Multilayered Porous Material: Poroelastic Waves with Thermal and Viscous Losses (Biot-Allard Model)

Application ID: 34531

In applications where pressure and elastic waves propagate in porous materials filled with air, both thermal and viscous losses are important. This is typically the case in insulation materials for rooms, lining materials in car cabins, or foams used in headsets and speakers. Another example is porous material in mufflers in the automotive industry.

In many cases, these materials can be modeled using the Poroacoustics material model (equivalent fluid model, only solving for the pressure) implemented in the Pressure Acoustics interface. Yet, the Poroacoustics model does not capture all of the effects and sometimes it is necessary to also include elastic waves in the porous matrix, solving a full poroelastic waves problem.

This is covered by the Poroelastic Waves interface, where the Biot-Allard model can be selected. This model includes the aforementioned viscous and thermal losses.

In COMSOL® software version 5.2a (and older):

The Poroelastic Waves interface of the Acoustics Module is based on the classical Biot theory used in Earth sciences. This model assumes that the saturating fluid is a liquid (water). The model only includes viscous losses. The material inputs are also different from those typically supplied with acoustic insulation materials.

The present model shows how the Poroelastic Waves interface, relatively simply, can be tailored to include the thermal and viscous effects as described by the Biot-Allard theory.

This model example illustrates applications of this type that would nominally be built using the following products: