基于GaAs激光器性能退化的可靠性度量方法

针对传统可靠性度量方法对高可靠性及长寿命的激光产品进行可靠性度量存在因模型假设不准确而出现可靠性度量错误风险的问题,基于性能退化轨迹提出了利用非参数局部线性回归估计对实际的退化模型进行直接估计的方法.该方法在确定实际模型后,利用失效阈值外推获得伪失效寿命时间,进而采用完全寿命时间数据进行可靠性度量.最后通过对GaAs激光器的退化数据进行可靠性验证分析,结果表明此方法提高了可靠性的预测精度,拟合程度高,稳健性好,采用非参数局部线性回归估计方法得到的结果合理、准确.     

Reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation

This paper presents an extension of reliability analysis of electronic devices with multiple competing failure modes involving performance aging degradation. The probability that a product fails on a specific mode is derived. Using this probability, the dominant failure mode on the product can be predicted. A practical example is presented to analyze an electronic device with two kinds of major failure modes–solder/Cu pad interface fracture (a catastrophic failure) and light intensity degradation (a degradation failure). Reliability modeling of an individual failure mode and device reliability analysis is presented and results are discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Testing and analysing capability performance for products with multiple characteristics

Process capability analysis is a vital part of an overall quality improvement programme. Numerous techniques and tools have been proposed for process capability analysis. Among these, indices and charts of process capability are simple and effective tools and widely used in the manufacturing industry. Many scholars have revealed numerous valuable aspects of previously developed tools and methods. Due to the rising demands of product quality, the current tools and methods are insufficient for enabling managers to make informed decisions. To address this gap, this study proposes a hypothesis testing procedure which determines whether the process capabilities satisfy the target level. Furthermore, this study proposes an integrated quality test chart (IQTC), which can display the process potential and performance for an entire product with smaller-the-better, larger-the-better and nominal-the-best specifications. The proposed procedure and IQTC incorporate the quality-level concept of the Six Sigma model and can be used to quantitate the relationships among the quality level, capability indices and process yield. They can be applied to assist managers in measuring, monitoring, analysing and improving process performance in a timely manner which will help ensure that the quality levels of their products meet customer demands. Finally, an example is provided to illustrate how to use the proposed procedure and IQTC.     

Real‐time Reliability Evaluation with a General Wiener Process‐based Degradation Model

The aim of this paper is to investigate the issue of real‐time reliability evaluation based on a general Wiener process‐based degradation model. With its mathematical tractability, the Wiener process with a linear drift has been widely used in the literature, to characterize the dynamics of the degradation process or its transformation. However, the nonlinear degradation process, which can't be properly linearized, exists in practice. The dynamics of such a degradation process can't be accurately captured by linear models. Here, a general Wiener process‐based degradation model is proposed, which covers a variety of Wiener process‐based models as its limiting cases. A two‐stage method is presented to estimate the unknown parameters. Two real‐time reliability evaluation procedures are presented for different conditions: one is the analytical evaluation procedure, and the other is the simulated evaluation procedure. It is shown that when new degradation information is available, the evaluation results can be adaptively updated. Moreover, to check out the proposed degradation model, a graphical method is provided. Finally, the validity of the proposed evaluation method is illustrated by a numerical example and two real‐world examples. Copyright © 2013 John Wiley & Sons, Ltd.     

基于Gamma退化过程的直升机主减速器行星架剩余寿命预测模型

鉴于Gamma过程具有平稳、独立增量等退化建模所需的属性,将其用于描述设备退化过程,并针对缺乏故障数据时难以进行剩余寿命预测的问题,利用设备运行中采集的表征其退化状态的大量间接状态参数和少量直接状态参数,建立了基于Gamma退化过程的剩余寿命预测模型;针对经验最大化算法中似然函数难以解析求解的问题,引入粒子滤波算法实现了模型参数估计;最后将模型应用于直升机主减速器行星架的剩余寿命预测,得到了不同时刻的预测结果及95%置信区间,验证了预测模型的有效性和准确性。     

Reliability and performance analysis for fault-tolerant programs consisting of versions with different characteristics

This paper presents a simple straightforward algorithm for evaluating reliability and expected execution time for software systems consisting of fault-tolerant components. The components are built from functionally equivalent but independently developed versions characterized by different reliability and performance. Both N-version programming (with parallel and sequential execution of the versions) and the recovery block scheme are considered within a universal model.     

Electro-mechanical modeling of Nb3Sn CICC performance degradation due to strand bending and inter-filament current transfer

Performance degradation of Nb₃Sn cable-in-conduit conductors (CICCs) is a critical issue in large-scale magnet design such as the International Thermonuclear Experimental Reactor (ITER) and the series-connected hybrid (SCH) magnets currently under development at the National High Magnetic Field Laboratory (NHMFL). Not only the critical current is significantly lower than expectations but also the voltage-current characteristic is observed to have a much broader transition from a single strand to a CICC cable. The variation of conductor voltage-current characteristic as a result of cable electromagnetic, mechanical and thermal interactions is challenging to model. In this paper, we use a new numerical model, called the Florida electro-mechanical cable model (FEMCAM) benchmarked against 40 different conductor tests, to study the influence of bending strain and current non-uniformity on the critical current and n-value of Nb₃Sn strands and CICC cables. The new model combines thermal bending effects during cool-down, electromagnetic bending effects during magnet operation and current transfer in strands with filament fracture. The n-value of a strand under bending is derived from integration of filament critical current over strand cross-section for full and no current transfer. The cable n-value is obtained from the power law relation of cable electric field and critical current curve. By comparing numerical results with measurements of advanced Nb₃Sn strands and various CICC cables, we demonstrate that FEMCAM is self-consistent in modeling inter-filament current transfer. The new model predicts that I_c degradation of bent strands initially follows closely full current transfer but starts deviating and falls between full and no current transfer with an increasing bending strain. The results agree with recent TARSIS measurements for less than 1% bending strain mostly interested in practice. The strand n-value degradation from FEMCAM with no filament current transfer agrees better with measurements than that from full current transfer. Finally, FEMCAM simulated cable n-values are compared with various CICC measurements. The results imply that FEMCAM is a useful tool for the design of Nb₃Sn-based CICCs and both thermal bending and electromagnetic bending play important roles in CICC performance.     

行波热声发动机的多负载声功输出特性

为进一步提高热声发动机的声功输出能力并为驱动多负载做准备,提出了热声发动机声功的多路引出方案。实验中以氮气为工质,工作压力为2．4MPa,在热声发动机环路压比稳定在1．20的情况下,从环路声容和谐振管处同时引出声功,获得了389．95W的最大声功,11．3％的最大声功输出效率以及16．0％的最大声功输出炯效率,这比单独从环路引出的最大声功和效率分别提高了51．4％,24．6％以及19．4％。     

基于EMD多尺度威布尔分布与HMM的轴承性能退化评估方法

轴承作为旋转机械中的重要部件,对其性能退化状态进行准确评估是开展预测性维护的重要前提。针对现有性能退化指标在鲁棒性和敏感性上的不足,提出一种基于多尺度威布尔分布与隐马尔可夫模型(Hidden Markov model,HMM)的滚动轴承性能退化评估方法。首先,采用经验模态分解(empirical mode decomposition,EMD)对轴承振动信号进行多尺度分解,将轴承振动数据分解到不同尺度的本征模态分量(intrinsic mode function,IMF)中;然后,通过峭度指标选取故障特征信息明显的IMF分量,并对各个IMF分量进行滑动窗口威布尔分布拟合,提取多尺度威布尔形状参数作为性能退化特征;最后,将轴承正常状态下退化特征参数输入隐马尔可夫模型(Hidden Markov model,HMM)进行训练,建立性能退化评估模型,从而实现轴承性能退化评估。试验结果表明,该评估方法可以有效反映轴承的性能退化趋势,与其他相关方法相比,该方法能够及时识别到轴承早期故障,并且具有较强的稳定性。     

Quality evaluation of internal cylindrical grinding process with multiple quality characteristics for gear products

Gears are among the most crucial components in the transmission systems of machine tools. Gear manufacturing includes a number of processing procedures. The grinding process is an important procedure involving high precision and fairly small grinding surfaces. For this reason, this study aimed at developing a quality assessment model for the internal cylindrical grinding process of gears. The Six Sigma quality indices (SSQIs) were used to directly assess the quality of the internal cylindrical grinding process due to their ability to directly reflect quality level and process yield. Since the process may include nominal-the-best (NTB), larger-the-better (LTB) and smaller-the-better (STB) quality characteristics, so we used the variable transformation method to normalise the specifications of each quality characteristic for the convenient and effective management and analysis of process performance for multiple quality characteristics. We then constructed a multi-characteristic process quality analysis chart (MPQAC) to simultaneously assess the quality levels of various quality characteristics. Furthermore, the MPQAC can provide references for process improvement. This ensures the quality of internal cylindrical grinding and enhances the quality of gear and machine tool products. Finally, a real-world application and numerical experiments demonstrate the effectiveness and practical applicability of the proposed method.     

The development of a target‐focused process capability index with multiple characteristics

Within an industrial manufacturing environment, Process Capability Indices (PCIs) enable engineers to assess the process performance and ultimately improve the product quality. Despite the fact that most industrial products manufactured today possess multiple quality characteristics, the vast majority of the literature within this area primarily focuses on univariate measures to assess process capability. One particular univariate index, C_pm, is widely used to account for deviations between the location of the process mean and the target value of a process. While some researchers have sought to develop multivariate analogues of C_pm, modeling the loss in quality associated with multiple quality characteristics continues to remain a challenge. This paper proposes a multivariate PCI that more appropriately estimates quality loss, while offering greater flexibility in conforming to various industrial applications, and maintaining a more realistic approach to assessing process capability. Copyright © 2010 John Wiley & Sons, Ltd.     

Time jitter influence on the performance of gamma–gamma turbulence FSO links with various modulation schemes

ABSTRACT

The research area of optical wireless communication links has attracted significant interest over the last years due to the significant advantages offered by this kind of technology. However, the performance of FSO communication systems depends strongly on the effects, which are related to the atmosphere along the propagation path such FSO links are using. More specifically, the weather conditions and atmospheric turbulence effects can deteriorate considerably the performance characteristics. In this work, we are studying the joint influence of atmospheric turbulence and time jitter effects on the average BER of an FSO link by presenting a new approach for various modulation schemes. Thus new closed-form mathematical expressions are derived for accurate estimation of the BER performance of the optical wireless communication systems. Finally, using the obtained expressions and typical parameter values for FSO links, the numerical results are presented and then verified through Monte Carlo simulations.     

基于贝叶斯理论及MCMC-MH算法推演地基土材料阻尼比的概率分布模型

浅层土壤的材料阻尼比参数分布可以通过多通道表面波(MASW)分析法提取的表面波衰减曲线来反演识别,但是衰减曲线对于较大深度和小空间尺度土壤性质的变化不敏感,反演的土壤材料阻尼比分布是非唯一的和不确定的.基于该研究建立了土体材料阻尼比随深度变化的先验概率分布模型,利用Nataf变换和Karhunen-Loeve将其分解为...     

Shape optimization of flow guides in three‐dimensional extrusion processes by an approximation scheme based on state variable linearization

A new scheme of shape optimization is applied to the design of a flow guide in flat‐die extrusion processes. In general, tremendous time is inevitably required for the optimization of large‐scale three‐dimensional extrusion processes. This is because the finite element analysis requires large computation time owing to the complexity of the die geometry and flow behaviour. The proposed scheme effectively reduces the computation time for the optimization process by approximating the objective function. This is achieved by introducing a transformed equation of the state variables. The scheme is then applied to the practical extrusion processes to produce ‘l’, ‘H’ and ‘L’ sections. The objective of the optimization is to make a balanced flow of the material in the exit region. Control points of a Bezier curve describing the outline of the flow guide are regarded as the design variables. Through application to large‐scale problems, the effectiveness and usefulness of the proposed scheme is demonstrated. Copyright © 2005 John Wiley & Sons, Ltd.     

基于微分求积法的变密度印刷纸带振动特性分析

采用微分求积法分析纸带面密度沿宽度方向线性变化时运动矩形纸带横向振动问题。建立了印刷运动纸带的横向振动模型。研究了变密度运动矩形纸带的无量纲振动频率与无量纲轴向运动速度、密度系数、纸带张力比之间的关系。数值计算结果表明,用微分求积法求解变密度运动矩形纸带横向振动问题是切实可行的。该研究结果为改善印刷纸带在印刷过程中的动态特性提供了理论依据。     

Reliability analysis of chatter stability for milling process system with uncertainties based on neural network and fourth moment method

A reliability analysis of the milling system with uncertainties is developed in this paper to predict reliable chatter-free machining parameters. The chatter reliability refers to the probability of no chatter for the dynamic milling system. Then a reliability model is established to predict the chatter vibration, in which the dominant modal parameters of the dynamic milling system are defined as random variables. To solve the reliable model with the second-order fourth-moment (SOFM) method, the limiting axial cutting depth is substituted by an explicit expression obtained using a neural network. Therefore, after distributions of the random parameters are experimentally determined, the reliability of the given machining parameters can be computed with the SOFM method. Furthermore, a reliable stability lobe diagram (RSLD) can be plotted to obtain more reliable and accurate stable region instead of the conventional SLD. A case study is performed to validate the feasibility of the proposed method. The reliability of the milling system was calculated with the SOFM method, the first-order second-moment (FOSM) method and the Monte Carlo simulation (MCS) method. The results from the SOFM method and MCS method were found to be more consistent. Moreover, a RSLD with the reliability level 0.99 was compared with a conventional SLD plotted using the mean values of the random parameters. Chatter tests shown that the RSLD with the higher reliability level was more accurate for predicting the chatter-free machining parameters.     

基于有限单元法的多间隙耦合齿轮传动系统非线性动态特性分析

针对齿轮传动系统的动态传递误差、单双边冲击状态、脱齿、拍击及混沌现象等复杂非线性动力学问题,在同时考虑齿侧间隙、轴承间隙、时变啮合刚度及齿面摩擦等非线性特性的基础上,首次提出一种基于有限单元法的多间隙耦合齿轮传动系统的非线性动态特性分析方法。以某单级斜齿轮传动系统为例,利用大型通用有限元分析软件AN-SYS/LS-DYNA建立耦合系统动力学模型,分析支撑状态下耦合系统的非线性动态特性,研究了不同转速及负载力矩对耦合系统非线性动态特性的影响规律。结果表明有限单元法能在满足高精度分析的条件下求解各种复杂工况的齿轮系统非线性动力学问题,为进一步研究齿轮传动系统非线性动力学问题提供有力工具。     

Buckling and free vibration finite strip analysis of composite plates with cutout based on two different modeling approaches

A Reddy type, third order shear deformation theory of plates is applied to the development of two versions of finite strip method (FSM), namely semi-analytical and spline methods, to predict the behavior of the moderately thick plates containing cutouts. The internal cutouts are modeled based on two different modeling approaches, and the effects of cutouts on the buckling critical stresses as well as natural frequencies are investigated.     

Calculation of mean outcrossing rates of non-Gaussian processes with stochastic input parameters — Reliability of containers stowed on ships in severe sea

Mean outcrossing rates can be used as a basis for decision support for ships in severe sea. The article describes a procedure for calculating the mean outcrossing rate of non-Gaussian processes with stochastic input parameters. The procedure is based on the first-order reliability method (FORM) and stochastic parameters are incorporated by carrying out a number of FORM calculations corresponding to combinations of specific values of the stochastic parameters. Subsequently, the individual FORM calculation is weighted according to the joint probability with which the specific combination of parameter values is expected to occur, and the final result, the mean outcrossing rate, is obtained by summation. The derived procedure is illustrated by an example considering the forces in containers stowed on ships and, in particular, results are presented for the so-called racking failure in the containers. The results of the procedure are compared with brute force simulations obtained by Monte Carlo simulation (MCS) and good agreement is observed. Importantly, the procedure requires significantly less CPU time compared to MCS to produce mean outcrossing rates.     

基于VOF法的风暴潮洪水演进三维数值模拟

为了提高风暴潮灾害应急处置能力,确保防潮安全,文章建立了耦合流体体积函数(VOF)法的三维非稳态水气两相流k-ε模型,采用等效糙率的方法处理城市密集建筑群,既考虑了其阻水作用,又考虑了其蓄水作用。针对天津市滨海新区海河与永定新河之间区域的风暴潮洪水演进数值模拟与分析,对100年一遇风暴潮洪水淹没情况进行分析,并对不同频率的风暴潮洪水的严重性进行了比较。结果表明,随着风暴潮发生频率的增加,风暴潮淹没范围逐渐减小,水深随着频率的增加是逐渐减少的,该研究为海堤安全管理、风暴潮灾害的快速科学评估提供了理论依据和技术支持。