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More specifically, the learning outcome should be:
Knowledge:
Basic insight into the theoretical foundation and practical applications of RAMS assessment and optimization.
Skills:
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Being able to identify and use framework and methods available to solve RAMS assessment and optimization tasks, and to select suitable methods for also more complicated situations. Solve optimization problems in practice. Assess RAMS performance for systems.
General competence:
Understand RAMS as an important cornerstone of industrial and commercial systems and in the public administration.
Topics lectured
Topics to be covered are as part of the course are (organized according to whether the application is mainly for safety-critical systems or production-critical systms, or both) presented below. Note that more than one lecture may be used to cover one particular topic. See the lecture plan for more details.
Reliability
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analyses of safety-critical systems
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- Development of reliability requirements
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- Methods for developing reliability requirements for safety-critical systems and barriers, with basis in risk analyses
"Safety integrity level (SIL) is a key reliability performance measure used for safety-critical systems. The SIL Reliability requirements are therefore often given as SIL requirements are identified in an extension of the risk analysis, using methods often refered to as SIL allocation, SIL targeting and SIL classification. Key methods like Layers of protection analysis (LOPA), risk graph, and minimum SIL are presented and discussed." - Extension of methods for quantifying the reliability of safety-critical functions - analytical approaches & dynamic modeling approaches.
"In TPK 4120, some analytical formulas were introduced to calculate the average probability of failure on demand (PFD). It was also shown how the average PFD may be calculated using Markov methods and fault tree analysis. This reliability measure is of high importance in relation to SIL, as a relationship is established between a SIL requirement and the maximum PFD tolerated for a safety function. "
In this course, we go one a step further and :Introduce some other methods for quantifying the average PFD:The introduce the foundations for analytical formulas presented in a standard called IEC 61508 (in part 6), which builds on slightly different assumptions than the analytical formulas from TPK 4120. - The analytical formulas in the PDS method
- Petri Nets, which is an alternative and more flexible approach than e.g., Markov method state models.
- Study reliability of "high demand systems", where another reliability measure, the average system failure rate (called PFH), is recommended rather than the average PFD. One example of a high demand safety system is a machine that carry out safety-critical functions. Also PFH is linked to SIL. a key standard for reliability of safety-critical systems), the PDS method (a method along with a set of analytical formulas widely adapted in the Norwegian oil and gas industry, but which has a wider application area), and dynamic modeling, using Petri Nets."
- Special analysis challenges (possible candidates for under this heading):
- Partial and imperfect testing
- Follow-up of SIL requirements in the operational phase
SIL follow-up:
- "The reliability of a safety-critical function is influenced over time after the system has been put in operation. Just like if you buy a car: We may think that the car has some kind of inherent reliability performance in light of what it costs, the type of engine, manufacturer reputation, safety systems installed with the car and so on. Once you start to drive it, its performance may change over time depending on your driving habits, how much you drive, where you drive, how often you send it to the garage for maintenance and checks and os on. You may collect some data about the car's performance, such as how often it does not start "on demand", milage, and how often some of the safety-features fail, and based on this (often limited information as you should not have much failures) you may try to estimate the reliability. In fact, you are trying to estimate the reliability as it has been up till a certain point in time. "
It is the same thing we would like to do with a safety-critical system: With rare data we would like to estimate the reliability using the information that we have. If the performance is not sufficient (in light of e.g. the SIL requirement), we need to do something. This "something" is also discussed as part of this topic.
Relevance:
- Some examples showing the relevance of this topic may be found with consultancy companies, such as with Safetec, Lloyd's Register Consulting, and DNV-GL (link to the GL-part of the services), and Lilleaker Consulting. Manufacturers like ABB, Siemens, AkerSolutions, FMC, Kongsberg Maritime and many more need to design systems in light of SIL requirements, and also demonstrate (sometimes with assistance of the consultancy companies) that the SIL requirements are met. End users, like railway service providers like Jernbaneverket, oil companies like Statoil, Det Norske, GDF-Suez, Shell and Conoco-Phillips among some, and owners of smelting plants, owners of water power stations must demonstrate that the SIL requirements continue to be met throughout the life of the systems.
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