James Lowman

Engineering design of chemical processes motivates a deeper understanding of how to both improve the physical fidelity and feasibility of multiphysics simulation, where multiphysics refers to multiple coupled physicochemical phenomena involving three key aspects: Momentum, Energy, and Mass Transport. The fidelity of a multiphysics simulation is the degree to which both the model and the numerical method are able to reproduce the behavior of a system observed in the real world. The feasibility of replicating a behavior within a multiphysics simulation requires that a model encapsulate the physics of the proposed system, without exceeding the ability to solve such a system, all while retaining "real-world" meaning. This is accomplished by reducing the system complexity with justified mathematical and physical assumptions, and choices of numerical methods capable of providing timely solutions to the partial differential equations that arise from such models.

Modeling a bioreactor is a complex proposition. There is cell microbiology suspended in a fluid that supplies nutrients and provides waste removal, there are bubbles in the liquid providing oxygen, and all of these phases are contained in a reactor vessel that will have moving parts like an impellor to stir the contents constantly. Simulating any one of these components is a hard problem, attempting to combine models for them all has never been accomplished. James' research centers around finding models to approximate each system, finding numerical methods that are accurate and robust to capture the dynamics and mathematics of each system, and combining all of them together to simulate the hydrodynamics of a working bioreactor.

To capture the cells suspended in liquid, the drift-flux model is being utilized as it can accurately predict how the cells will move relative to the fluid by approximating a relative velocity between the two phases algebraically. To capture the effect and distribution of bubbles within the fluid, the Eulerian-Eulerian two-fluid model is used to distinguish the continuous phase (liquid) and discontinuous phase (gas) as two distinct phases which interact by means of interphase-momentum-transfer terms. Both models have been implemented in the discontinuous Galerkin finite element method in order to properly capture and stabilize advecting mass flows. Coupling the liquid phase to a multi-mixture model will allow for space-time predictions of nutrient density in the fluid, and combining all three models will allow for a complete hydrodynamic simulation of a bio-reactor.

• Finite Element Methods (FEM)
• Discontinuous Galerkin FEM
• The applied mathematics of continuum mechanics
  • Fluid Dynamics
  • Computational Fluid Dynamics
  • Numerical Methods of solving complex partial differential equations of continuum mechanics
• Software implementation of Multiphysics models in the NGSolve FEM framework

• 2019, Masters of Applied Science (MASc), Chemical Engineering, University of Waterloo
• 2016, Bachelor of Mathematics (BMath), Applied Mathematics, University of Waterloo