ITR Collaborative Research: Enabling Microscopic Simulators To Perform System-Level Analysis

研究：一个跨学科的研究团队，在四所大学，正在合作进行这个中型的信息技术研究（ITR）项目，旨在系统地弥合复杂材料系统的微观描述和直接工程重要性的系统级分析之间的差距。将开发一种数学辅助计算方法，使微观级模拟器能够直接执行系统级分析，而无需通过宏观（偏微分或积分微分）演化方程对材料系统进行中级描述。具体来说，基于时间步进的集成平均“粗糙”计算上层结构将“包裹”在最先进的微观动态模拟器上，如分子动力学、动力学蒙特卡罗、格点-玻尔兹曼或混合代码。这种方法将使微观模拟器能够执行复杂的非线性分布过程的高级系统级分析：稳定性，分岔，“粗”集成，灵敏度和控制任务。计划中的算法将在大规模并行机器上运行。计算框架将由以下基本要素组成：(i)选择描述粗行为的感兴趣统计量（例如分布矩）；（ii）将宏观初始条件“提升”为一致微观构型的集合；（iii）根据体现当前物理系统最佳描述的微观模拟器，在相同（短）时间内，系统中每个初始微观构型的演化；（iv）对演化的微观构型的集合进行平均（“限制”），以提供宏观的演化系统状态；(v)在有限的宏观初始条件下执行前三步。这种新方法在其实现上是健壮的，并且在其科学和工程应用范围内是可移植的。它普遍适用于所有宏观描述在概念上是可能的，但在封闭形式中不可用的系统。它规避了获取和关闭宏观模型的困难，同时精确地计算提取了宏观模型在封闭形式下所能获得的信息。这提供了ITR与一系列应用领域之间的联系。影响：该研究的影响将是在最先进的微观级模拟和快速系统级分析能力之间建立强大而普遍的联系。虽然研究重点是在非均质硬材料和复杂流体中的具体问题，但计算框架适用于广泛的复杂系统，包括生物系统及其加工和功能。由于它有可能彻底改变工程系统级分析，它可能会对教育产生影响，并进一步推动微电子、生物信息学和纳米技术的发展。

Research:An interdisciplinary research team, at four universities, is collaborating on this medium-size Information Technology Research (ITR) project aimed at systematically bridging the gap between microscopic descriptions of complex material systems and systems-level analysis of direct engineering importance. A mathematics-assisted computational methodology will be developed that will enable microscopic-level simulators to perform systems-level analysis directly, without the need to pass through an intermediate level description of the material system through macroscopic (partial differential or integro-differential) evolution equations. Specifically, an ensemble-averaged "coarse" time-stepper-based computational superstructure will be "wrapped around" state-of-the-art microscopic dynamic simulators, such as molecular dynamics, kinetic Monte Carlo, Lattice-Boltzmann or hybrid codes. This methodology will enable microscopic simulators to perform advanced systems-level analysis: stability, bifurcation, "coarse" integration, sensitivity, and control tasks, of complex, nonlinear distributed processes. The planned algorithms will run on massively parallel machines.The computational framework will consist of the following basic elements: (i) choice of statistics of interest (e.g. distribution moments) for describing the coarse behavior; (ii) "lifting" of a macroscopic initial condition to an ensemble of consistent microscopic configurations; (iii) evolution over the same (short) time period of each initial microscopic configuration in the ensemble according to a microscopic simulator that embodies the best current description of the physical system; (iv) averaging ("restriction") over the ensemble of the evolved microscopic configurations to provide a macroscopic evolved system state; and (v) execution of the previous three steps over a finite set of macroscopic initial conditions. This new approach is robust in its implementation and portable in its range of scientific and engineering applications. It has general applicability to all systems for which a macroscopic description is conceptually possible, yet unavailable in closed form. It circumvents the difficulty in obtaining and closing such macroscopic models, while computationally extracting precisely the information that would be obtained by a macroscopic model, had the model been available in closed form. This provides the link between ITR and a spectrum of application areas.Impact:The impact of the research will be on establishing a powerful and general link between state-of-the-art microscopic-level simulations and fast systems level analysis capabilities. Although the research focuses on specific problems in heterogeneous hard materials and complex fluids, the computational framework is applicable to a broad range of complex systems, including biological systems, their processing and function. Since it has the potential to revolutionize engineering systems-level analysis, it could have educational impact as well as furthering advances in microelectronics, bioinformatics and nanotechnology.