INTEC Acoustics
FDTD
The Finite-Diference Time-Domain (FDTD) and related numerical techniques for solving the acoustic wave equations have been studied at INTEC's Acoustics Group since the early 90's. New development have been made with respect to the numerical technique itself (non-cartesian and non-structured grids, compact schemes, moving windows, sub-gridscale features) and with respect to the range of physical situations it can be applied to (visco-thermal effects, nonlinear propagation, background flow (LEE), fluid structure interaction). Below you will find a few highlights of this research.
FDTD Demo
If you are unfamiliar with the finite difference time domain numerical technique for simulating sound propagation, you may like to have a look at the Java applet you can find on this page. It uses separate grids for acoustic pressure and particle velocity. The grids are staggered in space and time. Staggered grids are the most efficient approach for modelling sound propagation. Some additional terms in the fluid dynamics equations such as convective terms are less easily discretized in this grid.
The demo applet only allows using basic acoustic features and sources, but it is still a useful didactic tool.
Sub gridscale features
Features much smaller than the acoustic wavelength, can have a significant influence on the acoustic behaviour. The grid size chosen for numerical simulation depends on the wavelength of the sound of interest at one hand and the fine-structure that needs to be modelled on the other. If the fine-structure is the limiting factor, sub gridscale modelling can provide an efficient solution. Two particular situations have been studied:
visco-thermal boundary layers
small opening used in Helmoltz resonator type structures.