Showing papers presented at "International Conference on Reliability, Maintainability and Safety in 2009"

Analysis on failure modes and mechanisms of LED

Abstract: The reliability of LED is key to its application system. In this paper, the frequent failure modes and mechanisms such as chip failure and packaging failure were investigated through several failure analysis cases. Based on these analysis results, several methods to improve LED's reliability are reported in this paper.

An artificial neural network approach for remaining useful life prediction of equipments subject to condition monitoring

Abstract: Accurate equipment remaining useful life prediction is critical to effective condition based maintenance for improving reliability and reducing overall maintenance cost. An artificial neural network (ANN) based method is developed for achieving more accurate remaining useful life prediction of equipment subject to condition monitoring. The ANN model takes the age and multiple condition monitoring measurement values at the present and previous inspection points as the inputs, and the life percentage as the output. Techniques are introduced to reduce the effects of the noise factors that are irrelevant to equipment degradation. The proposed method is validated using real-world vibration monitoring data.

Dynamic fault tree analysis based on Petri nets

Abstract: In traditional Dynamical Fault Tree analysis, it is necessary to modularize DFT tree firstly so as to obtain static subtrees and dynamic subtrees. Generally, Binary Decision Diagram (BDD) and Markov chains are utilized in the DFT to process static and dynamic subtrees, respectively. However, due to the possibility of state combinatorial explosion problem in Markov chain, it is difficult to analyze system with DFT in some cases. This paper investigated Petri net method in DFT in order to solve this problem. An example of processor system is analyzed with the proposed Petri net based DFT, which contains many dynamic logic gates in two classes. The analysis results show that the proposed method can overcome the state combinatorial explosion problem and guarantee high accuracy.

Performance analysis of mobile agent-based wireless sensor network

Abstract: In this paper, we describe a reliability model which can be used to analyze the performance and power consumption in resource constrained, data rate scarce, mobile agent-based wireless sensor network (WSN) systems. The primary model is referred to as a generalize access structure congestion (GGC) system [3] which is an extended model from a circular sequential k-out-of-n congestion (CSknC) [2]. There are many other reliability models which can be used to study WSN systems, but they are not suitable to analyze and address mobile agent-based multisensory WSN systems. These systems are not based on a centralized architecture because they use mobile agent technologies to distribute decision tasks at local nodes. By employing mobile agent technologies, the systems can make accurate decisions quickly and reduce data rate and data redundancy problems. An important research problem is to determine how to maintain efficient duty cycle by using multiple types of sensors without centralized architecture and with mobile agent technologies. From the GGC model, we can develop a method to determine an optimal power management scheme by computing an efficient duty cycle in mobile agent-based multisensory WSN systems.

Structural health monitoring of bridges using acoustic emission technology

Abstract: Bridges are important part of society's infrastructure and reliable methods are necessary to monitor them and ensure their safety and efficiency. Bridges deteriorate with age and early detection of damage helps in prolonging the lives and prevent catastrophic failures. Most bridges still in used today were built decades ago and are now subjected to changes in load patterns, which can cause localized distress and if not corrected can result in bridge failure. In the past, monitoring of structures was usually done by means of visual inspection and tapping of the structures using a small hammer. Recent advancements of sensors and information technologies have resulted in new ways of monitoring the performance of structures. This paper briefly describes the current technologies used in bridge structures condition monitoring with its prime focus in the application of acoustic emission (AE) technology in the monitoring of bridge structures and its challenges.

Precursor parameter identification for power supply prognostics and health management

Abstract: Prognostics and health management (PHM) seeks to identify and isolate reliability problems in products (diagnostics) and predict a product's remaining useful life (prognostics). In this paper, a four-step PHM approach for power supplies is presented: 1) precursor parameter identification based on historical data analysis and failure mechanism analysis; 2) baseline establishment by conducting experiments under different environmental and usage conditions and characterizing precursor parameters for healthy power supplies; 3) baseline verification by conducting similar experiments for fielded power supplies; and 4) testing. Precursor parameter identification for one switch-mode power supply (SMPS) was carried out. The power metal-oxide semiconductor field-effect transistor, insulated-gate bipolar transistor, and the Schottky diode were identified as the majority cause by historical data analysis. Gate oxide leakage current, threshold voltage, transconductance, junction temperature, VCE (on), and contact resistance were determined to be monitored parameters for this SMPS after a failure mechanism analysis.

A framework for cost-effective and accurate maintenance combining CBM RCM and data fusion

Abstract: Cost-effectiveness and accuracy are two basic criteria for good maintenance. Reducing maintenance costs can increase net profit, while accurate maintenance actions can sustain continuous and reliable operation of equipment. As instruments and information systems tend to become cheaper and more reliable, condition-based maintenance has become an important tool for running a plant or a factory. This paper presents a novel condition-based maintenance framework that uses reliability-centered maintenance to save money and employs the data fusion strategy for improving condition monitoring, health assessment, and prognostics. This framework can help obtain optimal maintenance performance with good generality.

SLD constant-stress ADT data analysis based on time series method

Abstract: Constant Stress Accelerated Degradation Testing (CSADT) is commonly used to evaluate the lifetime of long lifetime and high reliable products, such as Super Luminescent Diode (SLD). Previous works on CSADT use deterministic function to describe the product degradation and they are not considered adequately. This paper proposes a CSADT data analysis method based on time series method. It proposes a time series modeling procedure to model product performance degradation data. An example of SLD CASDT is given as an application of the modeling technique and the estimation method is presented.

Ant colony optimization approach to heterogeneous redundancy in multi-state systems with multi-state components

Abstract: An algorithm based on ant colony optimization (ACO) has been developed and employed to address the problem of optimum redundancy allocation in series-parallel multi-state systems (MSS) consisting of multi-state components. The objective is to obtain a minimum cost configuration of the system that satisfies the given reliability and weight constraints and the consumer load demand occurring in different operating time intervals. The demand distribution is presented as a piecewise cumulative load curve. The multi-state components are chosen from a list of products available in the market and have their characteristic feeding capacity, reliability, weight and cost. The capacity of the system, thus, strongly depends upon the selection of constituent components. The algorithm allocates heterogeneous redundancy i.e. non-identical components (of maximum two types) are allowed in each subsystem The search of optimal system structure in the ACO algorithm presented in the paper implements a multinomial probability based method to compute exact system reliability index. A penalty function is coupled to handle the constraints and restrict the search near the feasible region. The algorithm is very easy to apply and still obtains very good solutions with promising time efficiency. Two illustrative examples are given to validate the algorithm and to demonstrate its performance.

An approach to generate software test data for a specific path automatically with genetic algorithm

Abstract: We focus on software reliability with testing coverage, which will grow with increment of the coverage. We expect to improve quality of software testing with it automated. An approach of generating test data for a specific single path is presented in this paper, different from the predicate distance applied by most test data generators based on genetic algorithms. A similarity between the target path and execution path with sub path overlapped is designed as fitness value to evaluate the individuals of a population and drive GA to search the appropriate solutions. Several experiments are taken to examine the effectiveness of the designed fitness function, which evaluate performance of the function with the convergence ability and consumed time. Results show that the function performs well compared with other two typical fitness functions for specific paths.

An adaptive threshold based on support vector machine for fault diagnosis

Abstract: Considering the drawback of the big error when using fixed threshold in fault diagnosis for hydraulic servo system, many factors that may affect the fault threshold are analyzed. By integrating the key factors in threshold model, such as modeling error, random disturbance, input instructions, system current status and etc, an adaptive threshold scheme for fault diagnosis is proposed in this paper, which is based on a pattern recognition algorithm called support vector machine (SVM). It is very effective to adaptively adjust the fault threshold according to a variety of influencing factors. And the robustness is improved by the proposed method, which is verified by experimental results.

SOA based mobile application software test framework

Abstract: The most important issues of the test framework are its generality, reusability and scalability in a specific area. Mobile application software that constantly updates and improves makes it especially difficult for these points. This paper first proposes the definition of mobile application software, as well as its classification, and summarizes the mobile application software testing technology. Then we introduce the thought of service-oriented architecture into this area, and adopt COM technique, aims at designing a mobile application software test framework. During the design, we focus on the technical implementation and interface definition. Finally a test platform is built based on the framework and used to test a typical software of mobile phone. The test results show that the test framework greatly improved the testing flexibility and provided a good foundation for implementation and expansion of mobile application test.

Review and comparison of system reliability optimization algorithms considering reliability estimation uncertainty

Abstract: System reliability optimization involves the selection of components and a system architecture to maximize reliability. Most existing studies assume that the reliability values of the components are deterministic, and known with certainty. However, in practice the reliability of the component is just a point estimate, and therefore, there is some uncertainties associated with it. In this paper, we review and critique the available different methodologies for system reliability optimization which explicitly considers uncertainty. One approach is defining a lower percentile of system reliability distribution and using this lower-bound limit as the objective function to be maximized. Another approach is formulating the problem as a multi-objective optimization problem, i.e., maximizing the reliability estimate and minimizing the associated variance. Finally, we will review a new approach where the objective function is to minimize the coefficient of variation of the system reliability estimate with respect to a minimum system reliability constraint and other system level constraints

Validation and verification methodologies in A380 aircraft reliability program

Abstract: Reliability Validation and Verification (V&V) has become a major issue in every industry nowadays. In the development of an embedded system, it is important to be able to determine if the system meets specifications and if its outputs are correct. This is the process of V&V. Airbus applied this V&V process in safety assessment on A380 from aircraft level to supplier level. Aircraft level safety process was implemented for the first time on a large-scale commercial aircraft. To ensure the achievement of goal reliability before entry into service, Airbus has put in more tests on A380 beyond the safety requirements from FAA. This paper presents the methodology of V&V process in A380 aircraft reliability program with the example case study of how Engine Alliance implemented this process in GP7200 design for safety and reliability.

Study on software reliability design criteria based on defect patterns

Abstract: Software reliability design criteria, one of the primary means to improve software reliability, could help to summarize experience and lessons learned Nowadays, more and more organizations are putting emphasis on the collection and utilization of software defects Software defects are the root causes for software failures Therefore, software reliability design criteria based on the analysis of the defects could avoid the occurrence of similar defects and improve software quality This paper investigates the idea of studying software reliability design criteria on the basis of defect patterns Through the analysis of defect data, we advance a defect classification suitable for each software development phase and the definition of software defect patterns The software defect patterns in requirement analysis, design and coding phase are listed One method to solve the problem of how to convert from defect patterns to reliability design criteria is proposed Subsequently the reliability design criteria in requirement analysis, design and coding phase are expounded by using the method The reliability design criteria are tested to be practical and valid in application examples

Software FMEA approach based on failure modes database

Abstract: A classification method of software failure modes based on software IPO process is presented. And then two database called general failure modes database (GFMD) and special failure modes database (SFMD) are proposed based on this classification method. Furthermore, a new approach of software FMEA which is based on GFMD and SFMD is presented. This approach which makes the analysis process of FMEA more operable and the failure modes obtained from analysis more comprehensive improves the efficiency of Software FMEA. Meanwhile GFMD and SFMD also offer a platform for the analyzers to accumulate and share their experience. The case study shows that this approach mentioned in this paper is effective in the practice.

Diagnostics of prestressed concrete structures by means of acoustic emission

Abstract: Development of the framework of diagnosis system for prestressed concrete structures was the purpose of the performed research. The evaluation criteria are based on the destructive processes ongoing in material. The method of acoustic emission (AE) was used as the basic testing technique. The following conclusion can be drawn from the performed observation: AE depends on the level of destruction process, but not on the level of loading. Evaluation of technical condition of structure based on randomly selected sections may lead to incorrect results because of possible localization of deterioration.

Health assessment and prognostics of electronic products

Abstract: Traditional reliability predictions based on handbook methods are inaccurate and misleading. In this paper, we will show a prognostics and health management (PHM) approach, which is more suitable for reliability (remaining life) assessment, since it considers actual operational and environmental loading condition for individual product. The process for PHM implement to electronics has been discussed, as well as numerical implementation examples for both industry and defense purposes.

Simulation-based optimal design for accelerated degradation tests

Abstract: Accelerated degradation test (ADT) is widely used to evaluate the reliability of highly reliable products with long life if there exists a product quality characteristic whose degradation over time can be related to reliability. It is still a main challenge that how to design optimal plan, including sample size, measurement frequency, and termination time, for ADT which can result in the most accurate estimation within predetermined budget. This paper presents a novel approach of optimal design for ADT based on Monte Carlo simulation. There are three key steps in the approach: simulating; modeling; optimizing, by which it is convenient to set up a framework for applications. In this paper, we first apply a widely-used mix-effect model to describe a typical ADT problem. Next, the optimal test plans are obtained by minimizing the estimate of the mean-squared error of the estimated 100pth percentile of the product's lifetime distribution by statistical analysis of simulating degradation data of test units under the constraint that the total experimental cost does not exceed a predetermined budget. Finally, an example is provided to illustrate the proposed method and evaluations are made to assess the sensitivity of optimal plans to misspecifications of values of the parameters.

Research on security monitoring and health management system of medium-range UAV

Abstract: A certain type of general medium-range unmanned air vehicle (MRUAV) is equipped with reconnaissance devices to carry out real-time observation of foe position day and night. They perform target location and artillery adjustment for the operational and tactical missile. The security monitoring and health management system for the MRUAV can realize some functions: performing security monitoring and failure early-warning for the whole process of UAV involving takeoff, flight, and recovery; continuously recording the telemetry data during flight as well as the equipment operation and maintenance information, and integrating these data for performance degrade trend analysis, life-time cumulating, and remaining life forecasting, to diagnose potential failures and provide maintenance suggestion; providing information integrated management for the whole UAV system. The purpose of this system is to synthesize equipment detection, fault diagnosis, and maintenance management into a whole to establish an integrative maintenance management and support platform based on information of UAV system, and ultimately realize the autonomous logistics support.

Life cycle cost analysis for design optimization under uncertainty

Abstract: Life cycle cost is the total cost incurred in the life cycle of a product, including design, development, production, operation, maintenance, support and disposal. Life cycle cost analysis can help engineers to identify equipment and process selection not on the initial purchase cost but rather on the total cost. A reasonable life cycle cost model can lead to a reliable design. In this paper, several life cycle cost methods and models are analyzed to help engineers to make a decision and the life cycle reliability-based design model is provided.

Statistical analysis for weibull distributions in presence of right and left censoring

Abstract: Series system reliability is based on the minimum life time of its components. Its dual, the parallel system, is based on maximum. Here, we consider the statistical analysis of both, series and parallel, systems where the components follow the Weibull parametric model. Our perspective is Bayesian. Due to the mathematical complexity, to obtain the posterior distribution we use the Metropolis-Hasting simulation method. Based on this posterior, we evaluated the evidence of the Full Bayesian Significance Test (FBST) for comparing the reliabilities of the components. The reason for using FBST is the fact that we are testing precise hypotheses. We also compute the probability of a particular component be responsible for the system failure. An example illustrates the methodology.

Asset life prediction using multiple degradation indicators and lifetime data: A gamma-based state space model approach

Abstract: This paper proposes a Gamma-based state space model to predict engineering asset life when multiple degradation indicators are involved and the failure threshold on these indicators are uncertain. Monte Carlo-based parameter estimation and model inference algorithms are developed to deal with the proposed Gamma-based state space model. A case study using real data from industry is conducted to compare the performance of the proposed model with the commonly used proportional hazard model (PHM). The result shows that the Gamma-based state space model is more appropriate to deal with the situation when the failure data is insufficient.

Bayesian analysis of incomplete data from accelerated life testing with competing failure modes

Abstract: A Bayesian method is proposed for analyzing incomplete data obtained from constant stress accelerated life testing when there are two or more failure modes, or competing failure modes. The incompleteness is mainly due to censoring, as well as masking which might be the case that the failure time is observed, but its corresponding failure mode is not identified. Furthermore, sensitivity analysis is performed to check model sensitivity. The method is illustrated by an example for validation, which also shows that the method provides better estimators than MLE by incorporating available prior information in the case of small sample sizes.

Maintainability virtual evaluation method based on fuzzy multiple attribute decision making theory for civil aircraft system

Abstract: Maintainability evaluation is the main method to assess the maintainability level of product. Maintainability design attributes of civil aircraft are determined by analysis of maintainability influencing factors; and the calculation method of each attribute is proposed by the means of maintenance task virtual simulation, rapid upper limb assessment and maintainability checklist. In terms of multiple attribute decision-making theory, the pretreatment methods of maintainability attributes are proposed, and the comprehensive maintainability evaluation model of civil aircraft system is established based on fuzzy theory and multiple attribute decision making method in this paper. Moreover, an instance combined with comprehensive evaluation of two different types of nose landing gear system is given to illustrate the effectiveness of the model.

Dynamic numerical simulation for ship-OWT collision

Abstract: At present, more and more offshore wind farms have been built and numerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines (OWT) has great practical significance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic process of the collision between a typical 3MW offshore wind turbine model with monopile foundation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and adaptive mesh for large structure deformation have been taken into consideration. A new conceptual sphere-shell crashworthy device for OWT is proposed, and the good performance of the new device under ship-OWT front impact and side impact has been verified from both views of theoretical analysis and numerical results. The sphere-shell crashworthy device can use its own structure deformation to absorb the collision energy from the ship. As a result, the key structure of the OWT and the electric control equipments contained in it can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. Moreover, in the collision, the damage of the ship could also be reduced to a great degree due to the sphere configuration design of the crashworthy device

Multi-state component importance analysis using multi-state multi-valued decision diagrams

Abstract: Component importance analysis helps identify the vulnerabilities within a system and quantify the criticality of the system components. Multi-state component importance analysis poses unique challenges to the existing methods that are primarily based on binary-state applications. This paper presents a multi-state multi-valued decision diagram-based analytical method for multi-state component importance analysis. The advantages of the proposed method are illustrated through the comparison to a Monte Carlo simulation-based method and the detailed analysis of a case study.

A fault diagnosis model for embedded software based on FMEA/FTA and bayesian network

Abstract: Failure Modes and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) are two effective fault analysis technologies and the integration of them is also applied widely in many industry domains. But when they are used for fault diagnosis, the ability of inference is not very enough and especially they are not suitable to use the fault related symptoms to do some posterior inference. To solve this problem, this paper combines FMEA and FTA based on Bayesian Network (BN) to form a fault diagnosis analysis model. Case study shows that this model has a good FMEA/FTA fusion ability and posterior inference ability for embedded software fault diagnosis.

Application of oil analysis to the condition monitoring of large engineering machinery

Abstract: The running condition of large engineering machine is evaluated by physical and chemical analysis, spectroscopic analysis, ferrography analysis and oil contaminated analysis. According to the questions that occur in the running equipment, the paper proposes some feasible suggestions and measures. Monitoring examples demonstrate that it is effective application of oil analysis to the condition monitoring and fault diagnosis.

Study on real-time test script in automated test equipment

Abstract: In this article we propose a generic test script for real-time embedded software system testing, which has been applied to ATE (Automated Test Equipment). After a summary of the theory about embedded software automated test based on test script, the design philosophy and implementation details are described. We have chosen an ATE and integrated python interpreter into it. Modules for test control are developed on base of python's expandability. To ensure real-time, we have trimmed python interpreter's source code. This test script has advantages of simple, flexible, controllable, reusable and portable. The use of third party python tools results in decreased test script development time. A number of real-time embedded systems are tested by this script technology. Both the correctness and the real-time performance are validated.