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- 저자 : A. Carreno (검색결과 3 건)
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Adaptive time-step control for modal methods to integrate the neutron diffusion equation
Carreno, A.,Vidal-Ferrandiz, A.,Ginestar, D.,Verdu, G. Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2
The solution of the time-dependent neutron diffusion equation can be approximated using quasi-static methods that factorise the neutronic flux as the product of a time dependent function times a shape function that depends both on space and time. A generalization of this technique is the updated modal method. This strategy assumes that the neutron flux can be decomposed into a sum of amplitudes multiplied by some shape functions. These functions, known as modes, come from the solution of the eigenvalue problems associated with the static neutron diffusion equation that are being updated along the transient. In previous works, the time step used to update the modes is set to a fixed value and this implies the need of using small time-steps to obtain accurate results and, consequently, a high computational cost. In this work, we propose the use of an adaptive control time-step that reduces automatically the time-step when the algorithm detects large errors and increases this value when it is not necessary to use small steps. Several strategies to compute the modes updating time step are proposed and their performance is tested for different transients in benchmark reactors with rectangular and hexagonal geometry.
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Time-dependent simplifi ed spherical harmonics formulations for a nuclear reactor system
A. Carreno,A. Vidal-Ferrandiz,D. Ginestar,G. Verdú 한국원자력학회 2021 Nuclear Engineering and Technology Vol.53 No.12
The steady-state simplified spherical harmonics equations (SPN equations) are a higher order approximation to the neutron transport equations than the neutron diffusion equation that also have reasonablecomputational demands. This work extends these results for the analysis of transients by comparing oftwo formulations of time-dependent SPN equations considering different treatments for the time derivatives of the field moments. The first is the full system of equations and the second is a diffusiveapproximation of these equations that neglects the time derivatives of the odd moments. The spatialdiscretization of these methodologies is made by using a high order finite element method. For the timediscretization, a semi-implicit Euler method is used. Numerical results show that the diffusive formulation for the time-dependent simplified spherical harmonics equations does not present a relevant lossof accuracy while being more computationally efficient than the full system.
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( J. A. Calderon ),( F. A. Vasquez ),( L. Arbelaez ),( J. A. Carreno ) 한국부식방식학회 2017 Corrosion Science and Technology Vol.16 No.2
Chelating solutions can be damaged by strong acids during oil production. To design effective corrosion inhibitors and other alternatives for corrosion control, it is important to understand not only the behavior of the system under operating condition but also the kinetics of electrochemical reactions during the corrosion process. In this study, the electrochemical behaviors of P-110 steel in aqueous fluids based on ethylenediaminetetraacetic acid (EDTA) compounds under various temperatures and hydrodynamic regime conditions were assessed. Electrochemical measurements were conducted using rotating disc electrodes manufactured. Electrolytes were prepared using aqueous compounds of EDTA like diammonium salt, disodium salt, and tetrasodium salt. Potentiodynamic polarization, electrochemical impedance, and mass loss tests were performed in order to assess the corrosion kinetic in electrolytes. Hydrodynamic effects were observed only in the cathodic polarization curve. This proves that hydrodynamic regime plays an important role in the corrosion of steel mainly in disodium and diammonium EDTA solutions. Two cathodic reactions controlled the corrosion process. However, oxygen level and pH of the electrolyte played the most important role in metal corrosion. Corrosion rates in those fluids were decreased drastically when oxygen concentration was reduced.
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