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     

利用镀膜样品进行冲击波温度测量的问题和思考

针对当前进行金属冲击波温度测量中普遍使用的“金属基板／间隙／镀膜样品／透明窗口”的实验装置结构（“四层介质模型”）,详细分析了金属基板与镀样品之间的间隙对辐射法测温的影响。给出了镀膜样品与窗口之间的界面（记为“样品／窗口”界面）上的温度的解析解,并且对该界面温度的势弛豫特性进行了详细讨论。研究表明：由于冲击波穿过金属板与镀样品之间的间隙时,在金属基板与镀膜样品界面上形成了一高温界面层,使“样品／窗     

可控爆轰平面加载样品回收装置

介绍了一种可控爆轰平面加载样品回收装置，该装置包括一个近似平面波发生器和一个“动量陷阱”式样品腔体。工作原理是由近似平面波发生器加速一块飞片，经适当长空腔飞行后与样品腔体碰撞，产生高压冲击波对样品实现冲击波压缩，并由“动量陷阱”式腔体回收样品，飞片材料为４５钢。此装置可在１．５￣３．５ｋｍ／ｓ范围内实现飞片击靶速度的连续调节，并且具有较理想的飞片击靶平面性，经测定在直径３０ｍｍ的范围内飞片弯曲的时     

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。     

FeMnNi合金冲击加卸载历程研究

采用激光速度干涉仪(VISAR),应用逆向加载实验装置FeMnNi飞片/蓝宝石窗口和FeMnNi飞片/LiF缓冲层/LiF窗口,分别对低相变阈值金属FeMnNi合金含相变的低压和高压冲击加卸载历程进行实验研究。参阅文献[3,4]分析了实验结果。在低压加载下,FeMnNi合金样品存在α→ε相变,卸载时存在逆相变ε→α及逆相变引发的卸载稀疏冲击波;在高压加载下,FeMnNi合金样品存在α→ε相变,卸载时可能存在逆相变ε→γ和γ→ε行为及逆相变引发的卸载稀疏冲击波。     

关于球面飞层加载对比法测量及Whitham关系的讨论（1）

分析了球面飞层加栽对比法测量进行阻抗匹配数据处理在物理上遇到的困难;提出了在球面会聚冲击波运动规律满足Whitham关系的条件下,能够满足阻抗匹配要求的样品设计方法和减小阻抗匹配数据处理不确定度的方法;提出了在同一发实验中获取多个Hugoniot压力点的方法。对样品设计引入的实验不确定度进行了简单讨论。与感兴趣的读者共同讨论。     

Whitham公式在球形内爆实验中的适用性研究

球形内爆实验是实现超高压状态方程测量的方法之一,Whitham公式可对球面聚心冲击波的传播特性进行描述。文中给出了确定Whitham公式系数的方法,针对使用两种不同厚度样品球形内爆实验,通过Whitham系数不确定度分析及其求解方程组的性态分析,探讨了Whitham公式在球形内爆实验中的适用范围。结果表明,样品厚度过薄时,Whitham公式不能应用;当0．8〈A1=R1／R0〈0．857且A2=R2／R0〈0．657时,在内爆实验的结果分析和处理中应用Whitham公式可能会取得较好的结果。     

基于反向撞击法的JB-9014炸药Hugoniot关系测量

为了获得JB-9014未反应炸药的Hugoniot关系，在火炮加载平台上利用反向撞击技术对JB-9014炸药进行一维平面冲击实验。将JB-9014炸药样品作为飞片安装于弹托前表面，将镀膜氟化锂窗口作为装置靶。利用火炮加速弹托，使炸药样品以一定速度撞击镀膜氟化锂窗口，通过光子多普勒测速仪(photonic Doppler velocimetry，PDV)测量炸药样品击靶速度以及炸药/镀膜氟化锂窗口界面粒子速度。最终根据冲击波阵面守恒关系计算获得了JB-9014炸药冲击Hugoniot数据，采用正交回归直线拟合得到了炸药样品在3.1～8.2 GPa压力范围内的冲击Hugoniot关系:D_s=2.417+2.140u_s (D_s和u_s的单位均为km/s)。结果表明:该方法测试精度较高，响应时间快(小于5 ns)，同时该方法可以对炸药的反应情况进行检测，便于判断实验是否测得真实的未反应炸药冲击Hugoniot数据。     

冲击加载下样品软回收过程中的侧向稀疏效应

通过数值模拟, 计算冲击加载下样品经历一维应变加载过程和侧向稀疏过程产生的塑性功, 给出试样内部从冲击加载开始到进入回收桶前全过程的应力随时间变化的历程。结果表明:侧向稀疏过程开始后,样品在径向汇聚波的作用下受循环拉、压载荷作用,拉压循环的振幅在中等冲击压力下达到最大。如果振幅超过了材料的层裂强度,样品中心将发生拉伸破坏不能完整回收。侧向稀疏与一维应变加载产生的塑性功之比随冲击速度的增加而减小。在冲击速度为某临界值时,侧向稀疏产生的塑性功与一维应变加载产生的塑性功相等。在一定的冲击速度下,采用低初始屈服应力的材料可减轻侧向稀疏效应。对理想塑性材料的理论分析表明,侧向稀疏与一维应变加载产生的塑性功之比随冲击速度与屈服强度比值的增大而减小,与数值模拟结果一致。     

反应金属冲击反应过程的理论分析

基于1维冲击波理论和粉末材料的冲击温度计算模型对反应金属的冲击响应行为、冲击温度及冲击反应过程进行了理论分析,分别考虑了材料密实度、冲击速度对冲击压力、冲击温度的影响;结合粉末材料冲击温度计算结果及冲击反应的化学动力学方法,提出了考虑反应效率的反应金属冲击反应理论模型。利用新模型得到的计算结果与已有实验结果吻合较好。反应金属的冲击反应行为受密实度、冲击速度及材料种类影响明显。 更多还原     

Shock waves in an elliptical cavity with varying height

Transient shock waves in a confined elliptical chamber are experimentally investigated. Quantitative results of the pressure distribution are obtained for an air-filled cavity. Lower bounding surfaces of different geometrical shapes can be inserted making it possible to get chambers with varying height. An electrical discharge across a pair of electrodes inside the cavity gives rise to the shock waves. Double pulsed holographic interferometry is used to study the propagation and focusing process of the waves. The results are quantitatively evaluated by using the method of two-reference-beam holography. The angular pressure distribution behind the converging wave front is presented for different geometries of an air-filled cavity. The pressure distribution is non-homogeneous but symmetric along the wave front. The pressure level is higher for the geometry where the height of the chamber decreases with the radial distance from the outgoing focus and lower for increasing height of the chamber. In addition, shock waves in a water-filled cavity are studied. In this case qualitative results are obtained. Received 3 November 1996 / Accepted 5 January 1997     

Experimental study of toroidal shock wave focusing in a compact vertical annular diaphragmless shock tube

The paper reports results of experiments regarding toroidal shock wave focusing in a vertical shock tube as a part of a series of converging shock wave studies. This compact vertical shock tube was designed to achieve a high degree of reproducibility with minimum shock formation distance by adopting a diaphragmless operating system. The shock tube was manufactured in the Institute of Fluid Science, Tohoku University. An aspheric lens shaped cylindrical test section was connected at the open end of the shock tube to visualize the diffraction and focusing of the toroidal shock wave released from the ring shaped shock tube opening. Pressure transducers were flush mounted on the shock tube’s test section to measure pressure histories at the converging test section. Double exposure holographic interferometry was employed to quantitatively visualize the shock waves. The whole sequence of toroidal shock wave diffraction, focusing, and its reflection from the symmetrical axis were successfully studied. The transition of reflected shock waves was observed.     

Control of pressure distribution in shock generators with elliptic cross-sections

Theoretical investigation of a liquid shock generating device with an elliptically shaped chamber is presented. A device of such kind has been previously fabricated and tested experimentally. Experimental observations confirmed the results of earlier theoretical analysis of the problem, showing that shock waves produced by an electric discharge at one of the foci of the elliptic chamber will converge at the second focus after the reflection off the cavity wall. In the present paper a previous two-dimensional model is extended to account for the height variation in the chamber. Expression for the pressure distribution behind the converging wave front is obtained and a relation between the shape of the upper bounding surface of the chamber and pressure distribution behind the converging wave front is investigated. It is shown that a desired pressure distribution may be obtained by an appropriate choice of the upper surface of the chamber.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Super-spherical cumulation: shock collapse which is more intense than the spherical one

A shock wave implosion in an axisymmetric chamber with a convex bounding wall is studied experimentally, analytically and numerically. The converging shock front area in this geometry shrinks quickly as the shock wave approaches the center point. The analytical theory predicts that the corresponding rate of post-shock pressure and density increase in this case exceeds essentially that achieved in the classical cylindrical or spherical shock implosions, hence, the phenomenon is referred to as “super-spherical cumulation”. The experiments confirm higher intensity of the super-spherical implosion compared with the cylindrical one, both driven by identical high-current pulsed electric discharges. The converging shock stability is analyzed in the framework of the CCW theory. The numerical results obtained using a locally-adaptive unstructured grid technique agree well with the theoretical predictions of the converging shock wave intensity. Received 28 January 1998 / Accepted 6 November 1998     

Specific features of incident and reflected blast waves

On the basis of numerical modeling specific features of shock wave reflections were analyzed. It was found, that after diaphragm rupture self-modeling pressure and velocity distributions nearby the shock front establish. But in some special cases the temperature behind the shock front can rise. This peculiarity should be taken into account when performing experiments with high reactive gaseous mixtures. The temperature on the shock front and the velocity gradient behind it are uniform in the case of strong blast wave reflections. This effect is observed in the zone with an elevated temperature profile behind the incident blast wave. The reflected triangular waves conserve a quasi-self-modeling character by pressure. Typical experiments were carried out to verify the theoretical predictions. The effects of reflected wave acceleration in the case of triangular waves and the self-similar character of the pressure profiles were observed.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Shock wave in a gas-liquid medium

The propagation of weak shock waves and the conditions for their existence in a gas-liquid medium are studied in [1]. The article [2] is devoted to an examination of powerful shock waves in liquids containing gas bubbles. The possibility of the existence in such a medium of a shock wave having an oscillatory pressure profile at the front is demonstrated in [3] based on the general results of nonlinear wave dynamics. It is shown in [4, 5] that a shock wave in a gas-liquid mixture actually has a profile having an oscillating pressure. The drawback of [3–5] is the necessity of postulating the existence of the shock waves. This is connected with the absence of a direct calculation of the dissipative effects in the fundamental equations. The present article is devoted to the theoretical and experimental study of the structure of a shock wave in a gas-liquid medium. It is shown, within the framework of a homogeneous biphasic model, that the structure of the shock wave can be studied on the basis of the Burgers-Korteweg-de Vries equation. The results of piezoelectric measurements of the pressure profile along the shock wave front agree qualitatively with the theoretical representations of the structure of the shock wave.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 65–69, May–June, 1973.     

Reflection of a spherical blast wave from a planar surface

Numerous authors have carried out rather extensive studies in the last twenty to thirty years of the problem of the interaction of shock and blast waves with obstacles in their paths. Owing to the complexity of the problem, they assumed certain limiting cases for the shock wave interactions in which the parameters behind the shock wave were usually taken to be constants. The first wave diffraction studies involving variable parameters behind the front were presented in [1, 2], wherein a development of the theory of “short waves” (blast waves at a substantial distance from the center of an explosion) and their reflection from a planar surface was given. The theory of short waves assumes that the jump in pressure at the wave front and the region over which the parameters vary are small. The problem concerning reflection of a blast wave from a surface was also considered in [3, 4], wherein a solution in the region behind the reflected wave was obtained at initial times. The initial stage in the reflection of a blast wave from a planar, cylindrical, or spherical surface (the one-dimensional case) was studied in [5]. In this paper we investigate the interaction of a spherical blast wave, resulting from a point explosion, with a planar surface; we consider both regular and non-regular reflection stages. In solving this problem we use S. L. Godunov's finite-difference method. We obtain numerical solutions for various values of the shock strength at the instant of its encounter with the surface. We present the pressure fields in the flow regions, the pressure distribution over the surface at various instants of time, and the trajectories of the triple point. The parameter values at the front of the reflected wave are compared with results obtained from the theory of regular reflection of shock waves.     

Stability of converging cylindrical shock waves

An experimental and numerical study was made of converging cylindrical shock waves. The goal of the present study was to clarify the movement and instability of the converging cylindrical shock waves. Experiments were conducted in an annular shock tube of 230 mm o.d. and 210 mm i.d. connected to a cylindrical test section of 210 mm diameter. Double exposure holographic interferometry was used to visualize the converging cylindrical shock waves. Incident shock Mach numbers ranged between 1.1 and 2.0 in air. A numerical simulation was conducted using the TVD finite difference scheme. It was found in the experiments that although the initial shock wave configuration looked cylindrical, it was gradually deformed with propagation towards the center and finally showed mode-four instability. This is attributable to the existence of initial disturbances which were introduced by the struts which supported the inner tube of the annular shock tube. This trend was significant for stronger shock waves indicating that at the last stage of shock wave convergence the initial perturbations of the converging cylindrical shock wave were amplified to form the triple point of Mach reflection. The numerical results correctly predicted the experimental trend.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Simulation of converging cylindrical GPa-range shock waves generated by wire array underwater electrical explosions

Results of one-dimensional numerical simulations of the parameters of the converging strong shock wave generated by electrical underwater explosions of a cylindrical wire array with different array radii and different deposited energies are presented. It was shown that for each wire array radius there exists an optimal duration of the energy deposition into the exploding array, which allows one to maximize the shock wave pressure and temperature in the vicinity of the implosion axis. The simulation results agree well with the 130-GPa pressure in the vicinity of the implosion axis that was recently obtained, which strongly indicates the azimuthal symmetry of the converging shock wave at these extreme conditions. Also, simulations showed that using a pulsed power generator with a stored energy of ~200 kJ, the pressure and temperature at the shock wave front reaches ~220 GPa and 1.7 eV at 0.1 mm from the axis of implosion in the case of a 2.5 mm radius wire array explosion. It was found that, in spite of the complicated equation of state of water, the maximum pressure at the shock wave front at radius r can be estimated as P ≈ (P*(r*/r) ^α , where P* is the known value of pressure at the shock wave front at radius r* ≥ r and α is a parameter that equals 0.62±0.02. A rough estimate of the implosion parameters of the hydrogen target after the interaction with the converging strong shock wave is presented as well.     

Regular versus Mach reflection for converging polygonal shocks

The onset of Mach reflection or regular reflection at the vertices of a converging polygonal shock wave was investigated experimentally in a horizontal annular shock tube. The converging shock waves were visualized by schlieren optics. Two different types of polygonal shock convergence patterns were observed. We compared the behavior during the focusing process for triangular and square-shaped shocks. It is shown that once a triangular shaped shock is formed, the corners in the converging shock will undergo regular reflection and consequently the shape will remain unaltered during the focusing process. A square-shaped shock suffers Mach reflections at the corners and hence a reconfiguring process takes place; the converging shock wave alternates between a square and an octagon formation during the focusing process.