Technical Papers and Presentations

In a continuation of our previous work on the modelling of the dynamic microstructural viscous and thermal dissipation mechanisms in cylindrical fibrous porous materials, we have now extended the approach to include isotropic 3D Kelvin foam cell geometries having cylindrical strut profiles.

In particular, the Thermoviscous Acoustic Fluid finite element modelling capabilities of COMSOL Multiphysics^®
are used to estimate the frequency-dependent viscous drag forces on the surface of the foam cell microstructure. Oscillatory heat transfer between the foam cell struts and the surrounding viscous fluid is included to allow for possible thermal expansion effects in the fluid. A representative elasticity matrix is estimated from the foam cell microstructure using periodic boundary conditions. These are then incorporated directly into the coupled poroelastic dynamic relations (Biot’s equations) allowing the prediction of vibroacoustic performance, without the requirement of traditional pore shape approximations or estimates of transport parameters.

The initial validations of the method are promising: in the low-frequency approximation representing essentially steady-state conditions, the method yields an exact comparison to a creeping flow CFD estimate of the Kelvin foam cell airflow resistance, and also to our analytical representation of the viscous drag forces on the Kelvin foam cell across the full frequency range.

This approach then allows the prediction of the vibroacoustic performance of the foam cell, using purely geometrical and constitutive material properties, helping to simplify the engineering of new material concepts for vibroacoustic applications. At this stage of development, the approach is highly suitable for periodic 3D printed lattice and foam cell structures, but may also be applied to foam cells having irregular strut profiles and geometries. The effects of closed, or-partially open cell membranes can also be considered.