Browsing by Author "Ozturk, Cemalettin"

Now showing 1 - 15 of 15

Citation - Scopus: 1
Assignment of Transit Container Bookings for a Transit Agency
(Vilnius Gediminas Technical University, 2010) Örnek, Mustafa Arslan; Eliiyi Türsel, Deniz; Sargut Z.; Ozturk, Cemalettin
Overseas containers sometimes cannot be directly shipped to their destinations, but first unloaded, temporarily stored and then loaded onto smaller vessels at interim ports to save cost and/or to transport them to their final destinations directly. The assignment of these transshipment containers to vessels necessitates several measures to be taken into account simultaneously. We develop a mathematical model that considers the assignment of such containers to different vessels while optimizing multiple objectives. We provide a numerical example and present our conclusions. © Izmir University of Economics, Turkey, 2010.
Citation - WoS: 35
Citation - Scopus: 36
Balancing and Scheduling of Flexible Mixed Model Assembly Lines
(Springer, 2013) Ozturk, Cemalettin; Tunali, Semra; Hnich B.; Örnek, Mustafa Arslan
Mixed model assembly line literature involves two problems: balancing and model sequencing. The general tendency in current studies is to deal with these problems in different time frames. However, in today's competitive market, the mixed model assembly line balancing problem has been turned into an operational problem. In this paper, we propose mixed integer programming (MIP) and constraint programming (CP) models which consider both balancing and model sequencing within the same formulation along with the optimal schedule of tasks at a station. Furthermore, we also compare the proposed exact models with decomposition schemes developed for solving different instances of varying sizes. This is the first paper in the literature which takes into account the network type precedence diagrams and limited buffer capacities between stations. Besides, it is the first study that CP method is applied to balancing and scheduling of mixed model assembly lines. Our empirical study shows that the CP approach outperforms the MIP approach as well as the decomposition schemes.
Citation - WoS: 19
Citation - Scopus: 24
Balancing and Scheduling of Flexible Mixed Model Assembly Lines With Parallel Stations
(Springer London Ltd, 2013) Ozturk, Cemalettin; Tunali, Semra; Hnich B.; Örnek, Mustafa Arslan
In this paper, we study flexible mixed model assembly lines with serially connected stages where stages may have one or more parallel stations. Station parallelism in flexible mixed model assembly lines improves system reliability and enables rapid adaptability to customer demand fluctuations. However, in order to effectively manage such lines under real-world conditions, there is a need to extend traditional assembly line management methods. This study extends the current research by simultaneously considering the problems of task assignment and model scheduling on parallel stations. Furthermore, scheduling of assigned tasks on each station is considered. We formulate the problem context first as a mixed integer programming model and then develop a decomposition scheme for large scale applications. Finally, we compare the performance of the proposed model and decomposition scheme using various size test instances.
Citation - WoS: 18
Citation - Scopus: 22
Capacitated Lot Sizing With Linked Lots for General Product Structures in Job Shops
(Pergamon-Elsevier Science Ltd, 2010) Ozturk, Cemalettin; Örnek, Mustafa Arslan
In this paper, we propose a mixed integer programming (MIP) model for a multi-level multi resource capacitated lot sizing and scheduling problem with a set of constraints to track dependent demand balances, that is, the amount left over after allocating the available inventory to the dependent demands. A part of this leftover amount may be kept as a reservation quantity to meet dependent demands of the following period under capacity restrictions. These constraints are necessary because we assume independent demands as well as dependent demands for all items in the product structure. They also are used to tighten the domain of on hand and backorder inventory levels. Although we allow backorders for independent demands only, this is not possible for dependent demands as backorders will disturb the whole demand balance of the product structure. Determination of setup costs is a crucial task when developing lot sizing and scheduling models, especially in a capacitated manufacturing environment with backorders. In this respect, the capacitated lot sizing with linked lot sizes (CLSPL) model we formulate needs not to consider setup costs to avoid unnecessary setups thanks to the new set of constraints, and to obtain feasible lot sizes and schedules. Finally, a numerical example and computational results in a job shop environment are also given, and future research directions are provided. (C) 2009 Elsevier Ltd. All rights reserved.
Citation - Scopus: 5
A Constraint Programming Model for Balancing and Scheduling of Flexible Mixed Model Assembly Lines With Parallel Stations
(IFAC Secretariat, 2012) Ozturk, Cemalettin; Tunali S.; Hnich B.; Örnek, Mustafa Arslan
In this paper, we study flexible mixed model assembly lines with serially connected stages where stages may have one or more parallel stations. Station parallelism in flexible mixed model assembly lines improves system reliability and enables rapid adaptability to customer demand fluctuations. In this paper we consider task assignment, model and task scheduling problems simultaneously. Due to its success in solving combinatorial problems, we develop a Constraint Programming model for the problem and test its performance using various size instances. The results reveal that, the model outperforms a Mixed Integer Programming model and a decomposition scheme given in the literature. © 2012 IFAC.
Citation - Scopus: 2
Cyclic Scheduling of Flexible Mixed Model Assembly Lines
(IFAC Secretariat, 2013) Ozturk, Cemalettin; Tunali S.; Hnich B.; Örnek, Mustafa Arslan
Mixed model assembly lines are used to produce multiple copies of given minimum part set (MPS). Considering only one copy (cycle) of the MPS while solving the mixed-model balancing and scheduling problem yields suboptimal solutions since blocking and idle times of stations between repeated copies are ignored. Modeling and solving this problem in a cyclic manner can significantly overcome these inefficiencies and improve the throughput of the line. In this paper, after investigating the nature of the problem, we propose exact and heuristic methods for practical applications and evaluate their performances on various size test instances. © IFAC.
Citation - WoS: 33
Citation - Scopus: 35
Cyclic Scheduling of Flexible Mixed Model Assembly Lines With Parallel Stations
(Elsevier Sci Ltd, 2015) Ozturk, Cemalettin; Tunali, Semra; Hnich B.; Örnek, Mustafa Arslan
In this paper, the problem of balancing and cyclic scheduling of flexible mixed model assembly lines with parallel stations is studied. To exploit the connection between balancing and cyclic scheduling problems for an efficient line management, they are considered simultaneously. A novel constraint programming model including problem specific symmetry breaking constraints is proposed to solve this problem. Experiments on extensive number of test instances with various sizes are also presented. (C) 2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
Citation - Scopus: 1
Integer Programming Model Formulations for Over Constrained Flight - Gate Assignment Problem
(Universite de Lorraine, 2015) Ozturk, Cemalettin; Örnek, Mustafa Arslan; Sugut I.
Flight - Gate assignment problems are complex real world problems involving different constraints. Some of these constraints include plane-gate eligibility, assigning planes of the same airline and planes getting service from the same ground handling companies to adjacent gates, buffers for changes in flight schedules, night stand flights, priority of some gates over others, and so on. In literature there are models to solve this highly complicated problem and tackle its complexity. In this study, we propose two different Integer programming (IP) models, namely, timetabling and assignment based models to solve the problem to optimality. These models prove to be highly efficient in that the computational times are quite short. We also provide the results for one day operation of an airport using real world data. Although, the research is still in progress, in the final section we present our conclusions based on our study done so far.
Citation - WoS: 10
Citation - Scopus: 14
A Mip Based Heuristic for Capacitated Mrp Systems
(Pergamon-Elsevier Science Ltd, 2012) Ozturk, Cemalettin; Örnek, Mustafa Arslan
Although Material Requirements Planning (MRP) is the most widely used production planning tool in today's manufacturing companies, its inability to perform an exhaustive capacity planning, lack of a comprehensive and integrated shop floor extension and using constant and inflated lead times necessitate intelligent methods for developing cost effective production plans. A single optimization model might be employed to overcome these limitations, but it would be intractable to use it in large manufacturing systems. Hence, in this paper, we propose a heuristic method called Capacity Allocater and Scheduler, CAS, to eliminate drawbacks of MRP systems and provide solutions for large-scale instances. The CAS procedure. based on iteratively solving relaxed Mixed Integer Programming (MIP) models, is built on a lot sizing and scheduling framework, which considers both supply alternatives and lot size restrictions simultaneously. Finally, we give a detailed numerical example to demonstrate how CAS may be used in practice, and provide our concluding remarks. (C) 2012 Elsevier Ltd. All rights reserved.
A Mixed Integer Programming Model for Multi-Period Dyeing and Batching Problem in a Yarn Plant
(Computers and Industrial Engineering, 2014) Ozturk, Cemalettin; Örnek, Mustafa Arslan
In a so-called multi-period yarn dyeing and batching problem, we try to determine the optimal batching of customer orders to be dyed in dye machines in each shift to minimize total lateness and earliness costs. In addition to weight, production quantity and volume capacity of the machines, there is a set of technical dyeing interaction constraints such as flotte, colour types, colour percentages and chemical recipe of customer orders when yarns are immersed in a large vat of coloured water known as the dye-liquor that includes dyestuffs, plus a range of chemicals to assist the dyeing process in the same shift. Furthermore, because of multi-period multi-shift nature of the problem, there is a setup carryover restriction which enforces that from shift to shift the colours must be processed in the increasing degree of darkness, i.e., in technical terms, the colour percentage of the batch increases. To the best of our knowledge, there is no study in the literature to solve this combinatorial optimization problem. Hence, in this paper, we first develop a novel mixed integer programming (MIP) formulation and then, we present a case study in a worldwide known yarn manufacturing company.
Citation - WoS: 7
Citation - Scopus: 9
A Note on A Mixed Integer Programming Model for Advanced Planning and Scheduling (aps)
(Elsevier Science Bv, 2010) Örnek, Mustafa Arslan; Özpeynirci, Selin; Ozturk, Cemalettin
In a recent paper, Chen and Ji [Chen, K., Ji, P., 2007. A mixed integer programming model for advanced planning and scheduling (APS). European journal of Operational Research 181, 515-522] develop a mixed integer programming model for advanced planning and scheduling problem that considers capacity constraints and precedence relations between the operations. The orders require processing of several operations on eligible machines. The model presented in the above paper works for the case where each operation can be processed on only one machine. However, machine eligibility means that only a subset of machines are capable of processing a job and this subset may include more than one machine. We provide a general model for advanced planning and scheduling problems with machine eligibility. Our model can be used for problems where there are alternative machines that an operation can be assigned to. (C) 2009 Elsevier B.V. All rights reserved.
Citation - WoS: 13
Citation - Scopus: 17
Operational Extended Model Formulations for Advanced Planning and Scheduling Systems
(Elsevier Science Inc, 2014) Ozturk, Cemalettin; Örnek, Mustafa Arslan
Since the basic reasoning of Manufacturing Resources Planning (MRPII) systems is flawed, a new breed of concepts called Advanced Planning and Scheduling systems CAPS) have recently emerged to overcome the problems occurring on the shop floor. In this study, we develop improved and extended mixed integer programming formulations for APS systems at the factory planning level. First, we develop a basic model which explicitly considers capacity constraints, operation sequences, processing times, and due dates in a multi-machine, multi-order, multi-item environment where an item can be processed on a given set of eligible machines. The extensions to the basic model include sequence dependent setups, and transfer times between machines. We also show that our model with a little modification could be used to quote delivery times for customer orders in case due dates are not specified. We provide numerical examples and our conclusions along with future research directions. (C) 2013 Elsevier Inc. All rights reserved.
Citation - WoS: 16
Citation - Scopus: 19
Optimisation and Constraint Based Heuristic Methods for Advanced Planning and Scheduling Systems
(University of Cincinnati, 2016) Ozturk, Cemalettin; Örnek, Mustafa Arslan
Manufacturing Resources Planning (MRPII) systems are unable to prevent capacity problems occurring on the shop floor because of the fixed lead time and backward scheduling logic. For this reason, a new breed of concepts called APS (Advanced Planning and Scheduling) systems emerged which include finite capacity planning at the shop floor level through constraint based planning. In this paper, we present a Constraint Programming (CP) model to show how optimization models could be used in this context. We also present a two phase heuristic to solve this complicated APS problem. While jobs are assigned to the best eligible machines to smooth the workload on the machines in the first phase, a constraint based scheduling heuristic schedules jobs once they are assigned to eligible machines in the second phase. We provide numerical tests and discuss the results for both the model and the heuristic. The concluding remarks and suggestions for future research are stated in the final section of the paper. © International Journal of Industrial Engineering.
Citation - Scopus: 2
Simultaneous Balancing and Scheduling of Flexible Mixed Model Assembly Lines With Sequence Dependent Task Time Increments
(Vilnius Gediminas Technical University, 2010) Ozturk, Cemalettin; Tunali S.; Hnich B.; Örnek, Mustafa Arslan
General tendency in mixed model assembly line literature is to separate balancing and model sequencing decisions to different time frames. However, today's competitive market conditions force decision makers to respond quickly to changing demand patterns. Therefore, assembly line balancing and mixed model sequencing problems should be considered together. In this paper, we state the problem structure with sequence dependent task time increments and flexibility in task assignment. Furthermore, we compare the performance of two approaches which are proposed to solve the stated problem by using various problem instances. © Izmir University of Economics, Turkey, 2010.
Citation - Scopus: 17
Simultaneous Balancing and Scheduling of Flexible Mixed Model Assembly Lines With Sequence-Dependent Setup Times
(2010) Ozturk, Cemalettin; Tunali S.; Hnich B.; Örnek, Mustafa Arslan
We consider Simultaneous Balancing and Scheduling of Flexible Mixed Model Assembly Lines with Sequence-Dependent Setup Times (SBSFMMAL-SDST). We propose alternate Mixed Integer Programming (MIP) and Constraint Programming (CP) formulations. Our experiments show that while the MIP models could not solve relatively small instances, the CP approach seems more promising. © 2010.