30/11/2012Single Event Level - SEL1 The Single Event Level SEL Angelo Farina Dip. di Ingegneria...
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Transcript of 30/11/2012Single Event Level - SEL1 The Single Event Level SEL Angelo Farina Dip. di Ingegneria...
30/11/2012 Single Event Level - SEL 1
The Single Event Level The Single Event Level SELSEL
Angelo Farina
Dip. di Ingegneria Industriale - Università di Parma
Parco Area delle Scienze 181/A, 43100 Parma – Italy
30/11/2012 Single Event Level - SEL 2
The Equivalent Continuous Level (LThe Equivalent Continuous Level (Leqeq):):
T
rifTeq dt
p
tp
TL
02
2
,
)(1log10
The continuous equivalent level Leq (dB) is defined as:
where T is the total measurement time, p(t) is the instantaneous pressure value and prif is the
reference pressure
• Leq,T dB (linear frequency weighting)
• LAeq,T dB(A) (“A” weighting)
30/11/2012 Single Event Level - SEL 3
Definition of SEL (Single Event Level)Definition of SEL (Single Event Level)
sTT
TLeqSEL 1log10 0
010
the SEL is the equivalent level packed in one second
30/11/2012 Single Event Level - SEL 4
Definition of SEL (Single Event Level)Definition of SEL (Single Event Level)
the SEL is the equivalent level packed in one second
SEL
1s
30/11/2012 Single Event Level - SEL 5
Example of SEL (Single Event Level)Example of SEL (Single Event Level)
Time history of the passage of an aircraft
45
55
65
75
85
95 L
ive
llo
So
no
ro in
dB
(A)
0 10 20 30 40 50 Tempo (s)
Fokker 50 - Esponenziale - FAST
30/11/2012 Single Event Level - SEL 6
Noise from roads and railwaysNoise from roads and railways
Angelo Farina
Dip. di Ingegneria Industriale - Università di Parma
Parco Area delle Scienze 181/A, 43100 Parma – Italy
30/11/2012 Single Event Level - SEL 7
Contnuous Line SourcesContnuous Line SourcesMany noise sources found outdoors can be considered line sources: roads, railways, airtracks, etc.
Geometry for propagation from a line source to a receiver
- in this case the total power is dispersed over a cylindrical surface:
d
R
r
dx XO
)(8log10
)(6log10
emissioncoherentdLL
emissionincoherentdLL
Wp
Wp
In which Lw’ is the sound power level per meter of line source
dx
r
WI
24
'
30/11/2012 Single Event Level - SEL 8
Coherent cylindrical fieldCoherent cylindrical field
• The power is dispersed over an infinitely long, pulsating cylinder:
rlg108'LL
rlg102lg10WL
Wlg10
W
W
ILr2
W
lg10I
Lr2W
lg10I
Ilg10L
Lr2
W
S
WI
WI
oo
o
oooI
r
L
In which Lw’ is the sound power level per meter of line source
30/11/2012 Single Event Level - SEL 9
““discretediscrete”” (and incoherent) linear sources (and incoherent) linear sources
Another common case is when a number of point sources are located along a line, each emitting sound mutually incoherent with the others:
Geometry of propagation for a discrete line source and a receiver
- We could compute the SPL at the receiver as the energetic (incoherent) summation of many spherical wavefronts. But at the end the result shows that SPL decays with the same cylindrical law as with a coherent source:
Lw’
Note that the incoherent SPL is 2 dB louder than the coherent one!
d
R
1
r 1 r i
S r i-1
i
a
]dB[6dlog10alog10LL Wpp
30/11/2012 Single Event Level - SEL 10
A road is a sequence of point sourcesA road is a sequence of point sources
d
V (km/h)EXAMPLE:
• V = 50 km/h
• Q = 500 vehicles/h
• Lw,1veic = 90 dB(A)
Hence:
• d = V/Q = 50000/500 = 100 m
• Lw’ = Lw,1vehicle – 10·log10(d) = 90 – 10·log10(100) = 70 dB(A)
Consequently, at a distance r = 50 m, we get:
• Lp,50m = Lw’ – 10·log10(r) – 6 = 70 – 10·log10(50) – 6 = 47 dB(A)
30/11/2012 Single Event Level - SEL 11
Definition of SEL (Single Event Level)Definition of SEL (Single Event Level)
sTT
TLeqSEL 1log10 0
010
The SEL is the equivalent level packed in one second
45
55
65
75
85
95
Liv
ello
So
no
ro in
dB
(A)
0 10 20 30 40 50 Tempo (s)
Fokker 50 - Esponenziale - FAST
Leq
SEL
30/11/2012 Single Event Level - SEL 12
Relationship between SEL and Lw’Relationship between SEL and Lw’
6log101000
log10 10101.
r
V
QLLeq vehicleW
3600log1065.7log101000
1log10 101010
VLwSEL
We did find that:
SEL is measured at the standard distance r = 7.5 m, and referes to just one of the Q vehicles passing each hour, packed in one second:
19.9log10 10 VLwSEL
When V=50 km/h, we get:
SEL = Lw – 26.19 dB(A)For a constant value of Lw, SEL decreases
with the speed of vehicles V
30/11/2012 Single Event Level - SEL 13
Computing the time profileComputing the time profile
r
R
r’(x)
x O
Lw
v (m/s)
v·t
11log10)(
11'log10)(22
10
210
tvrLwtLp
trLwtLp
Profilo Temporale - Lw = 90 dB, r = 50 m
10
15
20
25
30
35
40
45
50
-120 -90 -60 -30 0 30 60 90 120
Tempo (s)
Lp
(d
BA
)30
30/11/2012 Single Event Level - SEL 14
Effect of vehicle’s speedEffect of vehicle’s speed
Sound Power Level Lw increases with speed above 30 km/h
Emissione sonora vs. velocita'
88
90
92
94
96
98
100
102
0 50 100 150 200
Velocita' (km/h)
Lw
(d
BA
)
30/11/2012 Single Event Level - SEL 15
Effect of vehicle’s speedEffect of vehicle’s speed
Sound Power Level Lw increases with speed above 30 km/h
Emissione sonora vs. velocita'
89
90
91
92
93
94
95
10 100
Velocita' (km/h)
Lw
(d
BA
)
20 30 40 50 60 70 80
6 dB
/radd
.
Engine
Rolling
Aerodynamics
30/11/2012 Single Event Level - SEL 16
Time profile vs vehicle’s speedTime profile vs vehicle’s speed
Increasing the speed the profile becomes shorter and higher
Profilo Temporale
20
25
30
35
40
45
50
-120 -90 -60 -30 0 30 60 90 120
Tempo (s)
Lp
(d
BA
) 30
50
70
30/11/2012 Single Event Level - SEL 17
Immissione sonora vs. velocita'
55
56
57
58
59
60
61
62
63
64
65
10 100
Velocita' (km/h)
SE
L (
dB
A)
a 50
m
20 30 40 50 60 70 80
SEL vs vehicle’ speedSEL vs vehicle’ speed
SEL has a minimum around 70 km/h
3 dB/radd.
-3 dB/radd.
30/11/2012 Single Event Level - SEL 18
SEL vs vehicle’ speedSEL vs vehicle’ speed
SEL has a minimum around 70 km/h
Immissione sonora vs. velocita'
55
56
57
58
59
60
61
62
63
64
65
0 50 100 150 200
Velocita' (km/h)
SE
L (
dB
A)
a 50
m
30/11/2012 Single Event Level - SEL 19
Definition of personal exposure level (LDefinition of personal exposure level (Lepep):):
T
02rif
2
ep dtp
)t(p
h8
1log10L
The personal exposure level Lep (dB) is defined as:
where 8h is the standardised duration of a work day. Hence:
8h
Lep
h
TLL eqep 8
log10
30/11/2012 Single Event Level - SEL 20
Example of LExample of Lepep computation: computation:
1h 1h 2h 3h 1h 2h
7580
75
84
7578
dBh
L
dBh
L
ep
eq
4.818
102101103102101101log10
4.8010
102101103102101101log10
8.75.74.85.70.85.7
8.75.74.85.70.85.7