acoutics applications related to wind turbines webinar

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

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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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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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800 Hz

1000 Hz

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1250 Hz

1600 Hz


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2000 Hz

2500 Hz

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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

[email protected]

acoutics applications related to wind turbines webinar

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