爆炸载荷下聚氨酯泡沫材料中冲击波压力特性

采用间接测压法,对爆炸载荷作用下聚氨酯泡沫材料中的冲击波压力特性进行了研究。结果表明,在装药特性相同的爆炸载荷作用下,聚氨酯泡沫材料中的初始冲击波压力随初始孔隙度增大而显著下降;冲击波传播衰减效应受初始孔隙度影响同样显著,但不呈单一加快或减慢趋势;当初始孔隙度在０．２５左右时,聚氨酯泡沫材料对爆炸载荷具有较强的抗冲击减压效能。     

平板撞击下C30混凝土中冲击波的传播特性

采用1级气炮加载技术和锰铜应力计多点测试技术,开展了C30混凝土在平板撞击条件下的冲击压缩实验研究。基于锰铜应力计实测的应力波形,研究了混凝土中冲击波的传播特性,结果显示冲击波的应力峰值随传播距离呈现明显的衰减特性,衰减过程可分为2个阶段。在早期阶段,卸载波没有赶上前面传播的冲击波,冲击波应力峰值衰减较慢,主要是混凝土材料的本构粘性效应所引起的;而后期阶段应力峰值的快速衰减则归因于混凝土材料的本构粘性效应、后续的来自飞片自由面的反射波追赶卸载、边侧稀疏波卸载及波传播的几何弥散效应的共同作用;另外,冲击波在混凝土中传播的升时也随着传播距离逐渐增大,即由强间断波逐渐转化为弱间断波。     

爆炸荷载下泡沫铝材料中冲击波衰减特性的实验和数值模拟研究

通过实验和数值模拟对泡沫铝中冲击波传播特性进行了研究,结果表明:冲击波在泡沫铝中传播时显示明显的衰减特性;与此同时波头升时逐渐增加。这种衰减耗散特性主要来源于泡沫铝本身的本构粘性效应,而追赶卸载效应又会进一步促进冲击波的衰减。这为泡沫铝作为新型抗冲击缓冲材料提供设计基础。     

多孔材料中应力波的传播

针对多孔泡沫混凝土实验应力应变曲线的基本特点,提出并建立了一种可以考虑孔隙压实过程的材料本构模型及其数学形式.通过典型算例,分析了应力波在多孔材料中传播的耗散效应,指出多孔材料中的孔隙在被压实过程中能有效吸收应力波能量、降低应力波强度,在引起应力波衰减的诸因素中,孔隙压实所起的作用更大更显著.     

多孔材料下气体爆炸转扩散燃烧的特性研究

为分析多孔材料对预混气体爆炸特性参数的影响效果，采用自主搭建的爆炸实验平台，探究不同孔隙度和厚度的多孔材料对当量比为1的甲烷/空气预混气体爆炸的作用行为。实验研究表明，不同孔隙度的多孔材料对爆炸火焰和超压具有促进或抑制两种不同的影响。孔隙度较小时，爆燃火焰传播速度随着材料厚度的增大而降低，并在厚度较大时，火焰有短暂的传播延时现象。孔隙度较大时，预混火焰冲击多孔材料时发生淬熄，但随后一段时间内，由于负压抽吸作用，在已爆区域一侧的材料表面产生扩散燃烧现象，且扩散燃烧程度与材料厚度成反比关系。多孔材料的固相结构能降低压力的泄放效率，同时可吸收能量，进而提高爆炸超压的上升速率，降低超压峰值。当每英寸长度孔数δ=10的多孔材料促进火焰传播时，与当量比为1的预混气体爆炸相比，超压峰值最大可提高约2倍，造成更严重的后果。火焰冲击δ=20的多孔材料时发生淬熄，最大超压衰减可达47.17%，δ=30时最大超压衰减了24.62%。     

岩石对冲击波的非线性动态响应

对干燥、饱水、饱泵油大理岩和饱和砂岩进行了SHPB冲击压缩实验,得到了干燥岩石和饱和岩石的应力波衰减规律。在应力波传播过程中,其幅值有较大的衰减,干燥岩石的衰减最大,且孔隙度越大衰减越大,饱和岩石还存在较强的波弥散效应。在小于岩石屈服强度时,多次冲击加载下获得随冲击加载次数的增加,加载模量增大,残余应变减小的压实效应。这一结果可用于大型地震工程和防护工程的设计和建造。     

缝洞型多孔介质中多相流的有限体积法数值模拟

本文研究的碳酸盐岩油藏储集体属于缝洞型多孔介质.这类缝洞型多孔介质由裂缝、溶蚀孔洞和低孔隙度低渗透率的基岩组成.裂缝是空隙流体流动的主要通道;溶蚀孔洞大小从几厘米到数米不等,渗透率和孔隙度都很高,是流体主要的储集空间.由于缝洞型多孔介质空隙空间的复杂性和强非均质性,数值计算中基本控制方程的空间离散应采用非结构化网格的计算模型.本文采用有限体积法模拟缝洞型多孔介质中多相流体的流动,并给出了相应的单元中心格式有限体积法的计算公式.裂缝介质和溶洞介质中单元间多相流体的流动考虑为高速非达西流,其质量通量采用Forchheimer定律计算.非线性方程的离散选取全隐式格式,并采用Newton-Raphson迭代进行求解.通过两个二维模型注水驱油的数值模拟,验证了本文方法的有效性.     

水雾对爆炸冲击波衰减效应的实验研究

为了探究水雾特性与爆炸载荷衰减效果之间的关系，在爆炸驱动的激波管内两种不同特性的水雾环境下进行了不同强度的爆炸实验，并评估了两种水雾对爆炸冲击波超压和比冲量的衰减效果。实验结果表明：喷雾区域内的压力分为两个上升阶段，第一个阶段为透射冲击波的压力，第二个阶段为液滴二次雾化和弛豫过程导致的压力上升；冲击波掠过的喷雾区域越长，水雾对压力峰值和比冲量的衰减效果越好；冲击波强度的增加将削弱水雾对爆炸载荷的衰减效果；Sauter平均直径为136.04μm、体积分数为1.72×10-3的水雾使压力峰值衰减了34.2%～60.9%，使比冲量衰减了9%到54%;Sauter平均直径为255.34μm、体积分数为3.43×10-3的水雾使压力峰值衰减了48.4%～78.6%，使比冲量衰减了14%～66%；冲击波压力峰值的衰减率随着冲击波-雾滴之间的比例交换面积增加而线性减少。     

冲击波加载区域对冲击波速度和衰减的影响

以工程采用的冲击波衰减电探针测试方法为基础,通过数值模拟研究了冲击波加载区域对冲击波传播速度和冲击波衰减测量结果的影响。结果表明:对非一维平面正冲击波,冲击波的径向几何弥散对冲击波传播速度影响显著;针对本文算例,当电探针离自由面0.05mm时,冲击加载半径R=10mm、R=20mm比R=80mm所测电探针导通时间分别长7.79μs、1.28μs,一维平面波理论高估了实际测试的冲击波传播速度,冲击加载面积越小,冲击波衰减越快;在同一时刻(30μs)和同一位置(L=80mm),加载半径R=80mm的冲击压力是R=20mm的5倍还多,一维平面波理论低估了冲击波衰减程度,点撞击引起的散心冲击波则相反。因此目前获得的各种冲击波衰减经验公式应强调其加载条件和适用范围,特别是散心冲击波实验获得的冲击衰减拟合公式有可能降低设计安全阈值。     

坑道内爆炸条件下温压炸药的爆炸特性及其影响因素

温压炸药在坑道内爆炸时会产生多种毁伤元,对坑道内人员和设备造成严重威胁。基于不同药量的温压炸药爆炸试验,对坑道内爆炸条件下温压炸药的爆炸特性开展了研究,分析了爆炸热效应演化特征、冲击波传播规律和氧浓度降低情况,讨论了坑道对铝粉后燃的约束作用规律以及形成高烈度后燃效应的药量条件。研究表明：温压炸药火球辐射亮度高于TNT,且其火球温度峰值超过TNT温度峰值的1.3倍。在火球演化过程中,火球在后燃阶段的温度峰值较火球形态刚稳定时提升超过10%。在冲击波传播规律方面,超压峰值与正压时间的TNT当量系数分别约为1.4与1.65。另外,铝粉后燃产生的压缩波对冲击波能够形成多种补充效果,陡峭升压的压缩波能够使冲击波峰值升高,持续时间长但升压速率慢的压缩波能够限制冲击波的衰减,延长整体正压作用时间。受坑道约束作用,温压炸药爆炸火球将与坑道壁面发生相互作用,进而提高铝粉的燃烧烈度。当温压炸药质量立方根与坑道直径的比值大于0.28 kg^1/3/m时,将产生高烈度后燃效应。     

Dual-element directional shock wave attenuators

This study explores the interaction between shock waves and dual-element porous plates used to ameliorate the hazardous effects of these waves. Tests were performed in a shock tube to determine the effects that a pair of porous plates with directional resistance properties had on the initial peak pressure and impulse amelioration experienced by an end wall. Mild steel test specimens, ranging in porosity values from 6.6% to 41.1%, were mounted two at a time at different spacings in the test section. Each plate had directional properties, i.e. resistance to flow was different for flow coming from either side. Four plates were used, and 48 plate configurations were tested. Side wall and end wall pressure measurements and schlieren photographs were taken of the interactions. Tests were run at Mach numbers of 1.23, 1.35 and 1.42. The separation distances between the plate specimens were varied between 30 mm and 60 mm; however, the distance between the downstream plate and the end wall was kept constant at 140 mm for all tests.Both the initial peak pressure and impulse amelioration values were found to be dependant on the plate combination porosity. As the porosity of the combination increased, the amelioration values decreased. Complementary plate combinations produced differing results as different wave interactions occur when plate positions were interchanged. The porosity of the combined plates was found to have an overriding influence on the end wall peak pressure and impulse amelioration values when compared to the effect that plate arrangement (i.e. geometrical influences) had. Impulse amelioration values were found to increase as the separation distance between plates were increased. The amplitude of the end wall pressure trace was found to increase as the incident Mach number was increased. The significant attenuation of the incident shock wave obtained during this study is attributed to the system of multiple reflected and transmitted waves that are produced by the presence of the plate specimens in series. This increases the frequency of shock wave and barrier interactions, when compared to just using a single barrier.     

Wave propagation in transversely isotropic porous piezoelectric materials

Wave propagation in porous piezoelectric material (PPM), having crystal symmetry 6 mm, is studied analytically. Christoffel equation is derived for the propagation of plane harmonic waves in such a medium. The roots of this equation give four complex wave velocities which can propagate in such materials. The phase velocities of propagation and the attenuation quality factors of all these waves are described in terms of complex wave velocities. Phase velocities and attenuation of the waves in PPM depend on the phase direction. Numerical results are computed for the PPM BaTiO₃. The variation of phase velocity and attenuation quality factor with phase direction, porosity and the wave frequency is studied. The effects of anisotropy and piezoelectric coupling are also studied. The phase velocities of two quasi dilatational waves and one quasi shear waves get affected due to piezoelectric coupling while that of type 2 quasi shear wave remain unaffected. The phase velocities of all the four waves show non-dispersive behavior after certain critical high frequency. The phase velocity of all waves decreases with porosity while attenuation of respective waves increases with porosity of the medium. The characteristic curves, including slowness curves, velocity curves, and the attenuation curves, are also studied in this paper.     

Investigation of the special characteristics of the propagation and reflection of pressure waves in a porous medium

In view of the wide use of porous materials in technology there arises the need to investigate the dynamic processes taking place in them. The main difference between a porous substance and a solid condensed material is the fact that the condensed phase occupies only part of the volume of the porous medium, which leads to a lowered volumetric density and to a large degree of compressibility. There is particular interest in polymeric media with a small density on the order of 20 kg/m³, in which up to 98% of the volume is occupied by the gas phase. Such a density is achieved if the medium has a cellular structure of the foam, for example, in polyurethane foam plastics. At the present time, only the elastic properties of polyurethane foam plastics under the action of cyclic [1] and impact [2, 3] loads are known. Questions of the formation of pressure waves in such a medium, with the refraction in it of a shock wave from the gas, of the structure of the wave propagating over the foam plastic, as well as the special characteristics of its reflection from the interface, remain unclear. In the experiments described below, an investigation was made of pressure waves with intensities up to 20 bars in elastic polyurethane foams (PUF) with a porosity of 0.98 and the special characteristics of the reflection of such waves from a rigid wall were also determined.     

Oxyhydrogen combustion and detonation driven shock tube

The performance of combustion driver ignited by multi-spark plugs distributed along axial direction has been analysed and tested. An improved ignition method with three circumferential equidistributed ignitors at main diaphragm has been presented, by which the produced incident shock waves have higher repeatability, and better steadiness in the pressure, temperature and velocity fields of flow behind the incidence shock, and thus meets the requirements of aerodynamic experiment. The attachment of a damping section at the end of the driver can eliminate the high reflection pressure produced by detonation wave, and the backward detonation driver can be employed to generate high enthalpy and high density test flow. The incident shock wave produced by this method is well repeated and with weak attenuation. The reflection wave caused by the contracted section at the main diaphragm will weaken the unfavorable effect of rarefaction wave behind the detonation wave, which indicates that the forward detonation driver can be applied in the practice. For incident shock wave of identical strength, the initial pressure of the forward detonation driver is about 1 order of magnitude lower than that of backward detonation. The project supported by State Science and Technology Committee, National Natural Foundation of Science of China (19082012), Chinese Academy of Sciences and Project of National High Technology of China. In memory of academician Kuo Yonghuai's 90th anniversary.     

波在双孔隙与单孔隙介质界面上的反射与透射

基于Biot理论和双重孔隙介质理论研究了弹性波在双重孔隙介质与流体饱和单一孔隙介质 界面的反射和透射问题，在界面上假定裂缝孔隙流体相对于固体骨架的位移为零，推导了反 射系数和透射系数的计算公式，数值讨论了反射系数和透射系数随入射角和频率的变化关 系. 同时，讨论了双重孔隙介质中3种压缩波(P-1, P-2和P-3波)和一种剪切波(S波) 的频散和衰减特性.     

The reflected pressure field in the interaction of weak shock waves with a compressible foam

This paper deals with the waves that are reflected from slabs of porous compressible foam attached to a rigid wall when impacted by a weak shock wave. The interest is in establishing possible attenuation of the pressure field after a shock or blast wave has struck the surface. Foam densities from 14 to 38 kg/m³ were tested over a range of shock wave Mach numbers less than 1.4. It is shown that the initial reflected shock wave strength is accurately predicted by the pseudo-gas model of Gelfand et al. (1983), with a pressure ratio of approximately 80% of the value for reflection off a rigid wall. Evidence is presented of gas entering the foam during the early stages of the process. A second wave emerges from the foam at a later stage and is separated from the first by a region of constant velocity and pressure. This second wave is not a shock wave but a compression front of significant thickness, which emerges from the foam earlier than predicted by the pseudo-gas model. Analysis of the origin of this wave points to much more complex flows within the foam than previously assumed, particularly in an apparent decrease in average wave front speed as the foam is compressed. It is shown that the pressure ratio across both these waves taken together is slightly higher than that for reflection off a rigid wall. In some cases this compression wave train is followed by a weak expansion wave.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

A shock tube research facility for high-resolution measurements of compressible turbulence

A new shock tube facility with a 30.5 cm (1 ft) inside diameter is currently in operation that allows for high-spatial-resolution measurements of compressible turbulence. Small scales of turbulence behave very differently from large scales when they interact with shock or expansion waves. Highly resolved measurements can provide new information on the interaction at small scales. Another notable characteristic of the present facility is the ability to control the flow velocity behind the reflected shock through the porosity of the reflecting wall. Tests showed good flow quality with sufficiently long observation times. Measurements of piecewise average skin friction over short segments of the tube indicated strong viscous effects very close to the diaphragm where the shock is developing. The skin friction and the shock propagation speed virtually remained constant inside the working section of the shock tube in all investigated flow cases, even in low Mach number cases where viscous effects are stronger. The experimental results are compared with numerical simulations, including the effects of the reflecting porous wall and viscous effects.     

Experimental and numerical studies of underwater shock wave attenuation

The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.Received: 22 October 2002, Accepted: 17 June 2003, Published online: 5 August 2003PACS: 47.11.+j, 47.40.Nm, 47.55.Mh     

含电子相影响的多功能含能结构材料冲击压缩理论计算

为了更好地描述疏松态金属材料的冲击压缩特性,基于托马斯-费米原子统计模型,研究金属晶体中电子热行为对系统内粒子数、内能、压强等参数的影响,修改了描述疏松金属材料的Wu-Jing模型中的参数R的计算方法。结合混合物的冷能叠加原理,得到考虑电子相影响的疏松态混合物物态方程。并对不同配比的密实态W/Cu合金、不同疏松度的Al/Ni合金的典型多功能含能结构材料进行计算,获得其冲击压力-比容关系及冲击波速度-粒子速度关系,计算结果与实验结果吻合较好。结果表明,本文中模型对未反应条件下的金属材料冲击压缩特性预测较好;疏松材料的冲击压力-粒子速度关系并不呈现出密实材料的近似线性关系,其冲击压缩过程分为压实前和压实后2个明显的阶段;多功能含能结构材料的冲击压缩特性受材料孔隙率、材料配比等影响明显。     

A linear dynamic model for a saturated porous medium

A linear isothermal dynamic model for a porous medium saturated by a Newtonian fluid is developed in the paper. In contrast to the mixture theory, the assumption of phase separation is avoided by introducing a single constitutive energy function for the porous medium. An important advantage of the proposed model is it can account for the couplings between the solid skeleton and the pore fluid. The mass and momentum balance equations are obtained according to the generalized mixture theory. Constitutive relations for the stress, the pore pressure are derived from the total free energy accounting for inter-phase interaction. In order to describe the momentum interaction between the fluid and the solid, a frequency independent Biot-type drag force model is introduced. A temporal variable porosity model with relaxation accounting for additional attenuation is introduced for the first time. The details of parameter estimation are discussed in the paper. It is demonstrated that all the material parameters in our model can be estimated from directly measurable phenomenological parameters. In terms of the equations of motion in the frequency domain, the wave velocities and the attenuations for the two P waves and one S wave are calculated. The influences of the porosity relaxation coefficient on the velocities and attenuation coefficients of the three waves of the porous medium are discussed in a numerical example.