爆轰加载下弹塑性固体Richtmyer-Meshkov流动的扰动增长规律

研究了冲击波加载弹塑性材料扰动自由面的动力学演化过程,分析了高能炸药爆轰驱动时初始扰动与材料性质对扰动增长的影响.研究结果表明:初始扰动的振幅与波长之比越高,扰动越易增长,强度越高的材料扰动增长幅度越小;扰动增长被抑制时,尖钉的最大振幅与增长速度无量纲数之间存在线性近似关系,进一步理论分析表明尖钉的振幅增长因子与加载压力、初始扰动形态和材料强度有关,该理论关系作为扰动增长规律的线性近似在一定范围内适用于多种金属材料.     

二维空气动力学方程组分三片Riemann问题的数值解(Ⅰ)初值分布只含接触间断

对二维空气动力学方程组的分三片Riemann问题中只含接触间断的情况进行分类分析,并利用文献[1]所提出的正规三角形网格上Taylor-FVMMmB差分格式对该问题进行数值计算。从数值结果来看,分三片Riemann问题是二维空气动力学方程组Riemann问题中的最简单的初值分布,所形成解的结构也是最基本的。     

基于求解Riemann问题的界面处理方法

通过在界面处构造Riemann问题,根据流体的法向速度和压力在界面(接触间断)处连续的特性,利用Riemann问题的解不仅定义了ghost流体的值,而且对真实流体中邻近界面的点值进行了更新,使得在界面处的流体的状态满足接触间断的性质,给出了更加精确的界面边界条件,守恒误差分析表明该方法在界面计算过程中引入较小的误差.数值试验表明该方法能准确地捕捉界面和激波的位置.     

虚拟流体方法中界面处Riemann问题定义方式的改进

对RGFM中定义Riemann问题的方式进行改进,取距离界面适当远处的插值点处的状态作为Riemann问题的初值.并用数值算例对改进前后的RGFM进行比较.     

纳米固体材料的性能与界面微观结构

综述了纳米陶瓷ＴｉＯ２和纳米金属Ａｇ的力学性能，以及纳米离子导体ＣａＦ２和ＰｂＦ２等的离子导电性能，结合其界面微观结构特征，对上述纳米固体材料的优异性能进行了初步解释     

理想模型不宜运用的场景

物理习题一般以理想模型开展分析,以理想模型拟合现实场景,分析解决实际问题.但有些场景会出现按照理想模型分析得出的结论和实际情况不符的矛盾.这是由于理想模型的使用是有其局限性和适用范围的.这类问题场景和理想模型的理想化条件本身存在冲突,因此不能以理想模型来求解.但此     

Li1.5Al0.5Ge1.5P3O12/高分子固体电解质表界面结构与分子运动的固体NMR研究

相对于传统锂离子电池,全固态锂电池具有安全性能高、循环寿命长、能量密度高等优点,是目前锂电池研究领域的热点之一．作为全固态锂电池的核心组成部分,固体电解质是实现全固态锂电池高性能的关键材料．本文设计了一种高分子-锂盐-陶瓷的复合物固体电解质．通过多种固体核磁共振（NMR）方法研究了该材料中高分子-陶瓷的界面层结构和界面高分子链段的分子运动．     

模拟多介质界面问题的虚拟流体方法综述

虚拟流体方法为模拟具有清晰物质界面的多介质流动问题提供了一种简便途径.尤其基于多介质Riemann问题解的修正虚拟流体方法及其变体，能够真实考虑到界面附近非线性波的相互作用和物质性质的影响，可以有效解决各种界面强间断等挑战性难题，具有巨大的工程应用潜力.文章重点回顾了虚拟流体方法的发展历史，总结和对比了各种代表性版本在模拟可压缩多介质流时的界面条件定义方式和多维推广方式，并介绍了该方法的设计原则和精度分析方面的研究进展.文章还回顾了该方法在其他更广泛和更具挑战性典型科学问题中的最新应用进展，并对方法的优势和特点进行了总结.      

氧化物纳米材料表面结构与性质的固体核磁共振波谱研究

氧化物纳米材料的多种应用与其表面结构和性质密切相关.近年来,固体核磁共振波谱在相关研究中提供了关键信息.本综述总结了近期发展的、以固体核磁共振波谱为主的两种表征氧化物纳米材料表面结构和性质的方法,包括表面选择的同位素标记¹⁷O核磁共振波谱与动态核极化表面增强核磁共振波谱,并对氧化物纳米材料的固体核磁共振波谱研究的发展趋势进行了展望.     

电阻和理想二极管混联电路问题的讨论

1问题的提出【题目】如图1所示电路中,理想变压器原线圈与副线圈的匝数比n1∶n2=22∶5,原线圈接电压u1=220槡2sin100πt(V)的交流电,电阻R1=R2=25Ω,D为理想二极管,则通过副线圈的电流为多大?图1该题是江苏省南通市2013届高三第一次调研测试题,参考答案为3A.对于该题中学师生有两种解法.解法1:两支路电流之和等于干路中电流.设     

The Asymptotic Behaviors of Solutions to the Perturbed Riemann Problem near the Singular Curve for the Chromatography System

The Riemann problem for a simplified chromatography system is considered and the global Riemann solutions are constructed in all kinds of situations. In particular, the zero rarefaction wave, the zero shock wave and the zero delta shock wave are discovered in the Riemann solutions in some limit situations, which have infinite propagation speeds. Furthermore, these zero waves are analyzed by introducing the so-called double Riemann problem with three pieces of constant states. More precisely, we take the approximations of zero waves and investigate wave interactions in details before the limits are taken.     

固氩高压物态方程和弹性性质的密度泛函理论计算

 用平面波赝势方法结合局域密度近似密度泛函理论（DFT-LDA）计算了零温下固态氩晶体在压力0~82 GPa的p-V关系和弹性性质,计算结果与静高压实验数据符合较好,计算结果表明局域密度近似方法能较好地描述固氩晶体高压下的性质,采取合理的方法和计算参数,惰性气体固态晶体高压下的力学性质可以比较准确地计算出来,这可为一些还不能通过实验进行研究的物态分析提供借鉴。     

On the Initial Boundary Value Problems for the Enskog Equation in Irregular Domains

The paper is concerned with the Enskog equation with a constant high density factor for large initial data in L ¹(R ⁿ). The initial boundary value problem is investigated for bounded domains with irregular boundaries. The proof of an H-theorem for the case of general domains and boundary conditions is given. The main result guarantees the existence of global solutions of boundary value problems for large initial data with all v-moments initially finite and domains having boundary with finite Hausdorff measure and satisfying a cone condition. Existence and uniqueness are first proved for the case of bounded velocities. The solution has finite norm where q = (t ₀, x) is taken on all possible n-dimensional planes Q(v) in R ^n+l intersecting a fixed point and orthogonal to vectors (1, v), v R ⁿ.     

初始条件对粉末连杆锻造致密过程影响的模拟研究

为研究在不同初始条件(初始相对密度、摩擦因子)下对粉末连杆锻造致密过程的影响,运用塑性变形有限元软件DEFORM-3D对粉末连杆锻造过程进行了计算机模拟研究;研究结果表明,不同初始条件对粉末连杆锻造成形致密过程具有重要影响:(1)连杆锻造过程受到的等效应力集中在杆身部位,连杆两头的等效应力相对较小,说明其锻造过程各处所受等效应力不均匀,成形密度也不均匀;(2)初始相对密度较小的预锻坯锻造结束时,连杆大头处的材料不能达到致密,初始相对密度大的预成形坯,终锻致密效果好;(3)摩擦因数越大,连杆表面的材料流动阻力就越大,连杆大小两头就越难达到致密,说明摩擦因子对连杆相对密度分布均匀性有较大影响;通过对粉末连杆锻造致密过程影响的研究,为粉末连杆预锻坯和模具的优化设计及粉末锻造连杆的成形规律提供一定理论依据。     

Numerical method of the Riemann problem for two-dimensional multi-fluid flows with general equation of state

Based on the classical Roe method, we develop an interface capture method according to the general equation of state, and extend the single-fluid Roe method to the two-dimensional (2D) multi-fluid flows, as well as construct the continuous Roe matrix for the whole flow field. The interface capture equations and fluid dynamic conservative equations are coupled together and solved by using any high-resolution schemes that usually suit for the single-fluid flows. Some numerical examples are given to illustrate the solution of 1D and 2D multi-fluid Riemann problems.     

Comparison of the generalized Riemann solver and the gas-kinetic scheme for inviscid compressible flow simulations

The generalized Riemann problem (GRP) scheme for the Euler equations and gas-kinetic scheme (GKS) for the Boltzmann equation are two high resolution shock capturing schemes for fluid simulations. The difference is that one is based on the characteristics of the inviscid Euler equations and their wave interactions, and the other is based on the particle transport and collisions. The similarity between them is that both methods can use identical MUSCL-type initial reconstructions around a cell interface, and the spatial slopes on both sides of a cell interface involve in the gas evolution process and the construction of a time-dependent flux function. Although both methods have been applied successfully to the inviscid compressible flow computations, their performances have never been compared. Since both methods use the same initial reconstruction, any difference is solely coming from different underlying mechanism in their flux evaluation. Therefore, such a comparison is important to help us to understand the correspondence between physical modeling and numerical performances. Since GRP is so faithfully solving the inviscid Euler equations, the comparison can be also used to show the validity of solving the Euler equations itself. The numerical comparison shows that the GRP exhibits a slightly better computational efficiency, and has comparable accuracy with GKS for the Euler solutions in 1D case, but the GKS is more robust than GRP. For the 2D high Mach number flow simulations, the GKS is absent from the shock instability and converges to the steady state solutions faster than the GRP. The GRP has carbuncle phenomena, likes a cloud hanging over exact Riemann solvers. The GRP and GKS use different physical processes to describe the flow motion starting from a discontinuity. One is based on the assumption of equilibrium state with infinite number of particle collisions, and the other starts from the non-equilibrium free transport process to evolve into an equilibrium one through particle collisions. The different mechanism in the flux evaluation deviates their numerical performance. Through this study, we may conclude scientifically that it may NOT be valid to use the Euler equations as governing equations to construct numerical fluxes in a discretized space with limited cell resolution. To adapt the Navier–Stokes (NS) equations is NOT valid either because the NS equations describe the flow behavior on the hydrodynamic scale and have no any corresponding physics starting from a discontinuity. This fact alludes to the consistency of the Euler and Navier–Stokes equations with the continuum assumption and the necessity of a direct modeling of the physical process in the discretized space in the construction of numerical scheme when modeling very high Mach number flows. The development of numerical algorithm is similar to the modeling process in deriving the governing equations, but the control volume here cannot be shrunk to zero.     

过渡金属氮化物中单原子固溶和力学性能的第一性原理研究

基于密度泛函理论(DFT)的第一性原理,计算Si原子在Ti族和V族氮化物中以及B、C和Ge原子在TiN晶体中固溶的稳定结构,讨论置换型和间隙型固溶的低能量稳定结构与晶体间距的关系,研究金属氮化物和固溶原子固溶结构的力学性能.结果表明:Si原子在TiN、ZrN、HfN和TaN晶体中固溶以及Ge原子在TiN晶体中固溶情况为,单原子不进入对应过渡金属氮化物晶体中形成间隙固溶或置换固溶,随着晶体间距离变化单原子可以在晶体之间形成间隙固溶或置换固溶;Si原子在NbN以及B原子在TiN晶体中可以实现间隙固溶,而不能形成置换固溶;Si原子在VN和C原子在TiN晶体中固溶结构形式均为置换固溶.单原子固溶形成低能量置换型固溶体和间隙型固溶体的弹性常数、体模量和剪切模量均低于原过渡金属氮化物的对应值.     

Effect of Hydrolysis Conditions on the Direct Formation of Nanoparticles of Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions

The effect of the cation concentration, hydrolysis temperature, and composition in the CeO₂–ZrO₂ system on the direct precipitation of ceria–zirconia solid solutions and the structure of the precipitates from acidic aqueous solutions of (NH₄)₂Ce(NO₃)₆ and ZrOCl₂ by hydrolysis under hydrothermal conditions were investigated. Nanometer-sized (8–10 nm) ceria–zirconia solid solution particles in a composition range of 0 to 60 mol% ZrO₂ were directly precipitated from the solutions with total metal cation concentration less than 0.2 mol/dm³ by simultaneous thermal hydrolysis at 150–240°C. The crystalline phase of the precipitates gradually changed from cubic and/or tetragonal to monoclinic with increasing the cation concentration of the solution from 0.2 to 0.8 mol/dm³ at the starting composition of 50 mol% ZrO₂ under hydrolysis condition of 150°C for 48 h, which was attributed to decrease in the supply of hydrolyzed Ce component caused by decrease in the hydrolysis ratio of (NH₄)₂Ce(NO₃)₆. Ceria–zirconia solid solutions containing large amount of ZrO₂ maintained high specific surface area and small-sized crystallite after heat-treatment at 900–1000°C for 1 h.     

Exact Soliton Solutions for DNLS Equation by the Method of Riemann Problem with Zeros

With the procedure to solve explicitly the equations of the Riemann matrix with poles, multisoliton solutions to the DNLS equation are found formally. A single soliton solution is given explicitly and the asymptotic behaviors of multisoliton solutions are discussed.     

Accuracies and conservation errors of various ghost fluid methods for multi-medium Riemann problem

Since the (original) ghost fluid method (OGFM) was proposed by Fedkiw et al. in 1999 [5], a series of other GFM-based methods such as the gas–water version GFM (GWGFM), the modified GFM (MGFM) and the real GFM (RGFM) have been developed subsequently. Systematic analysis, however, has yet to be carried out for the various GFMs on their accuracies and conservation errors. In this paper, we develop a technique to rigorously analyze the accuracies and conservation errors of these different GFMs when applied to the multi-medium Riemann problem with a general equation of state (EOS). By analyzing and comparing the interfacial state provided by each GFM to the exact one of the original multi-medium Riemann problem, we show that the accuracy of interfacial treatment can achieve “third-order accuracy” in the sense of comparing to the exact solution of the original mutli-medium Riemann problem for the MGFM and the RGFM, while it is of at most “first-order accuracy” for the OGFM and the GWGFM when the interface approach is actually near in balance. Similar conclusions are also obtained in association with the local conservation errors. A special test method is exploited to validate these theoretical conclusions from the numerical viewpoint.