隧道表面爆破地震波的产生机制及传播特征

为了研究隧道表面爆破地震波的产生机制及传播规律,提出了隧道表面爆破振动平面应变理论模型,得到了隧道表面爆破振动场积分形式解;以龙南隧道爆破工程为背景,建立了有限元数值模型,通过现场测试验证了数值模拟与理论解答的准确性;提出了基于高分辨率Radon变换的隧道爆破地震波波场分离方法,结合理论解析与数值模拟得到了P波、S波、R波的传播特征,最后综合理论结果与波场分离结果提出了隧道爆破地震波作用分区。结果表明：隧道爆破产生P波、S波,R波在自由面迅速发育,3类波呈现指数衰减特征,S波衰减快于P波快于R波。随着爆心距的增大,垂直方向主要成分由S波转变为R波,水平方向主要成分由S波转变为P波,P波转变为R波。Ⅳ级围岩工况下,隧道爆破地震波作用分区为：隧道轴向距掌子面0～6.44 m为爆破近区,主导波型为水平S波;6.44～21.23 m为爆破中区,主导波型为水平P波;21.23 m外为爆破远区,主导波型为垂直R波。爆破分区分界点与单段最大药量呈线性关系,可通过爆破药量得到隧道爆破分区位置,用于隧道安全稳定性分析。     

起波钢筋高速动态拉伸力学性能研究

针对提高混凝土梁抗冲击爆炸性能的起波配筋新技术,采用理论分析与动态冲击拉伸试验相结合的方法,揭示了起波钢筋的快速拉伸变形作用机理,分析了拉伸速度、起波矢高等因素对起波钢筋抗拉强度的影响规律,确定了起波钢筋静态弹性极限强度计算方法。提出了起波钢筋等效拉伸应变率新概念,建立了弹性极限强度动力放大系数（dynamic increase factors,DIF）计算模型。研究结果表明,预先弯折起波使得钢筋在受力拉直过程中产生截面弯矩,起波钢筋的力学性能存在明显的应变率效应;起波钢筋弹性抗拉极限强度DIF随起波矢高的增高先增大后减小,存在一个最优起波设计矢高,可以使起波钢筋抗拉强度动态放大系数达到最大。研究成果可为进一步推动起波配筋技术在防护工程中的应用提供依据。     

静水槽孤立波的实验研究

本文在静水槽中复现出单孤立波,将实验得到的孤立波的波形和波速与理论值比较,极为接近。同时,考察了孤立波的碰撞行为,它表明了孤立波的粒子性。还验证了孤立波的非线性性质。     

爆炸波与地下结构物相互作用的动光弹性探讨

本文用动态光弹性探讨了地表爆炸产生的应力波与地下结构物相互作用的机理,根据等差条纹分布分析了P波、S波、von Schmidt波及R波与结构物基础的相互作用过程。研究表明R波是对地下结构物危害最大的波。可以采取防护措施来反射和消耗R波的能量。     

乘波构形和乘波飞行器研究综述

乘波构形的特点是高升阻比,下表面上的流动是均匀的,因此是推进系统/机身一体化设计的理想候选构形.乘波飞行器是源于乘波构形的高超音速飞行器,利用了乘波构形的高升阻比,并可为吸气发动机提供已知的均匀流场.本文比较全面地总结了乘波构形的生成方法和乘波飞行器的设计方法,介绍了乘波构形的优化方法及影响因素,给出了优化的乘波构形, 并介绍了乘波飞行器的研究进展,提出了今后的研究重点.      

等波高双孤立波直墙爬高的数值模拟

基于RANS方程、VOF方法以及修正的Goring造波方法建立了模拟活塞式推波板运动的二维数值波浪水槽,实现了双孤立波直墙爬高的数值模拟．利用动边界技术模拟造波机推波板的运动,有效地实现了不同波峰间距双孤立波的造波方法．在验证单孤立波直墙爬高的基础上,模拟了不同相对波高、相对波峰间距的等波高双孤立波的直墙爬高过程,给出了波面、速度场及波动能量的变化规律．数值模拟结果表明：对于等波高的双孤立波,当入射波波高较大及两个波峰间距相对较小时,跟随在后孤立波的爬高放大系数小于先导孤立波的爬高放大系数;双孤立波在直墙爬高过程中,波动场的势能时间过程线呈现三峰形态,其中居中的最大势能峰值出现在第二个孤立波与经直墙反射后反向传播的第一个孤立波完全对撞的时刻．     

爆轰波平掠惰性气体界面及其解耦现象的数值研究

采用基元化学反应模型和迎风TVD格式,数值研究了爆轰波平掠惰性气体界面时的物理现象及其作用机制,并用点隐方法克服化学反应源项引起的计算刚性。数值结果显示,当爆轰波平掠过惰性气体界面时,形成了爆轰波、界面、透射激波以及稀疏波相互作用的现象。在高N2比例稀释的可燃混合气体情况下,当爆轰波平掠过特定惰性气体界面时,它与惰性气体界面相互作用产生的稀疏波可以导致爆轰波的解耦。     

可燃气体中激波与障碍物作用在下游形成爆轰波的数值研究

对平面激波和单个矩形障碍物作用的过程进行了数值模拟,研究了反射产生的上行爆轰波在下游可燃气体中形成爆轰波的过程。数值结果表明,下游爆轰波形成过程主要有2种模式:爆轰波直接绕射和绕射波在上壁面反射,这和已有的实验结果是一致的。通过研究下游爆轰波的形成过程受入射激波马赫数、混合气体的压力和管道尺度的影响,分析了上游爆轰波向下游传播的波动力学过程,讨论了2种形成过程的作用规律和控制因素,阐明了下游爆轰波的形成规律。     

水平光面爆破激发地震波的成分及衰减特征

借助极化偏振分析方法,针对一组现场爆破实验,分析了水平光面爆破激发地震波的成分构成及特性,比较了不同波的衰减特征及各自对爆破振动的影响,并探讨了水平光面爆破的内在力学机理。结果表明,爆破振动中不同波的相对量值及主导波的类型均会随测点位置的改变而变化,爆源特性和沿传播路径的不同衰减共同决定波的成分构成及演化,各测点的优势振动方向也与波的成分构成密切相关。对于水平光面爆破,在光爆孔平面上,P波的影响可忽略,S波主要在竖直向振动,R波对水平及竖直向的振动均有贡献,其中水平向的振动主要由R波引起,而S波的竖直向振速在近区远高于R波,但归因于S和R波的不同衰减,R波在距离爆源22.5 m/kg^1/2(58~67 m)处开始主导竖直向的振动;在光爆孔平面外,P波的影响不可忽略,且在特定位置会成为优势波型。     

气相爆轰波传播过程中的自点火效应

基于基元反应模型和单步反应模型,对直管道中H₂-air混合气体中爆轰波的传播过程进行了数值模拟,揭示了气相爆轰波传播过程中的自点火效应。利用数值模拟方法计算了不同爆轰模型的点火延迟时间,并得到了爆轰波三波点的传播过程以及所形成胞格结构的尺寸。结果表明,胞格宽度与点火延迟时间成正比;爆轰波诱导区内气体的点火延迟时间与三波点的运动周期基本一致。进一步对结果分析可知,爆轰波的自维持传播取决于点火延迟时间(表征化学反应的特征时间)和三波点的运动周期(表征流动的特征时间)的匹配;当二者相匹配时,经过前导激波压缩后形成的高温高压爆轰气体,在短时间内实现了自点火,同时释放出大量的能量推动了爆轰波的前进,即爆轰波的稳定自维持传播依靠其自点火机制。     

Mathematical model of spiral waves propagating in the aorta

The spiral waves in the viscous incompressible fluid flow within an arterial vessel modeled by a thin elastic isotropic shell are studied. Asymptotic expansions are constructed for two types of spiral waves. The first type is spiral long wall waves generated (owing to the viscous fluid no-slip at the inner shell wall) by the longitudinal and twist harmonic waves that propagate along the wall. For these waves the amplitude distribution over the vessel cross-section has the form of a boundary layer localized near the inner shell surface. The second is short small-amplitude waves that practically fill the entire vessel cross-section. It is shown that for the short waves the transfer mechanismis the steady-state flow, the role of the longitudinal wall waves and the elastic characteristics of the shell being in this case insignificant.     

轴向冲击载荷作用下锥壳中弹性应力波传播的计算和实验研究

本文利用有限元分析和模型实验研究了在轴向冲击载荷作用下,锥壳中弹性应力波的传播、计算和实验结果表明,结构中存在着弹性纵波和弹性弯曲波的传播,它们传播的速度各不相同,使壳面承受不同的应力状态;讨论了纵波和弯曲波随壳面的衰减;实验指出,由于边界的影响,即使纵波的反射也会产生新的反射弯曲波沿锥面传播。     

线状脉冲激光激发双层圆柱的波传播

该文建立了一个物理模型来预测均匀、各向同性双层固体圆柱在激光烧蚀或热弹激发下的弹性波传播规律.在建模中忽略了激光源的光学穿透和材料的热扩散.采用空间和时间上的双重傅氏变换对理论模型进行求解,得到其位移场的变换解.通过对铝壳铜芯和铜壳铝芯的数值计算,得到不同内外径比下瞬态位移响应的时域和频域数值波形.用传播路径分析发现结果中存在界面反射波,这可以表明所建立的理沦模型和计算方法是有效的,同时其余波的传播也被分析和解释.     

The propagation of elastic stress waves in a conical shell under axial impulsive loading

The propagation of elastic stress waves in a conical shell subjected to axial impulsive loading is studied in this paper by means of the finite element calculation and model experiments. It is shown that there are two axisymmetrical elastic stress waves propagating with different velocities, i.e., the longitudinal wave and the bending wave. The attenuation of these waves while propagating along the shell surface is discussed. It is found in experiments that the bending wave is also generated when a longitudinal wave reflects from the fixed end of the shell, and both reflected waves will separate during the propagation due to their different velocities. Southwest Institute of Structural Mechanics     

Transient radiation by a submerged fluid-filled cylindrical shell

The radiation by a submerged fluid-filled cylindrical shell in response to a transient external pressure pulse is considered, and a semi-analytical model based on the Reissner–Mindlin shell theory is employed to simulate the interaction numerically. Two types of radiated waves that have been previously seen in experimental images for a submerged evacuated cylindrical shell are observed in both the external and internal fluids, the symmetric Lamb waves S₀ and the antisymmetric Lamb (or pseudo-Rayleigh) waves A₀. The third type of radiated waves is also observed that has not been explicitly imaged either experimentally or numerically for a submerged evacuated cylindrical shell, and it is demonstrated that these waves are the Scholte–Stoneley waves A. The effect that the complex structure of the radiated field has on the wave phenomena in the internal fluid is analyzed for shells of several different thicknesses, and the results of this analysis are summarized in the form of diagrams suitable for the use at the pre-design stage.     

Propagation of Harmonic Waves in an Orthotropic Cylindrical Shell on Elastic Foundation

An equation is derived, using Timoshenko shell theory, to analyze axisymmetric strain fields in an orthotropic cylindrical shell on an elastic foundation. Also a dispersion equation is derived to study the natural harmonic waves in a shell depending on the properties of the elastic foundation. The wave velocities computed by the numerical method proposed are in agreement with the analytical solutions, which confirms the reliability of the results     

非线性岩土中球壳对冲击波的动力响应分析

采用小参数摄动法和Ｌａｐｌａｃｅ变换研究了非线性弹性岩土中球壳对冲击波的动力响应问题。系统的非线性方程由小参数摄动渐近展开后，利用Ｓｔｏｋｅｓ－Ｈｅｌｍｈｏｌｔｚ矢量分解定理把它们简化为一系列的线性波动方程，并由Ｌａｐｌａｃｅ变换和本征函数给出了各线性波动方程的求解。最后，对平面冲击波和球面冲击波给出了球壳动力响应的应力结果。     

A boundary element method for calculating elastic waves scattered by axisymmetric inclusion

A Boundary Element Method (BEM) is described to compute the scattering of elastic waves by an axisymmetric inclusion in an infinite elastic medium. The boundary loads applied to the inclusion is expanded in terms of Fourier series in an infinite space. The boundary integral equation is solved in the general direction of the axisymmetric inclusion by BEM. The problem of the 3-D scattering of elastic waves is reduced to a 1-Done. According to the geometric features of the axisymmetric in clusion the ring shell elements are adopted in this method. A comparison is made with other BEM methods. The numerical results show this method can reduce the amount of calculation and enhance the speed of convergence. Supported by Foundation of Ph. D Program of State Education Commission of China     

Nonstationary motion of a shell on the surface of a heavy fluid

A three-dimensional nonstationary problem of vibrations of a flexible shell moving on the surface of an ideal heavy fluid. The forces due to surface tension are ignored. The problem is formulated in the space of the acceleration potential. The potential of the pulsating source is found by solving the Euler equation and the continuity equation taking into account the free-surface conditions (linear theory of small waves) and the conditions at infinity. The density distribution function of the dipole layer is determined from the boundary conditions on the surface of the shell. Formulas for determining the shape of gravity waves on the fluid surface and the natural frequencies of vibrations of the shell are obtained. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 66–75, July–August, 2009.     

Production of periodically modulated laser-driven blast waves in a clustering gas

To study hydrodynamic behavior on thin shell high Mach number blast waves, experiments have been performed in which spatially tailored shock waves have been launched in a gas of clusters using an intense 35 fs laser pulse. The target medium was first modified by destroying clusters in specific locations using a spatially modulated laser focus. Under subsequent intense laser irradiation, the efficient absorption properties of the remaining clustered regions compared to those regions with no clusters led to a pattern of hot and cold plasma resulting in a cylindrical blast wave with a periodic modulation imprinted on the shock front. This technique may provide a method for studying thin shell instabilities in strongly radiative blast waves.