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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 {2. The state {2. 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 {2. The state {2. 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

Characterization of plastic flow in two Zr-based bulk metallic glasses

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Science china(Technological sciences) 2006年第4期49卷 414-424页

作者： xing Dongmei1,2. zhang Taihua1, LI Weihuo3 & WEI Bingc{2.n3 1. state key laboratory of nonlinear mechanics (LNM), Institute of mechanics, chinese academy of Sci- ences, beijing 100080, {12. 2. College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300074, {12. 3. National Microgravity laboratory, Institute of mechanics, chinese academy of sciences, beijing 100080, {12. state key {2. of nonlinear mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences Beijing China College of Physics and Electronic Information Science Tianjin Normal University Tianjin China National Microgravity laboratory Institute of Mechanics Chinese Academy of Sciences Beijing China

Plastic deformation behaviors of Zr65Al10Ni10Cu15 and Zr52.5Al10Ni10Cu15Be12.5 bulk metallic glasses (BMGs) are studied by using the depth-sensing nanoindentation, microindentation and uniaxial compression. The Be-containing BMG exhibits a signifi- cantly improved overall plastic strain compared with the Be-free alloy during compressive tests. Both BMGs show a loading-rate-dependent serrated flow during nanoindentation measurements, but the Be-containing alloy exhibits a much lower critical loading rate for the disappearance of the serration than the Be-free BMG. The shear band patterns de- veloped during plastic deformation are investigated by microindentation technique, wherein much higher shear band density is found in the Be-containing alloy than in the Be-free alloy, indicating an easier nucleation of shear bands in the former BMG. The dif- ference in the plastic deformation behavior of the two BMGs can be explained by a free volume model.

关键词： Bulk metallic glass, plastic deformation, shear band, nanoindentation.

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 {2. he china academy of Aerospace Aerodynamics Beijing 100074China state key {2. 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 {2. zhang The state {2. 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

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 {2. xing The state {2. 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,2.10,2.:102.03] 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

A numerical study of a turbulent mixing layer and its generated noise

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Science china(Physics,mechanics & Astronomy) 2013年第6期56卷 1157-1164页

作者： LI Dong GUO Li zhang xing {2. guowei The state {2. laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of Sciences

A direct numerical simulation of a turbulent mixing layer with the Reynolds number 500 and the convective Mach number 0.6 is performed and the results obtained are used to study the turbulent flow field and its generated *** the present simulation,the numerical techniques of absorbing buffer zones,artificial convection velocity and spatial filtering are used to achieve nonreflecting boundary *** self-similarity is used to validate the present numerical *** large-scale coherent structures are plotted together with the acoustic waves,which demonstrates the directivity of acoustic *** Lighthill's source and space-time correlations are further *** main contributions to mixing noise are identified in terms of large-scale coherent structures,Lighthill's source and space-time correlations.

关键词： direct numerical simulation mixing layer space-time correlation noise

Numerical simulation of unsteady flows over a slow-flying bat

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Theoretical & Applied mechanics Letters 2015年第1期5卷 5-8页

作者： Shizhao Wang xing zhang {2. he Tianshu Liu The state {2. laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of Sciences Department of Mechanical and Aerospace Engineering Western Michigan University

This letter describes numerical simulation of the unsteady flow over a slow-flying bat by using the immersed boundary method based on the measured bat wing geometry and kinematics. The main vortical structures around the bat flapping wings are identified, illuminating the lift-generating role of the leading- edge vortices generated mainly in the downstroke. Furthermore, the lift decomposition indicates that the vortex lift has the dominant contribution to the time-averaged lift and the lift associated with the fluid acceleration has the relatively moderate effect.

关键词： Flapping flightBatLiftLeading-edge vortexVortex liftNumerical simulation

Self-propelled swimming of a flexible fllament driven by coupled plunging and pitching motions

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Journal of Hydrodynamics 2021年第1期33卷 157-169页

作者： Bing-lin Li Yi-wei Wang Bo Yin Xiang zhang xing zhang The state {2. laboratory of nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China key laboratory for {2. in Fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Science University of Chinese Academy of SciencesBeijing 100049China

This paper numerically investigates the self-propelled swimming of a flexible filament driven by coupled pitching and plunging motions at the leading *** influences of bending rigidity and some actuation parameters(including the phase offset between pitching and plunging,and the amplitudes of pitching and plunging motions)on the swimming performance are *** is found that with increasing rigidity,the swimming style gradually transits from the undulatory mode to the oscillatory *** plunging-pitching actuation is found to be superior to the plunging-only actuation,in the sense that it prevents the decrease of speed at high rigidity and achieves a higher efficiency across a wide range of *** comparison of the body kinematics with those of animal swimmers,and the classification of the wake structures are *** results of this study provide some novel insights for the bio-inspired design of autonomous underwater vehicles.

关键词： Self-propelled swimming flexible filament fluid-structure interaction(FSI) vortex structures immersed boundary method