Browsing by Author "Staiou, Efthimia"

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Citation - WoS: 2
Citation - Scopus: 5
A Literature Review on Supplier Selection Problem and Fuzzy Logic
(SPRINGER INTERNATIONAL PUBLISHING AG, 2022) Mert Paldrak; Gamze Erdem; Melis Tan Tacoglu; Simge Guclukol; Efthimia Staiou; Tan Tacoğlu, Melis; Paldrak, Mert; Guclukol, Simge; Staiou, Efthimia; Tacoglu, Melis Tan; Erdem, Gamze; C Kahraman; AC Tolga; SC Onar; S Cebi; B Oztaysi; IU Sari
Given the recent increasing competition in global market supplier selection and evaluation has attracted a great deal of attention especially at academic levels. Supplier selection problem is a complex problem since there exist a great number of unpredictable and uncontrollable factors which have a huge impact on decision-making process. Due to this complexity there are several criteria that must be taken into consideration such as cost quality on-time delivery proximity of suppliers long-term relationship etc. Although some of these criteria (quantitative) can be expressed using pure numeric scales some (qualitative) are linguistic due to the human assessments which contain some degree of subjectivity. Since involvement of human assessment causes vagueness for deterministic models the authors apply fuzzy logic which enables the decision makers to be able to convert their linguistic expressions into fuzzy numbers with the help of fuzzy membership functions. Considering that fuzzy logic plays a vital role in solving multi-criteria supplier selection problem this paper aims to present a review of supplier selection problem and its relation with fuzzy logic. In this paper several studies that highlight supplier selection problem and the importance of fuzzy logic involvement in the problem have been reviewed. An analysis of multi-criteria decision-making methods for supplier selection problem is conducted.
Citation - WoS: 1
Citation - Scopus: 4
Spare Parts Inventory Management System in a Service Sector Company
(SPRINGER-VERLAG SINGAPORE PTE LTD, 2022) Buse Atakay; Ozge Onbasili; Simay Ozcet; Irem Akbulak; Hatice Birce Cevher; Humeyra Alcaz; Ismail Gordesli; Mert Paldrak; Efthimia Staiou; Ozcet, Simay; Alcaz, Humeyra; Cevher, Hatice Birce; Onbasili, Ozge; Atakay, Buse; Akbulak, Irem; Staiou, Efthimia; NM Durakbasa; MG Gencyilmaz
Spare parts inventory management is crucial in the success of a service providing company. In this study the spare parts of a service provider in the automotive sector are classified according to their characteristics in groups and different inventory control policies are applied to the categorized groups. The Analytical Hierarchy Process (AHP) one of the Multi-Criteria Decision Making (MCDM) methods is used to classify the spare parts into groups. As a result of the application of AHP classes of spare parts are determined according to the VED analysis classifying the spare parts according to their criticality. Furthermore the ABC analysis performed by the company was improved by using cost and demand criteria. After performing both analysis three new classes of spare parts are determined with the combination of ABC and VED classification techniques. For each class an appropriate inventory control policy is decided according to the spare parts importance and criticality. Based on the literature review the (R S s) inventory control policy is chosen to be applied in each class taking into consideration the review period order up-to-level and reorder point of items. In the inventory control model the review period for the same class items is assumed to be constant based on the information provided by the company. For verification purposes necessary cost calculations including total ordering and holding costs are performed by means of Microsoft Excel. In order to be able to vastly observe the system behavior different cost scenarios are generated by increasing and decreasing the service level and review period of the system. Using OptQuest an optimization tool embedded into ARENA simulation software the different scenarios were analyzed and the total minimum cost is reached. For supporting the daily operations of the company a user-friendly decision support system is built where the end-user can easily add/remove spare parts to/from the system classify them and compare the results of inventory control policies with the current system. The DSS will also assist the company to manage and control their real-time inventory and perform spare parts stock level tracking and decide when to place orders.