Browsing by Author "Ozfirat P.M."

Now showing 1 - 9 of 9
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    A constraint programming heuristic for a heterogeneous vehicle routing problem with split deliveries
    (Bellwether Publishing, Ltd., 2010) Ozfirat P.M.; Ozkarahan I.
    This article considers fresh goods distribution of a retail chain store in Turkey. The problem is formulated as a vehicle routing problem with a heterogeneous fleet for which no exact algorithm has ever been designed to solve it. A fast and effective algorithm based on constraint programming is proposed for the solution. The procedure is tested on some of the benchmark problems in literature. The real-life case is first solved assuming that delivery of a customer cannot be split between vehicles. Then it is resolved considering split deliveries. Solutions of both strategies are compared with the current performance of the firm to determine a distribution strategy. Results indicate considerable improvement in the performance of the firm.
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    Setting order promising times in a supply chain network using hybrid simulation-analytical approach: An industrial case study
    (Elsevier B.V., 2011) Tunali S.; Ozfirat P.M.; Ay G.
    Supply chain management (SCM) involves the management of material and information flow among the members of chain such as vendors, manufacturing plants and distribution centers. The main processes in supply chain are production planning, control, distribution and logistics. Effective management of all these processes provides the manufacturing companies great advantages in time based competition. In order to gain a competitive edge, firms must be able to deliver their products fast and on-time. This can be managed by better production planning, scheduling and due-date setting. This paper suggests a hybrid approach for setting realistic order due dates for a produce-to-order manufacturing company operating within a supply chain environment. The proposed hybrid approach combines mathematical and simulation modeling to bring together the advantages of both approaches. © 2011 Elsevier B.V. All rights reserved.
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    An integer programming approach for the three-Dimensional cutting planning problem of marble processing industry
    (2012) Ozfirat P.M.
    The three-dimensional cutting problem is one of the major problems faced in the marble factories. Huge marble blocks coming from marble quarries are first cut into planes according to their depths. Then these planes are sized according to the length and width of the demanded products. In this study, the cutting problem of a marble processing factory is handled. Two different integer programming (IP) approaches are developed. In the first one, an IP model is built for each of the two cutting problems, which are cutting marble blocks into planes and sizing these planes. In the second approach, these two IP models are integrated together to handle the two different cutting operations together. The objective of both models is to minimize total spoilage of marble while finding the cutting designs of the marble blocks and marble planes. A number of real life problems are solved using both approaches. Computational results are compared statistically. Results showed that both approaches decrease the wasted amount of marble compared to the industry's average. © Springer-Verlag London Limited 2011.
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    A fuzzy analytic hierarchy process methodology for the supplier selection problem
    (World Scientific Publishing Co. Pte Ltd, 2012) Ozfirat P.M.; Tuna G.; Tuncel G.
    Purchasing activities of a company form a very important part in the operation of the company. The quality of production and services mainly rely on the performance of the suppliers. In addition, a large amount of the product's total cost belongs to the purchasing cost of its materials. Therefore, selecting the most suitable suppliers is very important for the firm. Unfortunately, most of the time, suppliers cannot provide the highest quality parts on-time at the lowest costs in the market. In other words, quality, delivery and cost objectives conflict with each other. In this study a fuzzy analytic hierarchy process approach is employed for the supplier selection problem of a textile company. First the selection criteria according to company's objectives are determined. Then the pair-wise comparisons are made on a fuzzy basis. Similarly, in the next step, the six alternative suppliers are compared by fuzzy means. Finally, the two suppliers which achieved the highest performance are advised to the company.
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    Operating room management in health care: Operations research and artificial intelligence approaches
    (IGI Global, 2013) Ozkarahan I.; Edis E.B.; Ozfirat P.M.
    Surgical units are generally the most costly and least utilized units of hospitals. In order to provide higher utilization rates of surgical units, scheduling of operating rooms should be done effectively. Inefficient or inaccurate scheduling of operating room time often results in delays of surgery or cancellations of procedures, which are costly to the patient and the hospital. Therefore, operating room scheduling and management problems have been an important area of research both for operations researchers and artificial intelligence researchers since the 1960s. In this chapter, the operations research and artificial intelligence solutions developed for operating room scheduling problems in the operational level are examined and discussed. The studies are classified according to the approaches employed. The chapter is aimed to be helpful for researchers who are willing to make contributions in this area as well as the practitioners who are looking for efficient and effective ways to handle the operating room management problem of their own. © 2013 by IGI Global. All rights reserved.
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    Operating room management in health care: Operations research and artificial intelligence approaches
    (IGI Global, 2014) Ozkarahan I.; Edis E.B.; Ozfirat P.M.
    Surgical units are generally the most costly and least utilized units of hospitals. In order to provide higher utilization rates of surgical units, scheduling of operating rooms should be done effectively. Inefficient or inaccurate scheduling of operating room time often results in delays of surgery or cancellations of procedures, which are costly to the patient and the hospital. Therefore, operating room scheduling and management problems have been an important area of research both for operations researchers and artificial intelligence researchers since the 1960s. In this chapter, the operations research and artificial intelligence solutions developed for operating room scheduling problems in the operational level are examined and discussed. The studies are classified according to the approaches employed. The chapter is aimed to be helpful for researchers who are willing to make contributions in this area as well as the practitioners who are looking for efficient and effective ways to handle the operating room management problem of their own. © 2015 by IGI Global. All rights reserved.
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    Integration of fuzzy analytic hierarchy process and multi-objective fuzzy goal programming for selection problems: An application on roadheader selection
    (IOS Press BV, 2015) Ozfirat P.M.; Ozfirat M.K.; Malli T.; Kahraman B.
    In this study a general methodology employing fuzzy analytic hierarchy process and fuzzy goal programming is developed for selection problems. The proposed methodology has two main sub-phases. In the first phase, fuzzy triangular numbers are used in order to represent the comparisons among decision criteria. Then lower and upper bounds as well as mid-values of priorities belonging to each decision criteria are computed. In the second phase these values and fuzzy triangular numbers are entered into the goal programming model and the model is solved to give the final priorities of decision criteria. Then the weighted sum of ratings for each selection alternative are found where the weights are final priorities from goal programming model. The proposed methodology is presented on a real life roadheader selection problem from mining industry. The results revealed that the methodology is easily applicable and provides satisfactory results. © 2015 - IOS Press and the authors. All rights reserved.
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    A fuzzy approach to selecting roof supports in longwall mining
    (South African Institute of Industrial Engineering, 2016) Yetkin M.E.; Simsir F.; Ozfirat M.K.; Ozfirat P.M.; Yenice H.
    As a decision-making problem, selecting proper machines and equipment plays a key role for mining sites and companies. Many factors affect this decision, and values belonging to these factors can be expressed numerically and/or non-numerically. In order to make the most appropriate decision, engineers must carry out an evaluation process that comprises all criteria that might affect decision-making. To achieve this, multi-criteria decision-making tools are used. As a result of technological developments, coal outputs in longwall mining have risen tremendously over the last decades, and longwall mechanisation has become unavoidable. The significance of powered roof supports in particular increases day-by-day, since the rate of roof support has to be in accordance with the rate of face advance in longwalls. In this study, an integrated fuzzy analytic hierarchy process and fuzzy goal programming model is used to select the most suitable powered roof supports. The procedure is applied to a real-life underground coal mine that is operated using the longwall method. Seven alternative powered roof supports are compared with each other, taking a total of 24 decision criteria under four main topics into account. In conclusion, the most suitable roof supports for the mine under study are determined and recommended to the decision-makers of the system. © 2016, South African Institute of Industrial Engineering. All rights reserved.
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    Risk Management for Surface Plants in Mines using Risk Matrix and BowTie Analysis
    (Technical University of Kosice, 2023) Ozfirat M.K.; Ozfirat P.M.; Yetkin M.E.
    Surface plants in mines are important parts of a mine operation. There exist offices, common areas, repair and maintenance shops, compressed air facilities, hydraulic facilities, areas where mine machinery and parts are stacked, transportation cranes and mine stock areas in surface plants. Therefore, while the mining operations are continuing, it is necessary to control all the work in the surface plants in terms of work safety and health. In this study, the risk matrix method is used to identify and prioritize the risks of surface plants in a mine. Then, the highest priority risk, which is found to be "Stock area and work environment", is considered using bowtie analysis. Four threats are determined for "Stock area and work environment" risk. These are improper ore or coal stock area, insufficient lighting in night works, lack of maintenance of field crane and dusty work environment. These threats are also modelled using bowtie analysis. As a result of this study, these threats, corresponding barriers and consequences can be managed by safety and operational engineers. © 2023 by the authors.