Fast Simulation and Fluid Flow in the Vocal Tract

Many functions of the vocal tract involve fluid flow. For example, important research including fluid flow includes:

• speech mechanisms and production
  • where and how sound is created
  • sound propagation and interaction with the air flow and vocal tract
• breathing, snoring, and Obstructive Sleep Apnea (OSA)
• swallowing

Not surprisingly, these studies involve some critical challenges, some of which are:

• Creating a mesh to be adequately detailed and flexible without being excessively fine for computations
• Resolution of the aeroacoustics requires careful boundary conditions, very fine spatial and temporal discretization, and careful solver settings
• Fluid Structure Interaction

Further, fast simulation methods for biomechanical materials improve the interactivity and usefulness of our OPAL model.

We are actively looking for graduate students and undergraduates who would like to participate in the activities below. Please contact us if you are interested in getting involved.

Our approaches include:

Reduced Dimension Methods

Deformable materials can sometimes be simulated at fast, interactive rates by using a reduced dimension basis to control the system dynamics. We believe this can be usefully applied to anatomical structures. For example, the FEM tongue model of [Vogt et al, 2006] has ~3000 degrees of freedom (DOF), but it seems reasonable that its typical dynamic behavior, including internal muscle activation and interaction with the jaw and mouth, can be accounted for by perhaps several hundred DOF. We are investigating this approach first for the tongue and then for other structures

Air and Fluid Flow using Variational Finite Difference Method

We are looking at two approaches to air and fluid flow. First, Batty et al. (2007) have shown a restatement of fluid incompressibility that leads to a simple and accurate discretization around complex geometry on regular Cartesian grids (which allow particularly fast solves). We use this to add air and fluid simulation capabilities to ArtiSynth. Second, air and fluid flow are simulated by connecting ArtiSynth to a commercial fluid simulation package (e.g., Fluent). This latter approach is expected to be slower but will validate our own fluid models and will extend our simulation capabilities. The VFDM approach should also be able to efficiently enforce incompressibility in elastic solid models, resulting in significant speed improvements for our deformable tissue models. We are also considering Smoothed Particle Hydrodynamics (SPH) methods to simulate fluid flow rather than the standard methods with meshes.

Multimaterial Coupling

The VFDM approach above recasts incompressible fluid dynamics as the problem of minimizing kinetic energy with respect to pressure. [Batty et al. 2007] demonstrated how this allows the coupling between fluid and immersed rigid bodies to be achieved essentially for free. We extend this theory to include viscosity, damped elastic tissue, multiple fluids and frictional contact, allowing the entire system to be treated as a single quadratic program (QP), thus permitting a simple variational discretization.