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Öğe Adaptability of just-in-time (JIT) philosophy to service systems: A case study(SAGE PUBLICATIONS LTD, 2007) Balci, Deniz; Kesen, Saadettin Erhan; Baykoc, Oemer FarukAlthough a great deal of successful research has been carried out in just-in-time (JIT) philosophy, few researchers have focused on the adaptation of JIT philosophy in service systems. Despite the recent improvements in the service systems, few studies have been carried out which examine the effects of the JIT philosophy on service systems which have a different structure to production systems. As a result of the benefits obtained from successful application of the JIT philosophy in the production systems, we have adapted the JIT philosophy for the service systems and examined the obtainable benefits. For this purpose, observation and time-scaling studies were made in an Adult Emergency Service in Turkey. Within the framework of the data acquired in this study, the existing system was modeled. By analyzing the simulation results, an alternative system has been proposed which can be applied to the system. Results show that the proposed system under the principle of JIT philosophy outperforms the existing system.Öğe Bütünleşik üretim ve dağıtım problemleri için yeni bir çözüm yaklaşımı: matematiksel modelleme(Selçuk Üniversitesi Mühendislik-Mimarlık Fakültesi, 2012) Kesen, Saadettin ErhanÜretim ve dağıtım faaliyetleri tedarik zinciri yönetiminde çok temel iki unsurdur. Literatürde bu iki problem genellikle birbirinden bağımsız olarak ele alınmaktadır. Ancak daha düşük sistem maliyeti için bu iki fonksiyonun bütünleşik olarak değerlendirilmesi gerektiği açıktır. Dolayısıyla kurumsal işletmeler sürdürülebilir rekabet için üretim ve dağıtım kararlarını birlikte almalıdır. Bu gereklilik üzerine son yıllarda üretim ve dağıtım problemlerinin entegre olarak ele alındığı çalışmalar artmaya başlamıştır. Bu çalışmada ilk olarak üretim problemi özdeş olmayan paralel makineler ortamına indirgenmiş ve bir matematiksel model önerilmiştir. Daha sonra dağıtım kararlarının verilmesinde araç rotalama problemi üzerinde durulmuş ve bir diğer matematiksel model geliştirilmiştir. Son olarak bu iki model temel alınarak üretim ve dağıtım problemlerini eş zamanlı çözen yeni bir model önerilmiş ve modelin geçerliliği örnek problem vasıtasıyla sağlanmıştır.Öğe Capacity-constrained supplier selection model with lost sales under stochastic demand behaviour(SPRINGER LONDON LTD, 2014) Kesen, Saadettin ErhanIn today's market conditions, volume of demand is quite uncertain and thus it is hard to estimate. In many cases, buyer is prone to use supply chain flexibility rather than inventory holding strategy to withstand demand uncertainty. We assume that the buyer releases a replenishment order to the supplier for each cycle (or period) under the contract which is mainly composed of four parameters: (1) supply cost per unit, (2) minimum order quantity, (3) order quantity reduction penalty and (4) maximum capacity of the supplier. Based on these parameters, there are two flexibility options that buyer should evaluate in the order of cycle (1) issue an order smaller than the minimum order quantity and pay the related penalty and (2) place no order and lose the sales. Hence, Q (lost) emerges as a critical buyer decision, the order quantity, below which no order is placed. Total expected supply cost plus lost sales, as a function of Q (lost) is presented. We derive the optimal Q (lost) that minimises the total cost function. Since capacity of each supplier is finite, we then develop a supplier selection model with total cost minimisation over the suppliers subject to capacity constraint that has a stochastic nature stemming from demand behaviour. Linearisation on the model is performed using chance-constrained programming approach. From a given set of supply bids from the potential supply chain partners, the buyer is able to make a quantifiable choice.Öğe The coordinated production and transportation scheduling problem with a time-sensitive product: a branch-and-cut algorithm(TAYLOR & FRANCIS LTD, 2017) Karaoglan, Ismail; Kesen, Saadettin ErhanIn many supply chain scenarios in which short lifespan products are considered, production and transportation decisions must be made in a coordinated manner with no inventory stage. Hence, a solution to this problem conveys information about production starting times of each product lot at facility and delivery times of the lots to various customer-sites located in different geographic regions. In this paper, we study a variant of the problem that single product with limited shelf life is produced at single facility. Once produced, production lot is directly distributed to the customers with non-ignorable transportation time by single vehicle having limited capacity before the lifespan. Objective is to determine the minimum time required to produce and deliver all customer demands. To this end, we develop a branch-and-cut (B&C) algorithm using several valid inequalities adopted from the existing literature to improve lower bounds and applying a local search based on simulated annealing approach to improve upper bounds. On test problems available in the literature, we evaluate the performance of the B&C algorithm. Results show the promising performance of the B&C algorithm.Öğe Evaluating Supply Chain Flexibility with Order Quantity Constraints and Lost Sales(Elsevier Science Bv, 2010) Kesen, Saadettin Erhan; Kanchanapiboon, Atipol; Das, Sanchoy K.In a flexible supply chain buyers and suppliers are willing to accommodate the uncertainties and variations in each other's businesses. In many instances the buyer may prefer to use supply flexibility, as opposed to an inventory holding strategy, to counter demand uncertainty. We consider the case where the buyer releases a fixed period replenishment order to the supplier under a supply contract defined by three parameters: (i) supply price per unit (ii) minimum order quantity and (iii) order quantity reduction penalty. Following a demand drop the buyer therefore has two flexibility options in the order cycle: (i) to place an order less than the supplier specified minimum order quantity and pay the associated penalty, or (ii) place no order and lose the sales for the current period. There is no penalty for not placing an order. A key buyer decision then is Q(lost), the order or replenishment quantity level below which no order is placed and the sales are lost. A model for deriving the expected supply and lost sales cost as a function of Q(lost) is presented, and it is shown that the optimal value of Q(lost) is the inflexion point of the lost sales cost and the quantity penalty. The model is then used to select the supplier that minimizes the procurement plus lost sales costs from a given set of supply bids and a known expected customer demand behavior. Finally, the buyer also has the option to make capital investments in the supplier so as to reduce the minimum order quantity and hence reduce the projected supply costs. We evaluate the economics of this tactic.Öğe From Analytical Perspective to Heuristic Approach: Travelling Salesman Problem With Discrete Fuzzy Travel Times(2009) İşleyen, Selçuk Kürşat; Kesen, Saadettin Erhan; Baykoç, Ömer FarukIn today's business, travelling times are affected by many factors such as traffic, weather, road etc. so deterministic approaches can not find any solution for problems where such an ambiguity happens. This paper deals with the Travelling Salesman Problem (TSP) in which travelling times are inaccurate. We use discrete fuzzy numbers to represent the uncertainty. Discrete fuzzy numbers are then converted to the triangular fuzzy numbers (TFNs). TFNs enforce the TSP model to have a non-linear objective function. Then we make an approximation and obtain linear model (LM) by inserting lower, medium, and lower values of the TFNs into one since non-linear model (NLM) can trap local optima. Finally, we develop Iterated Local Search (ILS) technique to get good solutions in a shorter time in the case that objective function is non-linear. NLM, LM and ILS are compared on a wide range of test problems that randomly generated. Results show that ILS technique is very promising and finds much better solutions in a very shorter computational time. Hence, it can be substituted in the place of NLM.Öğe A fuzzy AHP approach to personnel selection problem(ELSEVIER SCIENCE BV, 2009) Gungor, Zulal; Serhadlioglu, Guerkan; Kesen, Saadettin ErhanDue to the increasing competition of globalization and fast technological improvements, world markets demand companies to have quality and professional human resources. This can only be achieved by employing potentially adequate personnel. In this paper, we proposed a personnel selection system based on Fuzzy Analytic Hierarchy Process (FAHP). The FAHP is applied to evaluate the best adequate personnel dealing with the rating of both qualitative and quantitative criteria. The result obtained by FAHP is compared with results produced by Yager's weighted goals method. In addition to above-mentioned methods, a practical computer-based decision support system is introduced to provide more information and help manager make better decisions under fuzzy circumstances. (c) 2008 Elsevier B.V. All rights reserved.Öğe A Genetic Algorithm Based Heuristic for Scheduling of Virtual Manufacturing Cells (VMCs)(Pergamon-Elsevier Science Ltd, 2010) Kesen, Saadettin Erhan; Das, Sanchoy K.; Güngör, ZülalWe present a genetic algorithm (GA) based heuristic approach for job scheduling in virtual manufacturing cells (VMCs). In a VMC, machines are dedicated to a part as in a regular cell, but machines are not physically relocated in a contiguous area. Cell configurations are therefore temporary, and assignments are made to optimize the scheduling objective under changing demand conditions. We consider the case where there are multiple jobs with different processing routes. There are multiple machine types with several identical machines in each type and are located in different locations in the shop floor. Scheduling objective is weighted makespan and total traveling distance minimization. The scheduling decisions are the (i) assignment of jobs to the machines, and (ii) the job start time at each machine. To evaluate the effectiveness of the GA heuristic we compare it with a mixed integer programming (MIP) solution. This is done on a wide range of benchmark problem. Computational results show that GA is promising in finding good solutions in very shorter times and can be substituted in the place of MIP model.Öğe How important is the batch splitting activity in scheduling of virtual manufacturing cells (VMCs)?(TAYLOR & FRANCIS LTD, 2011) Kesen, Saadettin Erhan; Gungor, ZulalEspecially developed for small-to-medium companies that perform batch production, virtual manufacturing cells (VMCs) have attracted some researchers' close attention as they provide greater flexibility associated with flexible manufacturing systems (FMSs) and some of the scheduling simplicity related to cellular manufacturing systems (CMSs) without incurring much additional system cost. In a VMC, machines are dedicated to a part as in a regular cell, but machines are not physically located in a contiguous area. Batch splitting (also called lot streaming) activity emerges as a key element that management must decide whether to apply it. In this paper, we consider the case where there are multiple jobs with different processing sequences. There are multiple machine types, each of which has several identical machines and identical machines are distributed through the shop floor. Two scheduling objectives are makespan minimisation and total travelling distance minimisation. Under these circumstances, we developed two mixed integer linear programming (MILP) formulations with and without batch splitting. On a broad range of test problems, performances of the models are compared with each other and computational results show that batch splitting leads to more desirable system results while it increases the computational time. The decision maker or manager should make a trade-off between system performance and computational time efficiency.Öğe Konya İlinde Bulunan Özel Hastanelerdeki Hizmet Kalitesinin Ölçülmesi: Akademik Personele Yönelik Araştırma(Selçuk Üniversitesi, 2019) Güler, Büşra; Kesen, Saadettin ErhanHastanelerin sürekli gelişme göstererek kalitelerini artırmak, hastanın ihtiyaç ve beklentilerine cevap vermek sağlık sistemi içerisindeki rolünün gereğidir. Artan rekabete sahne olan sağlık sektöründe hastaneler başarılı olabilmek için teknolojik gelişmelere dayalı hizmet kalitesini artırmalıdırlar. Hastanelerdeki hizmet kalitesinin yükselmesi hastaların memnuniyet düzeyinin artmasını ve rekabette öne geçmelerini sağlayacaktır. Bu çalışmada Konya’da bulunan özel hastanelerin sundukları hizmet kalitesinin değerlendirilmesi amaçlanmıştır. Konya’da bulunan devlet üniversiteleri Konya Teknik, Selçuk ve Necmettin Erbakan üniversitelerinde çalışmakta olan akademik personel araştırmanın örneklem grubunu oluşturmuştur. Akademik personelin özel hastanelerdeki hizmet kalitesi boşluğu (algılama-beklenti) SERVQUAL (Service Quality Scale-Hizmet Kalitesi Ölçeği) ölçeği kullanılarak değerlendirilmiştir. Veriler SPSS 20 istatistiksel paket programı kullanılarak hizmet kalite boşluğu üzerinden analiz edilerek yorumlanmıştır.Öğe A Mixed Integer Programming Formulation for Scheduling of Virtual Manufacturing Cells (VMCs)(Springer London Ltd, 2010) Kesen, Saadettin Erhan; Das, Sanchoy K.; Güngör, ZülalWe present a multi-objective mixed integer programming formulation for job scheduling in virtual manufacturing cells (VMCs). In a VMC, machines are dedicated to a part family as in a regular cell, but machines are not physically relocated in a contiguous area. Cell configurations are therefore temporary, and assignments are made to optimize the scheduling objective under changing demand conditions. We consider the case where there are multiple jobs with different processing routes. There are multiple machine types with several identical machines in each type and are located in different locations in the shop floor. The two scheduling objectives are makespan minimization and minimizing total traveling distance. Since batch splitting is permitted in the system, scheduling decisions must tell us the (a) assignment of jobs to the machines, (b) the job starting time at each machine, and (c) the part quantity processed on different machines due to batch splitting. Under these decision variables, the objective function is to minimize the sum of the makespan and total traveling distance/cost. Illustrative examples are given to demonstrate the implementation of the model.Öğe New product design using FDMS and FANP under fuzzy environment(ELSEVIER SCIENCE BV, 2011) Gungor, Zulal; Delice, Elif Kilic; Kesen, Saadettin ErhanQuality function deployment (QFD) is a customer-oriented design approach in processing new product developments in order to reach maximum customer satisfaction. Design requirements (DRs) and part characteristics are important decision making problems during QFD activity processes for new product development. Here a Fuzzy decision-making system (FDMS) considering customer needs (CNs) as factors is proposed to formulate the problem. The structure of the FDMS is based on fuzzy control rules. Thus, CNs are determined as input variables and fuzzified using membership function concept. Weights of these factors are then fuzzified to ensure the consistency of the decision maker when assigning the importance of each factor over another. By applying IF-THEN decision rules, DRs of the firm are scored. This paper also uses Fuzzy analytic-network process (FANP) to determine the fulfillment levels of DRs of the firm. The comparison of FDMS with Fuzzy analytical network process (FAHP) is also presented. (C) 2011 Elsevier B.V. All rights reserved.Öğe Tam Zamanında Üretim Felsefesine Dayalı Bir Seri Üretim Hattının Simülasyon Tekniği İle Performans Analizi(Selçuk Üniversitesi, 2019) Sert, Mümüne; Kesen, Saadettin ErhanIn the literature, it is assumed that the orders are made of a single type of product in a justin-time production system. In this study, contrary to the literature, the production system in which orders can contain different product information is studied. A serial production line system working with kanban cards is modeled using the SIMAN language under various assumptions. Three different experiment clusters are designed by determining various factors. The effects of changes in factors are observed with these experimental clusters. Different performance measures are identified to observe the effect of change in factors. Findings of experimental results are reported.Öğe Tam zamanında üretim felsefesine dayalı otomatik yönlendirmeli araç sistemlerinin simülasyonu(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2004-06-28) Kesen, Saadettin Erhan; Baykoç, Ö. FarukOtomatik Yönlendirmeli Araç (OYA) Sistemleri son yıllarda imalat sektöründe malzeme taşıma ekipmanı olarak oldukça sık bir şekilde kullanılmaktadır. Literatürde OYA sistemleri ile ilgili bir çok çalışma olmasına karşın bu sistemlerin Tam Zamanında Üretim (TZÜ) Sistemine adaptasyonuyla ilgili az sayıda çalışma mevcuttur. Bu çalışmaların da neredeyse tamamında akış tipi üretim yapan sistemler ele alınmıştır. Bu çalışmada TZÜ felsefesine dayalı atölye tipi üretim yapan bir hipotetik sistemin simülasyon modeli geliştirilmiştir. Verilen fabrika yerleşiminde birden fazla araç seyahat edebilmekte ve iki yönlü akışa müsaade edilmektedir. Model kurulduktan sonra bu sistem için önemli olabilecek faktörler belirlenmiştir. Bu faktörler dikkate alınarak bir deney düzeneği hazırlanmıştır. Bu düzenekte her bir faktör için iki seviye seçilmiş ve faktöriyel tasarım yapılmıştır. Bu faktöriyel tasarım sonucunda faktörlerin performans kriterleri üzerindeki etkileri ve faktörler arası etkileşim incelenmiştir.Öğe Tam Zamanında Üretim Felsefine Dayalı Bir Seri Üretim Hattının Simülasyon Tekniğiyle Performans Analizi(Selçuk Üniversitesi Mühendislik Fakültesi, 2019) Sert, Mümüne; Kesen, Saadettin ErhanLiteratürde tam zamanında üretim sistemi konusunda siparişlerin tek tip üründen oluştuğu varsayılmıştır. Bu çalışmada ise literatürden farklı olarak siparişlerin farklı ürün bilgilerini içerebildiği üretim sistemi üzerinde durulmuştur. Kanban kartları ile çalışan bir akış tipi üretim hattı çeşitli varsayımlar altında SIMAN dili kullanılarak modellenmiştir. Çeşitli faktörler belirlenerek üç farklı deney seti oluşturulmuştur. Bu deney setleri ile faktörlerdeki değişikliklerin etkisi gözlemlenmiştir. Faktörlerdeki değişimin etkisini gözlemlemek için farklı performans ölçütleri belirlenmiştir. Sonuçlar istatistiksel olarak yorumlanmış ve analiz edilmiştir.
