爆炸冲击波作用下液体抛撒不同阶段运动规律分析

文章通过对采用高速摄影仪拍摄的爆炸冲击波作用下不同时刻液体抛撒运动图片的分析,得出了爆炸冲击波作用下液体抛撒不同阶段的运动规律.分析表明爆炸冲击波作用下,液体抛撒不同阶段有不同的特点,抛撒初期液体处于加速阶段并在较短的时间内获得最大速度,获得最大速度的液体由于表面张力、空气阻力及粘性的作用产生首次破碎与二次破碎,此阶段液体抛撒速度随时间呈指数关系衰减,二次破碎后的液滴由于仅受空气阻力的作用,受力形式发生改变,速度衰减减慢.     

黏性液体爆炸抛撒模型

黏性液体爆炸抛撒模型的建立对数值模拟黏性液体爆炸抛撒形成的抛撒云团过程具有重要意义。黏性液体爆炸抛撒包含液体初始驱动、空化效应产生、液体环形成、射流形成和断裂、液滴破碎等现象,这是一个复杂的物理过程。根据不同阶段、不同现象流动特征,建立牛顿黏性流体爆炸抛撒数学模型,计算得到液体抛撒速度、抛撒半径以及液滴尺寸分布。计算结果表明抛撒半径与黏度成正比,而抛撒速度衰减曲线曲率与之成反比。为验证数学模型的准确性设计试验,试验结果与结论一致,模型准确性得到验证。     

爆炸抛撒液体最大速度的确定

通过实验分析了液体量、装药量、液体性质等对液体抛撒初期最大速度的影响,采用回归分析的方法得出爆炸抛撒的最大速度和装药量、装药直径以及液体比重有显著的相关关系,得出了爆炸抛撒初速度的计算公式和能量利用系数的取值范围     

高速运动液体动态抛撒的新型实验方法研究

高速运动液体的爆炸抛撒研究对于爆炸水雾除尘,灭火航弹以及云爆弹等技术的发展有着重要的意义,利用真实场景实验研究耗资巨大,且不易测量.针对如何在实验室内开展动态高速液体云雾抛撒模拟实验研究的问题,开发出轻气炮加载,撞击式高速云雾抛撒实验装置.实验结果表明该装置客观真实地反映出了液体云团动态抛撒的发生发展过程.     

界面动力学对平界面稳定性的影响

研究了界面动力学因素对平界面稳定性的影响，在界面局部生长速率是界面过冷度和界面动力学的函数条件下，获得了扰动增长速率的显式表达式。结果表明，界面动力学因素对平界面具有稳定作用。     

圆台形FAE装置抛撒初期燃料运动特性研究

为研究圆台形燃料空气炸药（FAE）装置燃料抛撒运动特性，利用ANSYS/LS DYNA软件对燃料初始抛撒过程进行了数值模拟，得到了不同位置处的燃料抛撒初速，分析了中心抛撒药结构对燃料抛撒的影响，并进行了实验验证。结果表明:圆台形FAE装置不同位置处的燃料抛撒初速与截面比药量有关，燃料抛撒初速随截面比药量的增加而增加；相较于等直径中心抛撒药，采用变直径中心抛撒药时截面比药量一致性更好，有利于减小不同位置处燃料抛撒的速度差。     

生物组织低温作用下相变冻结界面研究

探讨了细胞及生物组织在低温下造成损伤和破坏的机理,给出了生物组织在低温冷冻探头作用下的相变冻结界面半径与低温冷冻探头壁面温度的关系,以及相变冻结界面随时间的变化、相变冻结界面扩展速率随时间的变化关系.     

高速破片在防雷舱结构中引起的冲击荷载的理论研究

运用一维平面波理论,研究大型高速破片在防雷舱结构中引起的冲击荷载,得到了初始冲击荷载的理论公式。与有限元计算结果进行比较,证明了理论公式的正确性。运用理论计算公式分析了破片参数对冲击荷载的影响,结果表明：破片速度与冲击荷载峰值成正比,速度越快,峰值越大;速度越慢,峰值越小。而破片速度对冲击荷载的衰减没有影响,即不同速度的破片在水中引起的冲击荷载具有相同的衰减规律。不同厚度破片引起的冲击荷载的具有相同的峰值,但有不同的作用时间。破片的越厚,荷载作用时间越长;破片越薄,荷载作用时间越短。最后基于理论分析确定了几何衰减的函数形式,采用数值试验数据进行回归分析,得到了冲击波的几何衰减系数。     

界面初始扰动形态影响RM不稳定过程的数值研究

采用Navier-Stokes (NS)方程对激波诱导扰动界面的Richtmyer-Meshkov (RM)不稳定增长过程进行了二维数值模拟,分析了初始扰动条件对反射波前后界面扰动增长的影响,并与已有的模型预测结果进行了对比和分析。研究结果发现:单模初始的扰动振幅和扰动波长都直接影响反射波前后的界面增长速率;多模随机初始的扰动振幅和扰动波长对于反射波前后界面增长的影响没有单模扰动明显,其扰动增长行为均和单模大波长扰动的增长行为相似。     

高速客车蛇行运动Hopf分叉的研究

建立了高速客车非线性系统数学模型,模型中考虑了轨道的整体弹性和阻尼。基于常微分方程的一次近似理论和Hopf分叉理论,研究了高速客车在直线和大半径曲线轨道上蛇行运动的Hopf分叉情况。借助于DEPAR延续算法解决了圆曲线上车辆系统平衡位置难以确定的难题,分析了轨道整体刚度和阻尼、圆曲线半径和外轨超高及转向架悬挂参数等因素对高速客车Hopf分叉速度的影响。研究表明,高速客车在大半径曲线上也有可能出现Hopf分叉现象,并且曲线半径越大、外轨超高越大,车辆的Hopf分叉速度越高,但最大值不会超过车辆系统在直线上运行时的Hopf分叉速度。车辆系统在弹性轨道条件下的Hopf分叉速度高于刚性轨道条件下车辆系统对应的Hopf分叉速度。不论是刚性轨道还是弹性轨道,转向架悬挂参数对车辆系统Hopf分叉速度的影响趋势是一致的。     

Non-linear waves along a rotating non-Newtonian liquid jet

A liquid jet may be curved due to the influence of wind or gravity but more commonly, as is the case in industrial prilling, due to the rotation of the container from which it emerges. In prilling, pellets are manufactured by utilising the breakup of a curved liquid jet, and liquids commonly used in prilling are non-Newtonian. In this paper we investigate the influence of rotation, surface tension and viscosity on the breakup of a spiralling slender power-law liquid jet with applications to industrial prilling. The non-linear evolution equations for the jet radius and axial velocity are solved numerically using the method of finite differences. Numerical simulations allow us to explore the effects of changing the amplitude (or alternatively the frequency) of initial disturbances on breakup lengths and the size of main and satellite droplets.     

Nonlinear spatial instability of an annular swirling viscous liquid sheet

Instability and breakup of a viscous annular liquid sheet that is exposed to co-flowing inner and outer gas streams have been investigated using a nonlinear spatial stability analysis. A perturbation expansion method is used with the initial amplitude of the disturbance as the perturbation parameter. The evolution of the two gas–liquid interfaces is tracked until the sheet breaks up and the breakup length is determined. The model is validated by comparison with available experimental data. The effects of liquid swirl strength, gas-to-liquid density ratio, radius of curvature ratio, and liquid viscosity on the sheet instability and breakup have been studied. The results show that at very low values of liquid swirl, it has a stabilizing effect on sheet breakup, but as the swirl strength increases, it strongly destabilizes the sheet. Also, with increasing swirl strength, the occurrence of the large surface deformations moves from the inner interface to the outer interface. The sheet breakup length increases slightly and then decreases rapidly with an increase in liquid swirl strength. Without liquid swirl, the axisymmetric mode is the dominant instability mode. However, with increasing liquid swirl strength, the higher helical modes become dominant and the breakup becomes increasingly asymmetric. When the undisturbed liquid sheet has a purely axial motion, the inner gas stream is more effective in sheet breakup than the outer gas stream. In the presence of liquid swirl, the outer gas stream is more disruptive than the inner gas stream. The breakup length becomes shorter as gas-to-liquid density ratio and the radius of curvature ratio increases. Increase in liquid viscosity tends to slow the disturbance growth and increases the sheet breakup length.     

Measurement of acoustic reflection coefficients by an ultrasonicmicrospectrometer

An ultrasonic microspectrometer (UMSM) was developed in order to evaluate the elastic properties of a solid specimen at a small spot on its surface. In this system, spherical-planar-pair (SPP) lenses were used, by which the acoustic reflection coefficient of a liquid/solid interface was measured as a function of the incident angle in the frequency range from 20 to 140 MHz. Using a specimen of fused quartz whose material constants were well known, the measurement accuracy was examined. The phase velocity of a leaky Rayleigh wave was obtained from the phase change of the reflection coefficient with 0.4% accuracy in this frequency range. For a specimen of steel with a large acoustic attenuation, bulk attenuation factors and their frequency dependence were successfully estimated by computer-fitting of the reflection coefficient. As an example of anisotropic materials, the reflection coefficient of X-cut quartz was also measured. Measured phase of the reflection coefficient was in good agreement with numerical calculation     

Instability and fragmentation of expanding liquid systems

This analysis pursues the underlying physics governing the expansion, dispersal and breakup of a thin walled steel right circular cylinder filled with liquid after being impacted by a high velocity aluminum sphere. The impact generates a radially expanding coherent thin shell of liquid which stays together to at least a diameter 8 times that of the original cylinder. An instability criterion is proposed and developed based on the opposing forces of stabilizing inertial pressures and destabilizing viscous resistance. This criterion is compared to test data where possible in order to ascertain its ability to predict liquid breakup of the shell. The breakup theory developed here predicts the extensive expansion of the unthickened liquid prior to fragmentation as observed in the experiments. This result lends some credence to the underlying physics pursued here and its ability to predict the onset of liquid fragmentation.     

不同厚度碳纤维布/环氧树脂复合材料孔隙率超声衰减模型

复合材料中孔隙的存在造成了材料性能的下降,因此,对材料孔隙的检测至关重要。本文利用异丙醇(IPA)添加量的不同,制备了不同层数、不同孔隙率含量的碳纤维(CF)布/环氧树脂层合板试件。采用脉冲反射法测试计算了CF布/环氧树脂层合板试件的超声衰减系数,通过金相显微分析对孔隙的分布、形状及尺寸进行了表征,运用MATLAB对金相显微图进行分析得到试件的孔隙率。讨论了孔隙率对材料的声速、声阻抗及超声衰减系数的影响规律,利用4组不同层数样本试件的孔隙率和超声衰减量的试验数据,给出了基于模型的孔隙率与材料层数、超声衰减量的拟合公式。结果表明,随着IPA添加量的增加, CF布/环氧树脂层合板(2 mm)孔隙率从1.09%增加到4.16%,材料的声速和声阻抗均下降,超声衰减系数从2.51 dB/mm增大到5.34 dB/mm。孔隙率为1%时,厚度从2 mm (8层)增加到5 mm(20层),衰减系数增大了0.54 dB/mm。     

垂直Bridgman法生长CaF2单晶传热过程的数值分析

采用有限元法对大尺寸氟化钙单晶的生长过程进行了传热分析,准稳态模型简化模拟计算过程.研究了梯度区不同的温度梯度对界面形状和晶体生长速度的影响,讨论了辐射传热对晶体生长过程传热的影响.研究表明:晶体生长过程中界面凸度发生变化;晶体生长速率与坩埚下降速率不一致;25 K/cm为合适的梯度区温度梯度;晶体内部辐射传热对单晶生长传热过程有重要影响.计算结果表明,3个时期的固相等温线的曲率小于液相的.根据数值模拟结果进行了晶体生长实验,生长出的晶体完整,透明,无宏观缺陷.     

建筑爆破倒塌过程的摄影测量分析(Ⅰ)——运动过程分析

以某一爆破拆除工程为例,通过近景摄影测量系统(包括近景摄影和图像处理),对建筑爆破拆除倒塌过程进行了定量分析,获得建筑倒塌运动过程中位移、转角、平动速度、转动角速度等参数。摄影测量数据与建筑倒塌过程的各受力状态进行了对比分析,提出将建筑物的倒塌过程分为爆破切口形成阶段、自由落体阶段、冲击撞地阶段和转动坍落阶段。     

位置条件对爆破震动信号分析中小波包时频特征的影响

爆心至测点的位置条件是影响爆破震动时频分布的主要因素之一。在考虑到段药量变化的情况下,位置条件由比例距离和高差系数来进行量化。运用小波包分析方法对监测获得的爆破震动信号进行时频特征分析,探讨时频分布与比例距离及高差系数之间的关系。试验研究发现,位置条件对震动波形小波包细节信号时频特征的影响主要体现在峰值质点振速、优势频率大小及波形衰减阻尼比的变化上。其中峰值质点振速随比例距离的增加呈指数衰减,其与高差系数的相关规律性不强;优势频率随比例距离增加也呈衰减趋势,高差系数对其有较大影响,但规律不明显;衰减阻尼比在不同的主振频带内与比例距离及高差系数有不同的关系,较低频率部分其阻尼比随着比例距离的增加而增大,较高频率部分则基本保持不变。     

SH-SAW propagation in layered functionally graded piezoelectric material structures loaded with viscous liquid

We investigate the properties of shear horizontal surface acoustic wave propagation in layered functionally graded piezoelectric material structures loaded with viscous liquid. The piezoelectric material is polarized in the z-direction and the material properties change gradually along the thickness of the layer. Interfacial mechanical conditions are continuity of particle velocity and stress components at the interface. We here assume that the liquid is electrically insulated and its permittivity is much less than that of the piezoelectric material. The solutions of dispersion relations are obtained for insulated liquid with electrically open or shorted conditions by means of transfer matrix method. The effects of the gradient variation of material constants on the phase velocity and attenuation are presented and discussed in detail. The analytical method and the results are useful for the design of the resonators and sensors.