Research On Modeling And Operation-maintenance Strategies Of Complicated K-out-of-n:G Systems Under Random Environment

Importance of k-out-of-n:G system cannot be over emphasized owing to its extensive applications in the wide fields of daily life,military,and industrial engineering.However,since such a system in practice is often complicated,and it is still a challenge to formulate this system,analyze its operational strategies.In this thesis,we intend to address a number of issues related with the k-out-of-n: G system,such as its reliability and maintenance strategies,and main contributions are stated as follows:The first system model focuses on probabilistic performance study of a repairable complex system with three subsystems coupled in a series configuration.All three subsystems have been differently configured and also have different operational schemes.The first subsystem has n units and works under the k-out-of-n: G scheme? The second subsystem has four identical units and associates with a defined work scheme 2-out-of-4: G?The third subsystem has two indistinguishable units and works under the1-out-of-2: G policy.The units failure rates of the subsystems are different and follow exponential distributions,however,there are two types of repair facilities available for repair general and copula repair.Under the consideration of the system with the operational duration,the failed unit was replaced with a new one and it was assigned for repair.In the complete shutdown condition,a copula repair has been employed to repair the system.Reliability measures have been studied for different values of failure and repair through supplementary variable and copula approaches.The numerical simulations by taking different values of k and n have been conducted,and the obtained results demonstrate the promising system performance.The second system model devotes to formulation of a system consisting of two subsystems each employing the k-out-of-n: G scheme.Therefore,the performance of a system that implements a k-out-of-n: G scheme employing a controller is estimated by the Copula methods.For this system,a partial or complete failure is admitted.If the system has partial failure,it is fixed by using general repair techniques? If the system is in complete failure,it is mended by the Copula repair techniques.Then,the system is investigated using the supplementary variable techniques and the Laplace transformation,and explicit expressions are to obtained related with availability,reliability,mean time to failure,sensitivity,and expected profit functions of this system,which are all numerically validated.The third system model assesses impacts of the system parameters on the model performance.Using the Copula’s attributes,the model performance of a system that utilizes a repair machines scheme of employing human operators is estimated.The methods of reliability measures are proposed to determine the reliability,performance,and strength of a serial system composed of two subsystems.Supplementary variable technique and Laplace transforms are proposed to solve the differential equations associated with the transition diagram.The numerical validation of explicit expressions for the system are performed,which includes the availability,reliability,mean time to failure,sensitivity,and profit function.The forth system model investigates the reliability characteristics of a parallel system,which is made up of three active units that run in parallel,with two of them having to be operational in order for the system to work.For such a system,two types of preventive maintenance strategies are proposed: online and offline preventive maintenance.After the first unit of each system fails,online preventive maintenance is performed.Following the failure of the second unit of each system,offline preventive maintenance is performed.Partial and complete failures are the two types of failures that may occur.Both systems can undergo exponential failure and repair.Supplementary variable technique,the Laplace transformation,and the Copula repair approach are used to solve the first-order differential equations.Clearly,the obtained results in this thesis are helpful to the practical design and maintenance of the k-out-of-n: G systems.