Civil Engineering Reference
In-Depth Information
ReZ - Measurement
ReZ - Prediction (TMM)
ReZ - Prediction (FEM)
ImZ - Measurement
ImZ - Prediction (TMM)
ImZ - Prediction (FEM)
30
20
10
0
−
10
−
20
−
30
200
400
600
800
1000
1200
1400
Frequency(kHz)
0
◦
of a multilayer
sound package bonded on to a rigid impervious wall. Measurement vs predictions. Mea-
surements reproduced from Brouard
et al.
(1994).
Figure 11.17
Surface impedance
Z
at an angle of incidence
θ =
Table 11.8
The parameters used to predict the results of Figure 11.18.
Material
Thickness
φ
σ
α
∞
ρ
1
E
ν
s
(N s/m
4
)
(
µ
m) (
µ
m) (kg/m
3
)
h
(mm)
( )
0.94 40
×
10
3
4
.
4
×
10
6
Glass wool
3.8
1.06
56
110
130
0 .1
10
10
7
.
×
Plate
1
2800
0.3 0.007
wool and the plate can be decoupled by inserting an air gap between the glass wool
and the plate. The air gap is simulated by a fluid layer. The new predicted transmission
loss is represented in Figure 11.18. The reinforcement of the transmission has decreased
noticeably.
It may be noticed that the effect of the decoupling was previously pointed by Shiau
et al
. (1988), for different configurations, and observed by Roland and Guilbert (1990)
for the case of the same glass wool bonded onto a plate made of concrete.
11.7.4 Diffuse field transmission of a plate - foam system
The material is a foam of thickness
h
=
2
·
54 cm bonded onto a 0.6 mm aluminium plate.
The parameters for the foam and the plate are given in Table 11.9. The transmission loss is
predicted using the transfer matrix method. The integration is usually performed up to an
angle smaller than 90
◦
(Mulholland
et al
. 1967), and the upper limit for the integration has
