Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 2Citation - Scopus: 2Vibration Analysis and Optimal Design of Multiscale Hybrid Flax Fiber/ Graphene Nanoplatelets Reinforced Laminates Using Modified Differential Evolution Algorithm(Elsevier Sci Ltd, 2025) Ayakdas, Ozan; Artem, Hatice Seçil; Artem, H. Secil; Savran, Melih; Aydin, Levent; Adali, SarpOne of the relatively recent developments in composites is using different material combinations and nano-scale reinforcements such as Graphene Nanoplatelets (GPLs) to develop hybrid fiber composites. A further development is the use of natural flax fiber in composites in response to a growing demand over the past few decades for affordable, lightweight, and environmentally-friendly materials. In order to meet this growing demand, in the present study composites based on graphene nanoplatelets and flax fibers are investigated considering their weight, cost, and natural frequency implications. Furthermore, the Modified Differential Evolution (MDE) algorithm is implemented for the optimum design problems involving the stacking sequences and weight fractions of GPLs in each layer. For the optimal design problems, natural frequency is defined as the objective function with the design variables specified as the orientations of flax fibers and the weight contents of GPLs in each layer. The effective material properties are computed based on Halpin-Tsai and the rule of mixture formulations. Navier solution approach is implemented to solve the eigenvalue problems with the stiffness matrix based on the Firstorder Shear Deformation Theory (FSDT). Optimal designs based on flax fibers, optimal GPL contents, and stacking sequences lead to efficient and environmentally-friendly composite plates. Optimum multiscale hybrid nanocomposite designs include high natural frequency, light weight, and cost-effectiveness compared to conventional carbon and glass fibers reinforced equivalents.Article Citation - WoS: 1Citation - Scopus: 1Experimental Investigation of Naca 4415 Airfoil Using Vibration Data for Stall Detection(Emerald Group Publishing, 2023) Ayaz Ümütlü, Hatice Cansu; Kıral, Zeki; Karadeniz, Ziya HaktanPurposeThe purpose of this study is to identify the possible relation between the vibration and the stall by using the vibration response of the airfoil. For this purpose, the root mean square values of the acceleration signals are evaluated to demonstrate the compatibility between the stall angles and the vibration levels. Design/methodology/approachAn experimental study is conducted on NACA 4415 airfoil at Reynolds numbers 69e3, 77e3 and 85e3. Experiments are performed from 0 & DEG; to 25 & DEG; of the angles of attack (AoA) for each Reynolds number condition. To observe the change of the vibration values at the stall region clearly, experiments are performed with the AoA ranging from 10 & DEG; to 25 & DEG; in 1 & DEG; increments. Three acceleration sensors are used to obtain the vibration data. FindingsThe results show that the increase in the amplitude of the vibration is directly related to the decrease in lift. These findings indicate that this approach could be beneficial in detecting stall on airfoil-type structures. Originality/valueThis study proposes a new approach for detecting stall over the airfoil using the vibration data.Article Citation - WoS: 4Citation - Scopus: 4Seismic Vulnerability Assessment of an Unanchored Circular Storage Tank Against Elephant's Foot Buckling(Springer, 2022) Bektaş, Nurullah; Aktaş, EnginPurpose Seismic vulnerability assessment of liquid containing storage tanks is the most vital relevance for industrial plants and society safety to endure damage during impending earthquakes. Because such systems also play an essential role in the public lifeline and also ensure continued use in emergencies. Furthermore, considering that the material contained in individual plants could be hazardous, requisite precautions have paramount importance against undesired leakage. The high internal pressure and axial forces exerted by the liquid in the steel tanks near the tank wall bottom produce elastic-plastic buckling, also known as Elephant's Foot Buckling (EFB). As far as the authors are aware, no study has been carried out that involves a critical assessment and comparison of IDA and truncated IDA-based EFB failure criterion. This study provides insight into incremental dynamic analysis (IDA) and truncated IDA-based seismic evaluation of cylindrical unanchored steel storage tanks by employing a developed pressure-based surrogate modeling approach. For this purpose, probability-based seismic assessment of a representative sample is considered based on IDA and truncated IDA approaches to identify the potential of the EFB failure and to explore potential enhancements in the sophisticated structural analysis model to prevent the hazardous effects of impending earthquakes. Methods Due to the significance of industrial plants for public safety and benefit, the structural response evaluation methods for different types of storage tanks have been widely reported. In the literature, the most comprehensive analytical assessment methodology is the IDA approach, in which nonlinear time-history analyses are considered in the finite element analysis model to assess the structural model's seismic performance. Results To generate fragility curves, both IDA approaches are employed, taking into consideration and ignoring uncertainty of material properties. The values of the two methods-based fragility curves approach each other as the magnitude of dispersion increases. Conclusion The two fragility curves give the probability of failures close to each other as the dispersion amount increases while considering the uncertainty of the material properties. In addition, fragility curves generated based on the truncated IDA have been found to give a higher probability of failure, up to 32.5 percent. When compared to the IDA-based fragility curves, the truncated IDA-based fragility curves were found to be on the conservative side.Article Citation - WoS: 5Citation - Scopus: 5Low Magnitude High Frequency Vibrations Expedite the Osteogenesis of Bone Marrow Stem Cells on Paper Based 3d Scaffolds(Springer, 2020) Karadaş, Özge; Meşe, Gülistan; Özçivici, EnginAnabolic effects of low magnitude high frequency (LMHF) vibrations on bone tissue were consistently shown in the literature in vivo, however in vitro efforts to elucidate underlying mechanisms are generally limited to 2D cell culture studies. Three dimensional cell culture platforms better mimic the natural microenvironment and biological processes usually differ in 3D compared to 2D culture. In this study, we used laboratory grade filter paper as a scaffold material for studying the effects of LHMF vibrations on osteogenesis of bone marrow mesenchymal stem cells in a 3D system. LMHF vibrations were applied 15 min/day at 0.1 g acceleration and 90 Hz frequency for 21 days to residing cells under quiescent and osteogenic conditions. mRNA expression analysis was performed for alkaline phosphatase (ALP) and osteocalcin (OCN) genes, Alizarin red S staining was performed for mineral nodule formation and infrared spectroscopy was performed for determination of extracellular matrix composition. The highest osteocalcin expression, mineral nodule formation and the phosphate bands arising from the inorganic phase was observed for the cells incubated in osteogenic induction medium with vibration. Our results showed that filter paper can be used as a model scaffold system for studying the effects of mechanical loads on cells, and LMHF vibrations induced the osteogenic differentiation of stem cells.