Application of perturbed semi-Markov processes in reliability

The paper is concerned with the application of perturbed semi-Markov (SM) processes in reliability problems. There are two kinds of perturbed SM processes presented in the paper. First of them was defined by Shpak and the second one was introduced by Pavlov and Ushakov. Shpak’s concept of perturbed SM is applied for calculating the approximate reliability function of many tasks operation process and Pavlov and Ushakov concept of that one is used to obtain the approximate reliability function of a repairable cold standby system with a switch