Nonequilibrium Zeldovich-von Neumann-Doring theory and reactive flow modeling of detonation

This paper discusses the Nonequilibrium Zeldovich-von Neumann-Doring (NEZND) theory of self-sustaining detonation waves and the Ignition and Growth reactive flow model of shock initiation and detonation wave propagation in solid explosives. The NEZND theory identified the nonequilibrium excitation processes that precede and follow the exothermic decomposition of a large high explosive molecule into several small reaction product molecules. The thermal energy deposited by the leading shock wave must be distributed to the vibrational modes of the explosive molecule before chemical reactions can occur. The induction time for the onset of the initial endothermic reactions can be calculated using high pressure-high temperature transition state theory. Since the chemical energy is released well behind the leading shock front of a detonation wave, a physical mechanism is required for this chemical energy to reinforce the leading shock front and maintain its overall constant velocity. This mechanism is the amplification of pressure wavelets in the reaction zone by the process of de-excitation of the initially highly vibrationally excited reaction product molecules. This process leads to the development of the three-dimensional structure of detonation waves observed for all explosives. For practical predictions of shock initiation and detonation in hydrodynamic codes, phenomenological reactive flow models have been developed. The Ignition and Growth reactive flow model of shock initiation and detonation in solid explosives has been very successful in describing the overall flow measured by embedded gauges and laser interferometry. This reactive flow model uses pressure and compression dependent reaction rates, because time-resolved experimental temperature data is not yet available. Since all chemical reaction rates are ultimately controlled by temperature, the next generation of reactive flow models will use temperature dependent reaction rates. Progress on a statistical hot spot ignition and growth reactive flow model with multistep Arrhenius chemical reaction pathways is discussed. The text was submitted by the authors in English.     

均匀炸药冲击起爆和起爆后的行为

 介绍并分析了Campbell等人研究均匀炸药冲击起爆和起爆后行为所获得的实验结果,但不涉及其冲击起爆条件。Campbell等人的实验表明,足够强的冲击波进入硝基甲烷后,经过若干微秒的感应时间,爆轰发生在隔板与炸药间的界面处。这就是说,在均匀炸药中,足够强的冲击虽非瞬时但直接（指不经过其它过程,如爆燃）引发了爆轰。重新处理后的实验数据表明：硝基甲烷起爆后,爆轰波的净爆速小于正常爆速;当进入硝基甲烷的初始冲击波的有效压力p_eff由8.82 GPa升至12.14 GPa时,感应时间t_ind的实验值由3.06 μs降至0.705 μs。以两相的排平（A,m）物态方程描述爆轰产物,较为严格地重新推导了基于热起爆理论的估算感应时间t_ind的公式。在上述p_eff的变化范围内,t_ind的理论值则由248 μs降至0.99 μs,明显地高于实验值。这表明,热起爆理论不适于描述硝基甲烷的冲击起爆行为。从本质上讲,热起爆理论对均匀炸药的冲击起爆行为的描述,不符合物质运动的微观图像,因此,它不适于描述均匀炸药的上述行为。     

一维非定常炸轰的特征线方法数值模拟

本文用特征线方法计算了一维非定常炸轰的发展和传播问题。为模拟炸药的化学反应,采用了一种冲击波引爆的唯象模型。以PBX-9404高级炸药为例给出了计算的POP图与实验结果的比较以及不同时刻波后流场的分布。     

The SURF model and the curvature effect for PBX 9502

SURF is a high explosive burn model based on the ignition & growth concept of hot-spot reaction. For the TATB based explosive PBX 9502, the model has been calibrated to shock-to-detonation transition experiments. To apply the SURF model for propagating detonation waves, the rate has to be extended to a higher pressure regime than is sampled by shock initiation experiments. The experimentally measured curvature effect – detonation speed as a function of front curvature or D _n(κ) – provides the appropriate data for calibrating the propagation regime. The calibration to the curvature effect is based on the ODEs for the reaction zone profile of a detonation wave in conjunction with a shooting algorithm to determine the rate model parameters, for a given κ, needed to obtain a specified detonation speed. A complication for calibrating PBX 9502 rate models arises from the kink in the experimentally measured D _n(κ) curve. This results from the fast and slow reactions that TATB exhibits. To account for this, we use an extension of the SURF model that utilises a sequence of two reactions. The first, with a fast rate, is due to molecular decomposition and is described by the original SURF formulation. The second, with a slow rate, is due to carbon clustering and is used to contribute additional energy from the formation of carbon bonds. The wave profile equations are generalised to the SURF-plus model. Model parameters are then determined for the propagation regime to fit the curvature effect data. The extended model is applicable to both the shock initiation regime and the propagating detonation wave regime.     

弹粘塑性双球壳塌缩热点反应模型

 基于Kim的弹粘塑性单球壳塌缩模型,考虑PBX炸药中的粘结剂效应,假设炸药和粘结剂均为弹粘塑性材料,建立了弹粘塑性双球壳塌缩热点反应模型,给出了炸药球壳在冲击压力作用下的速度、应变、温度和化学反应速率的时空分布,以及新的热点反应速率理论表达式。把新的热点反应项与Kim的低压下慢反应项和张震宇提出的高压反应速率方程相结合,得到了新的冲击起爆三项式细观反应速率模型。把该模型加入DYNA2D中,模拟了PBX-9501炸药的一维冲击起爆过程,结果表明：该模型除了可以解释炸药颗粒度和孔隙度的影响外,还可以较好地描述粘结剂强度和含量对PBX炸药冲击起爆感度的影响。     

一维冲击波和爆轰波计算程序SSS

本文叙述一维程序SSS的理论和结构。介质采用流体弹塑性模型。爆轰反应有四种可选方式:Arrhenius律、C-J比容法、方波法和Forest Fire方程。爆轰产物可选用HOM或JWL状态方程。SSS程序的特殊功能有,激光效应、爆轰增长、强爆炸波、散心爆轰和瞬时爆轰等,初始起爆或能量释放位置可任意设定。本程序部分参考了美国洛斯阿拉莫斯实验室的一维程序SIN。本文列举的算例把这两个程序作了比较。     

非均匀炸药冲击起爆和起爆后的行为

 介绍并分析了Campbell 等人及其他作者研究非均匀炸药冲击起爆和起爆后行为所获得的实验结果,但不涉及其冲击起爆条件。足够强的冲击波进入非均匀炸药后,爆轰将瞬时（指不经过感应时间）且直接（指不经过其他过程,如爆燃）被引发;非均匀炸药起爆后,其中传播的自始至终是一个不断增长的爆轰波,直至发展为正常爆轰,整个过程都是爆轰的增长（新定义）过程。不存在由反应冲击波不断增长并转变为爆轰波的所谓向爆轰的增长。所谓向爆轰的增长,实际上是爆轰的增长（按新定义）的初期;Craig原定义的爆轰的增长,实际上是爆轰的增长（按新定义）的后期;而所谓反应冲击波,实际上是增长中的初期爆轰波。爆轰的增长（按新定义）是所有猛炸药的特性,炸药反应不充分并逐渐趋于充分是爆轰的增长的化学机制。     

The mechanism of hot spot formation in condensed explosives

The hypothesis of an electrical mechanism of formation of detonation initiation zones (hot spots) in condensed explosives is considered. The hypothesis is based on the generation of electric fields and the appearance of shock-induced conductivity in the propagation of a shock wave (compression wave) in condensed dielectric media, including explosives. These physical phenomena can cause a local electrical breakdown, whose channel is identified with a hot spot. The available experimental data are analyzed from the point of view of the hypothesis suggested, and a procedure for verifying this hypothesis is outlined.     

基于多源卫星多光谱遥感数据的过火面积估算研究

露天生物质燃烧是重要的大气污染物排放源,导致空气质量恶化并引起气候变化。卫星遥感数据能够提供大尺度、多时相的监测信息,然而燃烧火点监测和火烧迹地监测两种方式都存在着局限性。以美国东南部地区为研究区域,通过结合卫星遥感获取的高分辨率燃烧面积数据及多时相的燃烧火点数据,建立时空匹配模型估算露天生物质燃烧过火面积。通过分析植被燃烧前后的光谱变化特征,基于高分辨率的Landsat-5 TM4波段(0.84 μm)与7波段(2.22 μm)数据, 利用差分归一化燃烧比(dNBR: the differential normalized burn ratio)提取燃烧面积数据;而燃烧火点数据则通过分析燃烧植被的热红外光谱特征利用MODIS 4与11 μm波段数据提取。结果显示,该地区燃烧面积与燃烧火点数量之间相关系数达0.63,并且二者之间的比例关系随植被类型而发生变化,林地、草地、灌木、耕地和沼泽五种植被类型对应的像元燃烧面积分别为0.69,1.27,0.86,0.72和0.94 km2。通过与美国火灾中心(national interagency fire center, NIFC)地面调查数据比对,模型估算的美国东南部过火面积数据较为精确,而同期的MODIS燃烧面积产品(MCD45)及燃烧源清单产品(global fire emissions database, GFED)遗漏了该区域大量的小面积燃烧事件。因此,本研究建立的过火面积估算模型能够提供更为精确的排放源参数信息,有利于区域空气质量模式准确地模拟露天生物质燃烧排放状况。     

Calibration of the Pseudo-Reaction-Zone model for detonation wave propagation

An approach for the calibration of an advanced programmed burn (PB) model for detonation performance calculations in high explosive systems is detailed. Programmed burn methods split the detonation performance calculation into two components: timing and energy release. For the timing, the PB model uses a Detonation Shock Dynamics (DSD) surface propagation model, where the normal surface speed is a function of local surface curvature. For the energy release calculation and subsequent hydrodynamic flow evolution, a Pseudo-Reaction-Zone (PRZ) model is used. The PRZ model is similar to a reactive burn model in that it converts reactants into products at a finite rate, but it has a reaction rate dependent on the normal surface speed derived from the DSD calculation. The PRZ reaction rate parameters must be calibrated in such a way that the rate of energy release due to reaction in multi-dimensional geometries is consistent with the timing calculation provided by the DSD model. Our strategy for achieving this is to run the PRZ model in a detonation shock-attached frame in a compliant 2D planar slab geometry in an equivalent way to a reactive burn model, from which we can generate detonation front shapes and detonation phase speed variations with slab thickness. In this case, the D _n field used by the PRZ model is then simply the normal detonation shock speed rather than the DSD surface normal speed. The PRZ rate parameters are then iterated on to match the equivalent surface front shapes and surface phase speed variations with slab thickness derived from the target DSD model. For the purposes of this paper, the target DSD model is fitted to the performance properties of an idealised condensed-phase reactive burn model, which allows us to compare the detonation structure of the calibrated PRZ model to that of the originating idealised-condensed phase model.     

Shock initiation of composition B and C-4 explosives: Experiments and modeling

Shock initiation experiments with composition B and C-4 HE were performed to obtain in situ pressure gauge data for the purpose of providing the ignition and growth reactive flow model with proper modeling parameters. A 100-mm-bore propellant-driven gas gun was utilized to initiate the explosive charges containing manganin piezoresistive pressure gauge packages embedded in the explosive sample. Experimental data provided new information on the shock velocity-particle velocity relationship for each of the investigated material in their respective pressure range. The run-to-detonation distance points in the pop plot for these experiments showed agreement with previously published data, and ignition and growth modeling calculations resulted in a good fit to the experimental data. Identical ignition and growth reaction rate parameters were used for C-4 and composition B, and the composition B model also included a third reaction rate to simulate the completion of reaction by the TNT component. This model can be applied to shock initiation scenarios that have not or cannot be tested experimentally with a high level of confidence in its predictions. This paper was presented at the International Conference “Shock Waves in Condensed Media,” St. Petersburg, September, 2006. The text was submitted by the authors in English.     

On the mechanism of hotspot initiation of detonation

A mechanism of the initiation of hotspots in heterogeneous solid high explosives was considered. It was demonstrated that the growth of hotspots may be associated with the propagation of a thermal wave in the deflagration regime only at an early stage of the process. The growth at later stages occurs in the reactive shock regime, a finding that renders the assumption about a very high deflagration wave velocity redundant.     

不同起爆方式对含铝炸药水中爆炸近场冲击波压力的影响

 采用SJZ-30和GSJ-15型高速扫描相机,对端面点起爆、侧边点起爆和中心点起爆方式下,HLZY-1含铝炸药水中爆炸近场冲击波传播过程进行了实验观测,通过数字化方法得到了炸药近场冲击波沿狭缝方向的扫描曲线和冲击波压力变化曲线。研究表明,起爆方式对炸药水中爆炸初始冲击波峰值压力以及近场冲击波峰值压力的衰减有重要的影响。研究结果可以为水中兵器战斗部的设计以及毁伤效能评估提供参考。     

Development of an explosion from an initiation source in a liquid high explosive

A numerical analysis of the development of combustion and explosion from a reaction hotspot in the bulk and in a thin layer of a liquid explosive placed between two flat solid surfaces is performed. A comparison of the theoretical results with experimental data shows that a satisfactory agreement between the measured and calculated flame speeds is possible only under the assumption of a multifold increase in the burning surface area due to its instability. An estimate of the parameters of the shock wave generated by an accelerating flame shows that the mechanisms of shock-wave and cavitation initiation of detonation cannot be ignored in analyzing the regimes of unsteady combustion of liquid explosives.     

On the structure and accuracy of programmed burn

Accurate computation of the evolution of a (typically curved) detonation front in a complex geometry, and of the state behind it, is a practical problem in the design of devices that use high-energy explosives. Direct numerical simulations are infeasible: accuracy demands high resolution of the smallest scale (the reaction zone), which is typically several orders of magnitude smaller than the device scale. Programmed burn is an engineering alternative that has been shown to produce acceptable results at a fraction of the cost. The underlying algorithm prescribes the trajectory of the detonation front a priori and replaces the actual reaction zone by a mock up that is a few computational cells thick and in which the reaction rate is taken to be a constant. The state of the explosive at the end of the reaction zone is thereby computed at a relatively modest cost, and the bulk of the computational effort is reserved for the region behind the reaction zone wherein the products of detonation perform useful work. The reasons for the remarkable fidelity to which the physical situation is captured by the programmed burn are not well-understood. This investigation, aimed at achieving such an understanding, considers a model problem for a steady, curved detonation propagating down a rate stick. It examines the pseudo-reaction-zone structure of the programmed burn, studies the sensitivity of the state of the reaction products to the choice of the reaction zone length, and compares the results to those for the actual, physical reaction zone. Conclusions are drawn as to the causes behind the success of the programmed-burn algorithm. The analysis is based on the asymptotic limits of small front curvature and small departures from the Chapman–Jouguet speed. Results are presented for ideal as well as nonideal explosives.     

未反应JOB-9003炸药冲击Hugoniot关系测试

 利用“粒子速度对比法”实验技术,通过电磁粒子速度计测量了PMMA飞片同时撞击PMMA样品与待测炸药样品界面的粒子速度u₁和u₂,获得了未反应JOB-9003炸药的冲击Hugoniot关系;利用叠加原理和疏松材料冲击绝热线的计算方法,对未反应炸药的冲击绝热线进行了计算。计算结果与实验数据符合较好。     

Effect of the Al/O ratio on the Al reaction of aluminized RDX-based explosives

Aluminum(Al) powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal measurements and underwater explosion(UNDEX) experiments were conducted. Lithium fluoride(LiF) was added in RDX-based explosives, as a replacement of aluminum, and used in constant temperature calorimeter experiments and UNDEXs. The influence of aluminum powder on explosion heat(Qv) was measured. A rich supply of data about aluminum energy release rate was gained. There are other oxides(CO_2, CO, and H_2O) in detonation products besides alumina when the content of RDX is maintained at the same levels. Aluminum cannot fully combine with oxygen in the detonation products. To study the relationship between the explosive formulation and energy release, pressure and impulse signals in underwater experiments were recorded and analyzed after charges were initiated underwater. The shock wave energy(Esk), bubble energy(Eb), and total energy(Et) monotony increase with the Al/O ratio, while the growth rates of the shock wave energy,bubble energy, and total energy become slow.     

Forest Fire Detection via Feature Entropy Guided Neural Network

Forest fire detection from videos or images is vital to forest firefighting. Most deep learning based approaches rely on converging image loss, which ignores the content from different fire scenes. In fact, complex content of images always has higher entropy. From this perspective, we propose a novel feature entropy guided neural network for forest fire detection, which is used to balance the content complexity of different training samples. Specifically, a larger weight is given to the feature of the sample with a high entropy source when calculating the classification loss. In addition, we also propose a color attention neural network, which mainly consists of several repeated multiple-blocks of color-attention modules (MCM). Each MCM module can extract the color feature information of fire adequately. The experimental results show that the performance of our proposed method outperforms the state-of-the-art methods.     

凝聚炸药爆轰波在高声速材料界面上的折射现象分析

凝聚炸药爆轰在边界高声速材料约束下传播时,爆轰波会在约束材料界面上产生复杂的折射现象.本文针对凝聚炸药爆轰波在高声速材料界面上的折射现象展开理论和数值模拟分析.首先通过建立在爆轰ZND模型上的改进爆轰波极曲线理论给出爆轰波折射类型,然后发展一种求解爆轰反应流动方程的基于特征理论的二阶单元中心型Lagrange计算方法来数值模拟典型的爆轰波折射过程.从改进爆轰波极曲线理论和二阶Lagrange方法数值模拟给出的结果看出,凝聚炸药爆轰波在高声速材料界面上的折射类型有四种:反射冲击波的正规折射、带束缚前驱波的非正规折射、带双Mach反射的非正规折射、带λ波结构的非正规折射.     

Assessment of ForeFire/Meso-NH for wildland fire/atmosphere coupled simulation of the FireFlux experiment

Numerical simulations using a coupled approach between Meso-NH (Non-Hydrostatic) LES (Large Eddy Simulation) mesoscale atmospheric model and ForeFire wildland fire area simulator are compared to experimental data to assess the performance of the proposed coupled approach in predicting fine-scale properties of the dynamics of wildland fires. Meso-NH is a non-hydrostatic, large eddy simulation capable, atmospheric research model. ForeFire insures a front tracking of the fire front by means of Lagrangian markers evolving on the earth’s surface according to a physical rate-of-spread model. The atmospheric model forces the fire behavior through the surface wind field, whereas the fire forces the atmosphere simulation through surface boundary conditions of heat and vapor fluxes. The FireFlux experiment, an experimental 32 Ha burn of tall grass instrumented with wind profilers and thermocouples, was designed specifically to estimate the atmospheric perturbation introduced by wildland fire. Comparisons of the simulations at different resolutions with the large-scale experiment validate the chosen coupling methodology and the choice of a coupled approach with a meso-scale atmospheric model for the prediction of wildland fire propagation. Distinct fire propagation behavior is simulated between coupled and non-coupled simulation. While the simulations did not reproduce high frequency perturbations, it is shown that the atmospheric model captures well atmospheric perturbations induced by combustion at the ground level in terms of behavior and amplitude.