基于广义Morse小波和EWT的移动荷载下结构时变频率识别

提出了基于广义Morse小波和经验小波变换的移动荷载作用下结构时变频率识别方法。首先介绍了经验小波变换技术和广义Morse小波特性,采用经验小波变换对结构响应信号进行分解,对分解得到的不同经验模式成分采用广义Morse小波分析,提取信号小波脊线识别结构瞬时频率。用一个数值算例验证了方法的有效性和精度。随后设计了一个移动小车通过钢板梁的模型试验,采用该方法识别其时变频率并与有限元计算结果进行对比分析,进一步验证方法的效果。     

Canny准则小波边缘检测在图像融合中的应用

提出了一种新的图像融合方法。该方法选择Canny准则作为边缘检测的基础,并结合小波变换算法,确定图像边缘位置。在小波域中,对高频信息依据其是否为边缘点采用不同的融合策略,对低频信息利用加权法进行融合,再进行小波逆变换重构融合图像。实验结果表明,提出的算法在抑制噪声的同时,能有效地突出边缘细节,更好地保持图像的空间分辨力。对于多聚焦图像的融合,偏差度为0.0520,熵为7.6609,相似度达到0.9985。     

BP-Neural-Network-Based Tool Wear Monitoring by Using Wavelet Decomposition of the Power Spectrum

In a drilling process, the power spectrum of the drilling force is related to the tool wear and is widely applied in the monitoring of tool wear. But the feature extraction and identification of the power spectrum have always been an unresolved difficult problem. This paper solves it through decomposition of the power spectrum in multilayers uzing wavelet transform and extraction of the low frequency decomposition coefficient as the envelope information of the power spectrum. Intelligent identification of the tool wear statuz is achieved in the drilling process through fusing the wavelet decomposition coefficient of the power spectrum by uzing a BP( Back Propagation) neural network. The experimental results show that the features of the power spectrum can be extracted efficiently through this method, and the trained neural networks show high identification precision and the ability of extension.     

基于小波和奇异值分解的图像边缘检测

针对传统图像边缘检测抑制噪声能力弱的问题,给出了一种小波变换和局部梯度场内奇异值分解相结合的边缘检测方法.首先在图像预处理阶段,为了提取准确的边缘特征,文中利用小波变换的时频局部化特性,对图像进行小波变换.该文对用小波求取的梯度场使用局部梯度奇异值分解的方法;利用奇异值的特性和良好的稳定性,使提取的边缘特征更加突出并且能够达到抑制噪声的目的.实验证明该文方法既能在无噪声影响的图像中提取出清晰完整的单边缘,又能在有噪声干扰的情况下提取出理想的边缘.     

一种改进的遥感图像融合方法

针对传统的IHS变换和Mallat算法在融合多光谱图像和高空间分辨力图像时存在的不足,提出了一种将IHS变换和平稳小波变换相结合的遥感图像融合方法;另外,对多光谱图像和高空间分辨力图像因空间分辨力的不同而带来的融合图像中所存在的虚假轮廓问题,提出在融合过程中先定位虚假轮廓出现的位置,然后加以处理的方法.仿真结果表明,本文算法在光谱失真上小于IHS变换法,克服了Mallat算法存在的方块效应,同时较好的抑制了虚假轮廓.     

Effects of Process Parameters on the Temperature Field in Ti-6Al-4V Alloy Blade Precision Forging Process

Blade precision forging is a high temperature and large plastic deformation process. Process parameters have a great effect on temperature distribution in billet, so in this paper, by taking a Ti-6Al-4V alloy blade with a tenon as an object, the influence of process parameters on the temperature distribution in precision forging process was investigated using 3D coupled thermo-mechanical FEM （finite element method） code developed by the authors. The results obtained illustrate that： （1） the gradient of temperature distribution increases with increasing the deformation degree; （2） with increasing the initial temperature of the billet, the zones of high temperature become larger, and the gradient of temperature distribution hardly has any increase; （3） friction factors have little effect on the distribution of temperature field; （4） with increasing upper die velocity, temperature of the billet increases while the temperature gradient in billet decreases. The results are helpful to the design and optimization of the process parameters in precision forging process of Ti-alloy blade.     

Effects of Process Parameters on the Temperature Field in Ti-6A1-4V Alloy Blade Precision Forging Process

Blade precision forging is a high temperature and large plastic deformation process. Process parameters have a great effect on temperature distribution in billet, so in this paper, by taking a Ti-6Al-4V alloy blade with a tenon as an object, the influence of process parameters on the temperature distribution in precision forging process was investigated using 3D coupled thermo-mechanical FEM (finite element method) code developed by the authors. The results obtained illustrate that: (1) the gradient of temperature distribution increases with increasing the deformation degree; (2) with increasing the initial temperature of the billet, the zones of high temperature become larger, and the gradient of temperature distribution hardly has any increase; (3)friction factors have little effect on the distribution of temperature field; (4) with increasing upper die velocity,temperature of the billet increases while the temperature gradient in billet decreases. The results are helpful to the design and optimization of the process parameters in precision forging process of Ti-alloy blade.     

梯度功能材料板瞬态温度场有限元分析

采用有限元法与有限差分法相结合的方法,对梯度功能材料板的瞬态温度场进行了分析,并且通过ＺｒＯ２和Ｔｉ－６Ａｌ－４Ｖ组成的梯度功能材料对本方法的正确性进行了检验,最后给出了加热、冷却过程的瞬态温度场分布。     

A spline wavelet finite‐element method in structural mechanics

The wavelet‐based methods are powerful to analyse the field problems with changes in gradients and singularities due to the excellent multi‐resolution properties of wavelet functions. Wavelet‐based finite elements are often constructed in the wavelet space where field displacements are expressed as a product of wavelet functions and wavelet coefficients. When a complex structural problem is analysed, the interface between different elements and boundary conditions cannot be easily treated as in the case of conventional finite‐element methods (FEMs). A new wavelet‐based FEM in structural mechanics is proposed in the paper by using the spline wavelets, in which the formulation is developed in a similar way of conventional displacement‐based FEM. The spline wavelet functions are used as the element displacement interpolation functions and the shape functions are expressed by wavelets. The detailed formulations of typical spline wavelet elements such as plane beam element, in‐plane triangular element, in‐plane rectangular element, tetrahedral solid element, and hexahedral solid element are derived. The numerical examples have illustrated that the proposed spline wavelet finite‐element formulation achieves a high numerical accuracy and fast convergence rate. Copyright © 2005 John Wiley & Sons, Ltd.     

地球低轨道卫星天线在轨热致振动分析

由于地球的频繁遮挡,当地球卫星在低轨道运行时,卫星的可展开天线会处在高低温交替的环境中,从而形成剧烈变化的温度场。剧烈的温度梯度变化会导致柔性较大的可展开天线发生热致振动,降低卫星全极化探测头部等关键部件的寿命。首先建立某型号卫星的物理模型,然后利用有限元法对其进行在轨时的空间瞬态热分析,得到可展开天线的温度场,将温度作为约束映射到结构仿真中,再在结构有限元模型上分析卫星的热变形,实现卫星天线热致振动的预测并为天线结构优化设计提供数据支持。对卫星模型进行热分析可以监测各时期的温度场以及预测有可能发生的热致振动,从而在不断优化设计的基础上避免这种不利的扰动。     

Broaching Performance of Superalloy GH4169 Based on FEM

The nickel-based superalloy GH4169 is an important material for high temperature applications in the aerospace industry. However, due to its poor machinability, GH4169 is hard to be cut and generates saw-tooth chips during high speed machining, which could significantly affect the dynamic cutting force, cutting temperature fluctuation, tool life, and the surface integrity of the parts. In this paper, the saw-tooth chip formation mechanism of superalloy GH4169 was investigated by the elasto-viscoplastic finite element method (FEM). Using the finite element software of ABAQUS/Explicit, the deformation of the part during high speed machining was simulated. The effective plastic strain, the temperature field, the stress distribution, and the cutting force were analyzed to determine the influence of the cutting parameters on the saw-tooth chip formation. The study on broaching performance has great effect on selecting suitable machining parameters and improving tool life.     

基于小波有限元法的连续梁移动荷载识别

将待识别车载简化为移动荷载投影到小波空间;车载所作用的连续梁模型以小波尺度函数为插值函数,以小波有限元法为建模方法,并通过单元转换矩阵实现了小波空间向物理空间的变换;采用部分加速度信号作为测得动响应数据,据此积分求出速度与位移响应并用于识别移动荷载。识别方法则借助了动态规划法与正则化法,避免了时程分析中的振荡现象。仿真算例验证了小波有限元用于连续梁模型移动荷载识别的可行性,且单元数较少;识别过程中所用一阶Tikhonov正则化法具有平滑去噪能力。     

小波基无单元法及其工程应用

论述数值计算中新的小波基无单元方法,即用小波基函数取代传统无单元方法中的幂级数基之后,使无单元法具有了小波变换的局域化和多分辨率等优良特性,并能有效地克服有限单元法的网格敏感性和单元之间应力不连续现象,从而不但拓展和丰富了无单元法的理论内容,也为其工程应用开辟了新的途径。     

基于约束独立成分分析的轴承复合故障特征提取方法

为从复合故障信号中提取各故障特征,提出一种离散小波变换(DWT)和约束独立成分分析(CICA)相结合的单通道复合故障诊断方法。首先通过DWT方法将单通道振动信号进行小波分解后,利用小波重构函数重构各层分解信号。然后取重构信号的包络信号作为CICA算法的输入矩阵,基于滚动轴承先验知识建立参考信号,从而分离出轴承各故障信号,提取故障特征。最后,在滚动轴承故障模拟实验台上进行了方法验证。结果表明:该方法可有效分离滚动轴承外圈和滚动体故障,实现了轴承复合故障的诊断。     

Phase field simulations of coupled microstructure solidification problems via the strong form particle difference method

This paper presents the development of a strong form-based collocation method called the particle difference method (PDM), capable of predicting the spatiotemporal evolution of polycrystalline material solidification through coupling of multi-phase and temperature fields. Cross coupled phase field evolution and heat transfer equations are discretized via the PDM to obtain the interface kinematics of polycrystalline boundary during solidification. A distinct feature of the PDM is its ability to represent derivative operators via a moving least-square approximation of the Taylor expansion through point-wise computations at collocation points. The method discretizes directly the strong forms using the pre-computed derivative operators at each collocation point and elegantly overcomes the topological difficulty in modeling intricate moving interfaces. To verify the efficacy of the PDM, numerical results are compared with those obtained from the conventional finite difference method for uniform and irregular distributions of the collocation points. The scalability of the parallelized PDM is tested by measuring its efficiency with increasing the number of processors. We also provide a solidification simulation with two ellipsoidal inclusions to demonstrate the capability of the PDM in complex moving interface problems with high curvature.     

An enrichment scheme for solidification problems

A new enriched finite element formulation for solving isothermal phase change problems is presented. We propose a fixed mesh method, where the discontinuity in the temperature gradient is represented by enriching the finite element space through a function whose definition includes a gradient discontinuity. Generally, in these types of formulations, the enrichment location (the location of the solidification front) is determined through a level set auxiliary scheme. In this work, this position is determined implicitly by constraining the temperature at the phase change boundary to be equal to the melting temperature. Several numerical examples are presented to show the application of the method.     

一种改进多分辨率图像融合算法

提出一种基于局部熵的多分辨图像融合算法。利用小波变换得到待融合图像的多分辨结构,同时得到图像的多分辨局部熵序列。以局部熵为判据,在图像多分辨结构相应各级上进行融合,得到融合图像的多分辨结构,利用小波逆变换重构融合图像。实验结果表明,该图像融合方法在保留TM多光谱图像光谱分辨率的同时,通过融合SPOT全色图像提高了空间分辨率,丰富了图像细节信息。     

滚动轴承振动信号的小波奇异性故障检测研究

该文以滚动轴承振动信号为分析对象 ,基于小波奇异性分析原理进行滚动轴承故障检测新方法的研究。通过求解待测信号的小波变换极大模来检测和识别信号中奇异点位置和奇异性大小 ,以及对噪声极大模的抑制处理 ,达到抑制或消除噪声的目的 ;最后 ,在剩余小波极大模的基础上进行信号重构 ,展现原待测信号中的故障信号模式。通过对铁路货车车轮用滚柱轴承振动信号的分析表明 ,此方法在大幅度地提高信噪比的同时 ,对由轴承损伤冲击造成的信号突变仍保持了较高的灵敏度和分辨率。为滚动轴承故障检测打下了良好的基础。     

纸张在弹性胶辊夹持下接触区域的数值分析

在准静态、无摩擦的条件下,应用级数形式的应力函数对复印机中纸张在弹性胶辊夹持下的接触问题进行了分析。模型源于复印机中的进纸单元,根据弹性理论,分别使用施密特正交化方法与无网格配点法对问题进行了求解,得到了接触区域的应力应变分布以及胶辊与纸张的表面速度比,为提高复印机胶辊的可靠性提供了参考。     

An XFEM plate element for high gradient zones resulted from yield lines

A high gradient of displacement field occurs when a yield line is formed in a plate with elasto‐plastic material. For such applications, the extended finite element method has shown to be an effective numerical method to capture the behavior of a plate with a locally nonsmooth displacement field, and a displacement field with a high gradient. In this article, a six‐node isoparametric plate element with extended finite element method formulation is presented to capture the elasto‐plastic behavior of a plate in small‐deformation analyses. The Hermite function is adopted at the element level to enrich both the translational and the rotational displacement approximation fields so that nonsmoothness in displacement fields near a yield line can be simulated. Copyright © 2013 John Wiley & Sons, Ltd.