Collaborative Research: SI2-SSE: A Petascale Numerical Library for Multiscale Phenomena Simulations

多尺度现象是理论、模拟和实验的巨大挑战。很难理解最高和最低尺度的现象，以及介于两者之间的所有现象。这一挑战体现在各个领域。宇宙学中一个长期存在的问题是理解宇宙结构的形成。在这个过程的计算机模拟中，挑战是在保持基本物理特性的同时提高网格分辨率。在酶的全原子分子动力学模拟中，挑战是模拟具有大量原子的系统，同时解决长程相互作用并具有足够高的吞吐量。这种模拟对于理解重要的生物过程和最终设计新药至关重要。多尺度现象的另一个主要例子是湍流，这是一个丰富而复杂的主题，与当今许多主要技术问题，包括气候，能源以及石油和生物危害的管理都有很大的相关性。了解湍流对于设计新的运输车辆，提高燃烧过程的效率和管理其环境污染至关重要。由于计算成本极高，即使使用当今研究人员可用的高端计算系统，模拟在历史上也受到限制，并且仍然如此。降低这种成本，并有效地使用计算资源，往往需要专业知识，以及大量的开发时间和成本，许多研究小组无法负担。该项目将开发一套功能强大的关键软件组件，为多尺度现象的模拟提供工具。该套件将实现最先进的技术，以降低通信成本，这已成为最重要的因素，总的模拟成本，特别是在较大的规模。它将提供一组灵活的功能，使其可用于跨学科的大量代码。特别是，该图书馆将包括用户友好的界面，傅立叶变换，光谱和紧凑的微分在三维空间，除了广泛使用的通信例程（转置，晕交换）。这种对可扩展性能和丰富特性的强调相结合，使得该套件在当今存在的其他库中独树一帜。考虑到多尺度现象模拟的巨大挑战，这个库将提供一条通往Exascale的现实道路。该套件将在开源许可证下提供。将通过项目网站、邮寄名单、用户调查和介绍开展用户外联活动。

Multiscale phenomena are a grand challenge for theory, simulations and experiments. It is difficult to understand phenomena at both highest and lowest scales, as well as all those in between. This challenge shows up in diverse fields. One of the long-standing problems in cosmology is understanding cosmological structure formation. In computer simulations of this process the challenge is increasing grid resolution while retaining the essential physics. In all-atom molecular dynamics simulations of enzymes the challenge is simulating systems with a large number of atoms while resolving long-range interactions and having sufficiently high throughput. Such simulations are critical in understanding important biological processes and eventually designing new drugs. Another prime example of multiscale phenomena is turbulent flows, a rich and complex subject of great relevance to many of the main technological issues of the day, including climate, energy, and the management of oil and biohazards. Understanding turbulent flows is critical for design of new transportation vehicles, improving efficiency of combustion processes and managing their environment pollution. Here simulations have been historically limited, and remain so, due to extremely high computational cost, even using the high-end computational systems available to researchers today. Reducing this cost, and efficiently using the computational resources, often requires specialized expertise, as well as significant development time and cost many research groups cannot afford. This project will develop a powerful suite of critical software components to provide tools for performing simulations of multiscale phenomena. The suite will implement state-of-the-art techniques for reducing communication cost, which has become the most important contributing factor to the total simulation cost, especially at larger scales. It will provide a flexible set of features that will make it usable in a great number of codes across the disciplines. In particular, the library will include user-friendly interfaces for Fourier transforms, spectral and compact differentiation in three dimensions, in addition to widely used communication routines (transposes, halo exchanges). This combination of emphasis on scalable performance and richness of features makes this suite unique among other libraries in existence today. Given the extraordinary challenge of simulations of multiscale phenomena, this library will provide a realistic path towards the Exascale. The suite will be available under an open source license. User outreach will be undertaken through the project website, mailing list, user surveys and presentations.