Proposed Reliability Models Research Articles

Time-Varying Reliability Analysis of Mechanisms with Strength Degradation Considering Clearances and Local Stiffness Effects

Mechanism systems are important components of dynamic mechanical systems. The time-varying reliability assessment of mechanism systems is of great significance for the safety and fault diagnosis of mechanical products. In this paper, a time-varying reliability evaluation method for mechanisms under the fatigue failure mode is proposed, which takes into account the joint effects of clearance, local structural stiffness, random load and random strength degradation. The proposed mechanism reliability models are established by nonlinear dynamic analysis considering failure factors and establishing random stress history characterization matrices. Additionally, the models are validated by the Monte Carlo simulation method. The results show that the mechanism clearance, local stiffness, and initial strength dispersion have a significant effect on the time-varying reliability of the mechanisms. Furthermore, both local stiffness and initial strength dispersion have a greater influence on the effect of clearance on the time-varying reliability of the mechanisms. The proposed reliability models can quantitatively analyze the dynamic effects of failure factors on the reliability of the mechanisms, which can be used for the stochastic remaining life evaluation and fault diagnosis of the mechanism systems.

Reliability modeling of competing failure processes with multi‐stage degradation

AbstractIn this paper, reliability models of competing failure processes for the product subject to degradation and random shocks are established, which are accompanied by degradation path slope change caused by specific shock patterns. The two related failure modes are hard failure arising from different random shocks, and soft failure due to consecutive structure damage or combined with a sudden increment of degradation because of an identical random shock. In sophisticated equipment like aircraft engine systems, the degradation path of performance parameters is characterized by multi‐stages when the product is more prone to fatigue or accelerated aging, as a consequence of experienced shocks. This article analyzes five random shock patterns that can change the slope of the degradation path and studies an example to explain the application of proposed reliability models as well as the sensitivity analysis of parameters.

A Novel Framework for the Operational Reliability Evaluation of Integrated Electric Power–Gas Networks

This paper proposes a new framework for the operational reliability evaluation of integrated electric power-gas networks (IEPGNs). First, a novel approach for modeling the failure modes of natural gas pipelines is presented. This approach utilizes the concept of virtual nodes and employs a gas release rate model to consider the pinhole, hole, and rupture failure modes of pipelines. Thereafter, a four-state Markov model for natural gas-fired generators (NGFGs) with dual-fuel capabilities is proposed. The area risk method is extended to include the proposed reliability models, and the partial reliability indices of the area risk method are evaluated using a non-sequential Monte Carlo simulation (NSMCS). A nonlinear optimization model is also proposed to calculate electric and gas load curtailments for each system state in NSMCS. This model is linearized to obtain a mixed-integer linear programming (MILP) model for reducing the computational burden. The computational performance of NSMCS is further improved by adopting cross entropy (CE)-based importance sampling (IS). Finally, the efficacy of the proposed framework is demonstrated on three test systems. Case studies validate the importance of considering the proposed reliability models of IEPGNs for operational reliability evaluation. The impacts of operational strategies on the operational reliability indices are also demonstrated.

Reliability Analyses of Wide-Area Protection System Considering Cyber-Physical System Constraints

Wide-area measurement, protection and control systems link the cyber power system with the physical power system to realize a cyber-physical power system (CPPS). This paper proposes a reliability modeling and assessment method for the wide-area protection system (WAPS). The proposed WAPS model takes into account the decision accuracy of protection algorithms with limited available data at the control center, and combines it with the tripping reliability of protection devices in corresponding substations to form the operation accuracy of WAPS. In particular, the directional comparison algorithm used in decision-making is functionally divided into three modules, namely the initiation module, the fault area positioning module, and the faulted element recognition module. The proposed reliability models are established based on the Permutation and Combination method under the assumption that the data acceptance rate of the control center is d. The sequential Monte-Carlo simulation is used to solve the proposed reliability indices. Finally, the WAPS reliability assessment is presented for the IEEE 14-bus system and the key influencing factors are identified and discussed.

To the problem of efficiency of reliability assessment of agricultural units

The theoretical analysis of the processes occurring in operation, which determine the reliability of the elements of agricultural units and machines, made it possible to develop a universal approach to the construction of mathematical models of reliability. Practical use of the proposed reliability models is advisable both for accelerated assessment and for predicting reliability at the resource design stage. This article proposes a method for assessing and predicting the reliability of a complex system, if there is information about the reliability level of a sample of its elements.

Trade-off between maintenance and protection for multi-state performance sharing systems with transmission loss

In a multi-state system with common bus performance sharing, the performance surplus from one element can be transmitted to other deficient elements as long as the total amount of transmission does not exceed the transmission capacity of the common bus. Existing literature fails to consider the transmission loss during the performance sharing process. Transmission loss widely exists in practice and is affected by many external factors. For example, the power transmission loss is affected by the distance, humility and temperature. In this research, we study a common bus performance sharing system consisting of N independent elements with consideration of performance loss during transmission. We propose three different transmission loss models that are frequently encountered in practice, and suggest their corresponding reliability evaluation algorithms. To improve the system availability, maintenance actions are taken to improve the component reliability, and protection is provided to defend the system against external impacts. We analyze the optimal trade-off between protection and maintenance by minimizing the system cost while satisfying a pre-specified system availability requirement. The proposed reliability models and algorithms are illustrated by a regional power distribution system. The numerical study has demonstrated the importance of considering transmission loss in reliability modeling and optimization.

Reliability Evaluation for Traction Power Supply System of High-Speed Railway Considering Relay Protection

Failures in the traction power supply system (TPSS) may cause high-speed trains to run behind the schedule or even suffer from downtime, which would directly affect the entire scheduling and cause inestimable loss. Therefore, it is crucial to evaluate the reliability of the TPSS to ensure that it can operate with high reliability. This paper proposes a method for evaluating the overall reliability of the TPSS associated with high-speed railway (HSR) considering relay protection. The impact of relay protection on the reliability of the TPSS is analyzed; then, the failure mode and effect analysis (FMEA) tables are established based on the main wiring diagram of the TPSS and its equipment composition to qualitatively analyze the failure modes of the primary and secondary equipment and their influence. According to the FMEA tables, the fault tree model of the traction substation and catenary system considering the relay protection is established, respectively, and the system reliability indexes are calculated through the Monte Carlo simulation. Different from existing studies, the reliability models established in this paper take into account the primary and secondary equipment of the TPSS and coupling relationship between them, and highlight the configuration of relay protection and its logic cooperating with each equipment. Through the analysis of practical example concerning the TPSS serving China’s HSR, it shows that rich and direct system reliability indexes can be obtained through simulation with the proposed reliability models and the evaluation method, and the impact of the relay protection on system reliability can be reflected, which provides an effective means for evaluating the overall reliability of the TPSS.

Predictive maintenance for aircraft components using proportional hazard models

Abstract Unscheduled maintenance can contribute significantly to an airline's cost outlay. Reliability analysis can help to identify and plan for maintenance events. Reliability analysis in industry is often limited to statistically based approaches that incorporate failure times as the primary stochastic variable, with additional strict assumptions regarding independence of events and underlying distributions of failure phenomena. This foregoes the complex nature of aircraft operations, where a whole range of operational factors may influence the probability of occurrence of a maintenance event. The aim of this research is to identify operational factors affecting component reliability and to assess whether these can be used to reduce the number of unscheduled occurrences (i.e. failures). To do so, a data-driven approach is adopted where historical operational and maintenance data is gathered and analysed to identify operational factors with a measurable influence on maintenance event occurrence. Both time-independent and time-dependent Proportional Hazard Models (PHMs), models which incorporate operational factors as covariates, are employed to generate reliability estimates. Results obtained from analysing historical data of a set of nine components with respect to unscheduled removals indicates that adopting new maintenance schedules, derived from the proposed reliability models, can reduce the number of unscheduled occurrences.

Fuzzy Dynamic Reliability Models of Parallel Mechanical Systems Considering Strength Degradation Path Dependence and Failure Dependence

Fuzzy dynamic reliability models of mechanical parallel systems with respect to stress parameters and strength parameters are developed in this paper. Strength degradation path dependence (SDPD) and failure dependence of components in the system are two main problems to be addressed in developing fuzzy dynamic reliability of mechanical systems, which are taken into account in the proposed reliability models. In addition, the SDPD sensitivity function and the failure dependence sensitivity function are defined to analyze the influences of the fuzzy characteristics of stress on the effects of SDPD and failure dependence of mechanical components on dynamic reliability. The bolted joint systems for connection between launch vehicle and satellite are chosen as illustrative examples to demonstrate the proposed model. Moreover, Monte Carlo simulations are carried out to validate the effectiveness of the proposed models. The results show that SDPD and failure dependence of components have significant impacts on fuzzy dynamic reliability of mechanical systems. Besides, the influences of the fuzzy characteristics of stress on SDPD sensitivity and that on failure dependence sensitivity are different.

A Reliability-Based Analysis of Bicyclist Red-Light Running Behavior at Urban Intersections

This paper describes the red-light running behavior of bicyclists at urban intersections based on reliability analysis approach. Bicyclists’ crossing behavior was collected by video recording. Four proportional hazard models by the Cox, exponential, Weibull, and Gompertz distributions were proposed to analyze the covariate effects on safety crossing reliability. The influential variables include personal characteristics, movement information, and situation factors. The results indicate that the Cox hazard model gives the best description of bicyclists’ red-light running behavior. Bicyclists’ safety crossing reliabilities decrease as their waiting times increase. There are about 15.5% of bicyclists with negligible waiting times, who are at high risk of red-light running and very low safety crossing reliabilities. The proposed reliability models can capture the covariates’ effects on bicyclists’ crossing behavior at signalized intersections. Both personal characteristics and traffic conditions have significant effects on bicyclists’ safety crossing reliability. A bicyclist is more likely to have low safety crossing reliability and high violation risk when more riders are crossing against the red light, and they wait closer to the motorized lane. These findings provide valuable insights in understanding bicyclists’ violation behavior; and their implications in assessing bicyclists’ safety crossing reliability were discussed.

Reliability models of wind farms considering wind speed correlation and WTG outage

Wind speed correlation and wind turbine generator (WTG) outage are two factors affecting the reliability model of wind farms, but they are not addressed simultaneously in the existing literature. Meanwhile, WTG outage is reported to be dependent with wind speed to some extent. Therefore, the extended reliability models of wind farms incorporating both of these two factors and the dependency between WTG outage and wind speed are proposed in this paper. To consider the uncertainties and dependencies of wind speed and WTG failure, Copula method is applied to simulate correlated random variables representing for wind speed and the number of failed WTG units. Moreover, the linear apportioning technique is used to create multistate reliability models of wind farms from hourly wind power models. A number of sensitivity analyses on the modified IEEE RTS with wind power are conducted to validate the proposed reliability models for generation adequacy assessment. Case studies show that the generation adequacy indices increase with the correlation of wind speed and WTG forced outage rate (FOR). It is meaningful to point out that the effect of dependency between wind speed and WTG FOR on generation adequacy is minimal when WTG outages are independent, but it will be substantially larger when WTG outages are highly dependent. The proposed multistate reliability models of wind farms provide foundation for the reliability assessment of power systems with wind power integrated.

Probabilistic Wind Energy Modeling in Electric Generation System Reliability Assessment

The power grid reliability impacts could be significant when a large amount of variable wind generation is integrated with the electric power system. The widely used deterministic reliability assessment method is invalid when modeling intermittency of wind energy sources. The energy based probabilistic reliability assessment models are required in system reliability impact assessment in order to consider the stochastic characteristic of wind resources. This paper investigates different stochastic characteristics in wind energy integration, including resource availability, generation facility outage and transmission availability. A probabilistic framework of reliability modeling for renewable resource integration such as wind energy conversion system is proposed in this paper. Using the proposed reliability models and framework, the cost of wind energy integration with the power gird for maintaining system adequacy and reliability can be evaluated realistically. The IEEE Reliability Test System (IEEE-RTS) system is utilized to demonstrate the developed models and methods. The methodology can be used for modeling the reliability of industrial and commercial facilities being serviced by wind farms and transmission lines.

A critique of the Reliability Analysis Center failure-rate-model for plastic encapsulated microcircuits

As the use of plastic encapsulated microcircuits (PEM) has escalated in the electronics industry, especially in applications in which "mission" success must be accomplished at "any cost", some researchers have proposed reliability models to predict their failure rates or mean times-to-failure. One organization that took on such a challenge was the US Dept. of Defense (DoD) Reliability Analysis Center (RAC). Despite its admirable aims, the model has inherent limitations which result in unrealistic predictions, which could negatively affect parts selection, environmental management and logistics support. This paper presents an analysis of the model developed by the RAC.