爆轰加载下金属材料的微层裂现象

通过在LiF窗口撞击镀膜面增加一薄层LiF和对LiF窗口反光面进行漫反射面镀膜处理的方法，对传统Asay窗诊断技术进行了改进，获得了微层裂物质高质量的实验信号。将改进后Asay窗技术与中能X射线照相及激光干涉测速技术相结合，实验给出了熔化状态下Sn材料微层裂物质不同时刻的密度空间分布图像及演化特征，且不同测试技术诊断结果半定量吻合。得到Sn材料微层裂物质的清晰物理图像，可为微层裂物理机理的认识和物理建模提供实验数据。     

爆轰加载下金属锡层裂破碎数值模拟

对爆轰加载下低熔点金属锡的层裂破碎问题开展了数值模拟。在利用实验数据对所采用数值方法和材料模型开展对比验证的基础上，通过对样品内部物理量时间及空间分布演化对比分析，剖析了冲击加-卸载中样品内部应力波与材料相互作用过程。此外，通过对比分析不同厚度锡样品在爆轰加载下的动态行为特征，进一步认识了自由面反射稀疏波、边侧稀疏波和入射稀疏波共同作用下层裂破碎演化机制。结果表明，当样品较薄时，层裂破碎行为由反射稀疏波主导；随着样品厚度的增大，反射稀疏波主导区缩小，入射稀疏波和边侧稀疏波主导区逐渐增大。     

可识别微层裂前界面的阶跃信号电探针测试技术

受微喷射物质干扰,现常用的测试技术难以对复杂结构金属样品微层裂前界面进行准确识别,针对该问题提出阶跃信号电探针测试技术。对传统电探针受微喷射物质干扰出现不正常放电现象的原理进行分析,设计阶跃信号形成电路。开展锡金属样品爆轰实验,对比传统电探针和阶跃信号电探针的放电波形,分析阶跃信号电探针数据解读方法,联合X光测试技术,对阶跃信号电探针放电波形阶跃信号高电平出现时刻进行检定。实验结果表明:阶跃信号电探针测试技术能够识别微喷射物质的干扰,可用于爆轰加载下金属样品微层裂前界面的识别。     

三角形波致LY12铝层裂的平板冲击实验研究

采用基于冲击波衰减动力学的实验技术,使平板碰撞层裂实验的LY12铝样品中,产生三角形冲击脉冲.采用VISAR技术记录样品自由表面历史,获得样品中发生层裂的信号.在经过高应力三角形波实验的软回收样品上,发现了两个层裂面.就样品中呈现三角形脉冲的平板冲击实验而言,样品中可以存在一些高拉伸应力区域并发生多次层裂.将该文提出的基于空穴聚集的层裂模型用于数值模拟这些特定条件的平板冲击试验,并将计算的样品自由面速度历史及样品中的损伤分布与实测的VISAR数据及软回收的样品层裂面等作了比较.研究表明,人为粘性、状态方程、本构方程以及层裂模型对于数值模拟三角形冲击脉冲引起的层裂有严重影响.     

一种适用于复杂加载状态下微喷射物质面密度测量的Asay膜方法

为了解决传统Asay膜方法不适用于复杂加卸载条件下微喷射物质面密度测量的问题,采用光子多普勒速度计（photonic Doppler velocimetry, PDV）测量微喷射物质速度结合传统Asay膜方法的膜速曲线发展了测试复杂加载条件下微喷射面密度的新方法。采用数值实验和轻气炮实验对新方法进行了分析和评估。针对3种典型微喷射物质速度分布情况,利用数值实验分析评估了实际应用场景下因PDV给出的微喷物速度偏离理论值对面密度测量的影响,通过对PDV给出的微喷物速度线性插值处理,可确保新方法与理论值测量偏差小于20%。通过轻气炮加载预置粉末样品实验对比评估了新方法和传统方法的测量效果,采用2种方法分别处理同一发实验数据,结果显示,新方法相较于传统Asay膜方法的测量偏差小于20%。     

晶粒尺寸对高纯铝板材层裂特性的影响

采用不同热处理工艺制备了3种晶粒尺寸（60、100、500 μm）的高纯铝板材,利用平板撞击实验研究了其层裂行为。通过改变飞片击靶速度,在靶板中实现初始层裂状态和完全层裂状态。基于自由面速度时程曲线和微损伤演化及断口显微形貌分析,讨论了晶粒尺寸对高纯铝板材层裂特性的影响规律。实验结果显示:（1）晶粒尺寸对高纯铝板材层裂特性的影响强烈依赖于冲击加载应力幅值,在低应力条件下,层裂强度与晶粒尺寸之间表现出反Hall-Petch关系,而在高应力条件下,晶粒尺寸对层裂强度几乎没有影响;（2）随着晶粒尺寸的增大,靶板损伤区微孔洞的尺寸和分布范围均增大,但数量显著减少,在微孔洞周围还发现比较严重的晶粒细化现象;（3）随着晶粒尺寸的增大,层裂微观机制从韧性沿晶断裂向准脆性沿晶断裂转变,且在断口上观察到少量随机分布的小圆球,归因于微孔洞长大和聚集过程中严重塑性变形引起的热效应。     

拉伸应变率对20钢层裂特性的影响

采用轻气炮加载技术和激光速度干涉(VISAR)测速技术相结合,对不同拉伸应变率条件下20钢的层裂特性进行了实验研究。通过改变飞片和样品的几何尺寸来调整拉伸应变率的大小,研究了拉伸应变率对20钢层裂强度的影响。实验的拉伸应变率的变化范围为104~106 s-1,最大拉伸应变率接近激光加载所能产生的拉伸应变率,相比激光加载,薄飞片技术容易保证一维应变条件。实验结果显示20钢的层裂特性明显依赖着拉伸应变率的大小,106 s-1条件下层裂强度比104 s-1时提高近70%。基于对数值计算结果的分析,讨论了影响层裂强度的主要外载荷因素。     

层裂微裂纹的形态及层裂程度的表征参量

层裂是冲击载荷造成材料破坏的一种典型方式。文中运用超声Ｃ扫描检测系统对层裂试件的微损伤形态进行检测，确是出在一维应变加载条件下的微裂纹形态呈钱币型；另一方面，根据钱币型微纹形态，通过对层裂损伤演化过程的分析，提出了一个描述层裂程度的无量纲参量，与层裂实验数据的对比说明了这个参量能够很好地描述层裂损伤程度。     

预应力对LY12铝层裂强度的影响

通过过盈配合的热装配方法和机械夹紧方法对LY12铝合金平面样品施加了径向预应变,采用平面飞片撞击方法获得了预应力对层裂特性的影响。结果表明:当飞片以500 m/s的速度撞击样品,预应变为0（无预应变）、25110-6、1 10810-6、1 88610-6时,层裂强度分别为1.130、0.935、0.755、0.643 GPa,初始预应力（变）明显降低了LY12铝层裂强度,证实了材料的层裂强度与初始应力状态密切相关,可为以后的非一维平面应变下的层裂研究提供参考。     

爆轰波对碰加载下平面金属样品动载行为实验研究

进行冲击波对碰加载简易平面金属Sn和W样品实验,采用X射线照相和激光干涉测速系统进行联合诊断,给出了2种材料冲击波对碰区表面微喷及主体破碎物质的直观图像,研究了Sn和W样品对碰区动力学行为,并比较分析2种材料对碰区特征的异同,给出了定性物理解释,实验结果可为爆轰波对碰加载下材料动力学特性的理论研究提供数据支撑。     

Experimental study of micro-spalling fragmentation from melted lead

In this paper, we conduct an experimental investigation of a Pb target shocked using high explosives through the use of an improved, non-radiographic diagnostic technique called an Asay window. In the case considered, the Pb sample is melted upon release at a shock-breakout pressure of about 38 GPa. By converting the measured velocity profile of an Asay window, the mass and density distributions as a function of spatial distance in the melted Pb sample were quantitatively obtained at different offsets, corresponding with the formation of micro-spalling fragments. The physical analysis is in reasonable agreement with the result for an Sn sample recorded by proton radiography.     

[100]LiF单晶在60 GPa以内冲击加载下的高压屈服强度特性

获取光学窗口自身的高压强度特性是开展材料高压高应变率冲击响应行为精密测量和数据反演的重要基础。利用平板撞击和双屈服面法,通过冲击-卸载、冲击-再加载原位粒子速度剖面精细测量和数据反演,获得了约60 GPa范围内[100]LiF屈服强度特性随冲击压力的变化规律。结果表明:在实验压力范围内,[100]LiF的屈服强度随加载压力的提高而显著提高,压力硬化效应显著;同时,LiF在冲击加载下的屈服强度高于磁驱准等熵加载结果,应变率硬化效应强于热软化效应。采用Huang-Asay模型确定了可描述冲击加载[100]LiF强度特性的本构模型参数,为LiF在强度、相变、层断裂等加窗测量实验中的深入应用和数据准确解读提供了重要支撑。     

Instability theory of shock wave in a channel

The instability theory of shock wave was extended from the case with an infinitefront to the case of a channel with a rectangular cross section.First,themathematical formulation of the problem was given which included a system ofdisturbed equations and three kinds of boundary conditions.Then,the general solutionsof the equations upstream and downstream were given and each contained fiveconstants to be determined.Thirdly,under one boundary condition and oneassumption,it was proved that all of the disturbances in front of the shock front andone of the two acoustic disturbances behind the shock front should be zero.Theboundary condition was that all of the disturbed physical quantities should approach tozero at infinity.The assumption was that only the unstable shock wave was concernedhere.So it was reasonable to assumeω=iγ,γwas the instability growth rate andwas a positive real number.Another kind of boundary conditions was that the normaldisturbed velocities should be zero at the solid wall of the cha     

水下声波传播过程的时域间断Galerkin有限元方法

本文构建了声压波动方程的改进时域间断Galerkin有限元方法.传统时域连续有限元方法在计算高梯度、强间断特征水中声波传播问题时往往会出现虚假数值振荡现象,这些数值振荡会影响正常波动的计算精度.为了解决这一问题,本文通过引入人工阻尼的方式构建了改进的时域间断Galerkin有限元方法,并针对具有高梯度、强间断特征的多障碍物复杂边界和层合液体介质声传播问题进行了计算.计算结果表明,与传统时域连续方法如N ew mark方法计算结果对比,所发展方法能较好地消除高梯度和强间断声压力波传播过程中虚假的数值振荡,具有较高的计算精度.问题的求解为进一步流固声耦合问题的研究奠定了基础.     

EXISTENCE OF BOUNDED SOLUTIONS ON THE REAL LINE FOR LIENARD SYSTEM

The existence of monotone and non-monotone solutions of boundary value problem on the real line for Lienard equation is studied. Applying the theory of planar dynamical systems and the comparison method of vector fields defined by Lienard system and the system given by symmetric transformation or quasi-symmetric transformation, the invariant regions of the system are constructed. The existence of connecting orbits can be proved. A lot of sufficient conditions to guarantee the existence of solutions of the boundary value problem are obtained. Especially, when the source function is bi-stable, the existence of infinitely many monotone solusion is obtained.     

基于相平均方法的折射绕射联合波浪模型

近岸带波浪运动的研究具有很重要的工程意义，近年来已获得了较丰硕的研 究成果并发展了许多波浪模型，而基于不同理论的波浪模型往往具有特定的适用性. 在海岸 工程中应用比较广泛的一类波浪模型以波能(波作用量)守恒为基本依据，如SWAN模型. 该 类模型在实际工程中已经得到了大量的应用，但该类模型未计及波浪绕射效应，成为其突出 的缺陷之一. 如何对模型做适当的改进，使之适用于波浪绕射的模拟，从而在原有基础上拓 广模型的应用范围是一项具有实际意义的研究工作. 该文采用波能(波作用量)守恒方程描 述近岸带波浪运动，通过引入绕射因子，得到折射、绕射联合波浪模型，从而拓广了模型的 应用范围. 通过实际算例验证，表明所建立的模型计及了波浪折射、绕射作用，对相平 均波浪模型在波浪绕射效应模拟方面的改进具有一定的意义.     

Existence of bounded solutions on the real line for Liénard system

The existence of monotone and non-monotone solutions of boundary value problem on the real line for Liénard equation is studied. Applying the theory of planar dynamical systems and the comparison method of vector fields defined by Liénard system and the system given by symmetric transformation or quasi-symmetric transformation, the invariant regions of the system are constructed. The existence of connecting orbits can be proved. A lot of sufficient conditions to guarantee the existence of solutions of the boundary value problem are obtained. Especially, when the source function is bi-stable, the existence of infinitely many monotone solusion is obtained.     

The genetically optimized tunnel-entrance hood

A numerical procedure is investigated for optimizing the design of tunnel-entrance hoods used for controlling the compression wave generated when a high-speed train enters a tunnel. Long hoods are required for long tunnels and train speeds exceeding about 350 km/h. The hood must minimize the maximum pressure gradient across the compression wave-front by taking advantage of the pressure-release provided by open windows distributed along one or both of its walls. The compression wave produced by the train can be evaluated by means of a rapid computational scheme devised and validated against experiment. Optimization is achieved by representing a possible distribution of windows by a binary string. The individuals in an initial, random population of such strings are allowed to ‘mate’ and evolve by ‘natural selection’ through several generations towards an optimal configuration by application of a genetic algorithm. The genetically fittest hood is associated with the minimum possible maximum pressure gradient for prescribed values of the train speed and hood dimensions. The algorithm yields an optimal design from among a theoretically unlimited number of possibilities; it can also supply near-optimal, smoothly varying window distributions (or optimize the variation in width of a long slit-like window in the hood wall) satisfying additional constraints imposed by the designer.     

Gravity wave radiation from unsteady rotational flow in an f-plane shallow water system

Spontaneous gravity wave radiation from an unsteady rotational flow is investigated numerically in an f-plane shallow water system. Unlike the classical Rossby adjustment problem, where free development of an initially unbalanced state is investigated, we consider development of a barotropically unstable zonal flow which is initially balanced but maintained by zonal mean forcing. Gravity waves are continuously radiated from a nearly balanced rotational flow region even when the Froude number is so small that balance dynamics is thought to be a good approximation for the full system. The source of gravity waves is discussed by analogy with the theory of aero-acoustic sound wave radiation (the Lighthill theory). It is shown that the source regions correspond to regions of strong rotational flow. The gradual change of rotational flow causes gravity wave radiation. We propose an approximation for these strong sources on the assumption that the dominant flow in the jet region is non-divergent rotational flow. In addition, we calculate the zonally symmetric component of gravity waves far from the source regions, solving the Lighthill equation. Using scaling analyses for perturbations, these gravity waves can be calculated with only one approximated source term that is related to the latitudinal gradient of the fluid depth and the latitudinal mass flux. In spite of its simplicity, this approximation not only explains the physical cause of gravity wave radiation, but gives an amount of source close to that obtained by classical approximation derived from vortical motion.     

波动方程数值模拟的一种显式方法——-界面节点公式的构建

针对成层介质中标量波动的数值模拟, 基于波速有限原理和波动方程柯西问题的解, 导出了界面点在一个短时间窗内的精确解, 由此给出了具有高阶精度的界面节点显式递推公式的一种构建方法, 并以构造弹性杆界面节点的递推公式为例说明其要点. 给出了与已有内节点递推公式的精度阶匹配的二阶和四阶界面节点递推公式. 由此构成的计算格式具有``异质格式'编程简便的特性, 更合理地考虑了界面影响. 最后, 通过数值试验检验这一匹配方案的精度和稳定性.