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Example 14: Sound-absorbing Material (miki model)

General

In Example 13, material properties of sound-absorbing materials are calculated using Excel, while, in this example, material properties can be calculated on the porous absorbing material tab.
The model of this example is created referring to the website of Architectural Institute of Japan (AIJ).
The characteristics of a sound-absorbing material is analyzed with the miki model (see the example 13 on the Femtet help menu).
Obtain this session's project file. (Right-click and choose 'Save link as')

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item

Settings

Analysis Space

Thickness in Depth Direction: 1 [mm]

Model Unit

Analysis Conditions

Item	Settings
Solver	Acoustic Analysis [Mach]
Analysis Type	Harmonic Analysis
Options	Select [Calculate loss].

The harmonic analysis tab and mesh tab are set as follows.

Tab	Setting Item	Settings
Mesh	General Mesh Size:	1
Harmonic Analysis	Frequency	Minimum: 100 [Hz] Maximum: 10000 [Hz]
	Interval	Select [Log Step] Number of Divisions: 100
	Frequency Sweep	Select Discrete Sweep.

Model

Create a rectangular sheet body, 50 x 1 [mm], and assign sound-absorbing material to the body. To its left, create a sheet body of air, 2 x 1 [mm].

Set the speed boundary condition, v, to the edge at the left end of the air domain. The other edges have no boundary conditions, resulting in outer boundary conditions of the rigid wall.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
0/Solid	Sound-absorbing Material	Sound-absorbing Material
1/Solid	AIR	000_Air

Material Name	Tab	Settings
Sound-absorbing Material	Sound Speed	Real Part: 340 [m/s]
	Density	1.144 [kg/m3]
	Porous Absorbing Material	Select [miki model] Flow Resistivity: 6900 [Ns/m4] Tortuosity: 1 Porosity: 1

Boundary Condition

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Settings

v/Edge

Sound Wave

Speed

1.0 [m/s]

Select [Specify the incident wave]

Outer Boundary Condition

Acoustic

Rigid Wall

Results

1. Frequency Response of Radiation Impedance

In the result table, go to the [Detailed Radiation Impedance] tab, select [Show all results summary], and click the [Graph] button. The frequency response graph will appear.

The figure is the same as in Example 13: Sound-absorbing Material (Table Input).

See Example 13 for calculating the frequency response of absorbing ratio.

Fig. 1 Frequency Response of Radiation Impedance (Table and Graph)