埋入混凝土结构中的PZT压电陶瓷温度特性研究

通过实验方法研究了覆盖不同厚度的橡胶层对PZT压电陶瓷温度特性的影响.分析了两种PZT压电陶瓷在混凝土试件中不同埋入深度条件下,其特征频率和等效电路参数的温度响应特性.实验结果表明特征频率与等效电路参数对温度的变化比较敏感.结合前期研究中发现的特征频率对应力的不敏感性,表明可利用其特征频率,对应用埋入的压电元件的等效电路参数进行结构应力监测中的应力-温度交叉传感进行修正.     

基于小波包和EMD的异步电动机轴承故障诊断方法

针对传统的异步电动机轴承故障诊断方法对于轴承的局部缺陷及早期故障的诊断效果不明显的问题,提出了一种采用小波包理论与EMD相结合的方式提取异步电动机轴承故障特征频率的方法。该方法先采用小波包理论对原始信号进行消噪及频带划分,接着采用EMD对小波分解重构得到的信号进行分解以获得固有内在模函数(IMF),最后将IMF经时频变换得到频谱图,根据故障特征频率得出诊断结果。实验结果证明,该方法可有效地提取出故障特征频率,并方便地判断出故障类型。     

基于SVM与D-S证据理论的异步电动机转子断条故障诊断方法

目前异步电动机转子断条故障诊断方法都是基于从定子电流中提取出特征频率来对转子状态作出诊断的方法,当异步电动机空载或轻载时,该特征频率易受基频泄露的影响而很难得到,同时该特征频率受转速波动影响很大,单纯根据该特征频率对转子状态作出判断缺乏准确性。针对上述问题,提出了一种运用SVM与D-S证据理论对异步电动机转子断条故障进行识别的诊断方法。该方法基于扩展Park法与FFT变换法,分别从定子电流信号和振动信号中提取转子断条故障的特征信息,利用SVM对异步电动机的状态进行模式识别,并将识别结果形成彼此独立的证据,而后根据D-S证据融合规则进行融合处理,从而实现对异步电动机转子断条故障的准确识别。实验结果表明,该方法可以对异步电动机转子断条故障作出准确判断。     

混凝土喷射机振动信号变分模态分解方法研究

混凝土喷射机是隧道、地铁和桥梁建设等工程项目中常用的一种机械设备。振动信号是混凝土喷射机的一个重要指标,通过研究混凝土喷射机的振动信号,可以得到其特征频率,从而为设备改进和故障诊断提供理论依据,而IVMD为特征频率的提取提供了一种新的方法。为了研究混凝土喷射机工作过程中的振动信号,以PS6I-J型混凝土喷射机为例,使用改进的变分模态分解方法,对变分模态分解中的k值,使用离散熵进行优化,从而过滤噪声分量。为信号处理领域提供了一种新的思路。     

基于自相关和经验模态分解的转子碰摩故障分析

针对转子故障振动信号具有周期性的特点,提出一种用于分离转子故障振动信号的新方法,该方法首先应用自相关处理对振动信号进行降噪处理,然后采用经验模态分解(EMD)对振动信号进行分解,得出各个本征模态函数(IMF),并对IMF进行频谱分析,从频谱图上可以清晰地观察出转子的故障特征频率.试验结果表明,振动信号经自相关处理后起到了很好的降噪效果,碰摩所产生的冲击信号上下不对称;EMD分解方法能有效地突出故障特征频率成分,该方法可广泛用于旋转机械振动信号时频分析领域.     

电动机联接性故障诊断方法及其应用

针对电动机联接性故障特征识别困难的问题,阐述了不对中故障、联接螺栓松动故障、基础刚度不足故障这3种典型电动机联接性故障的数学模型及其频谱特征,提出了利用经验模式分解方法对电动机的振动信号进行滤波处理,根据故障特征频率得出诊断结果。现场应用结果验证了该方法的有效性。     

AAindex数据库中傅里叶方法的多重氨基酸指数选择

波谱学方法研究蛋白质时,蛋白质序列的特征频率与蛋白质的位点、功能、空间结构对应.基于时间序列傅里叶变换的交叉谱原理,本文提出的“一个蛋白质关于多种氨基酸指数的一致谱”能够获取一个或多个蛋白质序列较显著的特征频率,再由特征频率去筛选与之对应的氨基酸指数.该方法与Lazovi(c)的筛选方法和筛选意义不同.结果显示,筛选出的氨基酸指数对应的性质多数与蛋白质的空间结构性质有关.蛋白质特征频率也许是用于特征提取的好方法,氨基酸指数筛选可被看作蛋白质数字表达的一种优化.     

基于改进瞬时功率法的电动机故障诊断

从采集的鼠笼异步电动机定子电流出发,建立了流方的概念,通过故障电流的自乘方放大并转移故障特征频率。根据瞬时功率的概念提出了基于改进瞬时功率法的电动机故障诊断方法,通过理论推导分别提取了转子断条故障和转子偏心故障在流方中的特征频率分量,有效地克服了转子断条故障特征频率容易被基频淹没的缺点,实现了对转子断条、偏心、复合等故障的辨别诊断。该方法与传统瞬时功率法相比,采集的数据量减半,避免了电压波动和采样误差对瞬时功率的影响。     

基于ZnO单晶声表面波射频标签的特性研究

针对基于声表面波技术的射频识别系统工作原理,提出利用COMSOL软件进行ZnO单晶材料射频波标签特性研究,进行多物理域耦合建模与仿真。提取出符合声表面波特性的模态图,得到正特征频率和反特征频率分别为268 MHz和275 MHz。通过对特征频率的仿真分析,计算ZnO单晶的相速度达到2 715 m/s;通过频率响应分析,画出标签位移与频率之间的关系图,获得了标签的幅频特性;最后讨论脉冲幅度编码对回波脉冲的影响。     

有源带通滤波器的设计

有源带通滤波器以其良好的幅频特性,在信号的分析与测量中得到广泛应用。根据标准有源带通滤波器原理,采用频域分析法,可得出有源带通滤波器的特征频率计算公式。在此基础上,推荐了一种快捷实用的参数选择方法,并对单级、两级串联有源带通滤波器进行了幅频特性数字仿真。     

Eigenvalue topology optimization of structures using a parameterized level set method

Preventing a structure from resonance is important in many real-world applications. Because an external excitation frequency can be lower than the fundamental eigenfrequency or between the eigenfrequencies of a structure, there is a strong need for eigenfrequency optimization technology to optimize the fundamental eigenfrequency and, in addition, the k-th eigenfrequency and to maximize the gap between eigenfrequencies. However, previous optimization studies on vibrating elastic structures that used the level set method have been devoted to the optimization of the fundamental eigenfrequency, whereas the higher-order eigenfrequencies optimization problem has seldom been considered. This paper presents an eigenfrequency optimization technology that is based on the compactly supported radial basis functions (CS-RBFs) parameterized level-set method, using the fundamental eigenfrequency, the eigenfrequency of a given higher-order, and the gap between two consecutive eigenfrequencies as the optimization objectives. Furthermore, to address the oscillation problem of the objective function, we adopt an exponential weighted optimization model of a number of the lower eigenfrequencies for multiple eigenvalue optimizations, and we utilize mode-tracking technology for the single eigenvalue optimization.In addition, we further extend the CS-RBFs parameterized level-set method to an optimization that is performed with geometric constraints, which means that the size and position of the regular holes in the structure can be optimized with the shape and topology. This approach is useful in real-world applications. The effectiveness of this method is demonstrated by several widely investigated examples that have various objectives.     

A piezoelectric cantilever-beam energy harvester (PCEH) with a rectangular hole in the metal substrate

In order to improve the energy conversion performance of a piezoelectric cantilever-beam energy harvester (PCEH), a novel PCEH is developed and designed according to the typical PCEH. Its middle layer is a metal substrate with a rectangular hole. The mathematical model of the PCEH is analyzed, and the mathematical expressions of the eigenfrequency, the displacement of the proof mass and the output voltage and power are derived. In order to verify the validity of the model, the eigenfrequency and frequency domain are analyzed by using COMSOL and Matlab, and the influence of frequency, load resistance and acceleration on voltage and power is studied. Finally, the experimental verification was carried out to further confirm. The results show that the first-order eigenfrequency of the novel PCEH is 43.7 Hz, the optimal output power is 10.69 mW. Therefore, the novel PCEH has a lower frequency, a wider frequency band, and higher output voltage and power, and improves energy conversion performance.

     

求旋转椭球形贮箱内液体小幅晃动基频的一种新方法

针对旋转椭球形贮箱内液体小幅晃动,建立了原点位于与箱于箱内静液面接触线处相切的圆锥的顶点的球坐标系,用高斯超几何级数解析表达速度势和波高的模态函数,通过伽辽金方法把变分方程转变为一个标准的特征值问题形式的频率方程,求解了不同尺寸比例的椭球形贮箱在不同的充液比和不同的Bond 数情况下液体小幅晃动的基频,把所求结果和已有...     

Finite-Frequency Identification: Test Frequency Bounds

A test harmonic signal underlies the finite-frequency identification method. It not easy to specify its frequencies, because they must be chosen in the range of eigenfrequencies determined by the coefficients of the identified object. A method of determining the eigenfrequency bounds for the identified object is developed.     

Designing plates for minimum internal resonances

Internal resonance is a nonlinear phenomenon for a structure when the eigenfrequencies of the structure are commensurable or close to being commensurable. Using optimization we have the possibility to control the eigenfrequencies, i.e., move an eigenfrequency, maximize a given eigenfrequency, or maximize the gap between eigenfrequencies. It is therefore also possible to design a structure that is as free as possible of internal resonance up to mode of order n.We consider plates made of two materials. The designs depend on the boundary conditions and on the frequency range within which the plate should be as free of internal resonance as possible. The two materials can either be two physical materials, or one can be a physical material and the other a weakening of the first material. By doing this we are in principle solving three different problems: a reinforcement problem, a problem of where to put holes in the structure, and, finally the more involved case (from a manufacturing point of view), of two different materials. The optimizations are performed using the finite element method for analysis and the topology optimization approach for design. The optimization problem is formulated using a bound formulation where the objective is to maximize a minimum detuning parameter. Special attention is given to the formulation of the conditions for internal resonance. Using the method presented in this paper it is possible to remove an unwanted nonlinear phenomenon without the use of a nonlinear model and without knowledge of the nonlinearities present in the system.     

Measurement of residual stresses in a plate using a vibrationaltechnique-application to electrolytic nickel coatings

A vibration method for the evaluation of the stress in a membrane is presented. The principle is based on the shift of the eigenfrequency of the modes due to the stress. The identification of the modes is obtained by an optical technique. The proposed method is applied to electrolytic nickel coatings. The results are compared with those obtained by X-ray analysis. The application of this type of measurement to other structures is discussed     

Control of damping oscillations by fractional differential operator with time-dependent order

The aim of the present paper is application of a differential operator of variable order in constitutive relations for viscoelastic materials. This operator is used for studying the vibrations of a one-degree-of-freedom oscillator, in which the viscoelastic deformation is governed by a servo order function. A method for numerical determination of the eigenfrequency of the fractional differential equation is proposed.     

飞机座舱减振降噪优化设计方法

采用结构拓扑优化的变密度法和形貌优化法,对模拟飞机座舱的四角固支声音箱体,进行了减振降噪的研究.比较优化前后结构固有频率的变化和对声压的影响,得出了结构拓扑优化对减振降噪作用的高效性.     

Shape optimization of a vehicle hat-shelf: Improving acoustic properties for different load cases by maximizing first eigenfrequency

This paper presents design optimization of the geometry of a vehicle hat-shelf. At first two existing finite element discretizations are investigated for two different element types. The structural model is then parameterized. Only four design variables have been chosen to control the shape modification of the hat-shelf. The aim of this paper is to decrease the vehicle interior noise due to three different excitations for two cases of fluid damping. With respect to the support conditions of the hat-shelf these three load cases and the two cases of different damping are considered simultaneously by maximizing the lowest eigenfrequency of the structural model. Although remarkable differences in the natural frequencies are discovered for the four discretizations, a similar dependence of the objective function in terms of the design variables is observed. Thus, a multigrid strategy can be applied. The coarsest mesh is used to obtain suitable initial sets of optimization variables, one of the finer meshes serves for a pre-optimization and the finest mesh is optimized to find the final set of parameters. While the lowest eigenfrequency of the original model is found at about 31 Hz, the corresponding value in the optimized variant exceeds 100 Hz being the upper bound of the frequency range under consideration. Evaluation of the noise transfer function proves that this strategy decreases its average between 4.4 and 13.9 dB.     

Digital signal processing and test rig testing results

Digital processing method of the vibrating system rotation angle in the measuring test rig is considered; it allows evaluating the eigenfrequency, amplitude and phase of the signal. The measurement results of the mass, center of gravity coordinates and inertia moments of the reference objects are provided. The measurement errors are determined.