Measurement of the Growth of Perturbations on Blast Waves in a Mixed Gas

We have performed a series of experiments examining the properties of high Mach number blast waves. Experiments were conducted on the Z-Beamlet laser at Sandia National Laboratories. We created blast waves in the laboratory by using ∼1000 J laser pulses to illuminate millimeter scale solid targets immersed in gas. Our experiments studied the validity of theories forwarded by Ryu and Vishniac (1987, 1991) and Vishniac (1983) to explain the dynamics of perturbations on astrophysical blast waves. These experiments consisted of a systematic scan of the decay rates of perturbations of known primary mode number induced on the surface of blast waves by means of a regularly spaced wire array. The amplitude of the induced perturbations relative to the radius of the blast wave was tracked and fit to a power law in time. Measurements were taken for a number of different mode numbers in a mixed gas consisting of 7.5 Torr xenon and 2.5 Torr nitrogen and the results are compared to theoretical predictions. It is found that two of the three mode numbers imply one polytropic index while the third case, which is the most complicated for several reasons, implies a higher polytropic index.     

伽玛射线暴:各向同性火球还是柱形喷流?

多数伽玛射线暴的光学余辉衰减较平缓且光变曲线未见明显拐折，通常认为它们产生于各向同性火球，GRBs970228,970508,971214,980329及980703等就是典型的例子，但柱型喷流模型其实也能对这类伽玛射线暴的余辉给出极好的拟合，因此它们完全有可能产生于柱形喷流，而并非一定是来自各向同性火球。     

Numerical analysis on dynamic deformation mechanism of soils under blast loading

Soil is considered as a three-phase medium consisting of solid particles, water and air. Its behavior is very difficult to predict, especially under high rate blast loading. In this study, a new three-phase soil model for shock loading is employed to facilitate a full simulation of explosion and the subsequent stress wave propagation in soils. Upon validating the model, extended numerical calculations are carried out and the results are analyzed to demonstrate the change of characteristic parameters of the soils, the inherent distribution of the pressure on individual phases and hence the deformation mechanisms of the soils under blasting loading. Two primary deformation mechanisms exist, one is the deformation of the soil skeleton formed by the solid particles; the other is the deformation of all individual soil phases. It is found that the response of soil near the charge is dominated by the second mechanism while the first mechanism dominates in areas beyond a certain scaled range. The location of the transition zone depends primarily on the initial state of the soil. The results are useful for establishing rational and practical soil models for engineering applications concerning blasting.     

Investigating the Astrophysical Applicability of Radiative and Non-Radiative Blast wave Structure in Cluster Media

We describe experiments that investigate the capability of an experimental platform, based on laser-driven blast waves created in a medium of atomic clusters, to produce results that can be scaled to astrophysical situations. Quantitative electron density profiles were obtained for blast waves produced in hydrogen, argon, krypton and xenon through the interaction of a high intensity (I ≈ 10¹⁷ Wcm⁻²), sub-ps laser pulse. From this we estimate the local post-shock temperature, compressibility, shock strength and adiabatic index for each gas. Direct comparisons between blast wave structures for consistent relative gas densities were achieved through careful gas jet parameter control. From these we investigate the applicability of different radiative and Sedov-Taylor self-similar solutions, and therefore the (ρ,T) phase space that we can currently access.     

Theoretical Concept to Understand Plan and Design Smooth Blasting Pattern

Considering different mechanical cutting tools for excavation of rock, drilling and blasting is said to be inexpensive and at the same time most acceptable and compatible to any geo-excavation condition. Depending upon strength properties of in-situ rock mass, characteristics of joint pattern and required quality of blasting, control blasting techniques viz., pre-split and smooth blasting are commonly implemented to achieve an undamaged periphery rock-wall. To minimize magnitude of damage or overbreak, the paper emphasized that in-situ stresses and re-distribution of stresses during the process of excavation should be considered prior to selection of explosive parameters and implementation of any suitable blast pattern. Rock structure being not massive in nature, the paper firstly explains the influence of discontinuities and design parameters on smooth-wall blasting. Considering the empirical equations for estimation of stress wave’s magnitude and its attenuation characteristics through transmitting medium, the paper has put forward a mathematical model for smooth blasting pattern. The model firstly illustrates that rock burden for each hole should be sub-divided into thin micro strips/slabs to understand the characteristics of wave transmission through the medium and lastly with the help of beam theory of structural dynamics have put forward a mathematical model to analyze and design an effective smooth blasting pattern to achieve an undamaged periphery rock-wall.     

Optimum design of metallic corrugated core sandwich panels subjected to blast loads

Recently, the naval industry has continued to develop innovative lightweight structural concepts with the purpose of seeking alternative replacements for conventional plate–beam metallic structures in selected areas of ships. This study investigated the optimum design of metallic corrugated core sandwich panels subjected to blast loads by using a combined algorithm, the Feasible Direction Method (FDM) coupled with the Backtrack Program Method (BPM), in which the corrugation leg, corrugation angle, face sheet thickness, core thickness and corrugation pitch are selected as design variables, and the axial compression, bending and buckling constraints and the side constraints of the manufacturing limitations on the sizes are considered. A corrugated core sandwich panel model in the combatant deckhouse of a naval ship is adopted in the optimum study. The results show that the corrugation leg, corrugation angle and core thickness are most important for the core component, and that the corrugation leg and face sheet thickness are most important for the face sheet component. The significance of the design varibles is discussed in detail. Optimization results may provide a useful reference for designers.     

Parameterization of the porous-material model for sand with different levels of water saturation

The experimental results for the mechanical response of sand (at different levels of saturation with water) under shock-loading conditions generated by researchers at Cavendish [Bragov AM, Lomunov AK, Sergeichev IV, Tsembelis K, Proud WG. The determination of physicomechanical properties of soft soils from medium to high strain rates, November 2005, in preparation; Chapman DJ, Tsembelis K, Proud WG. The behavior of water saturated sand under shock-loading. In: Proceedings of the 2006 SEM annual conference and exposition on experimental and applied mechanics, vol. 2, 2006.p.834–40] are used to parameterize our recently developed material model for sand [Grujicic M, Pandurangan B, Cheeseman B. The effect of degree of saturation of sand on detonation phenomena associated with shallow-buried and ground-laid mines. J Shock Vib 2006;13:41–61]. The model was incorporated into a general-purpose non-linear dynamics simulation program to carry out a number of simulation analyses pertaining to the detonation of a landmine buried in sand and to the interactions of the detonation products, mine fragments and sand ejecta with various targets. A comparison of the computed results with their experimental counterparts revealed a somewhat improved agreement with the experimental results in the case of the present model as compared to the agreement between the widely used porous-material/compaction model for sand and the experiments.     

A direction-sensitive underwater blast detector and its application for managing blast fishing

Little is known about the spatial and temporal distribution of blast fishing which hampers enforcement against this activity. We have demonstrated that a triangular array of hydrophones 1 m apart is capable of detecting blast events whilst effectively rejecting other sources of underwater noise such as snapping shrimp and nearby boat propellers. A total of 13 blasts were recorded in Sepangor bay, North of Kota Kinabalu, Sabah, Malaysia from 7th to 15th July 2002 at distances estimated to be up to 20 km, with a directional uncertainty of 0.2 degrees . With such precision, a network of similar hydrophone arrays has potential to locate individual blast events by triangulation to within 30 m at a range of 10 km.     

A comparative study of buried structure in soil subjected to blast load using 2D and 3D numerical simulations

The response of underground structures subjected to subsurface blast is an important topic in protective engineering. Due to various constraints, pertinent experimental data are extremely scarce. Adequately detailed numerical simulation thus becomes a desirable alternative. However, the physical processes involved in the explosion and blast wave propagation are very complex, hence a realistic and detailed reproduction of the phenomena would require sophisticated numerical models for the loading and material responses. In this paper, a fully coupled numerical model is used to simulate the response of a buried concrete structure under subsurface blast, with emphasis on the comparative performance of 2D and 3D modeling schemes. The explosive charge, soil medium and the RC structure are all incorporated in a single model system. The SPH (smooth particle hydrodynamics) technique is employed to model the explosive charge and the close-in zones where large deformation takes place, while the normal FEM is used to model the remaining soil region and the buried structure. Results show that the 2D model can provide reasonably accurate results concerning the crater size, blast loading on the structure, and the critical response in the front wall. The response in the remaining part of the structure shows noticeable differences between the 2D and 3D models. Based on the simulation results, the characteristics of the in-structure shock environment are also discussed in terms of the shock response spectra.     

福建地方爆破的识别

本文通过对福建地方爆破波形的分析 ,总结了本省地方爆破的一些波形特征 ,有利于今后对爆破的识别 ,并提出今后可进一步研究的方向