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

科学目标的SPP 2005年内的拟议研究项目的目的是提高我们的理解，在有限的几何形状，使用微观结构解析SPH模拟梯度新混凝土流动。在这方面，将特别关注剪切引起的颗粒迁移和润滑层的形成过程，其技术意义的混凝土泵送的动机。由于这些过程发生在长度尺度是显着小于工程长度尺度，解决表面耦合直接数值模拟（DNS）被认为是适当的方法。为了解决DNS的重要计算需求，将使用高性能计算方法（大规模并行分布式内存计算）。我们的模拟方法应明确考虑到新拌混凝土的多尺度性质，因为载体流体的流变性以及数值解析的骨料含量可以自适应地修改，以充分代表在合适的长度和时间尺度上的主导机制。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剪切引起的动态骨料离析过程中级配混凝土悬浮液。这意味着我们的模拟将强烈地与水合水泥悬浮液的化学反应性相关的时间尺度分离。因此，该项目的重点是流动过程中新拌混凝土微观结构的演变，即由于流体动力学和摩擦学效应而导致的离析效应，如不均匀的颗粒尺寸和浓度分布。我们的科学工作计划应按照这样的方式进行调整，即我们的模拟结果最终可以提供可靠的数据和知识基础，以开发泵送过程中新拌混凝土流动的粗粒度宏观模型。该数据基础应涵盖由配合比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年战略优先事项模块3的宝贵投入。一个计算优化的模拟框架SPH模拟是可用的。这个模拟框架是基于HOOMD-blue（高度优化的面向对象的多粒子动力学），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。与悬浮在连续载液中的任意形状刚性颗粒的模拟相关的核心算法（例如数据结构、时间积分例程）已经实现。因此，在拟议项目期间，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.