Thesis Format
Monograph
Degree
Doctor of Philosophy
Program
Mechanical and Materials Engineering
Supervisor
Tutunea-Fatan, Ovidiu-Remus
2nd Supervisor
Bordatchev, Evgueni
Affiliation
National Research Council Canada
Co-Supervisor
Abstract
Several species of plants and animals demonstrate an ability to resist the accumulation of contaminants natural to their environments. To explain this phenomenon, mechanisms that facilitate fouling resistance must be deciphered. Along these lines, this study is focused on the topography-based mechanisms observed in nature that represent one of several mechanisms employed by nature for underwater environments. The prevailing theory for the fouling resistant performance of sharkskin is that a positive correlation exists with its ability to reduce skin friction drag relative to what is expected for a flat surface. This correlation was investigated for three novel topographies inspired by sharkskin, fish-scales, and mollusks. Numerical simulations involving Large Eddy Simulation with the Wall Adapting Local Eddy-Viscosity model were carried out for turbulent flow conditions to determine the most effective dimensions of the three topographies for drag reduction. The maximum drag reduction attained in this study was 6.0%, 6.7%, and 6.1% for the bioinspired sharkskin, fish-scales, and mollusk surfaces. A flow field analysis revealed that each surface exhibited a reduction in turbulent velocity fluctuations near the surface. Following this, functional samples were fabricated in acrylic by means of a multi-axis machining center. Surface quality and form accuracy of the fabricated samples were assessed with an optical microscope and optical profilometer. Finally, a field study was conducted to investigate the fouling resistance of the samples by subjecting them to a flow of contaminated water for a period of 20 days. The flow conditions and characteristic dimensions of the geometry were chosen beforehand such that a subset of the samples was operating at drag reducing conditions, while the second subset was operating at drag increasing conditions. The results demonstrate for the first time that drag reduction is positively correlated with fouling resistance. The primary mechanism for this performance was identified as a decrease in inertial impaction of the fouling constituents as a consequence of the reduced turbulent velocity fluctuations.
Summary for Lay Audience
A surface resistant to the unwanted accumulation of fouling materials is of interest to many industries. To the marine transport industry, the accumulation of fouling in the form of barnacles, algae and other organisms annually represents a $150 billion dollar challenge. For the field of medicine, fouling of medical devices accounts for more than 2 million hospital contracted infections every year. Researchers are quite active in these areas along with many others, working toward solutions to reduce or even eliminate fouling. And while fouling remains an ongoing challenge for man-made structures, the surfaces of many plants and animals display a diverse set of defense mechanisms to resist fouling in their environments. Sharks and other fish, bivalves, sea stars, and algae each represent a limited collection of a much longer list of plants and animals with fouling resistance. Biomimicry is a scientific method that seeks to investigate, learn from, and imitate nature to help solve complex problems. The goal of this research is to investigate how nature uses surface textures and patterns of structures (i.e., topography) to achieve fouling resistance for underwater environments. As of today, biological sharkskin is widely regarded as the best fouling resistant surface. The research focus on sharkskin has primarily been on its ability to reduce the friction drag caused by water moving along its surface while swimming. Researchers have proposed that the same mechanisms leading to drag reduction also explain its fouling resistance. This research directly examined this connection by looking at the flow of water above several drag reducing topographies with computer simulations. The structures on the examined surfaces were designed to imitate natural surfaces. The results show that when water flows over the surface at the right conditions for drag reduction, the water layer near the surface is much calmer than when flowing over even a perfectly smooth surface. Physical experiments of these surfaces submerged in a contaminated flow of water showed that surfaces in drag reducing conditions had less fouling than the same surfaces in drag increasing conditions. Therefore, it seems as though some natural surfaces use one topography for both fouling resistance and drag reduction.
Recommended Citation
Hamilton, Benjamin W. University of Western Ontario, "A Study of Drag Reduction and Fouling Resistance on Bioinspired Surfaces with Functional Structures" (2023). Electronic Thesis and Dissertation Repository. 9900.
https://ir.lib.uwo.ca/etd/9900