Numerical study on the case effect of a bomb air explosion

When considering the bomb explosion damage effect, the air shock wave and high-speed fragments of the bomb case are two major threats. In experiments, the air shock wave was studied by the bare ex-plosives superseding the real cased bomb; in contrast, the bomb case influence was ignored to reduce risk. The air explosion simulations of the MK84 warhead with and without the case were conducted. The numerical simulation results showed that the bomb case significantly influenced the shock wave generated by the bomb: the spatial distribution of shock wave in the near field changed, and the peak value of shock wave was reduced. Breakage of the case and kinetic energy of the fragmentation consumed 3 and 38% of the explosion energy, respectively. The increasing factors of the peak over-pressure induced by the bare explosive on the ground and in the air were 1.43-3.04 and 1.37-1.57, respectively. Four typical stages of case breakage were defined. The mass distribution of the fragments follows the Mott distribution. The initial velocity distribution of the fragments agreed well with the Gurney equation.     

Influence of propagation direction on operation performance of rotating detonation combustor with turbine guide vane

Due to the pressure gain combustion characteristics, the rotating detonation combustor (RDC) can enhance thermodynamic cycle efficiency. Therefore, the performance of gas-turbine engine can be further improved with this combustion technology. In the present study, the RDC operation performance with a turbine guide vane (TGV) is experimentally investigated. Hydrogen and air are used as propellants while hydrogen and air mass flow rate are about 16.1 g/s and 500 g/s and the equivalence ratio is about 1.0. A pre-detonator is used to ignite the mixture. High-frequency dynamic pressure transducers and silicon pressure sensors are employed to measure pressure oscillations and static pressure in the combustion chamber. The experimental results show that the steady propagation of rotating detonation wave (RDW) is observed in the combustion chamber and the mean propagation velocity is above 1650 m/s, reaching over 84% of theoretical Chapman-Jouguet detonation velocity. Clockwise and counterclockwise propagation directions of RDW are obtained. For clockwise propagation direction, the static pressure is about 15% higher in the combustor compared with counterclockwise propagation direction, but the RDW dominant frequency is lower. When the oblique shock wave propagates across the TGV, the pressure oscillations reduces significantly. In addition, as the detonation products flow through the TGV, the static pressure drops up to 32% and 43% for clockwise and counterclockwise propagation process respectively.     

Blast resistance evaluation of urban utility tunnel reinforced with BFRP bars

To improve corrosion-resistance of shallow-buried concrete urban utility tunnels(UUTs),basalt fiber reinforced polymer(BFRP)bars are applied to reinforce UUTs.As the UUT must have excellent survival capability under accidental explosions,a shallow-buried BFRP bars reinforced UUT(BBRU)was designed and constructed.Repetitive blast experiments were carried out on this BBRU.Dynamic responses,damage evolutions and failure styles of the BBRU under repetitive explosions were revealed.The tunnel roof is the most vulnerable component and longitudinal cracks develop along the tunnel.When the scaled distance is larger than 1.10 m/kg1/3,no cracks are observed in the experiments.When the BBRU is severely damaged,there are five cracks forming and developing along the roof.The roof is simplified as a clamped-supported one-way slab,proved by the observation that the maximum strain of the transverse bar is much larger than that of the longitudinal bar.Dynamic responses of the roof slab are predicted by dynamic Euler beam theory,which can consistently predict the roof displacement under large-scaled-distance explosion.Compared with the UUT reinforced with steel bars,the BBRU has advantages in blast resistance with smaller deflections and more evenly-distributed cracks when the scaled distance is smaller than 1.260 m/kg1/3 and the steel bars enter plastic state.Longer elastic defamation of the BFRP bars endows the UUT more excellent blast resistance under small-scaled-distance explosions.     

耐1200℃陶瓷瓦重复使用性能

针对目前比较成熟的耐1 200℃陶瓷瓦开展了1 200℃多次重复热处理,研究了陶瓷瓦的结构和性能演变行为和重复使用性能。结果表明:1 200℃热处理20次后,耐1 200℃陶瓷瓦表现出良好的宏观热稳定性;重复热处理过程中,纤维间烧结,黏接熔融和石英纤维析晶及晶粒长大,使纤维直径发生变化,出现缩颈,进而导致了Z向收缩,收缩率达14%,从而使得压缩强度略有增大,隔热性能降低;经过1 260℃、11次单面辐射加热后,Z向收缩率为5.58%,隔热效果降低了7.59%,但隔热材料能够在6次重复加热后保持材料隔热性能不降低。     

MPI并行程序中通信等待问题的诊断方法及其应用

随着并行规模的扩大,现有通信等待问题的诊断方法存在内存开销大、测量时间开销大等问题。通过对现有通信等待问题诊断方法的深入分析,同时考虑测量开销可控的实际需求,建立基于热点函数的通信等待问题诊断模型。基于上述模型,总结出一种更精简、更实用的通信等待问题诊断方法。将该诊断方法分别应用到二维LARED集成、LARED-S、LAP3D等大规模MPI并行程序的通信等待问题诊断过程,应用效果表明本诊断方法可精确定位导致通信等待问题的关键代码段,给出的优化方案及性能提升空间对于后续的程序改进具有参考价值,其中根据诊断结果优化后的LARED-S程序性能提升32%,通信等待时间减少44%。