有限元在粘弹性细棒动力学参数反演中的应用

粘弹性材料具有良好的阻尼性能,在工程振动与噪声处理上的应用非常广泛。利用粘弹性材料进行阻尼结构设计并预测其动力学特性,需要知道准确的动力学参数。回顾粘弹性材料动力学参数测试的经典方法,并着重介绍共振法测试技术。研究共振法测试中细棒的动力学响应与动力学参数间的关系,在此基础上,基于共振法测试数据和有限元仿真,提出一种反演粘弹性材料动力学参数的新方法。首先根据幅值比反演出损耗因子,再根据共振频率反演出储能模量。通过具体算例验证可知,反演得出的动力学参数的相对误差均在4 % 以内,该反演方法不仅结果收敛、准确可靠且反演速度快,为在连续频率范围内的动力学参数反演奠定基础。     

角接触球轴承动态特性参数测试方法

基于共振法原理,提出了采用轴承组件的方法识别和测试轴承动态刚度和阻尼参数。建立了轴承组件等效参数识别模型,搭建了简易试验装置,测试了7602050TVP型轴承的刚度和阻尼,并进行了轴承组件模态仿真及分析。试验结果和模态仿真结果对比表明,采用轴承组件等效参数识别模型,轴承动态刚度和阻尼识别误差小,精度高。     

超声共振频谱法测量固体材料的弹性模量

弹性模量是工程材料重要的性能参数,是反映材料抵抗弹性变形能力的指标。弹性参数是温度的函数,准确测量变温环境下固体材料的弹性参数,对热工、材料、航空航天、工业应用方面有非常重要的意义。然而,国内缺乏变温环境下准确测量固体材料弹性参数的仪器。本文基于超声共振频谱法原理,研制了可在变温条件下工作的超声共振频谱法测量系统,系统包括超声传感器、声学发射和接收系统、恒温系统以及数据采集和分析系统。在30℃下分别测量了四种不同能量品质因数（Q值）的固体材料的弹性参数,测量的共振峰匹配误差（RMS）可小于0.04％,与国外先进商业仪器的测量结果有良好的一致性,对超声信号激励和接收方式做相应改变,可扩展该装置的测温范围。     

基于三次迟滞模型的超声电机圆环定子主共振响应

摘 要 将改进的三次多项式迟滞模型用于描述压电材料的弹性迟滞非线性特性,建立了压电材料二维非线性本构关系。根据Hamilton原理和Rayleigh-Ritz假设模态方法,建立了不考虑界面力时旋转行波超声电机圆环定子驻波振动的非线性动力学模型。用多尺度法求解定子的一次近似主共振响应,通过定常解分析,发现定子主共振响应中存在振幅跳跃和多解现象,着重分析了压电材料弹性迟滞非线性参数对主共振响应的影响。结果表明,迟滞参数a使幅频响应曲线左偏并出现多解现象,迟滞参数a和b同时影响系统响应振幅的大小。数值计算验证了解析解的正确性。从理论上揭示了压电材料弹性迟滞非线性对圆环定子主共振响应的影响,为超声电机的优化设计和控制提供了理论依据。     

基于共振法的黏弹性细棒力学参数宽频测试

在黏弹性细棒力学参数共振法测量的基础上提出了一种宽频测试方法。激振器产生了波形可控的宽频短脉冲信号,对黏弹性细棒进行纵向激励。利用激光测振仪分别测量激振器和细棒自由端的振动速度响应,通过自由端与激振端响应信号在宽频范围的幅值比和相位差,根据共振法原理可解算共振频率处的储能模量和损耗因子。另外,对测试过程进行了有限元仿真。结果表明:利用该测试方法,通过较少次数测试可得到与黏弹仪数据吻合的动力学参数,而有限元分析可对测试提供指导。     

粘弹性阻尼材料力学参数测试实验用双边附加自由结构阻尼试件设计方法研究

悬臂梁弯曲共振法测量粘弹性阻尼材料力学参数的实验中常以双边附加自由结构阻尼试件为实验对象。实验中试件设计的合理程度直接影响实验的测试精度。为了指导试件设计,通过灵敏度分析提出了影响系数的概念,并将其应用于分析试件的厚度比、共振频率比、密度比、损耗因子等参数的测量误差对粘弹性材料力学参数测试精度的影响中,进而对试件的设计提出一些有重要意义的技术规范。最后,基于悬臂梁弯曲共振法获取粘弹性材料力学参数的实验,分析了双边自由阻尼结构试件的适用范围。     

粘弹性阻尼材料阻尼处理及在船体振动控制中的应用

介绍了基于复刚度原理推导的自由及约束阻尼结构损耗因子理论评估计算公式,并对相关参数变化影响规律进行了理论分析,初步确定了阻尼结构形式及材料参数。为评估阻尼设计方案对实际船舶舱室的减振降噪效果,建立船舶局部舱室结构的1∶2.5缩比模型结构,采用模态锤击测量方法,对阻尼处理前、后舱室振动及噪声特性展开试验研究。试验结果表明,约束阻尼处理能明显抑制结构的模态共振。在2.5 mm厚舱室围板粘接1.7 mm厚约束阻尼层后,最大减振量为11 d B,最大降噪量达到9 d B。最后,对约束阻尼处理后的航行船舶进行实船噪声测试,噪声测试结果均满足IMO-468噪声指标要求。     

适用于生物薄膜材料的压电驱动高精度疲劳试验机构

为研究生物薄膜材料的疲劳行为及其机制，对其进行疲劳测试，利用压电振子作为疲劳试验机构的驱动力源，并基于系统共振方法设计了适用于昆虫薄膜材料的疲劳试验机构．首先，介绍压电驱动式疲劳试验机构的工作原理，然后建立动力学模型，获得机械系统的动态特性，并制作了样机．最后利用样机在蜻蜓翅翼上施加给定循环特性R=0．1的交变应力，通过对试验结果的观察，分析了蜻蜓翅翼由于疲劳破坏所引起的一系列裂纹产生、扩展的机理．制成的样机满足对生物薄膜材料进行疲劳试验所需的载荷小、加栽精度高、共振稳定可靠和抗干扰能力强等要求．     

采用Hot Disk测量岩土热物性的实验研究

分析比较当前几种材料热物性参数测试方法的优缺点,阐述了基于瞬态平面热源法的Hot Disk热常数分析仪的测试原理,并利用参考物质对仪器准确性及重复性进行了验证,同时探究了岩土样品含水率和密度对试验测试结果的影响.结果表明:Hot Disk热常数分析仪具有很好的准确性和重复性,适用于岩土热物性参数的测试;含水率对岩土热物性具有显著且规律性影响;密度对测试结果有影响,但影响有限.最后给出了适合该仪器的测试条件和建议.     

四边简支FGM矩形板非线性振动中的内共振

基于Reddy高阶剪切变形板理论、Galerkin法与Hamilton原理,在同时考虑几何非线性、材料物性参数随温度变化且材料组分沿厚度方向按幂律分布的情况下,通过理论推导建立起四边简支功能梯度材料矩形板受面内与横向简谐载荷共同作用下的非线性运动控制微分方程;在此基础上建立了受热载荷作用下的具有二阶模态的非线性运动控制微分方程。分析了面内静态载荷对于给定参数下系统不同内共振的影响,发现随着面内静态载荷的不同系统会出现1:1、1:2 与1:3的内共振关系。计算结果发现由于不同内共振关系对应的面内静态载荷不同,不同内共振关系下所求得的一阶频率大小各不相同,所对应的瞬态响应也会不同。     

Analysis of microwave ovens loaded with lossy process materials using the transmission-line-matrix method

The transmission-line-matrix (t.l.m.) numerical analysis technique is used in this paper to evaluate resonant frequencies and field parameters of the generated modes in microwave ovens loaded with lossy process materials. Analysis is made for the variation of resonant frequencies with the loss factor of the loading material. Temperature rise profile through the load is predicted from the calculated results of field parameters of sustained modes. The demonstrated data are for the dimensional parameters of a rectangular cavity of a commercial microwave oven operating at the standard heating frequency 915 MHz.     

Automatic Monitor for Microwave Resonators

An instrument was developed to simultaneously measure both the resonant frequency and the bandwidth (which is related to the loaded quality factor) of a resonant microwave cavity under continuous operating conditions. Voltages proportional to both parameters monitored are obtained at the output. The principle of operation, the main causes of error and the accuracy obtained for actual measurements are presented. This instrument could easily be connected to a digital data-acquisition system; it could also be adapted to study resonance phenomena at frequencies other than microwaves.     

Wavelet neural network control for linear ultrasonic motor drive via adaptive sliding-mode technique

A wavelet neural network (WNN) control system is proposed to control the moving table of a linear ultrasonic motor (LUSM) drive system to track periodic reference trajectories in this study. The design of the WNN control system is based on an adaptive sliding-mode control technique. The structure and operating principle of the LUSM are introduced, and the driving circuit of the LUSM, which is a voltage source inverter using two-inductance two capacitance (LLCC) resonant technique, is introduced. Because the dynamic characteristics and motor parameters of the LUSM are nonlinear and time varying, a WNN control system is designed based on adaptive sliding-mode control technique to achieve precision position control. In the WNN control system, a WNN is used to learn the ideal equivalent control law, and a robust controller is designed to meet the sliding condition. Moreover, the adaptive learning algorithms of the WNN and the bound estimation algorithm of the robust controller are derived from the sense of Lyapunov stability analysis. The effectiveness of the proposed WNN control system is verified by some experimental results in the presence of uncertainties.     

Low Temperature Elastic Constants of Polycrystalline MgB2

We have used a resonant ultrasound spectroscopy technique to measure the bulk and shear modulus of fully dense, polycrystalline MgB₂ between 4 and 300 K. Both moduli show good agreement with published first principle calculations. The internal friction shows a broad maximum around 40 K.     

Low Temperature Elastic Constants of Polycrystalline MgB2

We have used a resonant ultrasound spectroscopy technique to measure the bulk and shear modulus of fully dense, polycrystalline MgB₂ between 4 and 300 K. Both moduli show good agreement with published first principle calculations. The internal friction shows a broad maximum around 40 K.     

Dynamic in-plane resonant characteristics of piezoceramic and piezolaminated composite plates.

Piezolaminated composite plates have received considerable attention in various industrial applications due to their intelligent characteristics. In this investigation, two experimental measurement techniques are used to determine the in-plane resonant vibration of angle-ply laminated composites embedded with a piezoceramic layer (piezolaminated plates) for different stacking angles. The first method is a full-field optical technique, which is called the AF-ESPI (amplitude-fluctuation electronic speckle pattern interferometry). This is the major experimental method. The AF-ESPI method is used to determine the in-plane resonant frequency and corresponding mode shape of a single-layer piezoceramic plate and piezolaminated plates with five different stacking angles. The second experimental technique, the impedance analyzer, is employed to determine the in-plane resonant frequency. Finally, numerical computations based on the finite element analysis are presented for comparison of the two experimental results. Excellent agreement between the experimentally measured data and the numerically calculated results are found for in-plane resonant frequencies and mode shapes. This study indicates that the dynamic characteristics of inplane resonant vibrations for piezolaminated plates with different stacking angles are quite different.     

Improved processing for oil well cement evaluation-a with theoretical and laboratory data

A processing technique to measure cement impedance from ultrasonic pulse-echo waveforms, called normalized single mode (NSM) processing, is described. The technique is based on a physical model that represents the transducer in terms of its continuous plane wave kernel. Narrowband filtering to process a single resonant mode and all processing parameters are normalized to the modal frequency. The performance of NSM and a digital simulation of the present analog commercial processing, W2/W1, is compared for several environmental effects: casing thickness, eccentering, and added Gaussian noise. The computation is based on waveforms from a mathematical model and laboratory data. Results on model data show that NSM processing significantly reduces the impedance errors due to thickness variations, eccentering, and noise. Results on laboratory data indicate that the techniques yield comparable results for smooth machined casings, but that NSM processing significantly reduces measurement error and variance in a sample of the actual oil field casing.     

基础非线性振动的实用解析分析

用近似解析法分析了基础竖向振动的非线性特性，由此建立起基础共振频率、扰力幅值以及地基土动力特性参数间的理论关系，并将其与实验数据进行了比较。本文结果对动力机器基础设计、用共振法测定地基的变形模量和承载力具有实用价值。     

基于遗传算法的振荡器谐振回路的参数选择

针对振荡器谐振回路参数选择较多依赖于经验的问题,提出从振荡器的等效电路出发,得到描述振荡器的非线性微分方程,通过引入随机项来描述振荡器的内部电噪声,由此建立用于分析振荡器行为的非线性随机微分方程;并运用遗传算法对振荡器谐振回路进行参数优选,得到适应度以相位噪声最小为优化准则的参数,用该参数进行数值研究,结果表明了该方法的有效性,为振荡器的分析和谐振回路参数的优选提供了一种新方法.     

The modeling and determination of dynamic elastic modulus of magnesium based metal matrix composites

The aim of the present study was to determine elastic modulus of the magnesium-based composites containing different volume fraction of SiC particulates using an innovative free-free beam type impact based technique. This technique is based on classical vibration theory, by which the geometry and material properties of the metal matrix composites are related to resonant frequency of the test specimen. With the fundamental resonant frequency obtained from the experiment and density determined by the Archimedes' principle, the elastic modulus values were determined. In addition, a finite element model is proposed for different SiC weight percentage samples for the determination of dynamic elastic modulus using the first natural frequency corresponding to the flexural mode. The elastic modulus values obtained using finite element method were found to be in close agreement with the values obtained from the impact based experiments and in better agreement when compared to theoretical methods such as Halpin-Tsai method. Both the theoretical approaches, in common, exhibit the increasing trend of elastic modulus value with an increase in weight percentage of SiC particulates.