DSpace@ATÜ (Adana Alparslan Türkeş Bilim ve Teknoloji Universiti)
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A Study on the Production of Riblet Patterns Providing Micro-scale Flow Control through FDM-type 3D Printers
No full textThis study explores the Fused Deposition Modeling (FDM) additive manufacturing method as a practical alternative for flow characterization applications critical in aerospace technology. While there are significant studies in the literature on high-budget FDM devices for manufacturing high-dimensional consistency parts, research focusing on sub-millimeter riblet geometries using more accessible, practical, and flexible open-source devices remains limited. In this study, a printer that can be mechanically and programmatically modified was used to create parallel riblet patterns resembling wing structures on plates. Microscopic examinations and measurements were conducted on these riblets to address encountered issues. Observations revealed that hardware elements such as nozzle-table distance and nozzle circularity are crucial for homogeneous material extrusion. Additionally, it was observed that software-defined parameters like line width and flow rate significantly affect riblet dimensions. Particularly in experiments involving calibration of these parameters in open-source concept devices, riblet width, inter-riblet spacing, and riblet height were achieved with a high accuracy error rate of up to 1.83%, 1.33%, and 0.19%, respectively. Consequently, this study demonstrated the feasibility of producing riblets in this size and precision using widely available, cost-effective, and customizable FDM devices. Considering the significance of riblet structures in aerospace industries for flow control and surface modifications, this research aims to provide critical insights for the practical and effective production of more complex surface profiles in research and development activities
Investigation of the effect of geometric irregularities on capacity of traffic circles by using partial least squares regression method
No full textThis paper examined the impact of geometric irregularities on the intersection capacity at traffic circles. A new empirical capacity relation was proposed to predict the capacity of the traffic circles as a function of geometric elements, exit and circulating flows. Within this scope, first, the relationship between the vehicles entering from the minor approach and the circulating flow from the turning movement in the traffic circle was examined based on the K-Means cluster analysis method. The analysis was created in accordance with an exponential relationship between entry and circulating flow. Second, two clusters were selected by the partial least squares regression method to improve the model's effectiveness. Lastly, to validate the model, leave-one-out cross-validation was used to select the components that maximize the model's predictive ability. The results show that geometric parameters of a traffic circle create different effects on capacity, especially in different circulating flow conditions
Sustainable fabrication of lightweight geopolymer foams from silica-fume and zeolite tuffs: Utilizing Al as foaming agent for thermal insulation
No full textIn response to the increasing demand for eco-friendly thermal insulation materials in construction, this research focuses on the development of geopolymer foams with optimized thermal insulation properties. The study employs silica fume and zeolite tuff as primary raw materials, activated by sodium hydroxide and sodium silicate solution, and incorporates aluminum powder and sodium lauryl sulfate (SLS) as additives to enhance porosity and refine pore size distribution. A comprehensive analysis of technical properties, including compressive strength, porosity, bulk density, and thermal conductivity, is conducted to assess the influence of these additives. The findings demonstrate that SLS plays a main role in modifying the microstructure, resulting in more uniform and interconnected pores. The addition of moderate amounts of SLS (0.9 wt%) promotes the formation of consistent cell sizes and porosity, contributing to the overall structural integrity of the foams. The foams are predominantly amorphous, with some residual crystalline phases observed. Scanning electron microscopy (SEM) reveals the development of sodium aluminum silicate whiskers, which serve as reinforcement, enhancing the mechanical strength of the geopolymer matrix. The resulting geopolymer foams exhibit high porosity (64.36–81.32 %), low thermal conductivity (0.29–0.07 W/m·K), and sufficient compressive strength (0.96–2.71 MPa), indicating their potential as sustainable insulation materials for construction applications. © 2024 The Author
FARKLI GÖZENEKLİLİK VE AÇI DEĞERLERİNE SAHİP GEÇİRGEN AYIRICI PLAKA İLE DAİRESEL BİR SİLİNDİRİN AKIŞ KONTROLÜ
No full textFlow control of bluff bodies has been studied extensively to eliminate adverse effects of wake flow such as vibration and acoustic noise or resonance. The circular cylinder has been studied as the bluff body since it is basic geometry and has been used in engineering applications such as heat exchanger tubes, power transmission lines, chimney stacks, bridges, radio telescopes, power lines, offshore drilling rigs etc. In this study, a permeable splitter plate was located at various downstream locations to control the wake flow of the cylinder. All experiments were carried out in a large-scale closed-loop water channel in the Fluid Mechanics Laboratory at Cukurova University. PIV was used to measure the instantaneous velocity vector field in the wake region of the cylinder at Reynolds number Re=5000, which is based on the cylinder diameter, D. Four different splitter plate angle values (0 =0 degrees; 15 degrees; 30 degrees; 45 degrees), three different porosity values (epsilon=0.30; 0.50; 0.70) were investigated. The porosity (epsilon) of the separator plates is defined as the ratio of the total hole area to the plate surface area. All lengths are nondimensionalized by dividing by the cylinder diameter and shown with the * index. The splitter plate length kept to constant during the experiment as ls*=1. The distance between the leading edge of the splitter plate and the cylinder (lg*) is variable due to the rotation of the separator plate at certain angles in the flow direction. To overcome this, the distance between the splitter plate rotation axis and the cylinder was taken as a parameter and shown with the **. The gap between splitter plate midpoint and cylinder (lg**) kept to constant during the experiments as lg**=1.5. When the plates are rotated, the cross-section parallel to the flow decreases, which increases the interaction between the boundary layers. Since the permeable separator plates prevent the interaction of the boundary layers formed in the flow around the cylinder, the effect of the permeable separator plates increases in the downstream regions where the interaction of the boundary layers increases. Thus, the fluctuations are reduced, and a more stabilized trail flow occurs downstream of the cylinder. It was observed that the vortex formation was delayed with the increase of the separator plate angle. In this study, the effect of the separator plate angle and the effect of the plate permeability were clearly observed
Design and Modelling of Three-Port Bidirectional DC-DC Converter for PV-Battery Integrated DC Microgrid Systems
No full text19th Biennial Baltic Electronics Conference, BEC 2024 -- 2 October 2024 through 4 October 2024 -- Tallinn -- 203964This paper proposes a novel non-isolated bidirectional three-port converter (TPC) based on a KY boost converter and an interleaved boost converter for photovoltaic (PV) powered and battery-buffered systems. The proposed three-port converter integrates ports of the PV array, battery pack and DC microgrid bus bar. Proposed converter is composed of two power switch, an LC filter for battery, boost inductor for PV array and KY boost converter, which is consist of a charge pump capacitor and two series switches. In the proposed converter, the charge pump capacitor and boost inductor provide a voltage gain, thus, the number of series battery cells and PV array can be reduced for a lower cost. On the other hand, a two-control loop scheme has been designed to control power flow between the ports and perform a smooth transition between the loops. To test the effectiveness of the proposed TPC, a MATLAB/Simulink-based simulation model has been developed with a 1 kW PV array, 37 V 10 Ah battery pack and 64 V DC microgrid. The performance of the proposed converter has been analyzed for different case studies and loading conditions. According to the simulation results, 96% peak efficiency of the converter has been achieved and maximum power from PV has been extracted with MPPT mode selection. The results show that the proposed converter has some advantages in terms of the number of switches, multi-loop control, bidirectional power flow, cost and efficiency. © 2024 IEEE
Effects and mechanisms of conifer and broadleaf mixtures on soil characteristics in limestone mountains
No full textIn restoring the limestone mountain ecosystem, the core scientific issue for achieving ecological restoration and ecosystem stability lies in understanding the interaction mechanism between vegetation and soil. To address this, we focused on four types of artificial forest communities, each 30 years old, with varying ratios of coniferous and broad-leaved trees (0%–20%, 20%–50%, 50%–80%, 80%–100%) in typical limestone mountainous areas of the northern subtropical region. These forest communities were selected as research subjects to assess understory vegetation diversity, litter fall, and fine root characteristics. The study investigates the influence of various mixing ratios on the restoration of understory vegetation and soil systems. The findings reveal significant differences in litter fall stock, water capacity, annual decomposition rate, nutrient change rate, and fine root biomass of litter fall among different mixing proportions. With an increase in the proportion of coniferous trees, both standing litter fall and annual yield exhibit a decrease. Consequently, an effective strategy for restoring and enhancing fragile ecosystems in limestone mountainous areas involves establishing mixed forests or conducting forest transformations based on a moderate mixing proportion
Kültürel Mirasın Yeniden Kullanımında Çevresel ve İşlevsel Performansın Kullanıcılar Üzerinden Değerlendirilmesi: Hamamlı Konak Örneği
No full textBu çalışmada, yapım amacı dışında günümüzde yeni işleviyle yaşamını sürdüren bir kültürel mirasın çevresel ve işlevsel performansının belirlenmesi amaçlanmıştır. Özgün işlevini yerine getiremeyen Hamamlı Konak’a verilen yeni işlevin yapı sürdürülebilirliğine etkisinin, yeni kullanıcılarla yapılan anket sonuçlarına dayalı olarak çevresel ve işlevsel performans gibi kullanım süreci kriterleri kapsamında değerlendirilmesi amaçlanmıştır. Araştırmada, günümüzde Büyükşehir Belediyesi KUDEB ofisi olarak kullanılan binanın çevresel ve işlevsel gereksinimlerine, yapının ve mekanların adapte edilebilme düzeyi belirlenerek, yeni işlevin avantaj ve dezavantajlarının ortaya konulması amaçlanmıştır. Yeniden kullanılan binaların işlevsel performanslarının değerlendirilmesi, verilen işlevin sürdürülebilir kılınması için gerekli tedbirlerin alınması anlamında yarar sağlarken, değerlendirme ile yeniden kullanım potansiyeli olan binalarda adaptasyon sürecinde analiz edilmesi gereken bileşenler ve süreç; ulaşım, kentsel odak noktası olması, kentsel mekân oluşumu ve var olan mekânların mevcut işleviyle kullanımının yeterliliği olarak belirlenmiştir
Fast grid search: A grid search-inspired algorithm for optimizing hyperparameters of support vector regression
No full textThis study presents a fast hyperparameter optimization algorithm based on the benefits and shortcomings of the standard grid search (GS) algorithm for support vector regression (SVR). This presented GS -inspired algorithm, called fast grid search (FGS), was tested on benchmark datasets, and the impact of FGS on prediction accuracy was primarily compared with the GS algorithm on which it is based. To validate the efficacy of the proposed algorithm and conduct a comprehensive comparison, two additional hyperparameter optimization techniques, namely particle swarm optimization and Bayesian optimization, were also employed in the development of models on the given datasets. The evaluation of the models' predictive performance was conducted by assessing root mean square error, mean absolute error, and mean absolute percentage error. In addition to these metrics, the number of evaluated submodels and the time required for optimization were used as determinative performance measures of the presented models. Experimental results proved that the FGS-optimized SVR models yield precise performance, supporting the reliability, validity, and applicability of the FGS algorithm. As a result, the FGS algorithm can be offered as a faster alternative in optimizing the hyperparameters of SVR in terms of execution time
Geçiş metali (Mn ve Co) katkılı cds tabanlı fotovoltaik hücrelerin üretimi ve karakterizasyonu
No full textLisansüstü Eğitim Enstitüsü, Malzeme Mühendisliği Ana Bilim DalıBu çalışmada, kimyasal banyo yöntemiyle üretilen, hem Mn (%0.5, %1, %2) hem de Co (%1, %3, %5, %7) ile ayrı ayrı doplanmış CdS ince filmleri, indiyum kalay oksit (ITO) kaplı cam altlık üzerinde üretildi. Ek olarak N719, P3HT:PCBM ve PEDOT:PSS organik katmanları spin kaplama yöntemiyle birbirini takip edecek şekilde uygulanarak istenen cihaz konfigürasyonuna ulaşıldı. Mn ve Co içeren CdS ince filmlerin yanı sıra üretilen güneş hücreleri üzerinde kapsamlı XRD, SEM, EDS, geçirgenlik, absorpsiyon, PL analizleri gerçekleştirildi. Ayrıca üretilen cihazların J-V testleri de araştırıldı. XRD analizi ile üretilen CdS ince filmlerin kübik yapıda büyüdüğü görüldü. Mn atomlarının CdS yapısına eklenmesi, kristal kalitesinde kötüleşmeye işaret eden dislokasyon yoğunluğu ve mikro-gerilim sonuçları yardımıyla tespit edildi. Mn katkısının, CdS filmlerin geçirgenliği üzerinde olumlu bir etkisi olduğu görüldü. Özellikle %2 Mn katkılı CdS örneğinde 500-650 nm dalga boyu aralığında %90'dan fazla geçirgenlik elde edildi. Mn katkısı, CdS'nin yasak enerji bant aralığını artırdığı ve soğurma kenarında maviye doğru bir kayma oluştuğu belirlendi. Üretilen güneş hücrelerinin J-V ölçümlerinden, Mn katkısının CdS tabanlı hibrit güneş hücrelerinin verimliliğini artırdı görüldü. En yüksek güç dönüşüm verimliliğine % 2 Mn-katkılı CdS güneş hücresi ile ulaşıldı (%0.202). Co katkısı ise, CdS'nin birim hücre hacminde değişime ve CdS kristal boyutunda artışa neden oldu. Ayrıca Co katkısı ile CdS ince filmlerin tane boyutunda azalma meydana geldiği görüldü. Co katkısının CdS filmlerin optik geçirgenliğini artırdığı ve yasak enerji bant aralığını değiştirdiği görüldü. Photolüminesans sonuçlarına gelince, Co katkısının CdS filmlerinde ek kusur durumlarına neden olduğu tespit edildi. Co katkısının CdS tabanlı hibrit güneş hücrelerinin verimliliğini olumlu yönde etkilediği ve en yüksek verimlilik değerinin % 1 Co-katkılı CdS güneş pillerinden elde edildiği belirlendi (%0.488).In this study, CdS thin films were produced via chemical bath deposition method, individually doped with Mn (0.5%, 1%, 2%) and Co (1%, 3%, 5%, 7%), on indium tin oxide (ITO) coated glass substrates. Additionally, the desired device configuration was achieved by coating N719, P3HT:PCBM, and PEDOT:PSS organic layers, respectively, using spin coating method. Comprehensive XRD, SEM, EDS, transmittance, absorbance, PL analyses were conducted on both Mn and Co-doped CdS thin films and the fabricated solar cells. Furthermore, J-V tests were performed on the fabricated devices. XRD analysis revealed that the produced CdS thin films grew in a cubic structure. Addition of Mn atoms into CdS structure was determined to deteriorate crystal quality based on dislocation density and micro-strain results. Mn doping led to a positive effect on transparency of CdS films, particularly achieving over 90% transmittance in the wavelength range of 500-650 nm for CdS sample with 2% Mn addition. Mn doping was found to increase forbidden energy band gap of CdS, causing a blue-shift in absorption edge. J-V measurements of the fabricated solar cells indicated that Mn doping improved the efficiency of CdS based hybrid solar cells. Highest power conversion efficiency was achieved with a 2% Mn-doped CdS solar cell (0.202%). On the other hand, Co doping led to a change in the unit cell volume and increase in crystalline size of CdS. Additionally, a reduction in grain size of CdS thin films was observed with Co doping. Co doping was found to enhance optical transparency of CdS films and alter the forbidden energy band gap. Photoluminescence results suggested that Co doping caused additional defect states in CdS films. Furthermore, Co doping positively influenced the efficiency of CdS-based hybrid solar cells, with highest efficiency obtained from solar cells with 1% Co doping (0.488%)
The Effects of Different Drivers' Steering Inputs on the Response of Heavy Ground Vehicles to Crosswind Disturbances
No full textFeatured Application The control, stability, or even safety of a vehicle can be influenced by crosswinds. The findings of the current study can be helpful for the reliable design of ground vehicles with less wind sensitivity early in their development processes. The development of lateral disturbance compensation algorithms and autonomous vehicles can also benefit from the results of the study.Abstract The general approach in the previous studies was to ignore the driver's steering contribution to a vehicle while investigating the interactions between crosswind and vehicle. Therefore, the goal of this study is to find out how steering inputs by drivers affect a heavy-ground vehicle's dynamic reaction to crosswinds. In the investigation, a two-way interaction between vehicle dynamics and aerodynamic simulations was employed. The steering inputs of drivers were modelled using a driver model taken from the previous literature that is able to reproduce the steering responses of a human driver. The study's findings demonstrated that the steering inputs made by drivers significantly impacted how the vehicle responded to crosswinds. For instance, the greatest lateral displacement of the least skilled driver (Driver 1) was around 1.53 times the greatest lateral displacement of the most skilled driver (Driver 3) at the delay time of t delta,delay = 0.5 s in the steering input. Additionally, the maximum lateral displacement results of Driver 1 and Driver 3 at t delta,delay = 1.0 s became 1.39 and 1.56 times greater than their maximum lateral displacement results at t delta,delay = 0.5 s. Similarly, the total steering inputs of Driver 1 and Driver 3 at t delta,delay = 1.0 s were 1.4 and 2.2 times greater than their total steering inputs at t delta,delay = 0.5 s, respectively. In general, the results of a driver who is more skilled than Driver 1 (Driver 2) fall in between the respective results of Driver 1 and Driver 3. On the other hand, each driver's total steering inputs at t delta,delay = 0.5 s were roughly the same as their total steering inputs at t delta,delay = 0 s. In all delay scenarios for the start of the driver's steering inputs, the drivers' steering inputs amplified the yaw moment applied to the vehicle. Meanwhile, they diminished the lateral force and roll moment.Swedish Innovation Agency VinnovaNo Statement Availabl