Sharif Digital Repository

This paper outlines a quantitative risk assessment for an 110,000 ton/day ethylene oxide production plant in Iran. After a complete and detailed hazard identification study, done by HAZOP method, the purification column was found to be one of the most hazardous sections in this plant. As ethylene oxide with high concentration and inventory is present there. Fault tree analysis (FTA) technique has been used to identify the basic events responsible for top event occurrence and also calculation of top event frequency of occurrence. Human error has been calculated numerically and probability of human error has been estimated. Failure rate data were collected referring to several sources and... 

Fault tree analysis is one of the key approaches used to analyze the reliability of critical systems. Fault trees are usually analyzed using mathematical approaches or Monte Carlo simulation (MCS). This paper presents a Fuzzy-Monte Carlo simulation (FMCS) approach in which the uncertain data is generated by the MCS approach. The FMCS approach is applied to the Weibull probability distribution which is widely been used in the analysis of reliability, availability, maintainability and safety (RAMS). Using the fuzzy arithmetic, times to failure (TTF) of the components are generated. These results are processed by a kind of fault tree (e.g. time-to-failure tree) to produce the TTF of the whole... 

Network survivability refers to the ability of a network to maintain uninterrupted service regardless of the scale, magnitude, duration, and the type of failures. There is growing interest in attempts to quantify the network survivability in presence of various failures. We perceive that both performance and availability are integral components of survivability. Therefore, we propose a general composite model for survivability performance evaluation which is applicable to a wide range of networks. In this model, the excess loss due to failure (ELF) analysis is used to find the loss due to failure when the system is operating in gracefully degraded states. Fault tree method is used to model... 

The reliability analysis of critical systems is often performed using fault-tree analysis. Fault trees are analyzed using analytic approaches or Monte Carlo simulation. The usage of the analytic approaches is limited in few models and certain kinds of distributions. In contrast to the analytic approaches, Monte Carlo simulation can be broadly used. However, Monte Carlo simulation is time-consuming because of the intensive computations. This is because an extremely large number of simulated samples may be needed to estimate the reliability parameters at a high level of confidence. In this paper, a tree model, called Time-to-Failure tree, has been presented, which can be used to accelerate the... 

Nowadays, distributed embedded systems are employed in many safety-critical applications such as X-by-Wire. These systems are composed of several nodes interconnected by a network. Studies show that a transient fault in the communication controller of a network node can lead to errors in the fault site node (called original errors) and/or in the neighbor nodes (called follow-up errors). The communication controller of a network node can be halted due to an error, which may be a follow-up error. In this situation, a follow-up error leads to halt the correct operation of a fault-free controller while the fault site node, i.e. the faulty controller, still continues its operation. In this paper,... 

This paper presents transient and permanent fault injection into Verilog models of digital systems during the design phase by a developed simulation-based fault injection tool called INJECT. With this fault injection tool, it is possible to inject crucial fault models in all abstraction levels (such as swith-level) supported by Verilog HDL. Several fault models for injecting into Verilog models are specified and described. Analyzing the results obtained from the fault injections, using INJECT enables system designers to inform from dependable parameters, such as fault latency, propagation and coverage. As a case study, a 32-bit processor, namely DP32, has been evaluated and effects of faults... 

System fault-tree analysis is a technique for modeling dependability that is in widespread use. For systems such as embedded systems that include both hardware and software, the integration of hardware and software fault trees has proved problematic. In this paper, we present a method for reliability and safety analysis of embedded systems modeled by SystemC language. The evaluation is based on the fault trees generated from both hardware and software parts of the embedded systems described in the unified language. The unified modeling of both hardware and software of embedded systems using SystemC enables designers to be early aware from the safety and reliability of their designs more... 

Importance measures (IMs) are used for risk-informed decision making in system operations, safety, and maintenance. Traditionally, they are computed within fault tree (FT) analysis. Although FT analysis is a powerful tool to study the reliability and structural characteristics of systems, Bayesian networks (BNs) have shown explicit advantages in modeling and analytical capabilities. In this paper, the traditional definitions of IMs are extended to BNs in order to have more capability in terms of system risk modeling and analysis. Implementation results on a case study illustrate the capability of finding the most important components in a system. © 2018 World Scientific Publishing Company  

The main purpose of this study is to offer a new method for transient analysis of availability and survivability of a system with the identical components and one repairman and with every combination of components either standard system for example series systems, parallel systems, stand-by systems and K out of N systems or complex system. This method is a technique for fault tree evaluation too. The considered system is supposed to consist of n components and there are some composition of them that systems the failure occurs when one of its composition occur. Some concepts such as fault tree, Markov models, Eigen vectors and Eigen values are employed for analyzing the transient availability... 

Purpose - This paper aims to conduct a comprehensive fault tree analysis (FTA) on the critical components of industrial robots. This analysis is integrated with the reliability block diagram (RBD) approach to investigate the robot system reliability. Design/methodology/approach - For practical implementation, a particular autonomous guided vehicle (AGV) system was first modeled. Then, FTA was adopted to model the causes of failures, enabling the probability of success to be determined. In addition, RBD was used to simplify the complex system of the AGV for reliability evaluation purpose. Findings - Hazard decision tree (HDT) was configured to compute the hazards of each component and the... 

While the Control Flow Checking (CFC) methods are using the ordinary instruction set and general Arithmetic and Logic Unit (ALU) features to protect the programs against the transient faults, this paper presents a new kind of CFC method, called feature specific CFC. The idea behind this method is using a specific internal hardware in modern processors which provides the ability to monitor internal various parameters of the program. This method is a pure software method and the external hardware overhead is zero. Other overheads have been measured experimentally by executing the workloads on a Pentium system. The execution time overhead is between 42% and 67% and the program size overhead is... 

In this paper, minimal paths and cuts technique is developed to handle fault tree analysis (FTA) on the critical components of industrial robots. This analysis is integrated with the reliability block diagram (RBD) approach in order to investigate the robot system reliability. The model is implemented in a complex advanced manufacturing system having autonomous guided vehicles (AGVs) as material handling devices. FTA grants cause and effects and hierarchical properties to the model. On the other hand, RBD simplifies the complex system of the AGVs for reliability evaluation. The results show that due to the filtering of the paths in a manufacturing system for AGVs, the reliability is highly... 

Heavy-duty gas turbines are usually devised in power plants to generate electrical energy. Sudden failure in any of its parts or subdivisions will result in a decrement of the efficiency of the system or emergency shutdown of the system. The highest risk of failure in these turbines is subjected to the hot gas path (HGP) of the turbine. Due to the existence of uncertainty in diagnosing process or damage growth, in this research, a modified risk-based probabilistic failure analysis model using Bayesian networks (BN) was developed. First, a failure model was developed using the Fault Tree Analysis, and then it is transformed into a BN model. This model is capable of predicting and diagnosing... 

Application of Probabilistic Safety Assessment (PSA) to a Uranium hexafluoride (UF 6) production process is presented in this paper. The process is constituted from three main units: UF 4 conversion to UF 6, condensation of produced UF 6 gas and tail gas treatment. Radioactive gas is present in all parts of the process and occurrence of high pressure or high temperature in the process equipments may lead to radioactive release to workplace and environment. The work is mainly based on PSA experience in nuclear power plants. Accordingly for the process, eight group of Initiating Events (IE) that lead to UF 6 gas release have been identified using HAZOP study. For each IE, based on related...