Multi-state reliability analysis of rotor system using Semi-Markov model and UGF

In order to accurately reflect the performance degradation law of the aero-engine rotor system during its life span, a novel multi-state reliability analysis method for rotor system is proposed. The method is based on the combination of the Semi-Markov model with UGF technique. The Semi-Markov model is used to describe the performance degradation process of the components of the rotor system. The UGF technique is utilized to exhibit the relationship between the state performance and the performance probability of the components. Furthermore, the UGF of the entire rotor system is obtained by simplifying the system structure with the modularized method. Therefore, the reliability of the rotor system at different task performance levels can be evaluated easily. A practical case study based on a turboprop engine rotor system is performed to illustrate the implementation and efficiency of the proposed reliability analysis method. Meanwhile, compared with the conventional method, the analysis results indicate that the proposed method can reflect the performance degradation process of the rotor system more veritably and effectively

A New Method for Reliability Calculation of the Active Systems with Time-Dependent Failure Rates based on Weibull Distribution

Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the most studies in the reliability area, it is assumed that the failure rates of the system components are constant and have exponential distributions. This distribution and its attractive memory less property provide simple mathematical relationships in order to obtain the system reliability. But in real word problems, considering time-dependent failure rates is more realistic to model processes. It means that, the system components do not fail with a constant rate during the time horizon; but this failure rate changes over the time. One of the most useful statistical distributions in order to model the time-dependent failure rates is the Weibull distribution. This distribution is not a memory less one, so it was impossible to apply simple and explicit mathematical relationships as the same as exponential distributions for the reliability of a system. Therefore, researchers in this field have used simulation technique in these circumstances which is not an exact method to get near-optimum solutions. In this paper, for the first time, it is tried to obtain a mathematical equation to calculate the reliability function of a system with time-dependent components based on Weibull distribution. Also, in order to validate the proposed method, the results compared with exact solution that exists in literature