06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun... more 06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Karma modelli montaj hatlarında hattın düzgün ilerlemesi, üretim kısıtları ve müşteri talepleri doğrultusunda belirlenmiş olan çizelgelenmiş sıraya uyuma bağlıdır. Fakat çizelgelenmiş sıra kasıtlı ve kasıtsız araç sıra değişiklikleri nedeniyle bozulabilmektedir. Bozulan sırayı onarmak için boyahane ile montaj departmanları arasında araç yeniden sıralanma ara stoğu bulunmaktadır. Bu ara stok bozulan sırayı üç farklı şekilde onarmaktadır: Bunlar (i) araç sıralarının değiştirilmesi, araçların yeniden sıralanması, (ii) hatalı araçların ara stokta tutulan araçlarla değiştirilmesi, (iii) son olarak da ara stok kapasitesi ve araç hatalarına bağlı olarak yeniden ...
As a result of civil war in Syria and Turkey’s open-door policy, almost 3 million refugees moved ... more As a result of civil war in Syria and Turkey’s open-door policy, almost 3 million refugees moved to Turkey since March 2011. The unexpected arrival of a large number of refugees within a relatively short period of time caused inadequate planning of the government-operated camps to fulfill the humanitarian needs of those affected individuals. The purpose of this study is to develop an optimization model that helps in the distribution of humanitarian aid to the refugees. The multi-objective optimization model decides on the facility locations by integrating total transportation distance minimization and covered demand maximization. Uncertainties in the supply amount are captured through possible scenarios to determine the optimal facilities that will serve the demand points. We used a weighted sum method to solve the multiobjective optimization problem. Different weights are associated with the objective functions to represent the varying preferences of decision makers and examine how...
This study proposes a two-stage stochastic programming model to determine an optimal set of bus s... more This study proposes a two-stage stochastic programming model to determine an optimal set of bus stations that minimizes operational, environmental, and social costs under uncertain weather conditions and customer perceptions on sustainability. The first stage of the proposed model focuses on the derivation of a set of bus stations under uncertain demand and weather conditions. Then, the second stage determines an optimal vehicle capacity (i.e., bus size) to minimize the impact of vehicle shortages. In the proposed model, different customer perceptions on sustainability are conceptualized through a range of dissatisfaction levels. Weather conditions are considered as causing higher dissatisfaction for vehicle shortages in certain seasons. The proposed model is applied to a numerical case study for a bus transit network in a college town. This study also analyzes the effect of human behavior on system costs by comparing the proposed model with a traditional approach. The results provi...
Additive manufacturing (AM) brings significant freedom in design, yet it can get hard to produce ... more Additive manufacturing (AM) brings significant freedom in design, yet it can get hard to produce the same part at identical dimensional tolerances; this is also known as the reproducibility problem. Reproducibility, the ability to produce the same part under similar conditions, is one of the major challenges in AM as reproducibility plays an important role in the replacement of worn-out or damaged parts in an assembly. The objective of this paper is to identify the impacts of two most common factors (i.e., layer thickness and printing speed) on the dimensional accuracy of additively manufactured parts through a designed experiment. A fullfactorial experimental design involving these factors at three levels is implemented to investigate them. We printed a dog bone testing specimen by using Poly Lactic Acid (PLA) polymer and Fused Filament Fabrication (FFF) technology. The dimensional properties of the parts are then measured to statistically compare the variability in each level to d...
As a result of the ongoing Syrian civil war, almost 3 million refugees moved to Turkey since 2011... more As a result of the ongoing Syrian civil war, almost 3 million refugees moved to Turkey since 2011 because of security reasons. However, the government operated refugee camps have been largely inadequate to accommodate this huge number of refugees. Therefore, almost 91% of the Syrian refugees live out of government-operated camps. According to a Turkish Disaster and Emergency Management Agency (AFAD) report, 45.4% of the children under 5 years old who live out of camps are not vaccinated against polio. This presents a serious health threat to the local population and the whole region. In order to deal with this potential risk, local vaccine distribution strategies that encourage vaccination should be developed for the cities that are close to Syrian border. We develop a mathematical model with which we determine the optimal number of polio vaccines that needs to be administered for each age group and the region considering the vaccination history of individuals. Different vaccination...
Engineering design learning is one of the key components for an engineering degree; thus engineer... more Engineering design learning is one of the key components for an engineering degree; thus engineering design projects are commonly included in engineering curricula to help students cultivate design thinking and creative problem-solving skills. However, an engineering design project is prone to the following issues if it is not appropriately provided to engineering students. First, gender bias can occur when the design project is perceived to be more skewed to one gender in comparison to the other. Second, domain bias can occur when the discipline of the design project is not related to the chosen major and interest areas of a student. Third, ambiguity can arise from the lack of clarity on design objectives and the scope. These issues can lead to diminished engagement and self-efficacy for engineering students. In order to tackle these issues, this study performs a preliminary work to build a framework that appropriately assesses engineering design projects. The evaluation framework ...
Eksploatacja i Niezawodnosc - Maintenance and Reliability, 2021
The paper provides a multiple-experts Fuzzy-TOPSIS decision-making model for the selection among ... more The paper provides a multiple-experts Fuzzy-TOPSIS decision-making model for the selection among maintenance contractors based on the quality of tendering documents. The study introduces a set of selection criteria utilizing benefit and cost criteria from literature. The proposed model aggregates subjective linguistic assessments of multiple experts that express their opinions on the degree of importance of criteria and allows multiple decisionmakers to evaluate the compliance of contractors’ documents. For a case study, the model is applied to select among contractors tendering to maintain the heavy-duty cranes of an international steel company from literature. Several decision-making scenarios are investigated, and major changes in the final decision are observed. The changes in obtained results illustrate the need to better address uncertainties in rating and tendering an overqualified contractor at a higher cost.
Abstract Remanufacturing is the process of turning used products into new ones in terms of qualit... more Abstract Remanufacturing is the process of turning used products into new ones in terms of quality, functionality, and aesthetics with relatively lower product prices. The advent of additive manufacturing (AM) has opened new opportunities to increase the feasibility of various product design and repair options for remanufacturing. This study focuses on the successful implementation of AM in remanufacturing to transition towards sustainable product development. Although there are design guidelines scattered across literature, a clear set of rules or guidelines that facilitate remanufacturing using AM is not discussed. In this study, as a response, an enhanced TRIZ (ETRIZ) matrix that compiled and tailored existing guidelines for remanufacturing and AM is developed. ETRIZ not only overcomes the design-related contradictions that originated from remanufacturing, but also helps to increase AM applications in remanufacturing. Two case examples are provided to elaborate on and verify the application of the guidelines derived from the proposed methodology for the repair process and design for remanufacturing (DfRem), respectively. The ETRIZ tool is useful for industries and designers to improve product design in terms of remanufacturability and to implement AM in remanufacturing.
Various studies have discussed the coordination of product and supply chain design decisions for ... more Various studies have discussed the coordination of product and supply chain design decisions for global supply chain management. However, the impact of currency exchange rate uncertainty on the selection of product architectures and their suppliers has not been sufficiently addressed. As a response, this study proposes a two-stage stochastic optimization model in which the first stage determines the product architecture, and the second stage identifies suppliers for the modules and components in an optimal fashion based on the product architecture and uncertain currency exchange rates. The overall objective of two-stage stochastic programming is to determine the optimal product architecture that minimizes the expected total supply chain cost over uncertain currency exchange rate scenarios. The proposed model is applied to a bicycle supply chain case study for three global marketplaces associated with multiple currency exchange rates. The results demonstrate that optimal product architecture and its suppliers should be varied based on currency exchange rates and their uncertain fluctuation levels. Also, a product architecture for the supply chain of each marketplace maintains its optimality in the total supply chain cost, up to a specific exchange rate. The findings show the importance of joint integration between product and supply chain design when considering currency exchange rates. Additionally, the benefit of stochastic modelling is demonstrated by comparing the solution quality of the model with its deterministic counterpart.
Abstract Capturing the uncertainty associated with a decision maker (DM)’s judgments and preferen... more Abstract Capturing the uncertainty associated with a decision maker (DM)’s judgments and preferences is one of the most challenging parts of concept design evaluation as it depends on subjective linguistic terms. To address this drawback, we propose a novel approach for concept design evaluation that incorporates Z-number and axiomatic design (AD) concepts. Although pertinent literature advocates for the capture of uncertain information originating from DMs, the relevant need for information reliability has not been addressed. By incorporating Z-numbers, the confidence level of a decision or its reliability is taken into consideration, thus a more comprehensive perception of the DM is recorded. Then, these judgments and preferences are incorporated to AD to select the best design concept. Using data from the published literature, a case study is conducted to assess the impact of information reliability and the DM’s risk attitude with regards to available design options. The proposed approach is also compared with previously developed methods in order to show its benefits. The results demonstrate that the reliability of the information has a significant impact on final results; and assessment of confidence, or reliability of information, enhances the success for better decision-making.
In mixed-model automobile assembly lines, paint defective vehicles are the main reason for uninte... more In mixed-model automobile assembly lines, paint defective vehicles are the main reason for unintentional sequence alteration that stirs up the production sequence so that resequencing is required. This study aims to decide optimal spare vehicles that are held in the mix-bank buffer to be replaced instead of defective vehicles in order to regain the production sequence. We develop a hybrid solution methodology in which optimal spare vehicle content is determined by genetic algorithm (GA) and the releasing order of the vehicles to final assembly (FA) are decided by stochastic mixed integer programming (MIP) model. In addition to discussing the efficiency of the hybrid model, the following insights were gained: 1) not only FA but also paint shop constraints should be considered in production sequence determination when mix-bank buffer is efficiently used; 2) the decrease in defect rate improves sequence restoration linearly; 3) effect of an additional lane on SSAR increase is diminishing. [Received: 22 December 2018; Accepted: 28 October 2019]
International Journal of Production Research, 2020
The paper presents a Monte Carlo simulation model to estimate the average rate of energy expendit... more The paper presents a Monte Carlo simulation model to estimate the average rate of energy expenditure (Kcal/min) and, consequently, fatigue allowance in manual order picking systems with high demand rates. The study is limited to picking a low number of low weight items per order in a compact warehouse system with traditional layout configuration of parallel racks with equal size storage cubicles. Replicates of 10,000 orders with random order sizes and random locations of items per order are used to estimate the average rate of energy expenditure for female pickers with various combinations of body mass and walking speeds. Design for the average and design for percentile are investigated to estimate a maintainable work standard to maximise productivity while maintaining energy expenditure within acceptable limits. Results illustrate the significant impacts of body mass and walking speed on the productivity and rate of energy expenditure, especially for the above average weight picker. Moreover, results reveal the difficulty of adopting recommendations on limitations on energy input and degrade in aerobic capacity with age and health conditions when setting productivity limits for pickers with a wide range of weights.
Students in design courses work on projects that are influenced by ambiguity, gender orientation,... more Students in design courses work on projects that are influenced by ambiguity, gender orientation, and domain relatedness. This study investigates the impacts of these factors on student self-efficacy in order to increase retention in engineering disciplines. From a comprehensive literature review and feedback from engineering experts, an instrument is developed to assess student perceptions on tolerance to ambiguity (STA), project gender orientation (PGO), and project domain relatedness (PDR). Statistical analyses are conducted to examine the influence of STA, PGO, and PDR on student self-efficacy and collective efficacy. Results indicate that an increase in the gender orientation of the project decreases student self-efficacy. Furthermore, gender bias of the design project diminishes student tolerance to deal with ambiguous situations. Therefore, instructors should consider choosing more gender-neutral projects or make appropriate adjustments in project descriptions to minimize gen...
06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun... more 06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Karma modelli montaj hatlarında hattın düzgün ilerlemesi, üretim kısıtları ve müşteri talepleri doğrultusunda belirlenmiş olan çizelgelenmiş sıraya uyuma bağlıdır. Fakat çizelgelenmiş sıra kasıtlı ve kasıtsız araç sıra değişiklikleri nedeniyle bozulabilmektedir. Bozulan sırayı onarmak için boyahane ile montaj departmanları arasında araç yeniden sıralanma ara stoğu bulunmaktadır. Bu ara stok bozulan sırayı üç farklı şekilde onarmaktadır: Bunlar (i) araç sıralarının değiştirilmesi, araçların yeniden sıralanması, (ii) hatalı araçların ara stokta tutulan araçlarla değiştirilmesi, (iii) son olarak da ara stok kapasitesi ve araç hatalarına bağlı olarak yeniden ...
As a result of civil war in Syria and Turkey’s open-door policy, almost 3 million refugees moved ... more As a result of civil war in Syria and Turkey’s open-door policy, almost 3 million refugees moved to Turkey since March 2011. The unexpected arrival of a large number of refugees within a relatively short period of time caused inadequate planning of the government-operated camps to fulfill the humanitarian needs of those affected individuals. The purpose of this study is to develop an optimization model that helps in the distribution of humanitarian aid to the refugees. The multi-objective optimization model decides on the facility locations by integrating total transportation distance minimization and covered demand maximization. Uncertainties in the supply amount are captured through possible scenarios to determine the optimal facilities that will serve the demand points. We used a weighted sum method to solve the multiobjective optimization problem. Different weights are associated with the objective functions to represent the varying preferences of decision makers and examine how...
This study proposes a two-stage stochastic programming model to determine an optimal set of bus s... more This study proposes a two-stage stochastic programming model to determine an optimal set of bus stations that minimizes operational, environmental, and social costs under uncertain weather conditions and customer perceptions on sustainability. The first stage of the proposed model focuses on the derivation of a set of bus stations under uncertain demand and weather conditions. Then, the second stage determines an optimal vehicle capacity (i.e., bus size) to minimize the impact of vehicle shortages. In the proposed model, different customer perceptions on sustainability are conceptualized through a range of dissatisfaction levels. Weather conditions are considered as causing higher dissatisfaction for vehicle shortages in certain seasons. The proposed model is applied to a numerical case study for a bus transit network in a college town. This study also analyzes the effect of human behavior on system costs by comparing the proposed model with a traditional approach. The results provi...
Additive manufacturing (AM) brings significant freedom in design, yet it can get hard to produce ... more Additive manufacturing (AM) brings significant freedom in design, yet it can get hard to produce the same part at identical dimensional tolerances; this is also known as the reproducibility problem. Reproducibility, the ability to produce the same part under similar conditions, is one of the major challenges in AM as reproducibility plays an important role in the replacement of worn-out or damaged parts in an assembly. The objective of this paper is to identify the impacts of two most common factors (i.e., layer thickness and printing speed) on the dimensional accuracy of additively manufactured parts through a designed experiment. A fullfactorial experimental design involving these factors at three levels is implemented to investigate them. We printed a dog bone testing specimen by using Poly Lactic Acid (PLA) polymer and Fused Filament Fabrication (FFF) technology. The dimensional properties of the parts are then measured to statistically compare the variability in each level to d...
As a result of the ongoing Syrian civil war, almost 3 million refugees moved to Turkey since 2011... more As a result of the ongoing Syrian civil war, almost 3 million refugees moved to Turkey since 2011 because of security reasons. However, the government operated refugee camps have been largely inadequate to accommodate this huge number of refugees. Therefore, almost 91% of the Syrian refugees live out of government-operated camps. According to a Turkish Disaster and Emergency Management Agency (AFAD) report, 45.4% of the children under 5 years old who live out of camps are not vaccinated against polio. This presents a serious health threat to the local population and the whole region. In order to deal with this potential risk, local vaccine distribution strategies that encourage vaccination should be developed for the cities that are close to Syrian border. We develop a mathematical model with which we determine the optimal number of polio vaccines that needs to be administered for each age group and the region considering the vaccination history of individuals. Different vaccination...
Engineering design learning is one of the key components for an engineering degree; thus engineer... more Engineering design learning is one of the key components for an engineering degree; thus engineering design projects are commonly included in engineering curricula to help students cultivate design thinking and creative problem-solving skills. However, an engineering design project is prone to the following issues if it is not appropriately provided to engineering students. First, gender bias can occur when the design project is perceived to be more skewed to one gender in comparison to the other. Second, domain bias can occur when the discipline of the design project is not related to the chosen major and interest areas of a student. Third, ambiguity can arise from the lack of clarity on design objectives and the scope. These issues can lead to diminished engagement and self-efficacy for engineering students. In order to tackle these issues, this study performs a preliminary work to build a framework that appropriately assesses engineering design projects. The evaluation framework ...
Eksploatacja i Niezawodnosc - Maintenance and Reliability, 2021
The paper provides a multiple-experts Fuzzy-TOPSIS decision-making model for the selection among ... more The paper provides a multiple-experts Fuzzy-TOPSIS decision-making model for the selection among maintenance contractors based on the quality of tendering documents. The study introduces a set of selection criteria utilizing benefit and cost criteria from literature. The proposed model aggregates subjective linguistic assessments of multiple experts that express their opinions on the degree of importance of criteria and allows multiple decisionmakers to evaluate the compliance of contractors’ documents. For a case study, the model is applied to select among contractors tendering to maintain the heavy-duty cranes of an international steel company from literature. Several decision-making scenarios are investigated, and major changes in the final decision are observed. The changes in obtained results illustrate the need to better address uncertainties in rating and tendering an overqualified contractor at a higher cost.
Abstract Remanufacturing is the process of turning used products into new ones in terms of qualit... more Abstract Remanufacturing is the process of turning used products into new ones in terms of quality, functionality, and aesthetics with relatively lower product prices. The advent of additive manufacturing (AM) has opened new opportunities to increase the feasibility of various product design and repair options for remanufacturing. This study focuses on the successful implementation of AM in remanufacturing to transition towards sustainable product development. Although there are design guidelines scattered across literature, a clear set of rules or guidelines that facilitate remanufacturing using AM is not discussed. In this study, as a response, an enhanced TRIZ (ETRIZ) matrix that compiled and tailored existing guidelines for remanufacturing and AM is developed. ETRIZ not only overcomes the design-related contradictions that originated from remanufacturing, but also helps to increase AM applications in remanufacturing. Two case examples are provided to elaborate on and verify the application of the guidelines derived from the proposed methodology for the repair process and design for remanufacturing (DfRem), respectively. The ETRIZ tool is useful for industries and designers to improve product design in terms of remanufacturability and to implement AM in remanufacturing.
Various studies have discussed the coordination of product and supply chain design decisions for ... more Various studies have discussed the coordination of product and supply chain design decisions for global supply chain management. However, the impact of currency exchange rate uncertainty on the selection of product architectures and their suppliers has not been sufficiently addressed. As a response, this study proposes a two-stage stochastic optimization model in which the first stage determines the product architecture, and the second stage identifies suppliers for the modules and components in an optimal fashion based on the product architecture and uncertain currency exchange rates. The overall objective of two-stage stochastic programming is to determine the optimal product architecture that minimizes the expected total supply chain cost over uncertain currency exchange rate scenarios. The proposed model is applied to a bicycle supply chain case study for three global marketplaces associated with multiple currency exchange rates. The results demonstrate that optimal product architecture and its suppliers should be varied based on currency exchange rates and their uncertain fluctuation levels. Also, a product architecture for the supply chain of each marketplace maintains its optimality in the total supply chain cost, up to a specific exchange rate. The findings show the importance of joint integration between product and supply chain design when considering currency exchange rates. Additionally, the benefit of stochastic modelling is demonstrated by comparing the solution quality of the model with its deterministic counterpart.
Abstract Capturing the uncertainty associated with a decision maker (DM)’s judgments and preferen... more Abstract Capturing the uncertainty associated with a decision maker (DM)’s judgments and preferences is one of the most challenging parts of concept design evaluation as it depends on subjective linguistic terms. To address this drawback, we propose a novel approach for concept design evaluation that incorporates Z-number and axiomatic design (AD) concepts. Although pertinent literature advocates for the capture of uncertain information originating from DMs, the relevant need for information reliability has not been addressed. By incorporating Z-numbers, the confidence level of a decision or its reliability is taken into consideration, thus a more comprehensive perception of the DM is recorded. Then, these judgments and preferences are incorporated to AD to select the best design concept. Using data from the published literature, a case study is conducted to assess the impact of information reliability and the DM’s risk attitude with regards to available design options. The proposed approach is also compared with previously developed methods in order to show its benefits. The results demonstrate that the reliability of the information has a significant impact on final results; and assessment of confidence, or reliability of information, enhances the success for better decision-making.
In mixed-model automobile assembly lines, paint defective vehicles are the main reason for uninte... more In mixed-model automobile assembly lines, paint defective vehicles are the main reason for unintentional sequence alteration that stirs up the production sequence so that resequencing is required. This study aims to decide optimal spare vehicles that are held in the mix-bank buffer to be replaced instead of defective vehicles in order to regain the production sequence. We develop a hybrid solution methodology in which optimal spare vehicle content is determined by genetic algorithm (GA) and the releasing order of the vehicles to final assembly (FA) are decided by stochastic mixed integer programming (MIP) model. In addition to discussing the efficiency of the hybrid model, the following insights were gained: 1) not only FA but also paint shop constraints should be considered in production sequence determination when mix-bank buffer is efficiently used; 2) the decrease in defect rate improves sequence restoration linearly; 3) effect of an additional lane on SSAR increase is diminishing. [Received: 22 December 2018; Accepted: 28 October 2019]
International Journal of Production Research, 2020
The paper presents a Monte Carlo simulation model to estimate the average rate of energy expendit... more The paper presents a Monte Carlo simulation model to estimate the average rate of energy expenditure (Kcal/min) and, consequently, fatigue allowance in manual order picking systems with high demand rates. The study is limited to picking a low number of low weight items per order in a compact warehouse system with traditional layout configuration of parallel racks with equal size storage cubicles. Replicates of 10,000 orders with random order sizes and random locations of items per order are used to estimate the average rate of energy expenditure for female pickers with various combinations of body mass and walking speeds. Design for the average and design for percentile are investigated to estimate a maintainable work standard to maximise productivity while maintaining energy expenditure within acceptable limits. Results illustrate the significant impacts of body mass and walking speed on the productivity and rate of energy expenditure, especially for the above average weight picker. Moreover, results reveal the difficulty of adopting recommendations on limitations on energy input and degrade in aerobic capacity with age and health conditions when setting productivity limits for pickers with a wide range of weights.
Students in design courses work on projects that are influenced by ambiguity, gender orientation,... more Students in design courses work on projects that are influenced by ambiguity, gender orientation, and domain relatedness. This study investigates the impacts of these factors on student self-efficacy in order to increase retention in engineering disciplines. From a comprehensive literature review and feedback from engineering experts, an instrument is developed to assess student perceptions on tolerance to ambiguity (STA), project gender orientation (PGO), and project domain relatedness (PDR). Statistical analyses are conducted to examine the influence of STA, PGO, and PDR on student self-efficacy and collective efficacy. Results indicate that an increase in the gender orientation of the project decreases student self-efficacy. Furthermore, gender bias of the design project diminishes student tolerance to deal with ambiguous situations. Therefore, instructors should consider choosing more gender-neutral projects or make appropriate adjustments in project descriptions to minimize gen...
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