Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
Browse
37 results
Filters
Settings
Search Results
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: 3Boşluk İletim Tabakasız ve Esnek Organo Kurşun İyodür Perovskit Güneş Hücresinin Çevresel Etki Değerlendirmesi(Gazi Üniversitesi, 2022) Sarıaltın, HüseyinPerovskit güneş pilleri (PSC) esneklik ve düşük maliyetli rulodan ruloya üretim gibi avantajlarla birlikte son zamanlarda güç dönüşüm verimliliğinde de önemli bir ilerleme kat etmiştir. PSC'lerin ticarileştirilmesinden önce çevresel performansının yaşam döngüsü değerlendirme (LCA) yöntemi ile araştırılması önemlidir. Bu çalışmada, literatür verilerinden istifade edilerek, esnek Polietilen tereftalat (PET) alt tabaka ve boşluk iletim katmanı (HTL) eliminasyonunu içeren çözelti bazlı organo-kurşun iyodür perovskit güneş hücresinin beşikten kapıya yaşam döngüsü analizi (LCA) gerçekleştirilmiştir. 1 m2 hücre alanı üretiminden kaynaklanan çevresel etkiler altı Uluslararası Referans Yaşam Döngüsü Veri Sistemi (ILCD) kategorisinde belirlenmiştir. Analizin sonucunda, en fazla etki değerinin yüksek elektrik enerjisi tüketimine sahip vakum biriktirme işlemi gereksinimine sahip olan alüminyum metal elektrot tabakasının imalatından kaynaklandığı bulunmuştur. Ticari fotovoltaik teknolojilerle karşılaştırma yapabilmek için en yaygın kullanılan çevresel göstergelerden birisi olan küresel ısınma potansiyeli (GWP), birim kWh elektrik üretimi için hesaplanmıştır. Buna göre, bu çalışmada incelenen HTL'siz esnek (HFF) PSC'nin ticari PV'lerle rekabetçi GWP değerine ulaşmak için 15-20 yıl cihaz ömrüne ihtiyacı olduğu bulunmuştur.Article Citation - WoS: 2The Effect of the Temperature of Heat Treatment Process and the Concentration and Duration of Acid Leaching on the Size and Crystallinity of Nano-Silica Powders Formed by the Dissociation of Natural Diatom Frustule(American Scientific Publishers, 2022) Ülker, Sevkan; Güden, MustafaThe present study focused on the processing of nano-silica powders in varying sizes and crystallinities through IP: 846247.10 On: Wed, 14 Dec 2022 07:29:25 heat treatment (900-1200 degrees C), hydrofluoric acid leaching (1-7 N), and ball milling (1 h, 500 rpm) of natural Copyright American Scentfic P blishers diatom frustules. The starting natural frustules were determined to be composed of amorphous silica (88%) Delivered by Ingenta and quartz. The partially ordered crystalline low-quartz and or precursor to low-cristobalite started to form at-900 degrees C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 degrees C to 46% at 1200 degrees C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6-13.7 mu m to 7.2-6.7 mu m, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, a ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774-547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling.Article Citation - WoS: 1Citation - Scopus: 1Design of Demountable Reciprocal Frames With New Geometric Properties(Int. Association for Shell and Spatial Structures, 2022) Özen, Gülçin; Kiper, Gökhan; Korkmaz, KorayThis study aims to develop missing geometric knowledge for demountable reciprocal frames (RF). While designing a demountable RF, one should know the initial, in-process and final form of the RF. These processes require some specific geometric knowledge. There are some deficiencies about geometric properties in the previous studies about demountable RFs. In this study, the positions and the orientations of the nexors are found by using the Denavit-Hartenberg parameters. This information gives where the joints are placed, how they are oriented and take position according to one another. Besides, the influence of engagement length on the fan height and the base edge are analyzed. Thereby one will be able to find out how much space the RF covers with the known base edge. With the geometric knowledge obtained from this study, demountable RFs having different engagement lengths can be produced with the same nexors.Article A Novel Design Method of Deployable Semi-Regular Tessellated Surfaces With Plano-Spherical Units(Int. Association for Shell and Spatial Structures, 2022) Maral, Mesude Oraj; Korkmaz, Koray; Kiper, GökhanThe design of movable systems gives an opportunity to create transformable designs which respond to the environmental, functional, cultural, and aesthetical needs of today's architecture. This paper proposes a method for designing a family of deployable structures which can be applied to semi-regular tessellated planar surfaces such as roofs, walls, and shading devices. The generated modular approach and adaptability provides a wide usage area and various combinations for these designs. The regular convex polygon modules are designed as a network of the triangular units. The triangular unit is designed using Bennett's overconstrained plano-spherical linkage topology. The polygonal modules are assembled to each other in one-uniform semi-regular tessellations. The assembly of adjacent regular convex polygons in each tessellation is examined to find a proper solution for no collision during deployment and to properly fit a surface without any gaps or overlaps in the deployed position. The assembly method for creating 1-DoF deployable surfaces and mobility calculations for a unit, the polygonal modules, and the assemblies are computed, and motion studies are demonstrated with CAD models and exemplified for a square module for motion tests in a prototype.Article Citation - WoS: 2Citation - Scopus: 6Towards Integration of the Finite Element Modeling Technique Into Biomedical Engineering Education(World Scientific Publishing, 2022) Mihçin, Şenay; Çıklaçandır, SametBiomedical engineering (BME) is a multidisciplinary field, resulting in a heavy course load from different fields. We hypothesize that the engineering curriculum be tailored according to the requirements of the BME profession. In this study, we focus on the teaching of the finite element modeling (FEM) technique by redesigning the course to address the needs of the BME profession by some custom-made changes to meet the unmet needs. After the completion of the course, evaluation methods of the students were analyzed and detailed over a survey providing feedback from the students. The surveys were related to the teaching the theory of FEM, the laboratory sessions, and the project sessions. The survey results were evaluated using statistical methods. The Pearson correlation coefficient showed a linear agreement between theoretical and practical sessions indicating efficient blending of skills because of the custom-made changes. The survey analysis showed that the students were in favour of the changes, allowing them to be more resourceful and confident with their skills. The positive results indicate a positive attitude among the students towards their profession. As the course design addresses the needs of the profession allowing students to fit in better, the students might follow their own profession after graduation. A wider follow-up study might be planned next to compare the results between who received tailor-designed courses and those who did not.Article Transdiscal Screw Fixation in L5-S1 Spondylolysis: a Biomechanical Study Transdiscal Screw Fixation in L5-51 Spondylolysis(Bayrakol Medical Publishing, 2021) Aydın, Murat; Bulut, Tuğrul; Güden, Mustafa; Erel, NuriAim: This study aimed to investigate whether the L5-S1 transdiscal screw fixation is biomechanically sufficient against axial loads and the resulting shear forces. Material and Methods: Eighteen fresh calf spines under 1 year of age were used in this study. Two randomly selected spines were used as test materials. The inferior facet and ligamentum flavum were removed in 7 randomly selected spines. In these spines (transdiscal screw group), two transdiscal screws were placed bilaterally between 15 and S1. Tests were performed on the remaining 9 spines, while the spines were initially intact (intact group) and after creating a listhesis model (injury group). The extent of displacement occurring as a result of axial loading was noted in all groups in order to calculate the load-displacement curves. Results: The mean displacement as a result of successive axial loadings of 5000 N was as follows: 3 mm (range: 2.4 - 4 mm) in the intact group, 3.5 mm (range: 3 - 4.5 mm) in the transdiscal screw group and 4.5 mm (range: 3.9 - 5 mm) In the group with injury. The difference was statistically significant (p<0.05). None of the samples exhibited broken screws, screw deformation or dislocation, even in failure tests, in the transdiscal screw group. Discussion: These findings have shown that transdiscal screw fixation can be biomechanically sufficient against the shear forces occurring as a result of axial loading. We believe that this technique can be a good alternative as a fixation method for the L5-S1 spondylolisthesis.Article Citation - WoS: 6Citation - Scopus: 7Human-Robot Interfaces of the Neuroboscope: a Minimally Invasive Endoscopic Pituitary Tumor Surgery Robotic Assistance System(ASME, 2021) Dede, Mehmet İsmet Can; Kiper, Gökhan; Ayav, Tolga; Özdemirel, Barbaros; Tatlıcıoğlu, Enver; Hanalioğlu, Şahin; Işıkay, İlkayEndoscopic endonasal surgery is a commonly practiced minimally invasive neurosurgical operation for the treatment of a wide range of skull base pathologies including pituitary tumors. A common shortcoming of this surgery is the necessity of a third hand when the endoscope has to be handled to allow active use of both hands of the main surgeon. The robot surgery assistant NeuRoboScope system has been developed to take over the endoscope from the main surgeon's hand while providing the surgeon with the necessary means of controlling the location and direction of the endoscope. One of the main novelties of the NeuRoboScope system is its human-robot interface designs which regulate and facilitate the interaction between the surgeon and the robot assistant. The human-robot interaction design of the NeuRoboScope system is investigated in two domains: direct physical interaction (DPI) and master-slave teleoperation (MST). The user study indicating the learning curve and ease of use of the MST is given and this paper is concluded via providing the reader with an outlook of possible new human-robot interfaces for the robot assisted surgery systems.Article Citation - WoS: 3Citation - Scopus: 3Experimental Structural Stiffness Analysis of a Surgical Haptic Master Device Manipulator(American Society of Mechanical Engineers, 2021) Görgülü, İbrahimcan; Dede, Mehmet İsmet Can; Carbone, GiuseppeThis paper deals with haptic devices for master-slave telesurgical applications. Namely, a stiffness model fitting methodology and its fine-tuning are proposed based on experimental results. In particular, the proposed procedure is based on virtual joint structural stiffness modeling to be applied in time-efficient compliance compensation strategies. A specific case study is discussed by referring to the HISS haptic device that has been developed and built at Izmir Institute of Technology. Two different experimental setups are designed for stiffness evaluation tests. Experimental results are discussed to demonstrate their implementation in the proposed methodology for the fine-tuning of stiffness model.Article Citation - WoS: 12Citation - Scopus: 11Inverted Fins for Cooling of a Non-Uniformly Heated Domain(Yıldız Teknik Üniversitesi, 2015) Çetkin, ErdalThis paper shows that the peak temperature of a non-uniformly heated region can be decreased by embedding high-conductivity tree-shaped inserts which is in contact with a heat sink from its stem. The volume fraction of the high-conductivity material is fixed, and so is the volume of the solid region. The length scale of the solid domain is L. Inside there is a cube-shaped region with length scale of 0.1L and heat production 100 times greater than the rest of the domain. The location of this hot spot was varied to uncover how its location affects the peak temperature and the design of inverted fins, i.e. highconductivity tree-shaped inserts. The volume fraction of the high-conductivity tree was varied for number of bifurcation levels of 0, 1 and 2. This showed that increasing the number of the bifurcation levels decreases the peak temperature when the volume fraction decreases. The optimal diameter ratios and optimal bifurcation angles at the each junction level are also documented. Y-shaped trees promise smaller peak temperatures than T-shaped trees. The location of the vascular tree in the z direction also affects the peak temperature when the heat generation is non-uniform. In addition, the peak temperature is minimum when z = 0.65L even though the hot spot is located on z = 0.75L.