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Multi-Scale-Matching neural networks for thin plate bending problem

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Theoretical & Applied Mechanics Letters 2024年第1期14卷 11-15页

作者： Lei Zhang guowei he The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

Physics-informed neural networks are a useful machine learning method for solving differential equations,but encounter challenges in effectively learning thin boundary layers within singular perturbation *** resolve this issue,multi-scale-matching neural networks are proposed to solve the singular perturbation *** by matched asymptotic expansions,the solution is decomposed into inner solutions for small scales and outer solutions for large scales,corresponding to boundary layers and outer regions,***,to conform neural networks,we introduce exponential stretched variables in the boundary layers to avoid semiinfinite region *** results for the thin plate problem validate the proposed method.

关键词： Singular perturbation Physics-informed neural networks Boundary layer Machine learning

Chien-physics-informed neural networks for solving singularly perturbed boundary-layer problems

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Applied Mathematics and Mechanics(English Edition) 2024年第9期45卷 1467-1480页

作者： Long WANG Lei ZHANG guowei he The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China

A physics-informed neural network(PINN)is a powerful tool for solving differential equations in solid and fluid ***,it suffers from singularly perturbed boundary-layer problems in which there exist sharp changes caused by a small perturbation parameter multiplying the highest-order *** this paper,we introduce Chien's composite expansion method into PINNs,and propose a novel architecture for the PINNs,namely,the Chien-PINN(C-PINN)*** novel PINN method is validated by singularly perturbed differential equations,and successfully solves the wellknown thin plate bending *** particular,no cumbersome matching conditions are needed for the C-PINN method,compared with the previous studies based on matched asymptotic expansions.

关键词： physics-informed neural network(PINN) singular perturbation boundarylayer problem composite asymptotic expansion

Large-eddy simulation of circular cylinder flow at subcritical Reynolds number:Turbulent wake and sound radiation

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Acta Mechanica Sinica 2016年第1期32卷 1-11页

作者： Li Guo Xing Zhang guowei he China Academy of Aerospace Aerodynamics Beijing 100074China State Key Laboratory of Non-linear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

The flows past a number 3900 are simulated circular cylinder at Reynolds using large-eddy simulation （LES） and the far-field sound is calculated from the LES results. A low dissipation energy-conserving finite volume scheme is used to discretize the incompressible Navier- Stokes equations. The dynamic global coefficient version of the Vreman＇s subgrid scale （SGS） model is used to com- pute the sub-grid stresses. Curie＇s integral of Lighthill＇s acoustic analogy is used to extract the sound radiated from the cylinder. The profiles of mean velocity and turbulent fluctua- tions obtained are consistent with the previous experimental and computational results. The sound radiation at far field exhibits the characteristic of a dipole and directivity. The sound spectra display the -5/3 power law. It is shown that Vreman＇s SGS model in company with dynamic procedure is suitable for LES of turbulence generated noise.

关键词： Flows past circular cylinder Aerodynamicnoise Large-eddy simulation Unstructured grid Acousticanalogy

Self-propulsion of flapping bodies in viscous fluids: Recent advances and perspectives

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Acta Mechanica Sinica 2016年第6期32卷 980-990页

作者： Shizhao Wang guowei he Xing Zhang The State Key Laboratory of Nonlinear Mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences

Flapping-powered propulsion is used by many animals to locomote through air or water. here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These studies improve our understanding of the mutual interaction between actively flapping bodies and surrounding fluids. The results obtained in these works provide not only new insights into biolocomotion but also useful information for the biomimetic design of artificial flyers and swimmers.

关键词： Flapping motion Self-propulsion Symmetry breaking Passive flexibility Flow-mediated interaction

Subgrid-scale contributions to Lagrangian time correlations in isotropic turbulence

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Acta Mechanica Sinica 2009年第1期25卷 45-49页

作者： Jian Zhang guowei he Lipeng Lu LNM Institute of Mechanics Chinese Academy of Sciences.100190 Beijing China National Key Laboratory for Aircraft Engines Beihang University 100191 Beijing China

The application of large-eddy simulation （LES） to particle-laden turbulence raises such a fundamental question as whether the LES with a subgrid scale （SGS） model can correctly predict Lagrangian time correlations （LTCs）. Most of the currently existing SGS models are constructed based on the energy budget equations. Therefore, they are able to correctly predict energy spectra, but they may not ensure the correct prediction on the LTCs. Previous researches investigated the effect of the SGS modeling on the Eulerian time correlations. This paper is devoted to study the LTCs in LES. A direct numerical simulation （DNS） and the LES with a spectral eddy viscosity model are performed for isotropic turbulence and the LTCs are calculated using the passive vector method. Both a priori and a posteriori tests are carried out. It is observed that the subgrid;scale contributions to the LTCs cannot be simply ignored and the LES overpredicts the LTCs than the DNS. It is concluded from the straining hypothesis that an accurate prediction of enstrophy spectra is most critical to the prediction of the LTCs.

关键词： Isotropic turbulence Large eddy simulation Lagrangian time correlation Enstrophy spectra

Numerical simulation of drop oscillation in AC electrowetting

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Science China(Physics,Mechanics & Astronomy) 2013年第2期56卷 383-394页

作者： LI XiaoLiang he guowei ZHANG Xing The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

In this paper,a "macroscopic-scale" numerical method for drop oscillation in AC electrowetting is *** method is based on a high-fidelity moving mesh interface tracking(MMIT) approach and a "microscopic model" for the moving contact *** contact line model developed by Ren et al.[Phys Fluids,2010,22:102103] is used in the *** determine the slip length in this model,we propose a calibration procedure using the experimental data of drop spreading in DC *** the simulation,the frequency of input AC voltage varies in a certain range while the root-mean-square value remains *** numerical simulation is validated against the experiment and it shows that the predicted resonance frequencies for different oscillation modes agree reasonably well with the *** origins of discrepancy between simulation and experiment are analyzed in the *** investigation is also conducted by including the contact angle hysteresis into the contact line model to account for the "stick-slip" behavior.A noticeable improvement on the prediction of resonance frequencies is achieved by using the hysteresis model.

关键词： electrowetting oscillation contact line model hysteresis slip length

Lattice Boltzmann simulations of high-order statistics in isotropic turbulent flows

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Applied Mathematics and Mechanics(English Edition) 2018年第1期39卷 21-30页

作者： Guodong JIN Shizhao WANG Yun WANG guowei he Stake Key Laboratory of Nonlinear Mechanics (LNM) Institute of MechanicsChinese Academy of Sciences School of Engineering Science University of Chinese Academy of Sciences

The lattice Boltzmann method （LBM） is coupled with the multiple-relaxation- time （MRT） collision model and the three-dimensional 19-discrete-velocity （D3Q19） model to resolve intermittent behaviors on small scales in isotropic turbulent flows. The high- order scaling exponents of the velocity structure functions, the probability distribution functions of Lagrangian accelerations, and the local energy dissipation rates are investi- gated. The self-similarity of the space-time velocity structure functions is explored using the extended self-similarity （ESS） method, which was originally developed for velocity spatial structure functions. The scaling exponents of spatial structure functions at up to ten orders are consistent with the experimental measurements and theoretical results, implying that the LBM can accurately resolve the intermittent behaviors. This valida~ tion provides a solid basis for using the LBM to study more complex processes that are sensitive to small scales in turbulent flows, such as the relative dispersion of pollutants and mesoscale structures of preferential concentration of heavy particles suspended in turbulent flows.

关键词： mesoscopic modelling lattice Boltzmann method (LBM) isotropic turbulent flow structure function intermittency high-order statistics self-similarity

Independent component analysis of streamwise velocity fluctuations in turbulent channel flows

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Theoretical & Applied Mechanics Letters 2022年第4期12卷 233-240页

作者： Ting Wu guowei he The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China

Independent component analysis(ICA)is used to study the multiscale localised modes of streamwise velocity fluctuations in turbulent channel *** aims to decompose signals into independent modes,which may induce spatially localised *** height and size are defined to quantify the spatial position and extension of these ICA modes,*** contrast to spatially extended proper orthogonal decomposition(POD)modes,ICA modes are typically localised in space,and the energy of some modes is distributed across the near-wall *** sizes of ICA modes are multiscale and are approximately proportional to their *** modes can also help to reconstruct the statistics of turbulence,particularly the third-order moment of velocity fluctuations,which is related to the strongest Reynolds shear-stressproducing *** results reported in this paper indicate that the ICA method may connect statistical descriptions and structural descriptions of turbulence.

关键词： Independent component analysis Turbulent channel flow Proper orthogonal decomposition Third-order moment Localised modes

Space-time correlations of passive scalar in Kraichnan model

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Theoretical & Applied Mechanics Letters 2023年第5期13卷 338-340页

作者： Ping-Fan Yang Liubin Pan guowei he State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China School of Physics and Astronomy Sun Yat-Sen UniversityZhuhai 519082China

We consider the two-point,two-time(space-time)correlation of passive scalar R(r,τ)in the Kraichnan model under the assumption of homogeneity and *** the fine-gird PDF method,we find that R(r,τ)satisfies a diffusion equation with constant diffusion coefficient determined by velocity variance and molecular *** can be expressed in terms of the two-point,one time correlation of passive scalar,i.e.,R(r,0).Moreover,the decorrelation o R(k,τ),which is the Fourier transform of R(r,τ),is determined byR(k,0)and a diffusion kernal.

关键词： Space-time correlation Passive scalar Kraichnan model