Browsing by Subject "Logistics"

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Aras Kargo’nun kuruluşu ve Türkiye’nin lojistik sektorüne katkıları
(Bilkent University, 2020) Aras, Ecemnaz; Dadağlıoğlu, Eren; Yaşar, Elif Bircesu; Korkut, Beyza; Ateş, Ladin
1979 yılında Celal Aras ve kardeşleri Canpolat ve Hikmet Aras tarafından kurulan Aras Dağıtım ve Pazarlama, hızlı bir şekilde oluşturduğu dağıtım ağı gücüyle, bu gücün taşımacılıkta da kullanılması kararı alınarak 1989'da faaliyete geçen Aras Kargo'nun da temellerini oluşturmuştur. Aras Kargo, rakipleri Yurtiçi ve MNG Kargo ile beraber, Türkiye’de lojistik ve kargoculuk sektöründe önemli rol oynayan firmalardandır. Bu çalışmada, Türkiye’de kargoculuk ve lojistik sektörü, Aras Kargo’nun kuruluşu ve sektöre girişi, bu süreçte yaşanan zorluklar, Türk halkının kargoculuk sektörüne tepkisi, diğer kargo şirketleriyle yaşanan rekabet ortamı ve bu şirketlerin karşılaştırılması, Aras Kargo’nun vizyonu ve kendini yenilemesi başlıklarına değinilecektir.
Open Access
Coordinated logistics: replenishment with capacitated transportation for a supply chain
(POMS, 2014-01) Büyükkaramikli, N. C.; Gürler, Ü.; Alp, O.
In this study, we consider the integrated inventory replenishment and transportation operations in a supply chain where the orders placed by the downstream retailer are dispatched by the upstream warehouse via an in-house fleet of limited size. We first consider the single-item single-echelon case where the retailer operates with a quantity based replenishment policy, (r,Q), and the warehouse is an ample supplier. We model the transportation operations as a queueing system and derive the operating characteristics of the system in exact terms. We extend this basic model to a two-echelon supply chain where the warehouse employs a base-stock policy. The departure process of the warehouse is characterized in distribution, which is then approximated by an Erlang arrival process by matching the first two moments for the analysis of the transportation queueing system. The operating characteristics and the expected cost rate are derived. An extension of this system to multiple retailers is also discussed. Numerical results are presented to illustrate the performance and the sensitivity of the models and the value of coordinating inventory and transportation operations.
Open Access
Debris removal during disaster response: a case for Turkey
(Elsevier, 2016) Sahin, H.; Kara, B. Y.; Karasan, O. E.
Debris occurs from the ruin and wreckage of structures during a disaster. Proper removal of debris is of great importance because it blocks roads and prohibits emergency aid teams from accessing disaster-affected regions. Poor disaster management, lack of efficiency and delays in debris removal cause disruptions in providing shelter, nutrition, healthcare and communication services to disaster victims, and more importantly, result in loss of lives. Due to the importance of systematic and efficient debris removal from the perspectives of improving disaster victims quality of life and allowing the transportation of emergency relief materials, the focus of this study is on providing emergency relief supplies to disaster-affected regions as soon as possible by unblocking roads through removing the accumulated debris. We develop a mathematical model for the problem that requires long CPU times for large instances. Since it is crucial to act quickly in an emergency case, we also propose a heuristic methodology that solves instances with an average gap of 1% and optimum ratio of 80.83%.
Open Access
Distribution network design on the battlefield
(John Wiley & Sons, 2011-04-29) Toyoglu, H.; Karasan, O. E.; Kara, B. Y.
Ammunition, whether it be an arrow in the middle ages, a lead bullet in the 1800s, or a laser guided smart bomb today, has been the most prominent factor in determining the outcome of combat. Failing to supply the required amount of ammunition properly may lead to defeat. Our main objective in this study is to provide a decision support tool that can help plan ammunition distribution on the battlefield. We demonstrate through an extensive literature review that the existing models are not capable of handling the specifics of the problem in this study. To this end, we propose a novel three-layer commodity-flow location routing formulation that distributes multiple products, respects hard time windows, allows demand points to be supplied by more than one vehicle or depot, and locates facilities at two different layers. We derive several valid inequalities to speed up the solution time of our model, illustrate the performance of the model in several realistically sized scenarios, and report encouraging results. Finally, we introduce a dynamic model that designs the distribution system in consecutive time periods for the entire combat duration. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 58: 188–209, 2011
Open Access
Evaluation of ammunition and fuel supply systems of a Turkish armored battalion during mobilization and deployment using simulation
(2002) Özçevik, Aydın
In current wars, supply systems have become vital factors to reach military success. With improvements in technology, the capabilities and means of military units have also improved and as a result, the supply materials which military units require have also increased greatly. The timely delivery of supply materials to the combatant units is the key to success. The delivery of supply materials to combatant units at the right time and as needed can only be possible with the efficient planning of supply systems by staff officers. The insufficient evaluation of supply systems will cause interruptions in delivery of supply materials to combatant units and consequently prevent the combatant units from accomplishing their tasks. In this study, the existing ammunition and fuel supply systems of an armored battalion before alarm order is evaluated via simulation. By using the simulation models which were coded for existing systems, commanders will have the capability to detect potential problems and take precautions. The main objectives of this study are: (1) To evaluate existing systems via simulation because of difficulties in executing real world systems due to impediments in creating real world conditions and also economic reasons. (2) To detect the factors which have significant effects on the existing system. (3) To foresee the probable problems of the existing system by studying the simulation model outputs using statistical methods. (4) To select the most critical region of Turkey according to performance measures of interest. The codes of models are created by using ARENA 3.0 simulation program and SIMAN programming language.
Open Access
Evaluation of Army Corps artillery ammunition supply system via simulation
(2000) Utku, Durdu Hakan
Since the use of enhanced technology by the opposing forces, Turkish Armed Forces must adopt new tactics, employ appropriately upgraded delivery equipment to deliver rations, fuel, ammunition, personnel, repair parts to forces in forward areas to be able to react in time. Within the budget limits, the opportunity to explore new tactics and to test and evaluate new logistics material delivery equipment is correspondingly difficult and sometimes impossible. However, by the use of simulation, which is inexpensive, new supply distribution techniques employing different equipment combinations both currently existing and experimental can be tested. In this study, we evaluate the performance of the existing and new systems of army corps artillery ammunition supply systems. The objective is to see whether the systems operate properly and to select the system design.
Open Access
Evaluation of army corps artillery ammunition supply systems via simulation
(IEEE, 2002) Sabuncuoğlu, İhsan; Utku, D. H.
The purpose of this paper is to discuss the evaluation of different alternatives for the implementation of Turkish army corps artillery ammunition supply system. The objective is to see whether the alternative systems operate properly and to select the best system design. We find that the first alternative system cannot supply the units for all phases of an eight-day battle time while the second, the third, and the fourth systems can supply and yield better results. The third system is less costly than the second and the fourth systems. However, it has the drawback of too many vehicles in the convoy (i.e. congestion) which makes it susceptible to the enemy long distance and air assaults. The fourth system is the best of all from the point of the performance it yields; but, it costs more compared to the other systems.
Open Access
Evaluation of army corps food supply system using simulation
(2002) Pembe, Ozan
Food Supply System is one of the main elements of Army Logistics System. The ultimate objective in food supply system is to provide the food at the right time and at the right place. If this objective is achieved, the morale, the health and the strength of the soldiers on the battlefield will enormously enhance. In the literature, particularly in Turkish Army, there is no study which tests whether the existing food supply system operates properly or not under the war conditions and which shows the potential problem areas and which specify time standards under different scenarios. The objective of this study is to answer these questions by the help of simulation model of the system. This model can also be helpful to the staff officers who prepare logistic support plans. The simulation model of Army Corps Food Supply System is built in Arena 3.0. The results are analyzed by statistical methods. The related bibliography is also provided in the thesis.
Open Access
Evaluation of army corps food supply system using simulation
(IEEE, 2003) Pembe, O.; Sabuncuoğlu, İhsan
The Food Supply System is one of the main elements of the Army Logistics System. The ultimate objective in a food supply system is to provide the food at the right time and in the right amount at the right place. If this objective is achieved, the morale, the health, and the strength of the soldiers on the battlefield will enormously enhanced. The purposes of this study are to test if the existing food supply system of the Turkish Army operates properly under the war conditions; to identify the potential problem areas; and establish time standards for different scenarios. We use simulation as the modelling and analysis tool to answer the above questions. The proposed simulation model of the Army Corps Food Supply System is built in Arena and the results are analyzed statistically.
Open Access
A hierarchical solution approach for a multicommodity distribution problem under a special cost structure
(2012) Koca, E.; Yıldırım, E. A.
Motivated by the spare parts distribution system of a major automotive manufacturer in Turkey, we consider a multicommodity distribution problem from a central depot to a number of geographically dispersed demand points. The distribution of the items is carried out by a set of identical vehicles. The demand of each demand point can be satisfied by several vehicles and a single vehicle is allowed to serve multiple demand points. For a given vehicle, the cost structure is dictated by the farthest demand point from the depot among all demand points served by that vehicle. The objective is to satisfy the demand of each demand point with the minimum total distribution cost. We present a novel integer linear programming formulation of the problem as a variant of the network design problem. The resulting optimization problem becomes computationally infeasible for real-life problems due to the large number of integer variables. In an attempt to circumvent this disadvantage of using the direct formulation especially for larger problems, we propose a Hierarchical Approach that is aimed at solving the problem in two stages using partial demand aggregation followed by a disaggregation scheme. We study the properties of the solution returned by the Hierarchical Approach. We perform computational studies on a data set adapted from a major automotive manufacturer in Turkey. Our results reveal that the Hierarchical Approach significantly outperforms the direct formulation approach in terms of both the running time and the quality of the resulting solution especially on large instances.
Open Access
A hub covering network design problem for cargo applications in Turkey
(Palgrave Macmillan, 2009) Alumur, S.; Kara, B. Y.
Hub location problems involve locating hub facilities and allocating demand nodes to hubs in order to provide service between origin-destination pairs. In this study, we focus on cargo applications of the hub location problem. Through observations from the Turkish cargo sector, we propose a new mathematical model for the hub location problem that relaxes the complete hub network assumption. Our model minimizes the cost of establishing hubs and hub links, while designing a network that services each origin-destination pair within a time bound. We formulate a single-allocation hub covering model that permits visiting at most three hubs on a route. The model is then applied to the realistic instances of the Turkish network and to the Civil Aeronautics Board data set.
Open Access
Logistics of temporary testing centers for coronavirus disease
(Elsevier, 2022-11-04) Ozdemir, Irmak; Dora, Manoj; Dursunoğlu, Çağla Fatma; Yetiş Kara, Bahar
The ongoing COVID-19 pandemic has caused the death of millions of people, and PCR testing is widely used as the gold standard method to detect the infections to restrict the outbreak. Through the interviews conducted with people from the field in South Korea, the UK, and Turkey, we have found that there are numerous testing strategies worldwide. Those testing strategies include drive-through and home delivery testing capabilities, local test sites, and mobile test centers. Our primary motivation is to propose a generic model based on the best practices in the UK and South Korea. Also, we aim to present a case study on Turkey for the implementation of vital procedures and increase their availability. This paper represents a study on how to construct a temporary testing logistics system during the initial phases of pandemics to increase the availability of PCR testing with the primary objective of maximizing total sample collection. The design also considers minimizing the maximum walking distance to increase the convenience of sample collection for the people living in the neighborhoods. The proposed system consists of temporary testing centers and a central laboratory. Temporary testing centers perform direct tours to the potential areas to collect samples and bring the collected sample to the designated central laboratories located at central hospitals. Moreover, to represent the non-linear inheritance of the pandemic progress within a population, we consider diminishing sample potentials over time and coverage. This new problem is defined as an extension of the Selective Vehicle Routing Problem and Covering Tour Problem. We propose a mathematical model and four two-stage math-heuristic algorithms to determine the location and routing of the temporary testing centers and their lengths of stay at each visited location. The performances of the proposed solution methodologies are tested on two data sets. The first set is constructed by the confirmed cases of the districts of Seoul, Korea, and by the interview of health personnel of H+ Yangji Hospital COVID-19 semi-mobile booth application, and the second set is constructed by 99 hospital/health centers from distinct neighborhoods of 22 districts of Istanbul, Turkey. The Pareto set of optimum solutions is generated based on total sample collection and maximum walking distance. Finally, sensitivity analyses on some design parameters are conducted. © 2022 Elsevier Ltd
Open Access
A new formulation approach for location routing-problems
(Springer, 2012-12) Toyoglu, H.; Karasan, O. E.; Kara, B. Y.
A Location-Routing Problem (LRP) combines two difficult problems, facility location and vehicle routing, and as such it is inherently hard to solve. In this paper, we propose a different formulation approach than the common arc-based product-flow (Arc-BPF) approach in the literature. We associate product amounts to the nodes of the network resulting in a node-based product-flow (Node-BPF) formulation. Our main objective is to develop LRP models with fewer constraints and variables, which can be solved more efficiently. To introduce the proposed approach, we reformulate a complex four-index Arc-BPF LRP model from the literature as a three-index Node-BPF model, which computationally outperforms the former. We then introduce a heuristic method.