Modelo para un sistema multi estado reparable con tasas de reparación y fallas variables en el tiempo utilizando modelos de dinámica de sistemas equivalente

This paper treats with the reliability assessment of a Repairable Multi-State System (RMSS) by means of a Nonhomogeneous Continuous-Time Markov Chain (NH-CTMC). A RMSS run on different operating conditions that may be considered acceptable or unacceptable according to a defined demand level. In these cases, the commonly used technique is Homogeneous Continuous-Time Markov Chain (H-CTMC), since its solution is mathematically tractable. However, the H-CMTC involve that the time between state transitions is exponentially distributed, and the failure and repair rates are constants. It's certainly not true if the system components age with the operation or if the repair activities depend on the instant of time when the failure occurred. In these cases, the failure and repair rates are time-varying and the NH-CTMC is needed to be considered. Nevertheless, for these models the analytical solution may not exist and the use of others techniques is required. This paper proposes the use of an Equivalent Systems Dynamics Model (ESDM) to model a NH-CTMC. A ESDM represent the Markov Model (MM) by means of the language and the tools of the Systems Dynamics (SD), and the results are obtained by simulation. As an example, an RMSS with three components, failure rates associated with the Weibull distribution and repair rates associated with the Log-logistic distribution is developed. This example serves to identify the advantages and disadvantages of a ESDM to make model a RMSS and evaluate some reliability measures.This paper treats with the reliability assessment of a Repairable Multi-State System (RMSS) by means of a Nonhomogeneous Continuous-Time Markov Chain (NH-CTMC). A RMSS run on different operating conditions that may be considered acceptable or unacceptable according to a defined demand level. In these cases, the commonly used technique is Homogeneous Continuous-Time Markov Chain (H-CTMC), since its solution is mathematically tractable. However, the H-CMTC involve that the time between state transitions is exponentially distributed, and the failure and repair rates are constants. It's certainly not true if the system components age with the operation or if the repair activities depend on the instant of time when the failure occurred. In these cases, the failure and repair rates are time-varying and the NH-CTMC is needed to be considered. Nevertheless, for these models the analytical solution may not exist and the use of others techniques is required. This paper proposes the use of an Equivalent Systems Dynamics Model (ESDM) to model a NH-CTMC. A ESDM represent the Markov Model (MM) by means of the language and the tools of the Systems Dynamics (SD), and the results are obtained by simulation. As an example, an RMSS with three components, failure rates associated with the Weibull distribution and repair rates associated with the Log-logistic distribution is developed. This example serves to identify the advantages and disadvantages of a ESDM to make model a RMSS and evaluate some reliability measures

Integrated Power Systems in All Electric Ships: Dependability Oriented Design

This work aims at providing a comprehensive and, as far as possible, standard and widely supported approach to a dependable design of all electric ship integrated power systems. The proposed approach is based upon latest development of dependability theory made recently available, from its founding lexicon and taxonomy to investigation tools and relevant international rules. In its first part, this work analyses present rule requirements governing the discipline of designing an integrated power system serving an all electric ship. Analysis covers system definitions (what is what) in terms of taxonomy and associated concepts; system required performances both in terms of delivered services and in terms of reaction to anticipated reactions to predetermined fault scenarios. In its second part, this work briefly presents latest developments in the theory and in the tools theory brings along: lexicon, taxonomy, system analysis, benchmarking and enforcing techniques. During this development, emphasis is posed on the fact that design documentation, be it owners’ technical specification, classification society rule book or international standard, often recall dependability concepts, without fully exploiting the potential theory is promising, or the completeness of its definition corpus. In its third part, this work applies dependability concepts to a real case scenario, an integrated power system installed on a recent cruise ship vessel. This application, albeit suffering from an important lack of information, due to copyrighting and industrial intellectual property rights, produces an informative example on the enquiring method and relevant deliverable: a system model, obtained in a strongly standardized way that permits a comprehensive and accurate dependability study, to be realized using tools and techniques defined in international standard. Results of this analysis are, as a consequence of method strong structure, repeatable and consistent, and allow quick verification of requirements. Analysis results, even though partial and superficial owing to already mentioned lack of accurate information, are offering some original view points. They are commented and classified according to indexes defined earlier. In its fourth part, this works presents proposals to be applied to systems which exhibited low values of indexes. Such proposals are briefly analyzed in terms of index value variations; in doing this a quantification of improvement that could be obtained is given. Finally, in its fifth part, this work shortly presents future research directions to improve investigation method. This work reports elements of project management and maritime law as well, this in force of the multidisciplinary nature of dependability theory, and its repercussion on different sector of the marine industry, besides engineering. It is show how present method can fit the actual engineering process, and can provide a common language serving as substrate for various disciplines, like the ones mentioned