Search

The airline industry has shown significant growth in the last decade according to some indicators such as annual average growth in global air traffic passenger demand and growth rate in the global air transport fleet. This inevitable progress makes the airline industry challenging and forces airline companies to produce a range of solutions that increase consumer loyalty to the brand. These solutions to reduce the high costs encountered in airline operations, prevent delays in planned departure times, improve service quality, or reduce environmental impacts can be diversified according to the need. Although one can refer to past surveys, it is not sufficient to cover the rich literature of airline scheduling, especially for the last decade. This study aims to fill this gap by reviewing the airline operations related papers published between 2009 and 2019, and focus on the ones especially in the aircraft maintenance routing area which seems a promising branch.

Bu çalışmanın amacı, hava yolları endüstrisinin karmaşık problemlerinden biri olan bakım rotalama problemine yeni bir çözüm önerisi getirmektir.Çalışma kapsamında öncelikle, hava yolları endüstrisi operasyonlarının temel uygulama ve problemleri, bu uygulamaların literatürdekiyeri temel düzeyde ele alınmıştır. Hava yolları endüstrisi literatürü “Filo Atama, Uçak Rotalama, Bakım Rotalama ve MürettabatÇizelgeleme” başlıkları altında incelenmiştir. Önerilen, bakım planlamalı uçuş atama modeli, gerçek uçuş verileri ve tasarlanan uçuş filosuiçin uygulanmış ve bir uçuş programı oluşturulmuştur. Model iki amaç fonksiyonuna sahiptir. Birinci amaç fonksiyonu, kullanılmayan kalanyasal zamanı minimize etmeye çalışırken, ikinci amaç fonksiyonu kullanılmamış uçak kapasitesini minimize etmeye çalışır. İki amaçlımodel öncelikli hedef programlama ile çözülmüştür. As the main concentration of this study, maintenance routing is one of the most complicated problems of airline industry. In this study, airline industry operations’ main applications and subjects are basically summarized and a literature review is briefly presented. Study is conducted under headings of; “Fleet Assignment, Aircraft Routing, Maintenance Routing and Crew Scheduling”. A problem consist of real time flight data and a small size fleet is generated and the proposed model is solved to create a route with maintenance consideration. Model which solves the problem has two objective functions. While first objective function tries to minimize remaining legal flight hours of the aircrafts second objective function tries to maximize the capacity utilization of an aircraft according to the demand for the covered flight. The model is solved by using preemptive goal programming.

Logistics Centers (LCs) are among the most important facilities for rapid, cost effective, environmental friendly and secure logistics services to the urban logistics problems. Finding proper locations to LCs has an important effect on their success. In this study, LCs’ location selection problem for Istanbul Metropolitan area is investigated. Istanbul is a leading city of Turkey in many categories including various industries, import/export amounts, transportation infrastructure and population density. However, industrialization and urbanization have introduced numerous problems to Istanbul. New projects are continuously being announced for the problems of metropolis, however, they may also bring new problems if they are not punctiliously planned and applied. Hence, in this study, it is aimed to propose a systematic Multi-Criteria Decision-Making (MCDM) approach for the LCs’ location selection problem of Istanbul. In this approach, an integrated DEcision-MAking Trial and Evaluation Laboratory (DEMATEL) and Intuitionistic Fuzzy (IF) Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method is utilized. DEMATEL is used to analyse the decision criteria and IF-TOPSIS is used to evaluate candidate locations for LCs. Considering the vagueness inherent to this decision-making problem, IF sets are used for the evaluation process. Results are compared with the results of IF-VIKOR (VIše Kriterijumska Optimizacija kompromisno Rešenje– multi-criteria optimization and compromise solution) technique. First publihed online 19 March 2020

Risks caused by natural disasters, terrorist acts, economic fluctuations, and epidemic diseases, etc., result in disruptions. These anticipated or unexpected disruptions affect supply chain resilience degree adversely. A large body of literature exists on supply chain risks, and also the number of studies has increased with the effect of the COVID-19 pandemic. Literature review reveals that disruption factors have different effects on the supply chains, and considering these effects, proper actions should be performed. In this regard, initially, disruption factors existing in the literature are investigated and summarized. Afterward, a methodology based on Neutrosophic Fuzzy Decision Making Trial and Evaluation Laboratory (NF-DEMATEL) is utilized to assess the importance degrees of different disruption factors. The main aim of the proposed methodology is to help managers to take proper actions for disruption factors and state a risk management policy for future unexpected events.

The number of software projects has increased in recent years due to technological advancements. In addition to the other factors such as the qualifications of the staff, budget, leadership, the success of the projects also highly depends on how they are managed. There are various software project management models such as Waterfall, Prototype, Spiral, Incremental, Iterative and Agile, which have been applied in different types of software projects. Each has advantages and disadvantages over the other. Hence, any of them does not have absolute superiority over the others. Therefore, it is important to determine the most suitable one. In addition, depending on the sector, the conditions change and a solution methodology for the new problem environment is required. One of the biggest sectors, the banking sector, is specifically considered in this study. Conforming to the multi-criteria structure of the selection problem, Interval-Valued Neutrosophic Analytic Hierarchy Process (IVN-AHP) which is capable of providing solutions in fuzzy multi-criteria decision making environment is utilized in this study with the pairwise comparisons provided by the experts in the sector. Finally, the alternative software project management models are ranked, and the best one is obtained.

Customer satisfaction is an important factor for the success of the companies. Efforts for cost reduction and production productivity arenot enough for companies unless customer satisfaction is provided. For this reason, the aim of companies from all sizes is to provide thebest and fastest service to customers. Therefore, the establishment and operation of a logistics network is important for a company fromthe original point to the point of arrival of a product or service. In cargo companies, transportation is the main procedure in terms of timeand capacity constraints such as the number of vehicles, products and employees. With this aim, Vehicle Routing Problem with Backauls(VRPB) is investigated to reduce the total distance travelled by vehicles for a hypothetical postal service firm. It is assumed that there aremore than a hundred centers of the firm that send their vehicles to the reception centers after the distribution centers are visited. The P-Medianclustering model is used based on the distances of the centers to each other, since the exact algorithms cannot solve this problem dueto a great number of centers. Then, vehicles in each cluster routed by using a modified mathematical model. Günümüzde firmalar arası rekabetin kilit taşını müşteri memnuniyeti oluşturmaktadır. Daha az maliyet, daha çok üretim gibi hedefler müşteri memnuniyetini sağlanmadıkça firmalar için yeterli olmaz. Bu nedenle küçükten büyüğe bütün firmaların amacı müşteriye en iyi, en hızlı şekilde hizmet sunmak ve müşteri memnuniyeti sağlamaktır. Bir ürün veya hizmetin başlangıç noktasından varış noktasına kadar olan süreçte lojistik ağının çok iyi kurulması ve sürecin işlemesi bir firma için önemlidir. Özellikle temel görevi taşımacılık olan kargo firmalarının araç, ürün ve çalışan sayısı gibi kısıtlar ve zaman açısından çok iyi bir sürece sahip olması gerekmektedir. Bu amaçla, bu çalışmada posta hizmetleri için Araç Rotalama Problemi (ARP) üzerine çalışılmıştır. Araçlarını rotalarken önce dağıtım merkezlerine sonrasında kabul merkezlerine gönderen posta hizmetlerinin çok fazla şubesi bulunabilmektedir. Merkez sayısı çoğaldıkça en iyi çözümü veren algoritmalar bu problemi çözemeyeceği için merkezlerin birbirine olan uzaklıkları temel alınarak kümeleme metodu kullanılmıştır. Böylece birbirine yakın olan merkezler kendi içlerinde planlanarak toplam kat edilen uzaklık azaltılmaya çalışılmıştır.

The importance of information technologies in hotels has increased more in recent years due to the variety of required processes and the level of competitiveness in the sector. Depending on their contribution to creating value and increasing efficiency, hotel enterprises make important investments in information technologies. However, there are various criteria and alternatives in the selection process of the most suitable hotel information system. Moreover, the criteria affect each other in a fuzzy decision-making environment. Hence, two techniques are utilized synergistically in this study. IVIF-DEMATEL is initially performed to obtain the importance degrees of the criteria. Afterward, IVIF-TOPSIS is applied to reach the final rankings. An application is performed considering the case in the Turkish tourism sector, and the alternatives are ranked.

Determining the players’ playing styles and bringing the right players together are very important for winning in basketball. This study aimed to group basketball players into similar clusters according to their playing styles for each of the traditionally defined five positions (point guard (PG), shooting guard (SG), small forward (SF), power forward (PF), and center (C)). This way, teams would be able to identify their type of players to help them determine what type of players they should recruit to build a better team. The 17 game-related statistics from 15 seasons of the National Basketball Association (NBA) were analyzed using a hierarchical clustering method. The cluster validity indices (CVIs) were used to determine the optimum number of groups. Based on this analysis, four clusters were identified for PG, SG, and SF positions, while five clusters for PF position and six clusters for C position were established. In addition to the definition of the created clusters, their individual achievements were examined based on three performance indicators: adjusted plus-minus (APM), average points differential, and the percentage of clusters on winning teams. This study contributes to the evaluation of team compatibility, which is a significant part of winning, as it allows one to determine the playing styles for each position, while examining the success of position pair combinations.

In recent years, the direct effects of climate change and global warming on natural resources attracts the attention to the environmental studies. Nowadays, one of the most important issues on eliminating the destructive environmental effects of increased population is electric vehicles. However, locating the charge stations for electric vehicles is still an important problem especially for crowded cities. Moreover, in real life applications, uncertainties may occur when preferences are expressed in other terms; it is usually difficult for a decision maker to show his/her preferences by utilizing just one linguistic expression due to the difficulty and vagueness of the real problems. In this study, location selection problem for electric vehicles charging stations is considered as a multi-criteria decision making problem and hesitation of decision makers among several possible linguistic terms are considered. For this reason, in this study, probabilistic linguistic terms sets are used to evaluate criteria of locating charging stations. The main aim of this paper is to compare the possible locations of charging stations in Istanbul which is the most crowded city of Turkey. For this purpose, 39 different alternative locations were considered and ranked by using an extended version of TOPSIS to find best locations for installing charging stations.

Depending on the significant increase in the consumption and as a result in the production has caused some problems besides its utilities. One of the biggest concerns at this point is the adverse environmental effects of this growth. Hence, most of the companies take into account the environmental considerations during the design and implementation of their business facilities within their supply chains. As a result of these developments, the attempt to design supply chains greener has increased both practically and theoretically. Various studies have been performed dealing with green supply chains. However, in this study, it is focused on the greenness assessment of supply chains under four stages including inbound logistics, in-plant logistics, outbound logistics and reverse logistics. Different from the few studies in the literature, intuitionistic fuzzy (IF) approach which enables to handle fuzziness and hesitancy is used within DEMATEL and ANP techniques to measure supply chain greenness. The related steps are explicitly provided within the proposed methodology. In general, firstly the main dimensions of greenness are determined with the related indicators. Then, regarding the dependency between the dimensions, the relation network is obtained via IF-DEMATEL by taking the evaluations of supply chain experts. Afterwards, based on the network diagram and expert judgments, the importance weights of dimensions are provided with IF-ANP and used in the developed greenness scoring system. An application in a firm’s supply chain is performed to demonstrate the validation of the proposed methodology and consequently, the greenness score is obtained.

Klasik ulaştırma sistemlerinin çevresel kaygıları göz önünde bulundurulduğunda, elektrikli araçlarla (EA) ilgili çalışmalar önem kazanmış ve son yıllarda sayıca artmıştır. Bu noktada ele alınması gereken sorunlardan biri EA’lar için şarj istasyonlarının uygun yerlerinin belirlenmesidir. Bu çalışmanın temel amacı, İstanbul'daki elektrik şarj istasyonlarına ilişkin en uygun konumları yolların akışını değerlendirmeye alarak bulmaktır. Şarj istasyonlarının konumları, yolların kapsanan akışını maksimize etmeyi amaçlayan akış-yakıt ikmal lokasyon modeline dayanan bir model kullanılarak belirlenmiştir. Matematiksel model farklı “p” değerli için çözülmüş ve en iyi lokasyonlar belirlenmiştir., The studies about Electric Vehicles (EV) have gained importance and increased in the last years depending on the environmental concerns of the classic transportation systems. One of the problems to consider at this point is locating the proper points of electric charging stations for EVs. The primary objective of this research is to locate the electric charging stations in Istanbul considering the flow of the paths. The locations of electric charging stations are determined by using a mathematical model based on the flow-refuelling location model with the aim of maximizing the captured flow. The mathematical model is run for various values of “p” and the optimum locations are obtained.

With the increased volume of environmental studies, hybrid vehicle routing and recharging stations location problem for electric vehicles have become more important. The aim of this paper is to review the literature on hybrid vehicle routing problem from 2000 to latest researches in order to identify the current research and to provide direction for future research in this field. Researches are classified considering the research publication year and research fields. Research gaps are identified for future research areas.

Having become conscious about the importance of the environment much more than past nowadays, the environmentally benign applications also called as green applications have increased tremendously in the recent years. Although there are specific and individual studies in various fields from design of product to final delivery of it, there is a need to handle the subject as a whole and construct green supply chains. Before constructing a green supply chain, the first step is to assess the existing structure from the viewpoint of greenness. Hence, it is important to develop a systematic assessment approach and this study aims to analyze the existing literature by mainly clarifying the criteria and methods used in such assessment systems and provide directions for future studies. Moreover, this study also aims to provide a base for the academics and practitioners that are willing to develop a greenness assessment methodology for supply chains. For this aim, numerous studies have been analyzed under a proposed structure including four sub-sections which consist of a green supply chain.

Maintenance routing is one of the most complicated problems of operations research applications for airline industry. In this study, airline industry operations' main applications and subjects are basically mentioned and literature is briefly reviewed. This study is conducted under the headings of; Fleet Assignment, Aircraft Routing, Maintenance Routing and Crew Scheduling. Additionally, network models are explained basically on an example flight program. This study's purpose is to be a guide for the new researchers of this area through operations research applications for airline industry and to introduce maintenance routing problem literature.

Measuring satisfaction of patients and understanding their perceptions are important for the hospital management to respond to customers' growing demands for acceptable quality of healthcare services. The main purpose of this paper is to present a methodology that can be used in the healthcare service quality evaluation. IVIF-PROMETHEE method is applied for service quality evaluation based on patients' views in a real-life case study of a public hospital in Istanbul and the results are compared with the results from IVIF-TOPSIS method. Interval Valued Intuitionistic Fuzzy (IVIF) set is considered an appropriate tool because of the complexity and vagueness of the evaluation of healthcare services. The evaluation of the quality level of the healthcare service provides detailed information about the effects of considered criteria as well as creates opportunities in implementing effective procedures to overcome service quality problems via analysing the patients' views. The proposed methodology can be a useful tool for hospital management.

In this study, a multi-objective model for the reverse logistics network design (RLND) problem and a novel methodology are proposed. The proposed methodology is comprised of two stages: the centralised return centre (CRC) evaluation stage and the reverse logistics network design (RLND) stage. In the first stage an integrated ANP and fuzzy-TOPSIS methodology is utilised. In the second stage, using the CRC weights obtained in the first stage, the RLND model is solved via genetic algorithms (GAs). The proposed methodology is applied to a case from the Turkish white goods industry. The results are discussed and analysed.

Material handling system selection process has an important effect on productivity of manufacturing systems. Considering the importance of this process, it can be seen that there is a necessity to establish a systematic approach. In this study, to determine the best material handling system alternative, PROMETHEE approach is utilized. With the aim of taking into account the vagueness in the evaluation process and obtaining decision maker evaluations in an easier way with linguistic terms, fuzzy sets are utilized. To this end, a modified version of PROMETHEE is used. To foster the better understanding of the methodology, a real life application of a manufacturer is realized.

Material handling system selection process has an important effect on productivity of manufacturing systems. Considering the importance of this process, it can be seen that there is a necessity to establish a systematic approach. In this study, to determine the best material handling system alternative, PROMETHEE approach is utilized. With the aim of taking into account the vagueness in the evaluation process and obtaining decision maker evaluations in an easier way with linguistic terms, fuzzy sets are utilized. To this end, a modified version of PROMETHEE is used. To foster the better understanding of the methodology, a real life application of a manufacturer is realized.

Increasing environmental problems enforce companies to be more environmental responsible. A company’s environmental performance is not only related to the company’s inner environmental efforts, but also it is affected by the suppliers’ environmental performance and image. As a stakeholder of the company, a supplier with bad environmental image affects badly the company’s environmental image. Also, raw materials and semi-finished products supplied from out of the company recourses- suppliers- affects the products environmental features such as life cycle, re-usability, re-manufacturability, hazardous substances, etc. Considering these direct and indirect effects, managers should also consider environmental performances of their suppliers in their supplier evaluation process. In this paper, a methodology for the evaluation of suppliers’ environmental performances is proposed. In this methodology, a hybrid Fuzzy-Analytic Network Process and Fuzzy-Preference Ranking Organization METHod for Enrichment Evaluations approach is utilized. Additionally, a numerical example is given to foster the better understanding of the methodology and the obtained results are analyzed with sensitivity analyses.

Design of the facility layouts have important effects on the operational productivity and efficiency of a facility. Facility layout design problems (FLDP) are the problems that should consider the flow relations between departments and in the literature the use of Quadratic Assignment Problems (QAP) for these kinds of problems is very frequently applied. Since, for QAP, the FLDP is NP-Hard, in this study, Genetic Algorithms (GA) is utilized. The methodology is coded via Visual Studio C++ 6.0 and the program is called LO (Layout Optimizer). The methodology is tested with QAP library test problems and the difference between LO results and the best known results are less than %1 for each problem. The methodology is applied to a supplier in the structural electricity materials manufacturing sector and a %41 decrease in the transportation costs is expected with the redesign of the facility.

In this paper, the centralized return centers location evaluation problem in a reverse logistics network is investigated. This problem is solved via an integrated analytic network process- fuzzy technique for order preference by similarity to ideal solution approach. Analytic network process allows us to evaluate criteria preferences while considering interdependence between them. On the other hand, technique for order preference by similarity to ideal solution decreases the number of computational steps compared to simple analytic network process evaluation. An important characteristic of the centralized return centers location evaluation problem, vagueness, is adapted to the methodology via the usage of fuzzy numbers in the technique for order preference by similarity to ideal solution approach. Finally, a numerical example is given to demonstrate the usefulness of the methodology. The results indicate that, this integrated multi-criteria decision making methodology is suitable for the decision making problems that needs considering multiple criteria conflicting each other. Also, by using this methodology, the interdependences between the criteria may be considered for these kinds of problems in a flexible and systematic manner.

Urgent response is vitally important after unpredictable disasters and it is highly dependent to the location of the emergency centers. Considering this importance degree, in this study, a location selection methodology for emergency logistics centers (ELCs) is proposed. There are various influencing factors or criteria to choose the most convenient locations for ELCs. However, we focused on some of the most important and prior criteria to obtain a more feasible approach and less calculation intensity. The main point is ranking and weighting the convenient locations or cities for constructing an ELC in a region or country. The alternative locations are chosen through the mostly natural disaster-prone cities. Decision criteria are determined according to the expert opinions. Decision Making Trial and Evaluation Laboratory (DEMATEL) and Analytic Network Process (ANP) methods are integrated to determine the convenient locations considering the relations between criteria and alternative locations. Afterwards, a real life application of the proposed methodology is realized for the Turkey case. Finally, results are examined and analyzed in terms of their sensitivity on the criteria weight changes.

International audience; The fundamental objective of supply chain management (SCM) is to integrate various suppliers to satisfy market demand. Supplier evaluation and selection is very important for establishing an effective supply chain. As a matter of fact, supplier selection consists of both qualitative and quantitative criteria, so it is considered as a multi criteria decision making (MCDM) problem. Under incomplete or uncertain information, the fuzzy set theory allows us make decisions with approximate reasoning. In order to overcome the uncertainty which is constituted by vague situations in supplier selection, we utilize the “extension of the PROMETHEE method in a fuzzy environment” (F-PROMETHEE). In this chapter, multi criteria supplier selection based on a fuzzy PROMETHEE method with an application to supplier selection decision problem is conducted. The main advantages of the methodology are the user friendliness coming from the linguistic evaluations, and the consideration of the vagueness or fuzziness inherent to the decision making environment. Hence, the method can be an efficient and effective methodology to be used by decision makers on supply chains. The proposed methodology can also be applied to any other selection problem.

In this study, the vehicle routing problem with time windows (VRPTW) is investigated and formulated as a multi-objective model. As a solution approach, a hybrid meta-heuristic algorithm is proposed. Proposed algorithm consists of two meta-heuristics: Genetic Algorithm (GA) and Simulated Annealing (SA). In this algorithm, SA is used as an improvement operator in GA. Besides, a hypothetical application is presented to foster the better understanding of the proposed model and algorithm. The validity of the algorithm is tested via some well-known benchmark problems from the literature.

Reverse logistics network design (RLND) effectiveness has an important impact on the effectiveness of the whole supply network coordination. Considering that, in this study, the RLND problem is investigated and a hybrid genetic algorithms and simulated annealing (HGASA) methodology is proposed. This problem is applied to a preceding study which utilized genetic algorithms (GA) for the optimization. HGASA and GA results are tested with Wilcoxon rank-sum test for hundred runs and the results prove the difference between two approaches. Additionally, the averages and the standard deviations support that, the HGASA algorithm increases the probability of obtaining better solutions.

The concept of a supply chain exists for over twenty years but partners and configuration selection process still is rather unstructured. In order to increase value in any supply chain, a more comprehensive and integrative approach is required to select the right partners and establish the right configuration along the chain. Under economic growth wrong decisions does not jeopardize profitability dramatically. However, recent economy downtrends, has made the choice of suitable partners in the dynamic supply chain a key strategic concern. The nature of these decisions usually is complex and unstructured. This paper aims to present an intuitionistic fuzzy Chouquet integral operator based approach to partners and configuration selection. In order to bring structure in the evaluation process, the supply chain operations reference (SCOR) model developed by Supply Research Council is employed. The paper discusses the development of the value chain concept from partners selection perspective, outlines general similarities and differences of the value chain and the SCOR, and uses a simple V-form supply chain example to establish the proposed approach. Finally, results of the application and sensitivity of the results to the change in the selection criteria weights are discussed.

Locating an undesirable facility is a sophisticated problem, for the evaluation procedures involve several objectives and the solution to the problem calls for some compromises to be made between probable conflicting criteria. This paper addresses the problem of undesirable facility location selection using the analytic network process (ANP), a multi-criteria decision-making technique. The ANP technique enables us to consider both qualitative and quantitative criteria as well as the interdependencies and feedbacks. A number of criteria (benefits, opportunities, costs and risks) and their sub-criteria are considered for siting a new facility with which this study has dealt. The questions of what criteria would be considered and what the interdependencies between these criteria and their weights would be were discussed and determined via interviews with some competent authorities of the Istanbul Municipality and of two environmental organizations. Four representative locations were evaluated and the most convenient one was selected. This was followed by the sensitivity analyses of the results.