Direct numerical simulation of dynamic aggregate migration in fresh concrete using multi-scale Smoothed-Particle Hydrodynamics

2005年SPP中拟议的研究项目的科学目标旨在通过微观结构解析的SPH模拟来提高我们对受限几何形状中的分级新混凝土流动的理解。在这方面，将特别关注剪切诱导的颗粒迁移和润滑层形成过程，因为它们对混凝土泵送具有重要的技术意义。由于这些过程发生在比工程长度尺度小得多的长度尺度上，分辨率表面耦合直接数值模拟(DNS)被认为是合适的方法。为了解决域名系统的巨大计算需求，将使用高性能计算方法(大规模并行分布式内存计算)。我们的模拟方法将明确考虑新拌混凝土的多尺度特性，因为载体流体的流变性以及数值分解的骨料含量可以被自适应地修改，以在适当的长度和时间尺度上充分代表主导机制。考虑到我们对粒子迁移过程的兴趣，我们试图在模拟中表示的特征时间尺度将是粒子自扩散时间的顺序。换句话说，模拟的时间尺度必须足以研究级配混凝土悬浮液中剪切诱导的动态骨料离析过程。这意味着我们的模拟将从与水化水泥悬浮液的化学反应相关的时间尺度中分离出来。因此，本项目重点研究新拌混凝土在流动过程中微观结构的演变，即由于流体动力和摩擦学效应而导致的分离效应，如不均匀的颗粒尺寸和浓度分布。我们的科学工作计划应量身定做，以使我们的模拟结果最终能够为开发泵送过程中新拌混凝土流动的粗粒度宏观模型提供可靠的数据和知识基础。该数据基础应涵盖由混合设计和边界条件组成的特征空间。在这方面，本项目的预期产出被认为是对2005年战略计划单元3的宝贵投入。用于SPH模拟的计算优化的模拟框架是可用的。该模拟框架基于HOOMD-BLUE(高度优化的面向对象多粒子动力学)，并已在我们可以访问的计算机集群上证明了良好的并行性能。已经实现了与连续载体液体中悬浮的任意形状的刚性粒子的模拟相关的核心算法(例如数据结构、时间积分例程)。因此，在拟议项目的期限内，用于软件实施的时间相对较少。

The scientific objectives of the proposed research project within the SPP 2005 aim towards improving our understanding of graded fresh concrete flow in confined geometries using microstructure-resolved SPH simulations. In this regard, special attention will be devoted to shear-induced particle migration and lubrication layer formation processes motivated by their technological significance for concrete pumping. As these processes take place at length scales which are significantly smaller than the engineering length scale, resolved surface-coupled Direct Numerical Simulations (DNS) are considered appropriate approaches. In order to address the significant computational requirements of DNS, high-performance computing approaches will be used (massively parallel distributed memory computing). Our simulation approach shall explicitly take into account the multi-scale nature of fresh concrete in that the rheology of the carrier fluid as well as the numerically resolved aggregate content can be adaptively modified to adequately represent the dominating mechanisms at a suitable length and time scale. Given our interest in particle migration processes, characteristic time scales we attempt to represent in our simulations will be in the order of particle self-diffusion times. In other words, simulated time scales must be sufficient to study shear-induced dynamic aggregate segregation processes in graded concrete suspensions. This implies that our simulations will strongly be separated from time-scales associated with the chemical reactivity of hydrating cement suspensions. As a result, this project focuses on the evolution of fresh concrete microstructure during flow, i.e. resulting in segregation effects such as heterogeneous particle size and concentration distributions, due to hydrodynamic and tribological effects. Our scientific work program shall be tailored in such a way that our simulation results can ultimately provide a reliable data and knowledge basis to develop coarse-grained macroscopic models of fresh concrete flow during pumping. This data basis shall cover a feature space composed of mix design and boundary conditions. In that respect, the anticipated output of the present project is considered a valuable input to module 3 of the SPP 2005. A computationally optimized simulation framework for SPH simulations is available. This simulation framework is based on HOOMD-blue (Highly Optimized Object-oriented Many-particle Dynamics) and has previously proven good parallel performance on computer clusters we have access to. Core algorithms related to the simulation of arbitrary-shaped rigid particles suspended in continuous carrier liquids (e.g. data structures, time integration routines) have been implemented. Within the duration of the proposed project, comparatively little time will thus be devoted to software implementation.