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Home / Examples / Acoustic Analysis [Mach] / Example 15: Mass Law (Acoustic Analysis)
Example 15: Mass Law (Acoustic Analysis)
General
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The frequency response of the wall's transmittance is solved.
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An analysis that considers the weight of the wall is required. The acoustic analysis meets this condition and is performed here without accounting for the elastic wall. Refer to Example 6: Piezoelectric-Acoustic Couple Analysis for the analysis when the wall is an elastic material.
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Obtain this session's project file. (Right-click and choose 'Save link as')
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Results will vary depending on Femtet version and the PC environment.
Analysis Space
|
Item |
Settings |
|
Analysis Space |
2D |
|
Model Unit |
m |
|
Thickness in Depth Direction |
1.0 [m] |
Analysis Conditions
|
Item |
Settings |
|
Solver |
Acoustic Analysis [Mach] |
|
Analysis Type |
Harmonic Analysis |
|
Options |
Select [Calculate loss] |
|
Tab |
Setting Item |
Settings |
|
Harmonic Analysis |
Frequency |
Linear Step by Number of Divisions
Minimum: 100[Hz] Maximum: 4000 [Hz] |
|
Interval |
Number of Divisions: 4 |
Model
A wall is placed between air bodies.
Body Attribute and Material Property Setting
|
Body Number/Type |
Body Attribute Name |
Material Name |
|
0/Solid |
AIR |
000_Air * |
|
1/Solid |
WALL |
Wall |
|
2/Solid |
AIR |
000_Air * |
* Available from the material DB
|
Material Name |
Tab |
Material Name |
|
Wall |
Density |
1000 [kg/m3] |
|
Sound Speed |
10000 [m/s] |
Boundary Conditions
|
Boundary Condition Name/Topology |
Tab |
Boundary Condition Type |
Settings |
|
v/Edge |
Acoustic |
Speed
|
1 [m/s] Select [Specify the incident wave] |
|
z/Edge |
Acoustic |
Acoustic Impedance |
402.56[Pa・s/m] * |
* Set the specific acoustic impedance of air.
Results
The resulting sound pressure distribution at 1.075e+03 [Hz] is shown below.
The contour diagram based on the setting below is shown.
| Acoustic Analysis | 1: 1.075000E+3 [Hz] |
| Sound pressure [Pa] | Value |
| 0 [deg] | Linear |
Table 1. Setting in Result Field for Fig. 1
Fig. 1 Sound Pressure Distribution 1.075 [kHz]
Calculate the transmittance (T). The equation below will give the transmittance.
T = It/Ii
It: Can be acquired on the [Loss at Boundary] tab in the result table.
Ii: Can be acquired on the [Input Power] tab in the result table.
Calculate using the results from Femtet.
The results at 100 [Hz] are shown below.
Ii = 3.25 [W]
It = 201.28 [W]
-10・Log(3.25/201.2) = 17.9 [dB]
Calculation of theoretical values
20・Log(f・m) - 42.5 = 17.5 [dB]
Mass: m = 10 [kg], calculated from the width of the wall, 1 [cm], the thickness in the depth direction, 1 [m], and the density, 1000 [kg/m3] of the analysis model.
Frequency: f = 100 [Hz]
