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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Acil Tıbbi Yardım İstasyonlarının Yer Seçimi ve Planlaması
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2014) Konak, Ecem; Aytaç, Berrin
This study deals with the problem of optimally locating and designing emergency medical service systems. The problem is formulated as a multi-source capacitated fixed charge facility location model. The model minimizes the total cost of meeting demand while guaranteeing a maximum service response time. In order to determine the locations and capacities of emergency medical service locations, defined in terms of the number of emergency service vehicles, service requests are first assumed deterministic. The uncertainty in service requests is then introduced using a scenario-based two-stage stochastic programming approach together with the concept of service levels that allows a maximum number of service requests being not responded. Both optimization models are coded in JAVA programming language and solved using the optimization solver CPLEX. For the deterministic model, a two-stage constructive heuristic is proposed; the performance of the proposed heuristic is evaluated in terms of the solution quality and solution time using a large set of problem instances. The impact of the changes in the problem parameters on the performance of the heuristic is also investigated.
Akıllı Adapte Olabilen ve Terör Amaçlı Saldırılar Düzenleyen Düşmana Karşı Eldeki Kaynakların Optimal Kullanımının Oyun Kuramı Ekseninde İncelenmesi
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2012) Birihan, Hasan Tugay; Bakır, Niyazi Onur
Terrorism has recently reached the international extents, terrorist organizations have started to target more countries to achieve their political aims in global scale. Threatened countries are obliged to defend the targets within their territory for their economic interests and societal psychology. In this study, we examined the problem of defending these targets within the framework of economic measures. Defending these targets is so costly that for decreasing the cost of defending and the risk, analytical approach is required. Game-Theory is one the most effective approach used for the enemies adapting in accordance to their targets. Government?s aim is prevent terrorist attacks within their territory or minimizing the loss in the terrorist attack. In this government-terrorist game, we assume that attacker and the defender do not move simultaneously. The State primarily allocates security resources to targets that to be protected. On the other side, the terrorist observes the state and carries out terrorist attacks.In this study a model with two players, two potential targets in the government?s territory and analyzing the possibility of attack on this targets was established. Bayesian approach was used on the gain of the attacker and loss function of defender was defined. By using this model, it is aimed to investigate the worth of intelligence and its effect on decisions to be made.
Ankara'da Toplu Taşıma için Veriye Dayalı Analiz ve Planlama
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2018) Bakar, Merve; Kuyzu, Gültekin
Smart card automated fare collection systems are used in many transportation systems throughout the world as they provide effective and reliable payment opportunity. Smart card automated fare collection systems facilitate efficient and accurate fare collection in public transport systems. These systems enable the planners to implement more flexible pricing structures compared to traditional fare collection methods. Smart card systems record several pieces of data about the passengers, which can be used to improve the overall efficiency and service quality of the public transport network. In this work, we focus on analyzing smart card transaction data to understand spatial and temporal travel patterns of public transport passengers in Ankara, Turkey. One of our primary goals is to identify origin-destination pairs where the passengers are required to transfer through one or more intermediate points because of the lack of a direct service. We use a data set of about 30 million records corresponding to a one month period. The data includes records from bus and light rail transportation modes. Each record includes the smart card number, the transport mode, the bus/rail line, the boarding location, the boarding date and time, and the fare class of the passenger; but lacks the alighting location of the passenger. We first create a model to estimate the alighting location of each passenger. Then, we estimate origin-destination flows and their breakdown by several dimensions such as fare class, transportation mode, day of week, time of day and the frequency of the lines and the stations used. The estimation of alighting location of the passenger and the travel analysis are performed using RStudio program. Smart card data set of passenger travels on one-month period are analyzed according to smart card type; adult, student and teacher tickets. The most preferred public transportation vehicle is the bus with the usage rate of 61% in travels, the least preferred public transportation vehicle is the cable line. In addition to the travels on weekdays and weekends, density of the transit travels are analyzed according to time of day and frequency of the lines and the stations used. Keywords: Transportation, Public transport, Smart card data, Data analytics, Spatio-temporal analysis.
Approximate results for non-linear Cramér-Lundberg type risk model
(TOBB Ekonomi ve Teknoloji Üniversitesi, 2021) Allyyev, Yusup; Hanalioğlu, Tahir
Bu çalışmada doğrusal olmayan bir Cramér-Lundberg risk modeli ele alınmış, araştırılmış ve iflas olasılıkları, ?(u), hesaplanmıştır. Literatürde klasik model olarak da bilinen bu modelin doğrusal gösterimi şu şekilde tanımlanır: U(t)=u+ct-S(t) (1) Denklem (1)'deki U(t) risk süreci, belirli bir t zamanında bir sigorta şirketinin sermaye miktarını ifade eder, sabit u şirketin başlangıç sermayesidir, c – prim oranı, S(t)= ?_(i=1)^(N(t))?X_i, [0,t] aralığında meydana gelen kazalar için yapılan ödemelerden dolayı sermaye çıkışını tanımlayan bir ödüllü-yenileme sürecidir, N(t) bir yenileme süreci olup [0,t] aralığındaki toplam kaza sayısını belirtmektedir, X_i'ler ise, i. hasar için ödeme miktarını gösteren bağımsız ve aynı dağılıma sahip rasgele değişkenlerdir. Denklem (1)'de görüldüğü gibi şirketin prim gelirini ifade eden ct terimi zamanın doğrusal bir fonksiyonudur. Ancak bu varsayım gerçekçi değildir, çünkü bir sigorta şirketinin prim geliri her zaman doğrusal olarak artamaz. Bu, özellikle sigorta poliçesi sahipleri ile doymuş pazarlar için geçerlidir. Bu nedenle, prim gelirinin, monoton olarak artmasına rağmen, büyüme hızı zamanla azalan bir fonksiyon olarak modellenmesi tavsiye edilir. Bu nedenle, bu çalışmada aşağıdaki gibi ifade edilen, daha gerçekçi özel bir doğrusal olmayan matematiksel model inşa edilmiş ve incelenmiştir: V(t)=u+c?_(i=1)^(N(t))??ln(1+W_i)?+c ln(1+(?t-T?_N(t) ))-S(t) (2) Denklem (2)'de, W_i'lar (i=1,2,3… ) kazalar arasındaki süreleri gösteren pozitif, bağımsız ve aynı dağılıma sahip rastgele değişkenler dizisidir; T_N(t) = ?_(i=1)^(N(t))?W_i ise, W_i, i=1,2,3,… rastgele değişkenlerinin dizisine karşılık gelen bir ödüllü-yenileme sürecidir ve Logaritmik Risk Süreci olarak adlandırılan V(t) ise herhangi bir t zamanda şirketin sermaye dengesini tanımlar. Bu çalışmanın temel amacı, denklem (2)'deki doğrusal olmayan risk modelinin iflas etme olasılığını, ?(u), hesaplamaktır. Model oluşturulurken stokastik süreçler, yenileme süreçleri, ödüllü-yenileme süreçleri ve bu süreçlerin olasılıksal özellikleri kullanılmıştır. İlk aşamada doğrusal olmayan modelimizin iflas etme olasılığı için Lundberg tipi üst sınır bulunmuştur. Bu olasılık sınırları hesaplanmaya çalışılırken doğrusal olmayan denklemlerle karşılaşıldığında sayısal çözüm yöntemleri kullanılmıştır. Çeşitli senaryoları dikkate almak için farklı olasılık dağılımları ve parametreleri göz önünde bulundurup, regresyon modeli ile yaklaşık bir çözüm bulunmuştur. İkinci aşamada, bu doğrusal olmayan model için yukarıdan ve aşağıdan iflas olasılığının yaklaşık sınırları bulunmuştur. Bu aynı zamanda iflas olasılığı için Cramér tipi sınır olarak da bilinir. Bu amaçla, kazaları (hasarları) temsil eden {X_n } dizisi tarafından üretilen yenileme sürecinin kalan ömrünün limit dağılımını tanımlayan rastgele değişkeni X ?'ın istatistiksel özelliklerinden yararlanılmıştır. Özellikle, iflas olasılığının sınır ifadesinde bilinmeyen bir katsayı olan sabit bir C'yi belirlemek için X ?'ın moment çıkaran fonksiyonu kullanılmıştır. Bu ifadeleri sadeleştirmek ve kompakt bir forma dönüştürmek için kalkülüs yöntemleri kullanılmıştır. Benzer şekilde, iflas olasılıklarını incelemek ve hesaplamak için farklı senaryoları dikkate almak için çeşitli olasılık dağılımları ve parametreler kullanılmıştır.
Aras Kargo Ankara Bölgesi Ana Transfer Merkezi Çizelgelemesi ve Araç Çıkış Zamanları Koordinasyonu
(TOBB Ekonomi ve Teknoloji Üniversitesi Fen Bilimleri Enstitüsü, 2010) Dikmen, Onur; Ertoğral, Kadir
The problems related to parcel delivery have started receiving attention in the literature in recent years. Determination of the vehicle routes for desired service levels, network design, consolidation decisions, operational planning of transfer centers are commonly studied problems. This study addresses the coordination of the vehicle departure times from branches and the scheduling of the inbound vehicles to unloading gates at a central cross docking terminal of Aras Kargo. The objective is to maximize the weighted sum of vehicle departure times. The main constraint is to finish up the unloading operation of all vehicles until a target completion time. Integer programming is used for modeling the problem. The mathematical model, which is developed for different confidence levels, is based on a previously proposed model for the parallel machine scheduling problem. Because of the complexity of the problem, a two-phase heuristic approach is proposed. The heuristic approach first solves the assignment problem of vehicles to unloading gates using the linear relaxation of the model, and then it addresses the scheduling problem for each door separately. The efficiency of the heuristic approach is shown by numerical experiments. Additionally, for the purpose of observing the effects of uncertainty in the system and including the dynamic structure of the queue formation, a simulation model is developed. Using the simulation model, the effects of delays on truck departure times, optimization of the truck departure times, the increase in demand and relevant door assignment alternatives are examined. The results of the mathematical and simulation model are compared with each other as well.
Beklenmedik Uçak Yönlendirmelerini Azaltma: Zaman Serisi Analizi ve Yapay Sinir Ağları ile Modelleme
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2019-01-01) Doğan, Hazal Berve; Hanalioğlu, Tahir
In this study, a decision support system is designed in order to minimize the number of flights that are diverted unexpectedly. The aim is to reduce the expenses that arise when the aircraft is not able to land on the targeted airport due to the unfavorable weather conditions, such as rescheduling the timetable, overuse of aircraft fuel than planned, passengers' accommodation and ticket reissue. In order to reduce such temporal and financial losses caused by diverted flights, decision to take off or not is made before departure, while the decision to land or not is made during flight, after a brief analysis based on weather data of target airport. For the aircraft to land on target airport as scheduled, it is crucial that the weather forecasts for visibility range, ceiling and wind speed are within the limits of the safe flight requirements. Considering the significance of this decision regarding by finance, there is a need for a decision support system that is capable of boosting the process through optimal decision-making by forecasting airport weather conditions. In the first part of the study, weather is forecast using regression and time series analysis, of which methods can be detailed as auto regressive (AR), moving average (MA), auto regressive integrated moving average (ARIMA) and vector auto regressive (VAR). Although such forecast methods are relatively effective in achieving the desired result, neural network and fuzzy logic techniques are expected to present more accurate forecast with their complicated and advanced algorithm structure. In the second part of the study, neural networks are created with using MATLAB. The results which is obtained with these methods are compared time series analysis results. Improvement is measured by accuracy of the decisions of diverted flights. The measurements are recorded on the confusion matrix.
Bir Açık İnovasyon Aracının Sistematik Tasarımı
(TOBB Ekonomi ve Teknoloji Üniversitesi - Fen Bilimleri Enstitüsü - Endüstri Mühendisliği Anabilim Dalı, 2011) Çubukçu, Ahmet; Gümüş, Bülent
The importance of the concept of innovation is being emphasized in all over the world. With the spread of information and communication technologies, the concept of open innovation began to be more popular as a subtitle of innovation. Hence, studies and projects on this issue have gained momentum. Open innovation practices are attempted to be performed by different techniques and approaches in different sectors, but there are still no standards or commonality established in this area. Although some companies can successfully use open innovation without relying too much on their internal R&D to achieve technological progress, the methods and tools are not well-defined yet. In addition, research shows that the managers and practitioners in companies who are practically using the open innovation techniques and approaches are not very well aware of the open innovation concept itself. Since the amount of knowledge has increased drastically and also knowledge can be accessed from practically anywhere, taking advantage of open innovation has become a necessity for companies. The validation of the required knowledge and the decisions of how and where to use the knowledge can be supported by effective open innovation tools. Companies can improve their competitiveness with the use of the open innovation web portals as an effective open innovation tool. Open innovation web portals are one of open innovation tools that bring together companies and innovators on Web 2.0 platforms to reach the goal of innovation-based results. In this thesis, a structure of an open innovation web portal is designed using Quality Function Deployment (QFD) and Systematic Design methodologies. In addition, a detailed literature review about innovation, open innovation and design methodologies is presented. A field study on the open innovation awareness and benchmark study of various open innovation web portals are also presented.
Bir Dinamik Hibrid Esnek Akış Atölyesi Çizelgeleme Problemi
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2015) Uzel, Simay Sezgi; Kuyzu, Gültekin
This thesis is based on a real life hybrid flexible flowshop scheduling problem. Hybrid flowshop consists of multiple identical parallel machines in addition to characteristics of standard flowshop problem. Furthermore, with the possibility of skipping stages of jobs in the current manufacturing system is defined as hybrid flexible flowshop. The flexibility and being hybrid features of the system is usually ignored and is rarely discussed in the literature. In the phase of getting results for experimental studies of heuristic methods , the other papers in the literature that handle the hybrid flexible flowshop scheduling problems deal with the problems as much more limited than the real life. Aim of this thesis is to handle hybrid flexible flowshop scheduling problem with real life data. According to literature, hybrid flexible flowshop problem is already complex and studying with real life data increases the level of complexity. Additionally, while the problem is being analyzed, it is aimed to solve the dynamic scheduling problem to meet uncertain demands by digressing the assumption of being deterministic. Minimization of makespan is defined as the objective function. Heuristic methods are improved as a solution that is based on NEH algorithm with taking advantages of dynamic dispatching rules. Experimental studies are performed with open source library that is managed by Java based discrete event simulation. Thus, experimental data is generated and the effectiveness of heuristic algorithm is analyzed. Moreover, advised heuristic algorithms are studied with real life data. Consequently, the developed methods and the current methods, of which superiority were proved in literature, are discussed.
Bir Savunma Sanayii Firmasında Tedarikçi Seçimi Çalışması
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2018) Demir, Kübra Nur; Tekin, Salih; Hanalioğlu; İç, Yusuf Tansel
Supplier selection is one of the most important task for a company. In order to reach manufacturing aims and ensure customer satisfaction, every company would like to work with a trustworthy business partner. Working with a strong supplier mitigates risks in the manufacturing process and enhances competitive capacity and profit. Therefore, supplier selection is a strategical decision making problem. In today's world producing all the sub-parts in the same company is an inefficient planning. For this reason, companies are in need of different suppliers. In this study, supplier selection problem for a project which will kick off in defence company producing air vehicles is considered. Our aim is to minimize purchasing cost and maximize quality level and total weight of the purchased products. Supplier selection problem is addressed by a three-phased method. In the first step, candidate suppliers are evaluated for their technical competences with TOPSIS (Technique for Order Preference by Similarity to Ideal Solution). Appropriate suppliers are scored subjectively with AHP (Analytic Hierarchy Process) method in the second step. During the assessment, quality, compliance requirements, price, risk, safety, technological level and brand image are considered. One of the most important criteria for the companies in the aerospace or space sector is the quality. Supplier firms have to satisfy certain quality management system standards. In the last phase, orders are assigned to suppliers using objective programming with company's aims and constraints. Material costs are handled with a piecewise linear function in programming and lead times with total demand requirements are also included in the problem constraints. For the first model, lead times consist of mean values, in the second model. Leads times are considered as stochastic, that are handled with an heuristic approach inspired from Markowitz method. Company's previous orders are solved with newly developed method and results are compared. In addition, we also solve the supplier selection problem with another method from literature and compare the results. Sensitivity and scenario analyses are done in order to evaluate situations that may occur in the future or decrease value at risk in decision processes assessed either objectively or subjectively. During analyses, weights of criterias in AHP method, priorities in goal programming and confidence levels are investigated. Keywords: Multiple criteria decision making problem, Supplier selection, Multi objective programming, TOPSIS, AHP, Taguchi method, Markowitz method
Bir Traktör Fabrikasında Karışık Modelli Montaj Hattı Dengeleme – Deterministik ve Stokastik Ölçümlere Göre Analizler
(TOBB ETÜ Fen Bilimleri Enstitüsü, 2020) Uyanık, Aysın Şenel; Tekin, Salih
Assembly lines are systems that allow the products with multiple components and, mass demands, to be manufactured together in sequential workstations. Assembly lines and design are among the main factors that increase the efficiency of production in factories in the white goods and electronics sectors, especially in the automotive sector. Numerous studies have been carried out using deterministic, stochastic heuristic and fuzzy methods related to the design and balancing problems of assembly lines. In this study, the distribution of work steps to the operators during the daily working period was carried out in a real assembly line of a tractor factory. Since the parts belonging to more than one type of tractor model are assembled in the factory assembly line, mixed model assembly lines are examined. The duration of the operations for the assembly was measured by time study studies. Accordingly, it was observed that the working times were random and dependent on the worker. In a parallel type assembly line, worker-dependent working times are also taken into account randomly. Line stoppages are experienced on the assembly line due to factors such as lack of training, the presence of complex jobs, and reduced motivation of work. Line stops cause deviations in the number of tractors that need to be produced daily, thus causing losses in the factory. In a mixed model assembly line where multiple work steps take place, there may be minor variations between operating times. Balancing analyzes were used on the assembly line to measure all losses. Within the scope of the study, considering the work step differences in tractor models, a priority diagram was obtained with the model-based unified priority diagram method. Stochastic assembly line balancing study was performed according to the stochastic working times on the line and the analysis results were compared with the deterministic results. In addition to the advantages of using stochastic working times, heuristic results have been obtained for the solution of the assembly line balancing problem with the java algorithm, which gives the minimum number of stations to be opened in the cycle time determined using the intuitive method Arcus (1966) proposed COMSOAL method. The number of stations to be opened according to the algorithm is determined at different cycle times. Thus, a line structure prepared for sudden plan changes at the factory was obtained. According to the station distribution obtained as a result of balancing and job assignment on the assembly line, efficiency analyzes are presented and the results are evaluated.
Bir Yüksek Hızlı Tren Hattında Yolcu Sayısı Tahmin Modelleri Geliştirilmesi
(TOBB ETÜ Fen Bilimleri Enstitüsü, 2020) Ertem, Beyza Nur; Ertoğral, Kadir
Correct and reliable order forecasting has an important role in increasing the efficiency of companies. Similar to other sectors, the demand forecasts are very important in Food industry. Especially in one day shelf life products, it is a must to make accurate order forecast and prevent food waste excess. In this study an approach is developed for forecasting the passenger numbers in the the high speed train leg between Ankara and İstanbuls. The firms is a subcontractor to The Republic of Turkey State Railways. As a first step, it was aimed to create a daily order system and the forecasting with multiple regression of the passenger numbers who traveled Ankara-İstanbul and İstanbul-Ankara route in 'Business Plus' and 'Economy Plus' coaches using data from a catering company between 2016-2019 year. The accurate Passenger number estimation will create a better meal order and will lead into a financial savings. In our study several forecasting models are constructed based on different ways of data groping and the choices of independent regression variables. We selected the best three models among the models develop and we found the mean absolute percent error performance for selected models, which turn out to be quite accurate. In the second stage our study, using the same passenger data the Winters exponential smoothing method is studied to forecast the weekly meal consumption and the forecast accuracy is tested using MAPE values.
Bulanık Fonksiyonlar ile Bulanık Sistem Modelleme
(TOBB Ekonomi ve Teknoloji Üniversitesi, 2009) Ünal, Başak; Türkşen, İsmail Burhan
Bu çalışmada, yeni bulanık sistem modelleme yaklaşımları önerilmiştir. Önerilen yöntemlerin ve bu çalışmaya referans teşkil eden Türkşen'in [2008] ve Çelikyılmaz ve Türkşen'in [2007, 2008, 2009] önerdiği geliştirilmiş bulanık fonksiyonlar ile geliştirilmiş bulanık öbekleme yaklaşımının performansları yapılan deneyler ile analiz edilmiştir. Bu çalışma ile Hataway ve Bezdek [1993] tarafından önerilen bulanık öbek regresyon modeli ve Höppner ve Klawonn [2003] tarafından önerilen bulanık model öbekleme algoritmalarına sistemi modellemek için iki yeni çıkarsama algoritması önerilmiştir. Buna ek olarak, Höppner ve Klawonn'un [2003] önerdikleri bulanık model geliştirilerek alternatif bir öbekleme algoritması (Alternatif Bulanık Model - ABM) önerilmiştir. Buna bağlı olarak, sistemi modellemek için ABM'e de bir çıkarsama algoritması önerilmiştir. Öneriler ışığında geliştirilmiş modeller, önceki modeller ile karşılaştırılarak, önerilerin yeni sonuçları vurgulanmıştır.
Bütünleşik Performans Değerlendirme Yöntemi Önerisi ve Performans Tabanlı Bölüm Başarı Değerlendirmesi: Kurumsal Bir Şirkette Örnek Çalışma
(TOBB ETÜ Fen Bilimleri Enstitüsü, 2020) Şenel, Tahsin Uğur; Tekin, Salih
Enterprise companies, which make future strategic plan, need to view overall performance. In this direction, monitoring decision-making unit (DMU) performances is a critical issue. Therefore, it should be fair and consistent performance evaluation and prepared open and clear reports. To handle with these requirements, this study focusses on establishing a comprehensive method of performance evaluations (PE). As a framework of the study, in scope of effectivity and efficiency aspects, five main solutions are suggested to solve five main problems in PE. In the paper, football theorem is selected as a strategic concept. Then, right PE tool are selected in terms of strategic frame of companies firstly. In this study, we examine Balanced Scorecard (BSC) approach that considers not only financial but also non-financial topics to watch overall performance. BSC has key performance indicators (KPI) that show objectives and actualizations belonging to related DMU, and BSC also provides proper and summary reports including different perspectives. The next step is determination of KPI's weights. Analytic Hierarchy Process (AHP) is applied to determine KPI priorities. As a result of first two steps, effectivity could be followed easily for a company. Because BSC evaluates DMU'S separately, it does not provide satisfied comparison among different DMU's. Therefore, we propose Data Envelopment Analyses (DEA) that is linear program based non-parametric approach to follow efficiency. However, DEA works correctly for only homogeneous DMU's. As a third step, classification process is applied to ensure homogeneity. Then, using BSC KPI's as outputs and DMU budgets as input, DEA model is run for each class. As a last step, we separate DMUs into categories using effectivity and efficiency score obtained from previous stages. To determine category numbers, Hierarchical Clustering Analyze (AHCA) method is used and group elements are selected with applying K-Means Clustering Analyze technique. At the end, two case studies are given to show how developed model is applied within an enterprise company.
Çift Tutuculu Malzeme Taşıyıcı Robotlu Hücrelerde Enerji Duyarlı Çizelgeleme
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2019) Emiroğlu, Nurdan; Gültekin, Hakan
Robotic cells are serial production systems that consist of a number of machines and a material handling robot that transfers parts between the machines. At the same time, the robots in the system function to load/unload the machines. In the academic literature and the business world, minimization of the cycle time is the dominant objective for the optimization of production schedules. In parallel to this objective, robot movements are assumed to be at their maximum speeds and the energy savings that can be attained with the dynamic adjustment of the speeds is not taken into account. Within the scope of this study, considering the controllability of the move speeds of the dual-gripper robot, it is aimed to determine the optimal robot move sequence and the operation parameters of the robot. In other words, we considered the energy consumption and throughput rate objectives simultaneously as a bi-criteria optimization model. In order to solve this bi-criteria model we used the epsilon-constraint approach, one of the objectives is written as a constraint. For the problem, a mixed integer non-linear mathemetical model (MINLP) is developed. In order to increase the solution efficiency, the problem is reformulated as a mixed integer second order constrained mathematical model (MISOCP). Computational tests revealed that the MINLP model cannot guarantee the optimal solution in reasonable times for systems with two or more machines. Since it is also observed that the MISOCP model is not efficient for the systems with six or more machines, a heuristic solution method called Efficient Solution Generation algorithm (ETA) is developed. By using the created data sets, these three solution approaches are investigated through a computational study. Additionally, as a result of these tests, it is observed that an average energy savings of 17.7\% can be attained by considering controllability of robot move speeds.
Cnc Kesim Makinesi için Mükemmel Olmayan Önleyici Bakım Politikasının Geliştirilmesi ve En İyilenmesi
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2017) Koçer, Meltem; Hanalioğlu, Tahir
In thesis study, a sequential preventive imperfect maintenance model that minimizes the long-term operational cost per unit time is improved for random degrading machining center in defence and aerospace industry. Parameters used for the proposed Markovian maintenance algorithm are gathered from real life 2013- 2016 data sets which are provided from Turkish Aerospace Industries, Inc.(TAI). In contrast the traditional maintenance plans in literature and the current application status under process, a reliability-centred preventive maintenance policy is developed by monitoring continuously and collecting instantaneous information about the system's current condition. Whenever system's reliability reaches the threshold R, imperfect repair is performed to restore the system and enhance system condition in aim to maximize the average availability, reduce the number of possible breakdowns during the system lifetime and accomplish the goal of quality assurance. Besides, the combination system's failure rate increase factor and age reduction factor is taken in consideration as variant according to system usage and age in order to build hybrid hazard model. In improved approach, as planned maintenance cost, minimal repair cost and system operating cost changes according to time and maintenance cycle, breakdown cost are assumed as constant. In this preventive maintenance algorithm for complex equipment, the optimal system's reliability and number of maintenance cycle number, the interval time are reached under the criteria of the long term cost minimization of the system. Additionally, sub-systems are analyzed in scope of Bayesian theorem and it is determined which sub-systems are repaired at each maintenance cycle.
Çok Koalisyonlu Tam Kamyon Yükü Gönderici İşbirliği
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2016) Zehtabiyan, Soheyl; Kuyzu, Gültekin
We study formation of stable coalitions given a set of shippers and their lanes corresponding to regularly scheduled truckload shipment. In this thesis, selecting participants, deciding who should participate with whom, calculating the lowest cost operational solution and allocating the system-wide cost to the participants stand out as important problems. Collaborating shippers try to identify tours which consist of regularly scheduled shipment with minimal empty truck movements. Then, they must allocate the total cost of the collaborative solution to the participated firms and individual lanes such that the collaborative solution remains attractive to the participants. In the literature, solving the optimization problem minimization the total cost and allocating the calculated minimum cost are treated as successive but distinct phases. The cost minimizing optimization problem is solved with well-known operation research methods, while cooperative game theory concepts are used for cost allocation. The minimum cost solution may render finding an acceptable cost allocation impossible. Besides, similar works in the literature assume that the collaborating firms will forge a single grand coalition. However, as the collaboration grows in size, a single grand coalition may become impractical and also it might leave several lanes out of the coalition, depriving shippers of significant cost savings. In this study, we propose algorithm to design coalition structure which consist of multiple disjoint stable coalitions. Each coalition must have a minimum cost collaborative solution with an acceptable cost allocation. Due to the complexity of the task hand, we devised a heuristic to find good quality solutions to this problem.
Çok Modelli Üretim Yapan Montaj Hatlarında Eş Zamanlı Montaj Hattı Dengeleme ve İstasyonlar Arası Ara Stok Alanı Atama Problemi için Bir Çözüm Yaklaşımı
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2018) Göçer, Elif Gizem; Tekin, Salih; Ertoğral, Kadir
Assembly lines are important part of many production systems. One of the most basic problems about the design of the assembly lines is the assembly line balancing problem. The assembly line balancing problem is to determine the number of work stations (workers) for a given throughput rate, and to assign the tasks to the stations taking into account the precedence relations of tasks.The most common goal in this problem is to reduce the number of work stations. Different versions of the problem have been studied in the literature. In our thesis, we consider the assembly line balancing problem for a real-life assembly line of a dishwasher manufacturing plant. In our problem, task times are considered as random values, which is the case in most of the assembly lines. Our problem distinguishes from the classical assembly line problems by recognizing that the number of inter-station buffers is limited, and how these buffers are assingned is an important factor affecting the throughput rate. Because the buffer assignment affects the blockage probability of stations due to the random task times. Thus, assembly line balancing and the buffer allocation problem should be considered simultaneously in order to find the best solution under random task times. This thesis suggests a heuristic approach that assigns tasks to stations and allocates buffers between stations simultaneously for a given target throughput rate. The suggested heuristic involves an optimisation model for assigning tasks to the stations, a search heuristic for allocating buffers, and a simulation model to evaluate the performance of candidate solutions. We showed the benefits of the suggested approach using both a real life case and a set of random problems based on a problem from the literature.
Çok Tipli Devinimli Stok İçeren Havayolları Bakım Onarım Servislerinde Entegre Üretim Çizelgeleme ve Kapasite Planlama : Sabitleme ve Optimize Et Sezgisel Yaklaşımı
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2018) Öztürk, Fatma Sedanur; Ertoğral, Kadir
Maintenance, repair, and overhaul (MRO) activities for the airline sector are generally subject to some regulations to ensure the safety and the continuity of flights. The critical equipment on aircraft must go through MRO at regulated intervals for the continuing permission of use. Thus, the strict deadlines constraint overhaul activities. Several systems on aircrafts are of so-called rotable module type. These expensive rotable modules are overhauled by MRO companies and used repeatedly. MRO companies usually perform exchange programs with customer airlines regarding the expensive rotable modules. When an airplane comes for an MRO service involving rotable module, a ready-to-use module from the inventory of MRO company is exchanged with the rotable module extracted from the airplane so that the service time for the aircraft is minimized. The extracted module is overhauled in the MRO shop with a limited workforce capacity and the overhauled module is rotated back to the inventory for a future exchange. We tackle the overhaul and exchange scheduling problem together with the workforce planning for MROcompanies with an expedited overhaul option. We propose a mixed integer programming formulation of the problem as a finite planning horizon model where we assume that there are multiple types of rotables handled by the MRO company, and we minimize the sum of inventory holding and workforce-related costs. The salient features of the model are that we allow exchanges to be carried out earlier than their due dates, if it makes sense cost wise, up to a certain earliness limit, and we assume that there is an expedited overhaul option. The model uses two types of time buckets, small (days) and big (quarter-year), for overhaul scheduling and workforce planning, respectively. Both the problem and its model are new in the literature. We show that this planning problem is NP-Hard. We provide extensive numerical tests on a set of randomly generated problems and propose some managerial insights based on the results obtained. We introduced a mixed-integer programming model of this problem for the first time in the literature, and suggested a fix and optimize type heuristic solution procedure. We showed the performance of the suggested heuristic on a set of random problem.
Competitive Intermodal Hub Location Model With Endogenous Pricing
(TOBB ETÜ Fen Bilimleri Enstitüsü, 2019) Almalekı, Mohammad Reza; Tekin, Salih
Road transportation has successively captured the majority of the transportation market in most of the economies. Massive amounts of flows are moving through road network, which is resulting in an unsustainable economy with congestion and environmental problems. In order to tackle the problem, intermodality can be utilized in logistics networks. Railroad transportation is one of the smooth ways of transportation in several ways. It can reduce the congestion and also it is more cost effective. In order to be able to utilize the economy of scale and reduce the transportation cost in the logistics network, hubs can be established in some points of the network. Understanding the transition of demand under a competitive intermodal hub location model is the aim of this study. One of the most important factors in customer behavior is the price that the firm is charging and it is more reasonable to model the demand as a function of price. To do so, a discrete choice logit model is applied in a Mixed Integer Nonlinear Programming (MINLP) framework and an efficient heuristics solution is provided. Moreover, actual Turkish network data for rail transport is being considered in the model, on top of the CAB data and optimal price strategy is derived out of the model.
Değişik Tip Parça Üreten Robotlu Akış Hücrelerinde Döngüsel Çizelgeleme
(TOBB University of Economics and Technology,Graduate School of Engineering and Science, 2016) Çoban, Betül; Gültekin, Hakan
In this study, the considered problem is design of robotic cell producing multiple parts and consists of machines served by a single gripper robot. A single gripper robot can hold only one part at a time. In the system, while the parts are processing in the machines, transfers between machines and loading/unloading of machines is performed by a single robot. Each parts have to be proceed in all machines, there are specific process time according to parts and machines. In this system, cyclic production is preferred because both the robot performs activities by following computer codes and it is easy to implement and control. "n-unit cycle" as a sequence of robot activities in which the system returns to the same state after producing n parts is handled. In this problem, the aim is generated a solution method to simultaneously determine the optimal part sequence and robot move sequence that maximize throughput or equivalently minimize the long-run average cycle time. In the literature, there is no study that is determining n-unit cycle that minimizes the cycle time for multiple part-type production in m machines to simultaneously determine robot move sequences and part sequence. The mathematical model is developed as an exact solution method. Therefore, for this problem includes scheduling of robot moves and sequencing of parts simultaneously which is shown to be NP-hard, heuristic methods are developed because no available integer solutions are obtained particularly for largescaled problems. Experimental studies is performed to evaluate the performance of the proposed algorithms.

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Browsing Endüstri Mühendisliği Yüksek Lisans Tezleri / Industrial Engineering Master Theses by Department "Enstitüler, Fen Bilimleri Enstitüsü, Endüstri Mühendisliği Ana Bilim Dalı"