Research On Complex Electromechanical System Reliability And Maintainability Synthesis And Prediction Method

Complex electromechanical system is the lifeline of the national economy and security. With the advancement of science and technology, and the modern large scale production, complex electromechanical system regarded as the key element in manufacturing industry, is developing toward large-scale, automation, integration with mechanic, electric, hydraulic and computer technology, while the updating cycle is shorter and shorter. The failure rate is increasing, failure modes are various,and even the disater accident happens frequently, which are resulting from multi-function, improved performance, and heavy load of complex system. Therefore,how to effectively improve the quality and reliability of complex electromechanical system has become a key proposition and cannot be ignored in the national development strategy.Based on the long-term national development demands, this dissertation deeply analyzes the commom and the bottleneck problems of complex electromechanical system reliability and maintainability assessment with the point view of pre-analysis, condition-based reliability analysis, and failure-based reliability analysis, and engineering-oriented explores new breakthrough point through the approach of simplifying complex problem, theoretical research from the point view of engineering concept, and multi-disciplinary knowledge fusion.Complex electromechanical system reliability and maintainability synthesis and prediction are deeply and systematically studied, according to the principle the complex system can be transformed into an equivalent series and the parallel system, based on the Weibull process theory, Markov process theory, gray theory,information entropy and Bayes method. This research has achieved some positivereslts and applies them in practical engineeting. This paper has completed the following research work:In term of complexity of electromechanical system, variety of unit life distribution, and difficulty of overall test, this research focus on finding new idea and methods from the point view of system reliability synthesis. Based on Bayes method, the posterior density functions for different units are fitted with Beta distribution and L? distribution, and the test information of units is transfered into system test information according to moment equivalent method and the principle of information equivalent transformation. The binomial and exponential approximate confidence limits of the system reliability can be obtained, and the two approximate confidence limits are applied to automatic balanced recorder and drilling mud pump. According to the principle of information entropy equivalence, the binomial and exponential approximate confidence limits of the system reliability can also be obtained, which is applied to the drilling mud pump.The reliability confidence intervals of complex electromechanical system finally can be obtained by using the method proposed above. This research results are applicable to project demonstration, design and development stage, and can also be applied to pre-analysis, condition-based reliability analysis.Complex electromechanical system reliability prediction is an urgent proposition. Unit life simulation value can be obtained through Monte-Carlo simulation method, and then system life can be simulated according to reliability logical relationship between system and units, system life distribution finally can be inferred and the point and confidence interval of system reliability can be resolved. It is possible to get point and interval of complex system reliability avoiding overall life test based on unit reliability information. The result has been used in wind turbine and is suitable to pre-analysis. Considering immediate maintenance for the inservice system, Bayes confidence limits of the future failure time for complex electromechanical system are studied based on Weibull process without prior information, and verified by numerical examples, which is regarded as condition-based reliability prediction. Further, dynamic prediction model is built to predict fault numbers of the key components of complex electromechanical system in the future based on the grey theory. The point estimate and estimation accuracy of fault number of the key components forcomplex electromechanical system are discussed using the topological group in updating the model of the true value with the step by step method. The model is applied to the prediction of wind turbine blade failure number, which belongs to condition-based reliability prediction.Aiming to engineering requirement, maintainability evaluation method of complex electromechanical system is discussed. When repair time obeys exponential distribution, normal distribution, lognormal distribution, Weibull distribution, and Gamma distribution, the confidence interval of measurement of the overall system maintainability are given, which can be regard as condition-based and failure-based maintainability analysis. Further, system maintainability synthesis is discussed using unit repair information. When unit repair time obeys lognormal distribution, the confidence limit of system MTTR is given, which can be regarded as pre-analysis.There is a hope that the electromechanical system doesn’t breakdown in operation, once failure happens, the system can be quickly repaired. Therefore,system availability which integrated reliability and maintainability has become a new research direction in the reliability and maintainability engineering.Availability evaluation methods is discussed with the life-time/repair-time obey exponential/ exponential distribution, Gamma/ Gamma distribution, exponential/Gamma distribution, Weibull/ Gamma distribution respectively, and the interval estimations of the overall system availability are given, which can be regarded as the condition-based or failure-based availability analysis. When obtained unit failure and maintenance information, unit failure and maintenance information with different probability distribution are converted into exponential failure and exponential maintenance information according to information equivalent conversion principle. The approximate confidence limits of series repairable system availability can be calculated using Classical method and Bayes method separately, and precision analysis are carried out. This has been applied to wind turbine, which can be regards as pre-analysis. In addition, the problem of repairable complex electromechanical system availability estimate is discussed based on Markov process under the condition of two-state and multi-state, and the point estimation of availability is given. The method is applied to wind turbine, and regarded as failure-based availability analysis.