Browsing by Subject "Weighted tardiness"
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Item Open Access Factory level preventive maintenance in Turkish air force(Bilkent University, 2006) Ünlü, NuriyeIn this thesis, we study the Factory Level Preventive Maintenance Problem (FLPM) experienced by Turkish Air Force (TUAF). This problem is a specific case of Nonpreemptive Resource Constrained Multiple Project Scheduling with Mode Selection (NRCMPSMS); allocation of limited resources to competing activities of multiple project of different types in which the duration of an activity is determined by the mode selection and the activity flow is dependent on the type of the project. The objective is to determine the start (finish) time and the mode of each project’s each activity so that the minimal total weighted tardiness and total incurred cost are obtained. We proposed a heuristic for this problem definition which is composed of two phases and apply it to a real life problem experienced by TUAF. In the first phase, the aim is to construct an initial schedule with minimum total weighted tardiness and in the second phase, this schedule is improved in terms of total incurred cost by the mode selection exchanges. Since the activity due date information is not available but required in prioritization of the activities, we develop five FLPM specific activity due date estimation methods. We run the proposed heuristic for three different weight figures which are determined by the Analytic Hierarchy Process and the one being used by TUAF. In addition, we study the influence of the release and the due dates of the aircrafts on the objective functions. We propose a determination method for each of the release and the due dates that aims finding the tightness levels of these two parameters. The release date determination method that we propose relates the arrival rate of the aircrafts with the utilization of the bottleneck resource whereas the due date determination method that we propose relates the due dates of the aircrafts with the fraction of the number of tardy jobs in percentages. We investigate the performance of the activity due date estimation methods in terms of the objective functions and the computational effort required by the tightness levels of the release and the due date that are found by the determination methods that we propose.Item Open Access A new dominance rule for the total weighted tardiness problem(Taylor & Francis, 1999) Aktürk, M. S.; Yıldırım, M. B.We present a new dominance rule for the single machine total weighted tardiness problem with job dependent penalties. The proposed dominance rule provides a sufficient condition for local optimality. We show that if any sequence violates the dominance rule, then switching the violating jobs either lowers the total weighted tardiness or leaves it unchanged. We also develop a new algorithm based on the dominance rule, which is compared to a number of competing heuristics for a set of randomly generated problems. Our computational results of over 40000 problems indicate that the proposed algorithm dominates the competing heuristics in all runs.Item Open Access A new dominance rule to minimize total weighted tardiness with unequal release dates(Elsevier, 2001) Aktürk, M .S.; Özdemir, D.We present a new dominance rule by considering the time-dependent orderings between each pair of jobs for the single machine total weighted tardiness problem with release dates. The proposed dominance rule provides a sufficient condition for local optimality. Therefore, if any sequence violates the dominance rule then switching the violating jobs either lowers the total weighted tardiness or leaves it unchanged. We introduce an algorithm based on the dominance rule, which is compared to a number of competing heuristics for a set of randomly generated problems. Our computational results indicate that the proposed algorithm dominates the competing algorithms in all runs, therefore it can improve the upper bounding scheme in any enumerative algorithm. The proposed time-dependent local dominance rule is also implemented in two local search algorithms to guide these algorithms to the areas that will most likely contain the good solutions.Item Open Access Single CNC machine scheduling with controllable processing times to minimize total weighted tardiness(Elsevier, 2011) Akturk, M. S.; Ilhan, T.Advanced manufacturing technologies, such as CNC machines, require significant investments, but also offer new capabilities to the manufacturers. One of the important capabilities of a CNC machine is the controllable processing times. By using this capability, the due date requirements of customers can be satisfied much more effectively. Processing times of the jobs on a CNC machine can be easily controlled via machining conditions such that they can be increased or decreased at the expense of tooling cost. Since scheduling decisions are very sensitive to the processing times, we solve the process planning and scheduling problems simultaneously. In this study, we consider the problem of scheduling a set of jobs on a single CNC machine to minimize the sum of total weighted tardiness, tooling and machining costs. We formulated the joint problem, which is NP-hard since the total weighted tardiness problem (with fixed processing times) is strongly NP-hard alone, as a nonlinear mixed integer program. We proposed a DP-based heuristic to solve the problem for a given sequence and designed a local search algorithm that uses it as a base heuristic.