Journal articles on the topic 'Numerical Methods for Neutron Transport'
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Zhao, Zhengang, and Yunying Zheng. "Numerical Approximation for Fractional Neutron Transport Equation." Journal of Mathematics 2021 (March 13, 2021): 1–14. http://dx.doi.org/10.1155/2021/6676640.
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Fractional neutron transport equation reflects the anomalous transport processes in nuclear reactor. In this paper, we will construct the fully discrete methods for this type of fractional equation with Riesz derivative, where the generalized WENO5 scheme is used in spatial direction and Runge–Kutta schemes are adopted in temporal direction. The linear stabilities of the generalized WENO5 schemes with different stages and different order ERK are discussed detailed. Numerical examples show the combinations of forward Euler/two-stage, second-order ERK and WENO5 are unstable and the three-stage, third-order ERK method with generalized WENO5 is stable and can maintain sharp transitions for discontinuous problem, and its convergence reaches fifth order for smooth boundary condition.
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Aixiang, Huang, and Ma Yichen. "The application of modern numerical methods to the neutron transport equation." Transport Theory and Statistical Physics 26, no. 1-2 (January 1997): 65–83. http://dx.doi.org/10.1080/00411459708221775.
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Shafii, Mohamad Ali. "Solution methods of neutron transport equation in nuclear reactors." Jurnal ILMU DASAR 14, no. 2 (December 4, 2013): 59. http://dx.doi.org/10.19184/jid.v14i2.320.
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A few numerical methods that usually used to solve neutron transport equation in nuclear reactor are SN dan PN method, Monte Carlo, Collision Probability and Methods of Characteristics . First two methods have been developed using diffusion approach, and last three methods suitable are applicated for transport approximation. Those of three methods have important role in the desain of nuclear reactors. In addition to follow the development of advanced reactor designs, the three methods were chosen because they do not use diffusion approach these are more accurate methods, as well as less need considerable computer memory. Of all the existing methods, the CP method has several advantages among the others. Keywords : Neutron transport, SN, PN, CP, MOC, MC
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Yíldíz, C. "Calculation of the higher order eigenvalues for a homogeneous sphere using the FN method." Kerntechnik 66, no. 1-2 (January 1, 2001): 33–36. http://dx.doi.org/10.1515/kern-2001-0008.
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Abstract The transport of monoenergetic neutrons in spherical geometry with forward scattering and vacuum boundary conditions is considered. The scaled transport equation is solved using the Fn method by considering the pseudo-slab problem. Numerical results for the fundamental and higher order eigenvalues are presented for several significant figures. Some selected results are compared with those obtained using various methods in the literature. Finally, a few remarks about the behavior of the criticality eigenvalue of the neutron transport equation with forward scattering is given.
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Carta, M., S. Dulla, V. Peluso, P. Ravetto, and G. Bianchini. "Calculation of the Effective Delayed Neutron Fraction by Deterministic and Monte Carlo Methods." Science and Technology of Nuclear Installations 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/584256.
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The studies on Accelerator-Driven Systems (ADSs) have renewed the interest in the theoretical and computational evaluation of the main integral parameters characterizing subcritical systems (e.g., reactivity, effective delayed neutron fractionβeff, and mean prompt neutron generation time). In particular, some kinetic parameters, as the effective delayed neutron fraction, are evaluated in Monte Carlo codes by formulations which do not require the calculation of the adjoint flux. This paper is focused on a theoretical and computational analysis about how the differentβeffdefinitions are connected and which are the approximations inherent to the Monte Carlo definition with respect to the standard definition involving weighted integrals. By means of a refined transport computational analysis carried out in a coherent and consistent way, that is, using the same deterministic code and neutron data library for theβeffevaluation in different ways, the theoretical analysis is numerically confirmed. Both theoretical and numerical results confirm the effectiveness of the Monte Carloβeffevaluation, at least in cases where spectral differences between total and prompt fluxes are negligible with respect to the value of the functionals entering the classicalβeffformulation.
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Itoh, Naoki. "Transport Processes in Dense Stellar Plasmas." International Astronomical Union Colloquium 147 (1994): 394–419. http://dx.doi.org/10.1017/s0252921100026464.
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AbstractTransport processes in dense stellar plasmas which are relevant to the interiors of white dwarfs and neutron stars are reviewed. The emphasis is placed on the accuracy of the numerical results. In this review we report on the electrical conductivity and the thermal conductivity of dense matter. The methods of the calculations are different for the liquid metal phase and the crystalline lattice phase. We will broadly review the current status of the calculations of the transport properties of dense matter, and try to give the best instructions available at the present time to the readers.
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Burke, Paul E., Kyle E. Remley, and David P. Griesheimer. "GPU ACCELERATION OF DOPPLER BROADENING FOR NEUTRON TRANSPORT CALCULATIONS1." EPJ Web of Conferences 247 (2021): 04017. http://dx.doi.org/10.1051/epjconf/202124704017.
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In radiation transport calculations, the effects of material temperature on neutron/nucleus interactions must be taken into account through Doppler broadening adjustments to the microscopic cross section data. Historically, Monte Carlo transport simulations have accounted for this temperature dependence by interpolating among precalculated Doppler broadened cross sections at a variety of temperatures. More recently, there has been much interest in on-the-fly Doppler broadening methods, where reference data is broadened on-demand during particle transport to any temperature. Unfortunately, Doppler broadening operations are expensive on traditional central processing unit (CPU) architectures, making on-the-fly Doppler broadening unaffordable without approximations or complex data preprocessing. This work considers the use of graphics processing unit (GPU)s, which excel at parallel data processing, for on-the-fly Doppler broadening in continuous-energy Monte Carlo simulations. Two methods are considered for the broadening operations – a GPU implementation of the standard SIGMA1 algorithm and a novel vectorized algorithm that leverages the convolution properties of the broadening operation in an attempt to expose additional parallelism. Numerical results demonstrate that similar cross section lookup throughput is obtained for on-the-fly broadening on a GPU as cross section lookup throughput with precomputed data on a CPU, implying that offloading Doppler broadening operations to a GPU may enable on-the-fly temperature treatment of cross sections without a noticeable reduction in cross section processing performance in Monte Carlo transport codes.
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Bernal, Álvaro, Rafael Miró, Damián Ginestar, and Gumersindo Verdú. "Resolution of the Generalized Eigenvalue Problem in the Neutron Diffusion Equation Discretized by the Finite Volume Method." Abstract and Applied Analysis 2014 (2014): 1–15. http://dx.doi.org/10.1155/2014/913043.
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Numerical methods are usually required to solve the neutron diffusion equation applied to nuclear reactors due to its heterogeneous nature. The most popular numerical techniques are the Finite Difference Method (FDM), the Coarse Mesh Finite Difference Method (CFMD), the Nodal Expansion Method (NEM), and the Nodal Collocation Method (NCM), used virtually in all neutronic diffusion codes, which give accurate results in structured meshes. However, the application of these methods in unstructured meshes to deal with complex geometries is not straightforward and it may cause problems of stability and convergence of the solution. By contrast, the Finite Element Method (FEM) and the Finite Volume Method (FVM) are easily applied to unstructured meshes. On the one hand, the FEM can be accurate for smoothly varying functions. On the other hand, the FVM is typically used in the transport equations due to the conservation of the transported quantity within the volume. In this paper, the FVM algorithm implemented in the ARB Partial Differential Equations solver has been used to discretize the neutron diffusion equation to obtain the matrices of the generalized eigenvalue problem, which has been solved by means of the SLEPc library.
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Mimoun, Jordan G., Carlos Torres-Verdín, and William E. Preeg. "Quantitative interpretation of pulsed neutron capture logs: Part 1 — Fast numerical simulation." GEOPHYSICS 76, no. 3 (May 2011): E81—E93. http://dx.doi.org/10.1190/1.3569600.
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Pulsed neutron capture (PNC) logs are commonly used for formation evaluation behind casing and to assess time-lapse variations of hydrocarbon pore volume. Because conventional interpretation methods for Σ logs assume homogeneous formations, errors may arise, especially in thinly bedded formations, when appraising petrophysical properties of hydrocarbon-bearing beds. There exist no quantitative interpretation methods to account for shoulder-bed effects on Σ logs acquired in sand-shale laminated reservoirs. Because of diffusion effects between dissimilar beds, Σ logs acquired in such formations do not obey mixing laws between the Σ responses of pure-sand and pure-shale end members of the sedimentary sequence. We have developed a new numerical method to simulate PNC rapidly and accurately logs. The method makes use of late-time, thermal-neutron flux sensitivity functions (FSFs) to describe the contribution of multilayer formations toward the measured capture cross section. It includes a correction procedure based on 1D neutron diffusion theory that adapts the transport-equation-derived, base-case FSF of a homogeneous formation to simulate the response of vertically heterogeneous formations. Benchmarking exercises indicate that our simulation method yields average differences smaller than two capture units within seconds of computer central processing unit time with respect to PNC logs simulated with rigorous Monte Carlo methods for a wide range of geometrical, petrophysical, and fluid properties.
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Varma, Vishnu, Bernhard Müller, and Martin Obergaulinger. "A comparison of 2D Magnetohydrodynamic supernova simulations with the CoCoNuT-FMT and Aenus-Alcar codes." Monthly Notices of the Royal Astronomical Society 508, no. 4 (October 19, 2021): 6033–48. http://dx.doi.org/10.1093/mnras/stab2983.
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ABSTRACT Code comparisons are a valuable tool for the verification of supernova simulation codes and the quantification of model uncertainties. Here, we present a first comparison of axisymmetric magnetohydrodynamic (MHD) supernova simulations with the CoCoNuT-FMT and Aenus-Alcar codes, which use distinct methods for treating the MHD induction equation and the neutrino transport. We run two sets of simulations of a rapidly rotating 35M⊙ gamma-ray burst progenitor model with different choices for the initial field strength, namely $10^{12}\, \mathrm{G}$ for the maximum poloidal and toroidal field in the strong-field case and $10^{10}\, \mathrm{G}$ in the weak-field case. We also investigate the influence of the Riemann solver and the resolution in CoCoNuT-FMT. The dynamics is qualitatively similar for both codes and robust with respect to these numerical details, with a rapid magnetorotational explosion in the strong-field case and a delayed neutrino-driven explosion in the weak-field case. Despite relatively similar shock trajectories, we find sizeable differences in many other global metrics of the dynamics, like the explosion energy and the magnetic energy of the proto-neutron star. Further differences emerge upon closer inspection, for example, the disc-like surface structure of the proto-neutron star proves high sensitivity to numerical details. The electron fraction distribution in the ejecta as a crucial determinant for the nucleosynthesis is qualitatively robust, but the extent of neutron- or proton-rich tails is sensitive to numerical details. Due to the complexity of the dynamics, the ultimate cause of model differences can rarely be uniquely identified, but our comparison helps gauge uncertainties inherent in current MHD supernova simulations.
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Laletin, N. I. "Analysis of the surface pseudosources method (Gn-approximations) and comparison with other numerical methods for the neutron transport equation." Transport Theory and Statistical Physics 27, no. 5-7 (August 1998): 639–52. http://dx.doi.org/10.1080/00411459808205647.
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Salomoni, Valentina Anna Lia, and Nico De Marchi. "Numerical Solutions of Space-Fractional Advection–Diffusion–Reaction Equations." Fractal and Fractional 6, no. 1 (December 31, 2021): 21. http://dx.doi.org/10.3390/fractalfract6010021.
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Background: solute transport in highly heterogeneous media and even neutron diffusion in nuclear environments are among the numerous applications of fractional differential equations (FDEs), being demonstrated by field experiments that solute concentration profiles exhibit anomalous non-Fickian growth rates and so-called “heavy tails”. Methods: a nonlinear-coupled 3D fractional hydro-mechanical model accounting for anomalous diffusion (FD) and advection–dispersion (FAD) for solute flux is described, accounting for a Riesz derivative treated through the Grünwald–Letnikow definition. Results: a long-tailed solute contaminant distribution is displayed due to the variation of flow velocity in both time and distance. Conclusions: a finite difference approximation is proposed to solve the problem in 1D domains, and subsequently, two scenarios are considered for numerical computations.
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de Abreu, Marcos Pimenta. "Numerical methods for the generation of the spectrum of the multigroup slab-geometry discrete ordinates operator in neutron transport theory." Annals of Nuclear Energy 29, no. 15 (October 2002): 1837–53. http://dx.doi.org/10.1016/s0306-4549(02)00014-2.
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Awono, O., and J. Tagoudjeu. "A Preconditioned Minimal Residual Solver for a Class of Linear Operator Equations." Computational Methods in Applied Mathematics 10, no. 2 (2010): 119–36. http://dx.doi.org/10.2478/cmam-2010-0007.
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Abstract We consider the class of linear operator equations with operators admitting self-adjoint positive definite and m-accretive splitting (SAS). This splitting leads to an ADI-like iterative method which is equivalent to a fixed point problem where the operator is a 2 by 2 matrix of operators. An infinite dimensional adaptation of a minimal residual algorithm with Symmetric Gauss-Seidel and polynomial preconditioning is then applied to solve the resulting matrix operator equation. Theoretical analysis shows the convergence of the methods, and upper bounds for the decrease rate of the residual are derived. The convergence of the methods is numerically illustrated with the example of the neutron transport problem in 2-D geometry.
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Zhang, Liang, Bin Zhang, Cong Liu, and Yixue Chen. "Evaluation of PWR pressure vessel fast neutron fluence benchmarks from NUREG/CR-6115 with ares transport code." Nuclear Technology and Radiation Protection 32, no. 3 (2017): 204–10. http://dx.doi.org/10.2298/ntrp1703204z.
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An accurate evaluation of PWR pressure vessel fast neutron fluence is essential to ensure pressure vessel integrity over the design lifetime. The discrete ordinates method is one of the main methods to treat such problems. In this paper, evaluations have been performed for three PWR benchmarks described in NUREG/CR-6115 using ARES transport code. The calculated results were compared to the reference values and a satisfactory agreement was obtained. In addition, the effects of SN numeric and source distribution modeling for pressure vessel fast neutron fluence calculation are investigated. Based on the fine enough grids adopted, the different spatial and angular discretization introduces derivations less than 3 %, and fix-up for negative scattering source causes no noticeable effects when calculating pressure vessel fast neutron fluence. However, the discrepancy of assembly-wise and pin-wise source modeling for peripheral assemblies reaches ~20 %, which indicates that pin-wise modeling for peripheral assemblies is essential. These results provide guidelines for pressure vessel fast neutron fluence calculation and demonstrate that the ARES transport code is capable of performing neutron transport calculations for evaluating PWR pressure vessel fast neutron fluence.
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Palau, J. M., A. Rizzo, P. Tamagno, and C. De Saint Jean. "APPLICATION OF RECENT DEVELOPMENTS IN INTEGRAL DATA ASSIMILATION TO IN-DEPTH ANALYSIS OF UH1.2 EXPERIMENT AND TRANSPOSITION TO WHOLE PWR CORE." EPJ Web of Conferences 247 (2021): 15001. http://dx.doi.org/10.1051/epjconf/202124715001.
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Recent developments in the Integral Data Assimilation (IDA) methods within Bayesian framework have been achieved at CEA to tackle the problem of correlated experiments (through technological uncertainties) and neutron transport model numerical effects. Hence, reference Monte-Carlo and deterministic calculations (TRIPOLI4® and APOLLO3®) are used together to solve neutron transport equations and get the sensitivity profiles. Furthermore, the analysis of the mock-up experiments technological parameters is performed to get accurate uncertainties and correlations between the experiments (finally the covariance experimental matrix required for IDA). We apply here the IDA approach with a new, extend set of statistical indicators (Cook’s distance, Bayesian and Aikike Information criteria (BIC, AIC)) implemented in the nuclear physics CEA CONRAD code, to the integral experiments UH1.2 in reference and voided configurations (standard PWR fuel assembly in the EOLE mock-up reactor). The adjusted multigroup cross-sections and posterior covariances are compared by choosing different ingredients in the assimilation process. Finally, the investigated key neutron parameters; reactivity, reactivity worth (void effects) and fissions rates are transposed (with the same CONRAD code) to a standard PWR core. This in-depth analysis enables us to predict the residual uncertainties and biases due to the multigroup cross-section adjustments assessing at the same time the similarity of these integral experiments for the main PWR neutronic safety parameters. In addition, technological parameters uncertainties and their impact on Bayesian adjustment process are taken into account through a global experimental covariance matrix. We point out that the UH1.2 experiments bring relevant additional information to PWR keff calculations reducing significantly the posterior results but are less relevant for fission rate distribution in reference and voided configurations.
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Hoagland, Dylan S., and Yousry Y. Azmy. "Hybrid approaches for accelerated convergence of block-Jacobi iterative methods for solution of the neutron transport equation." Journal of Computational Physics 439 (August 2021): 110382. http://dx.doi.org/10.1016/j.jcp.2021.110382.
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Cheong, Patrick Chi-Kit, David Yat Tung Pong, Anson Ka Long Yip, and Tjonnie Guang Feng Li. "An Extension of Gmunu: General-relativistic Resistive Magnetohydrodynamics Based on Staggered-meshed Constrained Transport with Elliptic Cleaning." Astrophysical Journal Supplement Series 261, no. 2 (July 21, 2022): 22. http://dx.doi.org/10.3847/1538-4365/ac6cec.
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Abstract We present the implementation of general-relativistic resistive magnetohydrodynamics solvers and three divergence-free handling approaches adopted in the General-relativistic multigrid numerical (Gmunu) code. In particular, implicit–explicit Runge–Kutta schemes are used to deal with the stiff terms in the evolution equations for small resistivity. The three divergence-free handling methods are (i) hyperbolic divergence cleaning (also known as the generalized Lagrange multiplier), (ii) staggered-meshed constrained transport schemes, and (iii) elliptic cleaning through a multigrid solver, which is applicable in both cell-centered and face-centered (stagger grid) magnetic fields. The implementation has been tested with a number of numerical benchmarks from special-relativistic to general-relativistic cases. We demonstrate that our code can robustly recover from the ideal magnetohydrodynamics limit to a highly resistive limit. We also illustrate the applications in modeling magnetized neutron stars, and compare how different divergence-free handling methods affect the evolution of the stars. Furthermore, we show that the preservation of the divergence-free condition of the magnetic field when using staggered-meshed constrained transport schemes can be significantly improved by applying elliptic cleaning.
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Ma, Ji, Chen Hao, Lixun Liu, and Yuekai Zhou. "Perturbation Theory-Based Whole-Core Eigenvalue Sensitivity and Uncertainty (SU) Analysis via a 2D/1D Transport Code." Science and Technology of Nuclear Installations 2020 (February 1, 2020): 1–13. http://dx.doi.org/10.1155/2020/9428580.
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For nuclear reactor physics, uncertainties in the multigroup cross sections inevitably exist, and these uncertainties are considered as the most significant uncertainty source. Based on the home-developed 3D high-fidelity neutron transport code HNET, the perturbation theory was used to directly calculate the sensitivity coefficient of keff to the multigroup cross sections, and a reasonable relative covariance matrix with a specific energy group structure was generated directly from the evaluated covariance data by using the transforming method. Then, the “Sandwich Rule” was applied to quantify the uncertainty of keff. Based on these methods, a new SU module in HNET was developed to directly quantify the keff uncertainty with one-step deterministic transport methods. To verify the accuracy of the sensitivity and uncertainty analysis of HNET, an infinite-medium problem and the 2D pin-cell problem were used to perform SU analysis, and the numerical results demonstrate that acceptable accuracy of sensitivity and uncertainty analysis of the HNET are achievable. Finally, keff SU analysis of a 3D minicore was analyzed by using the HNET, and some important conclusions were also drawn from the numerical results.
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Li, Jin, Yunlin Xu, Dean Wang, Qicang Shen, Brendan Kochunas, and Thomas Downar. "DEMONSTRATION OF A LINEAR PROLONGATION CMFD METHOD ON MOC." EPJ Web of Conferences 247 (2021): 03006. http://dx.doi.org/10.1051/epjconf/202124703006.
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Coarse Mesh Finite Difference (CMFD) method is a very effective method to accelerate the iterations for neutron transport calculation. But it can degrade and even fail when the optical thickness of the mesh becomes large. Therefore several methods, including partial current-based CMFD (pCMFD) and optimally diffusive CMFD (odCMFD), have been proposed to stabilize the conventional CMFD method. Recently, a category of “higherorder” prolongation CMFD (hpCMFD) methods was proposed to use both the local and neighboring coarse mesh fluxes to update the fine cell flux, which can solve the fine cell scalar flux discontinuity problem between the fine cells at the bounary of the coarse mesh. One of the hpCMFD methods, refered as lpCMFD, was proposed to use a linear prolongation to update the fine cell scalar fluxes. Method of Characteristics (MOC) is a very popular method to solve neutron transport equations. In this paper, lpCMFD is applied on the MOC code MPACT for a variety of fine meshes. A track-based centroids calculation method is introduced to find the centroids coordinates for random shapes of fine cells. And the numerical results of a 2D C5G7 problem are provided to demonstrate the stability and efficiency of lpCMFD method on MOC. It shows that lpCMFD can stabilize the CMFD iterations in MOC method effectively and lpCMFD method performs better than odCMFD on reducing the outer MOC iterations.
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Abbott, W. E., and E. J. Allen. "Richardson Extrapolation Applied to Difference Methods for Numerically Solving the Neutron Transport Equation in Spherical Geometry." Nuclear Science and Engineering 108, no. 3 (July 1991): 278–88. http://dx.doi.org/10.13182/nse91-a23825.
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Andresen, H., R. Glas, and H.-Th Janka. "Gravitational-wave signals from 3D supernova simulations with different neutrino-transport methods." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 10, 2021): 3552–67. http://dx.doi.org/10.1093/mnras/stab675.
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ABSTRACT We compare gravitational-wave (GW) signals from eight 3D simulations of core-collapse supernovae, using two different progenitors with zero-age main-sequence masses of 9 and 20 solar masses (M⊙). The collapse of each progenitor was simulated four times, at two different grid resolutions and with two different neutrino transport methods, using the aenus-alcar code. The main goal of this study is to assess the validity of recent concerns that the so-called ‘Ray-by-Ray+’ (RbR+) approximation is problematic in core-collapse simulations and can adversely affect theoretical GW predictions. Therefore, signals from simulations using RbR+ are compared to signals from corresponding simulations using a fully multidimensional (FMD) transport scheme. The 9 M⊙ progenitor successfully explodes, whereas the 20 M⊙ model does not. Both the standing accretion shock instability and hot-bubble convection develop in the post-shock layer of the non-exploding models. In the exploding models, neutrino-driven convection in the post-shock flow is established around 100 ms after core bounce and lasts until the onset of shock revival. We can, therefore, judge the impact of the numerical resolution and neutrino transport under all conditions typically seen in non-rotating core-collapse simulations. We find excellent qualitative agreement in all GW features. We find minor quantitative differences between simulations, but find no systematic differences between simulations using different transport schemes. Resolution-dependent differences in the hydrodynamic behaviour of low-resolution and high-resolution models have a greater impact on the GW signals than consequences of the different transport methods. Furthermore, increasing the resolution decreases the discrepancies between models with different neutrino transport.
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Bocanegra Cifuentes, Johan Augusto, Davide Borelli, Antonio Cammi, Guglielmo Lomonaco, and Mario Misale. "Lattice Boltzmann Method Applied to Nuclear Reactors—A Systematic Literature Review." Sustainability 12, no. 18 (September 22, 2020): 7835. http://dx.doi.org/10.3390/su12187835.
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Nuclear engineering requires computationally efficient methods to simulate different components and systems of plants. The Lattice Boltzmann Method (LBM), a numerical method with a mesoscopic approach to Computational Fluid Dynamic (CFD) derived from the Boltzmann equation and the Maxwell–Boltzmann distribution, can be an adequate option. The purpose of this paper is to present a review of the recent applications of the Lattice Boltzmann Method in nuclear engineering research. A systematic literature review using three databases (Web of Science, Scopus, and ScienceDirect) was done, and the items found were categorized by the main research topics into computational fluid dynamics and neutronic applications. The features of the problem addressed, the characteristics of the numerical method, and some relevant conclusions of each study are resumed and presented. A total of 45 items (25 for computational fluid dynamics applications and 20 for neutronics) was found on a wide range of nuclear engineering problems, including thermal flow, turbulence mixing of coolant, sedimentation of impurities, neutron transport, criticality problem, and other relevant issues. The LBM results in being a flexible numerical method capable of integrating multiphysics and hybrid schemes, and is efficient for the inner parallelization of the algorithm that brings a widely applicable tool in nuclear engineering problems. Interest in the LBM applications in this field has been increasing and evolving from early stages to a mature form, as this review shows.
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Luycx, Mathilde, and Carlos Torres-Verdín. "Rapid forward modeling of logging-while-drilling neutron-gamma density measurements." GEOPHYSICS 83, no. 6 (November 1, 2018): D231—D246. http://dx.doi.org/10.1190/geo2018-0142.1.
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Neutron-activated gamma-ray (neutron-gamma) logging-while-drilling (LWD) measurements deliver bulk density estimates without using a chemical source. The assessment of bulk density is based on neutron-induced non-capture gamma rays, corrected for neutron transport by combining particle counts acquired at two gamma-ray detectors and two fast neutron detectors. Particle counts from all four detectors are necessary to deliver one density measurement whose accuracy compares well to that of the gamma-gamma density instruments. Thereafter, borehole environmental effects are mitigated with empirical corrections based on Monte Carlo (MC) modeling. Such corrections should be avoided for standoff values greater than 0.63 cm (0.25 in) because they are no longer independent of formation properties. Neutron-gamma density measurements are also influenced by bed-boundary and layer-thickness effects. Thinly bedded formations, invasion, high-angle/horizontal (HA/HZ) wells, and enlarged boreholes can all mask true formation bulk density when implementing conventional petrophysical interpretation. Although MC methods accurately simulate 3D environmental and geometrical effects, they are computationally expensive and are thus impractical for real-time interpretation. Layer-by-layer bulk density can, however, be estimated using rapid numerical simulations coupled with inversion procedures. We have developed a rapid modeling algorithm to accurately simulate LWD neutron-gamma density measurements. Simulations are based on a theoretical, albeit realistic, LWD neutron-gamma density tool operating with a 14.1 MeV pulsed neutron source. The algorithm uses flux sensitivity functions and first-order Taylor series approximations to simulate particle counts at each detector before they are processed with a density estimation algorithm. Rigorous benchmarks against the Monte Carlo N-particle code in vertical and HA/HZ wells, across diverse solid and fluid rock compositions, thin beds, and in the presence of invasion, yield average density errors of less than 1% ([Formula: see text]) in approximately [Formula: see text] the time required of MC modeling.
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Bereznev, V., A. Belov, and D. Koltashev. "APPLICATION OF THE FIRST AND LAST COLLISION METHODS IN ODETTA CODE FOR RADIATION SHIELDING CALCULATIONS." PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. SERIES: NUCLEAR AND REACTOR CONSTANTS 2021, no. 1 (March 26, 2021): 15–26. http://dx.doi.org/10.55176/2414-1038-2021-1-15-26.
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The research is devoted to the features of radiation shieldind calculations by the deterministic program ODETTA, which is intended for numerical simulation of the neutron and photon transport in shielding compositions of the nuclear facilities and based on the discrete ordinates method and finite element method on unstructured tetrahedral meshes. The article describes the methods of the uncollided radiation component calculations implemented in the ODETTA program for “ray” effect elimination which is typical for discrete ordinates method in weakly scattering media with localized radiation sources. In addition, the first collision method allows to correctly simulating point sources, and the last collision method allows calculating the required functionals at the detection points located outside the computational domain. The implemented methods have been tested on computational benchmarks and experiments, a brief description of which is given in the article. The results obtained were compared with analytical and experimental data, as well as with the results of calculations by the Monte Carlo method within the Scale 6.2.3 software package. The analysis of the influence of the calculated parameters is carried out and conclusions are drawn about the effectiveness of the implemented methods.
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Kato, Chinami, Hiroki Nagakura, and Taiki Morinaga. "Neutrino Transport with the Monte Carlo Method. II. Quantum Kinetic Equations." Astrophysical Journal Supplement Series 257, no. 2 (December 1, 2021): 55. http://dx.doi.org/10.3847/1538-4365/ac2aa4.
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Abstract Neutrinos have a unique quantum feature as flavor conversions. Recent studies suggested that collective neutrino oscillations play important roles in high-energy astrophysical phenomena. The quantum kinetic equation (QKE) is capable of describing the neutrino flavor conversion, transport, and matter collision self-consistently. However, we have experienced many technical difficulties in their numerical implementation. In this paper, we present a new QKE solver based on a Monte Carlo (MC) approach. This is an upgraded version of our classical MC neutrino transport solver; in essence, a flavor degree of freedom including mixing state is added into each MC particle. This extension requires updating numerical treatments of collision terms, in particular for scattering processes. We deal with the technical problem by generating a new MC particle at each scattering event. To reduce statistical noise inherent in MC methods, we develop the effective mean free path method. This suppresses a sudden change of flavor state due to collisions without increasing the number of MC particles. We present a suite of code tests to validate these new modules with comparison to the results reported in previous studies. Our QKE-MC solver is developed with fundamentally different philosophy and design from other deterministic and mesh methods, suggesting that it will be complementary to others and potentially provide new insights into physical processes of neutrino dynamics.
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Liu, Zhi Bin, Jin Ma, Bing Shu Wang, and Xin Hui Duan. "The Study on Homogeneous Parameters of Light Water Reactor by the Nodal Diffusion Method." Applied Mechanics and Materials 666 (October 2014): 144–48. http://dx.doi.org/10.4028/www.scientific.net/amm.666.144.
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Recent progress in the development of coarse-mesh nodal methods for the numerical solution of the neutron diffusion and transport equations is reviewed. Compared with earlier nodal simulators, more recent nodal diffusion methods are characterized by the systematic derivation of spatial coupling relationships which are entirely consistent with the multi-group diffusion equation. These relationships most often are derived by developing approximations to the one-dimensional equations obtained by integrating the multidimensional diffusion equation over directions transverse to each coordinate axis. The objective of this research is to develop accurate and efficient spatial homogenization method for coarse mesh analysis of light water reactors. More sophisticated methods for computing approximate equivalence parameters are also introduced and make use of nonlinear iterations between homogenized reactor calculations and local fixed-source calculations to compute equivalence parameters. This special feature induces the need for the study on homogeneous parameters of light water reactor which takes phenomena of different scale and their interaction into account by means of the nodal diffusion method.
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Shin, Jehyun, Seho Hwang, Seung Ho Jung, Weon Shik Han, Jeong-Sul Son, Myung Jin Nam, and Taehoon Kim. "Development of Site-Scale Conceptual Model Using Integrated Borehole Methods: Systematic Approach for Hydraulic and Geometric Evaluation." Water 14, no. 9 (April 20, 2022): 1336. http://dx.doi.org/10.3390/w14091336.
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Understanding the physical flow mechanisms in aquifer systems is essential in effectively protecting groundwater resources and preserving subsurface environments from a wide range of contaminants. A conceptual model is a simplified representation of a groundwater system and gaining knowledge about the geological features and parameters controlling the flow and transport processes is a crucial first step towards properly constructing a site-scale conceptual model. In this study, we present a multi-step workflow that involves integrated borehole techniques to gain information concerning groundwater flow. Measurements from core-scale to field-scale enable us to better build a subsurface geological structure divided into the unconsolidated layer and the fractured bedrock. In addition, neutron logging and mercury injection capillary pressure techniques allow for the development of vertical porosity distribution in the alluvial layer. For fracture characterization, the fracture geometry is delineated using a series of borehole imaging techniques and single-hole tests to differentiate the individual permeable fractures from other hydraulically inactive fractures. Combining the hydraulic and geometric evaluations, the presence of large-scale connective fracture networks is identified. Our high-resolution three-dimensional (3D) site-scale conceptual model is expected to contribute to improving the reliability and availability of numerical groundwater models.
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Choplin, A., L. Siess, and S. Goriely. "The intermediate neutron capture process." Astronomy & Astrophysics 648 (April 2021): A119. http://dx.doi.org/10.1051/0004-6361/202040170.
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Context. Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s- and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process), which is thought to result from the ingestion of protons in a convective helium-burning region, but whose astrophysical site is still largely debated. Aims. We investigate whether an i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars can develop and whether it can explain the abundances of observed r/s-stars. Methods. We computed a 1 M⊙ model at [Fe/H] = −2.5 with the stellar evolution code STAREVOL, using a nuclear network of 1091 species (at maximum) coupled to the transport processes. The impact of the temporal and spatial resolutions on the resulting abundances was assessed. We also identified key elements and isotopic ratios that are specific to i-process nucleosynthesis and carried out a detailed comparison between our model and a sample of r/s-stars. Results. At the beginning of the AGB phase, during the third thermal pulse, the helium driven convection zone is able to penetrate the hydrogen-rich layers. The subsequent proton ingestion leads to a strong neutron burst with neutron densities of ∼4.3 × 1014 cm−3 at the origin of the synthesis of i-process elements. The nuclear energy released by proton burning in the helium-burning convective shell strongly affects the internal structure: the thermal pulse splits and after approximately ten years the upper part of the convection zone merges with the convective envelope. The surface carbon abundance is enhanced by more than 3 dex. This leads to an increase in the opacity, which triggers a strong mass loss and prevents any further thermal pulse. Our numerical tests indicate that the i-process elemental distribution is not strongly affected by the temporal and spatial resolution used to compute the stellar models, but typical uncertainties of ±0.3 dex on individual abundances are found. We show that specific isotopic ratios of Ba, Nd, Sm, and Eu can represent good tracers of i-process nucleosynthesis. Finally, an extended comparison with 14 selected r/s-stars show that the observed composition patterns can be well reproduced by our i-process AGB model. Conclusions. A rich i-process nucleosynthesis can take place during the early AGB phase of low-metallicity low-mass stars and explain the elemental distribution of most of the r/s-stars, but cannot account for the high level of enrichment of the giant stars in a scenario involving pollution by a former AGB companion.
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Meliani, Zakaria, Yosuke Mizuno, Hector Olivares, Oliver Porth, Luciano Rezzolla, and Ziri Younsi. "Simulations of recoiling black holes: adaptive mesh refinement and radiative transfer." Astronomy & Astrophysics 598 (January 27, 2017): A38. http://dx.doi.org/10.1051/0004-6361/201629191.
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Context. In many astrophysical phenomena, and especially in those that involve the high-energy regimes that always accompany the astronomical phenomenology of black holes and neutron stars, physical conditions that are achieved are extreme in terms of speeds, temperatures, and gravitational fields. In such relativistic regimes, numerical calculations are the only tool to accurately model the dynamics of the flows and the transport of radiation in the accreting matter. Aims. We here continue our effort of modelling the behaviour of matter when it orbits or is accreted onto a generic black hole by developing a new numerical code that employs advanced techniques geared towards solving the equations of general-relativistic hydrodynamics. Methods. More specifically, the new code employs a number of high-resolution shock-capturing Riemann solvers and reconstruction algorithms, exploiting the enhanced accuracy and the reduced computational cost of adaptive mesh-refinement (AMR) techniques. In addition, the code makes use of sophisticated ray-tracing libraries that, coupled with general-relativistic radiation-transfer calculations, allow us to accurately compute the electromagnetic emissions from such accretion flows. Results. We validate the new code by presenting an extensive series of stationary accretion flows either in spherical or axial symmetry that are performed either in two or three spatial dimensions. In addition, we consider the highly nonlinear scenario of a recoiling black hole produced in the merger of a supermassive black-hole binary interacting with the surrounding circumbinary disc. In this way, we can present for the first time ray-traced images of the shocked fluid and the light curve resulting from consistent general-relativistic radiation-transport calculations from this process. Conclusions. The work presented here lays the ground for the development of a generic computational infrastructure employing AMR techniques to accurately and self-consistently calculate general-relativistic accretion flows onto compact objects. In addition to the accurate handling of the matter, we provide a self-consistent electromagnetic emission from these scenarios by solving the associated radiative-transfer problem. While magnetic fields are currently excluded from our analysis, the tools presented here can have a number of applications to study accretion flows onto black holes or neutron stars.
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Goriely, S., and L. Siess. "Sensitivity of the s-process nucleosynthesis in AGB stars to the overshoot model." Astronomy & Astrophysics 609 (December 22, 2017): A29. http://dx.doi.org/10.1051/0004-6361/201731427.
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Context. S-process elements are observed at the surface of low- and intermediate-mass stars. These observations can be explained empirically by the so-called partial mixing of protons scenario leading to the incomplete operation of the CN cycle and a significant primary production of the [see formula in PDF] neutron source. This scenario has been successful in qualitatively explaining the s-process enrichment in AGB stars. Even so, it remains difficult to describe both physically and numerically the mixing mechanisms taking place at the time of the third dredged-up between the convective envelope and the underlying C-rich radiative layer Aims. We aim to present new calculations of the s-process nucleosynthesis in AGB stars testing two different numerical implementations of chemical transport. These are based on a diffusion equation which depends on the second derivative of the composition and on a numerical algorithm where the transport of species depends linearly on the chemical gradient. Methods. The s-process nucleosynthesis resulting from these different mixing schemes is calculated with our stellar evolution code STAREVOL which has been upgraded to include an extended s-process network of 411 nuclei. Our investigation focuses on a fiducial 2 M⊙, [Fe/H] = −0.5 model star, but also includes four additional stars of different masses and metallicities. Results. We show that for the same set of parameters, the linear mixing approach produces a much larger 13C-pocket and consequently a substantially higher surface s-process enrichment compared to the diffusive prescription. Within the diffusive model, a quite extreme choice of parameters is required to account for surface s-process enrichment of 1–2 dex. These extreme conditions can not, however, be excluded at this stage. Conclusions. Both the diffusive and linear prescriptions of the overshoot mixing are suited to describe the s-process nucleosynthesis in AGB stars provided the profile of the diffusion coefficient below the convective envelope is carefully chosen. Both schemes give rise to relatively similar distributions of s-process elements, but depending on the parameters adopted, some differences may be obtained. These differences are in the element distribution, and most of all in the level of surface enrichment.
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Griffies, S. M., A. Gnanadesikan, K. W. Dixon, J. P. Dunne, R. Gerdes, M. J. Harrison, A. Rosati, et al. "Formulation of an ocean model for global climate simulations." Ocean Science 1, no. 1 (September 12, 2005): 45–79. http://dx.doi.org/10.5194/os-1-45-2005.
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Abstract. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews the numerical schemes and physical parameterizations that make up an ocean climate model and how these schemes are pieced together for use in a state-of-the-art climate model. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical ``virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves. We also present preliminary analyses of two particularly important sensitivities isolated during the development process, namely the details of how parameterized subgridscale eddies transport momentum and tracers.
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Griffies, S. M., A. Gnanadesikan, K. W. Dixon, J. P. Dunne, R. Gerdes, M. J. Harrison, A. Rosati, et al. "Formulation of an ocean model for global climate simulations." Ocean Science Discussions 2, no. 3 (May 20, 2005): 165–246. http://dx.doi.org/10.5194/osd-2-165-2005.
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Abstract. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) coupled climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews elements of ocean climate models and how they are pieced together for use in a state-of-the-art coupled model. Novel issues are also highlighted, with particular attention given to sensitivity of the coupled simulation to physical parameterizations and numerical methods. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical "virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves.
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Kulyamin, Dmitry V., Pavel A. Ostanin, and Valentin P. Dymnikov. "INM-IM: INM RAS Earth ionosphere F region dynamical model." Russian Journal of Numerical Analysis and Mathematical Modelling 37, no. 6 (December 1, 2022): 349–62. http://dx.doi.org/10.1515/rnam-2022-0028.
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Abstract A new INM RAS global dynamical model of Earth’s ionosphere F region (100–500 km), which takes into account plasma-chemical processes, ambipolar diffusion, and advective ion transport due to electromagnetic drifts and neutral wind is presented. The model includes parameterizations of polar electric fields induced by magnetospheric convection and simplified equatorial drifts considerations. The focus of the paper is directed on the description of specific methods developed and utilized in the ionospheric model. Key processes responsible for the formation of global ionospheric features are outlined and their representation in the model is evaluated. The main global ionospheric characteristic features, such as seasonal and diurnal cycles, the equatorial ionization anomaly (EIA), polar ionization caps and the main trough have been adequately reproduced based on this model.
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Shriwise, Patrick C., John R. Tramm, Andrew Davis, and Paul K. Romano. "TOWARDS CAD-BASED GEOMETRY MODELLING WITH THE RANDOM RAY METHOD." EPJ Web of Conferences 247 (2021): 03023. http://dx.doi.org/10.1051/epjconf/202124703023.
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The Advanced Random Ray Code (ARRC) is a high performance computing application capable of high-fidelity simulations of full core nuclear reactor models. ARRC leverages a recently developed stochastic method for neutron transport, known as The Random Ray Method (TRRM), which offers a variety of computational and numerical advantages as compared to existing methods. In particular, TRRM has been shown to be capable of efficient simulation of explicit three dimensional geometry representations without assumptions about axial homogeneity. To date, ARRC has utilized Constructive Solid Geometry (CSG) combined with a nested lattice geometry which works well for typical pressurized water reactors, but is not performant for the general case featuring arbitrary geometries. To facilitate simulation of arbitrarily complex geometries in ARRC efficiently, we propose performing transport directly on Computer-Aided Design (CAD) models of the geometry. In this study, we utilize the Direct-Accelerated Geometry Monte Carlo (DAGMC) toolkit which tracks particles on tessellated CAD geometries using a bounding volume hierarchy to accelerate the process, as a replacement for ARRC’s current lattice-based accelerations. Additionally, we present a method for automatically subdividing the large CAD regions in the DAGMC model into smaller mesh cells required by random ray to achieve high accuracy. We test the new DAGMC geometry implementation in ARRC on several test problems, including a 3D pincells, 3D assemblies, and an axial section of the Advanced Test Reactor. We show that DAGMC allows for simulation of complex geometries in ARRC that would otherwise not be possible using the traditional approach while maintaining solution accuracy.
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Rasch, Philip J., Danielle B. Coleman, Natalie Mahowald, David L. Williamson, Shian-Jiann Lin, Byron A. Boville, and Peter Hess. "Characteristics of Atmospheric Transport Using Three Numerical Formulations for Atmospheric Dynamics in a Single GCM Framework." Journal of Climate 19, no. 11 (June 1, 2006): 2243–66. http://dx.doi.org/10.1175/jcli3763.1.
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Abstract This study examines the sensitivity of a number of important archetypical tracer problems to the numerical method used to solve the equations of tracer transport and atmospheric dynamics. The tracers' scenarios were constructed to exercise the model for a variety of problems relevant to understanding and modeling the physical, dynamical, and chemical aspects of the climate system. The use of spectral, semi-Lagrangian, and finite volume (FV) numerical methods for the equations is explored. All subgrid-scale physical parameterizations were the same in all model simulations. The model behavior with a few short simulations with passive tracers is explored, and with much longer simulations of radon, SF6, ozone, a tracer designed to mimic some aspects of a biospheric source/sink of CO2, and a suite of tracers designed around the conservation laws for thermodynamics and mass in the model. Large differences were seen near the tropopause in the model, where the FV core shows a much reduced level of vertical and meridional mixing. There was also evidence that the subtropical subsidence regions are more isolated from Tropics and midlatitudes in the FV core than seen in the other model simulations. There are also big differences in the stratosphere, particularly for age of air in the stratosphere and ozone. A comparison with estimated age of air from CO2 and SF6 measurements in the stratosphere suggest that the FV core is behaving most realistically. A neutral biosphere (NB) test case is used to explore issues of diurnal and seasonal rectification of a tracer with sources and sinks at the surface. The sources and sinks have a zero annual average, and the rectification is associated with temporal correlations between the sources and sinks, and transport. The test suggests that the rectification is strongly influenced by the resolved-scale dynamics (i.e., the dynamical core) and that the numerical formulation for dynamics and transport still plays a critical role in the distribution of NB-like species. Since the distribution of species driven by these processes have a strong influence on the interpretation of the “missing sink” for CO2 and the interpretation of climate change associated with anthropogenic forcing herein, these issues should not be neglected. The spectral core showed the largest departures from the predicted nonlinear relationship required by the equations for thermodynamics and mass conservations. The FV and semi-Lagrangian dynamics (SLD) models both produced errors a factor of 2 lower. The SLD model shows a small but systematic bias in its ability to maintain this relationship that was not present in the FV simulation. The results of the study indicate that for virtually all of these problems, the model numerics still have a large role in influencing the model solutions. It was frequently the case that the differences in solutions resulting from varying the numerics still exceed the differences in the simulations resulting from significant physical perturbations (like changes in greenhouse gas forcing). This does not mean that the response of the system to physical changes is not correct. When results are consistent using different numerical formulations for dynamics and transport it lends confidence to one's conclusions, but it does indicate that some caution is required in interpreting the results. The results from this study favor use of the FV core for tracer transport and model dynamics. The FV core is, unlike the others, conservative, less diffusive (e.g., maintains strong gradients better), and maintains the nonlinear relationships among variables required by thermodynamic and mass conservation constraints more accurately.
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Zhang, Liang, Bin Zhang, Cong Liu, and Yixue Chen. "Analysis of Spatial Discretization Error Estimators Implemented in ARES Transport Code for SN Equations." Science and Technology of Nuclear Installations 2018 (July 9, 2018): 1–10. http://dx.doi.org/10.1155/2018/3965309.
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The discrete ordinates method (SN) is one of the mainstream methods for neutral particle transport calculations. Assessing the quality of the numerical solution and controlling the discrete error are essential parts of large-scale high-fidelity simulations of nuclear systems. Three error estimators, a two-mesh estimator, a residual-based estimator, and a dual-weighted residual estimator, are derived and implemented in the ARES transport code to evaluate the error of zeroth-order spatial discretization for SN equations. The difference in scalar fluxes on coarse and fine meshes is adopted to indicate the error in the two-mesh method. To avoid zero residual in zeroth-order discretization, angular fluxes within one cell are reconstructed by Legendre polynomials. The error is estimated by inverting the discrete transport operator using the estimated directional residual as an anisotropic source. The inner product of the forward directional residual and the adjoint angular flux is employed to quantify the error in quantities of interest which can be denoted by a linear functional of forward angular flux. Method of Manufactured Solutions (MMS) is adopted to generate analytical solutions for SN equation with scattering and the determined true error is used to evaluate the effectivity of these estimators. Promising results are obtained in the numerical results for both homogeneous and heterogeneous cases. The larger error region is well captured and the average effectivity index for the local error estimation is less than unity. For the series test problems, the estimated goal quantity error can be contained within an order of magnitude around the exact error.
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Montoya, Oscar Danilo, Ángeles Medina-Quesada, and Jesus C. Hernández. "Optimal Pole-Swapping in Bipolar DC Networks Using Discrete Metaheuristic Optimizers." Electronics 11, no. 13 (June 29, 2022): 2034. http://dx.doi.org/10.3390/electronics11132034.
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Bipolar direct current (DC) networks are emerging electrical systems used to improve the distribution capabilities of monopolar DC networks. These grids work with positive, negative, and neutral poles, and they can transport two times the power when compared to monopolar DC grids. The distinctive features of bipolar DC grids include the ability to deal with bipolar loads (loads connected between the positive and negative poles) and with unbalanced load conditions, given that the loads connected to the positive and neutral poles are not necessarily equal to the negative and neutral ones. This load imbalance deteriorates voltages when compared to positive and negative poles, and it causes additional power losses in comparison with balanced operation scenarios. This research addresses the problem of pole-swapping in bipolar DC networks using combinatorial optimization methods in order to reduce the total grid power losses and improve the voltage profiles. Bipolar DC networks with a non-solidly grounded neutral wire composed of 21 and 85 nodes are considered in the numerical validations. The implemented combinatorial methods are the Chu and Beasley genetic algorithm, the sine-cosine algorithm, and the black-hole optimization algorithm. Numerical results in both test feeders demonstrate the positive effect of optimal pole-swapping in the total final power losses and the grid voltage profiles. All simulations were run in the MATLAB programming environment using the triangular-based power flow method, which is intended for radial distribution system configurations.
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Barbone, Riccardo, Riccardo Mandrioli, Mattia Ricco, Rudolf Francesco Paternost, Vincenzo Cirimele, and Gabriele Grandi. "Novel Multi-Vehicle Motion-Based Model of Trolleybus Grids towards Smarter Urban Mobility." Electronics 11, no. 6 (March 15, 2022): 915. http://dx.doi.org/10.3390/electronics11060915.
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Trolleybus systems are resurfacing as a steppingstone to carbon-neutral urban transport. With an eye on smart city evolution, the study and simulation of a proper monitoring system for trolleybus infrastructures will be essential. This paper merges the authors’ engineering knowledge and sources available in the literature on designing and modeling catenary-based electric traction networks and performs a critical review of them to lay the foundations for proposing possible optimal alternatives. A novel multi-vehicle motion-based model of the DC catenary system is then devised and simulated in Matlab-Simulink, which could prove useful in predicting possible technical obstacles arising from the next-future introduction of smart electric traction grids, inevitably featuring greater morphological intricacy. The modularity property characterizing the created model allows an accurate, detailed, and flexible simulation of sophisticated catenary systems. By means of graphical and numerical results illustrating the behavior of the main electrical line parameters, the presented approach demonstrates today’s obsolescence of conventional design methods used so far. The trolleybus network of the city of Bologna was chosen as a case study.
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Pozdniakov, S. P., N. E. Sizov, and V. A. Lekhov. "THE SIZE OF THE SANITARY PROTECTION ZONE OF THE WATER INTAKE WELL IN THE LAYERED HETEROGENEOUS AQUIFER." Engineering Geology World 14, no. 2 (September 3, 2019): 74–81. http://dx.doi.org/10.25296/1993-5056-2019-14-2-74-81.
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Sanitary protection zones (SPZ) of water intakes allocate on the time of movement from the outer boundary of the zone to the water intakes. For example, for zone II it is the time of microbial contamination transport, accepted for target aquifers insufficiently protected from the surface, which is equal to 400 days. For zone III, this is the time of chemical pollution transport equal to the estimated lifetime of the water intake. To calculate the spatial position of the boundaries of these zones, analytical and numerical methods are used based on the integration of equations for the velocities of neutral particles in the groundwater flow, the flow field of which formed by the superposition of the natural flow velocities and the disturbances imposed on it by groundwater abstraction. When these methods are used, the only configuration of the sanitary protection zone that corresponds to some homogeneous or heterogeneous spatial field of hydraulic parameters obtained from field materials and (or) from the solution of the inverse problem is obtained as a result of calculations. At the same time, possible variations of SPZ boundaries are not considered due to local hydraulic heterogeneity, which is not taken into account in the water intake model. The article analyzes the influence of vertical hydraulic heterogeneity on the formation of sanitary protection zones in the layered heterogeneous aquifer. Random stationary fields of normally distributed logarithms of hydraulic conductivity were used as a basis for the model of hydraulic heterogeneity. As a result, the sizes of the first and second zones of sanitary protection were estimated and the comparative analysis of the received values with the sizes of SPZ was carried out, which were determined without taking into account model hydraulic heterogeneity. The analysis showed that the consideration of model hydraulic heterogeneity leads to a significant increase in the sanitary protection zones.
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Williams, M. M. R. "Computational methods of neutron transport." Annals of Nuclear Energy 12, no. 2 (January 1985): 101. http://dx.doi.org/10.1016/0306-4549(85)90125-2.
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Belas, Jaroslav, Beata Gavurova, Martin Cepel, and Matus Kubak. "Evaluation of economic potential of business environment development by comparing sector differences: perspective of SMEs in the Czech Republic and Slovakia." Oeconomia Copernicana 11, no. 1 (March 31, 2020): 135–59. http://dx.doi.org/10.24136/oc.2020.006.
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Research background: Improving business conditions and SME development are signs of a country’s macroeconomic stability. The issue of identifying and removing barriers to the development of firms in the SME segment is a priority in all countries with developed economies and its importance is currently increasing.
Purpose of the article: The main aim of this paper is to explore possible differences in entrepreneurs’ perception of the business environment based on the industry in which the company operates. The analysis contains also a national view, where a comparison between the Czech Republic and the Slovak Republic is performed.
Methods: Correspondence analysis was used to achieve the research objectives in order to examine the relations between the categorical variables. Its application is beneficial in cases where the graphic output is clearer than the numerical one.
Findings & Value added: The presented research makes it possible to identify problematic aspects of doing business in each sector and to create support mechanisms for the creation of effective structural policies. Entrepreneurs from the Czech Republic’s Production and Transport sectors agree with the statement that the business environment in the country is suitable for starting a business. As for business environment’s suitability for doing business, neither Slovak nor Czech entrepreneurs sector-wide agreed with the given statement. Czech entrepreneurs from the Services, Trade and Construction sectors, respectively, agree, fully agree with the statement that the business environment in the country is reasonably risky and allows for doing business. In the case of entrepreneurs from Slovakia, no significant correspondence is observed. Findings regarding the statement that the business conditions in the country have improved over the past five years are the following: In the Czech Republic, there is a perfect correspondence of the Transport sector and the agreement with the given statement. In the Slovak Republic, agreement was found with the given statement in the Transport sector and neutral position in the Production sector.
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Krawczynski, Henric, Roberto Taverna, Roberto Turolla, Sandro Mereghetti, and Michela Rigoselli. "Fitting XMM-Newton observations of the AXP 1RXS J170849.0−400910 with four magnetar surface emission models, and predictions for X-ray polarization observations with IXPE." Astronomy & Astrophysics 658 (February 2022): A161. http://dx.doi.org/10.1051/0004-6361/202142085.
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Context. Phase-resolved spectral and spectropolarimetric X-ray observations of magnetars present us with the opportunity to test models of the origin of the X-ray emission from these objects, and to constrain the properties of the neutron star surface and atmosphere. Aims. Our first aim is to use archival XMM-Newton observations of the magnetar 1RXS J170849.0−400910 to ascertain how well four emission models describe the phase-resolved XMM-Newton energy spectra. Our second aim is to evaluate the scientific potential of future spectropolarimetric observations of 1RXS J170849.0−400910 with the Imaging X-ray Polarimetry Explorer (IXPE) scheduled for launch in late 2021. The most salient questions are whether IXPE is able to distinguish between the different emission models, and whether IXPE can unambiguously detect the signatures of quantum electrodynamics (QED) effects in strong magnetic fields. Methods. We used numerical radiation transport calculations for a large number of different system parameters to predict the X-ray flux and polarization energy spectra of the source 1RXS J170849.0−400910. Based on the numerical results, we developed a new model to fit phase-resolved and phase-averaged X-ray spectral (i.e., XMM-Newton and IXPE) and spectropolarimetric (IXPE) data. In order to test the sensitivity of IXPE to strong-field QED effects, we fit a simulated IXPE observation with two versions of the model, i.e., with and without QED effects accounted for. Results. The fixed-ions condensed surface model gives the best description of the phase-resolved XMM-Newton spectra, followed by the blackbody and free-ions condensed surface models. The magnetized atmosphere model gives a poor description of the data and seems to be largely excluded. Simulations show that the IXPE observations of sources such as 1RXS J170849.0−400910 will allow us to cleanly distinguish between high-polarization (blackbody, magnetized atmosphere) and low-polarization (condensed surface) models. If the blackbody or magnetized atmosphere models apply, IXPE can easily prove QED effects based on ∼200 ksec observations as studied here; longer IXPE observation times will be needed for a clear detection in the case of the condensed surface models. Conclusions. The XMM-Newton data have such a good signal-to-noise ratio that they reveal some limitations of the theoretical models. Notwithstanding this caveat, the fits clearly favor the fixed-ions condensed surface and blackbody models over the free-ions condensed surface and magnetized atmosphere models. The IXPE polarization information will greatly help us to figure out how to improve the models. The first detection of strong-field QED effects in the signal from astrophysical sources seems possible if an adequate amount of time is dedicated to the observations.
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Dilber, I., and E. E. Lewis. "Variational Nodal Methods for Neutron Transport." Nuclear Science and Engineering 91, no. 2 (October 1985): 132–42. http://dx.doi.org/10.13182/nse85-a27436.
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Park, Hyungwon John, Jeffrey S. Reid, Livia S. Freire, Christopher Jackson, and David H. Richter. "In situ particle sampling relationships to surface and turbulent fluxes using large eddy simulations with Lagrangian particles." Atmospheric Measurement Techniques 15, no. 23 (December 13, 2022): 7171–94. http://dx.doi.org/10.5194/amt-15-7171-2022.
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Abstract. Source functions for mechanically driven coarse-mode sea spray and dust aerosol particles span orders of magnitude owing to a combination of physical sensitivity in the system and large measurement uncertainty. Outside special idealized settings (such as wind tunnels), aerosol particle fluxes are largely inferred from a host of methods, including local eddy correlation, gradient methods, and dry deposition methods. In all of these methods, it is difficult to relate point measurements from towers, ships, or aircraft to a general representative flux of aerosol particles. This difficulty is from the particles' inhomogeneous distribution due to multiple spatiotemporal scales of an evolving marine environment. We hypothesize that the current representation of a point in situ measurement of sea spray or dust particles is a likely contributor to the unrealistic range of flux and concentration outcomes in the literature. This paper aims to help the interpretation of field data: we conduct a series of high-resolution, cloud-free large eddy simulations (LESs) with Lagrangian particles to better understand the temporal evolution and volumetric variability of coarse- to giant-mode marine aerosol particles and their relationship to turbulent transport. The study begins by describing the Lagrangian LES model framework and simulates flux measurements that were made using numerical analogs to field practices such as the eddy covariance method. Using these methods, turbulent flux sampling is quantified based on key features such as coherent structures within the marine atmospheric boundary layer (MABL) and aerosol particle size. We show that for an unstable atmospheric stability, the MABL exhibits large coherent eddy structures, and as a consequence, the flux measurement outcome becomes strongly tied to spatial length scales and relative sampling of crosswise and streamwise sampling. For example, through the use of ogive curves, a given sampling duration of a fixed numerical sampling instrument is found to capture 80 % of the aerosol flux given a sampling rate of zf/w∗∼ 0.2, whereas a spanwise moving instrument results in a 95 % capture. These coherent structures and other canonical features contribute to the lack of convergence to the true aerosol vertical flux at any height. As expected, sampling all of the flow features results in a statistically robust flux signal. Analysis of a neutral boundary layer configuration results in a lower predictive range due to weak or no vertical roll structures compared to the unstable boundary layer setting. Finally, we take the results of each approach and compare their surface flux variability: a baseline metric used in regional and global aerosol models.
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Scheben, Fynn, and Ivan G. Graham. "Iterative Methods for Neutron Transport Eigenvalue Problems." SIAM Journal on Scientific Computing 33, no. 5 (January 2011): 2785–804. http://dx.doi.org/10.1137/100799022.
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Sahni, D. C., and Vinod Kumar. "Numerical solution of singular integral equations of neutron transport problems." Transport Theory and Statistical Physics 16, no. 7 (November 1987): 959–78. http://dx.doi.org/10.1080/00411458708204601.
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Noh, Taewan. "Nodal Transport Methods Using the Simplified Even-Parity Neutron Transport Equation." Journal of the Nuclear Fuel Cycle and Waste Technology(JNFCWT) 16, no. 2 (July 30, 2018): 211–21. http://dx.doi.org/10.7733/jnfcwt.2018.16.2.211.
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