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Abstract Maintenance helps to extend equipment life by improving its condition and avoiding catastrophic failures. Appropriate model or mechanism is, thus, needed to quantify system availability vis-a-vis a given maintenance strategy, which will assist in decision-making for optimal utilization of maintenance resources. This paper deals with semi-Markov process (SMP) modeling for steady state availability analysis of mechanical systems that follow condition-based maintenance (CBM) and evaluation of optimal condition monitoring interval. The developed SMP model is solved using two-stage analytical approach for steady-state availability analysis of the system. Also, CBM interval is decided for maximizing system availability using Genetic Algorithm approach. The main contribution of the paper is in the form of a predictive tool for system availability that will help in deciding the optimum CBM policy. The proposed methodology is demonstrated for a centrifugal pump.

Maintenance helps to extend equipment life by improving its condition and avoiding catastrophic failures. Appropriate model or mechanism is, thus, needed to quantify system availability vis-a-vis a given maintenance strategy, which will assist in decision-making for optimal utilization of maintenance resources. This paper deals with semi-Markov process (SMP) modeling for steady state availability analysis of mechanical systems that follow condition-based maintenance (CBM) and evaluation of optimal condition monitoring interval. The developed SMP model is solved using two-stage analytical approach for steady-state availability analysis of the system. Also, CBM interval is decided for maximizing system availability using Genetic Algorithm approach. The main contribution of the paper is in the form of a predictive tool for system availability that will help in deciding the optimum CBM policy. The proposed methodology is demonstrated for a centrifugal pump. [ABSTRACT FROM AUTHOR]

In this paper, a methodology for analysis of steady-state availability of repairable mechanical systems with opportunistic maintenance is presented, which is based on Semi-Markov process (SMP). SMP models; combining corrective maintenance with the opportunistic maintenance are proposed. The opportunistic maintenance is based on the condition of the component. An analytical framework is suggested for the solution of the SMP models. System steady-state availability is evaluated and compared in three cases of corrective maintenance; perfect, minimal and imperfect repairs; with and without opportunistic maintenance. The benefits of opportunistic maintenance are quantified in terms of the increased system availability. The proposed methodology is useful for maintenance engineers in implementing appropriate maintenance policy. The methodology is also helpful to designers to target a desired value of the system availability for the type and level of repair. The proposed methodology is demonstrated for a system, consisting of a centrifugal pump and the transmission unit in a series configuration. [ABSTRACT FROM AUTHOR]

Regulation of the world's rivers and alteration of natural flow regimes have led to the degradation of floodplains and wetlands. Here, we investigate plant-flood interactions in a floodplain wetland to determine whether a return to more natural flooding regimes using environmental water allocations can contribute to restoration from a degraded state., We use detailed field surveys to quantify the effects of flooding on a native rush, Juncus ingens, which has become invasive in floodplain grasslands in south-eastern Australia. We then apply these results to determine the likelihood of generating the flood regime required to control J. ingens in its new range, considering the regulated nature of the river system., Complete submergence for several months substantially reduced J. ingens stem densities, survival and recovery. However, rhizomes were able to survive, with new stems produced during subsequent partial submergence. Under current regulated conditions, the volume of environmental water needed to cause substantial stem decline, and potentially rhizome death, is extremely large - particularly for tall stems - even when used in conjunction with a natural flood peak., Synthesis and applications. Although repeated submergence events may cause stem decline of the invasive plant Juncus ingens, the present day operational constraints of the regulated river make it difficult to deliver the required volume and depth of water using environmental water allocations. Furthermore, shallow floods may actually provide favourable conditions for growth. This research is particularly relevant for other restoration projects where historical disturbance regimes can only be partially mimicked. Whilst a managed flood regime can be successful in achieving a range of conservation and restoration goals, there may be situations in which river regulation can limit the ability to effectively manage particular species using environmental water allocations alone. [ABSTRACT FROM AUTHOR]