直接驱动柱内爆流体力学不稳定性数值模拟

 给出了LARED-S程序对直接驱动柱内爆流体力学不稳定性模拟的物理方程，介绍了一种直接驱动柱内爆靶的结构，给出了模拟中使用活动网格追踪和其他一些需要注意的问题。对OMEGA激光器直接驱动柱内爆实验物理模型进行了简化处理：使用理想气体状态方程，假设烧蚀层、标识层和内部填充材料为同一介质，只在密度上有差别；采用全电离和单温近似，在内爆过程中仅考虑热传导过程而忽略辐射和非局域电子热传导等过程的影响。模拟结果表明：LARED-S程序与LASNEX程序的计算结果基本上符合。     

一种四面体网格局部自适应方法在有限元中的应用

通过提出一种针对三维四面体网格的区域整形技术，给出了一种简便实用的四面体网格局部自适应加密方法，并将其与流量修正有限元法结合，应用于三维高速流的计算     

Fluid–structural interaction with application to rocket engines

The objective of this work is to develop a finite element model for studying fluid–structure interaction. The geometrically non‐linear structural behaviour is considered and based on large rotations and large displacements. An arbitrary Lagrangian–Eulerian (ALE) formulation is used to represent the compressible inviscid flow with moving boundaries. The structural response is obtained using Newmark‐type time integration and fluid response employs the Lax–Wendroff scheme. A number of numerical examples are presented to validate the structural model, moving mesh implantation of the ALE model and complete fluid–structure interaction. Copyright © 1999 John Wiley & Sons, Ltd.     

柱几何Rayleigh-Taylor不稳定性的数值模拟

 给出了柱几何中流体力学方程组及其在数值模拟中采用的计算方法。对二维柱几何Rayleigh-Taylor不稳定性进行数值模拟，在线性阶段与线性理论符合得很好；不稳定性增长进入非线性区域的阈值依赖于界面的位置，并且明显不同于平面情况。     

Formulation,analysis and numerical study of an optimization-based conservative interpolation (remap) of scalar fields for arbitrary Lagrangian–Eulerian methods

We develop and study the high-order conservative and monotone optimization-based remap (OBR) of a scalar conserved quantity (mass) between two close meshes with the same connectivity. The key idea is to phrase remap as a global inequality-constrained optimization problem for mass fluxes between neighboring cells. The objective is to minimize the discrepancy between these fluxes and the given high-order target mass fluxes, subject to constraints that enforce physically motivated bounds on the associated primitive variable (density). In so doing, we separate accuracy considerations, handled by the objective functional, from the enforcement of physical bounds, handled by the constraints. The resulting OBR formulation is applicable to general, unstructured, heterogeneous grids. Under some weak requirements on grid proximity, but not on the cell types, we prove that the OBR algorithm is linearity preserving in one, two and three dimensions. The paper also examines connections between the OBR and the recently proposed flux-corrected remap (FCR), Liska et al. [1]. We show that the FCR solution coincides with the solution of a modified version of OBR (M-OBR), which has the same objective but a simpler set of box constraints derived by using a “worst-case” scenario. Because M-OBR (FCR) has a smaller feasible set, preservation of linearity may be lost and accuracy may suffer for some grid configurations. Our numerical studies confirm this, and show that OBR delivers significant increases in robustness and accuracy. Preliminary efficiency studies of OBR reveal that it is only a factor of 2.1 slower than FCR, but admits 1.5 times larger time steps.     

Effect of Ni doping on the structural and magnetic properties of FePt nanoparticles

A serial of FePtNi nanoparticles were investigated on their crystal structure and magnetic properties. The FePtNi nanoparticles were synthesized simultaneously by the reduction of iron (III) acetylacetonate, platinum (II) acetylacetonate and nickel (II) acetylacetonate with 1,2-hexadecanediol as the reducing agent. The X-ray diffraction patterns indicate that the addition of 8, 12, 17 at% Ni in FePt nanoparticles suppressed the transformation of the particles from disorder face-centered cubic to order face-centered tetragonal L1₀-phase under annealing treatment. However, further increasing Ni contents to 21 at%, the nanoparticle transformed to L1₂ phase. Doping of Ni into the FePt compound system may decrease coercivity and crystal anisotropy energy. A maximum coercivity of 7 KOe at room temperature was obtained for (Fe₅₂Pt₄₈)₉₂Ni₈ nanoparticles after annealing at 600 °C for 30 min.     

Improvements in speed for explicit,transient compressible flow solvers

Several explicit high‐resolution schemes for transient compressible flows with moving shocks are combined in such a way so as to achieve the highest possible speed without compromising accuracy. The main algorithmic changes considered comprise the following:

• replacing limiting and approximate Riemann solvers by simpler schemes during the initial stages of Runge–Kutta solvers, and only using limiting and approximate Riemann solvers for the last stage;
• automatically switching to simpler schemes for smooth flow regions;
• automatic deactivation of quiescent regions; and
• unstructured grids with cartesian cores or embedded cartesian grids.

The results from several examples demonstrate that speedup factors of 1:4 are attainable without compromising the accuracy of the traditional FCT schemes. Copyright © 2007 John Wiley & Sons, Ltd.     

二维对流扩散方程满足最大值原理的MMOCAA差分方法

Using FCT idea,the non-oscillation MMOCAA(The modified method of characteristics with adjusted advection) finite difference scheme satisfing the discrete maximum principle for convection-dominated diffusion equation in 2D is constructed.The scheme is free from oscillation,with which the problem is solved by the MMOCAA difference method based on 2-order Lag-range interpolation proposed by Jim.Douglas, Jr.(Numer.Math.,1999,83:353-369.). The error analysis of the new scheme and numerical example are given in the paper.The numerical example shows that the scheme has smaller numerical viscosity than the MMOCAA difference method based on bilineax Lagrange interpolation.