非周期激励作用下振动系统的谐响应分析

用谐响应分析的方法研究非周期激励作用下振动系统的稳态响应。通过精细离散的数值方法实现非周期激励简谐化,表示为有限个简谐激励的组合。分析节点数和采样时间对系数矩阵范数条件数的影响以及算法的误差来源。将微小时间段内的非周期激励简谐化,通过谐响应分析的方法求解每个简谐激励在该时间段内的响应,叠加求和得到其总响应,将该求解策略应用于其他时间段,得到整个时间区域上的振动响应,实现振动系统在多个非周期激励作用下的稳态振动响应分析。设计数值算例,并将数值解和解析解进行对比分析。     

随机振动幅值特征的图像测量方法

利用ＣＣＲ摄影机的线性时间积分成像机理,将数学图像处理技术与时间平均成像方法结合用于测量各态历经随机拓动的幅值统计特征,该测量方法只需摄取被测点在静态下的图像及其在随机状态下的一组连续的时间平均成像即可确定该点振动的位移动态范围、均值、均方值、方差和幅值概率密度曲线。该方法测量频率范围宽,对测量设备和实验条件的要求很宽松。实验表明方法具有很好的测量精度。     

阻尼连续体简谐基础振动的有限元实现方法

针对简谐基础激励下,阻尼连续体响应结果数值计算存在刚体位移、约束方式、载荷施加方式和数值算法稳定性等限制,依据连续体基础振动原理和有限元数值计算实现过程推导,提出一种求解简谐基础振动响应的有效方法——静力等效载荷法。该方法依据连续体等效载荷形式,结合通用有限元软件和自编数据处理程序,将简谐基础振动问题转化为固定基础的载荷简谐振动。通过某航空涡轮发动机气流测温探针简谐基础振动试验和仿真结果对比表明,静力等效载荷法能够有效地求解阻尼连续体简谐基础振动问题,具有实现简单、结果准确和响应结果直观的特点,且克服了时间历程法和反映谱法的诸多限制,为复杂阻尼结构简谐基础振动、基础冲击和非简谐基础振动等问题求解提供了新思路。     

简谐电压激励下静电谐波微电机的响应分析

提出了一种基于静电驱动的新型谐波微电机，描述了该微电机的基本工作原理。给出了微电机中静电场力的静态分量、动态分量和简谐电压激励下的载荷。将受迫振动的位移解表示为柔轮自由振动振型的级数形式，进而把按照Donnell壳理论建立的控制微分方程予以化简。利用壳体振型的正交性，确定了简谐电压激励下系统的动态响应，并总结了其规律。最后，分析了系统在电压激励下的共振特性，以及随主要系统参数的变化规律。       

混匀仪Thermomixer 5355振动分析与ADAMS虚拟仿真

研究艾本德混匀仪5355的振动结构和振动类型属于位移激励受迫振动,并且振动为简谐振动。基于数据采集DAQ技术和labview软件测量混匀仪5355振动系统,分析测量结果和运用振动微分方程验证系统属于简谐受迫振动,并且系统处于惯性状态,惯性力平衡激励力。设计新结构替代原有塑料热处理弹性材料,运用虚拟样机技术ADAMS建立新结构虚拟样机,并进行运动仿真分析,获取其位移、速度、加速度等仿真数据,通过仿真数据证明新结构属于位移激励的简谐受迫振动,系统状态和振动参数与原样机一致。     

基于ANSYS的多自由度系统的谐波响应分析

运用结构分析软件ANSYS中的谐波响应分析技术研究多自由度系统在简谐激励作用下的稳态受迫振动，并以双质量弹簧阻尼系统为例论述其有限元模型的构建、动力响应的计算以及动态特性的分析。结果表明，该技术不仅操作简单、易学，而且计算高效、精确，可用来求解任意线性结构的动力学问题。     

基于幅度加权编码激励的不锈钢焊缝TOFD成像检测研究

通过Hamming窗加权方法设计了幅度加权调频编码激励信号,将这种新型的激励方法与TOFD(Time-of-flight diffraction)检测方法相结合,综合提高了粗晶奥氏体不锈钢焊缝缺陷检测的时间分辨力、检测信噪比和缺陷定量定位精度,有效改善了粗晶焊缝超声检测中的难点问题。为分析设计的幅度加权调频编码激励信号的检测能力,针对奥氏体不锈钢母材试件和焊缝试件中的横孔缺陷,采用5 MHz探头分别进行了编码激励和常规激励的TOFD成像检测对比试验,结果表明:在相同的检测条件下,幅度加权调频编码激励可提高了图像和信号质量,使检测信号中的杂波和噪声得到抑制,缺陷上端和下端衍射波被准确区分,使各波形的时间宽度降低了30%,有效提高了TOFD检测的时间分辨力;获得的缺陷定位定量测量的平均相对误差为3.8%,较常规激励降低了47%,这种激励方法可在不提高激励电压和增益条件下,使不锈钢焊缝中缺陷检测的信噪比达16 d B以上,较常规激励平均提高了7 d B。     

旋转机械振动测量方式的选择

简述机械振动测量的三种方式,提出旋转机械振动测量方式选择中存在的问题;研究简谐激励下旋转机械振动传递的特性,从根据具体的测量目的和振动的分布特点两方面,指出了选择振动测量方式应考虑的因素。     

磁轴承激励下转子系统动力学特性

为分析磁轴承激励下转子系统的振动机理,应用一维有限元方法建立了双盘转子系统动力学特性计算模型,研究了不同类型磁轴承激励下转子系统的动力学行为。研究结果表明：同向旋转的扫频激励力激发了转子系统的正进动模态,而反向旋转的扫频激励力激发了转子系统的反进动模态,两种情况下转子系统均以圆轨迹进动;由于单向简谐激励力可以分解为同向旋转激励力和反向旋转激励力之和,因此在单向简谐扫频激励力作用下,转子系统的反进动和正进动模态均被激发,转子系统以椭圆轨迹进动;在双向简谐扫频激励力作用下,转子系统的进动方向和进动轨迹取决于两个激励力的相位差。研究成果为评估高压压缩机转子系统稳定性时磁轴承激励方案的选取提供了理论依据。     

基于ECT/EST双模成像系统的激励测量模式

电荷层析成像(EST)与电容层析成像(ECT)传感器结构类似,便于集成双模成像系统,以拓宽单模态系统的测量范围,提高成像精度。通过设计合理的激励测量策略,即可利用双模态传感器分时测量电容信号与电荷信号,获取足够的有效测量信息,保证重建图像质量。设计合理的C/V,E/V转换电路和多路选通电路,并在FPGA硬件平台上通过软件控制实现ECT与EST信号的分时测量及进行不同激励测量模式的切换,得到更多的有效测量值。模拟实验结果表明:该方法可以实现不同激励测量模式的切换,获取双模态测量信息。     

Modified ERA method for operational modal analysis in the presence of harmonic excitations

Operational modal analysis (OMA) is a procedure which allows to extract modal parameters of structures from measured responses to unknown excitation arising in operation. It is based on the assumption that the input to the structure is stationary white noise. In practice, however, structural vibration observed in operation cannot always be considered as pure white-noise excitation. In many practical cases, vibrations are induced by a combination of white-noise and harmonic excitations. Harmonic excitations in addition to random inputs can occur due to rotating components or fluctuating forces in electric actuators for instance. The usual way to compute modal parameters in the presence of harmonic excitations is to consider harmonically excited frequencies as being virtual eigenfrequencies of the structure. However, if the frequencies of the harmonic inputs are close to an eigenfrequency of the system, OMA procedures fail to identify the modal parameters properly. In this paper a modified ERA method is proposed, which can be applied as an identification procedure to include the effect of purely harmonic vibrations, assuming the harmonic frequencies are known a priori. The efficiency of the proposed approach is evaluated for an experimental example of a pinned–pinned beam structure excited by multi-harmonic loads superposed on random excitation.     

基础运动对漂浮式风电机组齿轮箱传动系统附加激励的影响

风电齿轮箱传动系统是漂浮式风电机组中传递力与运动的关键传动装置,受到频繁的基础运动影响,振动特性复杂。提出一种适用于非惯性坐标系下六自由度基础运动与含公转/自转运动构件六自由度振动位移的耦合建模方法,并利用集中参数法和拉格朗日方程建立了风电齿轮箱传动系统动力学模型,分析了基础运动对构件产生的附加激励以及振动响应影响。研究结果表明：基础运动会对传动系统中构件产生时变的附加参数激励,这些附加激励的特征频率主要以系统自身特征频率与基础运动频率及其倍频的组合频率为主;作用在构件上的附加激励幅值与纵荡、纵摇基础运动幅值及其频率呈现非线性关系,纵荡、纵摇基础运动的幅值越大、频率越高,附加激励中纵荡与纵摇运动之间的耦合效应也愈明显;基础运动会增大构件的径向与轴向振动响应,使其出现与基础运动频率相关的特征频率。     

多路分流齿轮传动系统的非线性振动特性研究

由于齿侧间隙和时变刚度等因素的影响,导致多路分流齿轮传动系统在运转过程中表现出次谐、超谐和混沌等非线性振动特性。为确认不同振源激励产生的响应强度,需要开展多路分流齿轮传动系统非线性振动特性研究。在考虑齿侧间隙、时变刚度和综合传动误差等因素的情况下,建立多路分流齿轮传动系统非线性动力学模型,采用四阶变步长龙格-库塔数值法求解多路分流齿轮传动系统的非线性振动特性,获得不同状态下多路分流齿轮传动系统的位移响应时间历程、相图、庞加莱映射图和快速傅里叶变换频谱图。研究结果表明,在不同工况条件下,多路分流齿轮传动系统会出现简谐、超谐、拟周期、混沌等多种非线性振动形式。所做研究为多路分流齿轮传动系统的振动控制及动态分流均衡设计提供了参考。     

旋转机械参数图形多尺度多结构元边缘检测

以旋转机械振动信号参数图形为研究对象,在600 MW模化汽轮机转子试验台上完成了转子正常、转子不对中和轴承松动故障的实验研究,得到了相应的振动参数三维图形。对不同故障的振动参数三维图形进行了二维灰度转化及图形预处理;依据多尺度滤波增强处理方法滤除了参数图形的噪声,增强了有用信息;利用多结构元边缘检测算子对参数图形进行了边缘检测。结果表明：多尺度多结构元边缘检测方法抗噪能力强,能够在滤除旋转机械振动信号参数图形中噪声的同时,有效地提取图形的边缘特征,适用于环境噪声较为复杂的旋转机械状态监测。     

Vibration response and harmonic wave propagation of ultrasonic arc drivers

A piezoelectric curvilinear arc driver designed for an ultrasonic curvilinear motor is evaluated in this study. A design of piezoelectric curvilinear arc driver is proposed and its governing equations, vibration behaviour and wave propagation are investigated. Then, analysis of forced vibration response or driving characteristics to harmonic excitations in the modal domain is conducted. Finite element modelling and analysis of the arc driver are also discussed. Analytical results of free vibration characteristics are compared favourably with the finite element results. Harmonic analyses of the three finite element models reveal changes of dynamic behaviours of three models and also imply operating frequencies with a significant travelling wave component. Parametric study of mathematical and finite element simulation results suggests that stable travelling waves can be generated to drive a rotor on the proposed curvilinear arc motor system.     

Vibration component separation by iteratively using stochastic resonance with different frequency-scale ratios

It is well-known that stochastic resonance (SR) is mainly used for signal denoising and weak signal detection. In this paper, we firstly find the frequency range selection characteristic (filtering characteristic) of re-scaling frequency SR (RFSR) caused by the driving frequency limitation of bistable SR. It then follows that a novel approach to separate vibration components with different frequencies by iteratively using SR is explored. The frequencies of most vibration signals exceed the driving frequency limitation, thus by use of different frequency-scale ratios, the vibration signals with different frequency range can be extracted by RFSR. Firstly, a small frequency-scale ratio is used to obtain the vibration signal with a narrow frequency range, i.e. low frequency vibration. As the output of SR may have a phase lag, a simple phase-shift correction method is proposed to improve the accuracy of signal component separation. The phase-shift corrected signal of RFSR output is separated from the original vibration signal and the residue is treated as the new vibration signal. Then, increasing the frequency-scale ratio according to a searching algorithm, the vibration signal with higher frequency can be obtained by RFSR. Through this iterative process, several harmonic vibration components can be separated from the original noisy vibration signal. The proposed method, empirical mode decomposition (EMD) and Hilbert vibration decomposition (HVD) are respectively applied to analyzing a simulated vibration signal and extracting the fault feature of a rotor system. The contrastive results show that this proposed method has good frequency resolution and can successfully separate monocomponent harmonic signals from a strongly noisy multicomponent harmonic vibration signal while EMD and HVD cannot.     

受简谐激励弹簧测力机构的主共振与奇异性分析

应用拉格朗日方程，得到有阻尼弹簧测力机构在简谐激励作用下具有周期系数的非线性运动微分方程Duffing-Mathieu方程；根据非线性振动的多尺度法，求得系统满足主共振情况的一次近似解以及对应的定常解，并对其进行数值计算，分析激振力、谐调值、阻尼、弹簧刚度等对系统的影响。应用奇异性理论分析方法得到系统主共振稳态响应的转迁集和分岔图。揭示一些新的动力学现象。     

Out‐of‐focus background subtraction for fast structured illumination super‐resolution microscopy of optically thick samples

We propose a structured illumination microscopy method to combine super resolution and optical sectioning in three‐dimensional (3D) samples that allows the use of two‐dimensional (2D) data processing. Indeed, obtaining super‐resolution images of thick samples is a difficult task if low spatial frequencies are present in the in‐focus section of the sample, as these frequencies have to be distinguished from the out‐of‐focus background. A rigorous treatment would require a 3D reconstruction of the whole sample using a 3D point spread function and a 3D stack of structured illumination data. The number of raw images required, 15 per optical section in this case, limits the rate at which high‐resolution images can be obtained. We show that by a succession of two different treatments of structured illumination data we can estimate the contrast of the illumination pattern and remove the out‐of‐focus content from the raw images. After this cleaning step, we can obtain super‐resolution images of optical sections in thick samples using a two‐beam harmonic illumination pattern and a limited number of raw images. This two‐step processing makes it possible to obtain super resolved optical sections in thick samples as fast as if the sample was two‐dimensional.     

Nonlinear vibration of plates by the hierarchical finite element and continuation methods

The hierarchical finite element (HFEM) and the harmonic balance methods are applied to analyse the geometrically nonlinear vibration of thin, isotropic plates. The von Kármán type of nonlinear strain–displacement relationships are used. Symbolic computation is employed in the derivation of the model. The equations of motion are solved by the Newton and continuation methods. Free and steady-state forced vibration are analysed. The excitations considered are harmonic plane waves at both normal and grazing incidence. The stability of the obtained solutions is investigated by studying the evolution of perturbations to the solutions. The convergence properties of the HFEM and the influence of the middle plane in-plane displacements are discussed and results compared with published experimental and numerical results.     

基于听觉原理的谐波频率自动提取方法

基于听觉系统的运行机制,提出一种可自动识别和提取信号中谐波频率的计算方法。首先,对信号进行基底膜带通滤波;其次,模拟听皮层时频感受野现象对不同时频域内信号进行二维傅里叶变换并提取幅值和频率信息,基于幅值信息的侧抑制结果,提出了一种谐波成分频率点的判据方法;最后,对提取得到的谐波频率点进行重组,从而可揭示信号中的主要频率成分以及各成分的时变情况。数值仿真和试验数据验证结果表明,所提方法可准确提取信号中的各谐波频率,并具有一定的抗噪声干扰能力,对于微弱谐波成分的频率提取亦有较好效果。