“…If they follow general distribution (e.g., uniform, gamma, and Weibull distributions), the Markov renewal process and simulation analysis are often used [11]. Yang et al studied the fluctuation mechanism of 3-state IA model through simulation analysis and concluded that when parameters, including the failure time, the maintenance time and the support delay time, follow exponential distribution, IA of system has no fluctuation [15,16]. The second aspect is a study of how to set up an IA model, solve the IA and analyze the IA fluctuation for multi-unit systems (series system and parallel system).…”