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arXiv 2021年

作者： Li, Jiequan Zhang, Qinglong Institute of Applied Physics and Computational Mathematics Beijing Center for Applied Physics and Technology Peking University China State Key Laboratory for Turbulence Research and Complex System Peking University China Department of Mathematics and Statistics Ningbo University China

In the computation of compressible fluid flows, numerical boundary conditions are always necessary for all physical variables at computational boundaries while just partial physical variables are often prescribed as physical boundary conditions. Certain extrapolation technique or ghost cells are often employed traditionally for this issue but spurious wave reflections often arise to cause numerical instability. In this paper, we associate this issue with the one-sided generalized Riemann problem (GRP) solver motivated by the accelerated piston problem in gas dynamics so that the extrapolation technique can be actually avoided. In fact, the compatibility arguments naturally requires to formulate the one-sided generalized Riemann problem and incorporate it into the numerical procedure of boundary conditions. As far as the interaction of nonlinear waves with physical boundaries, such a one-sided GRP solver shows significant effects, as numerical experiments demonstrate, on avoiding spurious wave reflections at the computational boundaries. Copyright © 2021, The Authors. All rights reserved.

关键词： Boundary conditions

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A Hybrid Numerical Simulation of Supersonic Isotropicturbulence

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Communications in Computational physics 2019年第1期25卷 189-217页

作者： Luoqin Liu Jianchun Wang Yipeng Shi Shiyi Chen X.T.He State Key Laboratory for Turbulence and Complex Systems Center for Applied Physics and TechnologyCollege of EngineeringPeking UniversityBeijing 100871China Department of Mechanics and Aerospace Engineering Southern University of Science and TechnologyShenzhen 518055China Institute of Applied Physics and Computational Mathematics Beijing 100088China

This paper presents an extension work of the hybrid scheme proposed by Wang et al.[***.229(2010)169-180]for numerical simulation of sub-sonic isotropic turbulence to supersonic turbulence *** scheme still utilizes an 8th-order compact scheme with built-in hyperviscosity for smooth regions and a 7th-order WENO scheme for highly compression regions,but now both in their con-servation formulations and for the latter with the Roe type characteristic-wise *** enhance the robustness of the WENO scheme without compromising its high-resolution and accuracy,the recursive-order-reduction procedure is adopted,where a new type of reconstruction-failure-detection criterion is constructed from the idea of *** addition,a new form of cooling function is proposed,which is proved also to be *** a combination of these techniques,the new scheme not only inherits the good properties of the original one but also extends largely the computable range of turbulent Mach number,which has been further confirmed by numerical results.

关键词： Supersonic turbulence hybrid scheme positivity-preserving ROR-WENO scheme compact scheme

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Effects of nozzle and fluid properties on the drop formation dynamics in a drop-on-demand inkjet printing

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applied Mathematics and Mechanics(English Edition) 2019年第9期40卷 1239-1254页

作者： A. B. AQEEL M. MOHASAN Pengyu LV Yantao YANG Huiling DUAN State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science Beijing Innovation Center for Engineering Science and Advanced Technology College of Engineering Peking University Beijing 100871 China National University of Sciences and Technology H-12 Islamabad Pakistan Center for Applied Physics and Technology Key Laboratory of High Energy Density Physics and Inertial Fusion Sciences and Application Collaborative Innovation Center of Ministry of Education Peking University Beijing 100871 China

The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the interior surface, and the fluid properties to achieve the stable droplet formation with higher velocity. It is found that a nozzle with contracting angle of 45° generates the most stable and fastest single droplet, which is beneficial for the enhanced printing quality and high-throughput printing rate. For this nozzle with the optimal geometry, we systematically change the wettability of the interior surface, i.e., different contact angles. As the contact angle increases, pinch-off time increases and the droplet speed reduces. Finally, fluids with different properties are investigated to identify the printability range.

关键词： inkjet printing drop-on-demand (DOD) droplet formation nozzle geometry surface wettability printability range

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On the supremum of the steepness parameter in self-adjusting steepness based schemes

arXiv

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arXiv 2021年

作者： Ruan, Yucang Tian, Baolin Zhang, Xinting He, Zhiwei State Key Laboratory for Turbulence and Complex Systems College of Engineering Peking University Beijing100871 China Sino-French Engineer School Beihang University Beijing100191 China Institute of Applied Physics and Computational Mathematics Beijing100094 China HEDPS and Center for Applied Physics and Technology College of Engineering Peking University Beijing100871 China

Self-adjusting steepness (SAS)-based schemes [1] preserve various structures in the compressible flows. These schemes provide a range of desired behaviors depending on the steepness-adjustable limiters with the steepness measured by a steepness parameter. These properties include either high-order properties with exact steepness parameter values that are theoretically determined or having anti-diffusive/compression properties with a larger steepness parameter. Nevertheless, the supremum of the steepness parameter has not been determined theoretically yet. In this study, we derive a universal method to determine the supremum using Sweby's total variation diminishing (TVD) condition [2]. Two typical steepness-adjustable limiters are analyzed in detail including the tangent of hyperbola for interface capturing (THINC) limiter and the steepness-adjustable harmonic (SAH) limiter. We also obtain the analytical expression of the supremum of the steepness parameter which is dependent on the Courant-Friedrichs-Lewy (CFL) number. Using this solution, we then propose supremum-determined SAS schemes. These schemes are further extended to solve the compressible Euler equations. The results of typical numerical tests confirm our theoretical conclusions and show that the final schemes are capable of sharply capturing contact discontinuities and minimizing numerical oscillations. Copyright © 2021, The Authors. All rights reserved.

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A novel hybrid neural network of fluid-structure interaction prediction for two cylinders in tandem arrangement

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Engineering Applications of Computational Fluid Mechanics 2025年第1期19卷

作者： Yanfang Lyu Yunyang Zhang Zhiqiang Gong Xiao Kang Wen Yao Yongmao Pei a State Key Laboratory for Turbulence and Complex Systems & Center for Applied Physics and Technology College of Engineering Peking University Beijing People’s Republic of Chinab Defense Innovation Institute Chinese Academy of Military Science Beijing People’s Republic of Chinac Intelligent Game and Decision Laboratory Beijing People’s Republic of China b Defense Innovation Institute Chinese Academy of Military Science Beijing People’s Republic of Chinac Intelligent Game and Decision Laboratory Beijing People’s Republic of China d Institute of Advanced Structure Technology Beijing Institute of Technology Beijing People’s Republic of China a State Key Laboratory for Turbulence and Complex Systems & Center for Applied Physics and Technology College of Engineering Peking University Beijing People’s Republic of China

Fluid-structure interaction (FSI) in multibody systems, a non-negligible phenomenon in engineering applications, has been extensively studied via traditional experimental and simulation methods with high cost and time consumption. Deep learning has shown promise in improving computing efficiency while ensuring modelling accuracy in FSI analysis. However, its current capabilities are limited when it comes to constructing multi-object coupling systems with dynamic boundaries. In this paper, we propose a novel FSI hybrid neural network solver integrated by an innovative fluid deep learning model and the structural motion equations for the vortex-induced vibration (VIV) modelling of two tandem cylinders. This well-designed solver, in sequence-to-point manner, can precisely predict the subsequent flow field state by coupling the historical multi-time fluid sequences and the current structural responses, moreover, derives the structural state at the next time based on the interaction forces. Therein, the fluid deep learning model consists of a wall shear stress model and an innovative flow field model with U-shaped architecture jointing the Fourier neural operator and modified convolution long-short term memory model. Two models effectively capture coupling interaction forces, and the latter has higher accuracy in modelling instantaneous flow fields compared with baseline Convolutional Neural Networks-based models with similar parameters. Compared to FSI benchmark case, the proposed FSI model demonstrates superior accuracy and robustness in constructing the nonlinear complex multi-vibration systems. And its prediction speed realises an improvement of over 1000 times than that of the numerical simulation. Significantly, the proposed FSI neural model has substantial potential for advancing FSI modelling of flexible structures featuring pronounced nonlinear deformation boundaries.

关键词： Flow-induced interaction fluid mechanics two tandem cylinders Fourier neural operator convolutional long-short term memory model

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Generating Function for Projected Entangled-Pair states

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PRX Quantum 2024年第1期5卷 010335-010335页

作者： Wei-Lin Tu Laurens Vanderstraeten Norbert Schuch Hyun-Yong Lee Naoki Kawashima Ji-Yao Chen Faculty of Science and Technology Keio University 3-14-1 Hiyoshi Kohoku-ku Yokohama 223-8522 Japan Center for Nonlinear Phenomena and Complex Systems Université Libre de Bruxelles B-1050 Bruxelles Belgium University of Vienna Faculty of Physics Boltzmanngasse 5 Wien 1090 Austria University of Vienna Faculty of Mathematics Oskar-Morgenstern-Platz 1 Wien 1090 Austria Division of Display and Semiconductor Physics Korea University Sejong 30019 Korea Department of Applied Physics Graduate School Korea University Sejong 30019 Korea Interdisciplinary Program in E·ICT-Culture-Sports Convergence Korea University Sejong 30019 Korea Institute for Solid State Physics The University of Tokyo Kashiwa Chiba 277-8581 Japan Trans-scale Quantum Science Institute The University of Tokyo Bunkyo Tokyo 113-0033 Japan Center for Neutron Science and Technology Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices School of Physics Sun Yat-sen University Guangzhou 510275 China

Diagrammatic summation is a common bottleneck in modern applications of projected entangled-pair states, especially in computing low-energy excitations of a two-dimensional quantum many-body system. To solve this problem, here we extend the generating-function approach for tensor-network diagrammatic summation, a scheme previously proposed in the context of matrix product states. Taking the form of a one-particle excitation, we show that the excited state can be computed efficiently in the generating-function formalism, which can further be used in evaluating the dynamical structure factor of the system. Our benchmark results for the spin-1/2 transverse-field Ising model and Heisenberg model on the square lattice provide a desirable accuracy, showing good agreement with known results. We then study the spin-1/2J1-J2 model on the same lattice and investigate the dynamical properties of the putative gapless spin liquid phase. We conclude with a discussion on generalizations to multiparticle excitations.

关键词： Quasiparticles & collective excitations Quantum many-body systems Quantum spin models Strongly correlated systems Many-body techniques Projected entangled pair states Tensor network methods

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Bacteria Flagella-Mimicking Polymer Multilayer Magnetic Microrobots

SSRN

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SSRN 2024年

作者： Wu, Zhiguang Lu, Liang Bai, Shuang Shi, Jiaqi Zhang, Zhuotao Pan, Yunlu Wang, Wei Wu, Wenfeng Sun, Shoubin Li, Xu Hou, Gang Huang, Tianyun Jia, Yuxin Zuo, Kaiwen Granovsky, Alexander Wu, He Nikolai, Perov School of Medicine and Health Harbin Institute of Technology Harbin China State Key Laboratory of Robotics and System Harbin Institute of Technology Harbin China The First Affiliated Hospital of Harbin Medical University Harbin China National Center for Respiratory Medicine State Key Laboratory of Respiratory Health and Multimorbidity National Clinical Research Center for Respiratory Diseases Institute of Respiratory Medicine Chinese Academy of Medical Sciences Department of Pulmonary and Critical Care Medicine Center of Respiratory Medicine China-Japan Friendship Hospital Beijing China College of Science Sichuan Agricultural University Chengdu China The Fourth Affiliated Hospital of Harbin Medical University Harbin China Department of Ophthalmology The Second Hospital Jilin University Changchun China Department of Advanced Manufacturing and Robotics College of Engineering State Key Laboratory for Turbulence and Complex Systems Peking University Beijing China Department of Mathematics Imperial College London United Kingdom Department of Computer Science University of Warwick Coventry United Kingdom Magnetism Department Faculty of Physics Lomonosov Moscow State University Moscow Russia Harbin Medical University China

Learning from natural bacteria flagellum, we demonstrate a magnetic polymer multilayer conical microrobot that bestow the controllable propulsion upon external rotating magnetic field with uniform intensity. The magnetic microrobots were constructed by template-assisted Layer-by-Layer technique technique and subsequent functionalization of magnetic particle onto the big opening of the microrobots. Geometric variables of the polymer microrobots, such as the diameter and wall thickness, can be controlled by selection of porous template and layers of assembly. The microrobots perform controllable propulsion through the manipulation of magnetic field. The comparative analysis of the movement behavior reveals that the deformation of microrobots may attributed to the propulsion upon rotating magnetic field, which is similar as that of natural bacteria. The influence of actuation frequencies and frequencies on the velocity of the microrobots is studied. Such use of polymer polymer multilayer tubular micro/nanoarchitectures results in significant savings in the processing costs and provides a simple and cost-effective fabrication route for the mass production of magnetic polymer microrobots. © 2024, The Authors. All rights reserved.

关键词： Bacteria

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Coupling effect of wall slip and spanwise oscillation on drag reduction in turbulent channel flow

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Physical Review Fluids 2020年第12期5卷 124601-124601页

作者： Zexiang Li Songsong Ji Huiling Duan Shilong Lan Jinbai Zhang Pengyu Lv State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science BIC-ESAT College of Engineering Peking University Beijing 100871 China Key Laboratory of High Energy Density Physics Simulation Center for Applied Physics and Technology Peking University Beijing 100871 China National Laboratory of Computational Fluid Dynamics Beihang University Beijing 100191 China

The coupling effect of the isotropic wall slip and the spanwise oscillation boundary conditions on the drag reduction and turbulence properties are studied by direct numerical simulations. As the slip length increases, the drag reduction gradually changes from the oscillation dominated to the slip dominated. The increase of slip length will decrease the maximum spanwise velocity of the fluid on the wall, which is responsible for the decreased ability of the oscillatory wall motion to reduce the skin-friction drag. The drag reduction decomposition shows that the contribution from the modifications of turbulent dynamics will undergo a shift from drag increase to drag reduction as the isotropic slip length increases. Compared with the respective no-slip reference flow, the drag reduction of wall slip in laminar and turbulent channel flows can be expressed in a unified form versus the outer scale slip length. Furthermore, many aspects of the turbulence properties are influenced by the coupling effect. First, the wall slip condenses the envelope range of the phase fluctuations caused by the oscillatory wall motion, as well as the magnitude of the periodic fluctuation of the phase-averaged friction coefficient. Second, an unexpected property of the coupled boundary condition is found that the existence of the Stoke layer delays the relaminarization process caused by the large slip length. Third, the wall slip would narrow the periodic inclination of the streaks and then inhibit the energy transfer process in the horizontal direction. Fourth, in terms of phase, the Stokes strain and the shear angle have the same lag phase with the spanwise velocity, while the hysteresis of turbulent dynamics leads to the larger lag phase of the streaks and phase-averaged friction coefficient. These new features are valuable for increasing knowledge on this topic.

关键词： Slip boundary effects turbulence Wall slip

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Charge transfer in ultrafast isomerization of acetylene ions

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Physical Review A 2022年第3期106卷 033111-033111页

作者： Wan-Dong Yu Hao Liang Cong-Zhang Gao Shunsuke A. Sato Bao-Ren Wei Alberto Castro Angel Rubio Liang-You Peng State Key Laboratory for Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics School of Physics Peking University 100871 Beijing China Institute of Applied Physics and Computational Mathematics Beijing 100088 China Center for Computational Sciences University of Tsukuba Tsukuba 305-8577 Japan Max Planck Institute for the Structure and Dynamics of Matter Luruper Chaussee 149 22761 Hamburg Germany Institute of Modern Physics Department of Nuclear Science and Technology Fudan University Shanghai 200433 China ARAID Foundation 50018 Zaragoza Spain Institute for Biocomputation and Physics of Complex Systems University of Zaragoza Calle Mariano Esquillor 50018 Zaragoza Spain Center for Computational Quantum Physics Flatiron Institute 162 Fifth Avenue New York New York 10010 USA Collaborative Innovation Center of Quantum Matter 100871 Beijing China Collaborative Innovation Center of Extreme Optics Shanxi University 030006 Taiyuan China Peking University Yangtze Delta Institute of Optoelectronics 226010 Nantong Jiangsu China

First-principle calculations are employed to investigate the ultrafast isomerization of the acetylene cation and dication. We use the time-dependent density functional theory together with the Ehrenfest dynamics to track the coupled electron-nuclear dynamics. For both the acetylene cation and the dication, we observe nonadiabatic behaviors during the isomerization. We find that the charge transfer not only alters the electronic structure through nonadiabatic transitions, but also plays a key role in the subsequent hydrogen migration. We show that nonadiabatic transitions affect the structural modification of the excited potential energy surface, and also facilitate the ultrafast isomerization through the creation of a channel of increased negative charge that facilitates the proton movement. For the acetylene cation, we find a timescale for hydrogen isomerization of 66±4 fs, which is consistent with previous pump-probe experiments and on-the-fly calculations. For the dication, we find nonadiabatic transitions occur before the isomerization and identify a similar channel for the proton. Moreover, we find the formation of vinylidene-like structures is always accompanied by a characteristic charge separation on the carbon skeleton. These heuristics will be useful in identifying tautomers and motivating the ultrafast charge-transfer detection methods for future experiments.

关键词： Atomic & molecular processes in external fields Chemical reactions Ultrafast phenomena Density functional theory

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Symbolic genetic algorithm for discovering open-form partial differential equations (SGA-PDE)

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Physical Review Research 2022年第2期4卷 023174-023174页

作者： Yuntian Chen Yingtao Luo Qiang Liu Hao Xu Dongxiao Zhang Eastern Institute for Advanced Study Yongriver Institute of Technology Ningbo Zhejiang 315201 People's Republic of China Department of Computer Science University of Washington Seattle Washington 98195 USA RealAI Beijing 100085 People's Republic of China Beijing Innovation Center for Engineering Science and Advanced Technology (BIC-ESAT) Energy and Resources Engineering (ERE) and State Key Laboratory for Turbulence and Complex Systems (SKLTCS) College of Engineering Peking University Beijing 100871 People's Republic of China National Center for Applied Mathematics Shenzhen (NCAMS) Southern University of Science and Technology Shenzhen Guangdong 518055 People's Republic of China Department of Mathematics and Theories Peng Cheng Laboratory Shenzhen Guangdong 518000 People's Republic of China

Partial differential equations (PDEs) are concise and understandable representations of domain knowledge, which are essential for deepening our understanding of physical processes and predicting future responses. However, the PDEs of many real-world problems are uncertain, which calls for PDE discovery. We propose the symbolic genetic algorithm to discover open-form PDEs (SGA-PDE) directly from data without prior knowledge about the equation structure. SGA-PDE focuses on the representation and optimization of PDEs. Firstly, SGA-PDE uses symbolic mathematics to realize the flexible representation of any given PDE, transforms a PDE into a forest, and converts each function term into a binary tree. Secondly, SGA-PDE adopts a specially designed genetic algorithm to efficiently optimize the binary trees by iteratively updating the tree topology and node attributes. The SGA-PDE is gradient free, which is a desirable characteristic in PDE discovery since it is difficult to obtain the gradient between the PDE loss and the PDE structure. In the experiment, SGA-PDE not only successfully discovered the nonlinear Burgers’ equation, the Korteweg–de Vries equation, and the Chafee-Infante equation but also handled PDEs with fractional structure and compound functions that cannot be solved by conventional PDE discovery methods.

关键词： Classical statistical mechanics complex fluids Neuronal dynamics Shock waves turbulence

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