Mühendislik Fakültesi / Faculty of Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11727/1401

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A Critical Assessment Of The Design Displacements Of Friction Pendulum Systems
(SOIL DYNAMICS AND EARTHQUAKE ENGINEERING, 2024-02) Alici, F. Soner; Sucuog, Haluk; Ozcamur, Ugurcan
The equivalent linear static procedure suggested in seismic codes for determining the maximum displacements of seismic isolation systems is evaluated comprehensively for friction pendulum isolators with respect to the benchmark nonlinear response history analysis procedure for a set of radii of curvature and coefficients of friction. A large set of selected and scaled near field ground motions recorded on stiff and soft soils are employed in comparative evaluations. It has been observed that equivalent linear static procedure significantly overestimates the maximum isolator displacements for all practical combinations of radius of curvature and friction coefficient. Overestimation is larger for ground motions on soft soils. Alternatively, a practical description of inelastic displacement spectra is introduced where the hazard is defined in terms of the 1-second spectral acceleration accounting for the seismicity and soil class of the site, and friction pendulum isolation systems are characterized by their radius of curvature and nominal friction coefficient. Employing the proposed design spectra in design and production may lead to significant reductions of the isolator sizes. Moreover, realistic estimation of maximum isolator displacements also leads to realistic estimation of isolator stiffness, as well as the internal design forces of both the isolation system and the superstructure through response spectrum analysis under design spectrum.
A Dss Development Study For Document Distribution Networks For Preparing Autonomous Vehicle-Integrated Distribution Systems
(DECISION, 2024-12) Derya, Tusan; Ic, Yusuf Tansel; Erbay, Mehmet Dogan; Konuk, Kubra; Fidan, Nihal
We propose a decision support system (DSS) to complete the tours of the routes of the traveler in charge of document distribution in the least amount of time for the document distribution task of a university to prepare autonomous vehicle-integrated distribution systems. A mathematical model-based decision support system is developed to determine distribution routes that optimize the total distance to target locations and obtain optimal system conditions for use in the migration of autonomous distribution systems. The purpose is to find the shortest-cost tours to cover all or subsets of edges in a network. Documents are shared and distributed by travelers to other related locations. Soon after, travelers will be replaced by autonomous vehicles. There are many application areas, such as newspapers and mail delivery systems. Therefore, the proposed model can be easily extended to other application areas, such as newspaper, cargo, and mail delivery systems, to construct autonomous vehicle-based systems.
A Fuzzy Computing Approach To Aggregate Expert Opinions Using Parabolic And Exparabolic Approximation Procedures For Solving Multi-Criteria Group Decision-Making Problems
(Başkent Üniversitesi Mühendislik Fakültesi, 2024-03-02) Ic, Yusuf Tansel
Triangular fuzzy numbers (TFNs) are widely used for selection problems to determine expert opinions using linguistic expressions. Some aggregation procedures are developed to determine expert opinions more accurately. However, there is a need for a simple and more useful procedure to solve the selection problems more suitably. For this purpose, our study offers a triangular, exparabolic, and parabolic area calculation-based approximation approach for TFNs to aggregate the possible hedges (very and more or less) for TFNs. Hence, this aggregation procedure provides a tuning opportunity for classical TFN expressions to capture possible tuning processes to reflect the hesitancies of experts. The technique for order preferences by similarity to ideal solution (TOPSIS) method is applied in the two studies from extant literature, and suitable alternatives are determined as a result of the ranking process. Finally, a comparative analysis is presented to illustrate the efficiency of the proposed procedure. The conventional TOPSIS model's ranking scores are very close for exemplified examples (i.e., 0.5308, 0.4510, 0.4550 and 0.5304, 0.4626, 0.4940), but the proposed model's result has fluctuated for the same examples (i.e., 0.346, 0,669, 0,567 and 0.208, 0.991, 0.148). So, the main advantage of the proposed aggregation procedure is the alternative ranking scores separation capability analyzed with their linguistic diversification.
A Hybrid Monte Carlo Simulation Risk Model for Oil Exploration Projects
(MARINE POLLUTION BULLETIN, 2023) Balas, Egemen Ander
A new 3-D Hybrid Monte Carlo Simulation (MCS) Risk Model is proposed in this study. The wind, wave, current, climate change, and tsunami sub-models of the Three-Dimensional Hydrodynamic Transport and Water Quality Model HYDROTAM-3D are interrelated with MCS, to obtain probability distributions for the simulation of environmental conditions. This is the only model that can incorporate the tsunami, storm, and sea level rise risks in oil exploration projects. The spill risk index (SRI) of 50 blue barrels spilled due to a blowout from the rig/port during fuel supply was circa 1 ton/ship as Tier I with an average annual occurrence probability of 1.0 x 10-6. The discharge of 4000 bbls for 6 h was modeled, resulting in the SRI of 546 metric tons from the riser blowout with SRI = 0.2 per meter, indicating a Tier II risk. The mean arrival time of this spill was found by MCS as 145 min.
A Multi-Objective Optimization Framework for Functional Arrangement in Smart Floating Cities
(EXPERT SYSTEMS WITH APPLICATIONS, 2024) Kirimtat, Ayca; Tasgetiren, M. Fatih; Krejcar, Ondrej; Buyukdagli, Ozge; Maresova, Petra
Before the terms "smart city" and "floating city" were introduced, the world's population had increased and land shortage across the world was already widely recognized. As a first challenge, the previous studies have developed the concept of a smart city as a creative answer, following that, several scientists proposed the floating city concept in the literature as a solution to the increased sea levels. Moreover, engineers, architects, and designers deal with city planning, for smart and floating settlements as a difficult design challenge, and evolutionary algorithms could be employed to address this complex problem by optimizing residents' needs. As a continuation of our previous studies on this topic, this time, we develop a multi-objective continuous genetic algorithm with differential evolution (DE) mutation strategy (MO_CGADE) and a multi-objective ensemble differential evolution algorithm (MO_EDE) to solve the problem on hand. Then, we compare the performance of the MO_CGADE and MO_EDE algorithms with the non-dominated sorting genetic algorithm (NSGAII) to maximize two conflicted objective functions, namely, scenery, and walkability in the proposed smart floating city model created in the Grasshopper Algorithmic Modeling Environment. The parametric model that we create in the Grasshopper software includes 64 decision variables, area constraints and objective functions to be optimized by MO_CGADE, MO_EDE, and NSGAII algorithms. Computational results show that MO_CGADE and MO_EDE algorithms generate better Pareto ranking results than the traditional NSGAII algorithm in terms of cardinality, distribution spacing, and coverage metrics.
A New Approach for Addressing Slip Ratio Optimization and Trajectory Tracking Challenges in Autonomous Tractor Operations
(32ND IEEE SIGNAL PROCESSING AND COMMUNICATIONS APPLICATIONS CONFERENCE, SIU 2024, 2024) Aydin, Gulsah Demirhan; Aydemir, Ali Bahadir; Kansou, Mohamad Thaer; Altinuc, Kemal Orcun
The usage of autonomous agricultural machines is increasing. In this study, two controllers have been designed for trajectory following and longitudinal tire slip ratio control of a rear-wheel independent traction electric autonomous tractor. The first controller is model predictive control (MPC) and the second controller is proportional integral derivative (PID) based. To evaluate the performance of the controllers in the simulation environment, a mathematical tractor model is prepared. Simulations have been made and performances of the designed controllers are shared.
A Performance Evaluation Study of Thin-Wall Tube Design in the Front Bumper Uses The Altered TOPSIS-Rank Order Clustering Algorithm-Integrated Approach
(MULTISCALE AND MULTIDISCIPLINARY MODELING EXPERIMENTS AND DESIGN, 2024)
Abstract The rising growth of the economy in developing countries led to a significant increase in the number of vehicles on the roads. The number of vehicles in road transport is also increasing significantly due to the increase in automobile ownership due to the increase in city populations. As a result of this increase, there is an increase in traffic accidents. For this reason, automobile manufacturers make significant efforts to develop lighter and more robust bumpers. Also, they used performance measurement studies for the thin-walled bumpers. The motivation of the study is based on the examines the dynamic performance of thin-walled bumpers within the impact of both oblique and axial compression. The crash performance of thin-wall tubes is analyzed based on factors such as speed, mass, and cross-section geometries. We developed a new rank order clustering (ROC) algorithm that integrated altered technique for order preferences by similarity to ideal solution (A-TOPSIS) method-based comparative analysis to determine the best thin-wall tube among the alternatives. For the first time in the literature, the A-TOPSIS results-integrated ROC algorithm is proposed to obtain the best tube profiles considering different expectations from their performance according to the determined criteria.Please check and confirm the edi t in the article title.OK.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 2 Given name: [Yusuf Tansel] Last name [Ic] and Author 4 Given name: [Bekir Batuhan] Last name [Sagol]. Also, kindly confirm the details in the metadata are correct.OK
A Pilot Study on Comparison of Teaching Workloads of Academicians Based on Working Periods During and Before the COVID-19 Pandemic
(Başkent Üniversitesi Mühendislik Fakültesi, 2025-01-25) Yorulmaz, Muhammed; Can, Gulin Feryal; Toktas, Pelin
The COVID-19 pandemic has had a profound impact on society, greatly changing the structure of social and working lives. Educational institutions, especially in higher education, were forced to suspend face-to-face education and switch to distance education. This change inevitably affected the working styles and workloads of academics. This study aims to explore the effects of the COVID-19 pandemic on academic teaching workloads by examining transaction data for a one-year period before and during the pandemic. The data were obtained from the system logs of a learning management system platform, which was used extensively during the pre-pandemic and pandemic periods, and were analyzed in terms of transaction density, day, and time of transactions. The findings from the pre-pandemic period showed that the academic workload was higher on weekdays than on weekends. However, with the transition to distance education during the pandemic, the difference between weekday and weekend workloads diminished significantly. Additionally, the working hours shifted during the pandemic by approximately one hour to later hours in the day.
A Revisit To The Plane Problem For Low-Frequency Acoustic Scattering By An Elastic Cylindrical Shell
(Başkent Üniversitesi Mühendislik Fakültesi, 2024-03-16) Yucel, Hazel; Ege, Nihal; Erbas, Baris; Kaplunov, Julius
The proposed revisit to a classical problem in fluid-structure interaction is due to an interest in the analysis of the narrow resonances corresponding to a low-frequency fluid-borne wave, inspired by modeling and design of metamaterials. In this case, numerical implementations would greatly benefit from preliminary asymptotic predictions. The normal incidence of an acoustic wave is studied for a circular cylindrical shell governed by plane strain equations in elasticity. A novel high-order asymptotic procedure is established considering for the first time all the peculiarities of the low-frequency behavior of a thin fluid-loaded cylinder. The obtained results are exposed in the form suggested by the Resonance Scattering Theory. It is shown that the pressure scattered by rigid cylinder is the best choice for a background component. Simple explicit formulae for resonant frequencies, amplitudes, and widths are presented. They support various important observations, including comparison between widths and the error of the asymptotic expansion for frequencies.
A Robust Aluminum Material Selection Process in the Aviation Industry: A Linear Discrete System Stability Test Perspective for Fuzzy Multicriteria Decision-Making
(Başkent Üniversitesi Mühendislik Fakültesi, 2024-04-10) Ic, Yusuf Tansel; Hamzaoglu, Burak Meric; Yurdakul, Mustafa
Aluminum parts are used in the aviation industry because of the need for light. However, in addition to lightness, critical parts that must have high strength properties have also been developed. The corrosion resistance, resistance to high temperatures, and workability were investigated in this case. It becomes difficult to choose among many aluminum materials that can be alternatives to each other when these features are included. The developed approach, which considers many of the features listed above and ultimately recommends to the user the most suitable aluminum material for the relevant critical part, will be used in overcoming the difficulties in this process. A material selection model is proposed in this paper for this purpose, and the decision-making model is demonstrated with examples from the aviation industry. Therefore, the developed model, which will enable the selection of the most suitable materials among alternative materials, especially for critical parts in the aviation industry, will guide professionals working in this field. For this purpose, the fuzzy TOPSIS method is used in the study, and suitable alternatives are determined. Finally, a robustness analysis is proposed to determine the most suitable aluminum material for highly uncertain situations. We apply a stability evaluation study based on process control theory in the robustness analysis.
Accelerating The Environmental Biodegradation Of Poly-3-Hydroxybutyrate (Phb) Via Plasma Surface Treatment
(BIORESOURCE TECHNOLOGY REPORTS, 2024-09-02) Akdogan, Ebru; Sirin, Hasret Tolga; Sahal, Gulcan; Deniz, Zulkuf; Kaya, Ayberk; Serdaroglu, Dilek Cokeliler
The surface of poly-3-hydroxybutyrate (PHB) was modified using a low-pressure plasma system with air as the process gas to accelerate its biodegradation rate in soil. The water contact angle of PHB was reduced from 98 degrees to 57 degrees after plasma treatment, rendering the surface hydrophilic and also induced an increase in the surface free energy. Etching on the surface was observed after the plasma treatment without a significant change in the surface crystallinity. AFM imaging showed that the plasma treatment increased the surface roughness by about 10 folds and created diverse surface structures. The soil burial test showed an approximately 1.5-fold increase in the biodegradation rate for the plasma-treated sample. Initial microbial attachment and biofilm formation were higher on the modified surface. This study demonstrated that the surface morphology created by plasma treatment promoted initial colonization and subsequent biofilm formation on the PHB surface, facilitating and accelerating its biodegradation in soil.
An Algorithmic Approach To Portfolio Construction: A Turkish Stock Market Case
(BORSA ISTANBUL REVIEW, 2024-11) Gulsen, Mehmet; Yildiz, Burak
The goal of building a diversified portfolio is to mitigate risks and manage risk-reward tradeoffs. Diversification is also crucial for ensuring the long-term success of a portfolio. Although passive investment has been on the rise in most developed markets, it has not gained wider acceptance in some emerging markets, such as T & uuml;rkiye. This study proposes an approach to construct a diversified portfolio that serves as a passive investment tool in the context of the Turkish stock market. Despite the long history of equity markets in T & uuml;rkiye, almost all available passive investment alternatives are prohibitively expensive, unlike those in developed markets. We design a simple methodology that addresses the essential components of building a successful portfolio while avoiding excessive fees. Additionally, we propose a dynamic balancing strategy that algorithmically adjusts the weight of each stock in the portfolio. We test this approach with historical data, demonstrating that it can achieve reasonable returns with minimal effort. Even when its performance does not beat the benchmark, the percentage deviation is still below the management fees charged for alternative investments.
An Effective Optimization Method for Integrated Scheduling of Multiple Automated Guided Vehicle Problems
(TSINGHUA SCIENCE AND TECHNOLOGY, 2024-10) Sang, Hongyan; Li, Zhongkai; Tasgetiren, M. Fatih
Automated Guided Vehicle (AGV) scheduling problem is an emerging research topic in the recent literature. This paper studies an integrated scheduling problem comprising task assignment and path planning for AGVs. To reduce the transportation cost of AGVs, this work also proposes an optimization method consisting of the total running distance, total delay time, and machine loss cost of AGVs. A mathematical model is formulated for the problem at hand, along with an improved Discrete Invasive Weed Optimization algorithm (DIWO). In the proposed DIWO algorithm, an insertion-based local search operator is developed to improve the local search ability of the algorithm. A staggered time departure heuristic is also proposed to reduce the number of AGV collisions in path planning. Comprehensive experiments are conducted, and 100 instances from actual factories have proven the effectiveness of the optimization method.
Assessing the Shield Termination Approaches in Aircraft Wiring to Against the Lightning Indirect Effects
(JOURNAL OF POLYTECHNIC-POLITEKNIK DERGISI, 2024) Atalay, Emre; Tuncer, Ahmet Turgut)
Lightning is a natural phenomenon where high voltages and currents suddenly discharge. It can be caused by clouds themselves, clouds between them, or clouds near the earth. Aircraft are at risk of being struck by lightning and there is currently no way to prevent this from happening. Instead, efforts are being made to protect by reducing the effects of lightning. Metal structures in aircraft form a Faraday cage which helps in preventing lightning currents from entering the aircraft. However, composite structures, which are becoming more prevalent in the aviation sector, are less efficient in doing so compared to metals. Additionally, openings such as windows in the aircraft can break the Faraday cage and allow strong electromagnetic fields to penetrate. Hence, all equipment used on board the aircraft must be adequately qualified and lightning-proof. The most popular technique used to reduce the indirect effects of lightning on electronics is cable shielding. In this study, various shielding termination techniques for their effectiveness against indirect effect of lightning examined and it is found that utilizing a 360 degrees backshell termination technique provided to be highly effective, providing protection of nearly 3 dB. The results obtained from the experiments are compared with simulation results and previous studies.