Fatih Cavdur | Uludag University (original) (raw)

Papers by Fatih Cavdur

European Journal of Operational Research, 1985

Uludağ üniversitesi mühendislik fakültesi dergisi, Apr 24, 2018

Bu çalıĢma, dengeli bir sınav programı oluĢturmak için kümeleme ve hedef programlama tabanlı bir ... more Bu çalıĢma, dengeli bir sınav programı oluĢturmak için kümeleme ve hedef programlama tabanlı bir yaklaĢım sunmaktadır. ÇalıĢmada, kiĢisel iĢ yükü açısından öğrencileri ve öğretim elemanlarını belirli bir düzeyde memnun edecek, dengeli bir sınav programı oluĢturmak amaçlanmaktadır. Bu kapsamda öncelikle, derslerin kredisi, baĢarı oranı ve türü olmak üzere üç parametre kullanılarak sınav kritiklik seviyelerinin belirlenmesi için Ward yöntemi ve k-ortalamalar kümeleme algoritması önerilmektedir. Daha sonra, belirlenen kritiklik seviyeleri ve diğer problem kısıtları dikkate alınarak bir hedef programlama modeli ile sınav çizelgesi oluĢturulmaktadır. Önerilen yaklaĢım, bir gerçek hayat problemi üzerinde örneklendirilmiĢtir. YaklaĢım sonucu oluĢturulan çizelge, gerçek hayatta oluĢturulan çizelge ile karĢılaĢtırıldığında, sınavların kritiklik seviyelerini de dikkate alan dengeli bir sınav çizelgesinin oluĢturulduğu görülmektedir. Buna ek olarak, önerilen yaklaĢımın daha büyük boyutlu gerçek hayat problemlerinde de kullanılma potansiyeli bulunmaktadır.

Marmara Üniversitesi fen bilimleri dergisi, Sep 30, 2018

Montaj hatlarında yeniden işleme istasyonları genellikle yalnızca uygun olmayan ürünlerin yeniden... more Montaj hatlarında yeniden işleme istasyonları genellikle yalnızca uygun olmayan ürünlerin yeniden işlenmesi için kullanılmaktadır. Bununla birlikte, yeniden işleme istasyonunun yalnızca bu amaçla kullanılması, özellikle montaj hattında hata oranının düşük olması durumunda, istasyonda bulunan kaynakların kullanım oranını düşürmektedir. Bu çalışmada, yeniden işleme istasyonunun standart bir iş istasyonu olarak kullanılmasını dikkate alarak çevrim süresini minimize etmeyi amaçlayan bir karışık-tamsayılı programlama modeli önerilmektedir. Önerilen model, montaj hattındaki farklı hata oranlarının yanısıra, yeniden işleme istasyonunun sadece montaj hattı sonunda değil, farklı pozisyonlarda konumlandırılmasını da dikkate almaktadır. Modelin performansı, literatürdeki çeşitli örneklemler üzerinde test edilmiştir.

Journal of The Faculty of Engineering and Architecture of Gazi University, Feb 28, 2022

 Development of an artificial neural network for earthquake intensity estimation  Network struc... more  Development of an artificial neural network for earthquake intensity estimation  Network structure optimization by considering different network designs  Determining an appropriate training algorithm for the determined network design In this study, using a multi-layer feed-forward artificial neural network, we estimate earthquake intensity based on the magnitude and the depth of an earthquake and the distance of the disaster victims from the epicenter of the earthquake. In this context, we use significant earthquakes database of the United States Geological Survey as the inputs of the artificial neural network. We first determine an appropriate network design by estimating earthquake intensity with different artificial neural network designs and then the best training algorithm for the appropriate network design by evaluating different algorithms for the corresponding network design. Figure A. Artificial neural network design Purpose: We aim to estimate the earthquake intensity via an artificial neural network. Theory and Methods: We obtain significant earthquakes data from the database of the United States Geological Survey. An artificial neural network is developed using the MATLAB Neural Network Toolbox. We first determine an appropriate network design by estimating earthquake intensity with different artificial neural network designs and then the best training algorithm for the appropriate network design by evaluating different algorithms for the corresponding network design. Results: In terms of the average performance parameters, the network structure with two hidden layers and five and ten hidden neurons in each respective layer is determined as the most appropriate design. We observe the best results in terms of performance parameters by using the Levenberg-Marquardt training algorithm with Bayesian Regularization for the corresponding network structure. Conclusion: Earthquake intensity estimation is critical in predicting the impact that will occur after a disaster. In this study, we estimate earthquake intensity via an artificial neural network. In future studies, associated with earthquake intensity, we can estimate the number of casualties, damages to the buildings, economic loss and so on. Integrating earthquake intensity estimation into other disaster operation management studies may be another future study direction.

International Journal of Advances in Engineering and Pure Sciences, 2021

Otomatik Depolama ve Geri-Alma (OD/GA) sistemleri için kurulum aşamasında performans analizlerini... more Otomatik Depolama ve Geri-Alma (OD/GA) sistemleri için kurulum aşamasında performans analizlerinin yapılması sistem tasarımının optimize edilmesi açısından önemlidir. Bununla birlikte, OD/GA sistemlerinin tasarımı gerçekleştirilirken, fiziksel tasarım parametrelerine ek olarak kontrol parametrelerinin de dikkate alınması gerekliliği karmaşık bir optimizasyon probleminin ortaya çıkmasına neden olmaktadır. Bu problemin ele alınmasında farklı parametre kombinasyonlarını içerecek şekilde esnek bir çözüm sistematiğinin geliştirilmesi önem kazanmaktadır. Bu çalışmada OD/GA sistemlerinin performans analizi için bir simülasyon modeli önerilmektedir. Önerilen model kullanılarak rassal depo içi atama politikası için farklı bekleme noktalarının (giriş, orta ve çıkış) dikkate alındığı senaryolar gerçekçi boyutlarda bir sistem için simüle edilerek sistem performansı ürünlerin sistemde geçirdikleri ortalama zaman, D/GA makinesinin ortalama seyahat süresi ve D/GA makinesi kullanım oranlarına göre ...

Fibers and Polymers, 2023

Safety Science, Apr 1, 2020

In this study, we present a spreadsheet-based decision support tool for allocating temporary-disa... more In this study, we present a spreadsheet-based decision support tool for allocating temporary-disaster-response facilities for relief supplies distribution. The tool developed in this study mainly consists of three main components as its database, decision engine and user interface. We develop the tool to run on a spreadsheet environment rather than producing a standalone application by aiming at providing more convenience for the user to perform tasks such as data manipulation and reporting. The paper also presents an example case for illustration. The tool allows the user (i.e., decision makers) to allocate temporary-disaster-response facilities under many different after-disaster situations (scenarios) considering the possible uncertainties to occur after a disaster (i.e., different affected population rates, planning periods etc.). Although we present some example cases in the paper for illustration purposes, the flexibility of the tool allows its users to consider other cases with many other scenarios. The tool can be used to help decision makers for allocating temporary-disaster-response facilities for planning relief supplies distribution operations.

Journal of the Association for Information Science and Technology, 2008

There are recent studies in the literature on automatic topic-shift identification in Web search ... more There are recent studies in the literature on automatic topic-shift identification in Web search engine user sessions; however most of this work applied their topic-shift identification algorithms on data logs from a single search engine. The purpose of this study is to provide the cross-validation of an artificial neural network application to automatically identify topic changes in a web search engine user session by using data logs of different search engines for training and testing the neural network. Sample data logs from the Norwegian search engine FAST (currently owned by Overture) and Excite are used in this study. Findings of this study suggest that it could be possible to identify topic shifts and continuations successfully on a particular search engine user session using neural networks that are trained on a different search engine data log.

Decision Support Systems, Dec 1, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Proceedings Of The Association For Information Science And Technology, Sep 22, 2005

... Tel: (412) 6249454; Fax: (412) 6487001. Email: H. Cenk Özmutlu ({hco, fcavdur, seda}@uludag... more ... Tel: (412) 6249454; Fax: (412) 6487001. Email: H. Cenk Özmutlu ({hco, fcavdur, seda}@uludag.edu.tr) Fatih Çavdur ({hco, fcavdur, seda}@uludag.edu.tr) Seda Özmutlu ({hco, fcavdur, seda}@uludag.edu.tr) Amanda Spink (aspink@sis.pitt.edu). ...

Politeknik dergisi, Jul 5, 2023

Bu makaleye şu şekilde atıfta bulunabilirsiniz(To cite to this article): Bakır M., Sebatlı-Sağlam... more Bu makaleye şu şekilde atıfta bulunabilirsiniz(To cite to this article): Bakır M., Sebatlı-Sağlam A. ve Çavdur F., "Bağlantısız paralel parti üretimi yapan makine çizelgeleme probleminin karışık-tamsayılı programlama ile çözümü", Politeknik Dergisi, *(*): *, (*).

Uludağ üniversitesi mühendislik fakültesi dergisi, Dec 31, 2018

Öz: İnsansız hava araçlarının askeri ve ticari uygulamalarının yanında, afet operasyonları yöneti... more Öz: İnsansız hava araçlarının askeri ve ticari uygulamalarının yanında, afet operasyonları yönetiminde de uygulama potansiyelinin bulunması, son zamanlarda bu alana olan ilginin artmasına neden olmuştur. İnsansız hava araçlarının hızlı, emniyetli ve esnek olmaları gibi avantajları afet öncesi ve afet sonrası çeşitli operasyonlarda tercih edilme nedenleri arasındadır. Bu çalışmada, yer araçları kullanılarak afet bölgesine ulaşım sağlanamadığı durumlarda, afet bölgesi durum tespiti için insansız hava araçlarının kullanımı ele alınmıştır. Bu kapsamda, afet bölgelerinin gözetlenmesinde kullanılacak olan insansız hava araçlarının rota planlaması için kümeleme ve matematiksel programlama tabanlı bir yaklaşım önerilmiştir. Çalışmada, sayısal uygulama yapılmış ve sonuçları analiz edilmiştir.

International Journal of Industrial Engineering-theory Applications and Practice, Nov 23, 2021

In this study, a mathematical programming model for using dynamically-positioned-rework stations ... more In this study, a mathematical programming model for using dynamically-positioned-rework stations for performing parallel tasks in assembly line balancing is proposed. We first introduce a nonlinear programming model, which is quadratic in constraints resulting from the modeling of the parallel task assignment and dynamic positioning of the rework station. We also establish some novel logical conditions in the model building process while deriving the proposed formulation. In the next step, we present appropriate variable transformations for linearization to take advantage of the algorithms for solving linear programs by noting that the quadratic expressions of the model are present as either the multiplications of binaries or binaries multiplied by continuous variables. After implementing the corresponding variable transformations, the model is transformed to a linear-mixed-integer program. A numerical example is then presented using the resulted linear model for illustration. We also perform some computational experiments using sample problems from the related literature to analyze the performance of the model

Politeknik dergisi, Mar 1, 2022

Montaj hatlarında yeniden işleme istasyonları genellikle uygun olmayan ürünlerin yeniden işlendiğ... more Montaj hatlarında yeniden işleme istasyonları genellikle uygun olmayan ürünlerin yeniden işlendiği bir istasyon olarak kullanılmaktadır. Bununla birlikte, yeniden işleme istasyonunun yalnızca bu amaç için kullanılması montaj hattı hata oranının düşük olması durumunda, bu istasyonda bulunan kaynakların verimsiz bir şekilde kullanılmasına neden olabilmektedir. Bu çalışmada, öncelikle, yeniden işleme istasyonunun paralel görevler için kullanılması dikkate alınarak çevrim süresini minimize etmeyi amaçlayan bir doğrusal olmayan karışık-tamsayılı programlama modeli sunulmuştur. Paralel görevlerle ilgili doğrusalolmayan kısıt, değişken dönüşümü ile doğrusallaştırılarak, model doğrusal-karışık-tamsayılı şekle dönüştürülmüştür. Buna ek olarak, çalışma kapsamında, problemin stokastik unsurları dikkate alınarak, tamsayılı programdan elde edilen sonuçların doğrulanması için de bir simülasyon modeli geliştirilmiştir. Geliştirilen model ile iki test problemi simüle edilerek, söz konusu problemler için tamsayılı programlama modelinden elde edilen çözümün uygulanabilirliği incelenmiştir. Anahtar Kelimeler: Montaj hattı dengeleme, çevrim süresi minimizasyonu, paralel görev atama, karışık-tamsayılı programlama, simülasyon.

International journal of production management and engineering, Jul 18, 2020

In assembly lines, rework stations are generally used for reprocessing defective items. On the ot... more In assembly lines, rework stations are generally used for reprocessing defective items. On the other hand, using rework stations for this purpose only might cause inefficient usage of the resources in this station especially in an assembly line with a low defective rate. In this study, a mixed-integer programming model for cycle time minimization is proposed by considering the use of rework stations for performing parallel tasks. By linearizing the non-linear constraint about parallel tasks using a variate transformation, the model is transformed to a linear-mixed-integer form. In addition to different defective rates, different rework station positions are also considered using the proposed model. The performance of the model is analyzed on several test problems from the related literature.

Proceedings Of The Association For Information Science And Technology, Oct 10, 2007

Recent studies on automatic new topic identification in Web search engine user sessions demonstra... more Recent studies on automatic new topic identification in Web search engine user sessions demonstrated that neural networks are successful in automatic new topic identification. However most of this work applied their new topic identification algorithms on data logs from a single search engine. In this study, we investigate whether the application of neural networks for automatic new topic identification are more successful on some search engines than others. Sample data logs from the Norwegian search engine FAST (currently owned by Overture) and Excite are used in this study. Findings of this study suggest that query logs with more topic shifts tend to provide more successful results on shift-based performance measures, whereas logs with more topic continuations tend to provide better results on continuation-based performance measures.

Information Systems Frontiers, May 15, 2012

This study addresses the problem of analyzing the temporal dynamics of business organizations. In... more This study addresses the problem of analyzing the temporal dynamics of business organizations. In particular, we concentrate on inferring the related businesses, i.e., are there groups of companies that are highly correlated through some measurement (metric)? We argue that business relationships derived from general literature (i.e., newspaper articles and news items) may help us create a network of related companies (business networks). On the other hand, relative movement of stock prices can give us an indication of related companies (asset graphs). Hence, our research addresses the problem of construction and analysis of the networks of business organizations, i.e., asset graphs and business networks, and exploring the relationships between these two types of networks. We start with the asset graphs. An asset graph is a network model of a stock market constructed based on pair-wise stock price correlations. Adapting the methodology from the literature, we present implementations with some extensions, such as consideration of different correlation metrics, global stock markets etc. A new asset graph model is also presented to capture the short term stock market dynamics and general market trends so that we can observe the effects of business events on the asset graphs. The second problem this study addresses is about business networks. We define a novel business network model that captures business events. Business networks are constructed based on the occurrences of company names in general literature, such as daily news. Our extended business network model captures not only the business relationships between several companies (co-occurrences two or more company names in the same document) with the links between the corresponding companies, but the business events which is about one particular company iv (occurrence of the company name in a document) by representing them with self-links or loops in the network. Finally, we combine our approaches mentioned above, asset graphs and business networks, to explore the relationships between these two kinds of networks, and hence, the relationships between the business events, and financial systems. Our approaches include finding the graph intersections, analyses on the stocks with strong negative correlations and 1neighborhood similarity analysis. Graph intersections illustrate the companies with significant stock correlations and the business events or relationships, which might be considered as the possible reasons for these strong correlations. Analysis about strong negative correlations assumes that if a company's stock price strongly negatively correlated with many others, then, a business event or relationship might be the reason for that, and hence, it might be captured in corresponding business networks. Finally, the analysis about the 1-neigborhoods shows how similar these neighborhoods are in the asset graphs and corresponding business networks. Our results illustrate the relationships between these two kinds of networks. v

Information Systems Frontiers, Apr 19, 2012

ABSTRACT In this paper, we present a novel business network construction approach, where the node... more ABSTRACT In this paper, we present a novel business network construction approach, where the nodes of the network correspond to the names of the companies in a particular stock market index, and its links show the co-occurrence of two company names in daily news. Our approach consists of two phases, in which search for the company names in the news articles and network construction operations are performed, respectively. To increase the quality of results, each article is classified as business news or not business news before these operations, and only the articles that are classified as business news are considered for network construction. The resulting network presents a visualization of the business events and company relationships during the corresponding time period. We study both co-occurrences as well as single occurrences of company names in the articles scanned in our analysis.

Natural Hazards Review, Feb 1, 2021

AbstractIn disaster operations management, the prepositioning of relief supplies might improve th... more AbstractIn disaster operations management, the prepositioning of relief supplies might improve the efficiency of the corresponding operations significantly. Developing new strategies based on this ...