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An elastic-plastic constitutive framework for micropolar continua

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An elastic-plastic constitutive framework for micropolar con...

在低中高三种Re数下圆管入口流的有限元分析

第五届国际非线性力学会议

作者： Zhu-ping Huang~1,Geng-kai Hu~2,Hong-wu Zhang~3 (1.LTCS and department of mechanics,peking University,Beijing 100871.china 2.department of Applied mechanics,Beijing Institute of Technology,Beijing 100081,china 3.SAIL,department of Engineering mechanics,Dalian University of Technology,Dalian 116024,china)

＜正＞In this paper,a rate-type constitutive framework in micropolar plasticity is presented. In order to describe the plastic dissipation in the deformation process,a set of internal variables is introduced,thus the Helmholtz free energy can be expressed as a function of the non-symmetric strain,rotation and internal *** the introduction of the loading（yield） surfaces both in the non-symmetric strain and rotation space,and in the work conjugate non-symmetric stress and couple stress space,a loading-unloading criterion for a micropolar plastic material is suggested,and three types of material response,namely hardening,softening and perfectly plastic behaviors are *** on a mechanical postulate of non-negative work proposed by the present authors,the normality condition and the corresponding incremental constitutive relations are *** present results can be applied for the description of path-dependent mechanical behaviors of micropolar elastic-plastic materials.

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水动力学研究与进展（A辑） 1994年第5期9卷 531-540页

作者：邵金雨吴望一卢文强北京大学力学系北京100871 中国科技大学研究生院北京100039

圆管入口流问题的研究已有很长历史,但理论结果与实验结果不能很好地符合。本文用改进的Newton-Raphson方法线化由Navier-Stokes方程导出的有限元方程,用波阵法求解线化后的方程组。最后在0～800的Re数范围内得到了速度场及入口长度,并... 详细信息

圆管入口流问题的研究已有很长历史,但理论结果与实验结果不能很好地符合。本文用改进的Newton-Raphson方法线化由Navier-Stokes方程导出的有限元方程,用波阵法求解线化后的方程组。最后在0～800的Re数范围内得到了速度场及入口长度,并给出了描述入口长度随Re数变化关系的拟合公式。数值解与实验结果的比较是令人满意的。本文还对简化Navier-Stokes方程(SNSE)与完整Navier-Stokes方程(CNSE)在求解本问题过程中的一致性作了数值研究,得出了当Re≥80时CNSE和SNSE结果一致的结论。

关键词：雷诺数有限元圆管入口流管流水力学

Construction of Optimal Truncated Low-Dimensional Dynamical systems directly from PDEs

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Communications in Nonlinear Science and Numerical Simulation 1998年第1期3卷 1-5页

作者： Hongliang ZHAO, Chuijie wu(LNM, Institute of mechanics, CAS, Beijing, 100080) (Air Force Institute of Meteorology, Nanjing, 211101) Email: cjwu@*** LNM Institute of Mechanics CAS Beijing 100080 China Air Force Institute of Meteorology Nanjing 211101 China

ＩｎｔｒｏｄｕｃｔｉｏｎＷｈｅｎａｐｐｌｙｉｎｇｔｈｅｍｅｔｈｏｄｓｏｆｄｙｎａｍｉｃａｌｓｙｓｔｅｍｓｔｏｓｔｕｄｙｔｈｅｄｙｎａｍｉｃａｌｂｅｈａｖｉｏｒｏｆｓｏｍｅＰＤＥｓ，ｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｓｔ... 详细信息

ＩｎｔｒｏｄｕｃｔｉｏｎＷｈｅｎａｐｐｌｙｉｎｇｔｈｅｍｅｔｈｏｄｓｏｆｄｙｎａｍｉｃａｌｓｙｓｔｅｍｓｔｏｓｔｕｄｙｔｈｅｄｙｎａｍｉｃａｌｂｅｈａｖｉｏｒｏｆｓｏｍｅＰＤＥｓ，ｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｓｔｅｐｉｎｔｈｅｐｒｏｃｅｓｅｓｉｓ...

关键词： low dimensional dynamical system partial differential equations optimization

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力学的几何化

力学与实践 2017年第4期39卷 323-332页

作者：武际可北京大学力学与工程科学系 100871

本文介绍了力学发展过程中,力学理论系统的几何化.把力学的动力系统归结于黎曼几何、辛几何的几何课题,以及对偶概念、对称概念、变换和不变量概念在力学中的普遍应用.

关键词：力学几何化对偶黎曼几何辛几何变换不变量

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可压缩均匀湍流中重粒子运动行为的先验研究

力学学报 2024年第1期56卷 23-33页

作者：宾远为武琦夏振华史一蓬北京大学湍流与复杂系统国家重点实验室北京100871 浙江大学流体工程研究所杭州310027

本研究以高精度可压缩均匀各向同性湍流直接数值模拟数据为基础,通过点粒子模型和单向耦合方式模拟了100万个重粒子在湍流中的运动.着重进行了两方面的研究,首先,通过使用不同滤波宽度的谱截断滤波器来获得大尺度流场,并研究了不同滤波... 详细信息

本研究以高精度可压缩均匀各向同性湍流直接数值模拟数据为基础,通过点粒子模型和单向耦合方式模拟了100万个重粒子在湍流中的运动.着重进行了两方面的研究,首先,通过使用不同滤波宽度的谱截断滤波器来获得大尺度流场,并研究了不同滤波尺度对粒子运动的影响;其次,设置了5种不同的粒子初速度,以研究粒子聚集性和运动学性质的演化.在研究粒子聚集性方面,使用了香农熵来描述粒子的瞬时聚集性,而稳态时的统计结果则通过概率密度分布函数来描述.研究结果表明,滤波尺度对不同Stokes数的粒子聚集效应产生不同的影响.具体而言,小尺度流动结构对低Stokes数的粒子聚集性有促进作用,而对高Stokes数的粒子聚集性则有抑制作用.此外,随着Stokes数的增加和截断波数的减小,粒子的速度和加速度的概率密度分布变得更为集中.另外,还发现颗粒的初始速度差异会在演化的初期产生明显影响,最终会趋于相同的统计定常状态.这一发现强调了湍流中粒子运动的复杂性和统计特性的重要性.

关键词：湍流重粒子湍流尺度

Orbit determination and prediction accuracy analysis for a regional tracking network

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Science china(Physics,mechanics & Astronomy) 2010年第6期53卷 1130-1138页

作者： ZHOU ShanShi 1,2,3 ,HU XiaoGong 1 & wu Bin 1 1 Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030,china 2 Graduate University of Chinese Academy of Sciences,Beijing 100049,china 3 Research Center of GNSS,wuhan 430079,china 1. Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai 200030 China2. Graduate University of Chinese Academy of Sciences Beijing 100049 China3. Research Center of GNSS Wuhan 430079 China

china's COMPASS satellite navigation system relies on a regional tracking network to provide navigation services. Limited by its geographic border,the regional network is able to cover only 30% of the medium-earth-orbits(MEO). Accuracy of determined and predicted orbits is not able to satisfy system requirements if the tracking data processing strategy for global tracking network processing is used for the regional network. Two major error sources for orbital prediction are accuracy of initial orbital elements and dynamical modeling. To achieve better prediction accuracy,we propose a two-step orbit determination and prediction strategy. For step 1,only solar radiation pressure(SRP) parameters are estimated along with the orbital elements and other parameters; for step 2,all parameters are estimated but the SRP parameters are tightly constrained to their step 1 estimates. Experimenting with data from a regional GPS network,we conclude for orbital prediction using the proposed two-step strategy,the average user range error(URE) for 24-h prediction arcs is better than 0.6 m.

关键词： orbit determination and prediction regional tracking network URE

AlGaN基深紫外LED光源灭活柯萨奇病毒研究

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发光学报 2024年第8期45卷 1391-1397页

作者：吴郁蓝习瑜张梓睿吴章鑫刘忠宇杨玲佳张山丽徐可贲建伟北京大学第三医院北京100191 武汉大学生命科学学院湖北武汉430072 中国科学院长春光学精密机械与物理研究所吉林长春130033

为探究在高温热处理AlN模板上制备的不同发光波长AlGaN基LED器件对病毒的灭活效率,本工作在发光波长257~294 nm范围内制备了7组不同发光波长AlGaN基深紫外LED器件,并探究其对柯萨奇病毒灭活效率。实验结果表明,高温热处理AlN模板可以将... 详细信息

为探究在高温热处理AlN模板上制备的不同发光波长AlGaN基LED器件对病毒的灭活效率,本工作在发光波长257~294 nm范围内制备了7组不同发光波长AlGaN基深紫外LED器件,并探究其对柯萨奇病毒灭活效率。实验结果表明,高温热处理AlN模板可以将AlN模板位错密度降低至1.33×10^(7)cm^(-2),为制备高效率AlGaN基LED器件奠定了良好基础;基于高温热处理AlN模板制备的AlGaN基LED器件,在灭活距离2 cm、紫外辐照时间30 s实验条件下,发光中心波长在257~278 nm之间的AlGaN基LED器件对柯萨奇病毒灭活率≥99.90%,而发光中心波长为288 nm、294 nm的LED对柯萨奇病毒灭活率仅为99.47%及96.15%。根据以上研究结果,波长在257~278 nm之间的AlGaN基LED器件适合在病毒消杀领域应用;在本工作实验条件下,波长大于288 nm的AlGaN基深紫外LED器件对病毒灭活效果较差。

关键词：高温热处理 AlN模板 AlGaN LED 病毒灭活

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Molecular wakes for ultrashort laser pulses

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Science china(Physics,mechanics & Astronomy) 2010年第6期53卷 1036-1039页

作者： CAI Hua,wu Jian,LU PeiFen,TONG YuQi,YANG Xuan,BAI XueShi,LI Hao,PAN HaiFeng & ZENG HePing State Key Laboratory of Precision Spectroscopy,East china Normal University,Shanghai 200062,china 1. State Key Laboratory of Precision Spectroscopy East China Normal University Shanghai 200062 China

The molecular wake-assisted interaction between two collinear femotosecond laser pulses is investigated in air,which leads to the generation of a controllable 1.8 mJ super-continuum pulse with an elongated self-guided channel due to the cross-phase modulation of the impulsively aligned diatomic molecules in air. For two parallel launched femtosecond laser pulses with a certain spatial separation,controllable attraction and repulsion of the pulses are observed due to the counter-balance among molecular wakes,Kerr and plasma effects,where the molecular wakes show a longer interaction distance than the others to control the propagation of the intense ultrashort laser pulses.

关键词： molecular wakes ultrashort laser pulse interaction super-continuum generation

Revisiting the breakdown of Stokes-Einstein relation in glassforming liquids with machine learning

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Science china(Physics,mechanics & Astronomy) 2020年第7期63卷 63-67页

作者： ZhenWei wu Renzhong Li School of Systems Science Beijing Normal UniversityBejing 100875China International Center for Quantum Materials and School of Physics Peking UniversityBeijing 100871China

The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time and T is the temperature. In many glassforming liquids, the breakdown of SE relation often occurred when the dynamics of the liquids becomes glassy, and its origin is still debated among many scientists. Using molecular dynamics simulations and support-vector machine method, it is found that the scaling between diffusion and relaxation fails when the total population of solid-like clusters shrinks at the maximal rate with decreasing temperature, which implies a dramatic unification of clusters into an extensive dominant one occurs at the time of breakdown of the SE relation. Our data leads to an interpretation that the SE violation in metallic glass-forming liquids can be attributed to a specific change in the atomic structures.

关键词： metallic glass-forming liquid machine learning Stokes-Einstein relation