Civil Engineering Reference
In-Depth Information
−
30
−
20
FEM
FTMM
FEM
FTMM
−
40
−
30
−
50
−
40
−
60
−
50
−
70
−
60
−
80
−
70
−
90
−
80
−
100
−
90
10
2
10
3
10
2
10
3
Frequency (HZ)
Frequency (HZ)
Figure 12.13
Space averaged quadratic velocity and radiated power of the receiver plate
of a plate - limp foam - plate system excited by a point force.
−
30
−
30
FEM
FTMM
FEM
FTMM
−
40
−
40
−
50
−
50
−
60
−
60
−
70
−
70
−
80
−
80
−
90
−
90
−
100
−
100
10
2
10
3
10
2
10
3
Frequency(HZ)
Frequency(HZ)
Figure 12.14
Space averaged quadratic velocity and radiated power of the receiver plate
of a plate - foam - plate system excited by a point force.
This correlation between FEM and FTMM is qualitatively acceptable and can be used
to estimate the insertion loss of a sound package. Figure. 12.15 shows the comparison
for the structure-borne insertion loss (SBIL) of the plate - foam - plate system using the
FTMM for two damping values of the bare panel:
η
1
0
.
3. The highly
damped panel may represent for instance a metal polymer sandwich panel (laminated
steel). In addition, the airborne insertion loss (ABIL), calculated using the same method, is
shown. The SBIL is obtained by taking the ratio of the acoustical - mechanical conversion
efficiencies obtained with and without the material (or, in db, taking the difference)
SBIL
=
10 log
10
input
radiated
=
0
.
007 and
η
1
=
with NCT
−
10 log
10
input
(12.58)
radiated
bare
The acoustical - mechanical conversion efficiency is defined by taking the ratio of the
acoustic radiated power to the mechanical input power:
radiated
/
input
. The latter is
