结构损伤诊断的模态柔度差曲率法

为了使损伤更加明确显示,在求得结构损伤前后的模态柔度差之后,建立模态柔度差曲率作为二维结构的损伤指标来诊断损伤。考虑多种损伤情况,对二维结构进行了数值模拟,并用不同类型的指标进行了诊断。对比结果表明,该文指标与模态柔度曲率差指标所得结果基本上是相同的,且该文方法计算工作量要小。为了弥补利用模态柔度曲率差指标在诊断三维结...     

基于混沌和二维近似熵的滚动轴承故障诊断

针对滚动轴承故障的特征频率处于较低频带,容易被噪声淹没而难于直接检测的问题,提出了在衡量二维时间序列复杂性方面具有普遍意义的二维近似熵,及基于混沌和二维近似熵的滚动轴承故障诊断方法。该方法利用混沌振子对微弱周期信号的敏感性,可以直接检测低频段内滚动轴承微弱的故障特征频率。同时,以二维近似熵作为测度,能够从二维角度全面地量化振子的相变规律,从而客观、准确地识别振子状态并确定故障类型。对滚动轴承内、外圈故障的诊断实例验证了该方法的有效性。     

248 nm紫外显微镜微纳线宽校准方法的研究

248 nm波长照明的紫外显微镜能够获得高达80 nm的光学分辨率,可以实现对掩模板的线宽和一维/二维栅格参数的测量。作为测量仪器的248 nm紫外显微镜需要对其进行校准。该显微镜测量范围在nm量级,校准使用400 nm一维栅格标准物质,通过对仪器不确定度和标准物质自身不确定度的评估,得到采集图像每个像素的扩展不确定度为0.178 nm,并给出了实际测量时的不确定度评价公式。     

高熵合金的制备成形加工工艺

高熵合金作为一类新型多组元的复杂合金材料,因其独特的优异性能引发了广泛的关注.与传统合金相比,高熵材料的制备工艺与传统材料具有相似性,但也有其特殊性.从不同维度出发,讨论与分析了各种形态高熵材料的制备成形加工工艺,主要包括三维块体材料、二维薄膜及薄板材料、一维纤维材料以及零维粉末材料.主要总结了电弧熔炼法、感应熔炼法、...     

DNA遗传算法的改进二维最大熵图像分割

传统的二维最大熵图像分割算法在求解阈值时将二维直方图的噪声和边缘区域近似为零,降低了分割精度。针对这一问题,本文提出了一种基于DNA遗传算法的改进二维最大熵快速图像分割算法。利用梯度-均值灰度直方图得到有用区域,并以改进的二维最大熵作为优化函数,采用DNA计算遗传算法得到二维最优阈值。实验表明该算法对图像分割去噪能力强,分割效果好,以及快速有效处理能力。     

基于贝叶斯信息融合的测量不确定度评定与实时更新

基于贝叶斯信息融合与统计推断原理,建立不确定度动态评定模型,对测量不确定度进行实时更新。引入最大熵原理和爬山搜索优化算法,确定先验分布概率密度函数及样本信息似然函数,结合贝叶斯公式求出后验分布概率密度函数,实现不确定度的优化估计。仿真及实例分析表明,基于贝叶斯和最大熵方法评定及更新的测量不确定度更加接近理论值。     

采集速率评价结果的不确定度

介绍了四参数正弦波最小二乘法评价通道采集速率指标、以及不确定度分析和评价过程,同时给出了一个分析评价实例,该过程及结论可应用在对于测量标准进行相应指标的不确定度分析上,也可用于估计指标本身的不确定度。     

动态有效位数评价结果的不确定度

介绍了四参数正弦波最小二乘法评价动态有效位数指标、以及不确定度分析和评价过程,同时给出了一个分析评价实例。该过程及结论可应用在对于测量标准进行相应指标的不确定度分析上,也可用于估计指标本身的不确定度。     

基于最大熵区间分析的测量不确定度评定

为了提高测量不确定度评定的精度,采用最大熵区间分析方法。首先通过贝叶斯模型结合最大熵算法建立模型;接着对输入量样本信息下限和上限区间的不对称性进行分析,引入Jaynes熵以及引入拉格朗日量得出最短区间;考虑了输入量的不确定度随概率分布的传递过程,最后对输入量样本信息通过划分区间比值来确定被测量的不确定度评定。实验仿真显示该算法计算测量不确定度的区间较小,评定结果更为精确。     

基于块体形状分类的爆堆块度三维几何参数估算

爆堆图像分析法是统计爆破后矿岩块度分布的主要方法,针对图像分割后得到的岩块二维图形,研究了通过岩块二维投影几何参数估算岩块体积的方法。统计分析岩体中节理面倾向、倾角和间距的概率分布,通过Monte Carlo随机模拟三维节理面网络,建立节理面切割的矿岩原始块度三维模型,利用3组相互垂直的平面切割块度三维模型获取块体二维轮廓。对于不同的二维形状参数φ值区间,分析三维形状参数ε和κ的变化规律并建立其与φ的关系式。利用块体形状分类方法将块度三维模型分成6个块体集合,根据形状假设理论,由统计数据得出块体实际体积的对数和球形假设估算的块体体积的对数呈线性相关,应用回归分析推导出得到通过三维形状参数估算岩块体积的公式,通过实验对比,根据二维几何参数估算的块体体积和块度模型的块体实际体积的分布规律一致。     

Simulation of wave propagation in three-dimensional random media

Quantitative error analyses for the simulation of wave propagation in three-dimensional random media, when narrow angular scattering is assumed, are presented for plane-wave and spherical-wave geometry. This includes the errors that result from finite grid size, finite simulation dimensions, and the separation of the two-dimensional screens along the propagation direction. Simple error scalings are determined for power-law spectra of the random refractive indices of the media. The effects of a finite inner scale are also considered. The spatial spectra of the intensity errors are calculated and compared with the spatial spectra of intensity. The numerical requirements for a simulation of given accuracy are determined for realizations of the field. The numerical requirements for accurate estimation of higher moments of the field are less stringent.     

Entropy propagation analysis in stochastic structural dynamics: application to a beam with uncertain cross sectional area

This paper investigates the impact of different probabilistic models of uncertain parameters on the response of a dynamical structure. The probabilistic models of the uncertain parameters are constructed using the maximum entropy principle, where different information is considered, such as bounds, mean value, etc. Nested probabilistic models are constructed with increasing information; as the information given increases, the level of entropy of the input model decreases. The response of the linear dynamical model is given in the frequency domain, and the propagation of the input uncertainty throughout the computational model is analyzed in terms of Shannon’s entropy. Low and high frequencies are analyzed because uncertainties propagate differently depending on the frequency band. A beam discretized by means of the finite element method with random cross sectional area (random field) is the application analyzed.     

随机多相材料微观结构的三维统计重构

根据材料平面图像提供的局限的统计信息重构随机材料的三维微观结构是科学与工程中广泛研究的重要课题,而仅由样本提供的信息进行统计重构一直是一个公开的问题.综述了近年来多相材料三维微观结构的统计重构所使用的Gaussian随机场、JQA法、随机优化、信息论和模式识剐等主要方法的研究情况,在此基础上,提出了一些有待解决的问题,并展望了发展前景.     

Uncertainty-based sensitivity indices for imprecise probability distributions

An uncertainty-based sensitivity index represents the contribution that uncertainty in model input X_i makes to the uncertainty in model output Y. This paper addresses the situation where the uncertainties in the model inputs are expressed as closed convex sets of probability measures, a situation that exists when inputs are expressed as intervals or sets of intervals with no particular distribution specified over the intervals, or as probability distributions with interval-valued parameters. Three different approaches to measuring uncertainty, and hence uncertainty-based sensitivity, are explored. Variance-based sensitivity analysis (VBSA) estimates the contribution that each uncertain input, acting individually or in combination, makes to variance in the model output. The partial expected value of perfect information (partial EVPI), quantifies the (financial) value of learning the true numeric value of an input. For both of these sensitivity indices the generalization to closed convex sets of probability measures yields lower and upper sensitivity indices. Finally, the use of relative entropy as an uncertainty-based sensitivity index is introduced and extended to the imprecise setting, drawing upon recent work on entropy measures for imprecise information.     

机械产品可适应性度量方法及应用

基于信息论中信息熵的概念,用构成产品的模块集合来描述产品的当前状态,提出用可适应信息熵函数来表征产品设计的复杂性和不确定性,在此基础上提出了新的基于可适应信息熵的产品可适应度的计算公式.提出了2种可适应度计算方法,即基于结构配置图的可适应度计算和基于功能结构图的可适应度计算.实例研究表明,该可适应度具有很好的可操作性和实用性,能够应用于产品的开发和设计实践.     

A simple method for prediction of chilling times for objects of two-dimensional irregular shape

A simple chilling time prediction method applicable to two-dimensional irregular shapes is proposed. The method uses the first term in the series analytical solution for convective cooling of a sphere in conjunction with two geometric parameters determined by empirical algebraic equations. The real geometric shape is related to an equivalent infinite ellipse using dimensional measurements of the shape, and the two parameters determined for the ellipse. Experimental measurements with seven irregular geometric shapes (38 runs) and finite element numerical method predictions were used to test the methodology for predicting chilling rates at the thermal centre position. Observed differences were largely explainable by data uncertainties. The method has theoretical capability to predict mass-average temperatures, but this capability has not been experimentally tested.     

Efficient structural reliability methods considering incomplete knowledge of random variable distributions

The determination of an exact distribution function of a random phenomena is not possible using a limited number of observations. Therefore, in the present paper the stochastic properties of a random variable are assumed as uncertain quantities and instead of predefined distribution types the maximum entropy distribution is used. Efficient methods for a reliability analysis considering these uncertain stochastic parameters are presented. Based on approximation strategies this extended analysis requires no additional limit state function evaluations. Later, variance based sensitivity measures are used to evaluate the contribution of the uncertainty of each stochastic parameter to the total variation of the failure probability.     

Three-dimensional polarization states of monochromatic light fields

The 3×1 generalized Jones vectors (GJVs) [E(x) E(y) E(z)](t) (t indicates the transpose) that describe the linear, circular, and elliptical polarization states of an arbitrary three-dimensional (3-D) monochromatic light field are determined in terms of the geometrical parameters of the 3-D vibration of the time-harmonic electric field. In three dimensions, there are as many distinct linear polarization states as there are points on the surface of a hemisphere, and the number of distinct 3-D circular polarization states equals that of all two-dimensional (2-D) polarization states on the Poincaré sphere, of which only two are circular states. The subset of 3-D polarization states that results from the superposition of three mutually orthogonal x, y, and z field components of equal amplitude is considered as a function of their relative phases. Interesting contours of equal ellipticity and equal inclination of the normal to the polarization ellipse with respect to the x axis are obtained in 2-D phase space. Finally, the 3×3 generalized Jones calculus, in which elastic scattering (e.g., by a nano-object in the near field) is characterized by the 3-D linear transformation E(s)=T E(i), is briefly introduced. In such a matrix transformation, E(i) and E(s) are the 3×1 GJVs of the incident and scattered waves and T is the 3×3 generalized Jones matrix of the scatterer at a given frequency and for given directions of incidence and scattering.     

FREQUENCY DISTRIBUTION OF CONTACT ANGLES IN RANDOM PACKINGS OF GRANULAR MATERIALS

For a certain spectrum of stable grain configurations in randomly packed granular aggregates it is possible to determine the frequency distribution of relative contact angles among neighboring grains. This possibility is explored in the present paper for both two-dimensional and three-dimensional random packings of granular materials. Two relationships are first derived for the local void ratios of any stable “Voronoi Cell“ within the spectrum of stable configurations for the two and the three dimensional random packings, respectively. These relationships depend on the local distribution of relative contact angles, i.e., directions of contact normals. These local void ratios are then related to the gross void ratios of the random 2-D and 3-D assemblies through two integral equations of the Fredholm type of the first kind, their arguments being the frequency distribution functions. The first integral equation corresponding to a two-dimensional random disk packing is solved, exactly by a set of exponential functional transformations. These exact distributions are shown to be generally Maxwellian, with tails favorably biased towards the population of denser “Voronoi Cells” that are statistically more stable. A discussion on the uniform solutions of the integral equation for three-dimensional random packing of spheres is also presented. However, its general solution is left for a future work.     

A computational technique for evaluating the effective thermal conductivity of isotropic porous materials

A computational technique based on Maxwell's methodology is presented for evaluating the effective thermal conductivity of isotropic materials with periodic or random arrangement of spherical pores. The basic idea of the approach is to construct an equivalent sphere in an infinite space whose effects on the temperature at distant points are the same as those of a finite cluster of spherical pores arranged in a pattern representative of the material in question. The thermal properties of the equivalent sphere then define the effective thermal properties of the material. This procedure is based on a semi-analytical solution of a problem of an infinite space containing a cluster of non-overlapping spherical pores under prescribed temperature gradient at infinity. The method works equally well for periodic and random arrays of spherical pores.