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7/28/2019 Acoutics Applications Related to Wind Turbines Webinar
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www.bksv.com
Brel & Kjr Sound & Vibration Measurement A/S.
Copyright 2009. All Rights Reserved. Tony Spica
Acoustics Applications for Wind Turbines
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Tony Spica Western Region Application Engineer
z Application Engineer and Sound PowerSolution Manager
z Graduate of the University of Michigan
Studied Sound Engineering
z Worked for Bruel and Kjaer in Detroit and relocatedto the Los Angeles area in August, 2008.
z Prior to Bruel and Kjaer, worked for AdvancedTechnology and Testing in Detroit as an NVHEngineer designing and qualifying NVH testsystems.
z Also worked for DLC Design testing loud speakers
and qualifying acoustic spaces in vehicles.z Pro-audio hobbyist and soccer player.
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Agenda
- Brief overview of new Bruel and Kjaer products
- Introduction to Sound Power testing
- Review of IEC 61400-11
- Noise Source Identification Techniques
- Using Acoustic Arrays with Turbines
- Noise Monitoring
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Latest B&K Hardware
z LAN-Xi Hardware
Dyn-X technology up to 160 dBdynamic range for narrowbandmeasurements.
Robust made for field and lab use.
Use with TEDS transducers.
One cable operation with PoE and PTP .
Use in a rack or distributed system save on cable costs.
Use stand alone for computer-lessrecording direct to SD card.
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B&K Hardware cont.
World Class Sound Level Meters
z 2250 and 2270 feature:
Frequency analysis
FFT Analysis
Full logging capability
Recording and triggered recording
No gain range setting always in range
Building acoustics measurements
Annotation microphone
Complete remote control and access via internet even 3G wireless!
z 2270:
Dual channel building acoustics
Intensity probe measurements Noise source mapping
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B&K transducers
Microphones
z Worlds most respected microphones
z Titanium and stain-less steel construction
z Extreme long term stability estimated spec in dB/1000 years
z Excellent environmental stability
z High Precision
Each Microphone comes with correction curves for microphone incidence and acousticspace. Allows use of a Pressure-field microphone in a diffuse field with confidence andaccuracy at high frequencies.
z Worlds first multi-field microphone Type 4961
Accelerometersz Excellent stability and accuracy
z Req-X allows for extended frequency response and correction for internalresonance frequency as well as various mounting techniques.
z Measure frequencies from DC and up to 26 kHz.
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LDS Wind Energy Shaker Suite
Heavy Duty Parts-Gearbox
-Generator
Small Parts
-Transducers
-Electronic devices
-Blades
Medium Size Parts-Electronic parts
-Cooling fans
www.bksv.com
Brel & Kjr Sound & Vibration Measurement A/S.
Copyright 2009. All Rights Reserved.
Introduction to Acoustics andSound Power Testing
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Basic Parameters of Sound (cont.)
2
2
10log10 op
p
pL =
25 /102 mNpo =
Pa0=2
0
10log10I
ILi =
2/1 mpWIo=
o
w
W
WL 10log10=
pWWo 1=
SoundPressure
Level
SoundIntensity
Level
SoundPower
Level
Receiver
Path
Source
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z Sound Power, W [ Watts ] : The rate per unit time at whichairborne sound energy is radiated by a source
0
log10W
WLW =
What is Sound Power?
dSIWS
n=
z Sound Power Level, where W0 =1 pW
W
Iz Sound Intensity, I [ W/m2 ] :
The rate of acoustic energy flowper unit area
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Sound Source :
Power W [Watt] Pressure p [N/m2]Electrical Heater :
Power W [Watt] Temperature t [C]
Sound Pressure vs. Sound Power
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Sound Pressure vs. Sound Power
z Sound Pressure
- Is dependent on the acoustic environment
- Is the product of the sound source(s) and the acousticenvironment
z Sound Power
- Is independent of the acoustic environment
- Is therefore a good parameter for making comparisons
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Sound Power= 0.01 Watt
Sound Levels Under Free-field Conditions
c
p
r
W
2
22 ==
Example:
dB100L
dB10
01.0
log10
dBW
Wlog10L
W
1210
0
10W
==
=
dB5.88L
dB10
1007.7
log10
dBlog10L
12
4
10
0
10
=
=
=
Pascal0.532
400000707.0cp
=
==
2mW
22
000707.0
5.12
01.0
r2
W
=
=
=
( )dB5.88L
dB1020
532.0
log10
dBp
plog10L
p
26
2
10
20
2
10p
=
=
=
W =0.01 Watt
Sound Power Sound PressureSound Intensity
LI = Lp under free-field conditions
r =1.5 m
Where
is the area of the
hemisphere
22r
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Methods for Sound Power Testing
z Free Field Method ISO 3744
Allows measurement in an essentiallyfree field
Measure Sound Pressure to obtain Sound Power
z Reverberation Room
Requires a reverb chamber
Measure Sound Pressure to obtain Sound Power
Compares a known sound power source to object under test
z Intensity Method
Can be performed in most environments
Does not require a special room
Calculates Sound Power from Sound Intensity measurements
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Why Use Standards in Acoustic Testing?
z Acoustic measurements are highly standardised
To make sure people use the same methods
To simplify comparison of results
z Standards for sound power determination
Three grades of sound power determination Precision (most accurate) Engineering (medium accuracy) Survey (least accurate)
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General view of ISO standards for Sound PowerStandard Accuracy
Test
environment
Volume of
sound sourceCharacter of noise
Sound power levels
obtainable
Optional information
available
ISO 3741 Precision Reverberation
room
Preferably less
than 2 % of test
room volume
Steady, broad-band,
narrow-band or
discrete frequency
A-weighted and in one-third-
octave or octave bands
ISO 3743-1 Engineering Hard-walled
room
ISO 3743-2 Engineering Special
reverberation
room
ISO 3744 Engineering Essentially free-
field over a
reflecting plane
No restrictions;
limited onlyby
available test
ISO 3745 Precision Anechoic or
hemianechoic
room
Characteristic
dimension less
than half
ISO 3746 Survey No special test
environment
A-weighted
ISO 3747 Engineering
or survey
Essentially
reverberant field insitu, subject to stated
qualification req.
Steady, broad-band,
narrow-band ordiscrete frequency
A-weighted from octave
bands
ISO 9614-1 Precision,
engineering
or survey
Positive and/or negative
partial sound power
concentration
ISO 9614-2 Engineering
or survey
Sound pressure levels as
function of time
Other frequency weighted
sound power levels
A-weighted and in octave
bands
A-weighted and in one-third-
octave or octave bands
Directivity information and
sound pressure levels as a
function of time; single-event
sound pressure levels; other
frequency weighted sound
power levels
Usingsoundpressure
Usingsoundintensity Band l imited (one-third-
octave 50 Hz-6 300 Hz) A-
weighted and in 1/3-octave
or octave bands. Grade of
accuracy is determined from
field indicators
Any
Any
Broadband, narrow-
band or discrete
frequency, if stationary
in time
No restrictions
Preferably less
than 1 % of test
room volume
No restrictions;
limited onlyby
available test
environment
Any, but no isolated
bursts
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PULSE Free Field Method
z Sound power determination accordingto:
ISO 3744 (engineering)
ISO 3745 (precision)
ISO 3746 (survey)
z Based on Sound Pressuremeasurements in a Free-Field orEssentially Free-Field
z Quick and easy to follow
z Do not require a special acoustic testfacility (when following ISO 3744 andISO 3746)
z Scalable solution
Move the microphone(s) to completethe measurement or measure
simultaneously in all the microphonepositions
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ParallelepipedHemisphereX
Y
Z
X
Z
Y
cc
2a2bl1
d
l2
l3
z Measure sound pressure at different microphone positions over a closedmeasurement surface totally enveloping the source or ending on areflecting plane
Sound Power Determination in a Free-Field
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Sound Power Determination in a Free-Field
z At each microphone position measure also the background noise,that is the noise with the measurement object switched off
z Determine the corrected surface sound pressure level Lpf, that isthe average sound pressure level corrected for background noiseand environmental correction factor
z The sound power level is:
)/log(10 0SSLL pfW +=where:
S is the area of the measurement surface [m2]S0=1 m2
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Free Field Method - choice of ISO standards
3746 (survey)
3745 (precision)
3744 (engineering )
User Defined
Hemisphere
Parallelepiped
Unequal
Equal
Parameter
ISO 3744
Engineering method
Grade 2
ISO 3745
Precision method
Grade 1
ISO 3746
Survey method
Grade 3
Test environment Outdoors or in a large roomAnechoic or semianechoic
roomOutdoors or indoors
Criterion for test
environment
Limitation for background
noise
Minimum number of
microphone positions9 10 4
dB22K dB0.52K dB72K
dB1.3
dB6
1
K
L
dB1.3
dB6
1
K
L
dB3
dB3
1
K
L
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Intensity scanning method
z Intensity Scanning Method
z according to ISO 9614-2
z do not require a special acoustic testfacility
z gives directional information
z tolerant of high background noiselevels
z a number of field indicators arecalculated to indicate:
the quality of the determination,
actions to increase the grade of
accuracy of determination
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Sound Power from Sound Intensity
z Sound Power equals the Surface integral of Sound Intensity
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Stationary Sources
Effects of External Sources
Sound Power based on Sound Intensityis insensitiveto background noise
0=S
SdIrr
WSdIS
=rr
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Point Measurements Sweeps
ISO 9614 Part 1 ISO 9614 Part 2
The Sound Power (Intensity) Standards
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Intensity, scanning, ISO 9614-2
z Advantages
Easier to follow than point-based methods
Can be used in-situ, no special acoustic test facility required
Gives directional information
Isolates the test object and allows segmentation of an object
z Disadvantages
Only gives engineering or survey grade measurements, noprecision grade
Experience required to acquire good scanning technique
Will (usually) take longer then the pressure-based methods
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Reverberation Room Method
z Pressure-based sound power method
z according to:
ISO 3741 (precision)
ISO 3743 (engineering)
z Very simple to follow
z Both multiple microphones and thetraversing microphone are supported
z Scalable solution
Move the microphone(s) to completethe measurement or measuresimultaneously in all the microphonepositions
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z Comparison Method:
Utilize a Reference Sound Source (B&K 4204)
LW is known for each 1/3 octave band
Measure LP with RSS Operating
Measure LP with Test Object Operating
Sound Power Measurement
LW = LW(RSS) - LP(RSS) + LPwhere
LW Sound Power of Test Object
LP Sound Pressure Level produced by Test Object
LW(RSS) Sound Power of Reference Sound Source
LP(RSS) Sound Pressure Level produced by Reference Sound Source
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Diffuse-field Methods, ISO 3741, ISO 3743
z Advantages
Comparison method (using reference sound source) very simpleto follow
Fast, when rotating microphone boom is used
ISO 3741 gives precision measurements, (ISO 3743 givesengineering)
z Disadvantages
Require use of a reverberation room meeting specifiedrequirements
Measurement of noise sources having narrowband contentplaces additional requirements on the room
Other uses of reverberation room are very limited
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www.bksv.com
Brel & Kjr Sound & Vibration Measurement A/S.
Copyright 2009. All Rights Reserved.
Testing Wind Turbines for Sound Powerand tonality with IEC 61400:11
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IEC 61400:11 Acoustics Emissions of Turbines
z Wind Turbine Noise Emissions are characterized
Provides the apparent A-weighted sound power levels, spectra, andtonality at integer wind speeds from 6-10 m/s (13-22 mph) for oneturbine.
With respect to a range of wind speeds and directions
Specifies location of acoustic measurement positions
Requires acquisition of meterological and wind turbine operationaldata
z Pre-requisites and related standards:
IEC 60651 SLM
IEC 60688 Microphones/transducers
IEC 60804 Integrating-averaging SLMs
IEC 61260 Oct. and 1/3 Oct. filters
IEC 61400-12 Turbine Power Performance Testing
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IEC 61400:11
z
Acoustics Instruments Must meet SLM Type 1 requirements and use a microphone with adiameter that is not larger than 13 mm (1/2 in.)
All measurements must be recorded
Constant frequency response from 45 Hz to 11.2 kHz.
Fractional octave filters must meet IEC 61260 requirements for Class1 filters.
Narrow band spectra analysis must meet IEC 60651 type 1requirements from 20 Hz 11.2 kHz.
Microphone is used with a primary wind screen with a diameter of90mm.
A secondary wind screen may be used. This wind screen shouldconsist of a hemispherical wire frame at least 450 mm in diameter
covered with a 13 to 25 mm layer of open cell foam. If a secondary windscreen is used, the influence on frequency response
must be documented and corrected for.
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What instrumentation fi ts the bill?
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IEC 61400:11
z Non-acoustic Instruments Anemometer
Should be within +/- .2 m/s from calibration value for the range of test.
Electric power transducer
Must meet accuracy requirements of IEC 60688 Class 1.
Wind direction transducer
Must be accurate to +/- 6 degrees.
Atmospheric pressure
+/-1 kPa
Temperature
+/- 1 degree C
All instrumentation should be calibrated at regular intervals withtraceability to a national or primary standards lab.
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IEC 61400:11
Microphone positions
- Primary position (1) is directlydownwind +/- 15 degrees.
-Additional microphonepositions at same distance Ras primary position +/- 20%.
-Distance R=H+D/2
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IEC 61400:11
Microphone Boardz The microphone is placed lying on a circular board at least 1 meter
in diameter.
z It must be acoustically hard
Plywood >12mm thick
Metal >2mm
z A larger board is recommend for
soft ground.
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IEC 61400:11
z Anometer and wind direction transducer are placed upwind at adistance of 2D-4D and a height from 10m to the rotor center.
z They should not be placed in the wake of another wind turbine.The wakeis considered to be 10 rotor diameters downwind of thewind turbine.
z Preferred Method:
Wind speed may be derived from electric output of turbine using apower vs. speed curve. This data does not have to come from theturbine under test but it is preferred that it is. If the data is collectedfrom another turbine, it should be of the same type and have the samecomponents as the turbine being tested.
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IEC 61400:11
Measurements at Position 1
z LAeq, background noise, and 1/3rd octave measurements (centerfrequencies from 50 Hz to 10 kHz) at each wind speed.
z Two minutes of Narrowband wind turbine noise and backgroundnoise are required at each integer wind speed. Thesemeasurements should be as close to integer wind speeds aspossible.
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IEC 61400:11 Apparent Sound Power
Measurements
y=0.0413x2 +8.6601x- 10.793
R2 =0.9802
30
35
40
45
50
55
60
65
70
75
80
6 6.5 7 7.5 8 8.5 9 9.5 10
Wind Speed (m/s)
dB(A)
z Create a second orderregression of the 30+measurements of the turbineat different wind speeds andanother for backgroundmeasurements.
z These regressions are usedto determine corrected SPLlevels at integer wind speedswhich are used to calculatesound power.
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IEC 61400:11 Apparent Sound Power
Sound Power can now be calculated using the formula:
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IEC 61400:11 Tonality
z Tonality is determined from the narrowband analysis over thesame wind speed range as the sound power level measurements. The narrowband analysis is performed with frequency resolution between 2 and
5 Hz for frequencies less than 2 kHz and 2-12.5 Hz for 2 kHz 5 kHz.
z Tones are identified by comparing levels of adjacent bands in thesame critical bandand correcting for background noise.
The calculation itself is intensive and not simple to perform manually.
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Wouldnt it be nice
If someone made a system that made this test easy?
It is a standard application inPulse!
Type 7914
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Noise Source Identif ication Techniques
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Noise Source Identification Techniques
Sound Pressure Map
Sound Intensity Map
z Sound Pressure Map Does not represent energy flow
Poor resolution
Easy to misinterpret
z Sound Intensity Map Directly represents energy flow
Good resolution
z Selective Intensity Map
Calculates the part of the full intensity
that is coherent with a reference signal
Selective Intensity
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Array Hardware and Applicat ions
z Arrays for Beamforming Wheel arrays and Random arrays
Optimized array geometry
Acoustical camera
z Modular Rectangular Arrays Holography (STSF, robot option)
Transient Holography (NS-STSF)
z Combo Arrays Low-frequency Holography (SONAH)
High-frequency Beamforming
Engine, Gearbox,
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Beamforming versus Non-Stat/STSF
Beamforming NS/STSF
Frequency range 500-20 kHz 50 - 6.4 kHz
Resolution Min{z,}
Area covered 60 deg. opening angle Size of array
Measured quantities Relative pressure Pressure, Particle velocity,
Intensity (calibrated)
Measurementdistance (z)
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Quick general solution for outdoor directional NSI
z 30 integrated microphones, 3.5 m diam.
z Suppresses noise from backz Resolution at 100 m and 1 kHz: 10 m
z Can separate contributions from differentwind turbines and buildings
z Can distinguish noise from hub and outerpart of blades at medium-high frequencies
Pentangle
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Actual measurement data...
Delay-And-Sum NNLS deconvolution
500 Hz
630 Hz
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Actual measurement data...
Delay-And-Sum NNLS deconvolution
800 Hz
1000 Hz
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Actual measurement data...
Delay-And-Sum NNLS deconvolution
1250 Hz
1600 Hz
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Actual measurement data...
Delay-And-Sum NNLS deconvolution
2000 Hz
2500 Hz
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Actual measurement data...
Delay-And-Sum NNLS deconvolution
3150 Hz
4000 Hz
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Noise Monitoring Solutions
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Why Perform Noise Monitoring?
z Requirement by local government
z Ease concerns of wind farm noise for neighboring communities
z Feedback for future site planning
z Use the same system during installation
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Noise Sentinel Option for noise monitor ing
Subscription Based Servicez Provides everything needed to meet
ongoing noise monitoring obligations
without having to own expensiveequipment
z We set up and manage the entiresystem 24 hours a day with automatic
data recovery
z We check the data and make clear
any data limitations or concerns
z Delivered by a professional servicesorganization with decades ofexperience in noise monitoringsolutions.
z Lower cost of operation during the life
of the service vs. purchasing andoperating your own system
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Predictor Software for Noise Contours of Farms
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Questions?
Tony Spica
Application Engineer