基于小波变换的爆破振动信号能量分布特征分析

为了深入研究爆破地震波特性,应用小波变换方法对具有短时非平稳特点的爆破振动信号进行了能量分布特征分析。根据小波变换的时-频特性和分层分解展开关系,将爆破振动时间历史信号用分层重构信号进行扫描,应用这些信号得到了不同频率带上爆破振动的相对能量分布和振动强度的时间变化规律。爆破振动信号实测结果分析表明,基于小波变换的能量分布特征分析可以更准确地给出爆破振动信号的细节信息。研究结果为分析爆破振动结构安全性提供了新的途径。     

一种基于训练数据的迭代改进核函数

To improve performance of a support vector regression, a new method for a modified kernel function is proposed. In this method, information of all samples is included in the kernel function with conformal mapping. Thus the kernel function is data-dependent. With a random initial parameter, the kernel function is modified repeatedly until a satisfactory result is achieved. Compared with the conventional model, the improved approach does not need to select parameters of the kernel function. Sim- ulation is carried out for the one-dimension continuous function and a case of strong earthquakes. The results show that the improved approach has better learning ability and forecasting precision than the traditional model. With the increase of the iteration number, the figure of merit decreases and converges. The speed of convergence depends on the parameters used in the algorithm.     

Multi-dimensional self-affine fractal interpolation model in tensor form

Iterated Function System (IFS) models have been explored to represent discrete sequences where the attractor of an IFS is self-affine either in R ² or R ³ (R is the set of real numbers). In this paper, the self-affine IFS model is extended from R ³ to R ⁿ (n is an integer and greater than 3), which is called the multi-dimensional self-affine fractal interpolation model. This new model is presented by introducing the defined parameter “mapping partial derivative”. A constrained inverse algorithm is given for the identification of the model parameters. The values of this new model depend continuously on all of the variables. That is, the function is determined by the coefficients of the possibly multi-dimensional affine maps. So the new model is presented as much more general and significant. Moreover, the multi-dimensional self-affine fractal interpolation model in tensor form is more terse than in the usual matrix form.     

ON THE CONTINUITY AND DIFFERENTIABILITY OF AKIND OF FRACTAL INTERPOLATION FUNCTION

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Hydraulic radius and transport in reconstructed model three-dimensional porous media

Methods for reconstructing three-dimensional porous media from two-dimensional cross sections are evaluated in terms of the transport properties of the reconstructed systems. Two-dimensional slices are selected at random from model three-dimensional microstructures, based on penetrable spheres, and processed to create a reconstructed representation of the original system. Permeability, conductivity, and a critial pore diameter are computed for the original and reconstructed microstructures to assess the validity of the reconstruction technique. A surface curvature algorithm is utilized to further modify the reconstructed systems by matching the hydraulic radius of the reconstructed three-dimensional system to that of the two-dimensional slice. While having only minor effects on conductivity, this modification significantly improves the agreement between permeabilities and critical diameters of the original and reconstructed systems for porosities in the range of 25–40%. For lower porosities, critical pore diameter is unaffected by the curvature modification so that little improvement between original and reconstructed permeabilities is obtained by matching hydraulic radii.     

基于参数识别视速度的双矢量粗对准方法（英文）

针对传统基于视速度双矢量粗对准中,由于传感器随机噪声的影响,存在对准精度差,收敛速度慢的缺点,提出了一种新型自适应Kalman滤波的参数识别粗对准方法。该方法通过对视速度运动进行建模,设计采用自适应Kalman滤波对模型参数进行参数识别,从而有效地消除视运动中的随机噪声,提高粗对准的精度和收敛速度。由于自适应滤波的特点,新方法不需要对传感器误差进行统计,使其在实际系统中具有更加广泛的应用价值。针对双矢量粗对准的计算特点,设计了一种矢量重构算法,从而尽可能地规避双矢量共线性问题,加快了粗对准的收敛过程。仿真与转台实验表明,与传统方法对比,新方法在相同的对准时间内具有更高的对准精度,在相同的对准精度下,具有更高的收敛速度。转台实验的最终对准精度为-0.1391°,标准差为0.012°。     

复合随机振动分析的扩阶系统方法

提出了随机结构系统反应的子空间次序正交分解的思想．基于这一思想，文中导出了一类用于考虑随机激励的随机结构复合随机振动分析的扩阶系统方法，从而可以应用传统的确定性结构随机振动各种分析方法求解复合随机振动问题．作为特例，本文给出了使用模态分析法求解的过程．将文中算例与随机模拟结果相比较，证实了本文思想与方法的实用性．     

Voxel-Scale Digital Volume Correlation

Among various correlation techniques to find the displacement field of a volume imaged by X-ray tomography at several deformation states, a new approach is proposed where the displacement is measured down to the voxel scale and determined from a mechanically regularized system using the equilibrium gap method, and an additional boundary regularization. It is shown that even if the underlying material behavior is not very well known, this approach leads to extremely small correlation residuals. An excellent stability of the estimated displacement field for noisy (reconstructed) volumes is also observed.     

Representation of discrete sequences with high-dimensional iterated function systems

Iterated Function System (IFS) models have been used to represent discrete sequences where the attractor of the IFS is self-affine or piece-wise self-affine in R ² or R ³ (R is the set of real numbers). In this paper, the piece-wise hidden-variable fractal model is extended from R ³ to R ⁿ (n is an integer greater than 3), which is called the high-dimensional piece-wise hidden-variable fractal model. This new model uses a “mapping partial derivative” and a constrained inverse algorithm to identify the model parameters. The model values depend continuously on all the hidden variables. Therefore, the result is very general.     

Stochastic finite element analysis of local average random fields

This paper discussed the concepts underlying a new approach to representation and analysis of homogeneous random Fields. An orthogonalized isoparametric local average model of random fields is proposed, and the optimum selection of random variables is determined based on the theory of nonlinear programming. The finite element method is used to develop a methodology for random field analysis. Numerical examples showing the accuracy and efficiency of the method are studied.     

Vibration parameter measurement using the temporal digital hologram sequence and windowed Fourier transform

Real time digital recording and numerical reconstruction of a temporal digital hologram sequence have become feasible in recent years. They provide a new measurement method which enjoys the valuable advantages of being full-field, noncontact and high precision. In this paper, a combined method of temporal digital hologram sequence and windowed Fourier transform is proposed to measure the kinematic parameters of random vibration. A series of holograms are recorded by CCD camera and the original phase can be reconstructed by Fresnel reconstruction algorithm. The three-dimensional windowed Fourier transform is used to filter noise in phase and extract the instantaneous kinematic parameters of the specimen, such as the displacement, velocity and acceleration. An experiment is conducted on a chloroprene rubber latex membrane. Results demonstrate that the proposed method determines the vibration parameters precisely and enjoys many merits.     

Representation of discrete sequences with N-dimensional iterated function systems in tensor form

Iterated Function System (IFS) models have been used to represent discrete sequences where the attractor of the IFS is self-affine or piecewise self-affine in R ² or R ³ (R is the set of real numbers). In this paper, the piecewise hidden-variable fractal model is extended from R ³ to R ⁿ (n is an integer greater than 3), which is called the multi-dimensional piecewise hidden variable fractal model. This new model uses a “mapping partial derivative” and a constrained inverse algorithm to identify the model parameters. The model values depend continuously on all the hidden variables. Therefore the result is very general. Moreover, the piecewise hidden-variable fractal model in tensor form is more terse than in the usual matrix form.     

Exact Averaging of Stochastic Equations for Transport in Random Velocity Field

We present new examples of exactly averaged multi-dimensional equation of transport of a conservative solute in a time-dependent random flow velocity field. The functional approach and a technique for decoupling the correlations are used. In general, the averaged equation is non-local. We study the special cases where the averaged equation can be localized and reduced to a differential equation of finite-order, where the problem of evolution of the initial plume (Cauchy problem) can be solved exactly. We present in detail the results of the analyses of two cases of exactly averaged problems for Gaussian and telegraph random velocity with an identical exponential correlation function, which are informative and convenient models for continuous and discontinuous random functions. The problems in which the field has sources of solute and boundaries are also examined. We study the behavior of different initial plumes for all times (evolutions and convergence) and show the manner in which they approach the same asymptotic limit for two stochastic distributions of flow-velocity. A comparison between exact solutions and solutions derived by the method of perturbation is also discussed.     

随机剪切柱在地震激励下的演变随机响应

随机剪切柱是指固连于地面的剪切柱的某些物理参数是随机变量 ,该模型在Niigata地震激励下的响应属于演变随机响应。本文将新近发展起来的演变随机响应问题的统一解法 ,推广到用于求解随机结构振动响应问题。首先用这一方法求出每个样本结构的随机响应 ,然后用MonteCarlo法来进一步求随机结构的集合随机响应特性。这样 ,与单纯用Monte Carlo法进行数字模拟相比 ,可使计算工作量大为减少。本文用随机剪切柱的演变随机响应问题加以说明     

LS-SVM在随机振动在线自适应逆控制中的应用

针对随机振动试验中波形再现实现中的非线性和不确定性的特点,提出了一种基于最小二乘支持向量机的自适应逆控制方法.首先根据试验样本数据利用模糊贝叶斯推断确定最小二乘支持向量机的参数,然后给出了基于最小二乘支持向量机的自适应逆控制器的设计方法,最后给出了随机振动在线自适应逆控制结构.实验结果表明该方法的有效性.     

Analyticity of Homogenized Coefficients Under Bernoulli Perturbations and the Clausius–Mossotti Formulas

This paper is concerned with the behavior of the homogenized coefficients associated with some random stationary ergodic medium under a Bernoulli perturbation. Introducing a new family of energy estimates that combine probability and physical spaces, we prove the analyticity of the perturbed homogenized coefficients with respect to the Bernoulli parameter. Our approach holds under the minimal assumptions of stationarity and ergodicity, both in the scalar and vector cases, and gives analytical formulas for each derivative that essentially coincide with the so-called cluster expansion used by physicists. In particular, the first term yields the celebrated (electric and elastic) Clausius–Mossotti formulas for isotropic spherical random inclusions in an isotropic reference medium. This work constitutes the first general proof of these formulas in the case of random inclusions.     

A semi‐implicit scheme for 3D free surface flows with high‐order velocity reconstruction on unstructured Voronoi meshes

In this paper, we present a computationally efficient semi‐implicit scheme for the simulation of three‐dimensional hydrostatic free surface flow problems on staggered unstructured Voronoi meshes. For each polygonal control volume, the pressure is defined in the cell center, whereas the discrete velocity field is given by the normal velocity component at the cell faces. A piecewise high‐order polynomial vector velocity field is then reconstructed from the scalar normal velocities at the cell faces by using a new high‐order constrained least‐squares reconstruction operator. The reconstructed high‐order piecewise polynomial velocity field is used for trajectory integration in a semi‐Lagrangian approach to discretize the nonlinear convective terms in the governing PDE. For that purpose, a high‐order Taylor method is used as ODE integrator. The resulting semi‐implicit algorithm is extensively validated on a large set of different academic test problems with exact analytical solution and is finally applied to a real‐world engineering problem consisting of a curved channel upstream of two micro‐turbines of a hydroelectric power plant. For this realistic case, some experimental reference data are available from field measurements. Copyright © 2012 John Wiley & Sons, Ltd.     

Variation method for acoustic wave imaging of two dimensional targets

IntroductionAcousticwaveimaginghasagreatpotentialtobeappliedtonondestructivetesting ,medicalimaging ,geologicalprospectingandmaterialscienceetc.,andvariousimagingmethods,eachpossessingitsownpeculiarities,havebeenproposed .In 1 992 ,Moghaddam[1]putforwarda…     

On the numerical solution of structures with fractal geometry: The FE approach

The scope of the present paper is to present the numerical aspects of the theory developed in [1]. The fractal geometry of structure(s) is approximated either through the IFS (iterated function system) method or through the FI (fractal interpolation) method. These approximations of the fractal through classical curves and surfaces are combined with the FEM in order to get numerical results for important technical problems, which cannot be satisfactorily treated by other methods.

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Sommario Lo scopo del lavoro é quello di discutere gli aspetti numerici della teoria sviluppata in [1]. La geometria frattale della/e struttura é approssimata sia attraverso il metodo IFS (iterated function system) che il metodo FI (fractal interpolation). Queste approssimazioni frattali, attraverso curve e superfici classiche, sono combinate con il metodo degli elementi finiti, onde potere ottenere risultati numerici per importanti problemi tecnici che non potrebbero venire soddisfacentemente affrontati con altri metodi.

     

DIGITAL SPECKLE CORRELATION METHOD IMPROVED BY GENETIC ALGORITHM

The digital speckle correlation method is an important optical metrology for surface displacement and strain measurement. With this technique, the whole field deformation information can be obtained by tracking the geometric points on the speckle images based on a correlation-matching search technique. However, general search techniques suffer from great computational complexity in the processing of speckle images with large deformation and the large random errors in the processing of images of bad quality. In this paper, an advanced approach based on genetic algorithms (GA) for correlation-matching search is developed. Benefiting from the abilities of global optimum and parallelism searching of GA, this new approach can complete the correlation-matching search with less computational consumption and at high accuracy. Two experimental results from the simulated speckle images have proved the efficiency of the new approach.