可识别微层裂前界面的阶跃信号电探针测试技术

受微喷射物质干扰,现常用的测试技术难以对复杂结构金属样品微层裂前界面进行准确识别,针对该问题提出阶跃信号电探针测试技术。对传统电探针受微喷射物质干扰出现不正常放电现象的原理进行分析,设计阶跃信号形成电路。开展锡金属样品爆轰实验,对比传统电探针和阶跃信号电探针的放电波形,分析阶跃信号电探针数据解读方法,联合X光测试技术,对阶跃信号电探针放电波形阶跃信号高电平出现时刻进行检定。实验结果表明:阶跃信号电探针测试技术能够识别微喷射物质的干扰,可用于爆轰加载下金属样品微层裂前界面的识别。     

内部爆炸作用下钢筒变形过程的电探针测量技术

为了研究圆柱形爆炸容器在炸药爆炸作用下的变形过程,设计了电探针测量内部爆炸作用下钢筒变形的方法。采用数值模拟方法进行预估,在钢筒的中心进行了120g TNT和180g TNT当量球形装药下的爆炸加载实验,获得了爆炸不同时刻钢筒径向位移随时间的变化关系,电探针测量钢筒最大变形与实验后钢筒变形测量结果较好吻合。

     

滑移爆轰驱动下飞板运动姿态的连续电阻测试法

飞板运动姿态的测定是爆炸焊接机理研究的基础,针对传统电测方法存在干扰因素多、易产生弯曲波等缺陷,设计了一种适用于野外大当量下爆炸焊接飞板姿态实验的连续电阻测试方法。研制了3种不同结构的梯形支架型连续电阻探针元件,利用有限元程序分析了探针的导通压力和响应时间,在此基础上,对3种探针实施了爆炸焊接实验,实验结果表明:金属丝网型探针元件具有最优的导通效果,各段测试曲线光滑无毛刺。以该探针数据计算获得了待测飞板的运动姿态曲线,并与Richter简化模型下的近似计算公式结果进行了对比,两者基本一致。所述测试方法实现了炸药爆速和飞板变形曲线的连续、可靠和快速测量,为滑移爆轰驱动问题、爆轰产物状态方程等的研究提供了测试方法补充。     

内聚滑移爆轰加载下金属圆管压缩过程的工程分析

对内聚滑移爆轰加载下圆管压缩运动过程进行工程分析,分析解与数值模拟结果吻合。利用工程模型得到了不同管道参数（包括内径、厚度）下管道封闭所需要的炸药量和封闭时间表达式,可为相关研究工作提供参考。

     

爆炸加载下金属缝隙射流定量诊断实验研究

爆轰加载下金属飞片缝隙处会有射流产生,金属缝隙射流的喷射速度可达数千米/秒,而其射流线密度只有几个mg/cm量级。采用高速摄影以及脉冲软X光照相方法对缝隙射流进行了动态观测和(半)定量测量,通过不同条件下的系列实验获得了金属射流喷射特性和射流质量随飞片材料、加载压力、缝隙宽度以及加载方式等的变化规律,通过实验数据分析拟合,初步给出了射流质量随各影响因素变化的经验型定标率模型。     

微喷射物质作用下脉冲信号电探针的放电机理

针对脉冲信号电探针在微喷射物质作用下出现的“非正常”放电现象,提出了微喷射物质K+R_x等效电路模型,用以解释微喷射物质导通电探针放电机理。开展爆轰实验,联合X射线测试技术,确定了电探针放电区域处于微喷射区与微层裂区的过渡地带,并发现电探针的3类“非正常”放电现象。建立电路仿真模型,将微喷射物质等效成K+R_x电路,调节K+R_x等效电路模型参数,模拟电探针的3类“非正常”放电现象。仿真结果表明,K+R_x等效电路模型很好地解释了微喷射物质作用下脉冲信号电探针的放电机理。     

爆轰波对碰加载下平面金属样品动载行为实验研究

进行冲击波对碰加载简易平面金属Sn和W样品实验,采用X射线照相和激光干涉测速系统进行联合诊断,给出了2种材料冲击波对碰区表面微喷及主体破碎物质的直观图像,研究了Sn和W样品对碰区动力学行为,并比较分析2种材料对碰区特征的异同,给出了定性物理解释,实验结果可为爆轰波对碰加载下材料动力学特性的理论研究提供数据支撑。     

爆轰加载下柱壳断裂时刻微小差异测量方法

对于断裂时刻差异较小的对比实验,提出一种判读方法:同时采用高速摄影和干涉测速,利用高速摄影判读壳体断裂时刻应变,利用干涉测速获取壳体位移及应变曲线,两者结合得出较为精确的壳体断裂时刻差异。利用该方法得出45钢柱壳在JO-9159和JOB-9003两种炸药加载下断裂时间相差0.45 μs,钨合金柱壳在两种炸药加载下的断裂时间相差0.39 μs。同时该方法可以推广应用于单发壳体膨胀断裂实验中,更精确测定壳体的断裂时刻。     

爆轰加载下金属材料的微层裂现象

通过在LiF窗口撞击镀膜面增加一薄层LiF和对LiF窗口反光面进行漫反射面镀膜处理的方法,对传统Asay窗诊断技术进行了改进,获得了微层裂物质高质量的实验信号。将改进后Asay窗技术与中能X射线照相及激光干涉测速技术相结合,实验给出了熔化状态下Sn材料微层裂物质不同时刻的密度空间分布图像及演化特征,且不同测试技术诊断结果半定量吻合。得到Sn材料微层裂物质的清晰物理图像,可为微层裂物理机理的认识和物理建模提供实验数据。     

爆轰加载下银气溶胶源项实验研究

为研究钚气溶胶生成规律及源项分布,提出了一种密封环境下的金属气溶胶源项实验方法,利用爆炸容器及气溶胶采样器等实验设备,开展了钚替代材料银的气溶胶源项生成实验,分析了空气动力学直径小于10 μm的银气溶胶源项分布特性,并与外场扩散试验中钚气溶胶数据进行了对比。进一步采用不同炸药及加载装置,对相同银片样品进行加载实验,研究了加载峰值压力对银气溶胶源项分布的影响。研究结果表明,金属银可作为替代材料研究爆轰加载条件下钚气溶胶的源项参数,在一定实验条件下,二者归一化积累质量分布具有较高的一致性;爆轰加载产生的银气溶胶中,较小粒径气溶胶质量含量较高。气溶胶总量与加载峰值压力呈二次函数分布,当峰值压力超过某个临界值时,气溶胶总量将达到极值;此外,通过对同发次实验的3次不同采样数据进行分析,发现了较明显的气溶胶凝并和沉降现象。     

阶跃函数高精度逼近的结构拓扑优化方法

为了提高ICM(Independent Continuous and Mapping,即独立、连续及映射)方法求解结构拓扑优化问题的效率,本文改进了阶跃函数及其反函数的近似逼近函数——磨光函数和过滤函数。首先,分别对ICM方法的磨光函数和过滤函数按其近似性质进行了分类,分别提出了左磨函数及上磨函数和快滤函数、慢滤函数诸概念。然后得到了区分左磨函数和上磨函数、快滤函数和慢滤函数的两个判别定理;并得到了上磨函数、快滤函数、左磨函数及慢滤函数的对应定理。进而给出了磨光函数和过滤函数的使用准则及构造方法。采用高精度逼近阶跃函数的指数类函数做左磨函数,建立近似程度更高的结构拓扑优化模型。上述策略带来了模型非线性程度的提高,增加了求解难度。为此,针对该模型给出了精确对偶映射下的序列二次近似解法。最后,以位移约束下结构重量最轻化问题为例,叙述了相应的算法。与以往采用幂函数做磨光函数时算例结果的比较表明,该模型的提法合理,算法更加有效。由于提高了对阶跃函数及其反函数的逼近程度,从而显著减少了优化迭代的次数。     

Optimization study of spray detonation initiation by electric discharges

Development of air-breathing pulse detonation engines is faced with a challenging problem of detonation initiation in fuel sprays at distances feasible for propulsion applications. Extensive experimental study on initiation of a confined n-hexane spray detonation in air by electric discharges is reported. It is found that for direct initiation of spray detonation with minimal energy requirements (1) it is worth to use one discharger located near the closed end of a detonation tube and at least one additional discharger downstream from it to be triggered in-phase with primary shock wave arrival; (2) the discharge area should be properly insulated to avoid electric loss to metal tube walls; (3) discharge duration should be minimized to at least 50 μs; (4) discharge channel should preferably occupy a large portion of a tube cross-section; (5) test tube should be preferably of a diameter close to the limiting tube diameter; (6) gradual transition between the volume with electric discharger and the tube should be used; and (7) a powerful electric discharger utilized for generating a primary shock wave can be replaced by a primary shock wave generator comprising a relatively low-energy electric discharger, Shchelkin spiral, and tube coil. With all these principles implemented, the rated electric energy of about 100 J was required to initiate n-hexane spray–air detonation in a 28-mm tube at a distance of about 1 m from the atomizer. PACS 02.60.Cb; 05.10.Ln; 47.11.+j; 47.15.Cb; 47.40.Nm This paper was based on work that was presented at the 19th Inter-national Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27 - August 1, 2003     

Experimental study on the flow field behind a backward-facing step using a detonation-driven shock tunnel

The supersonic combustion RAM jet (SCRAM jet) engine is expected to be used in next-generation space planes and hypersonic airliners. To develop the engine, stabilized combustion in a supersonic flow field must be attained even though the residence time of flow is extremely short. A mixing process for breathed air and fuel injected into the supersonic flow field is therefore one of the most important design problems. Because the flow inside the SCRAM jet engine has high enthalpy, an experimental facility is required to produce the high-enthalpy flow field. In this study, a detonation-driven shock tunnel was built to produce a high-enthalpy flow, and a model SCRAM jet engine equipped with a backward-facing step was installed in the test section of the facility to visualize flow fields using a color schlieren technique and high-speed video camera. The fuel was injected perpendicularly to a Mach 3 flow behind the backward-facing step. The height of the step, the injection distance and injection pressure were varied to investigate the effects of the step on air/fuel mixing characteristics. The results show that the recirculation region increases as the fuel injection pressure increases. For injection behind the backward-facing step, mixing efficiency is much higher than with a flat plate. Also, the injection position has a significant influence on the size of the recirculation region generated behind the backward-facing step. The schlieren photograph and pressure histories measured on the bottom wall of the SCRAM jet engine model show that the fuel was ignited behind the step.Communicated by K. Takayama PACS 47.40.Ki     

Open-channel waves generated by propagation of a discontinuous wave over a bottom step

This paper presents the results of theoretical and experimental studies of open-channel waves generated by the propagation of a discontinuous dam-break wave over a bottom step. The cases where the initial tailwater level is higher than the step height (the step is under water) and where this value is smaller than the step height (at the initial time, water is absent on the step) are considered. Exact solutions are constructed using modified first-approximation equations of shallow-water theory, which admit the propagation of discontinuous waves in a dry channel. On the stationary hydraulic jump formed above the bottom step, the total free-stream energy is assumed to be conserved. These solutions agree with experimental data on various parameters (types of waves, wave propagation velocity, asymptotic depths behind the wave fronts). __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 31–44, January–February, 2008.     

Computation of backward-facing step flows by a second-order Reynolds stress closure model

This paper scrutinizes the predictive ability of the differential stress equation model in complex shear flows. Two backward-facing step flows with different expansion ratios are solved by the LRR turbulence model with an anisotropic dissipation model and the near-wall regions of the separated side resolved by a near-wall model. The computer code developed for solving the transport equations is based on the finite-volume-finite-difference method. In the numerical solution of the time-averaged momenum equations the Reynolds stresses are treated partially as a diffusion term and partially as a source term to avoid numerical instability. Computational results are compared with experimental data. It is found that the near-wall region of the separated side resolved by the near-wall model, the LRR model with a simple modification of an anisotropic dissipation model can predict backward step flows well.     

Local velocity measurements in a thermally-stratified sodium mixing layer using a permanent-magnet probe

Mean and fluctuating velocities have been measured in a sodium mixing layer experiment, i.e. in a fluid with very low Prandtl number (Pr10⁻²), with a miniature permanent-magnet velocity probe in the presence of strong temperature gradients. A mathematical model for the probe, based upon Faraday's law of induction and including thermoelectric as well as inertia effects due to the finite response time of thermocouples, is presented together with a new dynamic method to compensate for these effects. The sensitivity of the four different probes used in this experiment is in the range of 81–65 (μV/ms⁻¹). Electrical pertubations arising from large-scale thermoelectric effects inside the test section and their influence on the velocity signal are also discussed. The electronic measurement system, combining low noise and high resolution, was specially developed to match the experimental requirements. With this system it was possible to measure velocity RMS-values down to 1 mm/s corresponding to a voltage of 100 nV, and mean velocities with an accuracy of about 6 mm/s. This paper deals with the peculiarities of the measurement technique and its performance, but does not analyze the experimental results, which will be presented in a separate publication.     

Interaction of a solitary wave and a front step simulated by level set method

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