Browsing by Author "Karasan, Oya Ekin"

Now showing 1 - 6 of 6

Open Access
An analysis of cyclic scheduling problems in robot centered cells
(Elsevier, 2012) Yıldız, Serdar; Karasan, Oya Ekin; Aktürk, M. Selim
The focus of this study is a robot centered cell consisting of m computer numerical control (CNC) machines producing identical parts. Two pure cycles are singled out and further investigated as prominent cycles in minimizing the cycle time. It has been shown that these two cycles jointly dominate the rest of the pure cycles for a wide range of processing time values. For the remaining region, the worst case performances of these pure cycles are established. The special case of 3-machines is studied extensively in order to provide further insight for the more general case. The situation where the processing times are controllable is analyzed. The proposed pure cycles also dominate the rest when the cycle time and total manufacturing cost objectives are considered simultaneously from a bicriteria optimization point of view. Moreover, they also dominate all of the pure cycles in in-line robotic cells. Finally, the efficient frontier of the 3-machine case with controllable processing times is depicted as an example.
Embargo
Exact solution approaches for the minimum total cost traveling salesman problem with multiple drones
(Elsevier, 2023-01-04) Özbaygın Tiniç, G.; Karasan, Oya Ekin; Kara, Bahar Yetiş; Campbell, J.F.; Özel. A.
Deployment of drones in delivery operations has been attracting growing interest from the commercial sector due to its prospective advantages for a range of distribution systems. Motivated by the widespread adoption of drones in last-mile delivery, we introduce the minimum cost traveling salesman problem with multiple drones, where a truck and multiple drones work in synchronization to deliver parcels to customers. In this problem, we aim to find an optimal delivery plan for the truck and drones operating in tandem with the objective of minimizing the total operational cost including the vehicles’ operating and waiting costs. Unlike most studies in the literature where the objective is to minimize completion time, which means one needs to know only the arrival time of the latest arriving vehicle (truck or drone) at each synchronization point, we need to keep track of all the individual waiting times of the truck and the drones to properly account for waiting costs, which makes it more challenging to handle the synchronization. We provide a flow based and two cut based mixed integer linear programming formulations strengthened with valid inequalities. For non-compact models, we devise a variety of branch-and-cut schemes to solve our problem to optimality. To compare our formulations/algorithms and to demonstrate their competitiveness, we conduct computational experiments on a range of instances. The results indicate the superiority of utilizing branch-and-cut methodology over a flow based formulation. We also use our model to conduct sensitivity analyses with several problem parameters and to explore the benefits of launch and retrieval at the same node, the tradeoff between the number of drones and the operational cost, and the special case with a minimize completion objective with one drone. We also document very low waiting times for drones in optimal solutions and show solutions from minimizing cost have much lower cost than those from minimizing makespan.
Open Access
New exact solution approaches for the split delivery vehicle routing problem
(Springer Verlag, 2018) Özbaygın, Gizem; Karasan, Oya Ekin; Yaman, Hande
In this study, we propose exact solution methods for the split delivery vehicle routing problem (SDVRP). We first give a new vehicle-indexed flow formulation for the problem and then a relaxation obtained by aggregating the vehicle-indexed variables over all vehicles. This relaxation may have optimal solutions where several vehicles exchange loads at some customers. We cut off such solutions, in a nontraditional way, either by extending the formulation locally with vehicle-indexed variables or by node splitting. We compare these approaches using instances from the literature and new randomly generated instances. Additionally, we introduce two new extensions of the SDVRP by restricting the number of splits and by relaxing the depot return requirement and modify our algorithms to handle these extensions.
Open Access
Scheduling in a three-machine flexible robotic cell
(IFAC, 2006) Gültekin, Hakan; Aktürk, M. Selim; Karasan, Oya Ekin
In this study, a three-machine flexible robotic manufacturing cell in which the CNC machines are used is considered. These machines are highly flexible and are capable of performing several different operations. Each machine is assumed to be capable of performing all of the required operations of each part. As a consequence of this assumption, a new class of cycles is defined and three simple and widely used cycles among this class is proposed. The regions of optimality for these cycles as well as the worst case performances are derived.
Open Access
Traveling repairmen problem: A biogeography-based optimization
(Springer Cham, 2022-07-14) Öder Uzun, G.; Dengiz, B.; Kara, İ.; Karasan, Oya Ekin; Xu, Jiuping; Altıparmak, Fulya; Hassan, Mohamed Hag Ali; Márquez, Fausto Pedro García; Hajiyev, Asaf
Traveling Repairman Problem (TRP), which is also known by names cumulative traveling salesman problem, the deliveryman prob lem and the minimum latency problem, is a special variant of Traveling Salesman Problem (TSP). In contrast to the minimization of completion time objective of TSP, the desired objective of TRP is to minimize the cumulative latency (waiting time or delay time) of all customers. In this paper, a generalized version of TRP with multi depots and time windows, namely Multi Depot Traveling Repairman Problem with Time Windows (MDTRPTW) is considered. A group of homogeneous repairmen initi ate and finish their visit tours at multiple depots. Each customer must be visited exactly by one repairman within their provided earliest end latest times. Being a challenging Nondeterministic Polynomial-hard (NP hard) optimization problem, exact solution approaches are not expected to scale to realistic dimensions of MDTRPTW. Thus, we propose a biogeography-based optimization algorithm (BBOA) as a metaheuristic approach to solve large size MDTRPTW problems. The proposed meta heuristic is analyzed in terms of solution quality, coefficient of variation as well as computation time by solving some test problems adapted from the related literature. The efficacy of the proposed solution methodology is demonstrated by solving instances with 288 customers within seconds.
Open Access
The venue management problem: setting staffing levels, shifts and shift schedules at concession stands
(Springer, 2019) Ahipaşaoğlu, Ö.; Erkip, Nesim; Karasan, Oya Ekin
The aim of this research is to determine staffing requirements as well as shift scheduling, with the objective of maximizing the expected contribution from the venue. We specifically consider theaters where demand at concession stands is non-stationary, being largely dominated by the showtimes, the days of the week and the movie types. Determination of the number of workers and their shift in such facilities can be considered as a venue management problem. As one of the distinctive characteristics of our study, we maximize the expected contribution of venue operations while combining shift scheduling in a mathematical model. In addition to the objective function, shift scheduling differs from that in the standard literature, as shift beginning and end times are not restricted. Because of the highly variable demand in the venue management problem considered, flexible shifts are used, with flexible beginning and end times, as long as workers meet the specifications of the type to which they belong. We prove that the venue management problem under consideration is NP-complete. Under mild conditions, we show that the binary requirements of some of the variables in the model can be relaxed. Computational results of a case study are provided.