加筋复合材料圆筒结构的撞击识别

以加筋复合材料圆筒结构为对象,研究了复合材料结构的外部低速撞击识别问题。采用压电传感器获取发生低速撞击时在结构内产生的应力波信号。针对加筋复合材料结构的撞击位置识别,特别是监测区域边缘的位置识别问题,提出了基于传感器信号功率的两步法来估计撞击位置; 撞击载荷的重构采用系统辨识方法,通过分析系统辨识方法中传递函数的模型阶次和相关性系数的关系,提出了模型阶次选择的原则以进一步完善该方法。结果表明: 所提出的两步定位法可较好地估计所有监测区域的撞击位置,所改进的系统辨识方法可较好地识别非加筋区域上的撞击位置和撞击载荷时间历程; 当撞击点为加筋区域时,由于筋条对应力波传播的复杂影响导致撞击识别误差偏大。     

A novel MTTF estimator and associated parameter estimation method on heavily censoring data

Many reliability and maintenance decision problems need to estimate mean-time-to-failure (MTTF) of a particular product component and/or build its life distribution model as early as possible based on field failure data. The field failure data are often heavily censored. In this case, the exponential-assumption–based method can considerably overestimate the MTTF, and the classical parameter estimation methods such as the maximum likelihood method (MLM) cannot provide robust estimates. This paper aims to address this issue through proposing a novel method to estimate the MTTF and life distribution parameters. The proposed method first derives a nonparametric estimator of MTTF based on the decomposition of the integral expression of the theoretical MTTF and sample statistical characteristics. The estimated MTTF is then combined with a two-step single-parameter MLM to estimate the distribution parameters. A numerical experiment is carried out, and a real-world dataset is analyzed. The results show that the proposed method can provide accurate and robust estimates for the MTTF and distribution parameters. The method is applicable for any life distribution and offers practitioners an efficient tool for reliability analysis.     

A fast 3D shape measurement method based on sinusoidal and triangular fringe projection

Existing methods to measure 3D shape of complex object involve processing more than six captured images to obtain the absolute phase, which limit the measurement speed. This paper presents two sinusoidal fringes and two triangular wave fringes which is used to measure 3D shape of complex object. The two-step phase-shifting sinusoidal fringes and two-step phase-shifting triangular wave fringes are calculated to obtain the wrapped phase, and then the two-step phase-shifting triangular wave fringes are used to determine the fringe order. Due to decrease the number of projection fringes, the speed of measurement increases. The triangular wave fringe carries more information of the object than linear increasing/decreasing ramp fringe in the actual measurement, more noise in the base phase to be overcome, thus improving the measurement accuracy. The benefits can be widely applied in high-speed, real-time 3D measurement of complex shape. Experimental results have demonstrated that the proposed method is simple, but effective.     

基于Shannon 复数小波的复合材料结构时间反转聚焦多损伤成像方法

研究了一种基于压电传感器阵列和主动Lamb 波的结构损伤成像方法,有助于克服Lamb 波在板结构中、特别是在复合材料板结构中存在的频散、多种模式及模式转换的现象给结构健康监测带来的困难。分析了结构多损伤散射信号的时间反转聚焦原理,在此基础上提出了一种基于Shannon 复数小波和时间反转聚焦的信号合成成像方法。该方法中,确定Lamb 波响应信号的到达时刻是信号能够准确聚焦的关键因素之一。提出了利用Shannon 复数小波变换计算Lamb 波响应信号到达时刻的方法。在碳纤维复合材料板结构上对整套信号合成成像方法进行了验证。研究结果表明,该方法能够有效地对同一个监测区域中的多个损伤进行成像定位。相对于30 cm ×30 cm 的监测区域,定位误差不超过2 cm。该方法有助于结构健康监测技术的工程应用。      

非线性RLW方程的经济型差分-流线扩散法

本文对非线性正则长波(RLW)方程的周期初边值问题提出了一种基于线性有限元空间的经济型差分-流线扩散(EFDSD)法,利用能量估计方法证明了该方法的稳定性和收敛性,得到了L2模拟丰满误差估计和H1模丰满误差估计。与以前的方法相比,该方法具有稳定性能好,便于实际编程计算等优点。     

Numerical study of the three-dimensional wave equation using the mesh-free kp-Ritz method

This paper deals with numerical modeling of three-dimensional linear wave propagation based on the mesh-free kp-Ritz method. The mesh-free kernel particle estimate is employed to approximate the 3D displacement field. A system of discrete equations is obtained through application of the Ritz minimization procedure to the energy expressions. Convergence analysis and error estimates of the kp-Ritz method for three-dimensional wave equation are also presented in the paper. From the error analysis, we found that the error bound between the numerical and the exact solution is directly related to the radii of weight functions and the time step length. Effectiveness of the kp-Ritz method for three-dimensional wave equation is investigated by three numerical examples.     

一种基于速度三角波的转台动态响应性能的评价方法

针对目前暂无转台瞬时速度响应评价方法的问题,提出一种基于速度三角波信号的转台动态响应性能评价方法。此方法采用偏差的包络分布估算转台系统速度的偏差范围。经实验证明,此评价方法具有较强的可行性。     

光纤表面等离子体共振传感系统的数据处理

针对表面等离子体共振原理以及光纤传感的优越特性,本文提出并实现了一种基于光纤表面等离子体共振效应的传感检测系统,给出了系统数据分析的处理模型.该方法根据偏度-峰值检验,采用高斯分布检验对共振区域附近的测试数据进行了均值处理,通过理论分析进一步指出采用均值估计的线性模型可以有效地估计共振波长;同时,在保证检测精度的前提下给出了数据处理的最小运算长度.结果表明,可以使系统数据计算的工作量降低至原来的2%,从而提高了系统的处理效率.     

Two-step camera calibration method based on the SPGD algorithm

Given the rapid convergence characteristic of the stochastic parallel gradient descent (SPGD) algorithm, this study proposes a method that applies the algorithm to a two-step camera calibration method to resolve the frequent iteration and long calibration time deficiencies that exist under the traditional two-step camera calibration method, thereby achieving rapid calibration. The method first uses image coordinates obtained with subpixel positioning technology as initial values of control variables, in addition to positive disturbances produced on a two-dimensional plane, then uses two-step theory to calculate the average value of aberrations. Based on the same rationale, negative disturbances are then produced and the average value of the aberrations is calculated. Finally if, after assessing whether to continue with further iterations based on the difference in these values, continued iterations confirm new control variables based on the SPGD algorithm iteration formula, a new cycle is started until the results satisfy requirements. Theoretical analysis and experimental results show that the proposed rapid calibration method using the SPGD algorithm in the two-step camera calibration method is 3-4 times faster than the traditional two-step calibration method, and that it has significant potential value for use in certain time-constrained projects.     

A failure mechanism consistency test method for accelerated degradation test

Accelerated degradation test (ADT) is generally used to accelerate degradation processes in products to estimate their lifespan and to assess their reliability in a short period of time. How to perform the failure mechanism consistency test is crucial in the application of the ADT method. Existing failure mechanism consistency test methods assume that degradation rates among individual products are the same. However, these methods do not take degradation dispersions caused by manufacturing technologies into consideration. To address this issue, a failure mechanism consistency test method for ADT based on the activation energy invariant method and the likelihood ratio test is proposed. First, a degradation modeling method for ADT is introduced. Then, the logarithmic maximum likelihood function values of the degradation models are estimated based on the two-step maximum likelihood estimation (MLE) method. Finally, the decision rule is proposed based on the likelihood ratio test. The method mentioned above is, then, used on the real degradation data of carbon-film resistors and bullet O-rings, and its effectiveness is verified. Furthermore, based on the failure mechanism change point in RTV5370 siloxane rubbers, the simulated degradation data are degenerated to compare the proposed method with the method not considering individual differences in different ADT programs and degradation dispersions.     

服务机器人目标同时识别与位姿判定研究

目前机器人尚难以自主建立起目标姿态的概念,通过人机交互方式辅助机器人对目标建模则不失为一种可行方案。提出了一种基于新型目标模型的离线/在线两步目标识别与位姿判定系统。离线阶段采用人机交互方式构建目标模型,在线阶段通过场景图像与目标模型的特征点对应即可自动发现目标,并计算其相对于机器人的位姿。实验证明,该系统能够有效完成对纹理目标的同时识别与位姿判定。     

Parallel two-step phase-shifting digital holograph microscopy based on a grating pair

An optical configuration for parallel two-step phase-shifting digital holographic microscopy (DHM) based on a grating pair is proposed for the purpose of real-time phase microscopy. Orthogonally circularly polarized object and reference waves are diffracted twice by a pair of gratings, and two parallel copies for each beams come into being. Combined with polarization elements, parallel two-step phase-shifting holograms are obtained. Based on the proposed configuration, two schemes of DHM, i.e., slightly off-axis and on-axis DHM, have been implemented. The slightly off-axis DHM suppresses the dc term by subtracting the two phase-shifting holograms from each other, thus the requirement on the off-axis angle and sampling power of the CCD camera is reduced greatly. The on-axis DHM has the least requirement on the resolving power of the CCD camera, while it requires that the reference wave is premeasured and its intensity is no less than 2 times the maximal intensity of the object wave.     

基于贝叶斯更新的深水桥墩波浪动力响应概率模型

海洋环境中的深水桥墩长期受到不规则随机波浪动力作用。传统设计规范中采用的特征波浪计算方法,虽然简单高效,但是无法充分考虑波浪随机性和动力效应对结构的影响。该文以深水桥墩在波浪作用下的动力响应与静力响应之间的概率关系为研究对象,应用贝叶斯更新理论建立简单有效的深水桥墩波浪动力响应概率模型。通过对比深水桥墩动力时程分析结果,验证模型的有效性,并对样本数量和模型形式进行讨论。研究表明：基于贝叶斯更新理论的深水桥墩波浪动力响应概率模型可以快速准确地计算波浪作用下深水桥墩的动力响应,能够有效修正传统静力方法存在的偏差,并可在样本数据非常有限的情况下对深水桥墩的动力响应进行较好估计。     

Complex-wave retrieval from a single off-axis hologram

We present a new digital two-step reconstruction method for off-axis holograms recorded on a CCD camera. First, we retrieve the complex object wave in the acquisition plane from the hologram's samples. In a second step, if required, we propagate the wave front by using a digital Fresnel transform to achieve proper focus. This algorithm is sufficiently general to be applied to sophisticated optical setups that include a microscope objective. We characterize and evaluate the algorithm by using simulated data sets and demonstrate its applicability to real-world experimental conditions by reconstructing optically acquired holograms.     

基于管道声模态的消声器传递损失计算

传递损失是评价消声器声学性能的一个重要指标。提出了一种方法—管道声模态法代替传统方法估算传递损失。对进出口截面积较小的消声器进行计算和检验,与传统方法比较,结果基本吻合,且过程简单,提高传递损失的计算效率。对进出口截面积较大的消声器,中高频段由于大量高次波的出现,传统方法失效;但低频段管中声波以平面波为主,其结果与传统法一致。因此可以采用管道声模态法快速估算传递损失。     

非线性成层地基下基岩平稳地震动输入

采用二次反演计算基岩的平稳地震动输入。首先根据《建筑抗震设计规范》（GB 50011—2001）的地震影响系数曲线，利用加速度峰值等效原则迭代计算得到地面加速度平稳功率谱密度；然后通过等价线性化法计算地基各土层的剪切模量和阻尼比，将地面加速度平稳功率谱密度作为地面边界上的虚拟稳态输入，运用半无限长剪切梁上的一维波动方程，通过非线性迭代分析求得非线性分层地基下基岩的加速度平稳功率谱密度。该方法可为缺乏地面或基岩地震加速度记录资料的地区的堤坝等大型上部结构及隧道、管道等建筑物的随机地震响应分析提供较为可靠准确的基岩地震动输入，并可得到地基中不同深度的加速度、剪应变等动力响应的稳态峰值期望值，为应用随机理论进行工程抗震计算提供了依据。     

Signal-to-noise ratio analysis to estimate ocean wave heights from X-band marine radar image time series

This work analyses the structure of the different contributions to the image spectrum derived by the three-dimensional Fourier decomposition of sea clutter time series measured by ordinary X-band marine radars. The goal of this investigation is to derive a method to estimate the significant wave height of the ocean wave fields imaged by the radar. The proposed method is an extension of a technique developed for the analysis of ocean wave fields by using synthetic aperture radar systems. The basic idea behind this method is that the significant wave height is linearly dependent on the square root of the signal-to-noise ratio, where the signal is assumed as the radar analysis estimation of the wave spectral energy and the noise is computed as the energy due to the sea surface roughness, which is closely related to the speckle of the radar image. The proposed method to estimate wave heights is validated using data sets of sea clutter images measured by a marine radar and significant wave heights derived from measurements taken by a buoy used as reference sensor.     

Introducing two hyperparameters in Bayesian estimation of wave spectra

An estimate of the on-site wave spectrum can be obtained from measured ship responses by use of Bayesian modelling, which means that the wave spectrum is found as the optimum solution from a probabilistic viewpoint. The paper describes the introduction of two hyperparameters into Bayesian modelling so that the prior information included in the modelling is based on two constraints: the wave spectrum must be smooth directional-wise as well as frequency-wise. Traditionally, only one hyperparameter has been used to control the amount of smoothing applied in both the frequency and directional ranges. From numerical simulations of stochastic response measurements, it is shown that the optimal hyperparameters, determined by use of ABIC (a Bayesian Information Criterion), correspond to the best estimate of the wave spectrum, which is not always the case when only one hyperparameter is included in the Bayesian modelling. The paper includes also an analysis of full-scale motion measurements where wave spectra estimated by the Bayesian modelling are compared with results from ocean surface measurements by satellite and from a wave radar. The agreement is found to be reasonable.     

Precise and fast phase wraps reduction in fringe projection profilometry

Phase wraps in a 2D wrapped phase map can be completely eliminated or greatly reduced by frequency shifting. But it usually cannot be optimally reduced using conventional fast Fourier transform (FFT) because the spectrum can be shifted only by a integer number in the frequency domain. In order to achieve a significant phase wrap reduction, we propose a fast and precise two-step method for phase wraps reduction in this paper, which is based on the iterative local discrete Fourier transform (DFT). Firstly, initial estimate of the frequency peak is obtained by FFT. Then sub-pixel spectral peak with high resolution is determined by iteratively upsampling the local DFT around the initial peak location. Finally, frequency shifting algorithm that operates in the spatial domain is used to eliminate phase wraps. Simulations and experiments are conducted to demonstrate the superb computing efficiency and overall performance of the proposed method.     

Sinewave parameter estimation algorithm with application towaveform digitizer effective bits measurement

The authors present a high-performance (i.e. high-precision and high-speed) algorithm to estimate the four parameters of a sine wave from a sampled data record. The estimation errors are derived in closed form, and hence, controllable. The authors then propose a method to measure a digitizers effective bits based on this algorithm. Simulation results indicate that the proposed method gives excellent estimates of the true resolution of the simulated ideal digitizer. This proposed algorithm is noniterative and gives swift and consistent results