MDC: Direct Simulation of the Motion of Particles in Flowing Liquids

9527123 Joseph本项目将发展计算固液流动中大量颗粒在悬浮流体所施加的流体动力和扭矩作用下的三维运动的高效方法，并利用这些方法阐明颗粒流动的基本动力学和解决工程问题。目标是开发高性能、最先进的软件包，称为粒子移动器，能够在牛顿流体中模拟数千个二维粒子和数百个三维粒子的运动，由navier - stroke方程控制，以及几种流行的粘弹性流体模型。这样的模拟将是非常密集的计算。因此，必须开发最有效的计算方案，并使用最先进的并行算法在并行机器上实现它们。该项目将开发两种不同的计算方案，用于在并行计算机上模拟固液流动。第一种方法是对标准伽辽金有限元方法的推广，其中流体和粒子的运动方程被合并到一个单一的变分方程中，其中流体和粒子的速度都是原始的未知数。在第二种方法中，即嵌入方法中，流体流动被计算为仿佛粒子所占据的空间充满了流体。利用拉格朗日乘法器对粒子边界的无滑移边界条件进行约束。这允许使用固定网格，消除了重新网格划分的需要，这在并行实现中是一个明显的优势。新方案将用于研究微粒流中产生团簇和各向异性结构的微观结构（对相互作用）效应，对微粒流进行统计分析（平均值、波动水平和光谱特性），推导通常从实验中获得的工程相关性，并为两相流模型的发展提供线索和封闭数据，以及判断两相流模型性能的标准。它们还将用于解决工业上的实际问题，如牛顿流体和粘弹性流体中固体颗粒的沉降、流态化和浆液输送。

9527123 Joseph This project will develop highly efficient methods for computing the three-dimensional motion of large number of particles in solid-liquid flows, under the action of the hydrodynamic forces and torques exerted by the suspending fluid, and use these methods to elucidate the fundamental dynamics of particulate flows and solve problems of engineering interest. The goal is to develop high-performance, state-of -the-art software packages called particle movers, capable of simulating the motion of thousands of particles in 2-D and hundreds in 3-D domains, in both Newtonian fluids, governed by the Navier-Strokes equations, and in several popular models of viscoelastic fluids. Such simulations will be extremely computationally intensive. It is therefor imperative to develop the most efficient possible computational schemes, and to implement them on parallel machines, using state-of-the-art parallel algorithms. The project will develop two different computational schemes for simulating solid-liquid flows on parallel computers. The first is a generalization of the standard Galerkin finite element method in which both the fluid and particle equations of motion are incorporated into a single variational equation, containing both fluid and particle velocities as primitive unknowns. In the second approach, an embedding method, the fluid flow is computed as if the space occupied by the particles were filled with fluid. The no-slip boundary condition of the particle boundaries is enforced as a constraint using Lagrange multipliers. This allows a fixed grid to be used, eliminating the need for remeshing, a definite advantage in parallel implementations. The new schemes will be used to study the microstructural (pair interaction) effects which produce clusters and anisotropic structures in particulate flows, to produce statistical analyses of particulate flows (mean values, fluctuation levels and spectral properties), to derive engineering correlations of the kind usually obtained from expe riments, and to provide clues and closure data for the development of two-phase flow models and a standard against which to judge the performance of such models. They will also be used to solve practical problems of industrial interest such as sedimentation, fluidization an slurry transport of solid particles in Newtonian and viscoelastic fluids.