~~ The Department of Mechanical and Industrial Engineering Presents

Dr. Alireza Karimi

Postdoctoral Research Associate, Department of Aerospace and Mechanical Engineering, University of Notre Dame

Topic: Interplay of Fluid Dynamics and Collective Behavior of Microorganisms

Date: Monday, April 7, 2014

Time: 10:00am to 12:00pm (Refreshments from 9:30am to 10:00am)

Location: 348 Curry Student Center

Abstract: The collective motion of self-propelled microorganisms in a fluid environment is a ubiquitous phenomenon of nature and is at the core of a novel area of research known as active fluids. Scrutinizing the hydrodynamic interaction of swimming microorganisms and the surrounding fluid provides us significant insights about the underlying mechanisms of a wide range of physical phenomena, including biofilm formation, bioconvection, and evolution of algal blooms. In this study, we employed intensive numerical simulations of a deterministic model of the bioconvection to capture the characteristics of the patterns triggered by the coordinated swimming of algae in homogenous and stratified aquatic environments. The corresponding outcomes exhibit the same trend of pattern evolution as observed in experimental investigations in the literature. As a result of this study, the buoyancy ratio is introduced as the key parameter to determine if the bioconvcetive plumes are suppressed by stratification arising from thermal or solutal gradients in the ambient fluid. In addition, we elucidated the impact of viscoelasticity on the coordinated swimming of bacteria. The formation of biofilms is often associated with production of extracellular polymeric substances which impart viscoelastic behavior to the surrounding fluid. To investigate this process, we used a kinetic model developed to study the behavior of self-propelled rod-shaped particles in conjunction with Oldroyd-B constitutive equation and the Stokes equations. Using large-scale numerical simulations of the system, this study demonstrates that viscoelasticity promotes the localization of the fluctuations in the pattern of the system by inhibiting the formation of large-scale dense regions of bacteria. Further, suspensions of polymers with higher relaxation time are shown to slow down the collective motion of the microorganisms.

Brief bio: Dr. Alireza Karimi received his Bachelors and Masters degrees in Mechanical Engineering from Sharif University of Technology, Iran and his PhD degree in Engineering Science and Mechanics from Virginia Tech in 2012. In his dissertation, he developed a large-scale computational framework to study the pattern formation and complex dynamics in spatially extended chaotic systems. Presently, Dr. Karimi is a Postdoctoral Research Associate in the Department of Aerospace and Mechanical Engineering at the University of Notre Dame. His current research focuses on characterizing the complex interplay of fluid dynamics and collective behavior of swimming microorganisms using intensive numerical simulations. He has been honored with significant awards based upon his key scientific contributions including the prestigious Liviu Librescu Memorial Scholarship Award.