On the Location of a Constrained k-Tree Facility in a Tree Network with Unreliable Edges

Given a tree network T with n vertices where each edge has an independent operational probability, we are interested in finding the optimal location of a reliable service provider facility in a shape of subtree with exactly k leaves and with a diameter of at most l which maximizes the expected number of nodes that are reachable from the selected subtree by operational paths. Demand requests for service originate at perfectly reliable nodes. So, the major concern of this paper is to find a location of a reliable tree-shaped facility on the network in order to provide a maximum access to network services by ensuring the highest level of network connectivity between the demand nodes and the facility. An efficient algorithm for finding a reliable (k,l) – tree core of T is developed. The time complexity of the proposed algorithm is Olkn. Examples are provided to illustrate the performance of the proposed algorithm.

Weather Window Analysis in Connection With Operation and Maintenance of Ocean Renewable Energy Devices

There is an increasing need for utilization of ocean renewable energy (ORE) around Japanese coast because Japan is surrounded by ocean. Because technologies for harnessing ORE have not been mature enough, Japanese government selects some demonstration sites for ORE devices and some demonstration projects are going. As these projects are progressed, the operation and maintenance (O&M) activities will increase and become essential factors for the success of demonstration projects. Hence, weather window analysis is required to quantify the levels of access for ORE devices in the demonstration projects, and commercial projects in the future. In this paper, two new parameters are proposed in order to evaluate accessibility to ORE devices. One is the operational probability, and the other is the forecasted waiting time. The operational probability assesses weather duration with considering variability of wave condition. The forecasted waiting time is an expectation value of waiting time before O&M planners get next chance to arrange the O&M activities. In order to check the effectivity of the proposed 2 parameters, accessibility is evaluated for significant wave height in terms of the 2 proposed parameters, these are • Operational probability • Forecasted waiting time and 3 conventional parameters, these are • Excess probability • Persistence probability • Waiting time between windows The accessibility is evaluated at two locations along the Japanese coast. This study reveals that large differences are caused between persistence probability and operational probability when operational wave height limit occurs intermittently and required window length is long. The forecasted waiting time has the same variation tendency as the waiting time between windows.

Performance of Two-Component Systems with Imperfect Repair

Operational systems deteriorate over time and eventually fail by the failure of one or more of their components. Failed components are either replaced or repaired, and replacement is usually expensive. This article examines the behavior of repairable systems with imperfect repair, where a failed component is repaired once or more depending on factors such as repair cost, level of deterioration, and criticality of the component. When these systems are subjected to a customer use environment, their performance must endure different conditions. In imperfect repair, the performance of the system lessens after each failure. Three models of a two-component system studied are the series, parallel, and standby configurations, and the components are identical and independent. A closed form analytical expression for steady state operational probability is derived for different configurations under exponential distribution time to failure and repair time. Two examples are then discussed thoroughly.

A DIVIDE-AND-CONQUER ALGORITHM FOR FINDING A MOST RELIABLE SOURCE ON A RING-EMBEDDED TREE NETWORK WITH UNRELIABLE EDGES

Given an unreliable communication network, we seek a most reliable source (MRS) of the network, which maximizes the expected number of nodes that are reachable from it. The problem of computing an MRS in general graphs is #P-hard. However, this problem in tree networks has been solved in a linear time. A tree network has a weakness of low capability of failure tolerance. Embedding rings into it by adding some additional certain edges to it can enhance its failure tolerance, resulting in another class of sparse networks, called the ring-tree networks. This class of network also has an underlying tree-like topology, leading to its advantage of being easily administrated. This paper concerns with an important case whose underlying topology is a strip graph, called λ–rings network, and focuses on an unreliable λ–rings network where each link has an independent operational probability while all nodes are immune to failures. We apply the Divide-and-Conquer approach to design a fast algorithm for computing an MRS, and employ a binary division tree (BDT) to analyze its time complexity to be [Formula: see text].

Performance of Two-Component Systems with Imperfect Repair

Operational systems deteriorate over time and eventually fail by the failure of one or more of their components. Failed components are either replaced or repaired, and replacement is usually expensive. This article examines the behavior of repairable systems with imperfect repair, where a failed component is repaired once or more depending on factors such as repair cost, level of deterioration, and criticality of the component. When these systems are subjected to a customer use environment, their performance must endure different conditions. In imperfect repair, the performance of the system lessens after each failure. Three models of a two-component system studied are the series, parallel, and standby configurations, and the components are identical and independent. A closed form analytical expression for steady state operational probability is derived for different configurations under exponential distribution time to failure and repair time. Two examples are then discussed thoroughly.