A computational model of nutrient transport and acquisition by diatom chains in a moving fluid
Description
A computational model of the flexible diatom chains and nutrient dynamics in a moving fluid is presented in our dissertation. The chain is modelled as a collection of neutrally-buoyant cylinders connected by filaments. The motion of the fluid is governed by the incompressible Navier-Stokes equations. We use the immersed boundary method to couple the interaction of non-motile diatom chains with the viscous, incompressible, moving fluid, and with the nutrient that is advected by and diffusing in the fluid and also consumed by the cells. We apply our model to study the impact of length and flexibility of chains on nutrient uptake and transport in a turbulent environment. In those studies we consider two types of distributions of nutrient. One, where nutrient is introduced into the medium through point sources randomly distributed in space and time. Other, where initial nutrient concentration is uniform. The presented results suggest that the nutrient uptake per cell in a chain and nutrient fluxes towards cells increase with decreasing flexibility of the chain. The numerical experiments further suggest that the cells on the exterior of chains experience larger enhancement of nutrient flux due to flow than the cells on the interior. Our numerical solutions for nutrient mass transfer to diatom cells fall within the bounds of the known analytic solutions for limiting cases. These results confirm intuitive predictions, and open the door to possible experimental work to measure the nutrient transport and acquisition for chains with different elasticities