饱和土中爆炸波传播问题的数值模拟

应用流体弹塑性力学的框架描述了爆炸荷载作用下饱和土介质的本构模型,包括体积压缩关系和强度关系。应用LS-dyna软件分析了三相饱和土介质中的爆炸波传播及其与结构的相互作用问题,并与先前完成的试验结果进行了对比,两者吻合较好。饱和土中爆炸波传播的一些特殊现象被重现,表明本构模型的描述是可行的。     

PARTITION OF UNITY FINITE ELEMENT METHOD FOR SHORT WAVE PROPAGATION IN SOLIDS

IntroductionIt is known that standard finite element procedure is unable to simulate the wavepropagation with high oscillations or gradients in space in the media with reasonableefficiency and accuracy due to the nature of polynomial interpolation approxi…     

Vibration characteristics of FGM circular cylindrical shells filled with fluid using wave propagation approach

The vibration characteristics of a functionally graded material circular cylindrical shell filled with fluid are examined with a wave propagation approach. The shell is filled with an incompressible non-viscous fluid. Axial modal dependence is approximated by exponential functions. A theoretical study of shell vibration frequencies is analyzed for simply supported-simply supported, clamped-simply supported, and clamped-clamped boundary conditions with the fluid effect. The validity and the accuracy of the present method are confirmed by comparing the present results with those available in the literature. Good agreement is observed between the two sets of results.     

FLEXURAL WAVE PROPAGATION IN NARROW MINDLIN＇S PLATE

Appling Mindlin＇s theory of thick plates and Hamilton system to propagation of elastic waves under free boundary condition, a solution of the problem was given. Dispersion equations of propagation mode of strip plates were deduced from eigenfunction expansion method. It was compared with the dispersion relation that was gained through solution of thick plate theory proposed by Mindlin. Based on the two kinds of theories, the dispersion curves show great difference in the region of short waves, and the cutoff frequencies are higher in Hamiltonian systems. However, the dispersion curves are almost the same in the region of long waves.     

平板撞击下C30混凝土中冲击波的传播特性

采用1级气炮加载技术和锰铜应力计多点测试技术,开展了C30混凝土在平板撞击条件下的冲击压缩实验研究。基于锰铜应力计实测的应力波形,研究了混凝土中冲击波的传播特性,结果显示冲击波的应力峰值随传播距离呈现明显的衰减特性,衰减过程可分为2个阶段。在早期阶段,卸载波没有赶上前面传播的冲击波,冲击波应力峰值衰减较慢,主要是混凝土材料的本构粘性效应所引起的;而后期阶段应力峰值的快速衰减则归因于混凝土材料的本构粘性效应、后续的来自飞片自由面的反射波追赶卸载、边侧稀疏波卸载及波传播的几何弥散效应的共同作用;另外,冲击波在混凝土中传播的升时也随着传播距离逐渐增大,即由强间断波逐渐转化为弱间断波。     

Nonlinear and viscous effects on wave propagation in an elastic axisymmetric vessel

In this paper, a power series and Fourier series approach is used to solve the governing equations of motion in an elastic axisymmetric vessel with the assumption that the fluid is incompressible and Newtonian in a laminar flow. We obtain solutions for the wave speed and attenuation coefficient, analytically where possible, and show how these differ under a number of different conditions. Viscosity is found to reduce the wave speed from that predicted by linear wave theory and the nonlinear terms to increase the wave speed in comparison to the linear solution. For vessels with a wall stiffness in the arterial range, the reduction in the wave speed due to the viscous terms is approximately 10% and the increase due to the nonlinear terms is approximately 5%. This difference between the linear and nonlinear wave speeds was found to be largely constant irrespective of the number of terms considered in the power series for the velocity profile. The linear wave speed was found to vary weakly with stiffness, whilst the nonlinear wave speed was found to vary significantly with the stiffness, especially at low values of stiffness. The 10% variation in the wave speed due to the viscous terms was found to be constant with wall stiffness whilst the 5% variation due to the nonlinear terms was found to vary with wall stiffness. The importance of the number of terms considered in the power series is discussed showing that only a relatively small number is required in the viscous case to obtain accurate results.     

水下连续脉冲冲击波的声学特性

为探求金属爆炸索在水下爆炸声源研究领域的应用前景,设计了一种可以连续产生若干个脉冲冲击波的装置,称之为水下连续脉冲冲击波发生装置。利用小波分析对该装置产生的连续脉冲冲击波信号进行分解与重构,考察其频谱特性,并进一步分析了信号的声压级特性。结果表明：该装置产生的信号声压级较高,具有很强的声功率;信号包含频率十分丰富,雷管和金属爆炸索由于装药结构及传爆方式的不同,爆炸所产生的冲击波频谱特性也有所差异。雷管爆炸产生的冲击波主要分布在15.6 kHz以下的频带内,金属爆炸索爆炸产生的脉冲冲击波信号则主要分布在62.5 kHz以下的频带内;脉冲冲击波的个数和声持续时间可由爆炸索的排列方式和长度控制,脉冲冲击波间的时间间隔可调,发生装置稳定易控     

爆轰波拐角传播三维数值模拟

为了研究爆轰波在拐角中的传播特性以及拐角爆轰低压流场现象,用LSDYNA 3D程序对三种常见的拐角装药的爆轰波传播特性进行了数值模拟,清晰显示了爆轰波因拐角处爆轰波传播面积的变化而产生的衰减 增长过程,讨论了侧向三通中爆速的变化情况,并得到了拐角处低压爆轰区的尺寸。     

Assessment of filtered gas–solid momentum transfer models via a linear wave propagation speed test

The propagation speeds of linear waves in gas–solid suspensions depend strongly on the solids volume fraction and the wave frequency. The latter is due to gas–solid momentum transfer and allows a simple test on filtered gas–solid momentum transfer models. Such models may predict linear wave propagation speeds different from those obtained with the non-filtered model at wave frequencies higher than the filter frequency, but not at wave frequencies lower than the filter frequency.     

Numerical study on wave propagation in a low-rigidity elastic medium considering the effects of gravity

We discuss the effects of vertical gravity force on wave propagation when a material is intermediate between solid and fluid, especially we focus on what kinds of phase are generated and how it propagates on the surface. We introduce gravity terms into the 2D linear finite element method in order to account for the contribution from the gravity. Numerical simulations are conducted for a half-space model and a two-layered, single horizontal layer overlain on a half-space, model. Both models are compared between the results including and excluding the viscosity. The fastest phase propagating from a surface point source, a leaking Rayleigh wave for usual elastic material, is transformed into an interesting phase including some common features to the gravity wave when the gravity effect becomes significant. The viscosity does not affect the fastest phases, whereas it affects other latter phases appearing only for the two-layered model.     

爆炸容器内冲击波系演化及壳体响应的数值研究

对中心装药爆炸后冲击波的产生、传播和壳体动态响应全过程进行了数值研究。认为RDX瞬时爆炸 ,爆炸近场采用自相似解 ;冲击波传播和波系演化采用PPM (the Piecewise Parabolic Method)格式求解Eu ler方程 ;壳体响应采用有限元方法求解拉氏坐标系下由虚功原理得到的动力学方程。壳体内壁面边界条件分别采用强耦合和弱耦合方法处理。结果表明 :(1)当装药量相同时 ,薄壁壳体振型比厚壁壳体复杂得多 ,振幅也大 ;(2 )当装药量不同 ,壳体厚度相同时 ,爆炸场冲击波的演化过程不同 ;(3)对少量装药 ,产生的冲击波强度低 ,壳体变形小 ,是否考虑内边界运动 ,对计算结果的影响不大 ;(4 )在本文条件下 ,爆炸容器封头顶点所受的载荷最大 ,是最易发生破坏的地方 ,侧壁与爆点所在横截面的交线 ,也易破坏。     

Study on wave dispersion characteristics of piezoelectric sandwich nanoplates considering surface effects

In this study, the wave propagation properties of piezoelectric sandwich nanoplates deposited on an orthotropic viscoelastic foundation are analyzed by considering the surface effects (SEs). The nanoplates are composed of a composite layer reinforced by graphene and two piezoelectric surface layers. Utilizing the modified Halpin-Tsai model, the material parameters of composite layers are obtained. The displacement field is determined by the sinusoidal shear deformation theory (SSDT). The Euler-Lagrange equation is derived by employing Hamilton’s principle and the constitutive equations of piezoelectric layers considering the SEs. Subsequently, the nonlocal strain gradient theory (NSGT) is used to obtain the equations of motion. Next, the effects of scale parameters, graphene distribution, orthotropic viscoelastic foundation, and SEs on the propagation behavior are numerically examined. The results reveal that the wave frequency is a periodic function of the orthotropic angle. Furthermore, the wave frequency increases with the increase in the SEs.

     

煤体中爆炸应力波传播与衰减规律模拟实验研究

在岩石爆破理论的基础上分析了煤体中爆炸应力波的作用机理,借助损伤力学理论探讨了煤体在 爆炸应力波作用下的损伤断裂准则。煤体中爆炸应力波传播与衰减规律模拟实验结果表明:煤体中爆炸应力 波一般包含2段波形,第1段由压缩相和拉伸相组成简单波形,第2段是由多种作用形成的复杂波形;爆炸应 力波作用下,煤体首先承受压应力,而后承受拉应力,且压缩相的作用时间较拉伸相作用时间短;煤体中爆炸 应力波的衰减速度较一般岩体中的快,实验条件下应力波衰减因数符合=3-/(1-),爆炸应力波的主要 作用是在煤体中形成少量新裂隙、激活煤体中原生裂隙并打破煤体中瓦斯气体的平衡状态。     

垂直断层破碎带对Rayleigh波传播与场地地震动反应的影响

采用基于时域粘弹性人工边界的Rayleigh波输入方法,对具有不同宽度、不同剪切波速的垂直断层破碎带的场地进行了Rayleigh波作用下的动力时程反应分析,研究了垂直断层的宽度与剪切波速变化对Rayleigh波传播及场地地震动反应的影响。计算结果表明:在Rayleigh波入射一侧的中远场地表面,断层宽度与剪切波速的变化对地面峰值位移反应影响很小;在Rayleigh波入射一侧的断层角点以及距角点较近处,随着断层宽度的增大或剪切波速的减小,峰值位移反应均增大;在另一侧中远场地面的峰值位移反应随着断层宽度的增大或剪切波速的减小而减小,且水平位移峰值减小的程度略大于竖向位移峰值。由此可以看到,软弱的断层破碎带对通过的Rayleigh波有削弱作用,且破碎带越宽或剪切波速越小削弱作用越明显。     

Shear wave velocity in sand considering the effects of frequency based on particle contact theory

Since the shear waves involved in in-situ and laboratory measurement methods vary significantly in terms of the frequency range, it is necessary to consider the effects of frequency on the shear wave velocity. In this study, sand particles are assumed to be spherical solid particles with an equal radius and identical material properties, and sand skeletons are regarded as granular aggregations generated through the random packing of sand particles. It is also assumed that the sand particles only undergo elastic deformation during shear wave propagation. Based on a spherical particle model, a formula is obtained for calculating the shear wave velocity in sand, with the shear wave frequency as an extra influencing parameter. The quantitative calculations demonstrate that the shear wave velocity decreases with an increase of sand porosity, and accelerates with increases of vertical effective stress and elastic modulus of the sand particles. It is also indicated that both the particle density and Poisson’s ratio of the sand particles have negligible effects on the shear wave propagation. The frequency dispersion characteristics of shear wave propagating in sand are also discussed. Moreover, the critical frequency is defined and its analytical expression is derived. The calculation results obtained using the proposed equations agree well with the in-situ measurement results and bender element test data.     

煤气火焰传播规律及其加速机理研究

研究了煤气/空气预混气在两端封闭管道中的火焰传播加速现象和管道中有无障碍物时火焰的加速机理,认为火焰加速是由于火焰前未燃气体被前驱压缩波加热和障碍物诱导的湍流区对燃烧过程的正反馈造成的。实验结果表明,障碍物存在时,最大爆炸压力可提高20%,与理论计算一致;火焰传播特性随煤气浓度的变化而改变;障碍物阻塞比对火焰的速度和压力都有一定影响。     

在埋置框架中应力波传播的影响因素分析

基于埋置框架的回传射线矩阵法,分析桩土刚度比、荷载作用方向等对埋置框架轴力波、剪力波和弯矩波的影响,并与框架结构进行比较。结果表明:荷载作用方向对埋置框架的轴力波和弯矩波影响较大;由于土体的影响,埋置框架与普通框架的瞬态波有很大不同。     

高径比对砂岩单轴压缩声发射特性的影响研究

岩石尺寸效应对声发射特性的影响对于利用声发射技术监测岩石失稳破坏具有重要的实践意义.本文选择不同高径比的长石细砂岩试样开展单轴压缩声发射试验,探讨尺寸效应对岩石声发射事件数、振铃计数、峰值频率等声发射特性参数的影响.研究结果表明:根据岩石试件撞击数的增长速率,将试件破坏阶段分为突变期、平静期、爆发期三个阶段,随着岩石试...     

侧向稀疏波对非均质凝聚炸药冲击波起爆过程的影响

以压装TNT为例,开展二维拉氏实验,利用二维锰铜-康铜组合拉氏量计测量了轴对称位置和径向位置的压力时程曲线和径向位移曲线.同时利用二维拉格朗日分析计算程序RFLA对压装TNT的冲击波起爆过程进行了计算,分别得到了在2个不同径向位置上各个Lagrange位置上的质点速度、相对比容、比内能等时程曲线.研究结果展现了侧向稀疏...     

正方形排列四圆柱体绕流特性及互扰效应研究

基于计算流体动力学理论,运用大涡模拟方法对雷诺数Re=3900三维正方形排列四圆柱体结构群的绕流问题进行数值计算,主要分析来流攻角与间距比两个参数对四圆柱体结构群流体参数及流场模态的影响。结果表明:来流攻角与间距比均对四圆柱体结构群绕流特性有较强的影响;来流攻角θ=0°、22.5°、45°下,临界间距比分别为3.5、4.0、3.0;间距比的变化会导致下游圆柱表面压力系数分布发生改变;另一方面,间距比较小时,四圆柱体结构之间的互扰作用均以临近效应为主;随间距比增大,上游圆柱尾流对下游圆柱有显著影响,其互扰作用会转变尾激效应。