Title
Decision Support and Optimization in Shutdown and
Turnaround Scheduling
Authors
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Classification
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not available
Keywords
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Scheduling, Malleable jobs, Time-Cost Tradeoff, Project
Management, Stochastic Analysis, Optimization, Resource
Leveling
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This paper concerns the highly complex task of
scheduling large-scale maintenance activities during a
plants shutdown or turnaround. We model it as a discrete
time-cost tradeoff problem with capacity constraints and
individual working shifts for different resource types
with a cost function regarding a balanced resource
consumption. We introduce and model the problem, give an
overview on the large variety of related optimization
problems, and propose a framework for supporting managers
decisions in the planning process of such an event. Our
key component is an optimization algorithm complemented
with a risk analysis of solutions. We implemented a
two-phase solution method in which we first provide an
approximation of the tradeoff between project duration
and cost as well as a stochastic evaluation of the risk
for meeting the makespan. In a second, detailed planning
phase, we solve the actual scheduling optimization
problem for a chosen deadline heuristically and compute a
detailed schedule that we complement by evaluating upper
bounds for the two risk measures expected tardiness and
the probability of meeting the deadline. We present
experimental results showing that our methods can handle
large real-world instances within seconds and yield a
leveled resource consumption. For smaller instances a
comparison with solutions of a time-consuming mixed
integer program prove the high quality of the solutions
that our fast heuristic produces.
Source
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