Efficient numerical models for the tribological analysis of textured journal bearing systems

减少滑动轴承系统的摩擦和磨损可以显著地促进动力传动系统的高效设计。表面织构是一种新兴的减少摩擦和磨损的技术。用于在混合摩擦条件下连续运行的滑动轴承系统设计的数值模型，例如风力驱动或内燃机，通常只考虑表面粗糙度对摩擦和磨损的影响。将这些模型应用于纹理系统会导致显著的建模误差，或者需要使用高分辨率表面纹理离散化进行耗时的模拟。因此，在给定的应用中，确定减少摩擦和磨损的最佳纹理设计几乎是不可能的。因此，该项目的主要目标是开发、实施和验证一种有效的数值方法，用于具有粗糙、纹理轴表面的轴承系统的优化设计。与现有的包含Patir和Cheng的经验平均流模型的软件解决方案不同，本项目中的建模是基于均匀化的数学概念。均匀化基于渐近展开，与平均流动模型相反，它为任何表面粗糙度或纹理配置提供正确的结果。此外，平均解决方案的简单升级允许捕获局部效应。这个概念可以通过重复均匀化来扩展，这样就可以考虑粗糙度和纹理，而不必通过精细的计算网格来解决纹理问题。通过开发和实现各个模块，构建了一个完整的瞬态仿真模型。该模型结合了(i)考虑空化的流体动力学，（ii）通过计算弹塑性粗糙接触压力和弹性变形（EHL）的混合摩擦，以及（iii）通过流体和两种固体的能量方程的温度效应。最后利用物理模型对所得热弹流混合摩擦模型进行了扩展，以预测磨损。后者得到了加强，以考虑在磨圆接触尺度上磨合时轴和轴承发展的一致性。除了数值研究之外，还进行了实验来验证数值模型，并系统地研究了粗糙度和纹理对滑动轴承系统摩擦学特性的不耦合和协同效应。此外，还对表面织构的耐久性进行了研究。这涉及到使用不同的轴承材料，往往会弄脏，以及在混合摩擦条件下的测试。研究了混合润滑过渡速度向流体动力润滑过渡速度的变化等磨合磨损效应。

The reduction of friction and wear in sliding bearing systems can significantly contribute to the efficient design of a drivetrain. Surface texturing is an emerging technique to reduce friction and wear. Numerical models for the design of sliding bearing systems for applications with sequential operation under mixed friction conditions, e.g., wind power drives or internal combustion engines, commonly only incorporate the effect of surface roughness on friction and wear. The application of these models to textured systems leads to significant modeling errors or requires time-consuming simulations with highly-resolved surface-texture discretizations. Consequently, determining the optimal texture design for the reduction of friction and wear in a given application is nearly impossible. The main objective of this project therefore is the development, implementation and validation of an efficient numerical method for the optimal design of bearing systems with rough, textured shaft surfaces. In contrast to existing software solutions that incorporate Patir and Cheng’s empirical average flow model, the modeling in this project is based on the mathematical concept of homogenization. Homogenization is based on an asymptotic expansion, which - in contrast to the average flow model - provides correct results for any configuration of surface roughness or texturing. In addition, a simple upscaling of the averaged solution allows for capturing local effects. The concept can be extended by reiterated homogenization in such a way that roughness and textures can be taken into account without resolving the textures by fine computational meshes. By developing and implementing individual modules, a comprehensive model for transient simulations is assembled. This model incorporates (i) hydrodynamics taking into account cavitation, (ii) mixed friction by computing the elastic-plastic asperity contact pressure and elastic deformations (EHL) and (iii) temperature effects through energy equations for the fluid and the two solids. The resulting thermo-elastohydrodynamic/mixed friction model is finally extended by physical models for the prediction of wear. The latter are enhanced to account for the conformity of shaft and bearing developing during running-in on asperity contact scale. In addition to the numerical studies, experiments are conducted to validate the numerical model and to systematically investigate the uncoupled and synergistic effects of roughness and texture on the tribological characteristics of sliding bearing systems. Furthermore, the durability of surface textures is studied. This involves the use of different bearing materials that tend to smearing as well as tests under mixed friction conditions. Running-in/wearing-in effects such as the shift of the transition speed from mixed to hydrodynamic lubrication are studied as well.