Mass matrices by minimization of modal errors

A new approach to constructing mass matrices is presented, based on expressing it through use of a variable parameter. This allows the mass matrix to be adjusted in such a way that a simple eigenvalue problem get the best solution possible in terms of some error measure. This procedure is used to create both diagonal mass matrices and mixed mass matrices. © 1997 John Wiley & Sons, Ltd.     

通过模态滤波实现阵列式传感器系统的故障诊断

基于结构振动响应特性利用改进的模态滤波方法对阵列式传感器系统进行故障诊断。在梁结构表面均匀布置一组加速度计,利用模态振型对该系统的输出信号进行重构,将重构信号与实际信号之间的曲率误差作为敏感参数,对系统中的模拟故障传感器进行检测与识别,并加以实验验证。数值计算和实验结果表明:改进的模态滤波方法不仅可以直接有效地对传感器系统进行实时故障监测,而且该方法与外界激励力位置无关,具有良好的工程应用前景。     

Constrained least squares Fourier modal method for computing scattering from metallic binary gratings

In a recent article [J. Opt. Soc. Am. A27, 1694 (2010)], we proposed a rectangular truncation method to mitigate the convergence problems arising from the boundary matching conditions of a binary metallic grating. The proposed method may underestimate the total power in the scattered field for certain grating parameters. In this article, we extend this method to preserve the total power by introducing appropriate constraints and solving the resulting problem as a constrained least squares minimization problem. We provide examples to show that the new method provides a convergent solution for both lossy and lossless binary metallic gratings while preserving the total power.     

基于数据缩减的分频段小波模态参数快速识别

针对利用小波进行模态参数识别效率较低的问题,提出了一种基于数据缩减的分频段小波模态参数快速识别算法。利用奇异值分解对协方差信号在保留数据信息量的情况下进行缩减以减少参与计算的数据量,对正功率谱密度矩阵的奇异值分解确定识别系统的模态阶数及相应的频率范围,利用小波变换对缩减后的数据进行各阶模态逐频段识别。相比原始算法,文中方法减少了小波分析的数据量并避免了一些无用频带的小波分解从而减少计算量。通过对一个3阶线性时不变系统以及一个大桥模型的参数识别验证了文中方法在保持识别精度的情况下大幅度地提升了计算效率。     

Constrained optimization using a multipoint type chaotic Lagrangian method with a coupling structure

This article proposes a new constrained optimization method using a multipoint type chaotic Lagrangian method that utilizes chaotic search trajectories generated by Lagrangian gradient dynamics with a coupling structure. In the proposed method, multiple search points autonomously implement global search using the chaotic search trajectory generated by the coupled Lagrangian gradient dynamics. These points are advected to elite points (which are chosen by considering their objective function values and their feasibility) by the coupling in order to explore promising regions intensively. In this way, the proposed method successfully provides diversification and intensification for constrained optimization problems. The effectiveness of the proposed method is confirmed through application to various types of benchmark problem, including the coil spring design problem, the benchmark problems used in the special session on constrained real parameter optimization in CEC2006, and a high-dimensional and multi-peaked constrained optimization problem.     

基于不完备实测模态数据的结构损伤识别方法研究

在传统的基于模型修正的损伤识别中,由于实测模态信息有限而待识别参数过多,往往导致损伤识别方程出现较大误差,从而限制了该方法在复杂结构中的应用。为解决这一问题,对结构的自由度进行了分解,将损伤结构中模态振型的未测量部分表达为已测量到的模态振型、模态频率以及结构其它参数的函数。将损伤视为结构单元刚度的减小,利用完好结构的计算模态数据以及损伤结构扩充后的实测模态数据,建立了结构的损伤识别方程。运用信赖域优化算法对具有双重约束条件的目标函数进行最小化,识别出了结构各单元的刚度损伤参数。通过两个损伤识别数值仿真算例及实验验证,结果表明,在测点数量有限及测试噪声等不利因素影响下,所提方法只需运用少量的实测模态信息,即可实现结构损伤位置及程度的准确识别,同时算法具有较好的鲁棒性。     

Analysis of the global reduction of broadband noise in a telephone kiosk using a MIMO modal ANC system

The possibility of implementation of ANC system for global reduction of broadband noise in a telephone kiosk application has been studied in this paper. By using a modal model of the acoustic environment of the enclosure the shape modes and their frequencies are obtained and suitable bandwidth for the controller design is calculated. Analysis shows that because of existing of some degenerate modes in this application, the control action is complicated. Simulation results show that how positions and number of loudspeakers and microphones will change the performance of the controller and its corresponding control effort. Based on these results and analysis a reasonable size for the controller and proper locations for sensors and actuators are proposed. Simulation results also show the effectiveness of the proposed system in reduction of the acoustic potential energy in the kiosk.     

Optimal modal reduction of vibrating substructures

A structure which consists of a main part and a number of attached substructures is considered. A ‘model reduction’ scheme is developed and applied to each of the discrete substructures. Linear undamped transient vibrational motion of the structure is assumed, with general external forcing and initial conditions. The goal is to replace each discrete substructure by another substructure with a much smaller number of degrees of freedom, while minimizing the effect this reduction has on the dynamic behaviour of the main structure. The approach taken here involves Ritz reduction and the Dirichlet‐to‐Neumann map as analysis tools. The resulting scheme is based on a special form of modal reduction, and is shown to be optimal in a certain sense, for long simulation times. The performance of the scheme is demonstrated via numerical examples, and is compared to that of standard modal reduction. Copyright © 2003 John Wiley & Sons, Ltd.     

Collimation method of measurement of linear magnitudes

Principles for the construction and transformations of signals in optoelectronic collimation devices used in the measurement of linear displacements are considered. Translated from Izmeritel’naya Tekhnika, No. 10, pp. 23–26, October, 2008.     

环境激励下大型桥梁模态参数识别的一种方法

提出一种依据环境激励下结构振动响应的大型桥梁模态参数识别方法,该方法以限制带宽的经验模态分解（BREMD）和随机子空间识别（SSI）为基础,首先利用EMD将环境振动响应分解成一系列只含结构某一阶固有模态的本征模态函数（IMF）,然后利用SSI识别桥梁模态参数。针对大型桥梁自振频率低、模态密集的特点,引入屏蔽信号限制EMD过程中带宽以消除模态混叠;运用该法识别了赣龙铁路某特大桥的模态参数,并将其与峰值拾取法、SSI识别结果以及理论计算值进行对比,结果表明：该方法能有效的识别大型桥梁模态参数,屏蔽信号的引入解决了模态混叠问题,稳定图中的虚假模态得到抑制。     

Multiple path interference and differential modal delay reduction using spatial filters in a 4F system

Multiple path interference (MPI) and differential modal delay (DMD) are two major impairments in fiber optic communication systems. MPI can be found in a few mode fibers in which a higher order mode propagates as a weak replica of the signal and interferes with the fundamental mode at the output of the fiber link. DMD in multimode fibers (MMF) leads to intersymbol interference, which limits the bit rate-distance product of the system. A simple method is proposed to reduce MPI and DMD effects using spatial filters in a 4F system. Higher order modes have higher spatial frequency components. Therefore by choosing a proper spatial filter with a suitable bandwidth, a fraction of the unwanted higher order modes can be suppressed, and therefore MPI and DMD effects can be reduced.     

Stable and accurate method for modal analysis of multilayer waveguides using a graph approach

A method for calculating the propagation constants of allowed guided and leaky modes in multilayer planar waveguides is presented. We develop a two-way graph model to describe the tangential fields propagating in the waveguides. According to the special structure of the graph model, it is convenient to employ a topology scheme to derive analytical and closed-form dispersion equations for TE and TM modes. By comparing the dispersion equations formulated by series-expansion methods, approximation methods, and transfer-matrix methods, we find that the use of these equations for finding the eigenmodes has some benefits. First, this method can be easily employed to solve eigenmodes accurately in numerical computation without using series truncation. Second, the dispersion equations are exact. Moreover, all the eigenmodes can be determined according to the formulas without losing roots or causing numerical instability even for a waveguide with thick layers.     

Evaluation of a novel method of noise reduction using computer-simulated mammograms

A novel method of noise reduction has been tested for mammography using computer-simulated images for which the truth is known exactly. This method is based on comparing two images. The images are compared at different scales, using a cross-correlation function as a measure of similarity to define the image modifications in the wavelet domain. The computer-simulated images were calculated for noise-free primary radiation using a quasi-realistic voxel phantom. Two images corresponding to slightly different geometry were produced. Gaussian noise was added with certain properties to simulate quantum noise. The added noise could be reduced by >70% using the proposed method without any noticeable corruption of the structures. It is possible to save 50% dose in mammography by producing two images (each 25% of the dose for a standard mammogram). Additionally, a reduction of the anatomical noise and, therefore, better detection rates of breast cancer in mammography are possible.     

利用模态应变能变化率的结构损伤识别优化方法

针对结构损伤识别过程中存在的定位精度和量化分析不足的问题,提出一种基于结构振动响应的模态应变能变化率与优化技术相结合的损伤识别方法。利用两步法确定可疑损伤单元及对其损伤程度进行量化分析。通过有限元法建立结构的损伤特征模型,且利用单元模态应变能变化率指标构建损伤指标优化分析的目标函数。数值分析过程中,利用粒子群优化算法与遗传算法对设计变量进行优化分析。同时比较模态应变能变化率与小波分析两种方法下的损伤定位的量化分析效果和识别效率。在实际算例中,利用梁结构进行损伤识别优化方法的结果验证。结果证明该方法能够显著提高结构振动损伤和定位的有效性。该方法不仅能够快速和精准地进行结构损伤量化分析,比小波方法具有更好的定位效果,而且能够提高量化分析的识别效率。但该方法在实施过程中的定位精度容易受到噪声的影响,通过优化目标函数可在一定程度上提高该结构损伤识别方法的抗噪能力。     

An ndt method using piezoelectric polymer transducers and computerized vibrational spectroscopy

The normal mode vibrational spectrum of a particular object contains a wealth of information about the mechanical integrity of the object. The non-destructive evaluation of objects by observation of their vibrational spectra is facilitated by the combination of recently developed low mass, high compliance piezoelectric polymer transducers; a synchronized method for exciting the sample; and a small minicomputer capable of making digital Fourier transforms which convert the complicated, oscillatory, decaying signal from the transducer into the intensities and frequencies of normal modes.     

一种利用模态测量数据修正刚度矩阵的新方法

模型修正即为利用模态测量数据修正存在但不准确的有限元模型。本文在假定有限元模型的质量矩阵与刚度矩阵均为对称非负定矩阵,并且质量矩阵是精确的情况下,提出了一种修正刚度矩阵的新方法。该方法借助于矩阵的Kronecker积与拉直算子,把需修正的变量分离出来直接对其进行修正运算,得到了满足特征方程与正交性条件的最逼近有限元刚度矩阵的唯一修正矩阵。该方法不仅保证了修正矩阵带状稀疏的特点,而且修正过程简单易行。数值例子验证了该方法的有效性。     

Synthesis of platinum nanostructures in zeolite mordenite using a solid-state reduction method

Platinum nanoparticles and nanowires have been synthesized inside zeolite mordenite using a solid-state reduction method. Tetrammine platinum nitrate was introduced into the pores via incipient wetness impregnation and it was reduced using powder sodium borohydride. With this method it was possible to obtain single crystal nanowires along the edges of the zeolite particle. The molar ratio of the reducing agent to platinum atoms was a critical parameter for the formation of either uniform nanoparticles or nanowires. Using a regular aqueous sodium borohydride solution reduction it was not possible to obtain nanowires in this zeolite. To the best of the author's knowledge this is the first time sodium borohydride in its solid form is used as a reducing agent to form nanostructures and this is also the first time a solid-state method is used to form nanostructures in a zeolite.     

Modeling of cavities using the analytic modal method and an open geometry formalism

We present an eigenmode expansion technique for calculating the properties of a dipole emitter inside a micropillar. We consider a solution domain of infinite extent, implying no outer boundary conditions for the electric field, and expand the field on analytic eigenmodes. In contrast to finite-sized simulation domains, this avoids the issue of parasitic reflections from artificial boundaries. We compute the Purcell factor in a two-dimensional micropillar and explore two discretization techniques for the continuous radiation modes. Specifically, an equidistant and a nonequidistant discretization are employed, and while both converge, only the nonequidistant discretization exhibits uniform convergence. These results demonstrate that the method leads to more accurate results than existing simulation techniques and constitutes a promising basis for further work.     

On a mesh optimization method based on a minimization of interpolation error

In this article a new mesh optimization technique for finite element methods is presented. The mesh modification strategy is based on a minimization of an interpolation error estimate and can be viewed as a generalization of existing conformai map-type mesh generators. The new mesh results in an essential improvement of finite element approximation which is illustrated in numerical examples.     

Comparison between the modal identification method and the POD‐Galerkin method for model reduction in nonlinear diffusive systems

This paper presents a comparison between the modal identification method (MIM) and the proper orthogonal decomposition‐Galerkin (POD‐G) method for model reduction. An example of application on a nonlinear diffusive system is used to illustrate the study. The study shows that in both methods, the state formulation of the nonlinear diffusive equation may be similar. However, the ideas behind both methods are completely different. The considered example shows that, for both methods, reducing the order up to 99.5% gives enough accuracy to simulate the dynamic of the original system. It is also seen in this example that the reduced model given through the MIM are slightly faster and more accurate than the ones given through the POD‐G method. Copyright © 2006 John Wiley & Sons, Ltd.