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Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito
Scripta Materialia, 255, p.116366_1 - 116366_5, 2025/01
Times Cited Count:0Reduction of grain boundary cohesive energy by hydrogen has been considered as one of the candidate causes of grain boundary fracture in steels and aluminum alloys. Recently, the effects of grain boundary segregation elements have been investigated by first-principles calculations, but there are few studies that quantitatively estimate the grain boundary cohesive energy. In this study, we describe a quantitative evaluation method using first-principles calculation results and show some examples of experimental calculations.
Okada, Kazuho*; Shibata, Akinobu*; Kimura, Yuji*; Yamaguchi, Masatake; Ebihara, Kenichi; Tsuji, Nobuhiro*
Acta Materialia, 280, p.120288_1 - 120288_14, 2024/11
Times Cited Count:0 Percentile:0.00(Materials Science, Multidisciplinary)Center for Computational Science & e-Systems
JAEA-Evaluation 2024-001, 40 Pages, 2024/10
Research on advanced computational science for nuclear applications, based on "the plan to achieve the medium- and long-term goal of the Japan Atomic Energy Agency", has been performed by Center for Computational Science & e-Systems (CCSE), Japan Atomic Energy Agency. CCSE established a committee consisting of external experts and authorities which evaluates and advises toward the future research and development. This report summarizes the results of the R&D performed by CCSE in FY2023 (April 1st, 2023 - March 31st, 2024) and their evaluation by the committee.
Hasegawa, Yuta; Idomura, Yasuhiro; Onodera, Naoyuki
EPJ Web of Conferences, 302, p.03005_1 - 03005_9, 2024/10
We implemented the ensemble data assimilation (DA) method, the local ensemble transform Kalman filter (LETKF), into the mesh-refined lattice Boltzmann method (LBM) for turbulent flows. Both the LETKF and the mesh-refined LBM were fully implemented on GPUs, so that they are efficiently computed on modern GPU-based supercomputers. We examined the DA accuracy against the flow around a cylinder. The result showed that our method enabled accurate DA with spatially- and temporarily-sparse observation data; the error of the assimilated velocity field with the observation interval of and the observation resolution (1.56% of the total computational grids) was smaller than the amplitude of the observation noise, where is the period of the Krmn vortex and is diameter of the square cylinder.
Kawamura, Takuma; Shimomura, Kazuya; Osaki, Tsukasa*; Idomura, Yasuhiro
EPJ Web of Conferences, 302, p.11002_1 - 11002_8, 2024/10
In the field of nuclear engineering, complex simulations on exa-scale supercomputers generate large-scale data. To facilitate efficient analysis of such simulation data, one needs to share them among scientists at remote locations. However, data I/O and data transfer for such large-scale data are quite costly. To resolve these issues, we developed a remote in-situ visualization system IS-PBVR based on the particle-based volume rendering (PBVR), which is suitable for parallel processing on modern supercomputers. In this study, we extend IS-PBVR for VR visualization on multiple client PCs, thus developing a multi-point remote VR visualization. We apply this technique to fluid simulations on GPU-based supercomputers and verify its utility by sharing in-situ VR visualization between multiple client PCs.
Sitompul, Y.; Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro
EPJ Web of Conferences, 302, p.05004_1 - 05004_10, 2024/10
In fast reactor designs, it is of critical importance to avoid gas entrainment phenomena due to free-surface vortices. Numerical analysis is one of the key methods to understand these phenomena. However, the challenges in computational efficiency and accuracy of the previous numerical methods lead to exploring the Lattice Boltzmann method (LBM) as an alternative, known for its computational efficiency and capability in simulating complex flows. In this study, we implement free-surface LBM to accelerate gas entrainment analysis, significantly reducing computational costs while maintaining accuracy compared to traditional methods. Simulation results using LBM align well with experimental data, offering a promising avenue for faster analysis in future fast reactor designs.
Idomura, Yasuhiro
Physics of Plasmas, 31(10), p.102504_1 - 102504_10, 2024/10
Times Cited Count:0Hydrogen isotope mixing phenomena in tokamak plasmas are analyzed using global full-f gyrokinetic simulations. Model plasma parameters are chosen based on the hydrogen isotope pellet experiments on JET, in which hydrogen isotope mixing in the time scale of the energy confinement time occurred after injecting deuterium (D) pellets into hydrogen (H) plasmas. Two numerical experiments are conducted using plasma profiles before and after the D pellet injection. In both cases, turbulent fluctuations in the plasma core are characterized by ion temperature gradient driven turbulence, while in the latter case, trapped electron mode turbulence also exists in the outer region. In the former case, the density profile of bulk H ions is kept in a quasi-steady state, and the particle confinement time of bulk H ions is an order of magnitude longer than the energy confinement time. In the latter case, the density profiles of bulk H ions and pellet D ions show transient relaxation in the time scale of the energy confinement time, indicating the fast hydrogen isotope mixing. In the toroidal angular momentum balance, it is found that the hydrogen isotope mixing is driven by the toroidal field stress.
Machida, Masahiko; Yamada, Susumu; Kim, M.; Tanaka, Satoshi*; Tobita, Yasuhiro*; Iwata, Ayako*; Aoki, Yuto; Aoki, Kazuhisa; Yanagisawa, Kenichi*; Yamaguchi, Takashi; et al.
RIST News, (70), p.3 - 22, 2024/09
Inside the Fukushima Daiichi Nuclear Power Plant (1F), there are many locations with high radiation levels due to contamination by radioactive materials that leaked from the reactor. These pose a significant obstacle to the smooth progress of decommissioning work. To help solve this issue, the Japan Atomic Energy Agency (JAEA), under a subsidy from the Ministry of Economy, Trade, and Industry's decommissioning and contaminated water management project, is conducting research and development on digital technologies to improve the radiation environment inside the decommissioning site. This project, titled "Development of Technology to Improve the Environment Inside Reactor Buildings (Enhancing Digital Technology for Environment and Source Distribution to Reduce Radiation Exposure)," began in April of FY 2023. In this project, the aim is to develop three interconnected systems: FrontEnd, Pro, and BackEnd. The FrontEnd system, based on the previously developed 3D-ADRES-Indoor (prototype) from FY 2021-2022, will be upgraded to a high-speed digital twin technology usable on-site. The Pro system will carry out detailed analysis in rooms such as the new office building at 1F, while the BackEnd system will serve as a database to centrally manage the collected and analyzed data. This report focuses on the FrontEnd system, which will be used on-site. After point cloud measurement, the system will quickly create a 3D mesh model, estimate the radiation source from dose rate measurements, and refine the position and intensity of the estimated source using recalculation techniques (re-observation instructions and re-estimation). The results of verification tests conducted on Unit 5 are also presented. Furthermore, the report briefly discusses the future research and development plans for this project.
Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Materials Transactions, 65(8), p.899 - 906, 2024/08
Times Cited Count:0 Percentile:0.00(Materials Science, Multidisciplinary)It is indispensable to suppress hydrogen embrittlement (HE) to develop the strength of the Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the IGF initiation to suppress HE. In the present study, we investigated the stress, strain, and H concentration, which influence the IGF initiation, in actual fractured regions by simulation of a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the stress, strain, and H concentration, and discussed the IG crack initiation condition. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates IG crack initiation while the accumulation of H due to stress has little impact on it.
Watanabe, Tsutomu*; Ishikawa, Shuhei*; Kawashima, Masayuki*; Shimoyama, Ko*; Onodera, Naoyuki; Hasegawa, Yuta; Inagaki, Atsushi*
Journal of Wind Engineering and Industrial Aerodynamics, 250, p.105783_1 - 105783_17, 2024/07
Times Cited Count:1 Percentile:0.00(Engineering, Civil)This paper presents simulations of drifting snow using a Lagrangian particle dispersion model coupled with a large-eddy simulation code. The model accurately replicates observed features such as mass transport rate dependency on flow velocity and variations in particle size distribution. It also shows that the saltation layer height increases monotonically with flow velocity, contrary to conventional estimates. Additionally, the study confirms the transition from saltation to suspension near the estimated saltation layer height and finds that dense snow streamers are linked to small-scale low-speed streaks in near-surface flows.
Kobayashi, Keita
New Glass, 39(2), p.13 - 17, 2024/07
The atomic arrangement in glass structures lacks periodicity, and the information obtained experimentally reflects an average structure. Therefore, to estimate the three-dimensional structure of glass materials, molecular dynamics simulations are effective. The results of molecular dynamics calculations strongly depend on the interatomic potential. We have created a machine learning potential (MLP) trained on first-principles calculation results for silica materials. This paper outlines our research of structural analysis of high-density silica glass using machine learning molecular dynamics (MLMD) with the MLP. The MLMD successfully reproduced the experimental data of silica glass. Furthermore, it was revealed that changes in the medium-range order structure in high-density silica glass are characterized by the deformation behavior of ring structures within the Si-O covalent bond network due to the compression.
Nakata, Yuto; Sasaki, Takehiko*; Thomsen, B.; Shiga, Motoyuki
Chemical Physics Letters, 845, p.141285_1 - 141285_9, 2024/06
Times Cited Count:0 Percentile:0.00(Chemistry, Physical)Using density functional theory and metadynamics simulations, we study cellobiose hydrolysis and glucose hydrogenation with silica-supported platinum and palladium catalysts in hot water, relevant to green cellulose conversion. It is found that cellobiose hydrolysis can proceed by the attack of hydrogen atoms adsorbed on metal or protons spilled over to silica forming glucose. Glucose can then be hydrogenated by hydrogen atoms adsorbed at platinum/water interface forming sorbitol. The reaction barriers of hydrolysis and hydrogenation at platinum/water interface are both lower than that at palladium/water interface, which explains the experimental finding that the platinum performs as a better catalyst than palladium.
Ahmed, A.*; Uttarasak, K.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Toda, Hiroyuki*; Yamaguchi, Masatake; et al.
Journal of Alloys and Compounds, 988, p.174234_1 - 174234_9, 2024/06
Times Cited Count:3 Percentile:87.51(Chemistry, Physical)This study aims to clarify the growth process of the-phase in Al-Mg-Si alloys from the point of view of morphology evolution. For this research, the -phase orientation relationship, shape, growth process, misfit value, and interfacial condition between the -phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focus ion beam (FIB), and optical microscope (OM). Results include the identification of {111} facets at the edges of the -phase, as well as the proposal of two new three-dimensional shapes for the -phase. We purposed the morphology evolution during the growth process of MgSi crystal and calculated the misfit to understand the unstable (111) facet has a higher misfit value as compared to the (001) and (011) facets. Our observations provide how they influence the behavior of MgSi crystals.
Onodera, Naoyuki; Sugihara, Kenta; Ina, Takuya; Idomura, Yasuhiro
Keisan Kogaku Koenkai Rombunshu (CD-ROM), 29, 3 Pages, 2024/06
Gas-liquid two-phase flow analysis is one of the most important research topics in nuclear engineering because it is essential for safety evaluation and reactor design. However, it requires large-scale multi-scale simulations, and advanced numerical approaches are needed. To meet this challenge, we have continued to develop the Poisson solver for the multiphase flow analysis code JUPITER. In this study, we aim to improve the convergence of the pressure Poisson solver by formulating the Navier-Stokes equation without using the incompressible approximation. The convergence performance was measured on 8 GPUs for bubbly flow analysis in a circular tube. The results show that the computation time and the number of iterations are reduced by half compared to those using the incompressible approximation, which indicates the usefulness of the formulation in the present study.
Hasegawa, Yuta; Idomura, Yasuhiro; Onodera, Naoyuki
Keisan Kogaku Koenkai Rombunshu (CD-ROM), 29, 4 Pages, 2024/06
We implemented the ensemble data assimilation (DA) of turbulence by using the mesh-refined lattice Boltzmann method with the local ensemble transform Kalman filter (LBM-LETKF). We examined the accuracy of the data assimilation against a turbulent flow around a three-dimensional square cylinder. The DA error was comparable or less than the observation noise when the observation interval was a half of the period of the Krmn vortex street and the number of observation points was 0.195% of computational grid points. The LBM-LETKF enables DA of turbulence with spatially- and temporally- sparse observations.
Yamaguchi, Masatake
Nihon Genshiryoku Gakkai-Shi ATOMO, 66(6), p.291 - 294, 2024/06
First-principles calculations of lattice defects in metals became available around year 2000 and were gradually performed for planar defects such as surface and grain boundaries, point defects such as atomic vacancies, and line defects such as dislocation cores, in the order of ease of calculation. The author introduces some examples of first-principles calculations of microscopic properties, which seem to strongly influence macroscopic material properties.
Tsuchiya, Jun*; Shiga, Motoyuki; Tsuneyuki, Shinji*; Thompson, E. C.*
Physical Review Research (Internet), 6(2), p.023302_1 - 023302_6, 2024/06
We investigate the effect of nuclear quantum effects (NQEs) of hydrogen atoms on the elasticity of ice VII at high pressure and ambient temperature conditions using ab initio path-integral molecular dynamics (PIMD) calculations. We find that the NQEs of hydrogen contributes to the transition of ice VII from a static disordered structure to a dynamically disordered structure at pressures exceeding 40 GPa. This transition is marked by a discontinuous increase of the elastic constants. Comparison of molecular dynamics and PIMD calculations reveal that NQEs increase the elastic constants of ice by about 20% at 70 GPa and 300 K.
Yamaguchi, Akiko; Kurihara, Yuichi*; Nagata, Kojiro*; Tanaka, Kazuya; Higaki, Shogo*; Kobayashi, Toru; Tanida, Hajime; Ohara, Yoshiyuki*; Yokoyama, Keiichi; Yaita, Tsuyoshi; et al.
Journal of Colloid and Interface Science, 661, p.317 - 332, 2024/05
Times Cited Count:4 Percentile:81.53(Chemistry, Physical)no abstracts in English
Nagai, Yuki; Iwasaki, Yutaka*; Kitahara, Koichi*; Takagiwa, Yoshiki*; Kimura, Kaoru*; Shiga, Motoyuki
Physical Review Letters, 132(19), p.196301_1 - 196301_6, 2024/05
Times Cited Count:1 Percentile:72.81(Physics, Multidisciplinary)A quasicrystal is an ordered but non-periodic structure understood as a projection from a higher dimensional periodic structure. An anomalous increase in heat capacity at high temperatures has been discussed for over two decades as a manifestation of a hidden high dimensionality of quasicrystals. A theoretical study of the heat capacity of realistic quasicrystals or their approximants has yet to be conducted because of the huge computational complexity. To bridge this gap between experiment and theory, we show experiments and cutting-edge machine-learning molecular simulations on the same material, an Al-Pd-Ru quasicrystal, and its approximants. We show that at high temperatures, aluminum atoms diffuse with discontinuous-like jumps, and the diffusion paths of the aluminum can be understood in terms of jumps corresponding to hyperatomic fluctuations in six-dimensional space.
Ayoub, A.*; Wainwright, Haruko*; Sansavini, G.*; Gauntt, R.*; Saito, Kimiaki
iScience (Internet), 27(4), p.109485_1 - 109485_15, 2024/04
Times Cited Count:2 Percentile:86.32(Multidisciplinary Sciences)