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Öğe A Meshless Method Based on Symmetric RBF Collocation for Neutron Diffusion Problems(Polish Acad Sciences Inst Physics, 2019) Tanbay, Tayfun; Ozgener, B.In this study we have worked on the numerical solution of the multigroup neutron diffusion equation with the symmetric radial basis function collocation method. For the spatial approximation of the neutron flux, multiquadric, inverse multiquadric, and Gaussian basis functions are used as the interpolation functions. To test the performance of the method, both external and fission source problems are considered in two-dimensional Cartesian geometry. The effect of the shape parameter on the convergence and stability of the numerical algorithm is also investigated. The results have shown that, when the multiquadric is chosen, the symmetric RBF collocation method converges exponentially, and it is possible to obtain highly accurate multiplication factors and neutron flux distributions with this algorithm.Öğe Assessment of NOx emissions of the Scimitar engine at Mach 5 based on a thermodynamic cycle analysis(Pergamon-Elsevier Science Ltd, 2020) Tanbay, Tayfun; Uca, Muhammed Biqar; Durmayaz, AhmetThe Scimitar engine is a new advanced propulsion system designed to propel the aircraft A2 of the LAPCAT project. It is a hybrid system that utilizes the features of turbofan, ramjet and air-turborocket. Hydrogen and air are used as the fuel and oxidant, respectively, while helium is used to transfer heat from the hot incoming air to the hydrogen in the engine. In this study, we present a thermodynamic cycle analysis of the Scimitar engine for the assessment of NOx emissions. The combustion of fuel is studied in detail with an equilibrium model taking into account various dissociation and formation reactions since high levels of temperatures are achieved in its combustion chamber. The NOx emissions of the engine at Mach 5 and the effects of fuel and air flow rates, cruise speed and altitude on these emissions are presented by solving a nonlinear system of equations formed through our novel thermodynamic model. The results show that the NO emissions of the engine can be diminished significantly by decreasing air flow rate, cruise speed and altitude and by increasing the fuel flow rate. The variations of NO2 emissions with these parameters are similar except the variation with altitude which has an inverse effect as compared to the variation of NO. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Comprehensive Energy and Exergy Analysis of a Pressurized Water Reactor Driven Multi-Stage Flash Desalination Plant(2024) Akyürek, Erdem; Tanbay, TayfunNuclear energy-based seawater desalination is an environmentally friendly freshwater production approach. This study introduces a novel thermodynamic model integrating a pressurized water reactor’s (PWR) secondary cycle with a multi-stage flash (MSF) desalination facility to enhance freshwater production. The impacts of the design and operating conditions on thermal efficiency, utilization factor, gain output ratio, exergy efficiency, coefficient of ecological performance for cogeneration and exergy destruction factor are investigated. Results reveal that a higher live steam temperature and a reheater mass flow rate ratio is preferable for a better nuclear desalination performance. A larger freshwater production capacity is preferable for a better utilization factor, however increasing the capacity tends to decrease thermal efficiency, coefficient of ecological performance for cogeneration and exergy destruction factor. The selection of steam extraction location is important for very large scale plants, and the outlet of moisture separator is determined to be the best option. Parametric analysis shows that plant’s performance can be significantly improved by adjusting the design conditions. Thermal and exergy efficiencies of an optimized plant configuration are 3.01% and 4.70% higher, respectively as compared to a base plant. It is also found that steam generator and MSF unit cause 3.2% and 82% of the total irreversibility rate of PWR’s secondary cycle and MSF facility, respectively, and have the highest irreversibility rates for these sections of the plant.Öğe Energy and exergy analysis of the 1220 MW natural gas-fired Hamitabat combined cycle power plant(2023) Topal, Göksel; Tanbay, TayfunIn this study, the energy and exergy analysis of the 1220 MW Hamitabat combined cycle power plant (CCPP) that was renovated in 2017 with a 520 million € project is carried out. A thermodynamic model is built by applying the conservation of mass and energy principles and operating data are obtained from the plant operators. Exergy analysis is performed with the exergy balance equation to determine the exergy efficiencies and improvement potentials of all components. Also, parametric analyses are carried out to investigate the methods to enhance the performance of the plant. The plant has thermal and exergy efficiencies of 59.70% and 58.52%, respectively and these values are 13.70% and 13.52% higher than the thermal and exergy efficiencies of the original plant, respectively. Results showed that the combustion chamber (CC) has the highest rate of exergy destruction, and it is responsible for 77.61% of the total irreversibilities. The improvement potential of the CC is found to be 67.992 MW, and the prevention of heat loss from CC can increase the thermal and exergy efficiencies of the plant by 3.88% and 3.80%, respectively. Parametric analyses showed that the plant performance can be enhanced by increasing the inlet temperatures of high- and intermediate-pressure turbines, and decreasing the pressures of condenser and high-pressure turbine.Öğe Energy, exergy and ecological analysis and multiobjective optimization of the hydrogen-fueled Scimitar engine with fixed nozzle geometry(Pergamon-Elsevier Science Ltd, 2022) Tanbay, Tayfun; Durmayaz, AhmetIn this study, an energy, exergy and ecological analysis and multiobjective optimization of the Scimitar engine with fixed core nozzle outlet geometry are carried out at hypersonic cruise conditions. A single-objective optimization is performed first, which revealed that overall efficiency and coefficient of ecological performance are maximized with different optimum nozzle outlet areas, and it propounded the need for a multiobjective optimization. The single objective optimization also showed that decreasing the hydrogen fuel mass flow rate and cruise altitude together with increasing the air mass flow rate and cruise speed improve the performance of the engine. Then, the multiobjective optimization is performed with the utopia point method. It is concluded that for fuel and air mass flow rates of 3.99 kg/s and 178.6 kg/s, respectively, and cruise speed and altitude of Ma = 5.2 and 22 km, respectively, the optimum core nozzle outlet area is 4.00 m(2), when equal weight factors are used for overall efficiency and coefficient of ecological performance. A comparison with the base scenario results showed that the overall efficiency has increased from 55.1% to 57.3%, and the engine size is reduced from 5.38 m(2) to 4.00 m(2) with the multiobjective optimization. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Exergy and NOx Emission-Based Ecological Performance Analysis of the Scimitar Engine(Asme, 2020) Tanbay, Tayfun; Durmayaz, AhmetScimitar engine is a hypersonic hybrid engine designed to propel the LAPCAT A2 aircraft. In this study, a novel exergy and NO(x)emission-based ecological performance analysis of the engine is performed. For this purpose, first, a component-based exergy analysis for the cruise phase of the Scimitar engine in air-turborocket mode is performed and the exergy destruction rates of engine components are determined at Mach 5 by the thermodynamic model developed. Then, a novel objective function, the coefficient of emission-based ecological performance (CEEP) is defined as "the propulsive power produced per unit environmentally harmful exhaust gas emission rate," which can be utilized to assess the ecological impact of any jet engine. Finally, the impacts of cruise speed, altitude, and air and fuel mass flow rates on the exergetic and NO(x)emission-based ecological performance of the engine are investigated by the aid of the newly defined CEEP, together with the exergy efficiency and the coefficient of ecological performance. It is found that the combustion chamber is responsible for 57.36% of the overall exergy destruction rate of 123.80 MW at the cruise conditions, and CEEP relatively increases by 13.8% when the hydrogen fuel consumption rate is increased from 3.96 kg/s to 4.17 kg/s. Increasing the cruise speed from Ma = 4.88 to Ma = 5.2 and decreasing the altitude from 25 km to 23 km cause a relative degradation of 12.75% in CEEP.Öğe Fully meshless solution of the one-dimensional multigroup neutron transport equation with the radial basis function collocation method(Pergamon-Elsevier Science Ltd, 2020) Tanbay, Tayfun; Ozgener, B.In this paper a fully meshless method is proposed for the numerical solution of the one-dimensional multigroup neutron transport equation with anisotropic scattering. Both first-order and even-parity forms of the transport equation are studied. The radial basis function collocation method is chosen for the spatial treatment, and Legendre polynomials are used to approximate the angular variable. The selection of the Legendre polynomials instead of discrete ordinates approach resulted with a fully meshless algorithm in both independent variables. Multiquadric is utilized as the radial function. Seven problems are considered to evaluate the performance of the method. The results show that the method converges exponentially, and it is possible to obtain high levels of accuracies for the multiplication factor and neutron flux with a good stability in both spatial and angular domains. For the one-group isotropic benchmark problem, discrete ordinates solutions employing discontinuous linear finite elements for the spatial variable are also provided, and a comparison of the methods revealed that the fully meshless method produced more accurate results than the discrete ordinates-finite element scheme when the shape parameter is properly chosen. (C) 2019 Elsevier Ltd. All rights reserved.Öğe Impact of combustion chamber wall heat loss on the energy, exergy, ecology, NOx emission based performance and multiobjective optimization of the precooled scimitar engine(Pergamon-Elsevier Science Ltd, 2023) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (CEEP) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNOx in CEEP. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency.& COPY; 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Meshless solution of the neutron diffusion equation by the RBF collocation method using optimum shape parameters(Bursa Teknik Üniversitesi, 2019) Tanbay, TayfunThe meshless radial basis function collocation method is an efficient numerical technique for solving partial differential equations. The multiquadric is the most widely utilized radial function for this purpose; but it contains a shape parameter, which has a significant effect on the performance of the method. In this study, the meshless collocation method employing multiquadric as the radial function with optimum shape parameters is applied to the numerical solution of the multigroup neutron diffusion equation. The optimization of the shape parameter is performed by minimizing the Madych-Nelson function. One external and two fission source problems are solved to investigate the performance of the method. The results show that the meshless collocation method with optimized shape parameters yield a high level of accuracy with an exponential convergence rate.Öğe Modelling Road User Perceptions towards Safety, Comfort, and Chaos at Shared Space: The via Maqueda Case Study, Italy(Wiley-Hindawi, 2022) Akgun-Tanbay, Nurten; Campisi, Tiziana; Tanbay, Tayfun; Tesoriere, Giovanni; Dissanayake, DilumThis study aims to investigate the impacts of perception of infrastructure, sociodemographic characteristics, frequency of road use, and road user perception on safety, comfort, and chaos with respect to shared spaces. The case study area was the Via Maqueda, a shared street in Palermo, Italy. A face-to-face survey was conducted and the answers of 200 of the participants, who use three active travel modes, namely, walking, cycling, and micromobility, were analysed. The results obtained from the ordered logit models suggest that one-unit higher perception of infrastructure will increase safety and comfort perceptions for both walking and cycling. Females feel less safe while walking and less comfortable while cycling at shared spaces compared to males. Increasing the age group by one unit will decrease the safety and comfort perceptions for walking. The participants who use the shared spaces more frequently perceive that they feel more comfortable with cycling. Participants, particularly males, find the shared spaces less chaotic for walking when the perception of infrastructure is higher. Regarding the micromobility use at shared spaces, females feel less comfortable compared to males while using micromobility.Öğe Multiobjective optimization of a pressurized water reactor cogeneration plant for nuclear hydrogen production(Elsevier Ltd, 2024) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, energy, exergy, economic analysis and multiobjective optimization of a pressurized water reactor (PWR) nuclear cogeneration plant for hydrogen production through high-temperature steam electrolysis (HTSE) are carried out. HTSE requires energy in the form of both heat and electrical work. A novel parameter, namely the heat/total energy ratio, is defined, and used as a decision variable in optimization. In addition to energy ratio, hydrogen production capacity, reactor thermal power, live steam temperature, reheating mass flow rate ratio, reheating temperature and steam extraction location are considered as the decision variables to simultaneously optimize the thermal efficiency, thermal-to-hydrogen efficiency, utilization factor, exergy efficiency and total revenue of the cogeneration plant. The analysis and optimization focus on the secondary cycle of the PWR and the effects of hydrogen and electricity prices and ambient conditions are also taken into account since these prices have a significant impact on the optimum design. For a hydrogen price of 4 $/kg and an electricity price of 0.1 $/kWh, when equal preference is given to all objective functions, the optimum production capacity is 6.778 kg/s. The energy ratio has an optimum value if the optimization focuses exclusively on the thermal efficiency and total revenue. © 2023 Hydrogen Energy Publications LLCÖğe MULTIOBJECTIVE OPTIMIZATION OF A PWR NUCLEAR COGENERATION PLANT FOR HYDROGEN PRODUCTION(International Association for Hydrogen Energy, IAHE, 2022) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, the multiobjective optimization of a nuclear cogeneration plant for hydrogen production is carried out. The analysis focuses on the secondary cycle of a pressurized water reactor nuclear cogeneration plant providing process heat and electrical energy to a high-temperature steam electrolysis facility. The utopia point method is used to determine the values of heat/electricity energy ratio, hydrogen production capacity, live steam temperature and steam extraction node that yield a compromise optimum solution between thermal efficiency, thermal-to-hydrogen production efficiency, exergy efficiency and utilization factor. For a hydrogen production capacity of 7 kg/s, an energy ratio of 0.0561 results with the best overall performance, while an energy ratio of 0.10 gives the best performance for a capacity of 0.1 kg/s. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.Öğe Numerical Modeling of Photovoltaic Cells with the Meshless Global Radial Basis Function Collocation Method(Mdpi, 2025) Ispir, Murat; Tanbay, TayfunAccurate prediction of photovoltaic performance hinges on resolving the electron density in the P-region and the hole density in the N-region. Motivated by this need, we present a comprehensive assessment of a meshless global radial basis function (RBF) collocation strategy for the steady current continuity equation, covering a one-dimensional two-region P-N junction and a two-dimensional single-region problem. The study employs Gaussian (GA) and generalized multiquadric (GMQ) bases, systematically varying shape parameter and node density, and presents a detailed performance analysis of the meshless method. Results map the accuracy-stability-computation-time landscape: GA achieves faster convergence but over a narrower stability window, whereas GMQ exhibits greater robustness to shape-parameter variation. We identify stability plateaus that preserve accuracy without severe ill-conditioning and quantify the runtime growth inherent to dense global collocation. A utopia-point multi-objective optimization balances error and computation time to yield practical node-count guidance; for the two-dimensional case with equal weighting, an optimum of 19 intervals per side emerges, largely insensitive to the RBF choice. Collectively, the results establish global RBF collocation as a meshless, accurate, and systematically optimizable alternative to conventional mesh-based solvers for high-fidelity carrier-density prediction in P-N junctions, thereby enabling more reliable performance analysis and design of photovoltaic devices.Öğe Numerical modelling of groundwater radionuclide transport with finite difference-based method of lines(Springer, 2023) Tanbay, Tayfun; Durmayaz, AhmetIn this study, the advection-dispersion equation with decay is numerically solved by the finite difference-based method of lines (FD-MOL) to simulate groundwater radionuclide transport. Finite difference orders of 1,2,.,8 are used for spatial approximation, while the linearly implicit Euler scheme is employed adaptively for temporal discretization. Four different problems are investigated, and results show that FD-MOL provides accurate and stable numerical solutions. Coarse temporal grids can be utilized implicitly, for instance, a maximum step of 1000 years with 400 spatial nodes yields RMS errors of 7.508 x 10(-6), 7.395 x10(-5) and 7.705 x10(-6) in (234) (92) U, (230) (90) Th and (226) (88) Ra normalized concentrations, respectively, for the decay chain problem.Öğe On the Accuracy and Stability of the Meshless RBF Collocation Method for Neutron Diffusion Calculations(Bursa Teknik Üniversitesi, 2018) Tanbay, TayfunAccuracy and stability are the main properties that make an algorithm preferable to its counterparts in modelling of physical phenomena. The radial basis function collocation method is a novel meshless technique, which exhibits an exponential convergence rate for the numerical solution of partial differential equations. However, it is a global approximation scheme and the ill-conditioning of the collocation matrix may become a serious issue if dense sets of interpolation nodes or high values of shape parameters are utilized. This study discusses four strategies to improve the accuracy and stability of the radial basis function collocation method for the numerical solution of the multigroup neutron diffusion equation. These strategies include using a higher precision value for computations, utilizing higher exponents for the generalized multiquadric, decreasing the value of the shape parameter with the number of nodes and singular value decomposition filtering. The results have shown that by using a higher precision value, choosing a variable shape parameter strategy and filtering the smallest singular values of the collocation matrix it is possible to improve the performance of the meshless collocation method, while increasing the exponent of the multiquadric results in a more accurate but less stable algorithm.Öğe PARALLEL MESHLESS RADIAL BASIS FUNCTION COLLOCATION METHOD FOR NEUTRON DIFFUSION PROBLEMS(2024) Tanbay, TayfunThe meshless global radial basis function (RBF) collocation method is widely used to model physical phenomena in science and engineering. The method produces highly accurate solutions with an exponential convergence rate. However, due to the global approximation structure of the method, dense node distributions lead to long computation times and hinder the applicability of the technique. In order to overcome this issue, this study proposes a parallel meshless global RBF collocation algorithm. The algorithm is applied to 2-D neutron diffusion problems. The multiquadric is used as the RBF. The algorithm is developed with Mathematica and eight virtual processors are used in calculations on a multicore computer with four physical cores. The method provides accurate numerical results in a stable manner. Parallel speedup increases with the number of processors up to five and seven processors for external and fission source problems, respectively. The speedup values are limited by the constrained resource sharing of the multicore computer’s memory. On the other hand, significant time savings are achieved with parallel computation. For the four-group fission source problem, when 4316 interpolation nodes are employed, the utilization of seven processors instead of sequential computation decreases the computation time of the meshless approach by 716 s.
