Kalman Žiha

Redundancy and robustness of systems of events

The article aims to add a new impetus to rational and objective probabilistic evaluation of redundancy and robustness, based on uncertainties of systems and subsystems of events. An attempt is made to demonstrate the relevance of intuitive comprehension of redundancy and robustness of engineering systems of events. An event-oriented system analysis of a number of random observable operational and failure modes, with adverse probability distributions in a lifetime, may provide a deeper understanding of systems operational abundance and endurance. The system uncertainty analysis is based on the concept of entropy as defined in information theory and applied to probability theory. The article relates reliability, uncertainty, redundancy and robustness of systems of events and their application is illustrated in numerical examples.

Event oriented system analysis

This article presents an attempt towards a probabilistic event oriented system analysis in engineering. Engineering systems are represented as either complete or incomplete systems of events and as compounds of various subsystems of events. The event oriented system analysis investigates important subsystems in engineering systems, such as operational modes and failure modes and their interrelations. The analysis is also applicable to engineering systems with various relations among the sets of events, such as mutually exclusive and inclusive sets. Further, the systems and subsystems are subjected to probability and uncertainty analysis. The system uncertainty analysis is based on entropy. General relations among the probability, uncertainty of the system and uncertainties of the subsystems are derived by using information theory. Specific mathematical aspects and available methods in the uncertainty modelling of systems and subsystems are summarised. Numerical examples confirm the relevance of the event oriented system analysis and indicate potential improvements in system design.

Event oriented analysis of series structural systems

The event oriented analysis of technical objects is in general accomplished by representing them as complete or incomplete systems and subsystems of events. It is argued in the article how the compound engineering systems of events can be partitioned by inclusion-exclusion expansion into individual and common cause modes. The event analysis is based on the random variable model and employs the results of operational modes and effect analysis, of the reliability analysis and of the uncertainty analysis. The system redundancy and robustness are considered as uncertainties, due to the fact that really a number of events are possible, expressed by the entropy concept in probability theory, conditioned by operational and failure modes, respectively. Relative and average uncertainty measures are introduced to facilitate uncertainty interpretations in engineering problems. It is investigated how the sensitivity analysis of reliability measures can be applied to the assessments of system uncertainties. Numerical examples presented in the article illustrate the application of event oriented system analysis to series structural systems with common cause failures. Additionally, system performance presentation and optimization with constraints, as well as potential improvements in system analysis, design and maintenance are investigated.

STRENGTH AND RELIABILITY OF SHIPS 'AS-BUILT'

This report firstly presents the rule based scantlings and sectional properties of the example ship defined by using the nominal properties of mild shipbuilding steel. It also describes the way of collection of characteristic material specimens of rolled steel plates and bars delivered by the steel manufacturer to the shipyard for to the example ship. Secondly it summarizes the results of tensile testing in the Laboratory for experimental mechanics of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb of plates and bars denoted here as ‘in-built’ material properties for the example ship according to the production plans. The report then reminds on the rule based material properties for acceptance purposes. Next it considers the influence of ‘in-built’ mechanical properties with respect to the rule requirements on local, global and ultimate strength of ships. The report discusses material properties other than yield strength, which participate in the assessment of the overall ship safety such as the weld strength, buckling and fatigue strength, low temperature behavior, corrosion and reliability. The results of the tensile testing of ‘in-built’ materials are then applied to checking of the local, global and ultimate ‘asbuilt’ strength of the example ship’s hull instead of the ‘asdesigned’ strength defined by the nominal material properties. The report at the end discusses the differences between the ‘as-designed’ and the ‘as-built’ hull strength, fatigue life and reliability. It suggests minimization of the hull strength uncertainties by adopting the mechanical properties of ‘inbuilt’ materials. The conclusion supports the stirring idea of this report that in addition to the ‘as-designed’ strength, a ship deserves individualized assessment of the “as-built” ship hull strength based on the measured realistic ‘in-built’ properties.