ENSURING DEPENDABILITY OF UNIQUE HIGHLY VITAL SYSTEMS

Abstract

Aim. Dependability of products is usually researched with no regard to its genesis, while the causes of undependability are conventionally regarded as generalizing stochastic relationships that take into consideration “the result of interaction of a number of factors: the environment, system properties, process-specific, operational and other requirements.” Consequently, the evaluation of dependability indicators is based on the assumption that by the beginning of operation the product is in working order. Respectively, the relations between the dependability and the time are considered only for the product operation period. The best known dependability-to-time relation is the empirical failure function, the so-called U-shaped dependability curve, which no one yet was able to describe with simple mathematical formulas usable in engineering calculations. The presence of the first “hump” in the U-shaped curve is associated with the manifestation of design errors, manufacturing defects or incorrect assembly of products, yet the specific causes of this “hump’s” existence are not clarified in publications. The definition of the term “operability” does not rule out, and in practice there are often cases when design and development activities do not cover all the parameters that characterize the product’s ability to perform the specified functions or when some of the documented requirements are not coordinated with the values of functional parameters, while during manufacture the values of such parameters may exceed the specified limits. As the result, a seemingly operable structure that passes experimental development may not be fit in terms of specified dependability indicators. Methods. The dependability properties of any product are specified long before the operation and can only fully manifest themselves after its beginning. The paper shows a graph that reflects the conditional probability of fault-free operation per lifecycle stages of products long before the beginning of operation. The dependability of unique highly vital systems (UHVS) may be ensured from the very early lifecycle stages based on consecutive execution of certain design, process engineering and manufacturing procedures, as well as application of engineering analysis of dependability. Results. The paper examines the role and significance of each lifecycle stage in ensuring UHVS dependability. The procedures of the engineering method of ensuring dependability are listed, the principles of UHVS design principles are set forth. Basic tools for increasing dependability and its evaluation principles are shown. Conclusions. The paper shows the possibility of ensuring the dependability of UHVSs using engineering procedures implemented at each lifecycle stage before the beginning of operation. Such procedures would enable an adequate level of design, development, preproduction, manufacture, as well as the development of a UHVS dependability evaluation method based on a single theoretical and methodological basis.