Mühendislik Fakültesi / Faculty of Engineering
Permanent URI for this collectionhttps://hdl.handle.net/11727/1401
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Item Low Velocity Bird-Like Impact Behavior on Honeycomb Composite Structure(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-20) Ozturk, Okan; Elaldi, FarukComposite materials are widely used in primary aerospace structures such as wing components and fuselage panels; however, their major disadvantage is their vulnerability to transverse impact loads that can lead to internal delamination and fiber/matrix separation. In this study, the effect of a low-velocity impact which simulates bird impact on a honeycomb sandwich composite plates produced by a co-curing technique for a typical unmanned air vehicle (UAV) was studied both experimentally and numerically. The surface plates of the composite samples were produced from carbon fiber/epoxy prepreg material. Nomex honeycomb core material was used to make the composite sandwich structure via an autoclave process. For the bird-like impact test, the tip of the impactor was coated with thick, tough rubber to simulate a bird strike; the diameter of the impactor was 25 mm to ensure similarity with a bird called Pica nuttalli (magpie), which has a mass of 155 g and is the closest bird body to the simulations. Three different predetermined impact scenarios with kinetic energy 380 Joule, 276 Joule, and 224 Joule were applied to the samples with rubber impactors of similar density, to simulate bird impact events with different impact directions. The impact behavior was characterized by velocity-time, force-time, and displacement-time graphs. Different levels of damage were observed in the composite samples, but none of the sandwich test samples were perforated, and it could therefore be concluded that the unmanned air vehicle could land without risk to flight safety. Ultrasound, digital microscope, and tap inspections have been applied for test samples to determine damage area size and types. This low-velocity bird-like impact was also modeled and analyzed using Ansys numerical program to verify the results, and it was concluded that the verified model could also be used for the preliminary design verification of dynamic bird-impact tests within the 10% sensitivity range.Item Seismic Assessment of Electrical Equipment in Power Substations: A Case Study for Circuit Breakers(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-18) Kaatsiz, Kaan; Alici, Firat Soner; Erberik, Murat AltugElectric power is essential in post-earthquake periods for the continuous functionality of disaster management and emergency services. In addition, interruption of electric power can cause significant economic losses due to downtime of critical facilities. Therefore, it is very important to maintain seismic safety of electric power systems and components. There are existing seismic regulations and standards regarding electric power systems, especially in the United States of America (USA) and Europe. A similar regulation has been prepared recently in T & uuml;rkiye, which is a country in a seismically active region. This study focuses on the current state of practice regarding the seismic assessment of electrical equipment in power stations and implementation of the regulations on seismic qualification of these systems. Among many electrical equipment, circuit breakers have been selected for case study. The seismic assessment of the selected high voltage equipment has been performed according to the new regulation under the seismic hazard specifically defined for T & uuml;rkiye. The case study experiment presents the new methodology in evaluating and classifying the seismic response of high voltage electrical equipment and provides insight to the expected behaviour of circuit breakers under earthquake induced action.Item Observational Test Of R 2 Spacetimes With The S2 Star In The Milky Way Galactic Center(Başkent Üniversitesi Mühendislik Fakültesi, 2024-08-06) Yan, Jian-Ming; Zhu, Tao; Azreg-Ainou, Mustapha; Jamil, Mubasher; Nguyen, Hoang KyA novel class of vacuum metrics expressible in analytical form was recently found for pure 7Z2 2 gravity, based on a groundwork put forth by Buchdahl in 1962. These Buchdahl-inspired solutions offer a practical framework for testing 7Z2 2 gravity through empirical observations. Within a subclass of asymptotically flat Buchdahl-inspired vacuum spacetimes, we identified a parameter E measuring the deviation from the classic Schwarzschild metric, which corresponds to E = 0. In this paper, we employ observational data from the S2 star's orbit around Sgr A* in the Milky Way galactic center and perform Monte Carlo Markov Chain simulations to probe the effects of the new metrics on the orbit of the S2 star. Our analysis presented herein reports a range at 95% confidence level on the deviation parameter as E is an element of (-0.6690, - 0.6690, 0.4452). While no decisive evidence either in favor or in disfavor of the asymptotically flat Buchdahl-inspired spacetimes has been achieved, the obtained bound is compatible with the tighter results using other data of different nature as recently reported in Eur. Phys. J. C 84 (2024) 330. As a meaningful test probing into a strong-field regime, our present study calls for further observations with prolonged period and improved accuracy in order to tighten the bound for E using the S2 star orbit.Item Observational test of R 2 spacetimes with the S2 star in the Milky Way Galactic Center(Başkent Üniversitesi Mühendislik Fakültesi, 2024-08-06) Yan, Jian-Ming; Zhu, Tao; Azreg-Ainou, Mustapha; Jamil, Mubasher; Nguyen, Hoang KyA novel class of vacuum metrics expressible in analytical form was recently found for pure 7Z2 2 gravity, based on a groundwork put forth by Buchdahl in 1962. These Buchdahl-inspired solutions offer a practical framework for testing 7Z2 2 gravity through empirical observations. Within a subclass of asymptotically flat Buchdahl-inspired vacuum spacetimes, we identified a parameter E measuring the deviation from the classic Schwarzschild metric, which corresponds to E = 0. In this paper, we employ observational data from the S2 star's orbit around Sgr A* in the Milky Way galactic center and perform Monte Carlo Markov Chain simulations to probe the effects of the new metrics on the orbit of the S2 star. Our analysis presented herein reports a range at 95% confidence level on the deviation parameter as E is an element of (-0.6690, - 0.6690, 0.4452). While no decisive evidence either in favor or in disfavor of the asymptotically flat Buchdahl-inspired spacetimes has been achieved, the obtained bound is compatible with the tighter results using other data of different nature as recently reported in Eur. Phys. J. C 84 (2024) 330. As a meaningful test probing into a strong-field regime, our present study calls for further observations with prolonged period and improved accuracy in order to tighten the bound for E using the S2 star orbit.Item A Game-Changing Equation During The Etching Of Tuning Forks And Its Verification Through Experiments(Başkent Üniversitesi Mühendislik Fakültesi, 2024-08-05) Erbas, Kadir Can; Erdogan, Mebrure; Serdaroglu, Dilek cokeliler; Kocum, Ismail CengizQuartz tuning fork (QTF) sensors, characterized by simplicity, low cost, and high-quality factor, represent a significant subset. This study delves into the etching dynamics of QTF systems, crucial for sensor applications like quartz crystal microbalance (QCM). Both theoretical and experimental investigations into QTF etching, via methods like electro-etching for large-scale tuning forks (TF) and low-pressure radio frequency (RF) plasma treatment for QTFs, have been conducted. Surprisingly, post-etching measurements reveal a lower vibrational frequency for both large-scale TFs and QTFs compared to their bare counterparts, unlike QCM sensors. A novel formula correlating this frequency reduction to mass loss has been proposed and validated through lots of experiments. Notably, longitudinal homogeneity emerges as a pivotal factor influencing the accuracy of the proposed formula. In summary, the novel mathematical framework presented herein is poised to catalyze the widespread adoption of low-cost QTFs as mass-sensitive biosensors, marking a significant advancement in the field.Item Accelerated Evaluation of Blocking Flowshop Scheduling With Total Flow Time Criteria Using A Generalized Critical Machine-Based Approach(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-10) Han, Yuyan; Wang, Yuting; Pan, Quan-ke; Wang, Ling; Tasgetiren, FatihDespite the considerable advances in the research of the blocking flowshop scheduling problem (BFSP), several unresolved challenges persist. Algorithmic complexity presents hurdles. Although the insertion-based method is considered to generate superior solutions, its high computational demand diminishes the efficiency of algorithms, especially within large-scale sequences. The existing accelerated evaluation methods cannot utilize the existing information to quickly calculate the total flow time or the total tardiness time of the changed sequence after the job insertion, but recalculates it from scratch. This does not significantly reduce computational effort and needs to be further improved. In this paper, we delve into the intrinsic features of these challenges, proposing a generalized accelerated critical machine-based evaluation tailored for the total flow time and tardiness criteria of the BFSP with and without sequence-dependent setup times. First, we propose three theorems, one corollary, and their proofs based on the critical machine. Second, we propose the accelerated evaluation procedure based on these theorems to calculate the objectives related to the total flow time. Third, we also extend the proposed accelerated evaluation method to the BFSP with sequence-dependent setup times, aiming to significantly reduce the time complexity. Finally, we conduct four experiments on five well-known benchmarks (a total of 3540 test instances). Through statistical analysis, it becomes evident that our computational efforts have significantly decreased in computing both the total flow time and the total tardiness time. This performance enhancement is superior to the effectiveness of existing acceleration techniques.Item Automated Detection of type 1 ROP, type 2 ROP and A-ROP Based on Deep Learning(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-02) Yenice, Esay Kiran; Kara, Caner; Erdas, Cagatay BerkePurposeTo provide automatic detection of Type 1 retinopathy of prematurity (ROP), Type 2 ROP, and A-ROP by deep learning-based analysis of fundus images obtained by clinical examination using convolutional neural networks.Material and methodsA total of 634 fundus images of 317 premature infants born at 23-34 weeks of gestation were evaluated. After image pre-processing, we obtained a rectangular region (ROI). RegNetY002 was used for algorithm training, and stratified 10-fold cross-validation was applied during training to evaluate and standardize our model. The model's performance was reported as accuracy and specificity and described by the receiver operating characteristic (ROC) curve and area under the curve (AUC).ResultsThe model achieved 0.98 accuracy and 0.98 specificity in detecting Type 2 ROP versus Type 1 ROP and A-ROP. On the other hand, as a result of the analysis of ROI regions, the model achieved 0.90 accuracy and 0.95 specificity in detecting Stage 2 ROP versus Stage 3 ROP and 0.91 accuracy and 0.92 specificity in detecting A-ROP versus Type 1 ROP. The AUC scores were 0.98 for Type 2 ROP versus Type 1 ROP and A-ROP, 0.85 for Stage 2 ROP versus Stage 3 ROP, and 0.91 for A-ROP versus Type 1 ROP.ConclusionOur study demonstrated that ROP classification by DL-based analysis of fundus images can be distinguished with high accuracy and specificity. Integrating DL-based artificial intelligence algorithms into clinical practice may reduce the workload of ophthalmologists in the future and provide support in decision-making in the management of ROP.Item Approximation Theorems Via Pp-statistical Convergence on Weighted Spaces(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-08) Yildiz, Sevda; Bayram, Nilay SahinIn this paper, we obtain some Korovkin type approximation theorems for double sequences of positive linear operators on two-dimensional weighted spaces via statistical type convergence method with respect to power series method. Additionally, we calculate the rate of convergence. As an application, we provide an approximation using the generalization of Gadjiev-Ibragimov operators for P-p-statistical convergence. Our results are meaningful and stronger than those previously given for two-dimensional weighted spaces.Item Asymptotic Derivation of Consistent thin Shell Equations for a Fluid-Loaded Elastic Annulus(Başkent Üniversitesi Mühendislik Fakültesi, 2024-07-08) Yucel, H.; Kaplunov, J.; Ege, N.; Erbas, B.The classical time-harmonic plane strain problem for a fluid-loaded cylindrical elastic shell is revisited. The results of the low-frequency asymptotic analysis, including explicit formulae for eigenfrequencies, are presented. A refined version of the semi-membrane shell theory is formulated. It is shown that the shell inertia does not affect significantly the lowest eigenfrequencies. It is also demonstrated that the ring stress component has a parabolic linear variation.Item Improving The Performance of a MEMS-IMU System Based On A False State-Space Model By Using A Fading Factor Adaptive Kalman Filter(Başkent Üniversitesi Mühendislik Fakültesi, 2024-06-29) Akbas, Eren Mehmet; Cifdaloz, Oguzhan; Ucuncu, MuratIn this study, we introduce a novel algorithm, the low error rate adaptive fading Kalman filter (LERAFKF), designed to predict system states in the presence of uncertainty in both the system matrix and the model. The purpose of developing the LERAFKF is to address challenges arising from measurement difficulties, system parameter uncertainties, and state-space model inaccuracies. Several studies have utilized the Kalman filter (KF) and extended Kalman filter (EKF) algorithms to handle uncertainties in system parameters, corrupted measurements with unknown covariances, and incorrectly defined system modeling. Our work distinguishes itself by proposing a new approach that achieves lower error and deviation rates by combining the current Kalman estimation algorithm and the fading factor adaptive filter. To achieve this goal, we transformed the KF into an adaptive KF by introducing a forgetting factor, and the algorithm was subsequently reconfigured to calculate an optimized forgetting factor. In this study, we conducted simulations and measurements using both linear and nonlinear systems. The linear system represents the motion of an object, and the simulation involved measurements from the inertial navigation system (INS) sensor, specifically the Pololu IMU01b three-axis inertial measurement unit (IMU) sensor. We employed the SDI33 system with 9 degrees of freedom (DoF) mounted on a three-axis rotary table for the nonlinear system. This system simulates a missile as a 4th-order nonlinear system. Our findings demonstrate that the proposed LERAFKF filter outperforms KF and EKF in estimating system states, particularly in measurement-related error scenarios. Mean square error analysis further confirmed that LERAFKF exhibited the lowest error values, showcasing superior performance over KF and EKF in linear and nonlinear systems.