (THTL facility) which has been designed and constructed for experimental research on the physical phenomena, characteristics and performance of the safety systems involved in plants is used. To conduct tests for representing a sudden break condition in the loop, the THTL facility has been equipped by devices and sensors to record pressure and vibration signals during simulated accidents. Under steady condition, by an electrical signal an electric valve, Break valve, is opened and simultaneously pressure along pipe vibration signals close to valve is recorded. Comparing the experimental data to results from numerical modeling validated the implemented method.     

一种仿生壶腹嵴的振动传感特性研究

为了研究人耳半规管中壶腹嵴的振动传感特性,本文采用表面对称电极含金属芯PVDF纤维(SMPF)传感器,代替人体纤毛细胞感受器,并模仿人体壶腹嵴的结构,设计制备了一种仿生壶腹嵴。根据压电方程和振动理论,建立了仿生壶腹嵴的振动传感理论模型。搭建了实验系统,测试了仿生壶腹嵴的振动传感功能。实验结果表明,仿生壶腹嵴在液体压力作用下可以产生相应的变形,而通过SMPF的输出电荷信号,可以感知仿生壶腹嵴受到的振动激励,包括正弦与冲击振动的波形、频率和幅值。实验结果验证了理论模型,同时验证了人体半规管中,壶腹嵴具有振动感知的能力和作用。     

外流作用下管道流固耦合非线性动力学研究进展

管道广泛应用于海洋、核电以及航空航天等重大工程中,是采油平台、蒸汽发生器等重要工程装备的关键结构之一.当有外部流体经过时,管道会发生流固耦合振动行为,是导致重大装备振动破坏和失效的重要原因之一,已成为重大工程设计必须解决的关键问题.本文针对外流作用下柔性管道流固耦合非线性动力学机理这一科学问题,梳理了国内外学者的重要研究成果,重点分析了柔性管道分别在横向外流和轴向外流作用下的流固耦合非线性振动行为.从实验研究、仿真分析和理论建模等方面进行了深入地探讨,揭示了外部流体对管道动力学行为的影响机制.最后,对当前国内外研究现状进行了简要的总结,并给出了这一研究仍存在的难点与挑战.     

An accurate approximate formula for the natural frequencies of sandwich beams

The flexural beam approximation commonly used for evaluating the vibration frequencies of sandwich beams is shown to be of limited applicability. A formula proposed for evaluating the fundamental frequencies of cantilever sandwich beams is generalised for higher modes and other boundary conditions, and is shown to be in very good agreement with experimental and theoretical values.     

基于加速度传感器反馈的丝杠传动系统接触力控制

针对丝杠传动系统从自由空间运动过渡到约束空间力控制过程中,接触不同环境刚度时接触力的动态特性是不同的,并且存在冲击、高频振动甚至不稳定,以及稳态力跟踪阶段的扰动引起的不稳定问题,提出用加速度传感器反馈来增加系统力控制的阻尼,抑制在力控制的接触过渡过程和力维持跟踪过程中因为碰撞和外部扰动等原因产生的高频振动,克服单纯速度反馈控制带宽比较窄的局限性,增加系统的稳定性.建立了基于多传感器的实验平台,进行了接触力控制的实验比较研究,实验结果表明该方法是可行的.     

Numerical and experimental study of a vibration driver due to electromagnetic forces on a rotary permanent magnet

This paper presents the numerical modeling and the experimental verification of a rotary permanent magnet driver excited by an electromagnetic field. As the electromagnetic torque of the permanent magnetic rotor is a nonlinear function of external electromagnetic field and its rotation angle, it is difficult to compute it directly by using common electromagnetic analysis methods. Based on the concept of equivalent surface magnetic charge, the research explores a numerical method for calculating the drive torque of the rotary permanent magnet submitted to an electromagnetic field, and meanwhile, establishes the theoretical model for the electromagnetic torque due to the combined magnetic fields versus the excitation current and the rotation angle of the permanent magnet. This model may present the quasi-static and dynamic vibration drive process of the rotary permanent magnet under the electromagnetic field excitation. The research finally validates the theoretical analysis and the numerical modeling by experimental tests in terms of accuracy and feasibility of the driving system.     

Comparison between optically excited vibrations of silicon cantilever and bridge microresonators

A comparison, of the optically excited vibrations, including self-oscillations, of cantilever and bridge silicon microresonators is presented. The theoretical analysis and experimental investigations show that not only has the cantilever microresonator a greater vibration amplitude than the bridge structure, but also its resonance frequency is independent of the strain induced by boron doping and the deformation of the silicon wafer caused by assembly. These advantages could be of great value in achieving practical all-fibre optically addressed silicon microresonator sensors, which are used to measure physical parameters except for force or pressure, such as small masses, chemical components, vibration, temperature, etc.     

矩形脉冲激励的SMA振子的瞬态响应分析

研究了矩形脉冲激励下SMA振子瞬态响应的全局特性.采用多项式形式的本构方程描述SMA弹簧的恢复力,以此建立SMA振子的动力学方程;且将矩形脉冲激励的SMA振子的瞬态响应响应分为两个阶段:第一阶段是在外力恒定时的衰减振动;第二阶段是没有外力激励的衰减振动.讨论了平衡点的数目,给出了SMA振子的在不同条件下的相平面和时间历程图.最后,采用数值解验证理论分析结果的有效性.研究结果表明,对于不同强度及宽度的矩形脉冲激励,SMA振子会收敛到不同的稳定平衡点,收敛时间较短.     

Vibration and noise characteristics of flap type olive harvesters

The object of this study was to measure and evaluate the vibration and noise characteristics of five flap type portable harvesters using for olive harvesting and their effect on operator health during harvesting time.The vibration and sound pressure levels of different harvesters were measured at both idling and full load conditions. The vibration values of harvesters were measured and analyzed for both right and left hands and the sound pressure level was measured at ear level of the operator. The vibration total value was expressed as the root-mean-squares (rms) of three component values. The results indicated that in 10% of the exposed population traumatic vasospastic disease (TVD) appeared after 0.7–7.1 years for the left hand, 1.0–4.7 years for the right hand of the operator in continuous use of these harvesters, under usual working conditions.The sound pressure values at operator’s ear level of harvesters were found below risk levels when compared with ILO standards.     

FBG振动参数监测试验研究

通过对光纤光栅传感器进行理论分析,建立了由测量光纤光栅传感元件的波长而得到振动参数的理论模型,介绍了测量系统信号处理,并对光纤光栅与加速度计的试验结果进行了比较。     

Measurement and modeling of pulsatile flow in microchannel

An experimental study of pulsatile flow in microchannel is reported in this paper. Such a study is important because time-varying flows are frequently encountered in microdevices. The hydraulic diameter of the microchannel is 144 μm and deionized water is the working fluid. The pressure drop across the microchannel as a function of time is recorded, from which the average and r.m.s. pressure drops are obtained. The experiments have been performed in the quasi-steady flow regime for a wide range of flow rate, frequency of pulsations, and duty cycle. The results suggest that the pressure with pulsations lies between the minimum and maximum steady state pressure values. The average pressure drop with pulsation is approximately linear with respect to the flow rate. The theoretical expression for pressure has also been derived wherever possible and the experimental data is found to lie below the corresponding theoretical values. The difference with respect to the theoretical value increases with an increase in frequency and a decrease in flow rate, with a maximum difference of 32.7%. This is attributed to the small size of the microchannel. An increase in frequency of square waveform leads to a larger reduction in pressure drop as compared to rectangular waveform, irrespective of the duty cycle. The results can be interpreted with the help of a first-order model proposed here; the model results are found to compare well against the experimental results. A correlation for friction factor in terms of the other non-dimensional governing parameters is also proposed. Experimental study of mass-driven pulsatile flow in microchannel is being conducted for the first time at these scales and the results are of both fundamental and practical importance.     

基于MEMS的参量放大的设计与实现

参量放大效应是一种非线性振动放大效应,利用该效应可以极大地增加MEMS陀螺和加速度计等谐振式传感器的振幅,从而提高谐振式传感器检测灵敏度和信噪比。根据理论分析和有限元仿真结果,设计了一种MEMS参量放大结构。该结构采用SOG工艺加工,在950Pa左右的气压环境下对该结构进行了实验研究,并得到了该结构参激电压、相位与放大倍数之间的关系。实验结果表明：参量放大效应的实测结果与理论分析结果吻合很好,当参数激励电压为5.7V时,参量放大倍数超过50倍,大幅提高了结构的振幅,为以后应用参量放大效应提高MEMS惯性仪表性能提供了一种新方法。     

基于频域辨识模型的新型幂次趋近律滑模控制

针对刚柔耦合系统传统理论建模过程复杂、模型不准确问题,采用频域子空间方法来辨识实验系统中的电机模型和压电片模型。同时针对传统趋近律的到达时间较长以及抖振问题,提出一种新型幂次趋近律的滑模控制。理论分析表明在不影响抖振情况下可缩短到达时间和扩大传统幂次趋近律参数α的范围。考虑柔性梁振动特性对系统性能的影响,采用子滑模面的方法来设计滑模控制器。最终,实验结果表明所设计控制器能够实现对中心刚体角度的快速跟踪,并且能够快速抑制柔性梁的振动。     

On the forced vibration of the fiber partially immersed in fluid

In this paper an experimental and theoretical investigation of the forced vibration of a partially immersed fiber has been carried out. An optical method utilizing a forward light scattering pattern has been used to detect a small (<1.0 μm) vibration amplitude of the fiber. The physical and mathematical model of the partially immersed fiber vibration has been put forward. Based on an analytical solution of the model, natural frequencies of the partially immersed fiber vibration have been found; they are consecutive positive roots of the transcendental equation. An “effective” speed of the wave propagation over the fiber has been introduced, which allows one to find the physical meaning of normal modes of the partially immersed fiber vibration. Theoretical predictions agree well with experimental data. The sensor exhibits an excellent sensitivity and could be used for measuring physical properties of fluids and liquid level.     

Polyisoprene-nanostructured carbon composite – A soft alternative for pressure sensor application

Latest related research shows natural polyisoprene-nanostructured carbon composite (PNCC) as a promising piezoresistive material for soft pressure sensors. The main advantages of PNCC over conventional sensors are exceptional sensitivity in pressure range from 0.1 to 10 bar and possibility to be embedded into completely soft (hyper-elastic) structures.In this work we have elaborated a completely soft (hyper-elastic) PNCC pressure sensor prototype, made using functional multi-layer approach, when elementary layers of PNCC with different conductive filler concentration are cured together and form a uniform sensor body with integrated soft (hyper-elastic) electrodes. We proposed also a theoretical model to explain the observed positive piezoresistivity and used it for fitting of our experimental results.The prototype system elaborated could be used for counting interface events between sensor and external environmental factor. The achieved result could be a step towards the artificial skin, capable to sense non-destructive interaction with the external influence.     

Active vibration control of a flexible beam,based on flow source control

This paper presents a new method of actively controlling the vibration of a flexible beam by using a rigid body motion actuator based on flow source control. The proposed flow source controller generates a control input of a rotating angle instead of a torque that acts as an effort source control input. It is shown that the proposed flow source control improves the vibration suppression performance when disturbance forces such as friction forces are involved in the rigid body motion dynamics. The stability and the robustness to disturbance of the flow source controller are compared with an effort source controller. An optimal control theory is used to design the flow source vibration controller and a conventional PD controller is used for the motor position controller. Computer simulations and experimental results on a rotating beam system show that the vibration control performance achieved by the proposed flow source control method is superior to that of an effort source control method.     

基于啮合频率调制现象的齿轮振动信号辨识

齿轮是大多数旋转机械设备的核心零部件,也是主要的振动来源.为了评估齿轮箱的健康状态,从机械系统信号中提取齿轮箱的振动成分具有重要意义.齿轮的啮合频率包含了反映其运行状态的丰富信息,是进行齿轮在线监测和故障诊断的前提条件.通过理论分析和试验验证,解释了啮合频率调制现象,也就是当齿轮在重载条件下工作时,啮合频率会以啮合冲击的形式被调制到高频共振区.基于此现象,提出了一种齿轮振动信号辨识方法.在此方法中,通过迭代获得啮合能量比图,以确定啮合共振频带.此方法的性能通过试验台试验和叉车现场试验进行了验证.通过与快速谱峭度方法进行对比,证明所提出的方法适用于齿轮振动信号辨识,尤其是当齿轮处于重载条件时.     

Performance‐based near‐optimal vibration control for nonlinear offshore platforms with delayed input

This paper investigates the vibration control problem for offshore platform, where the nonlinear characteristics, delayed input and external wave force are considered in time domain. By introducing a delay‐free reconstructional vector and applying the maximum principle, the original vibration problem for offshore platform is formulated as a nonlinear two‐point‐boundary‐value (TPBV) problem with delayed items. The major contribution of this paper is that a performance‐based near‐optimal vibration control strategy is proposed by solving this nonlinear TPBV problem, which includes a feedback item with offshore platform system state, a feedforward item with wave force state, and a compensator for nonlinear and delayed items with infinite supersensitive component. In particular, the designed compensator is calculated from two group series of linear differential equations by introducing a parameter for expending the Maclaurin series of nonlinear and delay items. Meanwhile, an iterative algorithm is designed to make the proposed vibration control scheme computable based on the control performance in each iterative procedure. Finally, experimental results show that the displacement, velocity and performance index of an employed offshore platform achieved small values under the proposed control strategy and designed algorithm.