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望远镜光程稳定性测量方案设计与分析

中国激光 2024年第6期51卷 100-108页

作者：海宏文孙启程赵凯邹濡锐闫勇中山大学(珠海校区)天琴中心&物理与天文学院国家航天局引力波研究中心天琴前沿科学中心天琴计划教育部重点实验室广东珠海519082

空间激光干涉测距系统对望远镜的光程稳定性提出了皮米级的要求。为了测量望远镜光程稳定性,基于法布里-珀罗(F-P)干涉仪设计了望远镜光程稳定性测量方案。介绍了基于PDH(Pound-Drever-Hall)锁频技术将望远镜腔内的光程长度变化转为激... 详细信息

空间激光干涉测距系统对望远镜的光程稳定性提出了皮米级的要求。为了测量望远镜光程稳定性,基于法布里-珀罗(F-P)干涉仪设计了望远镜光程稳定性测量方案。介绍了基于PDH(Pound-Drever-Hall)锁频技术将望远镜腔内的光程长度变化转为激光频率变化的测量原理。根据已有的实验数据分析了在光程稳定性测量公式中对稳定性测量结果有影响的物理量,并对测量方案中各部件引入的外部噪声进行测量和分析。实验结果表明:光程稳定性测量公式中绝对激光频率测量误差和望远镜腔自由光谱范围测量误差对望远镜皮米级光程稳定性测量的影响非常小,影响量分别为7.1×10^(-9)pm/Hz1/2和5.0×10^(-3)pm/Hz1/2。在1~100 mHz频段内,与测量方案中电子噪声、拍频测量噪声和剩余幅度调制噪声等效的光程噪声分别为0.14、0.01、3.57 pm/Hz1/2。为实现望远镜的皮米级光程稳定性测量,需要进一步开展抑制剩余幅度调制噪声方面的研究工作。

关键词：测量望远镜光程稳定性谐振腔测量方案

基于SWOT分析的退役运动员转型高校体育教师发展策略研究

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安徽体育科技 2024年第2期45卷 13-17,30页

作者：袁刚孙启成左乐海军航空大学军事体育教研室山东烟台264001

运用文献研读、SWOT分析等研究方法,探讨退役运动员转型高校体育教师后其职业发展的困境与路径。研究认为:技能与经验是运动员退役转型的自身优势;教学、科研能力与文化适应不畅是其内在劣势;政策及高校对人才的需求是推动其群体转型的... 详细信息

运用文献研读、SWOT分析等研究方法,探讨退役运动员转型高校体育教师后其职业发展的困境与路径。研究认为:技能与经验是运动员退役转型的自身优势;教学、科研能力与文化适应不畅是其内在劣势;政策及高校对人才的需求是推动其群体转型的外部机遇;社会舆论是其退役转型的直接威胁。由此提出了实施差异化人才培养、多技能同步发展以及打造局部优势的非均衡发展策略,通过抓住主要矛盾来规避自身劣势和外部威胁,实现阻滞因素最小化。

关键词：退役运动员高校体育教师 SWOT分析发展

Kinetic granular temperature and its measurement using speckle visibility spectroscopy

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Particuology 2020年第1期18卷 160-169页

作者： Hui Yang Yonghai Zhu Ran Li qicheng sun School of Optical-Electrical and Computer Engineering University of Shanghai for Science and TechnologyShanghai 200093China Shanghai Key Laboratory of Modern Optical Systems University of Shanghai for Science and TechnologyShanghai 200093China State Key Laboratory of Hydroscience and Engineering Tsinghua UniversityBeijing 100084China

The occurrence of a mesoscopic scale in granular materials leads to a sharp increase in the number of interaction processes at both intra-and inter-scale *** mesoscopic scale is the main source of the complex macroscopic properties of granular *** quantification of mesoscopic disordered movements is often referred to as granular *** this paper,we first introduce the physical meaning of the original granular temperature of a kinetic nature,Tk,and then briefly summarize the advances made over the past few *** research group has focused on Tk measurement using speckle visibility *** principle of this technique and the instruments developed in our research group are briefly *** work shows great promise in the measurement of kinetic granular ***,a summary of granular temperature and some recent developments in speckle visibility spectroscopy measurements are presented.

关键词： Granular flow Mesoscopic process Granular temperature Speckle visibility spectroscopy

STUDIES ON STRUCTURAL AND MECHANICAL PROPERTIES UNDER ISOSTATIC COMPRESSION WITH LARGE-SCALE DISCRETE ELEMENT SIMULATIONS

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Acta Mechanica Solida Sinica 2014年第2期27卷 129-136页

作者： Jianguo Liu qicheng sun Feng Jin Qingkai Liu State Key Laboratory of Hydroscience and Engineering Tsinghua University High Performance Computing Center Institute of Applied Physics and Computational Mathematics

Granular systems undergo a jamming transition at point J simply by increasing the packing fraction. A large-scale parallel discrete element code （THDEM： TsingHua Discrete Element Method） was used to obtain a satisfying statistical description of the structural and me- chanical properties near point J. The isostatic compressions of 100,000 polydispersed frictionless particles were simulated on high performance computers to clearly observe the sophisticated con- figurations of force chains. The first peak of the pair correlation function, coordination number, spatial distribution of the packing fraction, and stress were calculated to analyze their variations with increasing packing fraction. The critical packing fraction at point J is determined to be 0.62. The incremental stress and coordination number from point J scale well with the power law, and coincide with previous theoretical predications. The distribution of the packing frac- tion is a normal distribution around the average value. The standard deviation decreases with increasing packing fraction, indicating the system is more uniform with a denser packing.

关键词： granular matter jamming transition force chains parallel computing

Numerical simulation of ae-olian sediment transport

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Chinese Science Bulletin 2001年第9期46卷 786-789页

作者： qicheng sun Guangqian Wang Tsing Hua Univ Dept Hydraul Engn Beijing 100084 Peoples R China

A discrete element model (DEM) is developed for aeolian sediment transport in the scope of investigation of the dynamic behavior of grains, in which the motion of individual grain is considered while velocity distribution of wind is given according to bed forms. The above model has been used for simulating the phenomenon of 4000 grains blown by wind, resulting in ripples and saltating paths, which shows good agreements with experimental observations. The result is helpful for revealing the intrinsic mechanism of sand flow.

关键词： aeolian sediment transport desertification discrete element model numerical simulation.

Crack spacing of unsaturated soils in the critical state

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Chinese Science Bulletin 2009年第12期54卷 2008-2012页

作者： sun JiChao WANG GuangQian sun qicheng State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China

The cracking mechanism of unsaturated soils due to evaporation is poorly understood, and the magnitude of crack spacing is usually hard to estimate. In this work, cracks were postulated to occur succedently rather than simultaneously, that is, secondary cracks appear after primary cracks as evaporation continues. Formulae of the secondary crack spacing and secondary trend crack spacing were then derived after stress analysis. The calculated spacing values were consistent with the published experimental data. Meanwhile, the effect of the Poisson ratio on the crack spacing was analyzed, which showed that the magnitude of crack spacing was proportional to the Poisson ratio in the range of [0.30, 0.35].

关键词：裂缝间距非饱和土临界状态开裂机理应力分析实验数据蒸发量泊松比

ANALYSIS OF PARAMETERS IN GRANULAR SOLID HYDRODYNAMICS FOR TRIAXIAL COMPRESSION TESTS

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Acta Mechanica Solida Sinica 2014年第1期27卷 15-27页

作者： Shixiong Song qicheng sun Feng Jin Chuhan Zhang State Key Laboratory of Hydroscience and Engineering Tsinghua University

Granular materials are omnipresent in industries and in nature. For small strains, elastic-plastic and hypoplastic constitutive relations are widely used in engineering practice, but they are not a significant reflection of the underlying physics. Under a unified thermodynamics framework explaining the physics of materials, granular solid hydrodynamics （GSH） was an ex- tension towards describing granular materials, not only solid-like, but also fluid-like behaviors. In this paper, the fundamentals of GSH are briefly treated and then simplified to analyze quasi- static deformations in triaxial compressions. The calculated stress-strain relations and volumetric strain are compared with experimental results. The influences of the major parameters in GSH, especially their cross coupling influences, are analyzed and their physical meanings are further clarified. After parameters were calibrated, the calculated stress values in the characteristic stress state are found to be within 22% of tested values. Meanwhile, the energy dissipation during triaxial compression is analyzed. The above results support and partially quantify GSH.

关键词： granular solid hydrodynamics granular materials triaxial compressions non-equilibrium state

Velocity profiles and energy fluctuations in simple shear granular flows

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Particuology 2016年第4期14卷 80-87页

作者： Chuanqi Liu qicheng sun Gordon G.D. Zhou State Key Laboratory for Hydroscience and Engineering Tsinghua University Beijing 100084 China Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu 610041 China

Rheology analysis of granular flows is important for predicting geophysical hazards and designing industrial processes. Using a discrete element method, we simulate simple shear flows in 3D under a constant confining pressure of 10 kPa. The inertial number proposed by the GDR MiDi group in France is adopted to distinguish rheology regimes, Both translational and angular velocity profiles are investigated, and both fluid-like and solid-like behavior modes are observed in the flows. The maximum angular velocity occurs near the localized deformation area. We also investigate the energy characteristics of the flows and find that at very small shearing speed, the mean kinetic energy density ek is close to zero, while the mean elastic energy density ec is much greater. At large shearing speed, ek increases. The fluctuating parts of the two types of energy increase with increasing shear speed. Thus, the mean energy density ratio ek/ec can be used in addition to the inertial number to distinguish flow regimes. These results provide insights from energetics into the rheological properties of granular flows.

关键词： Dense granular flows Simple shear Energy fluctuations

Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model

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Science China(Physics,Mechanics & Astronomy) 2014年第3期57卷 532-540页

作者： CHEN SongGui sun qicheng JIN Feng LIU JianGuo State Key Laboratory of Hydroscience & Engineering Tsinghua University

Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.

关键词： Bingham fluids multiple-relaxation-time lattice Boltzmann model tbw profiles drag coefficient