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Second-order two-scale computational method for ageing linear viscoelastic problem in composite materials with periodic structure

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Applied Mathematics and Mechanics(English Edition) 2016年第2期37卷 253-264页

作者： Yang ZHANG Junzhi CUI yufeng nie Department of Applied Mathematics Northwestern Polytechnical University Academy of Mathematics and Systems Science Chinese Academy of Sciences

The correspondence principle is an important mathematical technique to compute the non-ageing linear viscoelastic problem as it allows to take advantage of the computational methods originally developed for the elastic case. However, the correspon- dence principle becomes invalid when the materials exhibit ageing. To deal with this problem, a second-order two-scale （SOTS） computational method in the time domain is presented to predict the ageing linear viscoelastic performance of composite materials with a periodic structure. First, in the time domain, the SOTS formulation for calcu- lating the effective relaxation modulus and displacement approximate solutions of the ageing viscoelastic problem is formally derived. Error estimates of the displacement ap- proximate solutions for SOTS method are then given. Numerical results obtained by the SOTS method are shown and compared with those by the finite element method in a very fine mesh. Both the analytical and numerical results show that the SOTS computational method is feasible and efficient to predict the ageing linear viscoelastic performance of composite materials with a periodic structure.

关键词： second-order two-scale (SOTS) method ageing viscoelasticity composite material periodic structure

Microstructural Modeling and Multiscale Mechanical Properties Analysis of Cancellous Bone

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Computers, Materials & Continua 2020年第1期62卷 245-265页

作者： Zhiqiang Huang yufeng nie Yiqiang Li Research Center for Computational Science Northwestern Polytechnical UniversityXi’an710072China School of Applied Science Taiyuan University of Science and TechnologyTaiyuan030024China

This paper is devoted to the microstructure geometric modeling and mechanical properties computation of cancellous *** microstructure of the cancellous bone determines its mechanical properties and a precise geometric modeling of this structure is important to predict the material *** on the microscopic observation,a new microstructural unit cell model is established by introducing the Schwarz surface in this *** this model is very close to the real microstructure and satisfies the main biological characteristics of cancellous *** using the unit cell model,the multiscale analysis method is newly applied to predict the mechanical properties of cancellous *** effective stiffness parameters are calculated by the up-scaling multi-scale *** the distribution of microscopic stress in cancellous bone is determined through the down-scaling *** addition,the effect of porosity on the stiffness parameters is also *** predictive mechanical properties are in good agreement with the available experimental results,which verifies the applicability of the proposed unit cell model and the validness of the multiscale analysis method to predict the mechanical properties of cancellous bone.

关键词： Cancellous bone microstructural modeling multiscale analysis stiffness parameters stress distribution

XFEM for Fracture Analysis in 2D Anisotropic Elasticity

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Advances in Applied Mathematics and Mechanics 2017年第1期9卷 125-143页

作者： Honggang Jia yufeng nie Junlin Li School of Mathematics and Statistics Xuchang UniversityXuchangHenan 461000China Department of Applied Mathematics School of ScienceNorthwestern Polytechnical UniversityXi’anShaanxi 710129China School of Applied Science Taiyuan University of Science and TechnologyTaiyuanShanxi 030024China

In this paper,a method is proposed for extracting fracture parameters in anisotropic thermoelasticity cracking via interaction integral method within the framework of extended finite element method(XFEM).The proposed method is applied to linear thermoelastic crack *** numerical results of the stress intensity factors(SIFs)are presented and compared with those reported in related *** good agreement of the results obtained by the developed method with those obtained by other numerical solutions proves the applicability of the proposed approach and confirms its capability of efficiently extracting thermoelasticity fracture parameters in anisotropic materials.

关键词： Anisotropic materials thermoelasticity crack XFEM stress intensity factors

Acceleration Strategies Based on an Improved Bubble Packing Method

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Communications in Computational Physics 2014年第6期16卷 115-135页

作者： Nan Qi yufeng nie Weiwei Zhang Department of Applied Mathematics School of ScienceNorthwestern Polytechnical University127 Youyi West RoadXi’an 710129China.

The bubble packing method can generate high-quality node sets in simple and complex ***,its efficiency remains to be *** study is a part of an ongoing effort to introduce several acceleration schemes to reduce the cost of ***,allow the viscosity coefficient c in the bubble governing equations to change according the coordinate of the bubble which are defined separately as odd and normal bubbles,and meanwhile with the saw-shape relationship with time or ***,in order to relieve the over crowded initial bubble placement,two coefficients w1 and w2 are introduced to modify the insertion *** range of those two coefficients are discussed to be w1=1,w2∈[0.5,0.8].Finally,a self-adaptive termination condition is logically set when the stable system equilibrium is *** examples illustrate that the computing cost can significantly decrease by roughly 80%via adopting various combination of proper schemes(except the uniform placement example),and the average qualities of corresponding Delaunay triangulation substantially exceed *** shows that those strategies are efficient and can generate a node set with high quality.

关键词： Bubble packing method algorithm efficiency viscosity coefficient mesh generation Delaunay triangulation.

Fracture Analysis in Orthotropic Thermoelasticity Using Extended Finite Element Method

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Advances in Applied Mathematics and Mechanics 2015年第6期7卷 780-795页

作者： Honggang Jia yufeng nie Junlin Li Department of Applied Mathematics School of ScienceNorthwestern Polytechnical UniversityXi’an 710129China Taiyuan University of Science and Technology School of Applied ScienceTaiyuan 030024China

In this paper,a method for extracting stress intensity factors(SIFs)in orthotropic thermoelasticity fracture by the extended finite element method(XFEM)and interaction integral method is *** proposed method is utilized in linear elastic crack *** numerical results of the SIFs are presented and compared with those obtained using boundary element method(BEM).The good accordance among these two methods proves the applicability of the proposed approach and conforms its capability of efficiently extracting thermoelasticity fracture parameters in orthotropic material.

关键词： Fracture orthotropic thermoelasticity interaction integral method XFEM

Constructing reduced model for complex physical systems via interpolation and neural networks

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Chinese Physics B 2021年第3期30卷 78-87页

作者： Xuefang Lai Xiaolong Wang yufeng nie Research Center for Computational Science School of Mathematics and StatisticsNorthwestern Polytechnical UniversityXi’an 710129China

The work studies model reduction method for nonlinear systems based on proper orthogonal decomposition (POD)and discrete empirical interpolation method (DEIM). Instead of using the classical DEIM to directly approximate thenonlinear term of a system, our approach extracts the main part of the nonlinear term with a linear approximation beforeapproximating the residual with the DEIM. We construct the linear term by Taylor series expansion and dynamic modedecomposition (DMD), respectively, so as to obtain a more accurate reconstruction of the nonlinear term. In addition, anovel error prediction model is devised for the POD-DEIM reduced systems by employing neural networks with the aid oferror data. The error model is cheaply computable and can be adopted as a remedy model to enhance the reduction ***, numerical experiments are performed on two nonlinear problems to show the performance of the proposed method.

关键词： model reduction discrete empirical interpolation method dynamic mode decomposition neural networks

Dynamic thermo-mechanical coupled simulation of statistically inhomogeneous materials by statistical second-order two-scale method

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Acta Mechanica Sinica 2015年第5期31卷 762-776页

作者： Zihao Yang Junzhi Cui yufeng nie Zhiqiang Huang Meizhen Xiang Department of Applied Mathematics Northwestern Polytechnical University LSEC ICMSECAcademy of Mathematics and Systems ScienceChinese Academy of Sciences Institution of Applied Physics and Computational Mathematics

In this paper,a statistical second-order twoscale（SSOTS） method is developed to simulate the dynamic thcrmo-mechanical performances of the statistically inhomogeneous *** this kind of composite material,the random distribution characteristics of particles,including the shape,size,orientation,spatial location,and volume fractions,are all ***,the *** for the microscopic configuration of the statistically inhomogeneous materials is ***,the SSOTS formulation for the dynamic thermo-mechanical coupled problem is proposed in a constructive way,including the cell problems,effective thermal and mechanical parameters,homogenized problems,and the SSOTS formulas of the temperatures,displacements,heat flux densities and *** then the algorithm procedure corresponding to the SSOTS method is brought *** numerical results obtained by using the SSOTS algorithm are compared with those by classical *** addition,the thermo-mechanical coupling effect is studied by comparing the results of coupled case with those of uncoupled *** demonstrates that the coupling effect on the temperatures,heat flux densities,displacements,and stresses is very *** results show that the SSOTS method is valid to predict the dynamic thermo-mechanical coupled performances of statistically inhomogeneous materials.

关键词： Statistically inhomogeneous materials Dynamic thermo-mechanical coupled performances The SSOTS method The thermo-mechanical coupling effect

The Numerical Accuracy Analysis of Asymptotic Homogenization Method and Multiscale Finite Element Method for Periodic Composite Materials

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Computer Modeling in Engineering & Sciences 2016年第5期111卷 395-419页

作者： Hao Dong yufeng nie Zihao Yang Yang Zhang YataoWu Department of Applied Mathematics School of ScienceNorthwestern Polytechnical UniversityXi’an 710129PR China Research Center for Computational Science Northwestern Polytechnical UniversityXi’an 710129PR China

In this paper,we discuss the numerical accuracy of asymptotic homogenization method(AHM)and multiscale finite element method(MsFEM)for periodic composite *** numerical calculation of the model problems for four kinds of typical periodic composite materials,the main factors to determine the accuracy of first-order AHM and second-order AHM are found,and the physical interpretation of these factors is ***,the way to recover multiscale solutions of first-order AHM and MsFEM is theoretically analyzed,and it is found that first-order AHM and MsFEM provide similar multiscale solutions under some ***,numerical experiments verify that MsFEM is essentially a first-order multiscale method for periodic composite materials.

关键词： Asymptotic homogenization method Multiscale finite element method First-order AHM Slight fluctuations Second-order AHM Severe fluctuations

Precise orbit determination for a large LEO constellation with inter-satellite links and the measurements from different ground networks:a simulation study

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Satellite Navigation 2022年第3期3卷 38-50,I0002页

作者： Xingchi He Urs Hugentobler Anja Schlicht yufeng nie Bingbing Duan Institute for Astronomical and Physical Geodesy Technical University of MunichArcisstr.2180333MunichGermany College of Surveying and Geo-Informatics Tongji UniversitySiping Road 1239Shanghai200092China

Geodetic applications of Low Earth Orbit(LEO)satellites requires accurate satellite *** of using onboard Global Navigation Satellite System observations,this contribution treats the LEO satellite constellation independently,using Inter-Satellite Links and the measurements of different ground *** to geopolitical and geographical reasons,a ground station network cannot be well *** compute the impact of different ground networks(i.e.,global networks with different numbers of stations and regional networks in different areas and latitudes)on LEO satellite orbit determination with and without the inter-satellite *** results are based on a simulated constellation of 90 LEO *** find that the orbits determined using a high latitude network is worse than using a middle or low latitude *** is because the high latitude network has a poorer geometry even if the availability of satellite measurements is higher than for the other two ***,adding more stations in a regional network shows almost no improvements on the satellite orbits if the number of stations is more than *** the help of ISL observations,however,the satellite orbits determined with a small regional network can reach the same accuracy as that with the global network of 60 ***,satellite biases can be well estimated(less than 0.6 mm)and have nearly no impact on satellite *** does thus not matter if they are not physically calibrated for estimating precise orbits.

关键词： LEO satellite Orbit determination Ground station distribution Inter-satellite link