Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Yüksek Derecede Kurum Üreten 2b Gazyağı/hava Difüzyon Alevleri Üzerinde Diferansiyel Yayılımın ve Basıncın Etkileri(Gazi Üniversitesi, 2024) Korucu, Ayşe; Miller, RichardBu çalısmada, dört farklı ortam basıncında kurum, oluşum ve yıkım süreçlerini incelemek amacıyla, yoğun kurum üreten Gazyağı/Hava alevleri, gerçek gaz (GG) ve ideal gaz (İG) hal denklemleri ve Lewis (Le) sayısının bir olarak kabul edildiği modeller ele alınmıştır. Yarı-genel kurum oluşum ve yıkım modelini içeren indirgenmiş Gazyağı/Hava mekanizması (29-adım, 10 çeşit gaz) 2 boyutlu (2B) Direk Sayısal Simülasyon (DNS) verilerini oluşturmak için MPI FORTRAN ile kodu yazılmış bir program kullanılmıştır. Le sayısının bire eşit kabul edildiği alev tahminlerinin, Le sayısının bire eşit olmadığı (genelleştirilmiş difüzyon) durumların sayısal sonuçlarından elde edilen alev yapısı ve kurum özelliklerinin istatiksel olarak benzerlik sağlayıp sağlamadığı araştırılmıştır. Bu bağlamda yapılan çalışmanın sonucunda, ortam basınçları 1, 5, 10 ve 35 atm olan Le sayısının bir olarak kabul edildiği GGLE ve İGLE modelleri ile üretilmiş 2B DNS alev tahminlerinin kurum özelliklerinin ve alev yapılarının yanlış hesaplanmasına yol açtığı belirlenmiştir.Review Citation - WoS: 13Citation - Scopus: 13A Review on Battery Thermal Management Strategies in Lithium-Ion and Post-Lithium Batteries for Electric Vehicles(Yıldız Technical University, 2023) Güngör, Şahin; Göçmen, Sinan; Çetkin, ErdalElectrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conven- tional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and struc- ture of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as lay- er degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are doc- umented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries.Article Citation - WoS: 1Citation - Scopus: 2Oluklu alüminyum sandviç panellerde kor yüksekliğinin enerji sönümleme kapasitesine olan etkisi(Gazi Üniversitesi, 2020) Kılıçaslan, Cenk; Güden, MustafaIn this study, energy absorbing capacity of brazed and polyurethane adhesively bonded corrugated aluminum sandwich panels were investigated. In sandwich panels, Al 1050 H14 trapezoidal zig-zag corrugated cores and face and interlayer sheets were used. Each sandwich panel has core orientation of 0 degrees/0 degrees or 0 degrees/90 degrees. The cores used in these panels were smaller, core height is about 3 mm, in contrast to conventional sandwich cores. Impact tests were conducted at 3 and 6 m/s with spherical projectors. Adhesively bonded sandwich panels were also tested at 6 m/s with flat and conical projectors. Numerical models were prepared in LSDYNA to investigated the deformation behavior of cores. Panels tested with flat and conical projectors experienced complete perforation and absorbed more energy at configuration of 0 degrees/0 degrees core orientation. However, panels tested with spherical projectors were not perforated and they absorbed more energy at configuration of 0 degrees/90 degrees core orientation. Energy absorbing capacity of the panels were also compared to the panels having 9 mm height corrugated cores. The results showed that effective collapsing length was seen to increase due to increase in core height and impact energy distributed the whole panel surface more homogenous manner.Article Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article The Effect of Time Delay of Fluid Flow in a Vascularized Plate(MIM Research Group, 2018) Yenigün, Onur; Coşkun, Turgay; Çetkin, ErdalIn this study, we show the effect of time delay of coolant fluid flow into a vascularized plate on the peak temperature. Coolant flows along vascular channels which were embedded in a rectangular plate. Two kinds of vascular channel designs were investigated experimentally: parallel and tree-shaped. In the study, the peak temperatures were monitored and the coolant was pumped when the peak temperature reaches to 50°C, 70°C and 90°C. The performance comparison of two distinct designs is based on two criteria: the time required for the steady state condition after the coolant is pumped and the peak temperature after the steady state condition is conformed. The results show that the time required to reach steady-state condition increases as the time delay increases. The parallel and tree-shaped designs show similar performance (time required to reach steady state) with slightly improved performance in the tree-shaped design as the preset temperature for time delay increases. For instance, 4% decrease in the time required to reach steady-state with the tree-shaped design relative to the parallel design was achieved when the preset temperature for time delay is 90°C.Article Optimum Design of Anti-Buckling Behavior of Graphite/Epoxy Laminated Composites by Differential Evolution and Simulated Annealing Method(MIM Research Group, 2019) Akçaır, Mehmet; Savran, Melih; Aydın, Levent; Ayakdaş, Ozan; Öztürk, Savaş; Küçükdoğan, NilayStacking sequence design and optimization of 64 layered symmetric-balance graphite/epoxy laminated composite have been performed. The optimization problems aim to find the optimum stacking sequence maximizing the critical buckling load by single objective optimization approach. Differential Evolution (DE) and Simulated Annealing (SA) optimization algorithms are proposed to solve the problems. The effect of the aspect ratios (a/b) and in-plane biaxial compressive loading ratios (Nx/Ny) on critical buckling load are investigated. In order to see the effect of discrete increments of fiber orientation angle on critical buckling load, 1°, 5°, 15°, 30° and 45° fiber angle increments are also considered. The results show that (i) the proposed algorithms DE and SA exhibit comparable performance in terms of critical buckling load when compared Genetic algorithm (GA) and Generalized pattern search algorithm (GPSA), (ii) DE and SA find distinct stacking sequence configurations in terms of buckling load for the same laminated structure design problems.Article Optimal Design of the Type Iii Hydrogen Storage Tank for Different Carbon/Epoxy Materials by Modified Differential Evolution Method(MIM Research Group, 2019) Ayakdaş, Ozan; Aydın, Levent; Savran, Melih; Küçükdoğan, Nilay; Öztürk, SavaşIn this study, the main objective is to minimize the failure index of a cylindrical laminated composite hydrogen storage tank under internal pressure. The first step is to obtain the distribution of stress components based on Classical Laminated Plate Theory (CLPT). The second is to evaluate the burst pressure of the tank according to three different first ply failure criteria and then to compare the results with the experimental and numerical ones from literature. In the final part of the study, the best possible combination of winding angles, stacking sequences and thicknesses of laminates satisfying minimum possible stress concentration will be obtained for different Carbon/Epoxy materials by Differential Evolution Method. The stress components and, the burst pressures reached according to Hashin-Rotem, Maximum Stress, and Tsai-Wu first-ply failure criteria, have been complied with experimental and numerical results in the literature for Type III pressure vessels. Manufacturable Type-III tank designs have been proposed satisfying the 35 MPa burst pressure for different Carbon/Epoxy materials.Article Citation - WoS: 3Citation - Scopus: 4The Effect of Cooling on Mechanical and Thermal Stresses in Vascular Structures(Yıldız Teknik Üniversitesi, 2018) Çetkin, ErdalHere, we show how the vascular channel configuration and its shape affect the mechanical strength which is simultaneously subjected to heating and mechanical load. The material properties were defined as functions of temperature. The effect of channel cross-section on the coolant mass flow rate, peak temperature and peak stresses are documented. The results show that the resistances to flow of stresses and fluid is minimum with the circular channels while the resistance to the heat flow is the smallest with semi-circular channels. In addition, morphing the vascular design provides almost the smallest resistance to the heat flow with circular channels (0.3% difference in the peak temperature). This shows that even the convective resistances are the smallest with circular-cross section, overall thermal resistance is smaller in semi-circular design for the fixed fluid volume. The peak stress is smaller with hybrid design than the parallel designs for the entire pressure drop range. In addition, the effects of mechanical load, heating rate and reference temperature on the stress distribution are also documented. Furthermore, the thermal and mechanical stresses are also documented separately, and then compared with the coupled solution cases. The chief result of this paper is that for a coupled system minimizing only one of the resistance terms is not sufficient, all the resistances considered simultaneously in order to uncover the best performing design. In coupled solutions, we documented the simulation results with temperature dependent material properties and the resistances to the heat and fluid flow is affected by the mechanical deformations. In addition, the results show that the designs should be free to vary, the unexpected designs can be the best performing designs for the given parameters and constraints. Therefore, the design parameters based on the experience does not always yield the best performing designs as the objectives and constraints vary.Article Silika Yüzeylerin Islanma Hareketlerinin Moleküler Dinamik ile Modellenmesi(Gazi Üniversitesi, 2018) Barışık, MuratYeni üretim tekniklerine paralel olarak nano-boyutlu teknolojiler çok geniş bir uygulama alanında kullanılmaya başlanmakta ve yeni uygulamalar geliştirmek için keşfedilmesi ve anlaşılması gereken konular süratle artmaktadır. Bu doğrultuda, yeni uygulamalarda sıkça yer bulan silikon ve silikon-dioksitin mikro/nano boyutlardaki malzeme özelliklerinin anlaşılmasına büyük ihtiyaç oluşmaktadır. Özellikle bu yüzeylerin ıslanma hareketlerinin anlaşılabilmesi ve hatta kullanılacak uygulamaya göre ayarlanabilmesi sayısız uygulama için önem arz etmektedir. Bu nedenlerle, nano-teknolojide sıkça kullanılan silikon-dioksit malzemesinin ve su moleküllerinin nano-ölçeklerde moleküler olarak modellenmesi bu çalışmada gerçekleştirildi. Modelleme molekuler dinamik hesaplamaları ile yapıldı. Silikon-dioksit yüzey üzerinde nano su damlacıkları oluşturup, denge halinde oluşan ıslatma açısı ölçümleri yapıldı. Literatürde işlem yükünü azaltmak için sıklıkla uygulanan, katı yüzey termal titreşimlerinin ıslatmaya olan etkisinin ihmal edilmesi ve modellenmemesinin ıslatma açısına olan etkisi incelendi. Katı moleküllerin termal titreşimlerinin ıslatma modellenen ıslatma fiziğine baskın bir etkisi olduğu görüldü. Geçtiğimiz yıllarda doğa taklidi olarak bilinen çalışma çevreleri tarafından hayata geçirilmeye çalışılan Lotus yaprağı etkisi temelli yüzey ıslatma kontrolu moleküler seviyede uygulandı. Yüzey üzerinde oluşturulan nano boyutlardaki yüzey yapılarının ıslanma açısını değiştirebildiği gösterildi. Temiz (0 0 1) silika yüzeyinde nano ölçek çizgi gerilimi etkisi altında ölçülen ıslanma açısının deneysel silika ıslanma açısı aralığında olduğu bulundu.Article Citation - WoS: 7Citation - Scopus: 7The Importance of Internal Heat Gains for Building Cooling Design(Yıldız Teknik Üniversitesi, 2017) Coşkun, Turgay; Turhan, Cihan; Durmuş Arsan, Zeynep; Gökçen Akkurt, GüldenThis paper aims to investigate the effect of internal heat gains on the cooling load of a building. The house occupied by three adult men is selected as the case study for paper. The house is in the third floor of the apartment. The apartment has four flats and it has no insulation around the external walls. The heat dissipation from lighting devices, electrical equipment and the occupants are calculated by using the DesignBuilder v4 Beta release simulation program. The temperature of the house is observed during three weeks by using hobo data loggers and calibration of the measurements is made with respect to weather data file of the flat. Detailed schedule based on time of operation and occupancy is prepared to get more accurate results. Annual energy consumption and cooling load of the house is determined by using the dynamic simulation program.