Browsing by Author "Okbaz, Abdulkerim"

Now showing 1 - 4 of 4

Citation - WoS: 47
Citation - Scopus: 47
A Biocompatible, Eco-Friendly, and High-Performance Triboelectric Nanogenerator Based on Sepiolite, Bentonite, and Kaolin Decorated Chitosan Composite Film
(Elsevier, 2023) Yar, Adem; Okbaz, Abdulkerim; Parlayici, Serife
Recent advancements in triboelectric nanogenerators (TENGs) have primarily focused on improving power conversion and generation efficiency. However, challenges still exist in developing TENGs that are affordable and biocompatible. Chitosan, an abundant natural biopolymer derived from marine crustacean shells, and natural clays offer exciting possibilities for developing cost-effective and biodegradable TENG applications. In this study, we present the development of biocompatible and eco-friendly TENGs by incorporating clay-based compounds as natural fillers into chitosan. To construct chitosan/clay-based biocomposite TENGs, we have introduced sepio-lite, bentonite, and kaolin, as natural additives, into the chitosan biopolymer matrix. Decorating chitosan with natural clays improves the triboelectric properties of the TENGs, which in turn enhances the output voltage and significantly boosts the electric power density. Chitosan-based TENGs with 3 wt% sepiolite, 1 wt% bentonite, and 1 wt% kaolin demonstrate open circuit voltages of 863, 996, and 963 V, respectively. Moreover, when compared to pure chitosan-based TENG, the chitosan-based TENGs with 3 wt% sepiolite, 1 wt% bentonite, and 1 wt% kaolin show a maximum output peak power increase of 19, 54.4, and 32.6%, respectively. At 1.1 M omega load resistance, the maximum peak electric power densities of 20.4, 26.5, and 22.8 W/m2 are reached for chitosan-based TENGs with 3 wt% sepiolite, 1 wt% bentonite, and 1 wt% kaolin, respectively. Furthermore, we analyzed the surface potential, morphology, roughness, and dielectric constant of chitosan/clay composites to understand the relationship between them and electrical performance. The results demonstrate that the output performances of the chitosan/clay-based TENGs are quite high. TENGs made of biocompatible materials may not only pave the way for the production of environmentally friendly, cost-effective, and efficient TENGs for self-powered nano -systems and biomedical devices but may also shed light on new technologies utilizing natural materials.
Citation - WoS: 5
Citation - Scopus: 6
Control of the Flow Past a Sphere Near a Flat Wall Using Passive Jet
(PERGAMON-ELSEVIER SCIENCE LTD, 2019) Okbaz, Abdulkerim; Özgören, Muammer; Doğan, Sercan; Canpolat, Çetin; Akıllı, Hüseyin; Şahin, Beşir
In the present investigation, interactions between the vortices shedding from a single sphere and the boundary layer flow over a flat plate with various gap ratios have been investigated at Re = 5000 using the techniques of dye visualization and Particle Image Velocimetry. A passive jet has been created to control the flow past the sphere by a hole drilled into the sphere from the forward stagnation point to the rear of the sphere with various diameters. The results show that the complex flow downstream of the sphere, which is occurred from the combination of 'Carman vortex street and the boundary layer over the flat plate can be controlled by a passive jet. Because the jet flow interrupts periodicity of the vortices shedding from the sphere by supplying fluid flow into the wake with relatively high velocity. Presence of the hole significantly attenuates the magnitudes of the turbulence characteristics. Furthermore, the magnitudes of the turbulence characteristics decrease with increasing the hole diameter depending on the location of the sphere in the boundary layer. However, a larger hole diameter can result in higher turbulence levels in the region of the passive jet. Hence, the effectiveness of the each case (the diameter of the hole) changes with the location of the sphere over the flat plate.
Machine Learning Based Flow Simulator: Flow Around an Airfoil with Vortex Generators
(Elsevier, 2026) Aksoy, Muharrem Hilmi; Ispir, Murat; Malazi, Mahdi Tabatabaei; Okbaz, Abdulkerim
Controlling the flow structure around an airfoil is crucial for increasing lift and reducing drag. Delaying flow separation improves aerodynamic performance, especially in aircraft and wind turbines. In recent years, artificial intelligence and machine learning methods have emerged as fast and cost-effective alternatives to traditional approaches in fluid mechanics. In this study, we aimed to control the flow around the NACA (National Advisory Committee for Aeronautics) 4412 airfoil using vortex generators (VGs) and to develop a machine-learning-based flow simulator that predicts velocity components based on angle of attack, VG yaw angle, and spatial coordinates. Experimental measurements were conducted in an open-surface, closed-loop water channel at a Reynolds number of Re = 1.0 x 104 using a two-dimensional Particle Image Velocimetry (PIV) system. A total of 60,500 data points were collected per velocity component from 20 experimental cases within the range of alpha = 0 degrees-20 degrees and beta = 15 degrees-30 degrees. A Multilayer Perceptron (MLP) model implemented using TensorFlow was trained to predict the ensemble-averaged (u) and (v) velocity components. We analyzed the effects of hidden layer neuron count and mini-batch size, achieving the highest accuracy with 41 neurons and a batch size of 4, yielding R2 values of 0.978 for (u) and 0.950 for (v). The error distributions were symmetric and closely approximated a Gaussian distribution. Experimental results showed that VGs delayed early-stage flow separation at low alpha but became less effective at higher alpha. The MLP model successfully reconstructed major flow features, providing a reliable data-driven alternative to CFD-based methods. Future work will extend the model to various airfoils, VG designs, Reynolds numbers, and unsteady flows using time-resolved PIV data.
Citation - WoS: 8
Citation - Scopus: 9
Serbest Yüzey ve Bir Küre Art İzi Arasındaki Etkileşimlerin Araştırılması
(2018) Doğan, Sercan; Özgören, Muammer; Okbaz, Abdulkerim; Şahin, Beşir; Akıllı, Hüseyin
Bu çalışma, küre çapına göre tarif edilen Reynolds sayısının 2,5x103 ve 1x104 aralığında farklı daldırma yükseklikleri için açık bir su kanalında serbest su yüzeyi ve kürenin art izi bölgesi arasındaki akış yapısı etkileşimini sunmaktadır. Anlık ve zaman ortalaması alınmış hız alanı, akım çizgisi topolojisi, girdaplar ve hız konturları gibi akış modellerini göstermek için Parçacık Görüntülemeli Hız ölçme (PIV) ve boya görselleştirme teknikleri uygulanmıştır. Küre, serbest yüzeye kısmen daldırılma konumundan serbest yüzeyden iki küre çapı kadar aşağı doğru çeşitli daldırma konumlarına 0,25? h/D ?3,0 aralığında sabitlenmiştir. Daldırma oranı, küre alt kolunun serbest yüzey ile olan mesafesinin küre çapına oranı olarak tanımlanmıştır. Kürenin yerleştirildiği konumlara bağlı olarak, art izi bölgesinin özellikleri üç farklı akış olayı sergilemiştir. Bunlar; daldırma oranı 0,25? h/D ?1,0 aralığı için üniform akış bölgesi ve serbest yüzey arasındaki kısıtlı bir art izi bölgesi, daldırma oranı 1,25? h/D ?2,0 aralığı için serbest yüzey etkisinden dolayı simetrik olmayan akış modelleri ve daldırma oranı 2,5? h/D ?3,0 aralığı için simetrik akış yapıları olarak sınıflandırılmıştır. Akış fiziği açısından bahsedilen akış yapıları için daha detaylı sonuçlar karşılaştırılmalı olarak sunulmuş ve yorumlanmıştır.