Absorption of shocked benzene

Abstract

We used absorption spectroscopy to observe decomposition of benzene (C₆H₆) subjected to the passage of strong shock waves generated by projectile impact. These measurements were made using a recently developed double-beam, double-pass, fiber-optic-coupled apparatus. Near 13 GPa, we observe absorption throughout most of the visible region, with strong absorption occurring for wavelengths below 400 nm. The absorption is most likely due to a combination of molecular absorption and Mie scattering from carbon particles formed as a result of shock decomposition.     

Adaptive Runge–Kutta discontinuous Galerkin method for complex geometry problems on Cartesian grid

A Cartesian grid method using immersed boundary technique to simulate the impact of body in fluid has become an important research topic in computational fluid dynamics because of its simplification, automation of grid generation, and accuracy of results. In the frame of Cartesian grid, one often uses finite volume method with second order accuracy or finite difference method. In this paper, an h‐adaptive Runge–Kutta discontinuous Galerkin (RKDG) method on Cartesian grid with ghost cell immersed boundary method for arbitrarily complex geometries is developed. A ghost cell immersed boundary treatment with the modification of normal velocity is presented. The method is validated versus well documented test problems involving both steady and unsteady compressible flows through complex bodies over a wide range of Mach numbers. The numerical results show that the present boundary treatment to some extent reduces the error of entropy and demonstrate the efficiency, robustness, and versatility of the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.     

Development and validation of a SUPG finite element scheme for the compressible Navier–Stokes equations using a modified inviscid flux discretization

This paper considers the streamline‐upwind Petrov–Galerkin (SUPG) method applied to the unsteady compressible Navier–Stokes equations in conservation‐variable form. The spatial discretization, including a modified approach for interpolating the inviscid flux terms in the SUPG finite element formulation, and the second‐order accurate time discretization are presented. The numerical method is discussed in detail. The performance of the algorithm is then investigated by considering inviscid flow past a circular cylinder. Validation of the finite element formulation via comparisons with experimental data for high‐Mach number perfect gas laminar flows is presented, with a specific focus on comparisons with experimentally measured skin friction and convective heat transfer on a 15° compression ramp. Copyright © 2007 John Wiley & Sons, Ltd.     

用冲击压缩数据计算物质结合能的一个简便解析方法

 在材料性质满足：（1）可用波恩-迈耶势描述其结合能；（2）自由电子对热能的贡献可忽略不计；以及（3）冲击波速度关系式可用直线关系描述的条件下，本文导出了一个用冲击绝热线数据直接计算该材料结合能和格临爱森物态方程的简便解析公式。给出了用本文方法计算Be，Al，Cu，Ta，U等十七种金属的冷能和冷压方程的结果。将本文结果与徐锡申等和Zharkov等的数值计算结果相比较，发现在冲击压缩测量的实验误差范围内，大多数金属的符合程度是比较好的，但Be，Ni和Pb三种金属除外。本文中对上述偏差的可能原因也做了讨论。     

电子束辐照硬铝产生热击波及层裂的估算

 本文对LY-12铝受到强流低能相对论电子束辐照时产生的热击波及层裂效应进行了估算。在预估中等能量沉淀产生材料的动态响应时必须适当地考虑熔化过程。我们所用的状态方程是GRAY三相状态方程，它对熔化区域中的金属作了详细且在热力学上更为完善的描述。将计算值同实验结果进行比较表明，二者基本上是一致的。     

烟囱纵向冲击断裂试验与分析

本通过楔形烟囱模型、在纵向冲击波作用下烟囱断裂位置实验和分析，给出纵向冲击只能产生一道环向断裂，断裂位置与输入冲击波作用周期和烟囱本身固有周期之比有关的结论。     

A compact high‐order HLL solver for nonlinear hyperbolic systems

We present a new finite‐volume method for calculating complex flows on non‐uniform meshes. This method is designed to be highly compact and to accurately capture all discontinuities that may arise within the solution of a nonlinear hyperbolic system. In the first step, we devise a fourth‐degree Hermite polynomial to interpolate the solution. The coefficients defining this polynomial are calculated by using a least‐square method. To introduce monotonicity conditions within the procedure, two constraints are added into the least‐square system. Those constraints are derived by locally matching the high‐order Hermite polynomial with a low‐order TVD polynomial. To emulate these constraints only in regions of discontinuities, data‐depending weights are defined; these weights are based upon normalized indicators of smoothness of the solution and are parameterized by an O(1) quantity. The reconstruction so generated is highly compact and is fifth‐order accurate when the solution is smooth; this reconstruction becomes first order in regions of discontinuities. In the second step, this reconstruction is inserted in an HLL approximate Riemann solver. This solver is designed to correctly capture all discontinuities that may arise into the solution. To this aim, we introduce the contribution of a possible contact discontinuity into the HLL Riemann solver. Thus, a spatially fifth‐order non‐oscillatory method is generated. This method evolves in time the solution and its first derivative. In a one‐dimensional context, a linear spectral analysis and extensive numerical experiments make it possible to assess the robustness and the advantages of the method in computing multi‐scale problems with embedded discontinuities. Copyright © 2008 John Wiley & Sons, Ltd.     

BaCO3和TiO2粉末混合物冲击压缩性和BaTiO3冲击合成的实验研究

 利用高能炸药爆轰驱动冲击波、狭缝扫描闪光隙高速照相技术和阻抗匹配解原理，在10~100 GPa压力范围内，测量了BaCO₃和TiO₂粉末混合物的冲击绝热数据。同时，利用轴对称柱面和平面爆轰装置，进行了该混合物样品的冲击后回收实验和回收样品的X射线衍射分析，考察BaTiO₃的冲击合成。测量出的冲击绝热数据，以冲击波压力和比容平面上的结果为例，在约30和45 GPa两个压力值时，比容发生明显跃变。冲击绝热数据与回收样品X射线衍射分析结果相结合，判断出，这两个跃变分别对应于TiO₂从锐钛矿相转变到高压β-TiO₂相，BaCO₃与TiO₂开始急剧化学反应合成出BaTiO₃并放出CO₂。此外，在压力为10 GPa左右作回收实验，其回收样品的X射线衍射分析表明TiO₂由锐钛矿相完全转变为金红石相。     

Velocity variation of internal shock waves in gamma ray bursts: Observational properties

The work uses the data in the TTS mode of BATSE to analyze the time lags and pulse widths of GRB960113 and GRB960722 in high as well as low energy bands. The results show that their time lags increase monotonously. This phenomenon can reasonably be interpreted with the model of internal shock waves of γ-ray bursts (GRB). Perhaps we obtain the direct observational evidence for the fireball model of GRBs for the first time.