Supplier selection and collaboration for humanitarian relief supply chains

Toktaş Palut, Peral (Dogus Author)Humanitarian logistics is mainly divided into the following three planning stages in the disaster life cycle: (pre-disaster) mitigation phase, (post-disaster) response phase, and recovery phase. Relief supplier selection and collaboration is a very crucial part of the pre-disaster period to overcome the difficulties in the response phase which could not be done by government itself. The main objective of this study is to select the most appropriate relief suppliers in the pre-disaster period in terms of determined criteria. As a case study, the Anatolian side of Istanbul, Turkey is considered as the affected area. In order to achieve this goal, first Interpretive Structural Modeling (ISM) is used to identify and rank the criteria and to find the interactions among them. Among 15 criteria determined through the literature review and face to face surveys with experts, seven of them are found to be more important and affecting than the others. These criteria are geographic position, collaboration attribute, using information technology tools, data accuracy, evaluation and certification system, resource and information sharing, and trust development. Second, Analytic Network Process (ANP) is used to determine the weights of the criteria selected by the ISM method. Finally, the candidate suppliers are evaluated and ranked in terms of these criteria using the Analytic Hierarchy Process (AHP)-Rating technique. The framework proposed in this study provides practitioners with a tool for planning and carrying out humanitarian logistics activities

Coordination In A Two-stage Capacitated Supply Chain With Multiple Suppliers

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2009Bu tezin amacı, rassal talebe sahip merkezkaç bir tedarik zincirindeki envanter politikalarını kontratlar aracılığıyla koordine etmektir. Ele alınan sistem, sınırlı üretim kapasitesine sahip çoklu bağımsız tedarikçi ve bir üreticiden oluşan iki kademeli merkezkaç bir tedarik zinciridir. Tedarikçiler stok için üretim yapmakta ve envanter yönetiminde temel stok yöntemini kullanmaktadır. Üretici ise sipariş için üretim prensibine göre çalışmaktadır. Gerekli varsayımlar altında, her tedarikçi bir M/M/1 stok-için-üretim kuyruk sistemi; üretici ise gelişlerarası sürelerinin yaklaşık dağılımı bulunarak bir GI/M/1 kuyruk sistemi olarak modellenmiştir. Daha sonra, merkezi ve merkezkaç modeller geliştirilmiştir. Bu modellerin eniyi çözümleri karşılaştırıldığında, sadece en düşük temel stok seviyesine sahip tedarikçinin koordine edilmesi gerektiği görülmektedir. Bu nedenle, bu tedarikçi ve üretici arasında kontratlar hazırlanmıştır. Bu tezde transfer ödemesine dayalı üç farklı kontrat üzerine çalışılmıştır. Bu kontratlar, bekleyen sipariş maliyetini destekleme kontratı, Pareto iyileştirmeye dayalı transfer ödemesi kontratı ve maliyet paylaşımı kontratıdır. Her kontrat, koordinasyon yeteneği ve Pareto iyileştiren olup olmaması yönünden değerlendirilmiştir. Sonuç olarak, üç kontrat da tedarik zincirini koordine etmektedir. Pareto iyileştirme göz önüne alındığında ise, maliyet paylaşımı kontratının her iki üye tarafından da tercih edilmesi beklenebilir. Bu tezde ayrıca, merkezi ve merkezkaç sistemlerin SCOR Model performans ölçütleri açısından karşılaştırılması amacıyla sayısal bir çalışma da yer almaktadır.The aim of this thesis is to coordinate the inventory policies in a decentralized supply chain with stochastic demand by means of contracts. The system considered is a decentralized two-stage supply chain consisting of multiple independent suppliers and a manufacturer with limited production capacities. The suppliers operate on a make-to-stock basis and apply base stock policy to manage their inventories. On the other hand, the manufacturer employs a make-to-order strategy. Under necessary assumptions, each supplier is modeled as an M/M/1 make-to-stock queue; and the manufacturer is modeled as a GI/M/1 queue after deriving an approximate distribution for the interarrival times of the manufacturer. Then, the centralized and decentralized models are developed. When the optimal solutions to these models are compared, it is concluded that only the supplier with the minimum base stock level needs coordination. Therefore, contracts are prepared between that supplier and the manufacturer. Three different transfer payment contracts are studied in this thesis. These are the backorder cost subsidy contract, the transfer payment contract based on Pareto improvement, and the cost sharing contract. Each contract is evaluated according to its coordination ability and whether it is Pareto improving or not. The results denote that all three contracts can coordinate the supply chain. However, when the Pareto improvement is taken into account, the cost sharing contract seems to be the one that will be preferred by both members. In this thesis, also a numerical study is performed to compare the centralized and decentralized systems based on SCOR Model performance metrics.DoktoraPh

Coordination in a two-stage capacitated supply chain with multiple suppliers

Bu çalışmanın amacı, rassal talebe sahip merkezkaç bir tedarik zincirindeki envanter politikalarını kontratlar aracılığıyla koordine etmektir. Ele alınan sistem, sınırlı üretim kapasitesine sahip çoklu bağımsız tedarikçi ve bir üreticiden oluşan iki kademeli merkezkaç bir tedarik zinciridir. Tedarikçiler stok için üretim yapmakta ve envanter yönetiminde temel stok yöntemini kullanmaktadır. Üretici ise sipariş için üretim prensibine göre çalışmaktadır. Tedarikçilerin kapasitesi sınırlı olduğu için, gerekli varsayımlar altında her tedarikçi bir  stok-için-üretim kuyruk sistemi olarak modellenmiştir. Ayrıca, her tedarikçinin ortalama bekleyen sipariş miktarı ve ortalama envanter seviyesi elde edilmiştir. Diğer yandan, üreticinin gelişlerarası sürelerinin yaklaşık dağılımı bulunmuş ve gerekli varsayımlar altında üretici bir  kuyruk sistemi olarak modellenmiştir. Bunun yanı sıra, üreticinin sistemindeki ortalama iş sayısı ve ortalama bekleyen sipariş miktarı hesaplanmıştır. Daha sonra, kuyruk modellerinden elde edilen performans ölçütleri kullanılarak merkezi ve merkezkaç modeller geliştirilmiştir. Bu modellerin eniyi çözümleri karşılaştırıldığında, sadece en düşük temel stok seviyesine sahip tedarikçinin koordine edilmesi gerektiği görülmektedir. Bu nedenle, sadece bu tedarikçi ve üretici arasında kontratlar hazırlanmıştır. Bu çalışmada transfer ödemesine dayalı üç farklı kontrat üzerine çalışılmıştır. Bu kontratlar, bekleyen sipariş maliyetini destekleme kontratı, Pareto iyileştirmeye dayalı transfer ödemesi kontratı ve maliyet paylaşımı kontratıdır. Her kontrat, koordinasyon yeteneği ve Pareto iyileştiren olup olmaması yönünden değerlendirilmiştir. Sonuç olarak, üç kontrat da tedarik zincirini koordine etmektedir. Pareto iyileştirme göz önüne alındığında ise, maliyet paylaşımı kontratının her iki üye tarafından da tercih edilmesi beklenebilir. Anahtar Kelimeler: Tedarik zinciri koordinasyonu, çoklu tedarikçi, kontrat, envanter politikası.The aim of this study is to coordinate the inventory policies in a decentralized supply chain with stochastic demand by means of contracts. The system considered is a decentralized two-stage supply chain consisting of multiple independent suppliers and a manufacturer with limited production capacities. The suppliers operate on a make-to-stock basis and apply base stock policy to manage their inventories. On the other hand, the manufacturer implies a make-to-order strategy. Since the suppliers are capacitated, each supplier is modeled as an  make-to-stock queue under necessary assumptions. Furthermore, the average outstanding backorders and the average inventory level of each supplier are obtained. On the other hand, to model the manufacturer as a queuing system, first an approximate distribution is derived for the interarrival times of the manufacturer. The idea behind the approximation is the expectation that the supplier with the minimum base stock level affects the interarrival times of the manufacturer the most. Then, the manufacturer is modeled as a  queue under necessary assumptions. Moreover, the average number of jobs in the manufacturer's system and the average outstanding backorders at the manufacturer are obtained. After the supply chain has been modeled as a queuing system, the centralized and decentralized systems are taken into account. In the centralized system, there is a single decision maker who tries to optimize the overall supply chain. On the other hand, in the decentralized system, each member tries to optimize his own entity. The centralized system is also considered in this paper since the centralized solution is used as a reference point for the coordination of the decentralized system. In the centralized model, the objective of the single decision maker is to minimize the average total backorder and holding costs per unit time for the overall system. The decision variables are the base stock levels of the suppliers. On the other hand, in the decentralized model, each supplier tries to minimize his average backorder and holding costs per unit time. Since the decision variables are the base stock levels of the suppliers, the manufacturer is not included in the decentralized model. However, the decision of the supplier with the minimum base stock level also affects the manufacturer. When the optimal solutions to the centralized and decentralized models are compared, it is concluded that only the supplier with the minimum base stock level needs coordination. Also, it is found that a coordinating contract has to encourage the relevant supplier to choose a smaller base stock level than his decentralized solution. Therefore, the contracts are prepared accordingly between that supplier and the manufacturer.Three different transfer payment contracts are studied in this paper. These are the backorder cost subsidy contract, the transfer payment contract based on Pareto improvement, and the cost sharing contract. In the backorder cost subsidy contract, the manufacturer covers some part of the supplier's average backorder cost per unit time after the transfer payment. In the transfer payment contract based on Pareto improvement, the manufacturer pays the supplier an amount that makes the manufacturer as well off after the transfer payment as before. Finally, in the cost sharing contract, the manufacturer pays the supplier an amount such that the supplier covers some part of their average total costs per unit time after the transfer payment. Each contract is then evaluated according to its coordination ability and whether it is Pareto improving or not. If a contract is not Pareto improving even it coordinates the supply chain, then at least one of the members will not desire to participate in the contract. The analyses of the contracts point out that all three contracts have the ability to coordinate the supply chain. However, they differ in whether they are Pareto improving or not. It is found that only the backorder cost subsidy contract is not Pareto improving. Among the other two contracts, in the transfer payment contract based on Pareto improvement, only the supplier is better off after the contract and the manufacturer remains the same. On the other hand, in the cost sharing contract, both the supplier and the manufacturer can be better off after the transfer payment for an appropriately selected contract parameter. Therefore, the cost sharing contract seems to be the one that will be preferred by both members. Keywords: Supply chain coordination, multiple suppliers, contract, inventory policy

Logistics process improvement of Kapıkule Border crossing

Çekyay, Bora (Dogus Author) -- Önsel Ekici, Şule (Dogus Author) -- Özaydın, Özay (Dogus Author) -- Toktaş Palut, Peral (Dogus Author)In this study, logistics process improvement of Kapikule Border Crossing, one of the largest customs gates, has been evaluated. It is obvious that, any decrease in trade time is expected to realize positive impact on the logistics competitiveness of a specific country. In order to reduce time across all dimensions of the border process, the improvement of physical infrastructure and the proliferation of procedures are the most important issues that should be focused on. The aim of the study is to improve the Kapikule border crossing by reducing the process time. For this purpose, first, in-depth interviews were conducted with the Kapikule customs gate authorities in order to reveal explicitly the process flows. Subsequently, the current situation at the gate was simulated using the Arena simulation software. Finally, several improvement scenarios were tested to identify the ones that will have the highest impact on reducing the queues and the delays at the border

Effects of quotas on Turkish foreign trade: a gravity model

As stated by a European Union Commission Report (2009), Turkey's role as a world trade participant has grown in recent years, particularly as the country has been capitalizing more on its unique geopolitical position. Given the substantial trade volume and deep-rooted relations between Turkey and the EU, due attention should be paid to their trade and economic relations, and steps should be taken to improve these relations. Turkey is the biggest economy that is in a Customs Union (CU) with the EU, but not a member of the EU, along with Andorra, Monaco, and San Marino. When it joined the CU in 1996, Turkey removed all customs duties and equivalent charges as well as quantitative restrictions. However, some EU countries impose quota limits on Turkish road transporters that may indirectly restrict trade between Turkey and the country in question. This study has investigated the effect of road-transport quotas on Turkish foreign trade with EU countries. A gravity model estimated using panel data from 18 selected EU countries between 2005 and 2012 was used for this purpose. Furthermore, as one of the leading sectors using road transportation for Turkish exports to EU countries, the textile sector was analyzed as a case study. The results indicated that quotas have significant effects on total Turkish exports by road transport as well as Turkish textile exports to EU countries. The estimated loss of Turkish exports to the selected countries in the time period analyzed was 10.6 billion dollars of Turkey's total exports by road transport and 5.65 billion dollars of Turkey's total textile exports. Therefore, it can be concluded that the quota limitations are against CU regulations because they limit not only road transportation, but also trade between parties

Logistics process improvement of Kapikule border crossing

Önsel Ekici, Şule (Dogus Author) -- Çekyay, Bora (Dogus Author) -- Özaydın, Özay (Dogus Author) -- Toktaş Palut, Peral (Dogus Author) -- Conference full title: The 15th International Logistics and Supply Chain Congress (LMSCM), October 19, 2017 through October 20, 2017 in Istanbul, TurkeyIn this study, logistics process improvement of Kapikule Border Crossing, one of the largest customs gates, has been evaluated. It is obvious that, any decrease in trade time is expected to realize positive impact on the logistics competitiveness of a specific country. In order to reduce time across all dimensions of the border process, the improvement of physical infrastructure and the proliferation of procedures are the most important issues that should be focused on. The aim of the study is to improve the Kapikule border crossing by reducing the process time. For this purpose, first, in-depth interviews were conducted with the Kapikule customs gate authorities in order to reveal explicitly the process flows. Subsequently, the current situation at the gate was simulated using the Arena simulation software. Finally, several improvement scenarios were tested to identify the ones that will have the highest impact on reducing the queues and the delays at the border

İki kademeli bir tedarik zincirinin koordinasyonu

Toktaş-Palut, Peral (Dogus Author) -- Ülengin, Füsun (Dogus Author) -- Conference full title: Yöneylem Araştırması ve Endüstri Mühendisliği 32. Ulusal Kongresi - YAEM, 20-22 Haziran, İstanbul: Doğuş Üniversitesi.Bu bildiride, rassal talebe sahip merkezkaç bir tedarik zincirindeki envanter politikalarının sözleşmeler aracılığıyla koordine edilmesi amaçlanmaktadır. Ele alınan sistem, sınırlı üretim kapasitesine sahip çoklu bağımsız tedarikçi ve bir üreticiden oluşan iki kademeli merkezkaç bir tedarik zinciridir. Tedarikçiler stok için üretim yapmakta ve envanter yönetiminde temel stok yöntemini kullanmaktadır. Üretici ise sipariş için üretim prensibine göre çalışmaktadır. Tedarikçilerin kapasitesi sınırlı olduğu için, gerekli varsayımlar altında her tedarikçi bir M M/ /1 stok-için-üretim kuyruk sistemi olarak modellenmiştir. Ayrıca, her tedarikçinin ortalama bekleyen sipariş miktarı ve ortalama envanter seviyesi elde edilmiştir. Diğer yandan, üreticinin gelişler arası sürelerinin yaklaşık dağılımı bulunmuş ve gerekli varsayımlar altında üretici bir GI M/ /1 kuyruk sistemi olarak modellenmiştir. Bunun yanı sıra, üreticinin sistemindeki ortalama iş sayısı ve ortalama bekleyen sipariş miktarı hesaplanmıştır. Daha sonra, kuyruk modellerinden elde edilen performans ölçütleri kullanılarak merkezi ve merkezkaç modeller geliştirilmiştir. Bu modellerin eniyi çözümleri karşılaştırıldığında, tedarik zincirinin koordine edilmesi gerektiği görülmektedir. Bu bildiride, transfer ödemesine dayalı üç farklı sözleşme üzerine çalışılmıştır. Bu sözleşmeler, bekleyen sipariş ve elde tutma maliyetini destekleme sözleşmesi, Pareto iyileştirmeye dayalı transfer ödemesi sözleşmesi ve maliyet paylaşımı sözleşmesidir. Her sözleşme, koordinasyon yeteneği ve Pareto iyileştiren olup olmaması yönünden değerlendirilmiştir. Sonuç olarak, üç sözleşme de tedarik zincirini koordine etmektedir. Pareto iyileştirme göz önüne alındığında ise, maliyet paylaşımı sözleşmesinin tüm üyeler tarafından tercih edilmesi beklenebilir.Arçelik, Bosch, Pegasus, Ekol, LG, Borçelik, Ford Otosan, Casino Uzman

Bütünleşik tedarikçi seçimi ve sipariş miktarı belirleme problemine matematiksel modelleme yaklaşımı

Toktaş Palut, Pelin (Dogus Author) -- Conference full title: 37. Yöneylem araştırması ve Endüstri Mühendisliği Ulusal Kongresi; Yıldız Teknik Üniversitesi, İstanbul, 5-7 Temmuz 2017This study analyzes the integrated supplier selection and lot sizing problem of an international automotive supply industry company owning more than one production facility and supplier. A mathematical model is constructed to solve this problem which is very important for the competitiveness of the company. The aim of this study is to select the most appropriate local or global suppliers and to determine the lot sizes based on the production facility and product. The products are divided into two groups: complex and simple; and the suppliers are divided into three groups: local, strategic, and challenger. Only the simple products can be supplied from local suppliers. Local suppliers offer a quantity discount, whereas strategic and challenger suppliers offer a rebate based on the total value of the order. The objective function of the mathematical model is to minimize the total costs of the supply chain. The mathematical model is solved and the results are discussed

Modeling a supply chain as a queuing system

Ülengin, Füsun (Dogus Author) -- #nofulltext -- Conference full title: 5th IFAC Conference on Management and Control of Production and Logistics 2010 : Coimbra, Portugal, 8 - 10 September, 2010This study investigates a two-stage supply chain consisting of multiple suppliers at the first stage and a manufacturer at the second stage. The suppliers and the manufacturer have limited production capacities. The system operates in a manufacture-to-order environment, i.e. the suppliers and the manufacturer employ make-to-stock and make-to-order strategies, respectively. The inventory of each component at each supplier is controlled via base stock policy. The aim of this study is to model the supply chain as a queuing system. Under the necessary assumptions, each supplier is modeled as an M / M /1make-to-stock queue. Moreover, the average outstanding backorders and the average inventory level of each supplier are derived using the queuing model. On the other hand, the manufacturer is modeled as a GI / M /1 queue after deriving an approximate distribution for the interarrival times of the manufacturer. Furthermore, the average number of jobs in the manufacturer's system and the average outstanding backorders at the manufacturer are obtained using the queuing model.Int. Fed. Autom. Control (IFAC) ,Tech. Comm. Large Scale Complex Syst., Associacao Portuguesa de Controlo Automatico (APCA), Fac. Cienc. Tecnol. Univ. Coimbra (FCTUC), Fundacao para a Ciencia e Tecnologia (FCT

Structural equation modeling for analyzing the barriers and benefits of e-procurement

Palut Toktaş, Peral (Dogus Author) -- Conference full title: 8th International Conference on Industrial Engineering and Industrial Management, CIO 2014, 20th International Conference on Industrial Engineering and Operations Management, ICIEOM 2014 and International IIE Conference, IIIE 2014; Málaga; Spain; 23 July 2014 through 25 July 2014We perform an empirical study to analyze whether it would be beneficial for a company to switch from traditional procurement system to e-procurement system. For this purpose, we determine the main barriers and benefits of e-procurement systems, and using Structural Equation Modeling, we analyze the effects of the barriers and benefits on the e-procurement adoption decision. The results denote that barriers (benefits) of e-procurement systems have negative (positive) effect on the adoption decision. We also find that the effect of the benefits is higher than that of the barriers, indicating that it would be beneficial for the company to adopt the e-procurement system