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Item Metadata only Design and modeling of a PVDF-TrFe flexible wind energy harvester(Tubitak Scientific and Technological Research Council Turkey, 2023) 0000-0002-9777-6619; 0000-0002-0784-1537; Department of Mechanical Engineering; N/A; Beker, Levent; Kullukçu, Berkay; Faculty Member; Master Student; College of Engineering; Graduate School of Sciences and Engineering; 308798; N/AThis study presents the simulation, experimentation , design considerations of a Poly(vinylidene fluoride co-trifluoroethylene)/ Polyethylene Terephthalate (PVDF-TrFe / PET), laser-cut, flexible piezoelectric energy harvester. It is possible to obtain energy from the environment around autonomous sensor systems, which can then be used to power various equipment. This article investigates the actuation means of ambient vibration, which is a good candidate for using piezoelectric energy harvester (PEH) devices. The output voltage characteristics were analyzed in a wind test apparatus. Finite element modeling (FEM) was done for von Mises stress , modal analysis. Resonance frequency sweeps, quality factors, and damping ratios of the circular plate were given numerically. For a PVDF-TrFe piezoelectric layer thickness of 18 mu m and 1.5 mm radius, a damping ratio of 0.117 and a quality factor of 4.284 was calculated. Vmax was calculated as 984 mV from the wind setup experiments and compared with the FEM outputs.Publication Metadata only Development of a finite element model of the human cervical spine(Turkish Neurosurgery Society, 2014) N/A; N/A; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Zafarparandeh, Iman; Erbulut, Deniz Ufuk; Lazoğlu, İsmail; Özer, Ali Fahir; PhD Student; Researcher; Faculty Member; Faculty Member; Graduate School of Sciences and Engineering; School of Medicine; College of Engineering; School of Medicine; N/A; 37661; 179391; 1022The finite element model has been used as an effective tool in human spine biomechanics. Biomechanical finite element models have provided basic insights into the workings of the cervical spine system. Advancements in numerical methods during the last decade have enabled researchers to propose more accurate models of the cervical spine. The new finite element model of the cervical spine considers the accurate representation of each tissue regarding the geometry and material. The aim of this paper is to address the new advancements in the finite element model of the human cervical spine. The procedures for creating a finite element model are introduced, including geometric construction, material-property assignment, boundary conditions and validation. The most recent and published finite element models of the cervical spine are reviewed. / Sonlu eleman yöntemi efektif bir araç olarak omurga biyomekaniğinde yaygın kullanılmaktadır. Servikal omurga içerisinde meydana gelebilecek biyomekanik değişimlerin incelenmesine fırsat verebilmektedir. Geçtiğimiz on yıl içerisinde, geliştirilmiş olan nümerik metodlar sayesinde, daha gerçekçi omurga modellerinin çıkarılması sağlanmıştır. Günümüzde, servikal omurga modellerinde kullanılan geometri ve malzeme özellikleri olabildiğince gerçeğe yakın oluşturulabilmektedir. Bu makalenin amacı, sonlu eleman yöntemi kullanılarak insan servikal modellinin oluşturulmasını örneklerle açıklamaktır. Servikal omurga modelinin sonlu eleman yöntemi ile oluşturulmasının her bir adımı detaylı ele alınmıştır. Literatürde en son yayınlanan servikal omurga sonlu eleman modelleri incelenmiş ve karşılaştırılmıştır.Publication Metadata only Directional solidificaiton experiments in materials science laboratory of the international space station(Milli Savunma Üniversitesi Hava Harp Okulu, 2018) Department of Mechanical Engineering; Department of Mechanical Engineering; Şerefoğlu, Melis; Researcher; College of Engineering; 44888Solidification is taking place in industrial applications ranging from casting, welding, soldering to additive manufacturing. Even for materials that are shaped by plastic deformation or machining, the ingotor workpieceis generally produced by casting. Although application of these processesmay modifysolidification microstructure, theinitial cast structure still plays a deterministicrolein chemical and morphological distribution in the material. Material properties are highly dependent on these distributions as well as the microstructural featuresof the material. Therefore, investigatingmicrostructure evolution during solidification is crucial. on Earth, duetoconvection in the liquid during solidification of alloys,two-dimensional (2D)samples, i.e. thicknesses on the order of μm, must be used to avoid convection and obtain quantitativeresults. However, the wall thicknessesof cast componentsusedin industry are at least mm-thick. In order to understand the fundamentals of the solidification processin three-dimensional (3D)samples, and examine the direct effect of experimental parameters on microstructure selection, experiments wereperformed in microgravity conditions. Details of these microgravity experiments performed in the International Space Station as well as the ones performed on Earth in the Microstructure Evolution Laboratory are given in this article. Additionally, objectives of both μg and 1g experiments are summarized. / Katılaşma, döküm, kaynak, lehimleme ve katmanlı imalatgibi endüstriyel uygulamalarda gerçekleşmektedir. Plastik deformasyon veya işleme ile şekillendirilen malzemeler için bile, külçe veya iş parçası genellikle döküm ile üretilir. Bu işlemlerin uygulanması,katılaşma mikroyapısını değiştirebilmesine rağmendöküm sırasında elde edilen yapı,malzemedeki kimyasal ve morfolojik dağılımda belirleyici bir rol oynamaktadır. Malzeme özellikleri, malzemenin mikroyapısal niteliklerininyanı sıra bu dağılımlara oldukça bağımlıdır. Bu nedenle, katılaşma sırasında gerçekleşen mikroyapı evriminin araştırılması çok önemlidir. Yeryüzünde yapılan deneylerde, katılaştırma sırasında sıvıda oluşan konveksiyonu engellemek ve kantitatif sonuçlar elde edebilmek için, iki boyutlu (2B), yani kalınlığı μm mertebesinde olan numunelerkullanılmalıdır. Fakat, endüstride kullanılan döküm parçalarının duvar kalınlığı en az mm seviyelerindedir. Üç boyutlu (3B)numunelerde katılaşma sürecinin temellerini anlamak ve deneysel parametrelerin mikroyapı seçimi üzerindeki doğrudan etkisini incelemek için deneyler mikrogravite koşullarında gerçekleştirilmiştir. Bu makalede, Uluslararası Uzay İstasyonu’nda gerçekleştirilen bu mikrogravite deneylerinin ve yeryüzünde Mikroyapı Evrim Laboratuvarı'nda yapılan deneylerin detayları verilmiştir. Ekolarak, μg ve 1g deneylerinin amaçları özetlenmiştir.Publication Metadata only Dislocation activities in aluminum alloyed Hadfield steels(N/A, 2008) Şehitoğlu, Hüseyin; Department of Mechanical Engineering; Department of Mechanical Engineering; Canadinç, Demircan; Faculty Member; College of Engineering; 23433The work presented herein investigates the unusual strain hardening prevalent in Hadfield steel, which has not yet been linked to a clear cause, yet. The methodology adopted in this study is suppressing one of the dominant deformation mechanisms interactively dictating the work hardening of Hadfield steel, namely twinning and slip, and concentrating on the other. To achieve this end, Hadfield steel was alloyed with aluminium to increase the stacking fault energy, and thereby suppress twinning and give way to slip only. As a result of the thorough mechanical and micro structural analyses, we have concluded that the slip-related dislocation activities and the high-density dislocation walls brought about by slip in Hadfield steel significantly contribute to the work hardening of this material. / Öz: Bu çalışma, uzun bir süredir araştırılmasına rağmen, Hadfield çeliğinin henüz sebebi kesin olarak ortaya konulamayan olağan dışı sertleşme kapasitesine ışık tutmak amacıyla probleme değişik bir açıdan yaklaşmaktadır. Şimdiye kadar bu sertleşmenin sebebi olarak öne sürülen ve sertleşmeye olan katkıları birbirinden ayırt edilmesi güç olan ikiz ve kayma mekanizmalarından birini bastırarak diğerini inceleme yoluna gidilmiştir. Hadfield çeliği alüminyum ile alaşımlanarak dizim hatası enerji eşiği yükseltilmiş ve kayma mekanizmasının baskın olması sağlanmıştır. Yürütülen kapsamlı deneysel ve nümerik analizler sonucu varılan sonuç, aykırı yerleşim aktivitelerinin ve bunun doğal bir sonucu olan yüksek yoğunluklu aykırı yerleşim duvarlarının, Hadfield çeliğinin sertleşmesinde büyük katkı sahibi olduğunu ortaya koymuştur.Publication Metadata only Effect of modified blalock-taussig shunt anastomosis angle and pulmonary artery diameter on pulmonary flow(Turkish Society of Cardiology, 2018) Arnaz, Ahmet; Yalçınbas, Yusuf; Sarioglu, Tayyar; Department of Mechanical Engineering; Department of Mechanical Engineering; N/A; Department of Mechanical Engineering; Pişkin, Şenol; Pekkan, Kerem; Oğuz, Gökçe Nur; Researcher; Faculty Member; PhD Student; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; 148702; 161845; N/AObjective: This study aimed to identify the best graft-to-pulmonary artery (PA) anastomosis angle measuring pulmonary blood flow, wall shear stress (WSS), and shunt flow. Methods: A tetralogy of Fallot with pulmonary atresia computer model was used to study three different modified Blalock-Taussig shunt (mBTS) anastomosis angle configurations with three different PA diameter configurations. Velocity and WSS were analyzed, and the flow rates at the right PA (RPA) and left PA (LPA) were calculated. Results: A 4-mm and 8-mm diameter of RPA and LPA, respectively with vertical shunt angle produces the highest total flow. In the RPA larger diameter than the LPA configutations, the left-leaning shunt produces the lowest total PA flow whereas in the LPA larger diameter than the RPA configuratios, the right-leaning shunt produces the lowest total PA flow. Therefore, the shunt anastomosis should not be leaned through the narrow side of PA to reach best flow. As the flow inside the shunt increased, WSS also increased due to enhanced velocity gradients. Conclusion: The anastomosis angle between the conduit and PA affects the flow to PA. Vertical anastomosis configurations increase the total PA flow; thus, these configurations are preferable than the leaned configurations.Publication Metadata only Hybrid rocket engine test facility design(Milli Savunma Üniversitesi Hava Harp Okulu, 2016) Samur, Ali Emre; Hacıoğlu, Abdurrahman; Department of Mechanical Engineering; Department of Mechanical Engineering; Karabeyoğlu, Mustafa Arif; Faculty Member; College of Engineering; 114595Hybrid rocket engines is relatively less researched subject of chemical rockets. Using fuel and oxidizer in different phases hybrids are safe and cheap. Yet, they are not generating enogh thrust to deliver heavy payloads to edge of space. Continuing researches on low regression rates, combustion instabilities and propellant diversity would carry this very subject to space. In this essay, a lab-scale hybrid rocket engine is designed and performance calculations of this design is executed. As an interdisciplinary study, hybrid facility’s engine components are detail-designed, other components are explained as an input. PMMA and gaseous oxygen are chosen as fuel and oxidizer respectively due to their ease of availability and low-cost. Axial flow hybrid motor with a single injector is examined, including single port fuel grain. With the addition of DAQ sub-system, it would be available to record instant pressure and temperature values to study on. The main components of DAQ sub-system are included in related chapter. / Hibrit yakıtlı roket motorları, kimyasal roket motorlarının görece az araştırılmış alanıdır. Kullandıkları yakıt ve oksitleyiciler farklı formlarda olduğu için emniyetli ve ucuzdurlar. Ancak büyük ölçekli yükleri uzay ortamına taşıyacak kadar yüksek itki seviyelerine henüz ulaşmamışlardır. Düşük yanma hızı, yanma kararsızlıkları, yakıt çeşitleri gibi alanlarda yapılacak gelişmeler ile giderek artan uzay araştırmalarında yerini alacaktır. Bu makalede laboratuar şartlarında çalıştırılacak bir hibrit roket motorunun tasarımı ve bu tasarıma esas hesaplamaları yapılmıştır. Disiplinlerarası bir çalışma gerektiren bu tasarımda motor bloğu detaylı olarak tasarlanmış, diğer bileşenleri ise tasarıma yönelik açıklanmıştır. Kolay bulunurluk ve ekonomik oluşları nedeniyle yakıt olarak PMMA, oksitleyici olarak da gaz oksijen seçilmiştir. Eksenel akışlı hibrit motorda tek nokta enjeksiyon ile tek silindirik portlu yakıt çekirdeği incelenmiştir. Veri toplama düzeneğinin de sisteme dahil edilmesi ile motor üzerinden anlık sıcaklık ve basınç bilgileri alınarak çalışmalara esas değerler kayıt altında alınabilir. Veri toplama düzeneğine ait ana bileşenler ilgili bölümde açıklanmıştır. Hibrit motor bileşenleri, ana oksitleyici sistemi, ateşleme sistemi ve veri toplama sistemi elemanları incelenmiştir. Yapılan hesaplamalara göre şekillenen motor, yapılabilirlik açısından piyasada hazır bulunan ürünlerle uyumlu olacak şekilde kurgulanmıştır. Halihazırda ülkemizde üzerinde çalışma yapılabilecek kurulu bir hibrit roket motoru test düzeneği bulunmamaktadır. Bu tezde motor bloğunun detay, tüm sistemin ise kavramsal tasarımı yapılmıştır. İhtiyaç duyulan fon ve uygun çalışma takviminin sağlanması durumunda bu tasarım gerçeklenerek ülkemizin ilk hibrit roket motoru test düzeneği olarak yerini alabilir.Publication Metadata only Intraoperative fluoroscopic safety assessment of femoral head implants with 3-dimensional risk parameters to minimize cut-out(Turkish Assoc Orthopaedics Traumatology, 2023) Department of Mechanical Engineering; Department of Mechanical Engineering; Subaşı, Ömer; Aslan, Lercan; Oral, Atacan; Demirhan, Mehmet; Seyahi, Aksel; Lazoğlu, İsmail; Manufacturing and Automation Research Center (MARC); Graduate School of Sciences and Engineering; School of Medicine; College of EngineeringObjective: This study aimed to introduce a method to extract the 3-dimensional spatial position of the femoral head implant from 2-dimensional fluoroscopic projections, allowing surgeons to assess fixation much more accurately and prevent cut-out complications in proximal femoral nailing. Methods: To define a safety region for the tip in the femoral head, a novel 3-dimensional distance-based risk parameter called TSD3D was introduced. An intersection algorithm was developed that solely takes the fluoroscopic anteroposterior and lateral distances to reveal the 3-dimensional location of the screw or Kirschner wire tip, enabling the utilization of the 3-dimensional parameter. Orthogonal perspectives of 6 femur proximal bone substitutes with randomly inserted Kirschner wires were imaged under fluoroscopy. The developed algorithm was used to calculate the implant tip location in 3-dimensional from 2-dimensional images for each case. Algorithm accuracy was validated with the computed tomography-obtained 3-dimensional models of the same femur substitutes. Results: The newly introduced risk parameter successfully visualizes 3-dimensional safety regions. Utilizing the 2-dimensional fluoroscopic distances as inputs to the algorithm, the 3-dimensional position of the implanted Kirschner wire tip is calculated with a maximum of 9.8% error for a single Cartesian-coordinate measurement comparison. Conclusion: By incorporating the newly introduced 3-dimensional risk parameter, surgeons can more precisely evaluate the position of the implant and avoid cut-out complications, instead of relying solely on misleading 2-dimensional fluoroscopic projections of the femoral head.Publication Open Access Single-center experience with routine clinical use of 3D technologies in surgical planning for pediatric patients with complex congenital heart disease(Aves, 2021) Yıldız, Okan; Köse, Banu; Güzeltaş, Alper; Haydin, Sertaç; Department of Mechanical Engineering; Department of Mechanical Engineering; Pekkan, Kerem; Faculty Member; College of Engineering; 161845Purpose: this study was planned to assess the application of three-dimensional (3D) cardiac modeling in preoperative evaluation for complex congenital heart surgeries. Methods: from July 2015 to September 2019, 18 children diagnosed with complex congenital heart diseases (CHDs) were enrolled in this study (double outlet right ventricle in nine patients, complex types of transposition of the great arteries in six patients, congenitally corrected transposition of the great arteries in two patients, and univentricular heart in one patient). The patients' age ranged from 7 months to 19 years (median age, 14 months). Before the operation, 3D patient-specific cardiac models were created based on computed tomography (CT) data. Using each patient's data, a virtual computer model (3D mesh) and stereolithographic (SLA) file that would be printed as a 3D model were generated. These 3D cardiac models were used to gather additional data about cardiac anatomy for presurgical decision-making. Results: all 18 patients successfully underwent surgeries, and there were no mortalities. The 3D patient-specific cardiac models led to a change from the initial surgical plans in 6 of 18 cases (33%), and biventricular repair was considered feasible. Moreover, the models helped to modify the planned biventricular repair in five cases, for left ventricular outflow tract obstruction removal and ventricular septal defect enlargement. 3D cardiac models enable pediatric cardiologists to better understand the spatial relationships between the ventricular septal defect and great vessels, and they help surgeons identify risk structures more clearly for detailed planning of surgery. There was a strong correlation between the models of the patients and the anatomy encountered during the operation. Conclusion: 3D cardiac models accurately reveal the patient's anatomy in detail and are therefore beneficial for planning surgery in patients with complex intracardiac anatomy.