非线性弹性介质中冲击波斜反射的研究(Ⅱ)

利用前文结果求解了冲击波在固壁及滑动刚壁两种边界面上的斜反射问题。在滑动刚壁的情,很可能出现马赫反射图象。     

铅飞层中斜冲击波对碰马赫反射行为实验研究

采用线阵多普勒光纤探针测速技术（Doppler pins system，DPS）和高速光电分幅相机照相两种精密诊断技术，对铅飞层中斜冲击波对碰后的反射行为进行了观测。获得了飞层对碰部位速度-时间历史曲线和凸起形貌演化图像，给出了凸起轮廓发展演化过程、压力分布等实验数据和信息。结合冲击波反射理论，对铅飞层对碰区动力学现象进行了分析和解释，证实铅飞层中斜冲击波对碰后发生了马赫反射。     

空气冲击波遇运动刚壁反射时壁面超压的计算

本文分析了空气冲击波与运动刚壁的相互作用,给出了运动刚壁正反射或斜反射时壁面峰值反射超压的计算公式。当刚壁速度为零时,这些公式退化成空气冲击波遇固壁相互作用的计算公式。     

金属铅在斜冲击波对碰加载下动态行为的数值模拟

高强度冲击加载作用下金属材料的动态物理行为是当前冲击波领域基础研究和工程应用最为关注的焦点。采用光滑粒子法(SPH)开展不同位置起爆诱发的斜冲击波对碰加载金属铅的二维数值模拟研究，得到了金属铅内入射斜冲击波的角度和强度，并利用极曲线方法理论上导出发生马赫反射时的临界入射角和入射马赫数关系。根据计算结果可知，金属铅内入射斜波对碰后将发生马赫反射。随着起爆位置与金属铅表面距离的增加，不仅金属铅内入射冲击波强度和入射角增加，而且形成的马赫杆宽度也在增加。由自由面速度剖面给出了马赫杆宽度及张角，结果与理论预测的结果吻合较好。     

钢化玻璃冲击波毁伤效应测试结果分析

为研究爆炸冲击波对钢化玻璃的毁伤阈值，开展了钢化玻璃冲击波毁伤效应实验。对每一发实验进行了爆炸参数测试，获得了冲击波超压随时间变化历程的实验数据。通过对实验数据的处理与分析，得到了爆炸冲击波基本参数，包括正反射超压、冲击波到时、正压作用时间、正反射冲量、负反射超压、负压作用时间和负反射冲量等。将实验结果与CONWEP计算结果进行了比较，比较结果表明二者误差很小，证明冲击波测试结果准确可靠。对冲击波正负反射参数进行了比较，结果表明冲击波正反射参数明显高于冲击波负反射参数。     

舱内爆炸角隅汇聚反射冲击波超压特性研究

为研究密闭舱室内爆角隅汇聚反射冲击波超压特性,利用缩比模型进行了某典型舱室内爆试验,得到远离角隅、两面角隅和三面角隅处的冲击波载荷,结合数值模拟研究了3种特征位置处冲击波传播规律及载荷特征。研究结果表明:远离角隅处壁面反射冲击波超压曲线呈现单峰结构,反射冲击波以球面波传播;距两面角隅一定范围内冲击波超压曲线呈现双峰结构,两面角隅冲击波超压曲线呈现单峰结构,角隅汇聚反射冲击波以椭球状传播;距三面角隅一定范围内冲击波超压曲线呈现多峰结构,三面角隅冲击波超压曲线呈现单峰结构,角隅汇聚反射冲击波以球面波传播;在合理假设条件下,根据量纲分析及数值模拟结果,得到首次冲击时角隅汇聚反射冲击波载荷经验计算公式。     

真实空气冲击波的正反射和正规反射

本文讨论了真实空气中冲击波的正反射和正规反射,并用H.L.Brade拟合的空气状态方程进行了计算。计算结果表明,当入射冲击波超压小于约20大气压时,反射冲击波的超压值和动压值实际上和理想气体计算结果一致,当入射冲击波较强时,则反射冲击波参数比理想气体结果显著增大。     

不同状态方程对固体介质中斜激波反射的影响

相比气体,固体介质在高压下的状态方程更为复杂,形式也多种多样.现有关于固体介质中激波反射的理论研究,一般直接采用某种状态方程,缺乏对采用不同状态方程得到的结果的对比.本项工作采用激波极曲线的理论分析方法,选择4种不同组合形式的状态方程(一次冲击激波采用线性的冲击波速度与粒子速度关系式,二次冲击激波采用Gr(u|¨)neisen状态方程;一次冲击和二次冲击激波均采用冲击波速度与粒子速度关系式:一次冲击激波采用线性冲击波速度与粒子速度关系式,二次冲击激波采用刚性气体状态方程;以及一次冲击激波和二次冲击激波均采用刚性气体状态方程),研究固体介质中的斜激波反射,比较了采用不同组合形式的状态方程对反射激波波后压力的影响.利用量纲分析方法讨论了简化状态方程达到较高精度的条件.此外,用ANSYS/LS-DYNA软件,对激波极曲线理论给出的结果进行了验证.本项工作可为固体介质中激波反射问题状态方程的选取提供一定的指导.     

TVD格式中压缩波判别的人工压缩法

提出了ＴＶＤ格式中的一种新型人工压缩技术和ＭａｘＥｔａ 方法,并以此对平面冲击波传播反射问题以及三维冲击波的坑道扩散问题进行了数值模拟,取得了很好的结果。     

空中强爆炸冲击波地面反射规律数值模拟研究

为准确预测空中强爆炸产生的冲击波载荷分布，基于欧拉坐标系建立了能够模拟具有高密度比、高压力比的强激波问题的二维多介质流体数值方法。结合网格自适应技术，对1 kt TNT当量的空中强爆炸在不同爆炸高度下的冲击波地面反射过程进行了数值模拟，并考虑了真实气体状态方程和空气随高度不均匀分布的影响。计算得到了地面上距爆心投影点大尺度范围内的反射超压和冲量等冲击波载荷分布，并给出了冲击波载荷随爆高的变化规律。     

An experiment on imploding conical shock waves

Over the past decade and a half there have been a number of numerical studies of the reflection of oblique axisymmetric shock waves from the axis of symmetry. Many of these have shown a complex Mach reflection pattern together with a strong toroidal vortex which significantly distorts the Mach disk. This geometry has never been captured experimentally. This note describes a special rig for the generation of strong imploding conical shocks, and presents photographs of the predicted reflection pattern. Received 4 October 2001 / Accepted 13 November 2001     

Over forty years of continuous research at UTIAS on nonstationary flows and shock waves

Analytical and experimental research on non-stationary shock waves, rarefaction waves and contact surfaces has been conducted continuously at UTIAS since its inception in 1948. Some unique facilities were used to study the properties of planar, cylindrical and spherical shock waves and their interactions. Investigations were also performed on shock-wave structure and boundary layers in ionizing argon, water-vapour condensation in rarefaction waves, magnetogasdynamic flows, and the regions of regular and various types of Mach reflections of oblique shock waves. Explosively-driven implosions have been employed as drivers for projectile launchers and shock tubes, and as a means of producing industrial-type diamonds from graphite, and fusion plasmas in deuterium. The effects of sonic-boom on humans, animals and structures have also formed an important part of the investigations. More recently, interest has focussed on shock waves in dusty gases, the viscous and vibrational structure of weak spherical blast waves in air, and oblique shock-wave reflections. In all of these studies instrumentation and computational methods have played a very important role. A brief survey of this work is given herein and in more detail in the relevant references.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Two-dimensional stress wave analysis in incompressible elastic solids

Two-dimensional stress waves in a general incompressible elastic solid are investigated. First, basic equations for simple waves and shock waves are presented for a general strain energy function. Then the characteristic wave speeds and the associated characteristic vectors are deduced. It is shown that there usually exist two simple waves and two shock waves. Finally, two examples are given for the case of plane strain deformation and antiplane strain deformation, respectively. It is proved that, in the case of plane strain deformation the oblique reflection problem of a plane shock is not solvable in general.     

Numerical investigations of shock waves in gas-particle mixtures

The propagation of shock waves in gas-particle mixtures in one- and two-dimensional geometries is numerically investigated. Two schemes for approximating conservation laws for particles, which are collectively treated as a continuum medium, are compared and discussed. Different models of the drag coefficient and Nusselt number, directly affecting the interaction between the gas and particle phases, are used for obtaining shock profiles, and the results are compared. The oblique shock reflections at a solid wedge in a gas-particle mixture are simulated. The results demonstrate that the reflection pattern changes as the shock propagates along the wedge, revealing strong non-selfsimilarity of the phenomenon.Received: 22 May 2003, Accepted: 28 August 2003, Published online: 12 November 2003 Correspondence to:T. Saito     

Three-dimensional effects on regular reflection in steady supersonic flows

The reflection of shock waves between two symmetrical wedges is investigated for the case of three-dimensional flows. Oblique shadowgraphs at various optical angles of yaw and pitch were used to examine the nature of fully three-dimensional flows, with wedge aspect ratios as low as 0.25 being considered. These images were used to construct surface models of the overall flow field for various reflection patterns and aspect ratios, which provides a visual indication of the flow field shape. For a Mach number of 3.1, and suitable wedge angles, the flow field with regular reflection on the tunnel centreline and Mach reflection further out is examined. The point of transition from regular reflection to the peripheral Mach surfaces is identified for various wedge angles and aspect ratios. It is shown that the transition points move outwards from the central plane as the aspect ratio decreases. This shows that three-dimensional flows favor regular reflection, because of the increasing curvature of the incident shock as the wedge becomes narrower, causing a decrease in the local angle of incidence. The height of the Mach stem is shown to be highly dependent on the geometry of the test wedge models. The Mach stem height decreases with aspect ratio due to the three-dimensional relieving effect, where the increase in lateral flow relieves the pressure over the surfaces of the wedges. Experimental evidence of the existence of the strong oblique shock solution in steady flows is presented.Received: 7 July 2003, Revised: 20 October 2003, Accepted: 6 November 2003, Published online: 10 February 2004PACS: 47.40.Nm Correspondence to: B.W. Skews     

A numerical study of oblique shock wave reflections over wedges in an ideal quantum gas

The various oblique shock wave reflection patterns generated by a moving incident shock on a planar wedge using an ideal quantum gas model are numerically studied using a novel high resolution quantum kinetic flux splitting scheme. With different incident shock Mach numbers and wedge angles as flow parameters, four different types of reflection patterns, namely, the regular reflection, simple Mach reflection, complex Mach reflection and the double Mach reflection as in the classical gas can be classified and observed. Both Bose–Einstein and Fermi–Dirac gases are considered.      

Effects of a Single-pulse Energy Deposition on Steady Shock Wave Reflection

The effects of energy deposition in the free stream on steady regular and Mach shock wave reflections are studied numerically. A short-duration laser pulse is focused upstream of the incident shock waves. It causes formation of the expanding blast wave and the residual hot-spot interacting in a complex way with the steady shock wave reflection. It was found that the laser energy addition in the free stream may force the transition from regular to Mach reflection in the dual solution domain. In contrast to previously reported numerical results, the transition from Mach to regular reflection has not been reproduced in our refined computations since the Mach reflection is restored after the flow perturbation.