1,721,514 research outputs found
Reliability simulation of a multi-configurable power generation system
No full textThe power generation system of the Type 23 Frigate is multi-configurable, with a range of operator rules for choosing a configuration under various operational requirements or subsystem failures. YARD built a model of this system under contract to Yarrow Shipbuilders Ltd., in order to forecast the system availability as a function of mission profile, and thus identify any potential weaknesses in the system or its equipment, and non-compatibilities with specified target requirements. The model uses discrete-event Monte-Carlo simulation, and includes the system topography, start-up and random failures, and the system operating rules. The complexity of these operating rules required the concepts of a knowledge-based system approach to be applied to the problem, giving an interesting combination of O.R. and Expert Systems methodologies
Nonpreemptive multi-server priority queues
No full textHokstad recently published an approximate method for calculating the behaviour of an M/G/m queue. This note applies his results to the nonpreemptive priority situation with two priority classes having the same service-time distribution. Laplace transforms and the first two moments of the waiting-time distributions are given
Risk analysis using an embedded CPA package
No full textThis paper presents a method for evaluating risk in projects using a CPA package embedded in a simulation control framework. An implementation on a personal computer and a demonstration example are described. The key new features of this approach are firstly its ability to deal with a wide range of sources of uncertainty, including uncertainties in the network's structure and uncertain resource constraints, and secondly new indices of criticality
Assessing Extension of Time delays on major projects
No full textThis paper describes the standard methods currently available for assessing Extension of Time delays on major projects, and issues around such assessment. Network-based techniques have been much developed, and are powerful and credible tools for assessing the effect of a small number of discrete impacts on a project, where major reactive management actions have not been needed. The paper points out the problems inherent in such methods in other, more complex situations, and describes the contribution that other methods using cause mapping and System Dynamics can make. These, however, are also not universally useful, and the paper describes how the two methodologies can be used together to produce useful analyses of the impact of delays on a project
Reorder levels for lumpy demand
No full textIf demand for a product occurs in a few large orders, classical techniques are not suitable for setting the reorder level. When gamma-distributed sized orders arrive stochastically, with usually no more than one during a lead-time, approximate expressions for the optimum reorder level and resulting expected stock-out are derived. Experimental results suggest that this is a good approximation
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