Scopus
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Publication Implementation of DBSCAN Method in Star Trackers to Improve Image Segmentation in Heavy Noise Conditions(2023) Nevsan ŞENGİL; Şengil, Nevsan; Türk Hava Kurumu Üniversitesi, Uzay Mühendisliği Bölümü, Ankara, TürkiyeStar trackers are currently the most accurate sensors for determining the attitude of a spacecraft. These sensors comprise not only highly capable optical detectors and processor units but also complicated software solvers. One of the main solvers employed in star trackers is image segmentation. In this study, the aim is to develop a hybrid image segmentation method which is a combination of both global thresholding and density-based spatial clustering of applications with noise (DBSCAN) method to increase detection probability of the stars in heavy noise. Secondly, a sorting algorithm is added to list the detected stars in terms of their brightness to increase the efficiency of the star tracking algorithm. Then, this new approach and two different conventional segmentation methods are applied to the Orion star constellation image polluted with Gaussian, salt and pepper, and uneven background noises. The resulting images of these segmentation methods are compared in terms of denoising capabilities. Although computationally more expensive, the proposed DBSCAN-based hybrid method displays a background pixel recovery performance of 99.5%, compared to Otsu global thresholding and adaptive thresholding methods’ 73.5% and 79.9% recovery values, respectively. Additionally, it has been demonstrated that the sorting algorithm successfully listed the detected stars in accordance with their brightness.Publication Aerodynamic Shape Optimization of a Missile Using a Multiobjective Genetic Algorithm(Hindawi Limited, 2020-06-08) Ahmet Şumnu; İbrahim Halil Güzelbey; Orkun ÖğücüThe aim of this paper is to demonstrate the effects of the shape optimization on the missile performance at supersonic speeds. The N1G missile model shape variation, which decreased its aerodynamic drag and increased its aerodynamic lift at supersonic flow under determined constraints, was numerically investigated. Missile geometry was selected from a literature study for optimization in terms of aerodynamics. Missile aerodynamic coefficient prediction was performed to verify and compare with existing experimental results at supersonic Mach numbers using SST k-omega, realizable k-epsilon, and Spalart-Allmaras turbulence models. In the optimization process, the missile body and fin design parameters need to be estimated to design optimum missile geometry. Lift and drag coefficients were considered objective function. Input and output parameters were collected to obtain design points. Multiobjective Genetic Algorithm (MOGA) was used to optimize missile geometry. The front part of the body, the main body, and tailfins were improved to find an optimum missile model at supersonic speeds. The optimization results showed that a lift-to-drag coefficient ratio, which determines the performance of a missile, was improved about 11-17 percent at supersonic Mach numbers.Publication An Experimental and Numerical Investigation of an Improved Shearing Process with Different Punch Characteristics(Faculty of Mechanical Engineering, 2020-06-15) Mahmoud Gomah; Murat Demiral; Demiral, MuratBlanking and piercing shearing processes have been widely used to manufacture workpieces for industrial, commercial and testing purposes. During the operation, the punch is exposed to higher stresses and, due to the cycled contact of opposite surfaces, it can be worn significantly. As its surface directly affects the quality of sheet products and causes some surface defects, its performance plays a significant role. In this study, various tools with different characteristics were investigated for an improved shearing process. First, a novel punch with a hemispherical ball at the centre of its flat face was tested and compared with a conventional one. The process was simulated using ABAQUS/Explicit finite element (FE) program, in which the Johnson-Cook material model with its complementary damage model was used to represent the behaviour of the sheet material. Based on this, an optimum geometry for the proposed punch was determined. Secondly, the wear resistance of TiN, CrN, TiSiN, AlCrN and AlTiN coated punches, produced with physical vapour deposition (PVD) technique, and of the polycrystalline diamond compact (PDC) cutter were compared based on scanning electron microscope (SEM) micrographs after 1000 strokes under dry cutting conditions.Publication Science Missions Using CubeSats(National Space Science Center, Chinese Academy of Sciences, 2020) M E SEYEDABADI; M FALANGA; M AZAM; N BARESI; R FLÉRON; V JANTARACHOTE; ORTIZ V A JUAREZ; YAYA J J JULCA; M LANGER; S MANUTHASNA; N MARTINOD; M R MUGHAL; M NOMAN; J PARK; A PIMNOO; J PRAKS; L REYNERI; A SANNA; T Ç ŞIŞMAN; J SOME; T ULAMBAYAR; Xiaozhou YU; Xiaolong DONG; L BALDISPublication On the Eddy Current Losses in Metallic Towers(Center of Biomass and Renewable Energy Scientia Academy, 2020-01-09) Ibrahim Mahariq; Svetlana Beryozkina; Huda Mohammed; Hamza KurtThe existence of magnetic field around high-voltage overhead transmission lines or low-voltage distribution lines is a known fact and well-studied in the literature. However, the interaction of this magnetic field either with transmission or distribution towers has not been investigated. Noteworthy it is to remember that this field is time-varying with a frequency of 50 Hz or 60 Hz depending on the country. In this paper, we studied for the first time the eddy currents in towers which are made of metals. As the geometrical structures of towers are extremely complex to model, we provide a simple approach based on principles of electromagnetism in order to verify the existence of power loss in the form of eddy currents. The frequency-domain finite difference method is adapted in the current study for simulating the proposed model. The importance of such a study is the addition of a new type of power loss to the power network due to the fact that some towers are made of relatively conductive materials.©2020. CBIORE-IJRED. All rights reservedPublication Iris segmentation techniques to recognize the behavior of a vigilant driver(IEEE, 2020-02) Abdullatif BABA; Baba, AbdullatifPublication The hazardous waste location and routing problem: an application in Marmara Region in Turkey(Springer Science and Business Media LLC, 2020-01-30) Durdu Hakan Utku; Serpil Erol; Utku, Durdu HakanPublication Design and analysis of a quad‐band substrate‐integrated‐waveguide cavity backed slot antenna for 5G applications(Hindawi Limited, 2020-04-04) Tayfun OkanPublication Is there a novel Einstein–Gauss–Bonnet theory in four dimensions?(Springer Science and Business Media LLC, 2020-07) Metin Gürses; Tahsin Çağrı Şişman; Bayram TekinAbstractNo! We show that the field equations of Einstein–Gauss–Bonnet theory defined in generic $$D>4$$D>4 dimensions split into two parts one of which always remains higher dimensional, and hence the theory does not have a non-trivial limit to $$D=4$$D=4. Therefore, the recently introduced four-dimensional, novel, Einstein–Gauss–Bonnet theory does not admit an intrinsically four-dimensional definition, in terms of metric only, as such it does not exist in four dimensions. The solutions (the spacetime, the metric) always remain $$D>4$$D>4 dimensional. As there is no canonical choice of 4 spacetime dimensions out of D dimensions for generic metrics, the theory is not well defined in four dimensions.Publication High temperature behavior of non-local observables in boosted strongly coupled plasma: a holographic study(Springer Science and Business Media LLC, 2020-07) Atanu Bhatta; Shankhadeep Chakrabortty; Suat Dengiz; Ercan KilicarslanAbstractIn this work, we perform a holographic analysis to study non local observables associated to a uniformly boosted strongly coupled large N thermal plasma in d-dimensions. In order to accomplish the holographic analysis, the appropriate dual bulk theory turns out to be $$d+1$$d+1 dimensional boosted AdS-Schwarzschild blackhole background. In particular, we compute entanglement entropy of the boosted plasma at high temperature living inside a strip geometry with entangling width l in the boundary at a particular instant of time. We also study the two-point correlators in the boundary by following geodesic approximation method. For analyzing the effect of boosting on the thermal plasma and correspondingly on both non local observables, we keep the alignment of the width of region of interest both parallel and perpendicular to the direction of the boost. We find our results significantly modified compared to those in un-boosted plasma up to the quadratic order of the boost velocity v. More interestingly, the relative orientation of the boost and the entangling width play a crucial role to quantify the holographic entanglement entropy in the boundary theory. The breaking of rotational symmetry in the boundary theory due to the boosting of the plasma along a specific flat direction causes this interesting feature.