磁化尘埃等离子体中的冲击波及其横向扰动稳定性

利用双曲函数法得到ZKB方程的一组冲击波解,并对波在横向扰动下的动力学稳定性进行研究.对冲击波解进行线性稳定性分析,并构造高精度的有限差分格式求解所得本征值问题.结果表明：对于正耗散的情形,该冲击波在线性意义下稳定;对于负耗散情形,该冲击波在线性意义下不稳定.构造有限差分格式对受扰动的冲击波进行非线性动力学演化,结果表明：对于正耗散的情况,该冲击波是稳定的.     

Molecular dynamics simulations of microscopic structure of ultra strong shock waves in dense helium

Hydrodynamic properties and structure of strong shock waves in classical dense helium are simulated using non-equilibrium molecular dynamics methods. The shock speed in the simulation reaches 100 km/s and the Mach number is over 250, which are close to the parameters of shock waves in the implosion process of inertial confinement fusion. The simulations show that the high-Mach-number shock waves in dense media have notable differences from weak shock waves or those in dilute gases. These results will provide useful information on the implosion process, especially the structure of strong shock wave front, which remains an open question in hydrodynamic simulations.     

Formation of detonation waves in channels and interaction of the waves with penetrable screens

Two-dimensional channel flows with shock waves resulting from the detonation of a combustible gas mixture are considered. Conditions for detonation and the parameters of the shock waves are determined. The feasibility of reducing the shock wave intensity and loads on the structure by mounting a set of mesh screens in the channel is investigated. The numerical computation of detonation initiation in an air-hydrogen mixture and subsequent passage of shock waves through the mesh screens is carried out. Basic quantitative characteristics of shock wave reduction depending on the mesh screen penetrability and mutual arrangement of variously penetrable screens are obtained.     

氧碘化学激光器中相位扰动的模拟研究

 建立了含相位扰动的1维流场3维物理光学负载光腔模型。选用折叠非稳腔，模拟计算了斜激波中心距光轴不同距离时以及不同强度的斜激波对腔内光场相位分布和输出功率的影响。研究表明激光输出光束质量与腔内激波的分布位置和激波的强度有密切关系，应该避免激波中心近光轴时的强扰动效应引起的光束质量退变。实验装置的计算结果再现了实验现象。     

纳秒激光在铜靶材中诱导冲击波的实验研究

基于聚偏二氟乙烯压电传感器, 对铜靶材中纳秒激光脉冲诱导的冲击波传播过程进行了实验研究, 给出了铜靶材内冲击压强随激光脉冲能量和靶材厚度的变化规律. 实验结果表明: 500 mJ激光脉冲能量作用到2 mm厚的铜靶材产生的冲击压强达到2.1 MPa; 激光脉冲能量从200 mJ 增加到500 mJ, 在铜靶材厚度为2和4 mm条件下, 冲击压强分别增加了162%和231%; 而当铜靶材厚度从2 mm增加到6 mm时, 在400和500 mJ激光脉冲能量作用下, 铜靶材内冲击压强分别降低了32%和49%.     

LY12-M铝中冲击波衰减机理的实验研究

 应用锰铜压阻计测量了峰压为4.92 GPa的平面冲击波在LY12-M铝中的衰减规律，对试样进行了正电子寿命谱探测和维氏显微硬度测试，分析了位错等缺陷对冲击波非流体动力学衰减的影响，同时还对LY12-M铝的冲击硬化效应进行了探讨。     

Dispersive nature of high mach number collisionless plasma shocks: Poynting flux of oblique whistler waves

Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.     

Dust acoustic solitary and shock waves in strongly coupled dusty plasmas with nonthermal ions

The Korteweg-de Vries-Burgers (KdV-Burgers) equation and modified Korteweg-de Vries-Burgers equation are derived in strongly coupled dusty plasmas containing nonthermal ions and Boltzmann distributed electrons. It is found that solitary waves and shock waves can be produced in this medium. The effects of important parameters such as ion nonthermal parameter, temperature, density and velocity on the properties of shock waves and solitary waves are discussed.     

Acceleration of particles and generation of nonthermal emission in old supernova remnants

Particle acceleration by shock waves in old supernova remnants is studied. The radiative loss of gas behind the front of a shock wave, the streaming instability of magnetohydrodynamic waves, and the damping of waves on neutral atoms are considered. The calculated spectra of electromagnetic emissions are compared to observations of supernova remnant IC 443.     

Current discontinuities on superconducting cosmic strings

The propagation of current perturbations on superconducting cosmic strings is considered. The conditions for the existence of discontinuities similar to shock waves have been found. The formulas relating the string parameters and the discontinuity propagation speed are derived. The current growth law in a shock wave is deduced. The propagation speeds of shock waves with arbitrary amplitudes are calculated. The reason why there are no shock waves in the case of time-like currents (in the “electric” regime) is explained; this is attributable to the shock wave instability with respect to perturbations of the string world sheet.     

Overturning of nonlinear Alfvén waves in a collisionless plasma

An analysis is made of the overturning of nonlinear Alfvén waves in a collisionless plasma. It is shown that overturning is followed by the appearance of a region which broadens with time and consists of two collisionless shock waves which can be joined at the point s²=1. If only one Riemann invariant changes in the region of the collisionless shock waves, the waves are simple. The structures of the collisionless shock waves are constructed for different initial conditions of the nonlinear wave. The Whitham averaging method is used for this purpose. Conditions are obtained which are similar to the Rankine-Hugoniot adiabats for passage through the collisionless shock waves. The effect of overturning one of the collisionless shock waves, involving the zeroing of the density at the soliton peak on its trailing edge, is treated as a bifurcation for which a discontinuity occurs in an analog of the hydrodynamic velocity and phase of the nonlinear Alfvén wave. The width of one of the collisionless shock waves decreases with an increase in the parametera which determines the magnitude of the field discontinuity when overturning occurs.L. N. Tolstoi State University, Checheno-Ingushk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–67, January, 1993.     

激波与SF6球形气泡相互作用的数值研究

本文基于大涡模拟方法, 采用高阶精度格式对平面入射激波以及不同反射距离条件下的反射激波与SF₆重气泡相互作用过程进行了三维数值模拟. 数值结果清晰地显示了SF₆重气泡在激波作用下诱导Richtmyer-Meshkov不稳定性过程, 揭示了入射激波以及反射激波在气泡界面聚焦诱导射流的过程, 详细分析了不同反射距离条件下反射激波与SF₆重气泡作用过程及流场结构.     

Statistics of shock waves in a two-dimensional granular flow

We have investigated the dynamics of shock waves in a single layer of uniform balls in a small-angle two-dimensional funnel. When the funnel half-angle 0 degrees < or approximately beta < or approximately 2 degrees, the flow is intermittent and kinematic shock waves are observed to propagate against the flow. We have used fast video equipment and image analysis methods to study the statistics of the shock waves. It is found that their speed and frequency increase with the distance from the outlet. In particular, the shock speed scales as the ratio of the local funnel width to the width of the funnel outlet. Various kinds of interactions between shock waves are observed, including repulsion. New shock waves are only created at those sites where a close-packed triangular packing of the monodisperse balls fits across the funnel.     

Interactions of dispersive shock waves

Collisions and interactions of dispersive shock waves in defocusing (repulsive) nonlinear Schrödinger type systems are investigated analytically and numerically. Two canonical cases are considered. In one case, two counterpropagating dispersive shock waves experience a head-on collision, interact and eventually exit the interaction region with larger amplitudes and altered speeds. In the other case, a fast dispersive shock overtakes a slower one, giving rise to an interaction. Eventually the two merge into a single dispersive shock wave. In both cases, the interaction region is described by a modulated, quasi-periodic two-phase solution of the nonlinear Schrödinger equation. The boundaries between the background density, dispersive shock waves and their interaction region are calculated by solving the Whitham modulation equations. These asymptotic results are in excellent agreement with full numerical simulations. It is further shown that the interactions of two dispersive shock waves have some qualitative similarities to the interactions of two classical shock waves.     

冲击波在空气和熔石英元件界面传播的超快诊断

基于球面波在弹性介质界面上的反射和折射特性的基本理论,采用超快时间分辨的光学诊断技术,研究了532nm纳秒激光辐照熔石英元件表面产生的冲击波在空气和样品界面的传播特性,获得了冲击波在材料内部传输以及在空气与样品界面反射的时间分辨图像。结果表明:激光脉冲与材料作用在前后表面产生了向体内传输的冲击波,且产生的冲击波在玻璃与空气界面处反射为两个波,即反射波和反射剪切波;反射波和反射剪切波的强度与入射冲击波的入射角有关。     

On the viscous and inviscid stability of magnetohydrodynamic shock waves

We study the viscous and inviscid stability of shock waves in barotropic and full magnetohydrodynamics. We show that there are magnetohydrodynamic shock waves that are one-dimensionally stable as viscous shock profiles while they are multidimensionally strongly unstable as planar shock discontinuities.     

Nonlinear analysis of traffic flow on a gradient highway

We investigate the slope effects upon traffic flow on a single lane gradient (uphill/downhill) highway analytically and numerically. The stability condition, neutral stability condition and instability condition are obtained by the use of linear stability theory. It is found that stability of traffic flow on the gradient varies with the slopes. The Burgers, Korteweg-de Vries (KdV) and modified Korteweg-de Vries (mKdV) equations are derived to describe the triangular shock waves, soliton waves and kink-antikink waves in the stable, meta-stable and unstable region respectively. A series of simulations are carried out to reproduce the triangular shock waves, kink-antikink waves and soliton waves. Results show that amplitudes of the triangular shock waves and kink-antikink waves vary with the slopes, the soliton wave appears in an upward form when the average headway is less than the safety distance and a downward form when the average headway is more than the safety distance. Moreover both the kink-antikink waves and the solitary waves propagate backwards. The numerical simulation shows a good agreement with the analytical result.     

Ion-acoustic shock waves with negative ions in presence of dust particulates

Dust acoustics shock waves have been investigated experimentally in a homogeneous unmagnetized dusty plasma device containing negative ions. When the negative ion density larger than a critical concentration ‘rc’ negative shock waves were observed instead of positive shock waves. Again when it is nearly equal to ‘rc’ both positive and negative shock waves propagate. The experimental findings are compared with modified KdV-Burgers equation. The velocity of the shock waves are also measured and compared with the numerical integration of modified KdV-Burgers equation.     

基于速度干涉仪的冲击波精密调速实验技术研究

冲击波精密调速技术是惯性约束聚变研究的关键技术之一. 针对冲击波精密调速诊断技术的要求, 以神光III原型上脉宽为3 ns的两台阶整形激光脉冲为源, 用石英晶体做窗口材料, 模拟了双冲击在石英晶体中传输和追赶的过程. 利用两发典型双冲击波调速的实验数据, 验证了神光III原型具有的精密调速能力. 实验结果表明, 在驱动源、 靶和诊断系统参数一致的条件下, 两发实验获得的实验结果中两次冲击出现的时刻, 冲击波速度都很一致. 通过精细分析, 发现在两次冲击交会的时刻, 干涉条纹清晰度和完整性变化最大, 最终数据处理获得的冲击波速度偏差也最大. 同时, 在二次冲击的冲击波速度有较大增加的条件下, 并没有观察到冲击波阵面的反射率的明显增加. 本文的实验结果作为一个数据依据, 为全面开展冲击波调速实验提供了有效的方法.     

Interacting electromagnetic shock waves in general relativity

It is shown that the continuity conditions of Lichnerowicz must generally be relaxed in favour of the O'Brien-Synge conditions in the case of shock electromagnetic waves. This is in particular true when two electromagnetic shock waves are in collision. Gravitational impulse waves are produced as a result of the weakened conditions. An exact solution exhibiting this behaviour is derived, and the effect of the impulse waves on a measuring device are compared with experimental results of Weber.