From Red Cells to Soft Porous Lubrication

• Main Author: Zhu, Zenghao
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Biomechanics; Fluid mechanics; Mechanical engineering
• ISBN: 9781658434485; 165843448X

In this dissertation, we report a biomimetic study to examine the lift generation inside a soft porous layer and its applications to soft porous lubrication. The study is inspired by the exquisite design of the endothelial glycocalyx layer (EGL) that covers the inner surface of our blood vessels. The EGL is believed to play a key role in providing a smooth cushion for the red blood cells to move frictionlessly inside a tightly fitting capillary (Feng and Weinbaum, JFM, 422, 281, 2000). The mechanism behind this phenomenon is that, significantly enhanced lubrication pressure is generated as the red blood cell glides over the soft porous EGL. Applying lessons learned from microcirculation, we aim to answer the following questions: (i) What are the transport properties (Kp) through different kinds of fibrous porous structures? (ii) What is the fundamental mechanism that governs the soft porous lubrication as a planing surface glides over a randomly distributed fibrous porous layer at different scales, with or without lateral pressure leakage? (iii) What is the fundamental mechanism that governs the gravity-driven gliding motion of a planar board over a soft porous layer? (iv) What is the fundamental mechanism that governs the soft porous lubrication with organized, oriented fiber matrix? To answer these questions, a systematic experimental and theoretical study is performed in this dissertation, where (1). A novel experimental approach is developed to investigate the compression-dependent Darcy permeability of soft porous media. Especially, we are proposing new correlations that describe the change of the permeability of random fibrous porous media as a function of its compression. The results will be valuable for examining porous media flow, especially for the case when the permeability is difficult to be measured directly. (2). We have further performed a systematic study to investigate the Darcy permeability of a highly organized, oriented fiber array. For the first time, a linear combination method is experimentally validated to estimate the permeability of fiber arrays with any orientations. (3). A unique experimental setup is developed to examine the lift generation and lubrication performance as a planing surface glides over a large-scale porous layer (19 mm in thickness). A comprehensive experimental study is performed to study the pore pressure distribution inside the soft porous layer, the frictional loss, as well as the effect of lateral leakage. Comparison between the experimental results and the theoretical predictions are performed. The validity of the theory of soft porous lubrication is proved conclusively. (4). We have further developed a new experimental setup to examine soft porous lubrication in a small-scale porous layer (~3 mm). The hydrodynamic similarity of the soft porous lubrication theory in different size scales is experimentally validated. Furthermore, a novel theoretical model for estimating the lubrication performance, fp, the contribution of fluid lifting pressure to total lifting pressure, is developed. Via comprehensive dimensional analysis, we obtained five dimensionless parameters that determine the lubrication performance fp for the motion of a planing surface over a soft porous layer. (5). A novel experimental setup is developed for investigating the soft porous lubrication when a planar board slides downhill on a tilted porous layer. Differing from previous studies, this study investigated the gliding motion with fixed applied loading instead of fixed prescribed compression of the porous layer. (6). A comprehensive theoretical study is performed to investigate the lubrication when a planar board glides over an oriented fiber array. Both fluid phase and solid phase lifting forces are theoretically modelled at different fiber orientations. Dimensional analysis has been performed, which helps to better understand soft porous lubrication with oriented fiber network. The comprehensive experimental and theoretical studies presented herein provide the foundation for the application of highly compressible porous media for soft lubrication with minimal frictional losses. It also sheds some lights on the biophysics study of the EGL.