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Time-dependent neutron transport calculation with a parallel discontinuous finite element S N code SNIPER

Nuclear Engineering and Design 2025年 442卷

作者： Boran Kong Tao Dai Ni Dai Institute of Applied Physics and Computational Mathematics Beijing 100094 China

Discontinuous finite element method (DFEM) based discrete ordinates (S N ) is an important numerical method for solving time-dependent transport equation due to its geometry adaptivity and high accuracy. The parallel strategies of DFEM S N can be divided into Gauss-Seidel and block Jacobi. In this article, the parallel performance of several Gauss-Seidel parallel strategies and the block Jacobi strategy are compared and analyzed. The thresholds of fixed source scaling factor method (FSSFM) are analyzed through 2D C5G7-TD benchmarks. Also, a 2D time-dependent Fourier analysis is performed. Fourier analysis results show that the convergence behavior of time-dependent S N calculation is insensitive to the S N quadrature order. With the increase of the number of inner iterations, the spectral radius decreases. With the increase of fission-time term ratio w and scattering ratio c , the spectral radius increases. From the numerical results of the C5G7-TD benchmarks with a parallel S N code SNIPER, it can be concluded that the online-judged strategy achieves the highest parallel efficiency among several Gauss-Seidel parallel strategies. Block Jacobi parallel strategy saves about 30 % total time than the Gauss-Seidel strategy. Also, for transient calculation, FSSFM with reasonable thresholds decreases the number of outer iterations by an order of magnitude.

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Mitigation of the ablative Rayleigh–Taylor instability by nonlocal electron heat transport

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Matter and Radiation at Extremes 2022年第5期7卷 47-54页

作者： Jun Li Rui Yan Bin Zhao Jian Zheng Huasen Zhang Xiyun Lu Department of Modern Mechanics University of Science and Technology of ChinaHefei 230026China Collaborative Innovation Center of IFSA(CICIFSA) Shanghai Jiao Tong UniversityShanghai 200240China Department of Mathematics and Physics Nanjing Institute of TechnologyNanjingJiangSu 211167China Department of Plasma Physics and Fusion Engineering University of Science and Technology of ChinaHefeiAnhui 230026China Institute of Applied Physics and Computational Mathematics Beijing 10094China

The effects of electron nonlocal heat transport (NLHT) on the two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) upto the highly nonlinear phase are reported for the first time through numerical simulations with a multigroup diffusion model. It is found thatas well as its role in the linear stabilization of ARTI growth, NLHT can also mitigate ARTI bubble nonlinear growth after the first saturationto the classical terminal velocity, compared with what is predicted by the local Spitzer–Härm model. The key factor affecting the reductionin the linear growth rate is the enhancement of the ablation velocity Va by preheating. It is found that NLHT mitigates nonlinear bubblegrowth through a mechanism involving reduction of vorticity generation. NLHT enhances ablation near the spike tip and slows down thespike, leading to weaker vortex generation as the pump of bubble reacceleration in the nonlinear stage. NLHT more effectively reduces thenonlinear growth of shorter-wavelength ARTI modes seeded by the laser imprinting phase in direct-drive laser fusion.

关键词： bubble nonlinear stabilization

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A 3D-shockwave volume rendering algorithm based on feature boundary detection 14

A 3D-shockwave volume rendering algorithm based on feature b...

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14th IADIS International Conference Computer Graphics, Visualization, Computer Vision and Image Processing 2020, CGVCVIP 2020 and 5th IADIS International Conference Big Data Analytics, Data Mining and computational Intelligence 2020, BigDaCI 2020 and 9th IADIS International Conference Theory and Practice in Modern Computing 2020, TPMC 2020, Part of the 14th Multi Conference on Computer Science and Information Systems, MCCSIS 2020

作者： Wang, Huawei He, Liu Ai, Zhiwei Cao, Yi Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China CAEP Software Center for High Performance Numerical Simulation Beijing100088 China

ISBN: (纸本)9789898704214

The mechanism of shockwave propagation in complex environments plays an important role in the damage and protection assessment. At present, domain experts are realizing shockwave propagation numerical simulations with high scientific confidence on thousands of processing cores, and thus large-scale three-dimensional (3D) data fields containing fine physical features are output. It is desired to effectively reveal complex spatial structures of shockwaves in the data fields so as to facilitate domain experts to make in-depth observation and analysis. In this paper, a volume rendering algorithm based on feature boundary detection is proposed to visualize 3D shockwave data fields. In the algorithm, a two-dimensional (2D) boundary detection technique is generalized to the 3D case and further used to extract feature data containing the wavefronts, and then, the feature data are resampled and composited in the ray-casting manner. The algorithm has been preliminarily applied to 3D shock fields, and the results show that the algorithm can effectively analyze the shockwave features and clearly show the 3D spatial structures of the wavefronts. © Proceedings of the 14th IADIS International Conference Computer Graphics, Visualization, Computer Vision and Image Processing 2020, CGVCVIP 2020 and Proceedings of the 5th IADIS International Conference Big Data Analytics, Data Mining and computational Intelligence 2020, BigDaCI 2020 and Proceedings of the 9th IADIS International Conference Theory and Practice in Modern Computing 2020, TPMC 2020 - Part of the 14th Multi Conference on Computer Science and Information Systems, MCCSIS 2020. All rights reserved.

关键词： Visualization

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Exact and approximate fluxonium array modes

arXiv

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arXiv 2024年

作者： Sorokanich, Stephen Hays, Max Warrington, Neill C. Applied and Computational Mathematics Division National Institute of Standards and Technology GaithersburgMD20899-8910 United States Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Center for Theoretical Physics Massachusetts Institute of Technology CambridgeMA02139 United States

We present an exact solution for the linearized junction array modes of the superconducting qubit fluxonium in the absence of array disorder. This solution holds for arrays of any length and ground capacitance, and for both differential and grounded devices. Array mode energies are determined by roots of convex combinations of Chebyshev polynomials, and their spatial profiles are plane waves. We also provide a simple, approximate solution, which estimates array mode properties over a wide range of circuit parameters, and an accompanying Mathematica file that implements both the exact and approximate solutions. © 2024, CC BY.

关键词： Chebyshev polynomials

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Propagation of gaseous detonation across inert layers 38th

Propagation of gaseous detonation across inert layers

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38th International Symposium on Combustion, 2021

作者： Wang, Yuan Huang, Chengyang Deiterding, Ralf Chen, Haitao Chen, Zheng Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100094 China SKLTCS CAPT BIC-ESAT College of Engineering Peking University Beijing 100871 China Aerodynamics and Flight Mechanics Research Group University of Southampton Boldrewood Campus Southampton SO16 7QF United Kingdom

In rotating detonation engines and explosion accidents, detonation may propagate in an inhomogeneous mixture with inert layers. This study focuses on detonation propagation in a stoichiometric H2/O2/N2 mixture with multiple inert layers normal to the detonation propagation direction. One- and two-dimensional simulations considering detailed chemistry are conducted. The emphasis is placed on assessing the effects of inert layer on detonation reinitiation/failure, detonation propagation speed, detonation cell structure and cell size. Specifically, the inert layer thickness and the spacing between two consecutive inert layers are varied. Either detonation reinitiation or failure across the inert layers is observed. It is found that successful detonation reinitiation occurs only at relatively small values of the inert layer thickness and spacing. For each given value of the inert layer spacing, there is a critical inert layer thickness above which detonation fails after crossing the inert layers. This critical inert layer thickness is found to decrease as the inert layer spacing increases. The detailed process of detonation reinitiation across the inert layers is analyzed. The interaction between the transverse shock waves is shown to induce local autoignition/explosion and eventually over-driven detonation development in the reactive layer. The averaged detonation propagation speed in the inhomogeneous mixture is compared to the CJ speed and very good agreement is achieved. This indicates that the inert layer does not affect the detonation propagation speed once successful detonation reinitiation happens. Unlike the detonation speed, the detonation cell structure and cell size are greatly affected by the inert layer results. For the first time, large cellular structure with size linearly proportional to the inert layer spacing is observed for detonation propagation across inert layers. Besides, a double cellular structure is observed for relatively large spacing betwee

关键词： Detonation

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A One-Stage High-Order Gas-Kinetic Scheme for Multi-Component Flows with Interface-Sharpening Technique

SSRN

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SSRN 2023年

作者： Li, Shiyi Luo, Dongmi Qiu, Jianxian Jiang, Song Chen, Yibing Institute of Applied Physics and Computational Mathematics Beijing100191 China School of Mathematical Sciences Fujian Provincial Key Laboratory of Mathematical modeling and High-Performance Scientific Computation Xiamen University Fujian Xiamen361005 China

We propose a one-stage high-order gas-kinetic scheme (GKS) with interface-sharpening technique for the 4-equations model of compressible multi-component stiffened-gas flows. The scheme is constructed based on the framework of a one-stage efficient high-order GKS (EHGKS), which can achieve uniform high-order accuracy in both space and time. The main idea in the construction of the new scheme consists of three parts. Firstly, different from the original EHGKS, the non-oscillatory kinetic (NOK) flux is introduced to compute the leading term and the related flux evaluations, which enables the modified EHGKS suitable for stiffened gases, together with no pressure and velocity oscillations across the contact discontinuities. Then the modified scheme is utilized to discrete the conservative parts of the 4-equations model. Secondly, in order to avoid the oscillations across material interfaces, a high-order GKS is derived to solve the non-conservative parts of the 4-equations model following the idea of Abgrall [1]. Finally, to further reduce the over diffusion near a material interface, a simple interface-sharpening technique is developed, which combines the idea of interface construction and downwind scheme. The numerical results demonstrate that the proposed scheme can not only achieve the designed uniform accuracy in both space and time, but also sharply capture material interfaces. © 2023, The Authors. All rights reserved.

关键词： Kinetics

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DeePKS+ABACUS as a Bridge between Expensive Quantum Mechanical Models and Machine Learning Potentials

arXiv

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arXiv 2022年

作者： Li, Wenfei Ou, Qi Chen, Yixiao Cao, Yu Liu, Renxi Zhang, Chunyi Zheng, Daye Cai, Chun Wu, Xifan Wang, Han Chen, Mohan Zhang, Linfeng AI for Science Institute Beijing100080 China Program in Applied and Computational Mathematics Princeton University PrincetonNJ08544 United States HEDPS CAPT College of Engineering School of Physics Peking University Beijing100871 China Department of Physics Temple University PhiladelphiaPA19122 United States Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Huayuan Road 6 Beijing100088 China DP Technology Beijing100080 China

Recently, the development of machine learning (ML) potentials has made it possible to perform large-scale and long-time molecular simulations with the accuracy of quantum mechanical (QM) models. However, for high-level QM methods, such as density functional theory (DFT) at the meta-GGA level and/or with exact exchange, quantum Monte Carlo, etc., generating a sufficient amount of data for training a ML potential has remained computationally challenging due to their high cost. In this work, we demonstrate that this issue can be largely alleviated with Deep Kohn-Sham (DeePKS), a ML-based DFT model. DeePKS employs a computationally efficient neural network-based functional model to construct a correction term added upon a cheap DFT model. Upon training, DeePKS offers closely-matched energies and forces compared with high-level QM method, but the number of training data required is orders of magnitude less than that required for training a reliable ML potential. As such, DeePKS can serve as a bridge between expensive QM models and ML potentials: one can generate a decent amount of high-accuracy QM data to train a DeePKS model, and then use the DeePKS model to label a much larger amount of configurations to train a ML potential. This scheme for periodic systems is implemented in a DFT package ABACUS, which is open-source and ready for use in various applications. © 2022, CC BY.

关键词： Density functional theory

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Giant retardation effect in electron-electron interaction

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Physical Review A 2022年第3期105卷 L030801-L030801页

作者： Zhimin Hu Gang Xiong Zhencen He Zhihao Yang Naoki Numadate Chengwu Huang Jiamin Yang Ke Yao Baoren Wei Yaming Zou Chensheng Wu Yulong Ma Yong Wu Xiang Gao Nobuyuki Nakamura Key Laboratory of Radiation Physics and Technology of Ministry of Education Institute of Nuclear Science and Technology Sichuan University Chengdu 610064 China Key Laboratory of Nuclear Physics and Ion-Beam Application (MOE) Institute of Modern Physics Fudan University Shanghai 200433 China Laser Fusion Research Center China Academy of Engineering Physics Mianyang 621900 China Institute for Laser Science The University of Electro-Communications Tokyo 182-8585 Japan Institute for Applied Physics and Computational Mathematics Beijing 100088 China Beijing Computational Science Research Center Beijing 1000193 China

In electron-electron interactions in electromagnetic systems, retardation in the exchange of a virtual photon is essentially important as the first-order quantum electrodynamics correction. However, the retardation effect is generally so small that it is buried in unretarded electric and magnetic interactions and thus has yet to be directly probed. Here, we present a giant contribution of the retardation effect in an electron-electron interaction via observing strong electric-dipole-allowed radiative transition rates. The relative transition rates are obtained for two dominant radiative transitions from the 1s2s22p1/22p3/2 inner-shell excited state of boronlike tungsten and bismuth ions to 1s22s22p1/2 and 1s22s22p3/2, and it was found that the transition rate ratio between the two transitions is affected by the retardation effect up to more than 100%.

关键词： Electronic transitions Relativistic & quantum electrodynamic effects in atoms, molecules,& ions

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Enhanced strong-coupling stimulated Brillouin amplification assisted by Raman amplification

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Physical Review E 2023年第1期107卷 015204-015204页

作者： Y. Chen C. Y. Zheng Z. J. Liu L. H. Cao C. Z. Xiao School of Electrical and Information Engineering Anhui University of Science and Technology Huainan Anhui 232001 China Key Laboratory for Micro-/Nano-Optoelectronic Devices of Ministry of Education School of Physics and Electronics Hunan University Changsha 410082 China Institute of Applied Physics and Computational Mathematics Beijing 100094 China HEDPS Center for Applied Physics and Technology Peking University Beijing 100871 China Collaborative Innovation Center of IFSA (CICIFSA) Shanghai Jiao Tong University Shanghai 200240 China

Higher intensity of strong-coupling stimulated Brillouin scattering (SC-SBS) amplification is achieved by supplementary Raman amplification. In this scheme, a Raman pump laser first amplifies the seed pulse in the homogeneous plasma, and then a SC-SBS pump laser continues the amplification in the inhomogeneous plasma in order to suppress the spontaneous instability of pump lasers. The intensity of the seed laser gets higher and the duration of the seed laser gets shorter than that in the pure SC-SBS scheme with the same incident energy, while the energy conversion efficiency is not significantly reduced. We also found that the SC-SBS amplification is seeded by the leading pulse of Raman amplification. The results obtained from envelope coupling equations, Vlasov simulations, and two-dimensional particle-in-cell simulations agree with each other. This scheme offers a possible way to improve the SC-SBS amplification in experiments.

关键词： High-energy-density plasmas Laser-plasma interactions Plasma instabilities

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Classical and machine learning interatomic potentials for BCC vanadium

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Physical Review Materials 2022年第11期6卷 113603-113603页

作者： Rui Wang Xiaoxiao Ma Linfeng Zhang Han Wang David J. Srolovitz Tongqi Wen Zhaoxuan Wu Department of Materials Science and Engineering City University of Hong Kong Hong Kong China AI for Science Institute Beijing 100080 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing 100088 China Department of Mechanical Engineering The University of Hong Kong Hong Kong China Hong Kong Institute for Advanced Study City University of Hong Kong Hong Kong China

BCC transition metals (TMs) exhibit complex temperature and strain-rate dependent plastic deformation behavior controlled by individual crystal lattice defects. Classical empirical and semiempirical interatomic potentials have limited capability in modeling defect properties such as the screw dislocation core structures and Peierls barriers in the BCC structure. Machine learning (ML) potentials, trained on DFT-based datasets, have shown some successes in reproducing dislocation core properties. However, in group VB TMs, the most widely used DFT functionals produce erroneous shear moduli C44 which are undesirably transferred to machine-learning interatomic potentials, leaving current ML approaches unsuitable for this important class of metals and alloys. Here, we develop two interatomic potentials for BCC vanadium (V) based on (i) an extension of the partial electron density and screening parameter in the classical semiempirical modified embedded-atom method (XMEAM-V) and (ii) a recent hybrid descriptor in the ML Deep Potential framework (DP-HYB-V). We describe distinct features in these two disparate approaches, including their dataset generation, training procedure, weakness and strength in modeling lattice and defect properties in BCC V. Both XMEAM-V and DP-HYB-V reproduce a broad range of defect properties (vacancy, self-interstitials, surface, dislocation) relevant to plastic deformation and fracture. In particular, XMEAM-V reproduces nearly all mechanical and thermodynamic properties at DFT accuracies and with C44 near the experimental value. XMEAM-V also naturally exhibits the anomalous slip at 77 K widely observed in group VB and VIB TMs and outperforms all existing, publically available interatomic potentials for V. The XMEAM thus provides a practical path to developing accurate and efficient interatomic potentials for nonmagnetic BCC TMs and possibly multiprincipal element TM alloys.

关键词： Interatomic & molecular potentials Materials modeling

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