Hydrodynamics of swimming alga
Mohammad Farhan Abdul Samad
Date of Issue2018
School of Mechanical and Aerospace Engineering
The Reynolds number is a useful dimensionless term which compares the ratio between inertial forces to that of viscous forces. Movement at low Reynolds number implies that a body is overwhelmingly subjected to viscous forces from its surrounding medium relative to its own inertial forces. Therefore, motion of an object in the low Reynolds region number is only achieved through the time independent deformation of more than two degrees of freedom (Purcell, 1987). Take a scallop for example, with only a single degree of freedom, a scallop will not obtain net motion regardless how fast it opens and closes whereas a flexible oar with two degrees of freedom will be able to achieve net motion. (Purcell, 1987) Microorganisms are great examples of bodies that move with low Reynolds number. In this project, we study the movement of microorganisms, specifically the Chlamydomonas Reinhardtii, through the stochastic movement of its flagellum which is a tiny thread-like appendage that allows it to swim. The C. reinhardtii is already a well-documented unicellular eukaryote model organism that has two seemingly identical flagellums that grow to approximately 10 micrometers in diameter and is found in abundance in soil and fresh water bodies (Grossman, 2003). More commonly known as alga, the C. reinhardtii is being propelled within any given space by its two flagella that grow to about 12 micrometers in length each that swim with a breast-stroke like swimming pattern. (Ruffer and Nultsch, 1985). The study of C. reinhardtii motility can help us understand how it swims towards light or nutrient sources thus a better understanding of the photosynthesis of algae. In this project, we try to study and understand the stochastic flagella behaviour pattern and its influence in the overall motility of C. reinhardtii. Through previous studies about the motility of the C. reinhardtii, it is of the opinion that it swims forward and alters its swimming direction by the synchronous and asynchronous breast stroke action of its two anterior flagella, respectively (Goldstein, 2009). To date, there are very little models that attempt to illustrate the motion of C. reinhardtii. The model used by Drescher suggests that C. reinhardtii is merely subjected to 2 generic forces namely drag force and propulsion force, which does little to explain the undeniable influence the flagellar movement plays in its motion (Drescher, 2010). This project explores the various concepts such as the boundary element method (BEM) and Fourier analysis to analyse and understand motility on the C. reinhardtii and its flagella to help us build a more detailed model of C. reinhardtii. With this, we can expect our model to illustrate and solve for its swimming velocity and trajectory while taking into account the influence of the flagellar behaviour. Going a step further, we can then utilize our model to theoretically predict C. reinhardtii behaviour when parameters such as size, frequency of beating and phase difference of beating are varied and hence we can better understand what life is like for C. reinhardtii at a very low Reynolds number.
DRNTU::Engineering::Mechanical engineering::Fluid mechanics
Final Year Project (FYP)
Nanyang Technological University