Compton散射下强激光等离子体空气冲击波波前的传输特性

 根据球对称激光等离子体空气冲击波在自由空间中传输的约束条件，对多光子非线性Compton散射的强激光等离子体空气冲击波波前的传输特性进行了研究，给出了散射下空气冲击波波前的运动方程，并进行了数值模拟。结果表明：该冲击波的衰减过程不仅与爆炸源和爆炸过程的特性、释放总能量、空气的弹性有关，而且还与散射有关，散射效应使冲击波的初始半径增大，衰减过程加快，能量转移率提高；数值模拟与实验结果符合得很好。     

液体中激光等离子体冲击波波前传播特性研究及测试

将空气中球对称冲击波衰减波前传播公式推广到非完全中心对称情况，根据对光学阴影法对激光等离子体冲击波波前测试数据的计算分析，提出液体中点源激光等离子体冲击波旋转椭球面波前传播公式.并且用声学方法对水中和酒精中的激光等离子体冲击波波前进行实验测试，结果表明测试结果与计算公式相吻合. 关键词： 激光 等离子体冲击波 旋转椭球面     

空气中激光等离子体冲击波的传输特性研究

根据球形对称冲击波在自由空间中传播的约束条件,提出了空气中激光等离子体冲击波在中远场的传播公式.并用探针式超声换能器实测了能量为10-110mJ、脉宽为15ns、波长为106μm的Nd∶YAG激光作用于铝靶表面产生的等离子体空气冲击波,用此公式计算的结果与实验数据符合得很好 关键词：     

激光熔蚀过程中等离子体冲击波压缩层能量演化

从冲击波基本性质出发,在冲击波压缩层内物质密度均匀的前提下,结合流体力学守恒方程得到冲击波压缩层的机械能通用表达式。继而,分析了激光等离子体球面衰减冲击波情况下冲击波压缩层机械能演变,发现压缩层内的机械能随着冲击波的外向传播出现增大;进而提出波后等离子体区域可能存在其他储能机制,该能量在不断向外界输送能量。最后通过铝靶熔蚀实验,证实了等离子体区域内存在电场能。     

强激光与稠密等离子体作用引起的冲击波加速离子的研究

用二维PIC（Particle-in-Cell）程序模拟研究了强激光与稠密等离子体靶作用产生的无碰撞静电冲击波的结构和这种冲击波对离子的加速过程,研究发现由于冲击波前沿附近的双极电场的作用,具有一定初速度的离子能被该双极场俘获并获得加速,最终能够被加速到两倍冲击波速度.冲击波加速可以得到准单能的离子能谱,叠加在通过鞘层加速机理产生的宽度离子能谱上.还对不同激光强度和不同等离子体密度情况下形成的冲击波进行了比较.研究表明,强度相对较低的激光在高密度等离子体中可以产生以一定速度传播的静电孤波结构,后者只能加速 关键词： 强激光 稠密等离子体 无碰撞静电冲击波 离子加速     

空气中激光支持爆轰波实验及理论分析

为了研究激光击穿空气产生的等离子体爆轰波形成机制和传播规律,利用高能量CO2激光器产生强激光,进行了空气中产生激光支持等离子体爆轰波实验。实验中:设置了诱导靶板,用于诱发和定位空气中的激光支持爆轰波;以激光器升压过程球隙放电产生的光信号作为触发源,触发高时间分辨率(纳秒级)的高速相机,记录了激光支持爆轰波的成长和传播全过程。分析了激光支持爆轰波的形成机理和传播规律。采用C-J爆轰理论,计算了激光支持爆轰波的压力和温度。研究结果表明:激光支持等离子体爆轰波形成初期,等离子体爆轰波发光体为球形;随着时间增加,等离子体爆轰波发光体的形状类似流星,且头部为等离子体前沿吸收层,亮度较高,而尾部等离子体温度较低,亮度较弱。等离子体爆轰波高速向激光源的方向移动,爆轰波速度高达18 km/s,温度约为107K。随着激光强度的减弱,爆轰波速度迅速按指数规律衰减,当爆轰波吸收的激光能量不能有效支持爆轰波传播时,爆轰波转变为冲击波。     

超强激光场等离子体中电子纵向运动的研究

在数值求解一维Maxwell场方程和流体运动方程的基础上,得到了超强激光场下等离子体中电子纵向运动的行波解,并分析了等离子体静电场对电子纵向运动的影响. 关键词： 等离子体 相对论 电子 超强激光场     

吸气式激光推进中激光能量沉积过程的数值模拟

 结合辐射输运方程,在流体力学方程组的能量方程中加入包括空气吸收的激光能量以及高温气体向周围辐射损失的能量源项,转化为辐射流体力学方程组,建立了用于模拟吸气式激光推进中能量沉积过程的物理力学模型和计算方法。该辐射流体力学计算程序可以很好地模拟激光能量沉积过程中空气对激光能量的吸收、等离子体对激光的屏蔽作用以及激光维持的爆轰波的传播规律,计算得到激光能量的沉积效率约为57%,激光维持的爆轰波的传播速度与同等条件下的理论和实验结果吻合得较好。     

激光烧蚀水下金属产生冲击波和空泡效应的研究

采用自行研制的高灵敏度光束偏转测试系统,对脉冲激光烧蚀水下金属产生的等离子体冲击波和空泡效应进行了实验研究。实验得到了激光等离子体冲击波的传播规律、冲击波与激光空泡的分离过程、空泡的脉动特性以及空泡溃灭冲击波的形成机制。结果表明,空泡最大和最小泡径、振荡周期均随着脉动次数的增加呈减小趋势,且减小幅度较大。最小收缩泡径由泡能和腔内含气量共同决定。在同一次脉动过程中,空泡膨胀所需的时间明显大于收缩所需的时间。     

激光与固体靶面烧蚀等离子体的能量耦合计算

 强激光辐照下固体靶表面迅速汽化产生靶蒸气等离子体,激光穿过等离子体区到达固体靶表面的过程就是激光束与等离子体的能量耦合与交换过程。采用具有五阶精度的WENO差分格式和简易等离子体状态方程模型对激光与等离子体相互作用的复杂物理过程进行了数值计算,分析了激光束能量在等离子体区中的吸收、屏蔽效应等动态耦合规律以及激光支持等离子体前驱冲击波传播。数值模拟结果表明：激光能量是支持靶面等离子体运动的唯一原因,能量屏蔽效应对激光与等离子体能量耦合有很大影响,通过控制激光脉冲宽度,可以合理调节屏蔽效应的影响。     

理想气体球面强冲击波一般自模拟运动模型

应用理想气体一维不定常流自模拟运动基本微分方程，详细讨论了球面强冲击波波后气体自模拟特性，推导出具有自模拟运动特性的球面强冲击波传播公式的一般形式.分析结果表明：球面强冲击波自模拟运动模型不必从具有奇异性质的点源出发，冲击波初始速度和自模拟温度函数解一般不存在趋于无穷大的问题.Taylor点爆炸冲击波自模拟模型只是一般自模拟模型中假设自模拟运动总能量为定值条件下的特例. 关键词： 理想气体 球面强冲击波 自模拟运动     

Real time NDE of laser shock processing with time-of-flight of laser induced plasma shock wave in air by acoustic emission sensor

Acoustic emission sensor is used to research the time-of-flight of the shock wave induced by laser-plasma in air for real time nondestructive evaluation (NDE) of laser shock processing. The time-of-flight of the shock wave propagating from the source to the sensor declines nonlinearly and similarly at the different distances for different laser energies. The velocity of the shock wave at the distance of 30 mm increases faster than that of the distance of 35 mm. The relationship between the laser energy and the distance is almost linearly when the signal with distortion is measured by acoustic emission sensor. Finally, Taylor solution is used to analyze the experimental results, and the empirical formula between the energy of the shock wave and the laser energy is established, which will provide a theoretical basis for real time NDE of laser shock processing.     

Observation of shock transverse waves in elastic media

We report the first experimental observation of a shock transverse wave propagating in an elastic medium. This observation was possible because the propagation medium, a soft solid, allows one to reach a very high Mach number. In this extreme configuration, the shock formation is observed over a distance of less than a few wavelengths, thanks to a prototype of an ultrafast scanner (that acquires 5000 frames per second). A comparison of these new experimental data with theoretical predictions, based on a modified Burger's equation, shows good agreement.     

核爆聚变电站发电时的冲击波超压传播规律

 核爆聚变电站在发电时会产生冲击波,其超压传播规律是核爆聚变电站洞壁设计的重要基础。现有公式在描述冲击波峰值超压时存在一定的不足（如相对误差大等）。通过理论分析得到新的冲击波峰值超压公式、正压作用时间τ₊和冲击波传播系数ω,最终得到冲击波超压的传播规律。通过对比分析表明,新公式比现有公式更加适合求解核爆聚变电站发电时所产生的冲击波峰值超压。     

Reflectance of acoustic horns and solution of the inverse problem

A method is described for solving the inverse problem of determining the profile of an acoustic horn when time-domain reflectance (TDR) is known only at the entrance. The method involves recasting Webster's horn equation in terms of forward and backward propagating wave variables. An essential feature of this method is a requirement that the backward propagating wave be continuous at the wave-front at all locations beyond the entrance. Derivation of the inverse solution raises questions about the meaning of causality in the context of wave propagation in non-uniform tubes. Exact reflectance expressions are presented for infinite exponential, conical and parabolic horns based on exact solutions of the horn equation. Diameter functions obtained with the inverse solution are a good match to all three horn profiles.     

Dynamic compaction of copper powder: 2D numerical simulation and experimental results

Abstract

A method for plate-impact dynamic compaction of copper powder has been developped. The optimization of the experimental set-up (impedance adjustments, tensile wave traps, relative thickness of impactor and target,…) is presented.

2D axisymetrical numerical simulations have been performed with a Lagrangian finite element code. Geometrical characteristics of the experimental set-up as well as the dynamic response of the powder (Reaugh equation of state) and of the material of the set-up have been taken into account. These simulations show that, due to the difference in shock velocities in the container and in the powder, the powder is submitted to 2D loading waves. As a matter of fact the powder may be loaded by a non-planar shock wave propagating in the as-expected direction, as well as by a sweeping wave initiated at the bottom of the powder container, and propagating obliquely from the bottom-up. This second wave loads the bottom of the powder first. The influence of the impactor thickness as well as its material on the shock front shape and on the shock density-pressure history of the material has been studied. 1D simulations are shown not to evaluate properly the stress history and the energy deposition in the powder sample.

Metallographic observations as well as X-ray tomography experiments have been performed on consolidated samples. A very good agreement has been found between results of 2D numerical simulations and the observed final shape and density maps of the samples. The shape of deformed powder particles are also in agreement with the expected shock history.     

Acoustic shock wave propagation in a heterogeneous medium: a numerical simulation beyond the parabolic approximation

Numerical simulation of nonlinear acoustics and shock waves in a weakly heterogeneous and lossless medium is considered. The wave equation is formulated so as to separate homogeneous diffraction, heterogeneous effects, and nonlinearities. A numerical method called heterogeneous one-way approximation for resolution of diffraction (HOWARD) is developed, that solves the homogeneous part of the equation in the spectral domain (both in time and space) through a one-way approximation neglecting backscattering. A second-order parabolic approximation is performed but only on the small, heterogeneous part. So the resulting equation is more precise than the usual standard or wide-angle parabolic approximation. It has the same dispersion equation as the exact wave equation for all forward propagating waves, including evanescent waves. Finally, nonlinear terms are treated through an analytical, shock-fitting method. Several validation tests are performed through comparisons with analytical solutions in the linear case and outputs of the standard or wide-angle parabolic approximation in the nonlinear case. Numerical convergence tests and physical analysis are finally performed in the fully heterogeneous and nonlinear case of shock wave focusing through an acoustical lens.     

水下爆炸冲击波数值仿真研究

由于在水下爆炸冲击波的数值仿真研究中,水的状态方程、人工黏性系数和网格尺寸对数值计算结果影响很大,采用常规TNT炸药的水下爆炸为例,以冲击波的峰值压力和比冲量为衡量指标,研究了这3个主要影响因素对数值仿真结果的影响。首先,通过采用常用的5种水的状态方程进行系列仿真,给出了各种状态方程的适用范围;其次,讨论了人工黏性系数对计算结果的影响,并给出了一次与二次人工黏性系数的建议取值范围;最后,通过对不同炸药当量及不同网格尺寸开展系列运算,从而得到不同炸药当量在满足工程计算精度要求下所对应的建议网格尺寸,并得到了不同炸药当量所对应的建议网格尺寸的表达式。     

On exact solutions of modified complex Ginzburg-Landau equation

The one-dimensional modified complex Ginzburg-Landau equation has been studied by the use of the Conte and Musette method. This method permits us to derive all the known exact solutions in a unified natural scheme. These solutions are expressed in terms of solitary wave, periodic unbounded wave, and shock type wave. We also find previously unknown exact propagating hole. The degeneracies of modified complex Ginzburg-Landau equation have also been examined as well as several of their solutions.