Introduced in this paper are key issues about the lifetime and maintenance of pipelines in service. Some important conceptions are discussed, namely （1） The lifetime and probabilities of failures （PoF） of pipeline...Introduced in this paper are key issues about the lifetime and maintenance of pipelines in service. Some important conceptions are discussed, namely （1） The lifetime and probabilities of failures （PoF） of pipelines are defined,and their determination and calculation are discussed; （2） The key issues about the maintenance and safety of pipelines are demonstrated, and the optimal maintenance periods of pipelines are calculated.展开更多
In the optimal maintenance modeling, all possible maintenance activities and their corresponding probabilities play a key role in modeling. For a system with multiple non-identical units, its maintenance requirements ...In the optimal maintenance modeling, all possible maintenance activities and their corresponding probabilities play a key role in modeling. For a system with multiple non-identical units, its maintenance requirements are very complicated, and it is time-consuming, even omission may occur when enumerating them with various combinations of units and even with different maintenance actions for them. Deterioration state space partition (DSSP) method is an efficient approach to analyze all possible maintenance requirements at each maintenance decision point and deduce their corresponding probabilities for maintenance modeling of multi-unit systems. In this paper, an extended DSSP method is developed for systems with multiple non-identical units considering opportunistic, preventive and corrective maintenance activities for each unit. In this method, different maintenance types are distinguished in each maintenance requirement. A new representation of the possible maintenance requirements and their corresponding probabilities is derived according to the partition results based on the joint probability density function of the maintained system deterioration state. Furthermore, focusing on a two-unit system with a non-periodical inspected condition-based opportunistic preventive-maintenance strategy;a long-term average cost model is established using the proposed method to determine its optimal maintenance parameters jointly, in which “hard failure” and non-negligible maintenance time are considered. Numerical experiments indicate that the extended DSSP method is valid for opportunistic maintenance modeling of multi-unit systems.展开更多
We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum ha...We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum handoff delay subject to the sensing reliability and link maintenance constraints.There are two cases that should be considered:1)the SU performs spectrum handoff successfully during the current frame,and 2)the SU successfully performs the spectrum handoff using several frames.We develop a dynamic programming algorithm for RCSS to identify the optimal sensing sequence for the first case,and an updating algorithm for RCSS to improve the handoff performance for the second case.The numerical results confirm that the proposed RCSS handoff scheme can achieve better handoff delay performance than others when the received signal-to-noise ratios of the Pus' signals on different channels are non-identical.展开更多
文摘Introduced in this paper are key issues about the lifetime and maintenance of pipelines in service. Some important conceptions are discussed, namely （1） The lifetime and probabilities of failures （PoF） of pipelines are defined,and their determination and calculation are discussed; （2） The key issues about the maintenance and safety of pipelines are demonstrated, and the optimal maintenance periods of pipelines are calculated.
文摘In the optimal maintenance modeling, all possible maintenance activities and their corresponding probabilities play a key role in modeling. For a system with multiple non-identical units, its maintenance requirements are very complicated, and it is time-consuming, even omission may occur when enumerating them with various combinations of units and even with different maintenance actions for them. Deterioration state space partition (DSSP) method is an efficient approach to analyze all possible maintenance requirements at each maintenance decision point and deduce their corresponding probabilities for maintenance modeling of multi-unit systems. In this paper, an extended DSSP method is developed for systems with multiple non-identical units considering opportunistic, preventive and corrective maintenance activities for each unit. In this method, different maintenance types are distinguished in each maintenance requirement. A new representation of the possible maintenance requirements and their corresponding probabilities is derived according to the partition results based on the joint probability density function of the maintained system deterioration state. Furthermore, focusing on a two-unit system with a non-periodical inspected condition-based opportunistic preventive-maintenance strategy;a long-term average cost model is established using the proposed method to determine its optimal maintenance parameters jointly, in which “hard failure” and non-negligible maintenance time are considered. Numerical experiments indicate that the extended DSSP method is valid for opportunistic maintenance modeling of multi-unit systems.
基金supported by the National Natural Science Foundation of China under Grant No. 61172067
文摘We consider the spectrum handoff delay of a Secondary User(SU)in cognitive radio networks.We propose a spectrum handoff scheme based on Recommended Channel Sensing Sequence(RCSS),which aims to optimise the spectrum handoff delay subject to the sensing reliability and link maintenance constraints.There are two cases that should be considered:1)the SU performs spectrum handoff successfully during the current frame,and 2)the SU successfully performs the spectrum handoff using several frames.We develop a dynamic programming algorithm for RCSS to identify the optimal sensing sequence for the first case,and an updating algorithm for RCSS to improve the handoff performance for the second case.The numerical results confirm that the proposed RCSS handoff scheme can achieve better handoff delay performance than others when the received signal-to-noise ratios of the Pus' signals on different channels are non-identical.
