Civil Engineering Reference
In-Depth Information
Transmission loss of a plate - wool - plate system
The second example is taken from Villot
et al
. (2001). It consists of the transmission
loss of a double wall system made up of a steel plate, a mineral wool and a laminated
plate. The system measures 1
.
3
×
1
.
3 m and is excited by a diffuse acoustic field. The
mineral wool is modelled as a poroelastic layer and the panels as thin plates in bending.
The parameters of the three layers are given in Table 12.2. The comparison between tests
and predictions is shown in Figure 12.5. Good agreement is observed, especially at low
frequencies where size effects are important.
Transmission loss of an orthotropic plate
The next transmission loss example illustrates the use of the TMM for an orthotropic
panel. In this case, the properties of the material and thus the structural wave number and
the transmission coefficient are heading dependent. The example, taken from Leppington
et al
. (2002), considers a 1
.
4
×
0
.
9 m orthotropic panel excited by a diffuse field. The
properties of the panel are given in Table 12.3. Note that these physical properties are
derived from the following parameters:
D
11
=
21
.
34 Nm;
D
12
+
2
D
66
=
27
.
78 Nm;
Table 12.2
Parameters of the steel wool - laminated plate system.
∝
Material
Thickness,
φσ
ρ
1
E
ν
s
(N s/m
4
)
(
µ
m) (
µ
m) (kg/m
3
)
(Pa)
h
(mm)
10
11
2
.
1
×
Steel plate
0.75
7850
0.3
0.03
10
3
10
3
Mineral wool
30
0.95 34
×
1 0 0
0 0
×
0 . 8
10
8
Laminated plate
3
1360
6
×
0.15 0.15
70
60
50
40
30
20
10
Prediction: FTMM
Test
0
10
2
10
3
10
4
Frequency (Hz)
Figure 12.5
Transmission loss of a double wall system system; experimental data taken
from Villot
et al
. (2001).
