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    EXPERIMENTS OF VORTEX-INDUCED VIBRATION FOR A SMOOTH CIRCULAR CYLINDER AT MASS RATIOS 3
    (Centre for Applied Ocean Technology, Marine Institute, 2022) Colakoglu, Sukru Cem; Dobrucali, E.; Kükner, Abdi; Duranay, Aytekin; Kinaci, Omer Kemal
    Studies involving vortex-induced vibrations (VIV) are generally conducted in water when the mass ratio is low and in air when it is high. VIV in water gained much attention in the last decade due to the possibility of harnessing hydrokinetic energy and most of the literature on this subject is limited to mass ratios of m* < 2. However, it is known that increasing mass ratio also increases energy harnessing efficiency. In this study, we consider smooth circular cylinders in VIV covering a mass ratio range of 3 < m* < 4 at TrSL3 flow regime. Although studies focusing on this range are not so many, there are considerable discrepancies in results in terms of the amplitude response of the cylinder. Experiments are conducted to allow cross-flow motions while restricting inline vibrations. Our results are discussed in comparison with other experiments published in the literature. We have not observed a correlation between the mass-damping parameter and the maximum amplitudes as previous studies suggest. This is considered to be due to the unreported features of the experimental setups: Cylinder positioning, test section width, and the type of test basin are considered to be affecting the cylinder’s VIV response. Our experiments show that increasing mass ratio narrows down the range of synchronization while the maximum achieved amplitude sails around A* ? 0.9. © Journal of Ocean Technology 2022.
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    The effects of different working fluids on the performance characteristics of the Rankine and Brayton cycles
    (Elsevier Ltd, 2024) Kanberoğlu, Berna; Ozsari, Ibrahim; Dobrucali, E.; Gonca, Guven
    In this study, 143 different working fluids have been analyzed for Rankine and Brayton cycles in terms of performance characteristics such as power, thermal and exergy efficiency, and EFECWOD. The selection of working fluid is a significant consideration in the design of both these cycles, as it can importantly affect the performance and efficiency of the system. As of late, there has been growing interest in investigating the effects of various working fluids on the performance characteristics of these cycles. This article aims to determine the ten best among different working fluids according to the determined criteria using the Technique for Order of Preference by Similarity to Ideal Solution, which is a multi-criteria decision method. In the decision-making process, the importance scale of the analytical hierarchy process was used to determine the weight values of the criteria to be used in the TOPSIS analysis to obtain more accurate results. Artificial Neural Network method is employed to identify the optimal working fluid as well. As a conclusion of this thermodynamic analysis of the performance characteristics for Rankine and Brayton cycles using various working fluids, the Rankine cycle achieved the maximum power of 12,277 kW, the maximum efficiency of 93 %, and the maximum EFECWOD value of 9962 kJ/m3 with hydrogen, helium, and dimethylcarbonate as the respective working fluids. Furthermore, hydrogen exhibits the highest power output of 2493 kW in the Brayton cycle. Nitrogen demonstrates the highest efficiency at 44 %, while R141b achieves the highest exergy efficiency at 98 %. Lastly, the fluid with the highest EFECWOD value is R13, with a measurement of 4932 kJ/m3. © 2023 Hydrogen Energy Publications LLC