Rheology of dense sheared granular mixtures: computational and experimental studies on the effects of particle size distributions

项目编号：0932735首席研究员：Hill， kimberly隶属关系：明尼苏达大学主要研究目标是确定致密颗粒混合物流变学的控制特征。单分散致密颗粒材料流变模型的最新进展没有一个机制来纳入局部粒径分布对混合物流变学的影响。流变性能取决于物质的浓度，而微粒混合物容易分解这一事实使其变得更加复杂。通常，致密颗粒流的流变表达式与粒径有明确的依赖关系，尽管混合物的代表性粒径并不明显。在许多情况下，平均粒度不足以预测一般的流变趋势。本研究将解决颗粒混合物的流变性对粒径分布的依赖问题。采用离散元法（DEM）对软球进行计算模拟。边界条件将包括自由表面重力驱动的流动和恒压和恒体积边界驱动的剪切细胞，以研究相关边界效应的重要性。实验将包括库埃特剪切流和自由表面重力驱动流在小型和大型旋转鼓。边界力和数字图像分析将验证许多计算。粒径分布将包括不同尺寸和浓度的二元混合物，三级混合物，最终，多种尺寸。将研究粒径分布，包括粒径的平均值、中位数和标准差的影响。其他考虑因素是平均Veronoi体积分数和粒子间力的概率分布函数，因为它们取决于粒子大小分布和流动条件。更好地了解密集颗粒混合物适用于粉末加工和混合、泥石流的预测和缓解以及河流和溪流的环境恢复。在研究中包括来自代表性不足群体的本科生，将更好地培养未来的土木工程师，为相关工程问题制定长期成功的解决方案。相关的教学材料将在美国国家地球表面动力学中心（NCED）的gidakiimanaaniwigamig（我们的地球小屋）夏令营和明尼苏达州德卢斯附近的Fond du Lac部落和社区学院的课后项目中为K-12教师及其学生开发。

Proposal Number: 0932735Principal Investigator: Hill, KimberlyAffiliation: University of MinnesotaThe central research goal is to determine the governing features of the rheology of dense granular mixtures. Recent advances in rheological models for monodisperse dense granular materials do not have a mechanism to incorporate the effect of local particle size distributions on the rheology of mixtures. The rheological properties are dependent on species concentration, further complicated by the fact that particulate mixtures tend to unmix. Typically, expressions for the rheology of dense granular flows have an explicit dependence on particle size, though the representative particle size for a mixture is not obvious. In many cases average particle size is not sufficient for predicting general rheological trends. This research will address the question of the dependence of rheology of granular mixtures on particle size distribution. Computational simulations will be performed using the Distinct Element Method (DEM) for soft spheres. Boundary conditions will include free surface gravity-driven flows and constant pressure and constant volume boundary-driven shear cells to investigate the importance of associated boundary effects. Experiments will include Couette shear flow and free-surface gravity-driven flows in small and large rotating drums. Boundary force and digital image analysis will validate many computations. Particle size distributions will include binary mixtures of distinct sizes and concentrations, tertiary mixtures, and, ultimately, multiple sizes. Particle size distribution will be investigated, including the effect of mean, median and standard deviations of the particle sizes. Other considerations are the average Veronoi volume fractions and probability distribution functions of interparticle forces as they depend on particle size distributions and flow conditions. Better understanding of dense particulate mixtures is applicable to powder processing and mixing, prediction and mitigation of debris flows, and environmental restoration of rivers and streams. Including undergraduates from underrepresented groups in research will better train future civil engineers for developing longer-term successful solutions to relevant engineering problems. Related teaching materials will be developed for K-12 teachers and their students at the National Center for Earth-surface Dynamics' (NCED) gidakiimanaaniwigamig (Our Earth Lodge) summer camps and after-school programming at the Fond du Lac Tribal and Community College near Duluth, Minnesota.