Electrostatic microgenerators of energy with a high specific power

Operation regimes of an electrical energy microgenerator based on a multilayered structure consisting of a metal, a dielectric with a built-in charge, a microgap, and a moving electrode, whose operation principle is based on electrode vibrations in the force field of the space charge of the dielectric, are analyzed. Specific features of electromechanical conversion of energy due to vibrations of the electrode surface in submicron gaps are found. It is demonstrated that such microgenerators in the low-frequency regime (10–100 Hz) can produce power sufficient for providing energy for modern microcircuits (up to 1–10 mW/cm²) without using any other power sources.     

Direct electrodynamic electromagnetic-acoustic transformation in a normal polarizing field: III. Dependence of the acoustic field on macroscopic parameters of transformation medium

Frequency dependences of shear displacements in solids with different conductivities are numerically calculated on the basis of exact analytical expressions for projections of elastic displacements in a solid. It is shown that shear displacements in well-conducting materials at not too high quasistationary frequencies are independent of the electrical conductivity. This is determined by both the skin effect and the fact that the main agent responsible for transferring the energy of a source-generated quasi-stationary field is its magnetic component. In relatively weakly conducting materials, displacements may be proportional to the electrical conductivity. For well-conducting materials, a good approximation containing no integrals and allowing determination of both the transformation efficiency and angle of injection of elastic vibrations near the radiation-stabilization point is obtained.     

Nominal tracking simulation in conditions of mechanical vibrations impact on the manipulation robots

This paper presents a procedure for the calculation of manipulator tip deviations from a nominal trajectory in conditions of mechanical vibrations impact, which are transmitted through the basis on the carrying structure of manipulator. Vibrations are simulated by a simple sine function or by “white noise”. For “white noise” simulation the system program RAN is used which generated a random number in the interval [0, 1]. This paper also presents the real vibrations plots recorded on tape which could be utilized after A/D conversion in a robot design phase.     

The vibrations of a textile machine rotor with nonlinear characteristics

In this paper the free vibrations of a textile machine rotor which rotates with constant angular velocity are considered. The rotor consists of a weightless shaft and a disc with variable mass. The force in the shaft is assumed to be nonlinear. Mass of the disc is varying due to the winding up of the textile band. Severe vibrations occur due to the mass varying. When the nonlinearity is small and the variation of the mass is a function of “slow time,” the vibrations can be denoted not only numerically but also analytically by use of the multiple scales method. The results are compared.     

线切割加工中钼丝振动主动控制的试验研究

分析快走丝电火花线切割机床加工过程中电极丝振动的产生机理，指出钼丝振动所反映的主要模态是原运动弦系统二阶以上的固有模态以及各种强迫振动模态。由试验所得的频谱图上看到，在线切割加工中钼丝振动的固有频率（高频）与走丝系统的其他振动频率（低频）是完全分离的，且低频振幅较大。由此得出控制丝振的关键在于的抑制钼丝的低频振动。提出丝振主动控制策略，机理性试验证明：施加主动控制后，丝振振幅为常规被动控制的十几分     

Model-based dynamic compensation of load cell response in weighing machines affected by environmental vibrations

This work proposes and validates experimentally a model-based scheme for the compensation of environmental vibrations affecting load cell measurements in automatic weighing machines. Weighing machines are often adversely affected by low frequency vibrations which may arise from the coupled effects of machine frame flexibility and the excitation induced by internal (inertial) or external (impact) vibration sources. These vibrations are generally named “environmental vibrations”, since they seem to arise from the environment around the machine. Environmental vibrations have a detrimental effect on load cell responses and can in turn deteriorate machine performances. It is usually ineffective to try overcoming this problem by low-pass filtering load cell measurements: low cut-off frequencies usually downgrade machine speed by both introducing delay and increasing filtered signal rise time. Since automatic weighing machines need to operate at ever increasing speed, alternative approaches must be investigated. In this work it is suggested to make use of the mechanical models of the weighing machine and the load cells to process supplementary accelerometer measurements and compute an effective compensation of the effect of environmental vibrations on load cell response. The technique is here applied to a multi-head weighing machine in order to prove its effectiveness and implementability in industrial devices with real-time controllers.     

Regenerative semi-active vortex-induced vibration control of elastic circular cylinder considering the effects of capacitance value and control parameters

A regenerative semi-active control system based on self-tuning Fuzzy proportional-derivative (PD) control strategy is applied to suppress the vortex-induced vibrations (VIV) of an elastically supported circular cylinder at low Reynolds numbers. Of particular interest was the effect of control parameter and capacitance on the VIV reduction and energy regeneration capabilities of adopted semi-active control system. A collaborative simulation which couples a Fuzzy PD controller along with the adjustable electromagnetic (EM) damper and corresponding energy harvesting circuit (implemented in MATLAB/Simulink) to the computational fluid dynamic (CFD) plant model (implemented in Fluent) is employed. It appears that the cylinder displacement amplitude, capacitor charging speed, and maximum stored electrical energy vary with the controller parameters and capacitance value. It is shown that the selected regenerative semiactive control system can store maximum energy in a capacitor in prescribed limiting time, along with the highest level of cylinder oscillation reduction which is the primary goal of current work.     

An experimental study of accelerating phase change heat transfer

The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). Furthermore, the present study considered constant heat flux boundary conditions unlike many of the previous researches adopted constant wail temperature conditions. Therefore, in the present study, modified dimensionless parameters such as Ste^* and Ra^* were used. Also, general relationships between melting with ultrasonic vibrations and melting without ultrasonic vibrations were established during the melting of PCM. Experimental observations show that the effect of ultrasonic vibrations on heat transfer is very important throughout the melting process. The results of the present study reveal that ultrasonic vibrations accompany the effects like agitation, acoustic streaming, cavitation, and oscillating fluid motion. Such effects are a prime mechanism in the overall melting process when ultrasonic vibrations are applied. They enhance the melting process as much as 2.5 times, compared with the result of natural melting. Also, energy can be saved by applying ultrasonic vibrations to the natural melting. In addition, various time-wise dimensionless numbers provide conclusive evidence of the important role of ultrasonic vibrations on the melting phenomena.     

Self-diagnosis of smart structures based on dynamical properties

When we talk about “smart structures” we can think about different properties and capabilities which make a structure “intelligent” in a certain sense. Originally, the expression “smart” was used in the context that a structure can react and adapt to certain environmental conditions, such as change of shape, compensation of deformations, active vibration damping, etc. Over the last year, the expression “smart” has been extended to the field of structural health monitoring (SHM), where sensor networks, actuators and computational capabilities are used to enable a structure to perform a self-diagnosis with the goal that this structure can release early warnings about a critical health state, locate and classify damage or even to forecast the remaining life-time. This paper intends to give an overview and point out recent developments of vibration-based methods for SHM. All these methods have in common that a structural change due to a damage results in a more or less significant change of the dynamic behavior. For the diagnosis an inverse problem has to be solved. We discuss the use of modal information as well as the direct use of forced and ambient vibrations in the time and frequency domain. Examples from civil and aerospace engineering as well as off-shore wind energy plants show the applicability of these methods.     

Using antenna arrays for reference-free measurement of speed of ultrasound and thickness of concrete articles

A reference-free method is considered for concurrent measurement of the speed of ultrasonic vibrations and the thickness of concrete constructional products with ultrasonic antenna arrays that use the “focusing to a plane” algorithm.     

A low power consumption control scheme: application to a piezostack-based active mount

Piezostack-based active mounts have shown great efficiency for vibration control in a wide frequency range. In this paper, we investigate the performances of the global semi-active control strategy presented by Ichchou et al. [1] for a control system consisting of an active mount and a supported mass. The control strategy allows extracting vibrations energy of the supported mass, storing it in accumulators to be reused for powering in part the actuators (two piezostacks). Consequently, energy needs are reduced versus good control performances comparable to those of the active control based on the negative velocity feedback. The performances of the controller are evaluated in both frequency (transmitted force) and time (acceleration) domains which show that vibrations of the supported mass due to base excitations are efficiently attenuated with the proposed law. An energetic analysis confirms the reduced energy requirement compared to the active scheme.     

带颗粒减振剂碰撞阻尼的减振特性

传统碰撞阻尼的工作原理大都建立在动量交换、摩擦耗能的范围内,动量交换并没有将振动能量永久地消耗掉,摩擦对于高频振动具有较好的减振效果,而对于低频振动效果较差。为此提出一种以微细颗粒塑性变形将振动能量永久消耗掉的新型的碰撞阻尼,称为带颗粒减振剂碰撞阻尼。分别对在传统单体碰撞阻尼和带颗粒减振剂碰撞阻尼作用下悬臂梁减振效果进行试验研究。试验结果表明：以微细颗粒塑性变形消耗振动能量的带颗粒减振剂碰撞阻尼具有优秀的减振效果,远远超过传统单体碰撞阻尼器。带颗粒减振剂碰撞阻尼在低频振动(低于50 Hz)中仍然具有良好减振性能,这是其他碰撞阻尼所缺乏的特性。机械振动多为低频振动,带颗粒减振剂碰撞阻尼具有广阔的应用前景。     

Design and analysis of a new magneto rheological damper for washing machine

In this article, a new magneto rheological (MR) sponge damper is proposed for suppression of vibrations in a washing machine. The article presents design optimization of geometric parameters of MR sponge damper (MRSD) using the finite element analysis (FEA) and first order derivative techniques for a washing machine. The article explains the hysteresis behavior and the relationship of damping force with input current for the proposed MRSD. Moreover, the characteristics of the MRSD such as energy dissipation and equivalent damping coefficient are investigated experimentally in terms of input current and excitation amplitude. The passive dampers installed in washing machine are ineffective in reducing unwanted vibrations at resonant frequencies due to real time unbalanced mass. For this purpose, a test setup is established in order to compare the performance of passive dampers with the proposed MRSDs in a washing machine. It is noticed that MRSDs reduce average vibrations of 75.61 % in a low frequency band, whereas in a high frequency band, the MRSDs lessen average vibrations of 30.57 % in a washing machine. In order to determine the performance of proposed design MRSD, a detailed comparison of the performance parameters, such as total damping force, passive force, maximum average vibrations after suppression by MR dampers, maximum current and power ratings is provided with the existing designs of MR damper for washing machine from the literature.     

直动型溢流阀的流固耦合建模与动态特性研究

直动型溢流阀被广泛用于水下动力设备的供能调节,但下潜水深的变化时常使得其动态稳定性无法保证,以至于在到达一定水深之后,溢流阀阀口会出现异常的压力波动现象,影响其正常的工作状态。为此,开展流固耦合分析,建立了直动型溢流阀的两自由度动力学模型。通过无因次化后模型的求解,实现了对试验测试信号中振动深度的准确复现,并进一步分析了溢流阀阀芯的轴向和纵向振动状态随水深的变化,以及在部分深度下阀芯振动的多稳态共存现象。所建立的动力学模型中的非线性因素为试验测试信号中发现的压力波动特征提供了理论解释,从而为通过对溢流阀的优化设计来解决溢流阀的大振幅脉冲振动提供了模型支撑。     

滚动轴承早期缺陷振动的简化模型

建立了滚动轴承早期缺陷振动的线性简化模型,依据该模型分析了滚动轴承早期缺陷引起振动的特性。理论分析和实际测量表明:滚动轴承早期缺陷激励出轴承的固有振动,产生了脉冲冲击波;非周期早期缺陷振动为正常振动信号叠加一个或几个离散脉冲冲击波,产生垃圾音,周期早期缺陷振动为正常振动信号叠加一串串周期脉冲冲击波,产生内圈伤音、外圈伤音或滚动体伤音;脉冲冲击波是滚动轴承早期缺陷引起的异常声的主要原因。     

基于ZigBee技术的无线电能采集终端的设计

本文提出了一种基于ZigBee技术实现的三相电能无线采集终端的设计方案,分析了从电能测量到数据收发过程的系统工作原理。在电能测量部分,利用ADI公司的一种高精度三相电能测量IC ADE7758作为电能测量芯片,使用Microchip公司的高性能单片机PIC18LF4620作控制器。在数据收发部分采用支持IEEE802 15．4无线通信协议的ZigBee技术,用Chipcon公司的射频芯片CC2420,实现采集的电能数据的无线收发通信。该系统可以实现对三相电能的无线自动采集功能。     

Electrical contact resistance for a conductive Velcro system

Conductive Velcro fasteners are employed as a joining material for various types of connections due to their detachable properties, especially when an electrical connection is established. Due to microscopic actual contact spots between the fibers and hooks in the Velcro joints, a large electrical contact resistance is established that could cause heat and potentially short-circuit. In this study, the electrical contact resistance behaviors in the conductive Velcro are estimated according to the electrical load, frequency and load amplitude. The wear behavior due to these effects is investigated after long exposure to dynamic loading under a specific frequency at a low load amplitude.     

Invited review article: Photopyroelectric calorimeter for the simultaneous thermal, optical, and structural characterization of samples over phase transitions

The study of thermophysical properties is of great importance in several scientific fields. Among them, the heat capacity, for example, is related to the microscopic structure of condensed matter and plays an important role in monitoring the changes in the energy content of a system. Calorimetric techniques are thus of fundamental importance for characterizing physical systems, particularly in the vicinity of phase transitions where energy fluctuations can play an important role. In this work, the ability of the Photopyroelctric calorimetry to study the versus temperature behaviour of the specific heat and of the other thermal parameters in the vicinity of phase transitions is outlined. The working principle, the theoretical basis, the experimental configurations, and the advantages of this technique, with respect to the more conventional ones, have been described and discussed in detail. The integrations in the calorimetric setup giving the possibility to perform, simultaneously with the calorimetric studies, complementary kind of characterizations of optical, structural, and electrical properties are also described. A review of the results obtained with this technique, in all its possible configurations, for the high temperature resolution studies of the thermal parameters over several kinds of phase transitions occurring in different systems is presented and discussed.     

铝板带材轧机振动测试分析

针对某铝板热轧机严重振动问题，测试了轧辊垂直振动、主传动系统扭振和液压压下系统压力与主电机电枢电流等参数，分析了其振动特点。采用拟三维有限元模型分析了同系统的固有特性。测试与分析表明，铝板热轧机振动的主要形式是强迫振动，主要振因来源于工作辊轴承和支承辊轴承特征振动。     

覆盖件模具拼接特征对球头刀铣削振动的影响

为了分析曲面拼接特征对振动的影响,建立了考虑拼接特征、曲面特征的未变形切屑厚度模型;基于曲面拼接区的未变形切屑厚度建立了考虑时滞变化的铣削动力学模型,通过数值计算综合分析了过拼接缝时冲击振动、刀具轴向位置角、拼接缝宽度对铣削振动的影响;最后基于淬硬钢曲面拼接铣削实验验证了考虑曲面拼接特征的铣削振动预测模型的准确性,并基于不同拼接特征下的铣削振动计算出了相应的加速度信号幅值和分形维数。研究结果表明:淬硬钢曲面拼接特征使铣削振动的非线性特征减弱,某一频段的振动能量集聚,据此情况可分析出不同拼接特征下的最佳加工工艺参数。