一种便携式冲击波超压测试系统

针对现在军用和民用对爆破的测量需求,提出了一种基于现场可编程逻辑门阵列FPGA和ICP传感器的便携式冲击波超压测试系统。测试系统主要以FPGA为主控芯片,采用ICP压电传感器,包含信号放大调理电路,AD转换电路,存储器模块以及工作状态显示电路。系统具有光触发、节点互触发和多节点同步触发等多种触发方式,连续重触发功能,以及多次采集时FLASH分块存储功能。系统上位机是以VC++为开发工具设计的软件,用于对数据进行分析、处理和显示。实验结果表明系统工作可靠,操作简便,能够实现对爆破冲击波超压的测试。     

Supersonic flow characteristics in laser grooving

The gas flow structure in laser grooving has been evaluated by numerical simulation and experiments in this study. A nozzle designed with a specific arrangement of compound jets for laser grooving has been tested. For this nozzle configuration the compressible flow structure of a shock wave induced by a supersonic side jet has been predicted in a numerical simulation using FLUENT, a computational fluid dynamics code and visualized in the experiment where the wall pressure on the grooving zone was evaluated and measured for jets impinging on the substrate at varying attacking angles of the side jet. The results obtained numerically and experimentally were comparable. In addition, the relationships between the material removal efficiency and the flow structure have also been established. It transpired that the attacking angle made a significant and dramatic improvement on the flow structure and grooving appearance and that a large wall pressure with a clear grooving profile can be obtained for attacking angles between 40° and 50° in the present test setup.     

Autoignition of surrogate fuels at elevated temperatures and pressures

Autoignition of Jet-A and mixtures of benzene, hexane, and decane in air has been studied using a heated shock tube at mean post-shock pressures of 8.5 ± 1 atm within the temperature range of 1000–1700 K with the objective of identifying surrogate fuels for aviation kerosene. The influence of each component on ignition delay time and on critical conditions required for strong ignition of the mixture has been deduced from experimental observations. Correlation equation for Jet-A ignition times has been derived from the measurements. It is found that within the scatter of experimental data dilution of n-decane with benzene and n-hexane leads to slight increase in ignition times at low temperatures and does not change critical temperatures required for direct initiation of detonations in comparison with pure n-decane/air mixtures. Ignition times in 20% hexane/80% decane (HD), 20% benzene/80% decane (BD) and 18.2% benzene/9.1% hexane/72.7% decane (BHD) mixtures at temperature range of T  1450–1750 K correlate well with induction time of Jet-A fuel suggesting that these mixtures could serve as surrogates for aviation kerosene. At the same time, HD, BD and BHD surrogate fuels demonstrate a stronger autoignition and peak velocities of reflected shock front in comparison with Jet-A and n-decane/air mixtures.     

激光对金属铜微孔加工的热力学过程研究

采用纳秒激光脉冲对铜金属进行了打孔实验,对微孔形貌进行了观察并对其热力学过程进行了相应的分析。研究表明,微孔的形貌是由凹坑和周围隆起组成,坑深随着脉冲能量的增加而增加。热力学分析表明,激光辐照金属打孔需要两个基本条件：一是激光脉冲能量的沉积,使金属材料发生熔化、汽化以及电离等相变,使得材料更容易去除;激光等离子体作为二次热源会更有效把激光脉冲能量耦合到金属表面;二是激光等离子体的冲击波效应,这种效应会把发生相变的材料有效及时排出,从而有效形成微孔。     

乙烯着火延迟的激波管测量与分子碰撞理论分析

在75%和96%两个不同的稀释度下,测量了乙烯/氧气/氩气混合气的着火延迟时间,实验当量比为1,压力为1.3-3.0 atm,温度为1092-1743 K.实验结果表明,着火延迟时间的对数与温度倒数呈良好的线性关系,在两个稀释度下,着火延迟时间随着温度增加而减少.通过回归分析,得到了乙烯着火关联式.计算得乙烯着火延迟在96%稀释度时是75%稀释度的5倍.采用分子硬球碰撞模型,计算了不同稀释度下,乙烯与氧分子的碰撞次数,在96%稀释度下,乙烯与氧气分子碰撞次数为1.53×10²⁹/（s·cm³）,而在75%稀释度下,该碰撞次数增加为5.99×10³⁰/（s·cm³）,约为前者40倍,而着火延迟时间的差异在两条件下仅为5倍的关系,可能由于位阻因子的影响所致.     

A contribution to the great Riemann solver debate

The aims of this paper are threefold: to increase the level of awareness within the shock-capturing community of the fact that many Godunov-type methods contain subtle flaws that can cause spurious solutions to be computed; to identify one mechanism that might thwart attempts to produce very-high-resolution simulations; and to proffer a simple strategy for overcoming the specific failings of individual Riemann solvers.     

Computation and experimental validation of N_{2}-CH_{4}-Ar mixture flows behind normal shock wave

Different vibration-dissociation-vibration coupling models have been used to compute the nonequilibrium N-CH-Ar mixture flow behind a normal shock wave. A three-temperature model was used and the diffuse nature of vibrational relaxation at high temperatures was accounted for. The numerical results obtained with the Treanor and Marrone model (preferential or non preferential) and the Park model of vibration-dissociation-vibration coupling are compared. These results show that the temperatures and the concentrations are mainly affected by the value of the characteristic temperature U in the preferential model of Marrone and Treanor. An assessment of the more realistic model was realized by comparing numerical results with shock tube experiments. The influence of argon addition on the nonequilibrium emission of CN behind the shock wave was also numerically studied and compared to experimental measurements. Received 1 September 1995 / Accepted 10 December 1996     

Noh's constant-velocity shock problem revisited

We present the solutions to Noh's shock tube problem in planar, cylindrical, and spherical geometry. This problem has the well-deserved reputation of being challenging to numerical methods. Since the gas is initially cold there are infinitely many reflections of the shock between the fixed wall and the piston as the piston moves with constant velocity towards the wall. An implicit adaptive grid algorithm allows us, for the first time, to generate the complete solutions in these three geometries. We discuss them in detail, in particular follow the shock over many reflections, and perform numerical consistency checks. For the planar case the exact analytical solution is derived, and the numerical error in all physical quantities is found to be less than 1% on a 100 grid-point computational domain. For the converging geometries an approximate analytical theory is presented, and the deviations between the theory and the numerical results are found to be less than 10% on the same domain. A substantial part of this total error is due to errors in the approximate analytical results. We discuss the physics of the shock reflection in the three geometries, and analyze in particular the finite amount of entropy that is produced after the the first shock reflection. In an appendix we present some details of our code and demonstrate that the adaptive grid permits us to carry out computations of extreme precision. The reliability of our solutions in all three geometries allows them to become demanding tests for 2D and 3D codes. Received 16 April 1996 / Accepted 15 August 1996     

Boundary linear integral method for compressible potential flows

A boundary linear integral method based on Green function theory has been developed to solve the full potential equation for subsonic and transonic flows. In this integral method, potential values in the flow region are determined by potential values represented by boundary integrals and a volume integral. The boundary potential values are obtained by implementing the boundary integrals along boundary segments where a linear potential relation is assumed. The volume integral is evaluated in a grid generated by finite element discretization. The volume integral is evaluated only outside the body. Therefore there is no extra boundary treatment required for evaluation of the volume integral. The source term is assumed to be constant in an element integral volume. The volume integral needs to be evaluated only once and can be stored in computer memory for further usage.     

Extreme Shock Models

The standard assumptions in shock models are that the failure (of the system) is related either to the cumulative effect of a (large) number of shocks or that failure is caused by a shock which is larger than a certain critical level. The present paper is devoted to the second kind. Here the standard setting is that the shocks X_k, k 1, and the times between the shocks Y_k, k 1, are independent, identically distributed random vectors (X_k, Y_k), k 1. In particular, X_k and Y_k may well be dependent (the typical case). The main object of interest is the time to failure, T_(t), where T_n = _kn Y_k and (t) is the first exceedance time, viz. the first time that X_k > t. We derive moment relations and asymptotic distributions of T_(t) as t increases in such a way that P{X₁} > t} tends to 0. A final section discusses some extensions; more general events of failure, the non-i.i.d. case, and point process convergence for a particular case.