SGER: Granular Lubrication: Progressive modeling and experimentation of a novel lubrication mechanism

SGER：颗粒润滑：一种新型润滑机制的渐进建模和实验项目摘要由于液体润滑剂在极端温度下会分解，研究人员提出在宏观尺度滑动接触中使用固体流动颗粒作为润滑机制。此外，已知纳米/微米级接触中的液体润滑剂由于配合部件之间的静摩擦而破坏MEMS器件的动态操作。 粒状颗粒，提出作为干润滑剂，已被称为降低摩擦和分离的剪切细胞实验中的滑动表面。虽然流动的颗粒一直被认为是流体流动的联想，颗粒流科学界在模拟这些流动方面并没有取得同样的成功。已经开发了模型来预测料斗、输送机、倾斜和剪切单元中的流动颗粒的行为。然而，这些模型强加了粗略的假设（例如，均匀的颗粒尺寸/形状、无摩擦表面、忽略重力等）并已解决了最简单的情况和流动几何形状。第一原理统计力学与连续介质方法相结合，提供了适度的，往往只是定性的协议与实验数据。 在宏观尺度上的相互作用的颗粒已被建模使用相同的Navier-Stokes流体模型应用于液体。关键的区别是，混合物的性质，如粘度，导热系数和密度的本构关系，必须推导出碰撞颗粒和帐户的非弹性。这表明，一个简化的，新颖的方法来模拟这些离散粒子系统将是非常有价值的。基于格点的细胞自动机（LBCA）建模是使用定义良好的规则来开发能够预测真实的离散时空系统的计算机模拟，例如在颗粒流中看到的这些系统。离散的，时间的，粒子型系统出现在摩擦学，生物学和自然界的润滑颗粒，分子单体，干泥石流，分别。由于明确定义的规则必须来自对真实的系统的观察，因此必须开发出从中可以导出规则的实验。 拟议的SGER期间将有丰富的知识价值。我们将开发一种新的基于格子的建模方法来模拟颗粒润滑流，称为细胞自动机，它能够模拟滑动接触几何中碰撞颗粒的相互作用。LBCA模拟是基于规则为基础的数学粒子相互作用，将获得从颗粒径向轴承，将在这项工作中开发。此外，CA模拟的结果将与现有的连续模型进行比较。 颗粒流试验轴承将能够测量流动参数速度、固体分数、颗粒温度和滑动。它将有一个透明的外壳，使粒子相互作用的数字视频和发展的碰撞规则。将根据视频开发数字颗粒跟踪测速（DPTV）方案，以便可以从颗粒轴承中获取数据。这种复杂的机械颗粒系统将是迄今为止第一个颗粒润滑的轴颈轴承。对于多组分摩擦学流动，能够测量摩擦学参数的实验性颗粒轴承将为这些极其复杂的流动在收敛间隙几何形状中的行为提供有价值的见解。LBCA建模方法能够预测离散的、相互作用的颗粒系统的行为，这些系统随着时间的推移而演变，这项工作将突出其在颗粒流中的实施速度和灵活性，这项工作将通过开发一个基于网络的模块来在线运行离散时间系统的LBCA，从而广泛影响未来的颗粒流和摩擦学工作人员。该模块将位于一个网站和一个简单的演示将介绍在城市匹兹堡公立高中。此外，PI和研究生将在高中进行演讲，介绍为多组分流动和难以预测的物理实验开发新实验和模型的重要性。最后，这项工作将作为一种催化剂，增加LBCA接近预测多组分流动，即颗粒流的摩擦学应用。

SGER: Granular Lubrication: Progressive modeling and experimentation of a novel lubrication mechanismProject SummarySince liquid lubricants break down at extreme temperatures, researchers proposed using solid flowing particles as a lubricating mechanism in macro-scale sliding contacts. Additionally, liquid lubricants in nano/micro-scale contacts have been known to disrupt dynamic operation of MEMs devices due to stiction between mating components. Granular particles, proposed as dry lubricants, have been known to lower friction and separate sliding surfaces in shear cell experiments. While flowing granules have always been considered reminiscent of fluid flows, the granular flow scientific community has not had the same success in modeling these flows. Models have been developed to predict the behavior of flowing granules in hoppers, conveyors, inclines, and shear cells. However, these models have imposed gross assumptions (e.g., uniform particle sizes/shapes, frictionless surfaces, neglected gravity, etc.) and have been solved for the simplest cases and flow geometries. First principle statistical mechanics coupled with continuum approaches have provided modest and oftentimes qualitative-only agreement with experimental data. Interacting granules at the macro-scale have been modeled using the same Navier-Stokes fluid models applied to liquids. The key difference is that constitutive relationships for mixture properties such as viscosity, thermal conductivity, and density must be derived for colliding granules and account for inelasticity. This suggests that a simplified, novel approach to modeling these discrete particle systems would be of great value. Lattice-based cellular automata (LBCA) modeling is the use of well-defined rules to develop a computer simulation capable ofpredicting real discrete, spatial-temporal systems such as these seen in granular flows. Discrete, temporal, particletype systems appear in tribology, biology, and nature as lubricating particulates, molecules monomers, and dry debris flows, respectively. Since the well-defined rules must come from observations of the real systems, experiments from which the rules can be derived must be developed. The proposed SGER period will be rich in intellectual merit. We will develop a new lattice-based modelingapproach for modeling granular lubrication flows, known as cellular automata, which is capable of simulating the interactions of colliding granules in a sliding contact geometry. The LBCA simulation is based on the rule-based mathematics of particle interaction that will be obtained from the granular journal bearing that will be developed in this work. Additionally, results from the CA simulations will be compared to those from existing continuum models. The granular flow test bearing will be capable of measuring the flow parameters velocity, solid fraction, granular temperature and slip. It will have a transparent encasing to enable digital videography of the particle interactions and for developing the rules of collision. A digital particle tracking velocimetry (DPTV) scheme will be developed from the video, so that the data can be obtained from the granular bearing. This complex mechanical granular system will be the first granular-lubricated journal bearing to date. Fundamental to multi-component tribological flows, an experimental granular bearing capable of measuring tribological parameters would provide valuable insight into the behavior of these extremely complex flows in converging gap geometries. The LBCA modeling approach is capableof predicting the behavior of discrete, interacting particulate systems that evolve over time and this work will highlight its speed of implementation and flexibility in granular flows.This work will broadly impact the future granular flow and tribology workforce by developing a web-based module for running LBCA for discrete temporal systems online. The module will be located on a website and a simple demo will be introduced at an urban Pittsburgh public high school. Additionally, the PI and graduate student will conduct presentations at the high school on the importance of developing new experiments and models for multi-component flows and hard to predict physics experiments. Lastly, this work would serve as a catalyst for increasing LBCA approached to predicting multi-component flows, namely granular flows for tribological applications.