Environmental Engineering Reference
In-Depth Information
7.3
MeasuringWindTurbineNoise
Measuring.decibel.levels.is.extremely.important..Decibels.are.the.least.impor-
tant.aspect.of.the.various.sounds.that.wind.turbine.blades.make. 3 .The.decibel.
(dB).is.a.logarithmic.unit.that.indicates.the.ratio.of.a.physical.quantity.(usually.
power.or.intensity).relative.to.a.speciied.or.implied.reference.level..A.ratio.in.
decibels.is.10.times.the.logarithm.to.base.10.of.the.ratio.of.two.power.quantities. 4 .
Being.a.ratio.of.two.measurements.of.a.physical.quantity.in.the.same.units,.it.is.
a.dimensionless.unit..A.decibel.is.one-tenth.of.a.bel,.a.seldom.used.unit.
Power.is.the.amount.of.energy.used.(or.generated).per.unit.of.time..Sound.
pressure.and.sound.intensity.is.shown.in.Figure 7.3..Sound.pressure.change.
with.different.frequencies.is.demonstrated.in.Figure 7.4,.and.Figure 7.5.illus-
trates.the.measuring.of.sound.
A,. B,. C—weighting. compensates. for. the. sensitivity. of. the. human. ear.. A,.
B,.C—weighted.levels.designated.as.dB(A)..Relative.response.has.less.level.
between. 63-250. Hz.. Sound. emissions. reduce. when. frequencies. increase.
(Figure 7.6).
7.4
ReduceNoiseinWindTurbineBlades
Of. growing. signiicance. is. the. aerodynamic. part. of. wind. turbine. noise:.
CTQ. (critical. to. quality).. It. is. gaining. importance. from. a. competitive. and.
Sound Pressure Decreases when Sound Intensity Decreases
140
Column B
Column C
Column D
120
100
80
60
40
20
0
1
2
3 4
Sound Intensity W/SQ.M
5
6
7
FIGURE 7.3
Sound.pressure.and.sound.intensity..(From.Rogers,.A..L..2006..University.of.Massachusetts..
Online.at:.www.renewableenenergy.world.com..With.permission.)
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