Use Of Fault Trees Research Articles

Refinement of operable state recovery algorithms for “AIST” small satellites on the basis of telemetric information

The article deals with the use of telemetric information, namely data on emergencies, failures and malfunctions occurring on AIST small satellites. These data are used for the refinement of standard algorithms of satellite operable state recovery. To this end, an analysis was made of the accumulated volume of telemetric information, consisting of two stages: searching for parameters exceeding the acceptable limits and establishing the causes of emergencies. A detailed study of the causes and consequences of emergencies made it possible to create two fault trees reflecting the ways of the propagation of failures in the small satellite onboard equipment. The use of fault trees and information on emergencies made it possible to refine the algorithms for the operable state recovery developed at the stage of designing AIST small satellites. Two examples of refined algorithms allowing the recovery of the operable state of small satellites after failure of on-board equipment are given in the article.

Risk modeling of communications, navigation, and surveillance complex systems of systems for future aviation

AbstractThe planned integration of Communications (C), Navigation (N), and Surveillance (S) by the U.S. Federal Aviation Administration (FAA) would convert their currently safely coordinated operations into a single vulnerable interdependent and interconnected CNS complex systems of systems (Complex SoS). We model the ensuing vulnerability of planned Complex SoS by tracing specific new interdependencies and interconnections manifested by their shared/common (i) States (variables), (ii) Decisions, (iii) Decision makers, and (iv) Resources (cyber‐physical) among the three C, N, and S systems?. Other contributions stem from our exploiting the use of fault trees (without the reliance on reliability data). Exploiting fault trees enabled us to quantify the accrued knowledge of interdependencies and interconnectedness tabulated in Tables 1–4 in terms of AND Gates (systems connected in Parallel), and OR Gates (systems connected in Series); and to discover dangerous shared C, N, and S systems on the critical path. Namely, if all systems (subsystems) in the minimal cut set fail, then the entire CNS Complex SoS would fail. Significantly, this modeling approach alerted the FAA on “what not to do” by identifying subsystems early in the planned integration of C, N, and S that would result in a single catastrophic failure of the planned CNS Complex SoS.

Assessment Methods Analysis of Models Reliability of Emergency Response in Emergency Situations

In this paper author showed that use of the of the models (plans) of emergency response in the emergency situations conditions developed for the Situational centers a priori doesn't guarantee their proper accomplishment. It is caused by existence of probability of failure in delivery and use of necessary resources for a variety of reasons. Authors proved need of check of models' feasibility degree before the moment of their application in real emergency situation. It gives the chance for advance adjustment of models. They proved complexity of the objective solution by a variety reasons: a lot of the involved structures, a variety of necessary resources, their spatial distribution and others. Authors carried out the analysis of the researches in this direction. They proved that any work doesn't solve problem in a complex. Authors described the most suitable for the specified task solution the method of Function-Interaction-Structure (FIS). They showed that use of Fault-Trees of the FIS method in combination with multi-Level system approach will yield the best result of developed models assessment, will provide knowledge of probability of implementation of the emergency reaction models which are in state of multi-level degradation of resources at the time of emergency.

Bayesian reliability models of Weibull systems: State of the art

Abstract In the reliability modeling field, we sometimes encounter systems with uncertain structures, and the use of fault trees and reliability diagrams is not possible. To overcome this problem, Bayesian approaches offer a considerable efficiency in this context. This paper introduces recent contributions in the field of reliability modeling with the Bayesian network approach. Bayesian reliability models are applied to systems with Weibull distribution of failure. To achieve the formulation of the reliability model, Bayesian estimation of Weibull parameters and the model’s goodness-of-fit are evoked. The advantages of this modelling approach are presented in the case of systems with an unknown reliability structure, those with a common cause of failures and redundant ones. Finally, we raise the issue of the use of BNs in the fault diagnosis area.

A safety-focused verification using software fault trees

When developing safety-critical software such as reactor protection systems (RPS) in nuclear power plants, a demonstration of software trust (e.g., safety) is not only absolutely essential but also usually mandated by government authorities. While automated generation of fault trees has become possible with increased use of formal specifications, industrial use of fault trees has been limited primarily to safety demonstrations that the system is free from behavior captured in the root node. In this paper, we propose to extend the use of automated fault tree for verification purposes. As a fault tree represents an abstract and partial behavioral model of software on credible causes leading to a hazard, it must still satisfy various properties (e.g., fairness, correctness). Verification of a fault tree is useful when developing safety-critical software because (1) it strengthens a safety-focused software development process; (2) it provides an opportunity to detect potentially critical errors early; and (3) it is less likely to experience a state explosion problem. This paper demonstrates how to convert a fault tree into a semantically equivalent logic formula so that they can be subject to formal verification using tools like Verification Interacting with Synthesis (VIS). We evaluated the feasibility of FTA’s applicability as a verification tool on a prototype model of a nuclear power reactor protection system (RPS) software to be deployed in plants under construction in Korea.

Integrating cyber attacks within fault trees

In this paper, a new method for quantitative security risk assessment of complex systems is presented, combining fault-tree analysis, traditionally used in reliability analysis, with the recently introduced Attack-tree analysis, proposed for the study of malicious attack patterns. The combined use of fault trees and attack trees helps the analyst to effectively face the security challenges posed by the introduction of modern ICT technologies in the control systems of critical infrastructures. The proposed approach allows considering the interaction of malicious deliberate acts with random failures. Formal definitions of fault tree and attack tree are provided and a mathematical model for the calculation of system fault probabilities is presented.

Preventing medical errors by designing benign failures.

One way to successfully reduce medical errors is to design health care systems that are more resistant to the tendencies of human beings to err. One interdisciplinary approach entails creating design changes, mitigating human errors, and making human error irrelevant to outcomes. This approach is intended to facilitate the creation of benign failures, which have been called mistake-proofing devices and forcing functions elsewhere. USING FAULT TREES TO DESIGN FORCING FUNCTIONS: A fault tree is a graphical tool used to understand the relationships that either directly cause or contribute to the cause of a particular failure. A careful analysis of a fault tree enables the analyst to anticipate how the process will behave after the change. EXAMPLE OF AN APPLICATION: A scenario in which a patient is scalded while bathing can serve as an example of how multiple fault trees can be used to design forcing functions. The first fault tree shows the undesirable event--patient scalded while bathing. The second fault tree has a benign event--no water. Adding a scald valve changes the outcome from the undesirable event ("patient scalded while bathing") to the benign event ("no water") Analysis of fault trees does not ensure or guarantee that changes necessary to eliminate error actually occur. Most mistake-proofing is used to prevent simple errors and to create well-defended processes, but complex errors can also result. The utilization of mistake-proofing or forcing functions can be thought of as changing the logic of a process. Errors that formerly caused undesirable failures can be converted into the causes of benign failures. The use of fault trees can provide a variety of insights into the design of forcing functions that will improve patient safety.

Probability and category redefinition in the fault tree paradigm.

Fault trees have been advocated as aids for problem solvers. However, research has suggested limitations in their usefulness. Fischhoff, Slovic, and Lichtenstein (1978) found that subjects given incomplete (pruned) trees were insensitive to omissions; these authors hypothesized that Tversky and Kahneman's (1974) availability heuristic was the mediating factor. Using a within-subjects design, subjects in Experiment 1 received both full and pruned trees and estimated probabilities for various reasons why a car would fail to start. To increase the availability of omissions, some Experiment 1 subjects first generated possible causes of starting failure. The basic Fischhoff et al. findings were replicated, but several aspects of the results argued against the availability hypothesis as the mechanism for judgment. Instead, subjects appeared to idiosyncratically redefine category membership when making judgments based upon pruned trees. By employing a sorting task in Experiment 2 we corroborated the results of Experiment 1: Subjects do redefine the actual contents of the categories when faced with an omission from the fault tree. The implications of these results for the use of fault trees as a problem solving aid are discussed.

Integrating Professional Ethics into the Technical Writing Course

As communication teachers attempting to bridge the gap between school and industry, we need to give students a true understanding of what it means to be a professional. We may be spending too much time trying to get them to write and speak like professionals without also imbuing them with sufficient understanding of their responsibilities to behave as professionals. Students need to be practiced in the communication and decision-making situations they will encounter in their workplaces. These decisions involve ethical reasoning as well as technical problem solving. Teaching students to appreciate the consequences of their recommendations, through the use of fault-trees and cost/benefit analyses in realistic simulations, effectively bridges the gap between the classroom and boardroom. A sample situation is explained and analyzed for its use in any technical communications class.

Using Fault Tree Methodologies in Availability Improvement Studies at Southern Company Services

This paper describes the methodology used in two availability improvement studies that made extensive use of fault trees. The studies were done for Georgia Power Company's Edwin I. Hatch Nuclear Plant, a General Electric boiling water reactor. The studies combined the classical methods of performing a reliability analysis; i.e., studying plant records of equipment performance, with the relatively newer fault tree methodologies. The fault tree provides a graphic, organized structure whereby the failure behavior of a system can be studied from a qualitative as well as a quantitative standpoint.

Failure Detection Method by Joint Use of Fault Trees and System Identification Techniques

A failure detection method for process plants, such as chemical plants, nuclear reactor plants, boiler systems, is proposed on the basis of the fault tree analogy with thresholds. The fault tree gives good knowledge on the structure of a plant. Based on this knowledge, the propagation of system anomalies can be traced at each gate from the primary level to the top event level. The failure detection coupled with fault trees, system identification which is performed at each gate level using measured process variables, and operator fuzzy information, leads to one of the methods for the safer system operation with experiences and abilities of operators.