Probing the Rheological Properties of Liquids Under Conditions of Elastohydrodynamic Lubrication Using Simulations and Machine Learning
Probing the Rheological Properties of Liquids Under Conditions of Elastohydrodynamic Lubrication Using Simulations and Machine Learning
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DOI：
10.1007/s11249-021-01457-3
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发表时间：
2021-09-01
影响因子：
3.2
通讯作者：
Jadhao, Vikram
中科院分区：
文献类型：
--
作者：
Kadupitiya, J. C. S.;Jadhao, Vikram
在弹性流体动力润滑 (EHL) 中，润滑剂承受超过 500 MPa 的压力和大于 105 s(-1) 的应变率。高压导致牛顿粘度急剧上升，高速率导致大的剪切应力和明显的剪切稀化。使用非平衡分子动力学模拟 (NEMD) 提取准确的流变特性在提高我们对 EHL 条件下润滑剂流动的理解方面发挥了关键作用。然而，NEMD 模拟生成的输出数据的高维性通常使得对分子尺度特征和流变特性之间的联系进行更深入的探讨具有挑战性。在本文中，我们探索使用机器学习来分析和可视化典型 NEMD 模拟中生成的高维输出数据。我们表明，描述角鲨烷剪切流的 NEMD 模拟数据的降维可以清晰地可视化随着剪切速率的增加从牛顿剪切稀化到非牛顿剪切稀化的转变，并提供剪切稀化与分子排列演化之间的相关性的可靠评估。端到端原子对在低压系统（0.1、100 MPa）的对取向张量分量中占主导地位，并提供取向张量与速率的最清晰分离。另一方面，侧原子对主导高压系统（P = 400 MPa）张量分量的最大变化，其表现出作为速率函数的取向张量的整体有限演化。使用与角鲨烷分子相关的所有 435 对取向张量的所有六个分量进行降维表明，低压下粘度随速率的降低与分子排列的变化密切相关。然而，对于高压，剪切稀化发生在饱和取向顺序下。
In elastohydrodynamic lubrication (EHL), the lubricant experiences pressures in excess of 500 MPa and strain rates larger than 105 s(-1). The high pressures lead to a dramatic rise in the Newtonian viscosity and the high rates lead to large shear stresses and pronounced shear thinning. The extraction of accurate rheological properties using non-equilibrium molecular dynamics simulations (NEMD) has played a key role in improving our understanding of lubricant flow in EHL conditions. However, the high dimensionality of the output data generated by NEMD simulations often makes a deeper interrogation of the link between molecular-scale features and rheological properties challenging. In this paper, we explore the use of machine learning to analyze and visualize the high-dimensional output data generated in typical NEMD simulations. We show that dimension reduction of NEMD simulation data describing the shear flow of squalane enables a clear visualization of the transition from Newtonian to non-Newtonian shear thinning with increasing shear rate and provides a reliable assessment of the correlation between shear thinning and the evolution in molecular alignment. The end-to-end atom pairs dominate the largest variations in pair orientation tensor components for low-pressure systems (0.1, 100 MPa) and provide the clearest separation of the orientation tensors with rate. On the other hand, the side atom pairs dominate the largest variation in the tensor components for the high-pressure systems (P = 400 MPa) which exhibit an overall limited evolution in orientation tensors as a function of rate. Dimension reduction using all the six components of the orientation tensors of all 435 pairs associated with a squalane molecule shows that the decrease in viscosity with rate for low pressures is strongly correlated with changes in molecular alignment. However, for high pressures, shear thinning occurs at saturated orientational order.