LARED-H程序的激光黑腔靶耦合数值模拟

LARED-H程序是一个可用于激光黑腔靶耦合数值模拟研究的二维辐射流体力学程序。黑腔等离子体所形成的复杂流场使单纯的拉格朗日网格在计算中产生严重扭曲，影响计算精度，并导致计算中断。拉氏加网格重分是计算激光黑腔靶耦合常用的算法。对LARED-H程序的积分网格重分方法在网格重构和物理量重映方面作了较大改进，并利用改进后的LARED-H程序模拟了“神光”-Ⅱ和“神光”-Ⅲ条件下的激光空腔靶耦合物理全过程。     

基于激光靶耦合问题的二阶精度重映算法

在现有二维激光靶耦合程序LARED-H中，用流体力学方程组描述等离子体的运动，流体计算以拉氏计算为主，经常由于网格的大变形导致数值计算提前终止。ALE方法是目前解决大变形问题中比较流行的方法，在二维空腔计算中，希望能在变形较大的地方采用欧拉区来解决大变形问题。高精度的重映算法是ALE算法中最重要的部分之一，本工作的目的就是研究适用于激光靶耦合问题的高精度重映算法。     

点火内爆靶辐射驱动不对称性全过程数值模拟

为满足分层掺杂点火内爆靶辐射驱动不对称性全过程物理分析的需求,在激光聚变二维总体程序LARED集成上发展了辐射输运建模下的多介质ALE方法-RTALE(Radiative Transfer Arbitrary-Lagrangian-Eulerian)。为提高多介质ALE方法的健壮性,发展了驰豫网格重构算法,该重构算法生成的新网格能自适应流场的变化。数值模拟了激波与气柱相互作用的RM不稳定性实验,模拟的气泡变形程度与试验结果基本一致,其中驰豫网格重构算法中的驰豫因子能够很好地反映流场密度梯度。基于辐射多群输运建模的LARED集成程序能够完整模拟辐射驱动不对称性条件下掺杂点火靶二维内爆过程,克服了传统ALE方法计算不下去和算不好的困难,界面变形程度也符合物理分析。     

斜入射激光平面靶耦合的数值模拟

LARED-H是一个柱对称二维三温非平衡辐射流体力学程序，主要用于黑腔物理研究，也可模拟正入射激光平面靶耦合过程，但无法模拟斜入射平面靶问题。实际上斜入射现象会经常发生，因此需要扩充LARED-H程序在直角坐标系下的功能，用于模拟斜入射激光平面靶耦合过程。引进拟直角坐标系，把直角坐标系与柱坐标系下的总体方程的差分格式统一，实现了直角坐标系下LARED-H程序的模拟能力。     

半导体多物理效应并行计算程序JEMS-CDS-Device设计与实现

针对复杂电磁环境下器件多物理效应机理研究需求,研发了半导体多物理效应并行计算程序JEMS-CDS-Device。介绍了JEMS-CDS-Device的架构设计与实现技术。程序基于非结构网格并行框架JAUMIN实现,采用有限体积法(FVM)离散,使用牛顿法全耦合求解"电-载流子输运-热"问题。程序采用"内核+算法库"形式架构,支持2维和3维非结构网格、千万自由度问题并行求解,支持物理方程、离散算法、材料物理模型等的扩展开发。     

激光支持等离子体流场的2维动态数值模拟

 采用高温气体（等离子体）电离度的一种近似计算方法，以及具有五阶精度的广义Godunov差分格式-加权本质无振荡格式，给出了高温气体状态方程的简便描述，并考虑激光与等离子体的相互作用和能量耦合模拟了强激光与固体靶相互作用时激光支持靶面等离子体流场的动态物理过程，并同理论模型结果进行了比较。结果表明：不考虑2维膨胀效应的理论模型结果比2维数值计算结果偏大，但两者只有接近一倍的差距，并无数量级的差别。考虑了膨胀效应的2维数值计算结果是可信的。     

激光相变烧蚀二维程序LHAP2D研制

激光相变烧蚀二维程序LHAP2D的物理方案给出了空气环境中强激光引起的金属靶相变烧蚀的二维整体物理图像，并从固态物质、液体材料、气体对激光反射、折射和吸收规律，热能传递，状态方程等方面对所涉及的复杂物理过程进行了详细描述，最后给出了含相变的可压缩、多尺度、多相流体力学方程组。该方案还重点对激光能量在靶的固、液、汽三相和环境空气中的沉积律进行了理论描述，物质的状态方程用Sesame库。强激光与靶相互作用所涉及的物理过程的特征时空尺度相差很大(可达数个量级)，并且还涉及空间上的强间断、大梯度分布和相变界面移动的动界面过程，对它进行数值模拟有极大的难度，尤其是扩展到二维情形以后。     

激光间接驱动惯性约束聚变二维总体程序——LARED集成程序

介绍了辐射流体力学程序LARED集成程序的物理背景、模型方程、数值方法和数值算例。该程序主要应用于激光间接驱动惯性约束聚变的二维整体模拟,兼顾激光直接驱动、辐射驱动靶丸内爆过程和流体不稳定性等物理过程的数值模拟。通过与实验数据、一维辐射流体力学程序进行比对,验证了程序的可靠性。该程序实现了多群输运建模下NIF点火靶的全过程数值模拟,并已应用于惯性约束聚变的物理研究。     

傅立叶变换与流体数值计算的耦合并行算法

针对傅立叶变换和流体数值计算耦合并行存在的问题,采用两种方式解决:多物理耦合通信方法和二维并行FFTW方法;并对这两种方法进行性能比较,结果表明:当处理器数目少时,采用多物理耦合通信方法计算效率高,当处理器上千时,采用二维并行FFTW方法可扩展性更好;最后,在上万处理机上采用上亿网格测试,并行效率达到50%,并给出数值模拟结果,验证了激光成丝现象.     

计算激光腔靶流场的EL—1D2D方法

针对激光腔靶内流场的复杂性给出了一种欧氏与拉氏格式相结合、一维与二维计算相结合的方法，我们把它称为ＥＬ－１Ｄ２Ｄ方法。这种方法在跟踪界面活动网格方法的基础上，建立了设置欧拉线以及在欧拉线的一侧进行网格自动合并的计算技术，从而适应了腔体内比较复杂的流动。数值试验的结果表明，用这种方法计算腔靶流场的运动可以得到合理的物理图象。     

刚体与SPH耦合的三维数值方法研究

 研究了刚性体与SPH（Smoothed Particle Hydrodynamics）方法相耦合的计算方法和技术,以此技术为核心,在原有三维综合拉氏程序CL3D的基础上,研制了适用于斜侵彻问题数值研究的刚性弹体与SPH靶体耦合计算的拉氏三维数值模拟程序CRSPH3D。针对金属材料编入了Johnson-Cook本构模型计算模块,针对混凝土材料编入了Johnson-Holmquist本构模型及与之配套的损伤模型和状态方程等的计算模块。用研制的计算程序对弹体分别正碰和斜碰穿透中厚铝靶和侵彻厚混凝土靶的过程进行了数值模拟计算和分析。结果表明,对于铝靶穿透问题,模拟计算得到的弹体剩余速度、弹体动能损失和贯穿图像与实验结果符合得较好。对于混凝土靶的侵彻问题也得到了与实验现象一致的、定性合理的图像。     

激光腔靶耦合二维辐射输运数值模拟

间接驱动激光聚变过程中,黑腔内物质处于非局域热动平衡(non-LTE)状态,而且辐射传输具有非平衡、各向异性等特点。为了精确描述黑腔辐射场的演化及其与物质的相互作用,最新研制的激光聚变二维总体LARED集成程序,基于non-LTE的多群辐射输运建模,首次实现了激光黑腔靶实验的全过程数值模拟。数值结果表明,辐射输运计算较好地反映了黑腔辐射场均匀性变化,腔壁光斑区与非光斑区X光发射强度比与实验测量值接近,靶丸压缩形状与实验图像定性一致。     

Numerical simulations of instabilities in the implosion process of inertial confined fusion in 2D cylindrical coordinates

In this paper, we introduce a multi-material arbitrary Lagrangian and Eulerian method for the hydrodynamic radiative multi-group diffusion model in 2D cylindrical coordinates. The basic idea in the construction of the method is the following: In the Lagrangian step, a closure model of radiation-hydrodynamics is used to give the states of equations for materials in mixed cells. In the mesh rezoning step, we couple the rezoning principle with the Lagrangian interface tracking method and an Eulerian interface capturing scheme to compute interfaces sharply according to their deformation and to keep cells in good geometric quality. In the interface reconstruction step, a dual-material Moment-of-Fluid method is introduced to obtain the unique interface in mixed cells. In the remapping step, a conservative remapping algorithm of conserved quantities is presented. A number of numerical tests are carried out and the numerical results show that the new method can simulate instabilities in complex fluid field under large deformation,and are accurate and robust.     

激光靶耦合过程中的激光能量沉积方程

 激光聚变靶物理研究用激光强率I随空间的变化来反映激光能量的沉积。目前激光靶物理研究使用的激光能量沉积方程在临界面处发散,讨论了造成这一非物理结果的原因,给出了合理的激光强度方程,并讨论了新旧两种激光强度方程对激光吸收的影响。     

The HyperCASL algorithm: A new approach to the numerical simulation of geophysical flows

We describe a major extension to the Contour-Advective Semi-Lagrangian (CASL) algorithm [D.G. Dritschel, M.H.P. Ambaum, A contour-advective semi-Lagrangian numerical algorithm for simulating fine-scale conservative dynamical fields, Quart. J. Roy. Meteorol. Soc. 123 (1997) 1097–1130; D.G. Dritschel, M.H.P. Ambaum, The diabatic contour advective semi-Lagrangian algorithm, Mon. Weather Rev. 134 (9) (2006) 2503–2514]. The extension, called ‘HyperCASL’ (HCASL), uses Lagrangian advection of material potential vorticity contours like CASL, but a Vortex-In-Cell (VIC) method for the treatment of diabatic forcing or damping. In this way, HyperCASL is fully Lagrangian regarding advection. A grid is used as in CASL to deal with ‘inversion’ (computing the velocity field from the potential vorticity field).     

An improved known vicinity algorithm based on geometry test for particle localization in arbitrary grid

The known vicinity algorithm based on the geometry test for the particle localization problem in the hybrid Eulerian–Lagrangian model was extended and enhanced aiming at the connected grids with convex polygon/polyhedral cells. Such extensions were achieved by proposing novel improvements. Specifically, a new “side function”, to determine the relative position of the particle and the cell, was introduced to build a more formal test process. In addition, a binary search method was developed to accelerate the particle in cell test and trajectory/face intersection test for grids consisting of arbitrary polygon/polyhedral cells. Further, the particle location problem without the known vicinity position was established and solved by special boundary treatment through considering the internal/external boundary and larger particle displacement in one single Lagrangian step. The improved algorithm was applied to the particle location problem with both two dimensional and three dimensional Eulerian grids. Additionally, the proposed algorithm was compared with the previous ones to exhibit its higher efficiency and broader application. Sample cases focusing the water impingement computation for aircraft icing were solved by adopting this algorithm assisted by the Lagrangian particle dynamics model, and the computational results were verified by the experiments.     

Augmented Algorithm for Generation of Constraints

It is found that Dirac's original consistency conditions do not suffice to generate all the secondary constraints and determine all the multipliers in front of the second-class constraints for the general singular Lagrangian sys tems. Cawley 's second counter example of Dirac's conjecture just has this feature. This may lead to the fact that the equivalence of Lagrangian and Hamiltonian formalism is not guaranteed and even dynamics of Hamil tonian formalism is not completely determined. In order to overcome the above difficulties, an augmen ted algorithm for generation of constraints-the algorithm of the extended consistency conditions is proposed. In this new algorithm, Cawley's second example is no longer a counter example of Dirac's conjecture.     

The discontinuous Petrov-Galerkin method for one-dimensional compressible Euler equations in the Lagrangian coordinate

In this paper, a Petrov-Galerkin scheme named the Runge-Kutta control volume (RKCV) discontinuous finite element method is constructed to solve the one-dimensional compressible Euler equations in the Lagrangian coordinate. Its advantages include preservation of the local conservation and a high resolution. Compared with the Runge-Kutta discontinuous Galerkin (RKDG) method, the RKCV method is easier to implement. Moreover, the advantages of the RKCV and the Lagrangian methods are combined in the new method. Several numerical examples are given to illustrate the accuracy and the reliability of the algorithm.     

Metric-based mesh adaptation for 2D Lagrangian compressible flows

In this paper, we present a method to compute compressible flows in 2D. It uses two steps: a Lagrangian step and a metric-based triangular mesh adaptation step. Computational mesh is locally adapted according to some metric field that depends on physical or geometrical data. This mesh adaptation step embeds a conservative remapping procedure to satisfy consistency with Euler equations. The whole method is no more Lagrangian.After describing mesh adaptation patterns, we recall the metric formalism. Then, we detail an appropriate remapping procedure which is first-order and relies on exact intersections.We give some hints about the parallel implementation. Finally, we present various numerical experiments which demonstrate the good properties of the algorithm.     

基于Riemann解的二维流体力学Lagrange有限点无网格方法

在高维流体力学计算中,对于多介质大变形等一类问题,采用有网格方法常遇到较大的困难.针对二维问题,研究了一种无网格方法——Lagrange有限点方法:在求解区域上设置适当的离散点集,视其中每一点为流体力学Lagrange点;对于点集的任一点,确定邻点集合,并基于该点同邻点集合的联系,应用Godunov方法将流体力学Lagrange方程进行离散;考虑到算法的稳健性,方法中可设置较多邻点并采用最小二乘法.将该方法应用于典型的数值算例,取得了良好效果.