既有铁路钢桥剩余疲劳寿命的概率性评估

中国铁路线上大量既有钢桥承受着日益繁重的交通荷载,其疲劳剩余寿命与使用安全已受到桥梁管理部门的高度重视,为避免不必要的维护与更换,应建立合理的既有钢桥使用安全评估方法。在建立能反映铆接钢桥疲劳破坏机理的脆断和韧断概率失效模型基础上,给出了疲劳可靠性分析的极限状态方程,并合理确定了随机变量的参数取值。建立了铆接钢桥构件双角钢概率疲劳破坏模型,基于Monte Carlo算法实现了铆接钢桥构件双角钢疲劳断裂失效概率的计算,编制了相应的概率断裂分析程序DAPFF。进而将概率断裂力学评估方法应用于京九线赣江桥的时变疲劳可靠度分析,并给出了赣江桥概率疲劳剩余寿命评估结果与维护对策。     

确定待定系数的一种方法

本文利用复变函数的理论，推导出一种确定待定系数的方法．     

Optimal control of single-server fluid networks

We consider a stochastic single-server fluid network with both a discounted reward and a cost structure. It can be shown that the optimal policy is a priority index policy. The indices coincide with the optimal indices in a semi-Markovian Klimov problem. Several special cases like single-server reentrant fluid lines are considered. The approach we use is based on sample path arguments and Pontryagins maximum principle. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于ZigBee的智慧温室蓄电池监测节点设计

针对传统温室监测节点蓄电池剩余电量问题,提出一种改进的基于ZigBee无线通信技术的温室节点无线监测方案,设计一个经济实用的低功耗ZigBee无线监测节点;以CC2530为主控芯片,通过控制不同的传感器和电池智能管理芯片DS2438及其外围电路,实现温室环境参数和各节点蓄电池电压、电流以及剩余电量的精确测量并实时显示;测试结果表明,系统运行稳定,数据检测精度达到0.001。     

A perturbed gamma degradation process with degradation dependent non‐Gaussian measurement errors

This paper proposes and illustrates a new perturbed gamma degradation process where the measurement error is modeled as a non‐Gaussian random variable that depends stochastically on the actual degradation level. The expression of the likelihood function for a generic set of noisy degradation measurements is derived, and the expression of the remaining useful life distribution of a degrading unit that fails when its degradation level exceeds a given threshold limit is formulated. A particle filter method is suggested, which allows one to compute the likelihood function and to estimate the remaining useful life distribution in a quick yet efficient manner. In addition, a closed‐form approximation of the perturbed gamma process is proposed to use in the special, yet meaningful, case where the standard deviation of the measurement error depends linearly on the actual degradation level. Finally, an applicative example is discussed, where the parameters of the perturbed gamma process, the remaining useful life distribution, and the mean remaining useful life of the degrading units are estimated from a set of noisy real degradation data.     

Multi-layered round robin routing for parallel servers

We study a system of several identical servers in parallel, where a routing decision must be made immediately on a job’s arrival. Jobs arrive according to a Poisson process, with their processing times following a discrete distribution with finite support. The processing time of a job is known on arrival and may be used in the routing decision. We propose a policy consisting of multi-layered round robin routing followed by shortest remaining processing time scheduling at the servers. This policy is shown to have a heavy traffic limit that is identical to one in which there is a single queue (no routing) and optimal heavy traffic scheduling. In light traffic, we show that the performance of this policy is worse than round robin routing followed by shortest remaining processing time scheduling. We also quantify the difference between round robin and multi-layered round robin routing, which in turn yields insights on the relative importance of routing versus (local) scheduling in such systems. AMS subject classifications: 68M20 · 60K25 (Work done while both authors were visitors at EURANDOM, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.)     

具有剩余寿命的M/G/1/K排队模型非负解的存在唯一性

研究了以剩余寿命作为增补变量的M／G／1／K排队模型．利用泛函分析中线性算子半群的积分半群理论讨论了该模型的瞬态解的存在唯一性问题．     

异物致损铁道车轴的疲劳强度及寿命评估

车轴是高速列车关键承载部件, 承受着源自车体、轨道的各种载荷,其疲劳行为直接关乎列车运行安全. 疲劳裂纹往往具有较强的隐蔽性和突然性,由车轴断裂发生的列车脱轨事件具有灾难性,因此确保车轴在运行中不发生失效事故, 对高速列车可靠运行至关重要.高速列车实际运营中, 车轴外表面受到各种异物击打, 会形成深度达毫米级的缺陷,破坏车轴表面完整性, 严重威胁车辆安全.本研究采用空气炮装置预制合金钢车轴小试样异物致损(foreign object damage, FOD)缺陷,采用扫描电子显微镜和体视显微镜观测损伤特征.开展高周疲劳试验获得光滑试样和FOD损伤小试样的疲劳S-N曲线,考虑载荷模式、表面质量和尺寸系数推证出全尺寸车轴的疲劳性能.断口分析表明, 裂纹于FOD附近多处位置萌生, 并在不同平面内连续扩展,最终汇聚为一个半椭圆形裂纹. 基于Peterson公式和El Haddad模型估算异物冲击速度100 m/s和138 m/s试样的理论疲劳极限远低于试验结果, 过于保守; 同时也远低于标准推荐值, 偏于危险. 最后,采用修正的Miner理论公式估算含FOD实物车轴的服役寿命,满足最低25年的服役寿命.      

Using degradation models to assess pipeline life

Longitudinal inspections of thickness at particular locations along a pipeline provide useful information to assess the remaining life of the pipeline. In applications with different mechanisms of corrosion processes, we have observed various types of general degradation paths. We present two applications of fitting a degradation model to describe the corrosion initiation and growth behavior in a pipeline. We use a Bayesian approach for parameter estimation for the degradation model. The failure‐time and remaining lifetime distributions are derived from the degradation model, and we compute Bayesian estimates and credible intervals of the failure‐time and remaining lifetime distributions for both individual segments and for the entire pipeline circuit.     

不完美维护活动干预下的设备剩余寿命估计

剩余寿命估计是保障设备安全性和可靠性的关键技术。现有文献在研究维护活动干预下的设备剩余寿命估计问题时,通常仅考虑维护活动对退化水平或退化速率的单一影响,忽略了维护活动对两者的双重影响。鉴于此,提出了一种考虑不完美维护活动影响的性能退化建模与剩余寿命估计方法,融合了维护活动对设备退化水平和退化速率的双重影响。首先基于扩散过程分阶段建立存在不完美维护活动干预下的随机退化模型,然后基于设备的状态监测数据和维护数据对模型参数进行极大似然估计和Bayesian更新,最后在首达时间的概念下,推导得到了剩余寿命的解析概率分布。实验结果表明,所提出方法能够大大提高存在不完美维护活动影响设备的剩余寿命估计精度。