ELASTOHYDRODYNAMICS AND FLEXIBLE BLADE COATING (COMPUTER, AIDED, ANALYSIS)

Elastohydrodynamic systems are characterized by the strong interactions of pressure and viscous forces arising from the flow of fluids in nonuniform narrow channels and elastic forces arising from the deformations of the walls of those channels.;This thesis reports theoretical predictions from a new model which is developed at different levels of complexity. The model is based on the lubrication approximation of flow in narrow channels and on both infinitesimal and finite deformation treatments of a thin elastic blade of large width. Newtonian and shear-sensitive liquids are considered.;The highly nonlinear set of differential and integrodifferential equations that governs the systems is solved numerically by a comprehensive method, namely, subdomains/Galerkin weighted residuals/finite element basis function/Schwarz-Wendroff approximation. No less important are Newton iteration and first-order continuation for tracing out families of solutions in the parameter space. Crucial to this strategy is a new automatic step-size control for first-order continuation which was developed for the present work.;For the first time the characteristic and peculiar response of the system, i.e. the curves of coating thickness versus loading, are reproduced clearly. In addition, the computed predictions uncover the mechanism by which the interacting forces produce the relative extrema in the curves of coating thickness versus loading.;Everyday coating processes as well as high technology ones contain plenty of elastohydrodynamic systems. The prototype in this thesis is Flexible Blade Coating, which has been in industrial operation for more than thirty years; it also occurs in spreaders, wipers, squeegees, and the like. Basically the system consists of very thin flexible blade which is clamped at one end; the other end is free but acts to limit or to smooth the liquid being coated. The amount of liquid deposited is controlled by loading the blade, i.e. by pushing it down against the substrate or web to be coated, which moves relative to the blade.;Two sets of experiments, one in an idealized apparatus and another on a continuous web with industrial research equipment, were carried out to validate the theory.