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Rescheduling parallel machines with controllable processing times
Ankara : The Department of Industrial Engineeringand the Graduate School of Engineering and Science of Bilkent University, 2012.Thesis (Master's) -- Bilkent University, 2012.Includes bibliographical references.In many manufacturing environments, the production does not always endure
as it is planned. Many times, it is interrupted by a disruption such as machine
breakdown, power loss, etc. In our problem, we are given an original production
schedule in a non-identical parallel machine environment and we assume that one
of the machines is disrupted at time t.
Our aim is to revise the schedule, although there are some restrictions that
should be considered while creating the revised schedule. Disrupted machine
is unavailable for a certain time. New schedule has to satisfy the maximum
completion time constraint of each machine. Furthermore, when we revise the
schedule we have to satisfy the constraint that the revised start time of a job
cannot be earlier than its original start time. Because, we assume that jobs are
not ready before their original start times in the revised schedule.
Therefore, we have to find an alternative solution to decrease the negative
impacts of this disruption as much as possible. One way to process a disrupted
job in the revised schedule is to reallocate the job to another machine. The other
way is to keep the disrupted job at its original machine, but to delay its start time
after the end time of the disruption. Since the machines might be fully utilized
originally, we may have to compress some of the processing times in order to
add a new job to a machine or to reallocate the jobs after the disruption ends.
Consequently, we assume that the processing times are controllable within the
given lower and upper bounds.
Our first objective is to minimize the sum of reallocation and nonlinear compression
costs. Besides, it is important to deliver the orders on time, not earlier or later than they are promised. Therefore, we try to maintain the original completion
times as much as possible. So, the second objective is to minimize the
total absolute deviations of the completion times in the revised schedule from the
original completion times.
We developed a bi-criteria non-linear mathematical model to solve this nonidentical
parallel machine rescheduling problem. Since we have two objectives, we
handled the second objective by giving it an upper bound and adding this bound
as a constraint to the problem. By utilizing the second order cone programming,
we solved this mixed-integer nonlinear mathematical model using a commercial
MIP solver such as CPLEX. We also propose a decision tree based heuristic
algorithm. Our algorithm generates a set of solutions for a problem instance
and we test the solution quality of the algorithm solving same problem instances
by the mathematical model. According to our computational experiments, the
proposed heuristic approach could obtain close solutions for the first objective for
a given upper bound on the second objective.Muhafız, MügeM.S