Ankara : The Department of Industrial Engineering and the Institute of Engineering and Science of Bilkent University, 2008.Thesis (Ph.D.) -- Bilkent University, 2008.Includes bibliographical references leaves 166-175Processing time controllability is a critical aspect in scheduling decisions since
most of the scheduling practice in industry allows controlling processing times.
A very well known example is the computer numerically controlled (CNC) machines
in flexible manufacturing systems. Selected processing times for a given
set of jobs determine the manufacturing cost of the jobs and strongly affect their
scheduling performance. Hence, when making processing time and scheduling
decisions at the same time, one must consider both the manufacturing cost and
the scheduling performance objectives. In this thesis, we have studied such bicriteria
scheduling problems in various scheduling environments including single,
parallel and non-identical parallel machine environments. We have included some
regular scheduling performance measures such as total weighted completion time
and makespan. We have considered the convex manufacturing cost function of
CNC turning operation. We have provided alternative methods to find efficient
solutions in each problem. We have particularly focused on the single objective
problems to get efficient solutions, called the -constraint approach. We have provided
efficient formulations for the problems and shown useful properties which
led us to develop fast heuristics to generate set of efficient solutions.
In this thesis, taking another point of view, we have also studied a conic
quadratic reformulation of a machine-job assignment problem with controllable
processing times. We have considered a convex compression cost function for
each job and solved a profit maximization problem. The convexity of cost functions
is a major source of difficulty in finding optimal integer solutions in this
problem, but our strengthened conic reformulation has eliminated this difficulty.
Our reformulation approach is sufficiently general so that it can also be applied
to other mixed 0-1 optimization problems with separable convex cost functions.Our computational results demonstrate that the proposed conic reformulation is
very effective for solving the machine-job assignment problem with controllable
processing times to optimality.
Finally, in this thesis, we have considered rescheduling with controllable processing
times. In particular, we show that in contrast to fixed processing times,
if we have the flexibility to control the processing times of the jobs, we can generate
alternative reactive schedules in response to a disruption such as machine
breakdown. We consider a non-identical parallel machining environment where
processing times of the jobs are compressible at a certain cost which is a convex
function of the compression on the processing time. When rescheduling, it is critical
to catch up the initial schedule as soon as possible by reassigning the jobs to
the machines and changing their processing times. On the other hand, one must
keep the total cost of the jobs at minimum. We present alternative match-up
scheduling problems dealing with this trade-off. We use the strong conic reformulation
approach in solving these problems. We further provide fast heuristic
algorithms.Gürel, SinanPh.D
