Monte Carlo Simulation of Particle Interactions at High Dynamic Range: Advancing beyond the Googol
Monte Carlo Simulation of Particle Interactions at High Dynamic Range: Advancing beyond the Googol
复制标题
高动态范围内粒子相互作用的蒙特卡罗模拟：超越古戈尔
DOI：
10.1086/590052
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Spaans
中科院分区：
文献类型：
--
作者：
C. Ormel;M. Spaans
我们提出了一种方法，将蒙特卡罗研究扩展到需要大粒子数动态范围的情况。其基本思想是，为了计算系统的碰撞演化，一些粒子相互作用比其他粒子更重要，需要更高的分辨率，而不太重要的、通常质量较小的粒子的行为可以被集中考虑。在这个近似值中，具有相同质量和结构参数的相同粒子组作为一个单位运行。分组的数量由缩放系数决定，缩放系数是一个自由参数，它决定了计算工作集中在哪些粒子上。讨论了选择变焦因子的两种方法：“等质量法”和“分布法”，其中群跟踪分布的质量密度，“分布法”还跟踪分布中的波动。这两种方法都与Smoluchowski凝血方程的解析解取得了很好的一致性。分组方法被进一步应用于涉及失控核的模拟，其中粒子相互作用率是粒子质量的强函数，以及包括灾难性碎裂的情况。对于失控模拟，之前关于失控时间尺度随着粒子初始数量的减少而减少的预测再次得到确认，延长到10160。天体物理学的应用包括对尘埃凝聚、行星小吸积和大型球状星团中恒星的动力学演化进行建模。该方法是计算粒子通过离散事件相互作用、粒子性质由结构参数表征的任何系统演化的有力工具。
We present a method which extends Monte Carlo studies to situations that require a large dynamic range in particle number. The underlying idea is that, in order to calculate the collisional evolution of a system, some particle interactions are more important than others and require more resolution, while the behavior of the less important, usually of smaller mass, particles can be considered collectively. In this approximation, groups of identical particles, sharing the same mass and structural parameters, operate as one unit. The amount of grouping is determined by the zoom factor—a free parameter that determines on which particles the computational effort is focused. Two methods for choosing the zoom factors are discussed: the “equal-mass method,” in which the groups trace the mass density of the distribution, and the “distribution method,” which additionally follows fluctuations in the distribution. Both methods achieve excellent correspondence with analytic solutions to the Smoluchowski coagulation equation. The grouping method is furthermore applied to simulations involving runaway kernels, where the particle interaction rate is a strong function of particle mass, and to situations that include catastrophic fragmentation. For the runaway simulations, previous predictions for the decrease of the runaway timescale with the initial number of particles are reconfirmed, extending to 10160. Astrophysical applications include modeling of dust coagulation, planetesimal accretion, and the dynamical evolution of stars in large globular clusters. The proposed method is a powerful tool to compute the evolution of any system where the particles interact through discrete events, with the particle properties characterized by structural parameters.