Study on reliability modelling of a hydraulic excavator system

The failure patterns of a well-known brand of a hydraulic excavator system used in different environments were modelled adequately with an NHPP (non-homogeneous Poisson process) having time-dependent log-linear peril rate functions. Using the fitted model, the reliability of the excavator system was estimated in different environments (cement plant, coal mine, iron ore mine, etc.). The system reliability was found to be very poor during the initial phase of operation and gradually improved with an increase in cumulative operating hours regardless of change in environment. Notwithstanding this general trend, the system reliability differed significantly in different environments for any given duration of operation and was particularly very poor in cement plants. With the help of the FMEA technique, high risk prone failure modes of the excavator system of the given model were identified and appropriate corrective measures were initiated. The failure patterns of the modified excavator system changed regardless of environment, so much so that an HPP (homogeneous Poisson process) model with constant peril rate could be fitted adequately to characterize the failure pattern of the system. The system reliability improved considerably in the initial phase of operation since start-up.     

Weibull model selection for reliability modelling

A large number of models have been derived from the two-parameter Weibull distribution and are referred to as Weibull models. They exhibit a wide range of shapes for the density and hazard functions, which makes them suitable for modelling complex failure data sets. The WPP and IWPP plot allows one to determine in a systematic manner if one or more of these models are suitable for modelling a given data set. This paper deals with this topic.     

Complex system reliability modelling with Dynamic Object Oriented Bayesian Networks (DOOBN)

Nowadays, the complex manufacturing processes have to be dynamically modelled and controlled to optimise the diagnosis and the maintenance policies. This article presents a methodology that will help developing Dynamic Object Oriented Bayesian Networks (DOOBNs) to formalise such complex dynamic models. The goal is to have a general reliability evaluation of a manufacturing process, from its implementation to its operating phase. The added value of this formalisation methodology consists in using the a priori knowledge of both the system's functioning and malfunctioning. Networks are built on principles of adaptability and integrate uncertainties on the relationships between causes and effects. Thus, the purpose is to evaluate, in terms of reliability, the impact of several decisions on the maintenance of the system. This methodology has been tested, in an industrial context, to model the reliability of a water (immersion) heater system.     

Circuit breaker failure data and reliability modelling

The results from an extensive study of SF6 and minimum-oil circuit breaker failures in the Swedish and Finnish transmission systems are presented. The study includes 1546 breakers with a total operating history of 16 384 years. In the study, a detailed analysis of a specific SF₆ type of breaker revealed which parts caused the failures and an estimation of their hazard rates was made. A model of complete reliability for this type of breaker is presented, illustrated by presenting the operating and maintenance history of a shunt reactor breaker in the Swedish transmission system.     

Plastic encapsulated ics in military equipment reliability prediction modelling

This paper introduces a reliability prediction model for plastic encapsulated integrated circuits to be used in professional or defence electronics applications. The first part is a comparison between different reliability prediction models: their hypotheses, assumptions and validity domains are examined; constructive criticism is made and model amendments proposed for plastic encapsulated ICs reliability prediction. The second part presents the model itself. It addresses also thermal and environmental aspects. The third part explains how numerical values are found to fill the model and how it reflects the reliability of today's state-of-the-art of plastic encapsulation. In conclusion, we present the improvements that this model can bring to reliability prediction, in the particular case of plastic packages.     

The reliability physics approach to failure prediction modelling

Empirically based failure rate modelling methodologies employed in reliability prediction handbooks, and deterministic modelling methods are both critically examined using microelectronic packages as vehicles. As an alternative, a coupled mechano-stochastic approach to reliability prediction modelling is presented. The goal is to use physics of failure principles with appropriate failure probability density distributions to design for failure-free operation and predict failure times for components now available, as well as new components resulting from new materials, technologies and processes. In addition, an approach for extending the model to aid in logistics support analysis is discussed.     

System reliability of timber trusses based on non-linear structural modelling

Structural design is today concerned with single component performance where each limit state is related to a single mode of failure of a single component. Further, in limit state codes the strength variables are related to a deterministic value (usually the 5-percentile). However, in a structure with a number of elements, two different effects (called system effects) can be found:

Petri Net modelling and reliability evaluation of distributed processing systems

A Petri Net model for the evaluation of reliability for the execution of a computer program in a distributed processing system (DPS) is developed. The execution of a program in a DPS may require access to several files residing at different sites and communication paths between several node pairs. The dynamic behaviour of the system under consideration is represented in the form of token movements within the model. Then, by using the reachability, firing, and marking concepts of Petri Nets, an algorithm is developed to study the two important reliability measures, namely, distributed computer program reliability (DCPR) and distributed processing system reliability (DPSR). The proposed algorithm is efficient in the sense that it directly generates all possible sets of path identifiers for the accessibility of a file which resides at more than one place and is required for the execution of a computer program residing at some other place without evaluating minimal S-T-paths for all S-T-connections. The developed algorithm has been implemented on a minicomputer.     

新型叠加系统均力机理的数值模拟分析

附加侧向力是引起叠加系统旋转效应的重要原因。基于有限元法(finite element method,FEM),分别对新型叠加系统均力结构的4个尺寸变量进行数值模拟分析。结果表明:在一定范围内,随着均力板惯性矩、厚度和轴承座高度增加,力传感器所受侧向力波动量减小;均力板的弹性模量在150 GPa附近,力传感器获得较小的侧向力波动量。由此可知,特定的均力结构能有效抑制附加侧向力。     

Geotechnical system reliability of slopes

In slope stability analysis it is customary to search for the critical slip surface considering the conventional factor of safety as an index of stability. With the development of reliability analysis approaches within a probabilistic framework, alternative definitions of the critical slip surface can be adopted. Thus one may define a critical slip surface as one with the lowest reliability index or one with the highest probability of failure. However, it is important to consider the slope stability problem in terms of a system of many potential slip surfaces. For such a system, the calculation of system reliability is appropriate and desirable. In this paper, system reliability bounds are calculated within a probabilistic framework. The ‘system reliability’ or the ‘system probability of failure’ must be estimated for comparison with the corresponding reliability or probability of failure with respect to a ‘critical’ slip surface. The general slope stability problem involving non-zero internal friction angle involves a non-linear performance function. Moreover, the expression for factor of safety is usually inexplicit except for the ordinary method of slices which is not accurate except when ‘ø = 0’. This paper addresses the system reliability for inexplicit and non-linear performance functions as well as for linear and explicit ones. Any version of the method of slices may be used although the proposed approach is presented on the basis of the Bishop simplified method. It is shown that the upper bound system failure probability is higher than the failure probability associated with a critical slip surface. The difference increases as the coefficient of variation of the shear strength parameters increases.     

故障转子系统轴心轨迹的自动识别研究

轴心轨迹是转子系统故障诊断的重要依据,将整周期重采样、归一化的极半径序列引入轴心轨迹自动识别系统。首先对振动信号进行整周期重采样以降低转速和采样频率对小波去噪效果的影响,然后利用小波变换对其去噪并合成提纯的轴心轨迹,最后计算具有平移、伸缩和旋转不变性的极半径序列作为轴心轨迹特征,采用BP神经网络进行识别。实验结果表明该方法具有良好的识别效果。     

Measurement and system impact of multipath interference from dispersion compensating fiber modules

Dispersion compensating modules (DCM) are key components in long distance and high-speed fiber-optic transmission systems. However, many types of DCMs exhibit multipath interference (MPI) that acts as noise in transmission and degrades the bit error rate of the system. Further, MPI generated in DCMs is mostly due to forward scattering and mostly of the coherent type. This type of MPI cannot be correctly measured using conventional measurement techniques that use electrical spectrum analysis to measure post-detection noise. We demonstrate an accurate and simple method of MPI measurement using a swept wavelength system apparatus. We discuss the strengths and limitations of this measurement method and show system results of Q penalty due to MPI from concatenated DCMs.     

分子筛纯化系统常见故障分析与处理

以酒钢21000m3/h空分设备调试过程中分子筛纯化系统出现的故障及采取的处理措施为重点,结合同行业在分子筛纯化系统操作中出现的问题,介绍分子筛纯化系统在操作、仪表等相关方面出现的常见故障,分析了故障原因,并提出了有针对性的解决方案。     

转子-滚动轴承-机匣耦合系统中滚动轴承故障的动力学分析

针对实际的航空发动机转子系统,建立了含滚动轴承故障的转子-滚动轴承-机匣耦合模型.在模型中,考虑了机匣运动,弹性支承与挤压油膜阻尼的作用,同时,充分考虑了轴承间隙、滚珠与滚道的非线性赫兹接触力以及由滚动轴承支撵刚度变化而产生的变柔性(Varying Cbmpliance)VC振动.在此基础上,建立了耦合系统中滚动轴承外圈、内圈及滚动体的损伤动力学模型,并运用数值积分方法进行了动力学仿真与分析.结果充分表明了本文提出的转子-滚动轴承-机匣耦合系统及滚动轴承故障动力学模型的正确有效性.     

Thermodynamic modelling of phase equilibria in Al-Ga-P-As system

A generalized thermodynamic expression of the liquid Al-Ga-P-As alloys is used in conjunction with the solid solution model in determining the solid-liquid equilibria at 1173 K and 1273 K. The liquid solution model contains thirtyseven parameters. Twentyfour of them pertain to those of the six constituent binaries, twelve refer to the specific ternary interactions. Additionally the liquid solution model also contains a specific quaternary interaction parameter. The latter has been evaluated here based on the experimental data available in the literature. The present research shows an excellent agreement between the derived and experimental values at 1173 K and 1273 K for the system. The article also presents a comparison between the evaluated values with those based on the regular solution model for the liquid alloys.     

Mathematical modelling of the cardiovascular system

This paper is an introduction to the special issue of the Journal of Engineering Mathematic (Volume 47/3–4, 2003) on the mathematical modelling of the cardiovascular system. This issue includes the 2003 James Lighthill Memorial Paper written by Pedley [1] on the mathematical modelling of arterial fluid dynamics. This introduction is written to bring cardiovascular biomechanics to readers with a background in mathematical modelling and computational mechanics. The importance of mathematical modelling for physiological understanding, diagnostics, prosthesis development, patient selection and medical planning is indicated and discussed shortly. A subdivision into models for cardiac mechanics, pressure- and flow-wave propagation, mass transfer and fully three-dimensional fluid-structure interaction is made and references are given to the different contributions of the issue.