Why Do a Biot Characterization of Acoustic Materials?
— One Word: Anticipation!
— Multilayer Systems
Biot Modeling and Properties of Porous Materials
— How to Model a Porous Material?
— What are the Equivalent Fluid Parameters?
— And What are the Elastic Parameters?
— In Conlusion…
Acoustic Simulation Software
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Why Do a Biot Characterization of Acoustic Materials?
One Word: Anticipation!
Acoustic simulation tools allow to anticipate and address noise problems from the very beginning of a product’s design.
Without these tools, acoustic problems are often detected during the final prototyping phase where other design choices are often fixed and difficult to modify. Thus, the late consideration of acoustics can lead to significant delays and additional costs in the design of the final product.
Phase 1: Simple Materials (Properties Characterization)
Phase 2: Complex Parts (NOVA)
Phase 3: Complex Models (VA-One, Siemens Virtual Lab, Actran, etc.)
Multilayer Systems
Transportation industries (automotive, aeronautics) incorporates in their products complex acoustic treatments often composed of multilayer systems integrating porous acoustic materials.
It is therefore essential to identify the physical properties of each material involved in the final product.
Biot Modeling and Properties of Porous Materials
How to Model a Porous Material?
Porous or fibrous acoustic materials have complex and very small structures. Modeling them at this level of detail is extremely complicated.
A more general approach is to consider the material as a homogeneous material with a fluid phase coupled to a solid phase.
What are the Equivalent Fluid Parameters?
Propagation equations in fluid and solid phases depend on the intrinsic properties of these materials.
By neglecting skeleton vibrations (rigid or limp solid phase), the material can then be seen as an equivalent fluid. Typically, up to seven parameters are required to model it (JCAL model, or Johnson – Champoux – Allard – Lafarge):
And What are the Elastic Parameters?
Considering the skeleton vibrations in addition to the equivalent fluid parameters, the following elastic parameters must be added to solve the Biot model:
In Conclusion…
Equivalent Fluid Parameters
+
Elastic Parameters
=
Biot Parameters
Acoustic Simulation Software
Main acoustic simulation software (ESI Group VA-One & NOVA, Hexagon Actran, Siemens Simcenter, Dassault System Simulia, Comsol, etc.) use these models to simulate acoustic porous materials. Then, a characterization of those acoustic materials is possible.
Different Ways to Obtain these Acoustic Parameters!
Direct Method
By measuring each of these properties on specific test bench, as Mecanum Porosity meter, airflow resistivity meter, tortuosity meter or QMA
Inverse Method
By extracting these properties via a mathematical approach of genetic algorithm minimisation of impedance tube measurements
Indirect Method
By extracting the various parameters via impedance tube measurement of the dynamic compressibility and dynamic density module (ASTM E2611)
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