Endüstri Mühendisliği Yüksek Lisans Tezleri / Industrial Engineering Master Theses

Permanent URI for this collectionhttps://gcris3.etu.edu.tr/handle/20.500.11851/613

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Ara Stok Alanı Bulunan Tek Robotlu Üretim Hücrelerinde Çizelgeleme
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2013) Gündoğdu, Emine; Gültekin, Hakan
This thesis considers the scheduling problem occurring in robotic cells consisting of a number of machines and a material handling robot which is responsible for loading/unloading of machines. Identical parts are produced with the same machine route, so flow shop assumption is valid. This is the first study considering a self-buffered robotic cell where the robot has a buffer space moving with it. The study is categorized into 3 main sections in terms of the buffer capacity. The first section, where the buffer capacity is 1, considers only 1-unit cycle in which one part is produced in one repetition. For this section, parameters for which each non-dominated cycle is optimal are determined. Moreover, the benefit obtained by using a self-buffered robot over a classical robot is found. As done in the first part, we determined non-dominated 1-unit cycle for double capacity buffer space and chose two of these cycles. Furthermore, to determine the performance of these cycles, a lower bound for the cycle time of optimal robot move cycle is developed. The final section of the study where the buffer capacity is assumed to be infinite, a new class of cycle called q-accumulated cycle is defined to provide more benefit from the buffer area. To find optimal q-accumulated cycle, optimal buffer capacity for given cell parameters and make comparison of a self-buffered robot and classical one, a computational study is conducted.
Bulanık Regresyon Modellerinin Tutarlılığı Üzerine Çalışmalar
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Özşahin, Selcen Gülsüm Aslan; Türkşen, İsmail
In today's World, collecting data is not a big issue in a proper and processable format with the help of recent technological developments but it is a big deal not only for the government bodies, private sector and also for the individuals. The main idea behind keeping data in a processable format is to discover the existing data patterns to estimate the future with the highest consistency. Enhancements in data collection, processing and estimation technics bring the strong knowledge from the past, ability to control processes and dominate the future based on the historical data. In other words, technical control on data management promises the power of knowledge to the all stakeholders in management and in many areas mainly in economics, engineering, and medical sciences as well as politics and public relations. One of the leading research area in data management is modeling which are namely stochastic models, statistical models, lineer modeling or fuzzy systems. Fuzzy Models are one of the most trendy and consistently estimating approach for modeling. In this study, the data set of Denmark which contains financial indicators as input and import amounts between 1993 and 2013 as output were used to create 221 different models by using Fuzzy C-Means Clustering Algorithm and Fuzzy Regression Analiysis with different number of clusters and degree of fuzziness in each model. With the help of high number of experimental models, evaluation of model consistency parameter, R-square, depending on the changes of number of clusters and degree of fuzziness have done and several inferences have been achieved. Last but not least, outstanding approach has been developed in this study which is named as Multi-Layer Fuzzy. In this approach more than one membership matrix calculated with at least two different number of cluster and degree of fuzziness values have been used in a single model and higher consistency in the estimations have been achieved as expected
Bulanık Sistem Modelleme
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Dilden, Elif Burcu; Türkşen, İsmail
While constructing a system model to find out input/ output relation, fuzzy functions (FF) method use Fuzzy c- means (FCM) algorithm to determine membership values. Instead of determining fuzzy rule bases (FRB) for each cluster, by using FF method each cluster is explained by functions. Proposed FF approach says that membership values and their user defined transformations should be add into the input matrices as independent variable with the real inputs. This suggestion is heuristic. In this study, we defined Fuzzy Normal Equations (FNE). Our proposed fuzzy normal equations explain the detail of how to add various transformations of membership values into the input matrices in fuzzy functions approach. We have modelled two real life data sets. One of them is Concrete Compressive Strength and the other one is Apple's Closing Stock Price data set. Fuzzy model performances compared with two benchmark strategies: Artificial neural networks (ANN) and adaptive neuro fuzzy systems (ANFIS).
Çift Tutuculu Robotik Hücrelerde Üretim Hızının En Büyüklenmesi: Sade Çevrimler
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2013) Dalgıç, Özden Onur; Gültekin, Hakan
In this study, we discuss pure cycles in $m$-machine dual gripper robotic cells. A material handling robot loads/unloads the machines and transports the parts between the machines. The robot is assumed to have dual grippers so that it can carry two parts simultaneously. Identical parts are to processed on machines which have the ability to perform all the operations that a part requires. Manufacturing systems in which there are flexible machines like CNC machines have this kind of ability. We consider pure cycles where each part is processed by only one of the machines and each machine processes exactly one part in a cycle. We first determine the feasibility conditions for the pure cycles and an algorithm that generates all feasible pure cycles for a given number of machines. We analyse 2-machine robotic cells in detail and prove that one of the particular five pure cycles among a huge number of feasible pure cycles always provides the optimal solution. We determine the parameter values in which each of the five cycles is optimal. In 2-machine robotic cells, we show that pure cycles in dual gripper robotic cells always dominate pure cycles in single gripper robotic cells. By using problem parameters, an experimental study is performed and the average and maximum benefits of using a dual gripper robot instead of a single gripper robot are determined. The effects of problem parameters are also examined.
Çok Dönemli Planlama Çevreninde Modüler Kapasiteli Ana Dağıtım Üssü Yer Seçimi ve Ana Dağıtım Üssü Ağı Tasarımı Problemleri
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2013) Seçerdin, Yusuf
In this study, multi-period hub location and hub network design problems with modular hub capacities are considered. This problem decides on the locations and the capacities of hubs, the design of the hub network, the allocation of demand nodes to hubs and the routes of flow in each period. Mixed-integer linear programming formulations are developed for both the single and the multiple allocation versions of the problems. Furthermore, several sets of valid inequalities are proposed for enhancing the models. The objective of the models is to minimize total costs which consist of flow routing cost, hub operating cost, hub and hub link establishment costs, and capacity establishment cost. It is possible to establish a new hub and expand the capacity of an existing hub in each period during the planning horizon. It is assumed that capacities of the hubs are modular and at most one capacity module can be established for each hub in each period. Models are solved on test problems with 5-periods that are generated from the CAB data set with 15 and 25 nodes. In addition, computational performance of the proposed valid inequalities are analyzed. The value of the multi-period approach is determined using the proposed weak and strong value of the multi-period solution.
Çok Hedefli Savunma Problemlerinde İstihbaratın Değeri
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Ersü, Buğra; Tekin, Salih
This paper presents an analytical approach that is intended to determine the value of intelligence in a homeland security problem with multiple targets under different scenarios. We analyze the strategies available to the decision maker and evaluate two separate intelligence resources on the basis of improvements in security resource allocation. Various scenarios that the decision maker might encounter as a result of the intelligence gathering activity were modeled using nonlinear programming. The defender should defend two targets against two independent terrorist organizations and thus decide on the security level that must be maintained to prevent a terrorist attack. The defender will bear the costs of security and receiving additional intelligence as well as the losses of a successful attack. The defender can make a decision with or without receiving additional intelligence. We consider both perfect and imperfect intelligence on terrorist attack preferences. An extensive numerical study is also provided to illustrate the defender behavior under realistic parameter value scenarios. Sensitivity of intelligence gathering and security resource allocation decisions are analyzed as part of our numerical study.
Eş Zamanlı Taşımacılık İhalelerinde Fiyat Teklifi Eniyileme
(2012) Akyol, Çağla Gül; Kuyzu, Gültekin
Bu tezde, tam kamyon yükü taşıyıcısı açısından eş zamanlı taşımacılık ihaleleri ele alınmıştır. Göndericilerin ihtiyaç duydukları güzergâhlar için taşıyıcılardan fiyat teklifi talep ettiği, taşıyıcıların fiyat tekliflerini gizli verdiği ve göndericilerin en düşük teklif veren taşıyıcının hizmetini satın aldığı taşımacılık ihalelerinde, taşıyıcıların karşılaştığı fiyat teklifi verme problemi üzerine çalışılmıştır. Çalışılan ihale yapısında, taşıyıcılar çok sayıda güzergâha eş zamanlı olarak teklif vermektedir. Fiyat tekliflerinin, taşıyıcıların kâr edebilmesi için yüksek ancak taşıyıcıların güzergâhları kazanabilmesi için ise düşük olması gerekmektedir. Ayrıca, taşıyıcılar ihale bitene kadar kazandığı güzergâhları bilmediğinden toplam maliyetini hesaplayamamakta ve bu durum güzergâhlar için vereceği teklifi belirsizleştirmektedir. Bu yüzden, taşıyıcının beklenen kârını maksimize etme amaçlı stokastik fiyat teklifi eniyileme problemi formüle edilmiş ve bu problemin çözümünde farklı en düşük rakip teklifi dağılımları için koordinat arama algoritması geliştirilmiştir. En düşük rakip teklifinin Normal Dağılım'a ve Ampirik Dağılım'a sahip olduğu durumlar için algoritma incelenmiştir. Geliştirilen algoritmanın taşıyıcının kârı üzerine etkisini göstermek amacıyla deneysel çalışmalar yapılmış ve olumlu sonuçlar alınmıştır.
Esnek İşlemli Akış Atölyelerinde İşlem Ataması ve Parça Sıralaması
(2013) Sucu, Seda; Gültekin, Hakan
Bu çalı¸smada 2 veya 3 makineli n adet farklı tip parça üreten akı¸s tipi üretim sistemleri ele alınmı¸stır. Sistemdeki her parça akı¸s tipi üretim sisteminin geregi olarak her ^ makinede aynı sırayla i¸slenmektedir. Her parçanın sistemdeki her makinede i¸slenmesi gereken belirli i¸slemler vardır. Bu i¸slemler "sabit" i¸slemlerdir. Sabit i¸slemlerin yanında sistemdeki belirli ardı¸sık makineler tarafından i¸slenebilen ve esnek i¸slem adı verilen bir i¸slem daha bulunmaktadır. Çalı¸smada ele alınan 2 makineli sistemlerde her parçanın i¸slenmesi gereken üç farklı i¸slem vardır. 'Ilk i¸slem sadece birinci, üçüncü i¸slem sadece ikinci makinede i¸slem görebilirken ikinci i¸slem her iki makinede de i¸slenebilen esnek i¸slemdir. 3 makineli sistemlerde esnek i¸slem sayısı ve esnek i¸slemin i¸slenebildigi^ makineler açısından degi¸sik alternatifler ele alınmı¸stır. Ayrıca bu bölümde makinelerin ^ özde¸s olmadıgı, yani esnek i¸slemin süresinin atandı ^ gı makineye göre de ^ gi¸sti ^ gi durum ^ ele alınmı¸stır. Çalı¸smadaki amaç, yayılma hızını enküçükleyecek ¸sekilde hem parça sıralamasına ve hem de esnek i¸slemlerin i¸slenecegi makinelere karar vermektir. ^ Problemin çözümü için öncelikle kesin çözüm yöntemi olarak karma tam sayılı matematiksel model geli¸stirilmi¸stir. Fakat matematiksel modelin çözüm süresinin uzun olması nedeniyle, kaliteli sonuçlar veren polinom zamanlı sezgiseller geli¸stirilmi¸stir. Deneysel çalı¸sma yapılarak geli¸stirilen çözüm yöntemlerinin performans analizi gerçekle¸stirilmi¸stir.
Farklı Servis Tipleri için Ana Dağıtım Üssü Yer Seçimi ve Kapasiteli İntermodal Ana Dağıtım Üssü Ağları Tasarımı
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Altuntaş, Saliha; Alev, Sibel Alumur
In this thesis, we study hub location and hub network design problems considering different transportation modes and different types of vehicles to serve different types of services. We propose three different problems in this regard. The objective of the first problem is to minimize total costs while providing predetermined service levels, the objective of the second problem is to maximize total profits while determining the service levels to be provided between origin-destination pairs, and the objective of the third problem is to maximize total demand of VIP service to be accepted considering a predetermined budget. All of the problems determine the location of hubs, the allocation of demand nodes to hubs, which hub links to establish, and how many vehicles of which type to operate on hub links to route the demand for different service types between given origin-destination pairs. For each problem, a mixed integer mathematical model is developed and different solution methods are proposed. Turkish network data set and the commercial solver CPLEX are used to solve the mathematical models and test the proposed heuristic methods. The values of the problem parameters on the Turkish network data set are determined based on the interviews made with the three largest cargo companies operating in Turkey. The results obtained by using the proposed heuristic methods are compared with the optimal solutions. In addition, a statistical analysis is conducted to observe the effects of changes in various problem parameters on the proposed heuristics.
Genel Müdahaleli Ödüllü Yenileme Süreci için Asimtotik Yaklaşım
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Ardıç, Özlem; Hanalioğlu, Tahir
In this study, a renewal-reward process with a general interference of chance is considered. Exact expressions and asymptotic expansions for some of the probability characteristic are obtained. Stochastic process X(t) is constructed and one dimensional distribution function is gotten. Then, under weak conditions, the ergodicity of the process X(t) is proved and exact expression for the ergodic distribution is obtained. Examples for the found exact expressions under different distributions (exponential distribution, Erlang distribution) are presented. Moreover, weak convergence theorem is proved for the ergodic distribution and two term asymptotic expansion is obtained for the limiting distribution. Besides, exact expressions for the moments of the ergodic distribution are found. Within some assumptions for the discrete interference of chance in general form, two term asymptotic expansions for the moments of the ergodic distribution are obtained. Additionally, kurtosis, skewness coefficient and coefficient of variation of the ergodic distribution are computed. Examples are given when the random variable expresses the discrete interference of chance has several distributions (Uniform distribution, symmetric triangular distribution, nonsymmetric triangular distribution, generalized Beta distribution). Finally, exact expressions and asymptotic expansions for the moments of the three important boundary functionals are obtained.
Hastanelerde Gerçek Zamanlı Konum Belirleme Sistemlerinin Etkinliğinin Artırılması
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Ersol, Duygu; Ünver, Nilgün
Mobile assets used jointly by several hospital departments affect hospital processes adversely when they are not shared in a systematic manner. Hospitals manage critical events such as patient care so accelerating operations such as searching-finding an asset and tracking an asset in real time is a necessity to meet the departments' needs immediately. To enable this using Real Time Locating System (RTLS) technology can be a good choice. Hospital systems without RTLS suffer from long asset to patient time due to searching an asset and taking the asset from a long distance point. Additionally, hospital departments are reluctant to share their assets even if they have unused ones, thinking that they may need the asset in the near future. In this study we develop asset selection rules which can be integrated to the RTLS technology. The analysis are based on TOBB University of Economics and Technology Hospital. This study aims decreasing asset to patient time, decreasing departments reluctance about sharing assets with other departments and quantifying the benefit of these rules. In the scope of this thesis, we developed three asset selection rules. These rules consider asset number of assets available in departments, asset distance and departments' asset demands while suggesting the asset to be selected. For the rules that use forecasting to calculate the departments' asset demand, seasonal ARIMA models are evaluated. Hospital's current status model and RTLS-integrated asset selection rules are tested in the simulation environment. All selection rules are compared pairwise and the performance measures are examined. The sensitivity of asset selection rules against different demand rates and different demand patterns varying among departments are analyzed. As a result, we observed that proposed asset selection rules gives robust responses to this sensitivity analysis.
İki Sipariş Seçenekli ve Taşıma Maliyetli Gazete Satıcısı Probleminde Sipariş Parti Büyüklüğünün Belirlenmesi
(2013) Nemutlu, Gizem Sultan
Bu çal ³mada, tek al c ve tek sat c n n bulundu§u, tek periyotluk sistemde; sezonsal ürünlerin sat ³ nda gerçekle³en rassal talebi kar³ lamak için sezon ba³ nda verilecek ve risk nötral al c n n beklenen kâr n enbüyükleyecek sipari³ miktar n n belirlenmesi problemi ele al nm ³t r. Literatürde, Gazete Sat c s Problemi kapsam nda ele al nan problemde, gerçekle³en talep sezon ba³ nda verilen sipari³ ile kar³ lanamad § nda yok satma maliyetine ya da aksi durumda sezon içerisinde sat lamayan ürünler için elde kalma maliyetine katlan ld § varsay lmaktad r. Yap lan çal ³mada belirtilen maliyetlere ek olarak ta³ ma maliyetinin de beklenen kâr etkiledi§i göz önünde bulundurulmu³ ve bu maliyet için tam dolu konteyn r tipi ta³ ma maliyet yap s kullan lm ³t r. Ek olarak, sezon içerisinde kar³ lanamayan talebin ertelenerek, sezon sonunda verilecek ikinci bir sipari³ ile kar³ lanabilece§i dikkate al nm ³t r. kinci sipari³ seçene§inin kârl bulundu§unda kullan ld § ve bu sipari³ için daha yüksek ta³ ma maliyetine ve talebi erteleme maliyetini de içeren sat n alma maliyetine katlan ld § varsay lm ³t r. Bu kapsamda, al c n n beklenen kâr n farkl talep da§ l mlar ve ikinci sipari³in büyüklü§ü üzerine yap lan farkl varsay mlar alt nda enbüyükleyen sipari³ miktar n belirlemede kullan lacak algoritmalar geli³tirilmi³ ve çözümlerin parametre de§i³imlerine göre duyarl l klar analiz edilmi³tir.
Kablosuz Algılayıcı Ağlarda Ağ Yaşam Süresi ve Ağ Güvenliği Eniyilemesi
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Yıldız, Uğur; Tekin, Salih
In this study, both lifetime and security in wireless sensor networks are jointly optimized. It is assumed that enemies try to steal gathered data with the key informations they have. In this study, mathematical models are developed for all possible sensor deployment and key assignment strategy combinations considering that both deployment and key assignment strategies can be applied deterministically and randomly depending on application area. Performance of the proposed solution methods and advantages of deployment and key assignment strategies are investigated on test problems. In addition to mathematical models, a mathematical programming based heuristic algorithm is developed to obtain feasible solutions for large instances. Computational experiments conducted on a set of test instances indicate that both the solution time and the efficiency of the proposed heuristic is quite promising.
Kapalı Döngü Tedarik Zinciri Ağı Tasarımı
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Kaya, Aycan; Alev, Sibel Alumur
In this thesis, we study the closed loop supply chain network design problem, which integrates reverse flows and reverse supply chain activities into the traditional forward supply chain activities. This network design problem requires strategic and tactical level decisions to be taken into account simultaneously. Within this context, a multi product and capacitated mixed integer linear programming model is developed. At the strategic level, the model decides where to open production and recovery facilities and which existing facilities to close. At the tactical level, the model decides on the amount of products that are obtained either from manufacturing or recovery to send to customers in the forward direction, the amount of used products to send from the customers to the recovery facilities in the reverse direction, and the total amount of products to be processed in production and recovery facilities. The aim of the proposed model is to maximize total profit. In order to achieve this, facility establishment / closing, production and recovery, procurement, capacity establishment, and transportation costs are minimized whereas the revenue obtained from the satisfied demand and recovery options is maximized. In addition to the deterministic model, a scenario based stochastic model considering uncertainty in the demand and return amounts is also proposed. Extensive sensitivity analysis is conducted to observe the effect of changes in the problem parameters on the optimal solutions.
M-makineli Esnek Operasyonlu Akış Tipi Sistemlerde Çizelgeleme
(2011) Demirtaş, Hatice Hande; Gültekin, Hakan
Bu çalışmada m makineli n adet parça üreten bir akış tipi üretim sistemi ele alınmıştır. Bu sistemde her parça makinelerde sırayla işlenmektedir. Her bir makinenin parça üzerinde yapması gereken belirli işlemler vardır. Bunun yanında önceden belirlenmiş ardışık iki makine, sabit işlemlere ek olarak, gereken bir işlemi daha yapabilecek kabiliyettedir. Aynı tip parça üretimi yapılan bu sistemde makineler arası stok kapasitesi sınırsız ya da sıfır kapasiteli olabilir. Amaç, yayılma zamanını enküçükleyecek şekilde, esnek işlemlerin her bir parça için hangi esnek makinede yapılacağına karar vermektir. Problemle uygulamada sıkça karşılaşılmaktadır. Esnekliği oldukça yüksek olan farklı uç kapasitelerine sahip CNC makinelerin kullanıldığı esnek üretim sistemleri karşılaşılan alanlardan birisidir. Çapraz eğitimli işçilerin bulunduğu montaj hatlarında ve PCB kart üzerine devre elemanlarının yerleştirildiği sistemlerde de aynı durumla karşılaşılmaktadır. Problem çözümü için, öncelikle problemin optimizasyon modeli yazılmış ve optimal çözümün özellikleri belirlenmiştir. Belirlenen bu özellikler ile bazı problemlerin kolayca çözülebileceği veya boyutlarının küçültülebileceği görülmüştür. Ancak bu indirgeme durumunda dahi, optimizasyon modelinin çözüm üretmesi uzun zaman almaktadır. Bu nedenle, optimal çözüm için ispatlanan özelliklerden yararlanılarak bir dinamik programlama algoritması geliştirilmiştir. Yapay polinom zamanlı bu çözüm yönteminin de, problem verilerine bağlı olarak, çözüm süresi oldukça uzun olabilmektedir. Bu nedenle, daha kısa sürede kaliteli çözümler üreten sezgisel bir yöntem geliştirilmiş, yöntemin etkinliği deneysel bir çalışma ile gösterilmiştir. Geliştirilen yöntemler, m makineli ve daha genel esneklik tanımına sahip sistemlerin çözümüne yönelik ilk adımı oluşturmaktadır.
Maliyet Odaklı Ana Dağıtım Üssü Yer Seçimi ve Kapasiteli İntermodal Ana Dağıtım Üssü Ağları Tasarımı
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Serper, Elif Zeynep; Alev, Sibel Alumur
In today's competitive environment, in order to decrease unit transportation costs, most firms in the cargo delivery sector use different transportation modes and different types of vehicles within their intermodal hub networks. Hub location and hub network design problems considering different transportation modes and different types of vehicles have not been addressed in the literature. In this study, we allow using different transportation modes and different types of vehicles in the hub network to be designed. We determine the location of the hubs, the allocation of demand nodes to these hubs, the hub links to be established between the hubs, and the type and number of vehicles that will serve on these hub links. The objective of the problem is to minimize total costs including the hub establishment costs, transportation costs, vehicle operating costs, vehicle renting costs, and material handling costs. A mixed-integer programming model is developed and a local search based heuristic algorithm is proposed for the solution of this problem. The heuristic algorithm is tested on the Turkish network and CAB data sets. The values of the problem parameters are determined based on the interviews made with the three largest cargo companies operating in Turkey. Extensive computational analyses are conducted in order to observe the effects of changes in the various problem parameters on the resulting hub networks.
Özdeş Parça Üreten Esnek İşlemli Akış Tipi Sistemlerde Çıktı Miktarının En Büyüklenmesi
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2013) İşler, Fatma; Gültekin, Hakan
In this study, two problems are considered. The first one is a 3-machine flowshop producing $n$ identical parts with a flexible operation. All machines in the system, performs a fixed operation on the parts and have the capability to produce an additional operation called the flexible operation. Flexible operation of each part must be assigned only one machine. The second problem is an $m$-machine flowshop with $(m-1)$ flexible operations. There is a flexible operation between each of two consecutive machines. In both problems, the objective is to determine the assignment of the flexible operations of all parts in order to maximize the throughput rate. We formulated the problems as Mixed Integer Programs. However as the problem size increases, the required CPU time to solve the models increases drastically. Therefore we developed heuristic algorithms for both problems, we also developed a dynamic algorithm for the first problem which can find the optimal solution more quickly than the mathematical model. To test the performances of heuristic algorithms, comprehensive computational studies are made. We coded mathematical models using GAMS interface with CPLEX 12 Solver and we coded the heuristic algorithms in C++ programming language. The results are analyzed, with respect to required CPU times and the percent gaps with the optimal solution.
Robotik Hücrelerde İki Kriterli Hat Dengeleme
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Ataşeven, Elif Büşra; Gültekin, Hakan
In this study, we consider a production line that consists of a number of machines and material handling robot. The robot does not perform any operations on the parts but loads/unloads the machines and transports the parts between the machines. The parts to be processed are assumed to be identical. A specific number of operations are to be performed on these parts on the machines. The robot can be transport a single part at a time and can load/unload a single machine at a time. The decisions to be made include i-the determination of the number of the machines on the line, ii-the determination of the assignment of operations to the machines, and iii-the determination of the robot move sequence. This problem is handled as a bicriteria problem that includes the minimization of the cycle time and the minimization of the number of machines used on the line. Two solution approaches are considered: Prioritization of the objectives and determination of the pareto optimal solutions by parameterizing one of the objectives. Mathematical programming formulations are developed for both of these methods. Computational studies are performed using different parameter combinations and the results are analyzed in detail.
Tam Kamyon Yükü Gönderici İşbirliğinde Güzergah Planlama ve Maliyet Dağıtımının Eniyilenmesi
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Öner, Nihat; Kuyzu, Gültekin
In truckload shipper collaboration, a group of shippers purchasing the services of carriers come together and try to identify tours which consist of regularly scheduled shipments with minimal empty truck movements with the hope of getting better rates from the carriers in return. Determining the best set of such tours is a challenging optimization problem, the solution of which yields the set of lanes and firms to be included in the collaboration, who will collaborate with whom, and the maximum amount of savings which can be achieved. Allocation of the total calculated cost to the participating firms and individual lanes will determine the final savings for each participating firm. If the allocated costs are not accepted by the participants, the collaboration will face the risk of collapse. In the literature, solving the optimization problem minimizing the total cost and allocating the calculated minimum cost are treated as two successive but distinct phases. In this work, we aim to merge these two phases by formulating an optimization model and develop column generation based algorithms for its solution.
Topoloji Kontrolü ile Kablosuz Algılayıcı Ağ Güvenliğinin İyileştirilmesi
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2013) Şendil, Melek; Kayhan, Ayşegül Altın
In this study, we aim to enhance the reliability of a WSN by a new partial redundancy protocol while maximizing network lifetime. We consider a network composed of a base station and many identical sensors with limited energy. The proposed mixed IP model PRF is built gradually. Initally, we develop the NRF model which maximizes network lifetime without any reliability protocol. Then to improve network reliability by eliminating possible massive data loss risks arising from overuse of central nodes, constraints that provide balanced use of sensors are added to get the bNRF model. Later FRF model is developed which employs balanced usage strategy and also forces each sensor to send multicopy of the same data on two node disjoint paths. In this model the purpose in sending multicopy on multipaths is to be able to transmit the data to the base station if a problem occurs on the path of the other copy of the same data. However using multicopy on multipath routing and balanced usage strategy at the same time decreases network lifetime significantly. Therefore a new model PRF which uses these protocols more efficiently is proposed. In PRF balanced usage strategy is considered but if there is a sensor whose extensive use leads to a better network lifetime, then it is allowed to be the central node. Moreover in this model only the sensors who send their own data through central node replicate their data and send it on two node disjoint paths. The performances of the models are evaluated according to some performance criteria such as lifetime, leftover energy, and conserved data. The tradeoff between network lifetime and reliability is examined. Finally to decrease the solution time of the PRF model a heuristic method is proposed.

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Browsing Endüstri Mühendisliği Yüksek Lisans Tezleri / Industrial Engineering Master Theses by Department "Institutes, Graduate School of Engineering and Science"