System Fault Tree Research Articles

Reliability analysis on the train control system in the CTCS-3 operating mode

Purpose This paper aims to study the reliability of the high-speed train operation control system in the Chinese Train Control System Level 3 (CTCS-3) operating mode. Design/methodology/approach Dynamic fault tree and Bayesian network method are adopted to analyze the reliability and weakness of the CTCS-3 system. Findings First, a physical architecture and data flow diagram of the CTCS-3 system are established according to the typical structure and functions of the CTCS-3 system. Second, the dynamic fault tree of the CTCS-3 system is constructed. Considering the prior probability of the bottom event and the existence of dynamic redundancy, the dynamic fault tree is transformed into a Bayesian net. The reliability of the CTCS-3 system is carried out based on the prior probability and the weakness that affects the reliability of the system based on the posterior probability is also analyzed by the Bayesian network. Finally, it is disclosed that the impact of the on-board subsystem on the reliability of the CTCS-3 system is generally greater than that of the ground subsystem. The two weakest modules in the onboard subsystem are the driver-machine interface (DMI) and balise transmission module (BTM) and the weakest one in the ground subsystem is Balise. The analysis results are generally consistent with the malfunctions in the field operation of China’s high-speed railway. Originality/value (1) By reasoning, the reliability of the train operation control system in the CTCS-3 operating mode meets the standard requirements. (2) Through backward reasoning, it is found that the failure of the onboard subsystem leads to a greater probability of failure of the train control system. (3) The DMI, BTM and automatic train protection computer unit modules are weak components in the onboard subsystem. Vital digit input&output, train interface unit and train security gateway are rarely involved in previous research, the result in this paper shows that these three modules are also weak components in the subsystem, which requires attention.

Failure Analysis for Hydraulic System of Heavy-Duty Machine Tool with Incomplete Failure Data

A hydraulic system is a key subsystem of heavy-duty machine tools with a high failure intensity, the failure of which often causes shutdown of production and economic loss in machining. Therefore, it is necessary to implement failure analysis to identify the weak links of system and improve the reliability. For hydraulic system, there is often an amount of failure data collected in field, which help to calculate the occurrence probability of basic events through fault tree analysis method. However, the data are incomplete and uncertain. To address this issue, this study presents a fault tree analysis methodology. Experts’ opinions are utilized, combined with field data based on the Dempster–Shafer theory and rough set theory to fill the incompleteness and eliminate the uncertainty. For application in a case study, a fault tree of the hydraulic system of heavy-duty machine tools is firstly constructed. Then, the importance analysis is performed to help identify the weak links of hydraulic system. The results show the critical basic events affecting the safety and reliability of a hydraulic system.

The α, β-Cut Intervals and Weakest t-Norm Based Importance Measure for Criticality Analysis in Intuitionisitic Fuzzy Fault Tree Analysis of LNG-ESD System

Different importance measures have been developed and widely utilized in system reliability analysis to measure the importance of system components. During operation period of a complex system, it becomes more difficult to collect exact failure data of system components i.e. the collected failure data may have some sort of uncertainties due to various reasons. Generally, triangular shaped fuzzy numbers or intuitionistic fuzzy numbers (IFNs) are used to quantify the various types of uncertainty in failure data of the system’s components and fuzzy arithmetic operations are utilized which computes each reliability index with wide range of prediction due to accumulating phenomenon of fuzziness. In this paper, different types of intuitionistic fuzzy number (IFN) are used to quantify the failure data uncertainty of the system’s components while α, β-cut intervals and weakest t-norm (Tw)-based arithmetic operations are employed to reduce the range of prediction for each reliability index. The objective of the present study is to develop Tw-based importance measure for criticality analysis in intuitionistic fuzzy fault tree analysis (IF-FTA) of a system, when different types of uncertainties in crisp failure data of basic events are quantified by different types of membership and non-membership functions. The developed importance measure applies system fault tree, α-cut and β-cut intervals, different types of intuitionistic fuzzy number (IFN) and weakest t-norm (Tw) based intuitionistic fuzzy arithmetic operations. To demonstrate the applicability of the proposed measure, a case study of liquefied natural gas terminal emergency shutdown system (LNG-ESD system) is performed. The IF-FTA of LNG-ESD system is presented to evaluate the fault intervals of the system at different levels using Tw-based arithmetic operations on different types of IFNs. The developed importance measure is applied to identify and rank the critical basic events in IF-FTA of LNG-ESD system. The proposed measure is also compared with some existing importance measures.

Reliability Evaluation of a Disaster Airflow Emergency Control System Based on Bayesian Networks

This study proposed a novel method for system failure reasoning based on Bayesian networks to solve emergency airflow control system reliability problems. A system fault tree model was established to identify the logical relationship between the units, which was then transformed into a Bayesian network fault analysis model to determine network node states and the conditional probability table, as well as to carry out diagnostic reasoning on the system node branches. The reliability analysis of the model based on Netica Bayesian tool shows that the probability of system failure caused by substation communication node is the highest under normal conditions, and data monitoring and central station communication nodes have a greater impact on intelligent control. By predicting and diagnosing system faults, the optimization of system design is realized on the framework of Bayesian network to improve the reliability, and there by establishing a theoretical foundation for future disaster prevention research.

A hybrid model for human-factor analysis of engine-room fires on ships: HFACS-PV&FFTA

In this study, an analysis of fire-explosion accidents in ship engine rooms was conducted. For analysis, a hybrid method including the Human Factors Analysis and Classification System (HFACS) and fuzzy fault tree analysis (FFTA) was used. Using the HFACS method, the factors in the formation of engine-room fires were classified according to a hierarchical structure. The possible accident scenarios and probabilities were calculated using the FFTA method. In this study, it was observed that fire-explosion accidents were concentrated in ships over 20 years old and that mechanical fatigue affected accident formation. In particular, when the increased hot surfaces due to the operation of a ship's engines while it is in motion are combined with oil/fuel leakage, fire-related accidents become inevitable. Failure to provide proper insulation also triggers the occurrence of accidents. It has been observed that some of such accidents occur because the materials used in maintenance and repair work are not original to the ship. During this study, the causes of accidents were examined to prevent fire-related accidents from occurring in engine rooms, and suggestions were made to prevent similar accidents from happening in the future.

Reliability and availability modeling of Subsea Xmas tree system using Dynamic Bayesian network with different maintenance methods

Subsea Xmas tree is a vital equipment for offshore oil and gas development. Aiming at the fault mode of subsea Christmas tree system under production conditions, the fault tree of subsea tree system was established, which was transformed into Dynamic Bayesian network, and the reliability and availability of subsea tree system with different repair states are quantitatively analyzed. In this paper, the DBNs are partially verified by the method based on three axes. The results show that the reliability of subsea vertical tree system is slightly higher than that of subsea horizontal tree system. After repair and maintenance, the performance of subsea tree system has been significantly improved, and the improvement of the system performance by preventive maintenance is more obvious. Compared with the perfect repair, the performance of the system with imperfect repair is not significantly reduced. Compared with perfect repair & preventive maintenance, the performance of the system with imperfect repair & preventive maintenance is slightly reduced. In addition, the influence of failure rates and degradation probability on reliability and availability is analyzed. By comparing the influence of failure rates on the system performance of non-maintenance and maintenance, it is found that the change of failure rates has the greatest influence on the reliability and the least influence on the availability of perfect repair & preventive maintenance. By comparing the performance of each component in the subsea tree system, it is found that the failure rates has the most obvious influence on the chock module, and gate valve and tree cap have the most significant influence on the reliability of the system. In order to improve the reliability of subsea tree system, it is necessary to improve the reliability of chock module, gate valve and tree cap.

Reliability analysis of helicopter emergency flotation system

The reliability of the emergency flotation system of helicopters is analysed by using fault tree analysis and the Monte Carlo method. We constructed a fault tree with the failure of system as the top event and obtained the minimal cut set, the ranking of the structural importance of the bottom events and the probability of the occurrence of the top event. Based on the system fault tree, a Monte Carlo simulation model of the emergency flotation system is established by using Matlab/Simulink. The results show that the Monte Carlo method is feasible and effective for the reliability analysis of the emergency flotation systems of helicopters. Furthermore, the comparison between the criticality importance and mode importance of each subsystem suggests that the control component is the weakest part of the emergency flotation systems, thereby providing a basis for system reliability design and fault diagnosis.

System Modeling and Fault Tree Analysis Based on AltaRica

With the increasing scale and complexity of system, it is very necessary to analyze the safety of complex system. Fault tree is an effective method to safety analysis. However, traditional fault tree relies on manual construction and analysis. When fault nodes and systems are complex, the efficiency and correctness of manual analysis can hardly be guaranteed. To the varied understanding of analysts, it is difficult to ensure the consistency of failure mode and system architecture due to the different understanding from safety analysts and system designers. The same node needs fault analysis again in different systems, which has poor reusability and low efficiency. AltaRica is a fault-oriented Safety Modeling Language. It takes the guard transformation system(GTS) as its core, describes nodes and faults with a style of reusable object-oriented language, and describes information of interaction between nodes and systems through interface connections between nodes and nested systems. Therefore, this paper proposed an automatic system modeling and fault analysis method and its detailed computer algorithm on single class node, multiple nodes and nodes with subsystems based on AltaRica. Finally we developed a software prototype and carry out the automatic modeling and fault analysis in a detailed example. The results showed that the proposed method, algorithm and software prototype can realize automatic graphical modeling of the system on AltaRica, the automatic fault analysis is correct and efficient, has reusability of modeling and fault analysis, and greatly improve the accuracy, objectivity and efficiency of fault modeling and analysis.

Remote Offshore Oil and Gas Platform SCADA System Fault Tree Design and Minimal Cut Sets Analysis

International Journal of Computer Sciences and Engineering (A UGC Approved and indexed with DOI, ICI and Approved, DPI Digital Library) is one of the leading and growing open access, peer-reviewed, monthly, and scientific research journal for scientists, engineers, research scholars, and academicians, which gains a foothold in Asia and opens to the world, aims to publish original, theoretical and practical advances in Computer Science,Information Technology, Engineering (Software, Mechanical, Civil, Electronics & Electrical), and all interdisciplinary streams of Computing Sciences. It intends to disseminate original, scientific, theoretical or applied research in the field of Computer Sciences and allied fields. It provides a platform for publishing results and research with a strong empirical component. It aims to bridge the significant gap between research and practice by promoting the publication of original, novel, industry-relevant research.

Fault Tree Interval Analysis of Complex Systems Based on Universal Grey Operation

The objective of this study is to propose a new operation method based on the universal grey number to overcome the shortcomings of typical interval operation in solving system fault trees. First, the failure probability ranges of the bottom events are described according to the conversion rules between the interval number and universal grey number. A more accurate system reliability calculation is then obtained based on the logical relationship between the AND gates and OR gates of a fault tree and universal grey number arithmetic. Then, considering an aircraft landing gear retraction system as an example, the failure probability range of the top event is obtained through universal grey operation. Next, the reliability of the aircraft landing gear retraction system is evaluated despite insufficient statistical information describing failures. The example demonstrates that the proposed method provides many advantages in resolving the system reliability problem despite poor information, yielding benefits for the function of the interval operation, and overcoming the drawback of solution interval enlargement under different orders of interval operation.

A Novel Weakest t-norm based Fuzzy Fault Tree Analysis Through Qualitative Data Processing and Its Application in System Reliability Evaluation

Abstract The quantification of the fuzzy fault tree analysis (FFTA) is based on fuzzy arithmetic operations. It is well known that the weakest t-norm (Tw)-based fuzzy arithmetic operations have some advantages. The Tw-based fuzzy arithmetic operations provide fuzzy results with less fuzziness and preserve the shape of fuzzy numbers. The purpose of this study is to develop a Tw-based fuzzy fault tree analysis (TBFFTA) to assess system reliability when only qualitative data such as expert opinions or decisions are available and described in linguistic terms. The developed TBFFTA applies Tw-based fuzzy arithmetic operations to evaluate the lower bound, best estimate, and upper bound top event probability of a system fault tree, where occurrence possibilities of basic events are characterized by triangular fuzzy membership functions. To demonstrate the applicability and feasibility of TBFFTA, a case study has been performed. The computed results have been compared with results analyzed by existing fuzzy approach. The comparative study concludes that TBFFTA reduces fuzzy spreads (uncertainty interval) and provides more exact fuzzy results.

Path Sets Combination Method for Reliability Analysis of Phased-Mission Systems Based on Cumulative Exposure Model

The modeling of phased-mission systems is difficult and the solving process is complex because of the relevance of the phase tasks and the sharing of components existing in different phases or between phases. To solve the problem, based on the cumulative exposure model, the path sets combination method of phased-mission systems is proposed. Aiming at the problem of the cross-stage correlation of components and its different failure rate in each phase, the cumulative exposure model considering the historical damage of components is used to solve by obtaining the cumulative damage distribution of each component in each phase. Firstly, a phased-mission systems reliability model is build by mapping phased-mission system fault trees into a Bayesian network. By traversing the Bayesian network, the minimal path sets of each phase are obtained. Secondly, the disjoint formulas introduced by variable elimination method are used to do the disjoint operation of the minimal path sets of each phase and the conditional probability relations of the common components are used to reduce the minimal path sets scale. Finally, the minimum disjoint path sets of each phase are combined and summed according to the component conditional probability relation. The path sets combination method of phased-mission systems avoids the large conditional probability table, large storage and large computation problems caused by the excessive discrete states in the traditional Bayesian method and the problem that the PMS-BDD method has strict requirements for variable ordering and is difficult to solve the system reliability with multiple failure distribution types of components. In the end, a phased-mission systems reliability modeling and solving is carried out for a geosynchronous orbit satellite, and compared with the PMS-BDD method, which verifies the correctness of the method.

A mixed model to evaluate random hardware failures of whole-redundancy system in ISO 26262 based on fault tree analysis and Markov chain

In order to ensure safety and reliability, some safety-related electrical and electronic (E/E) systems in vehicles need to be designed as a whole-redundancy system. Although ISO 26262 provides guidance for the analysis of random hardware failure, the problem of estimating whether the safety-related E/E systems, especially whole-redundancy system can meet the index of the ASIL level in ISO 26262 is still unsolved. Fault tree analysis (FTA) is one of the basic methods to analyze random hardware failure of a vehicle’s E/E systems quantitatively. In generic FTA, the quantitative analysis of dynamic logic gates, which usually exist in the fault tree of whole-redundancy system, cannot be calculated. Meanwhile, Markov chain can solve the problem of quantitative calculation of dynamic fault tree, but brings a side-effect of complicating the calculation of static logic gates in fault trees. In order to evaluate random hardware failure of a vehicle E/E system more concisely and effectively, and to estimate if a new safety-related E/E system’s random hardware failure rate can meet the index demand in ISO 26262, this study proposed a mixed model based on FTA and Markov chain. First, the definition of random hardware failure and fault classification were clarified. Then, a mixed model based on FTA and Markov chain was proposed. Finally, a whole-dual-redundancy steer by wire system was used as an example to test the validity of the mixed model. This study not only proposed a new mixed model based on FTA and Markov chain for the calculation of a whole-redundancy system’s random hardware failure rate, but also provided a new quantitative validation method for safety-related E/E systems in vehicles that need to meet the reliability index requirement in ISO 26262.

Soft error evaluation and vulnerability analysis in Xilinx Zynq-7010 system-on chip

Radiation-induced soft errors are an increasingly important threat to the reliability of modern electronic systems. In order to evaluate system-on chip's reliability and soft error, the fault tree analysis method was used in this work. The system fault tree was constructed based on Xilinx Zynq-7010 All Programmable SoC. Moreover, the soft error rates of different components in Zynq-7010 SoC were tested by americium-241 alpha radiation source. Furthermore, some parameters that used to evaluate the system's reliability and safety were calculated using Isograph Reliability Workbench 11.0, such as failure rate, unavailability and mean time to failure (MTTF). According to fault tree analysis for system-on chip, the critical blocks and system reliability were evaluated through the qualitative and quantitative analysis.

Application of fault tree approach for the causation mechanism of urban haze in Beijing—Considering the risk events related with exhausts of coal combustion

Haze weather has become a serious environmental pollution problem which occurs in many Chinese cities. One of the most critical factors for the formation of haze weather is the exhausts of coal combustion, thus it is meaningful to figure out the causation mechanism between urban haze and the exhausts of coal combustion. Based on above considerations, the fault tree analysis (FAT) approach was employed for the causation mechanism of urban haze in Beijing by considering the risk events related with the exhausts of coal combustion for the first time. Using this approach, firstly the fault tree of the urban haze causation system connecting with coal combustion exhausts was established; consequently the risk events were discussed and identified; then, the minimal cut sets were successfully determined using Boolean algebra; finally, the structure, probability and critical importance degree analysis of the risk events were completed for the qualitative and quantitative assessment. The study results proved that the FTA was an effective and simple tool for the causation mechanism analysis and risk management of urban haze in China.

Research on safety analysis for airborne system based on extended functional model

With the widespread use of embedded system in safety critical areas, system safety assurance has become one of the research hotspots of engineering technologies. System safety analysis mainly concentrates on the requirement specification and the recent design, and in the process of the actual development of the software, safety requirement analysis and design are two independent processes. This article expands the safety requirements described by fault tree into state diagram and proposes the new concept “fault state diagram,” which can unify safety requirement model and functional model. Based on the fault state diagram, this article proposes the method of airborne system safety analysis, including the following: gives out one method for abstracting and describing safety requirements from system fault tree based on Backus Normal Form; defines the transformation rules from fault tree logic gates and continuous time into state diagram elements; designs safety requirement information mapping table which translates safety requirements into state diagram elements; and designs the automatic construction algorithm of fault state diagram, which is based on the transformation rules and mapping table. Finally, a small gas stove control system case using the method proves the feasibility and effectiveness of the proposed method.

Analysis of Mine Hoist System Monitoring and Fault Diagnosis

This paper is Zhengli Coal JKMD3.5 × 4 (III) E-type floor-type multi-rope friction hoist for the study, in order to enhance the system to improve monitoring and fault diagnosis for the purpose of fuzzy fault tree analysis method as the lift system the method of fault diagnosis on hoist brake system fault tree analysis, the results of the analysis can play a guiding role in the daily repair and maintenance, thereby enhancing the safety and reliability of the hoist.

Methods to Establish the Fault Tree of Substation Automation System Based on HAZOP

Because of it’s complexity of substation, once the control system failure will cause huge losses, according to the fault characteristics, established the HAZOP method combined with the method of fault tree model, and the substation and protection and control system as an example, the modeling process complete sample. This method can standardize and establish fault tree, provides a scientific, reasonable means to discover substation system inherent or potential risk factors.

Impact of component unavailability uncertainty on safety systems unavailability

The increased and extended application of the probabilistic safety assessment requires appropriate consideration of uncertainties in the analyses and interpretation of the results. Inadequate treatment of uncertainties may lead to poorly supported or even wrong conclusions with final consequence of loss of adequate level of safety.Epistemic uncertainty results from the imperfect knowledge or incomplete information regarding the parameters values in the underlying model. Epistemic uncertainty is considered in the probabilistic safety assessment models by probability distributions associated with the uncertain parameters.This paper presents the results of the analysis of the introduction of probability distributions associated with component unavailability parameters, on the overall unavailability of the analyzed system. The normal and lognormal distributions are introduced as probability distributions associated with component unavailability. The minimal cut sets of the analyzed system are identified with application of the fault tree analysis. The distribution of the top event unavailability is assessed with application of the min cut upper bound approximation and Monte Carlo sampling.The analysis of the uncertainty propagation is demonstrated using the fault tree of the auxiliary feedwater system of the nuclear power plant. The implications of the introduction of different probability distributions for the components unavailability on the obtained results are analyzed. Obtained results include skewness and kurtosis as measures of the goodness-of-fit of the top event unavailability to the normal distribution.Obtained results show that the probability density function of the top event depends on the characteristics of the basic events unavailability distribution and the importance of the selected events. Introduction of the lognormal distribution for uncertainty characterization of the basic events unavailability results in positive kurtosis. Positive kurtosis is indicating increased probability of having top event unavailability larger than the mean value.Decision making based on the mean value of the top event unavailability in case of positive kurtosis of the probability density function results in risk underestimation.

A fuzzy-based reliability approach to evaluate basic events of fault tree analysis for nuclear power plant probabilistic safety assessment

Fault tree analysis has been widely utilized as a tool for nuclear power plant probabilistic safety assessment. This analysis can be completed only if all basic events of the system fault tree have their quantitative failure rates or failure probabilities. However, it is difficult to obtain those failure data due to insufficient data, environment changing or new components. This study proposes a fuzzy-based reliability approach to evaluate basic events of system fault trees whose failure precise probability distributions of their lifetime to failures are not available. It applies the concept of failure possibilities to qualitatively evaluate basic events and the concept of fuzzy sets to quantitatively represent the corresponding failure possibilities. To demonstrate the feasibility and the effectiveness of the proposed approach, the actual basic event failure probabilities collected from the operational experiences of the David–Besse design of the Babcock and Wilcox reactor protection system fault tree are used to benchmark the failure probabilities generated by the proposed approach. The results confirm that the proposed fuzzy-based reliability approach arises as a suitable alternative for the conventional probabilistic reliability approach when basic events do not have the corresponding quantitative historical failure data for determining their reliability characteristics. Hence, it overcomes the limitation of the conventional fault tree analysis for nuclear power plant probabilistic safety assessment.