Transcript Document

Research Study on Wind
Turbine Acoustics DRAFT
Interim Results II for WNTAG
March 7, 2014
Interim Report II
Interim Report II for WNTAG focuses on a comparison of sound metrics with
sound modeling to help inform and synchronize pre-construction estimates
with post-construction monitoring.
CONTENTS
• New terms
• Review of data collection
• Sound monitoring metrics
• Pre-construction sound predictions
• Attended sound monitoring
• Statistical confidence
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Review of data collection
• Four sites to date –
- all in Massachusetts
- all 1.5 MW or greater
• Five sound monitoring locations at each site
- 1/3 octave bands + other metrics at 100 ms to 1 s intervals
- Type I sound monitors
• Infrasound monitoring at one location (inside and outside) at one site
• One LIDAR location at each site
• One 10-meter met tower at each site
• Turbine operating conditions collected by operator
• Over 120,000,000 data records logged
• Over 150 sound level, meteorological, operational, and observational
variables
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Sound monitoring metrics
New terms
•
•
•
•
•
Site
Location
Background sound level vs ambient
L90 LAf max (1-sec)
L90 of the L90
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Consideration of new sound monitoring metric
for Turbine sound – L90 of Lafmax(1-sec)
49
Sound Pressure Level (dBA)
48
47
46
45
44
LAf
LAs
43
42
41
20:00 20:01 20:02 20:03 20:04 20:05 20:06 20:07 20:08 20:09 20:10
Time (mm:ss)
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Consideration of new sound monitoring metric
for Turbine sound – L90 of Lafmax(1-sec)
49
Sound Pressure Level (dBA)
48
47
46
LAf
45
LAs
1s LAf max
44
43
1s LAs max
1s Leq
42
41
20:00 20:01 20:02 20:03 20:04 20:05 20:06 20:07 20:08 20:09 20:10
Time (mm:ss)
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Consideration of new sound monitoring metric
for Turbine sound – L90 of Lafmax(1-sec)
49
Sound Pressure Level (dBA)
48
47
46
LAf
45
LAs
L90 LAf max
44
43
L90 LAs max
Leq
42
41
20:00 20:01 20:02 20:03 20:04 20:05 20:06 20:07 20:08 20:09 20:10
Time (mm:ss)
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Sound monitoring metrics – Background
sound
49
Sound Pressure Level (dBA)
48
47
46
45
44
LAf
LAs
43
42
41
00:00 00:01 00:02 00:03 00:04 00:05 00:06 00:07 00:08 00:09 00:10
Time (mm:ss)
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Sound monitoring metrics – Background
sound
49
Sound Pressure Level (dBA)
48
47
46
LAf
45
LAs
1s LAf max
44
43
1s LAs max
1s Leq
42
41
00:00 00:01 00:02 00:03 00:04 00:05 00:06 00:07 00:08 00:09 00:10
Time (mm:ss)
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Sound monitoring metrics – Background
sound
49
Sound Pressure Level (dBA)
48
47
46
LAf
45
LAs
L90 LAf max
44
43
L90 LAs max
Leq
42
41
00:00 00:01 00:02 00:03 00:04 00:05 00:06 00:07 00:08 00:09 00:10
Time (mm:ss)
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Background L90 - Variability
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Effect of wind speed on L90 – wind shear
Height
Wind Shear
Wind Speed
0.3
Wind
shear
exponents
Height
-0.2
0.6
Wind Speed
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Background L90 and Wind Speed are
significantly correlated
Slopes of 80-meter wind speed vs sound level for various
methodologies
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Wind speeds vary during any measurement
period
12%
10%
ws90
9 m/s bin
Frequency
8%
6%
4%
1.3 standard
deviations
2%
0%
0
1
2
3
4
5
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
80 m Height Wind Speed (in m/s)
Example of a 10-minute period at one site, showing the frequency of
occurrence of 0.5 m/s bins for 9 m/s average wind speed
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Pre-construction sound
predictions
Example of pre-construction modeling
methodology for one site 370 meters downwind
Sound Pressure Level (dBA)
60
55
Background L90
50
45
40
35
30
25
20
0
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2
3
4
5
6
7
8
9
10
80 meter LIDAR wind speed (m/s)
11
12
13
14
15
17
Example of pre-construction modeling
methodology for one site 370 meters downwind
Sound Pressure Level (dBA)
60
Background L90
55
50
Best fit L90 of L90
45
40
35
30
25
20
0
1
2
3
4
5
6
7
8
9
10
80 meter LIDAR wind speed (m/s)
11
12
13
14
15
Slope of brown line in db/meter per second
L90 of
L90 of
L90 of
L50 of
5-minute 5-minute 5-minute 5-minute
Location
L90s
Leqs
L50s
L90s
1
1.7
1.2
1.6
1.8
2
1.6
1.3
1.4
1.5
3
1.6
1.4
1.3
1.8
4
1.2
1.2
1.2
1.2
5
1.3
1.2
1.2
0.6
Average
1.5
1.3
1.3
1.4
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Example of pre-construction modeling
methodology for one site 370 meters downwind
Sound Pressure Level (dBA)
60
Background L90
55
Best fit L90 of L90
50
Model G=0.5+2
45
40
35
30
25
20
0
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2
3
4
5
6
7
8
9
10
80 meter LIDAR wind speed (m/s)
11
12
13
14
15
19
Example of pre-construction modeling
methodology for one site 370 meters downwind
Sound Pressure Level (dBA)
60
Background L90
55
Best fit L90 of L90
50
Model G=0.5+2
45
Model + Background
40
35
30
25
20
0
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2
3
4
5
6
7
8
9
10
80 meter LIDAR wind speed (m/s)
11
12
13
14
15
20
Example of pre-construction modeling
methodology for one site 370 meters downwind
Sound Pressure Level (dBA)
60
Background L90
55
Best fit L90 of L90
50
Model G=0.5+2
45
Model + Background
40
35
30
25
20
Modeled Turbine Leq
minus Bkg L90 (dB)
0
1
2
12
3
4
5
6
7
8
9
10
80 meter LIDAR wind speed (m/s)
11
12
13
14
15
10.3
10
9.2
8.9
7.5
8
7.3
7.7
7.2
6.1
6
4
2
0
0
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2
3
4
5
6
7
8
9
10
11
80 meter LIDAR wind speed (m/s)
12
13
14
15
21
Sound Pressure Level (dBA)
Measured L90s of turbine sound levels
60
Turbine + Bkg (filtered L90) - Day
55
Turbine + Bkg (filtered L90) - Night
50
Best fit L90 of L90
45
Model + Regr Bkg
40
35
30
25
20
0
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4
6
8
10
80 meter LIDAR wind speed (m/s)
12
14
22
Sound Pressure Level (dBA)
Perfect modeling of wind turbine sound
60
Model + L90 points
Best fit L90 of L90
Model G=0.5+2
Model + Background
55
50
45
40
35
30
25
20
0
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4
6
8
10
80 meter LIDAR wind speed (m/s)
12
14
23
Attended sound monitoring
Filtering background sound
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Filtering background sound
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Filtering background sound
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Statistical Confidence in
Measurements
New terms
•
•
•
•
•
•
Statistical Bias
Accuracy
Precision
Confidence Interval
Standard Deviation
Standard Error
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Comparing background to turbine-on
measurements
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Estimate means and confidence intervals
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Estimate means and confidence intervals
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Suggested strategy for using different metrics
for background and turbine-on measurements
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Conclusions
Some specific conclusions from the report
• Background sound levels vary by time of year, time of day, and day
of week.
• Natural short-term variation is partly a function wind speed and wind
shear
• Sound levels measured on the ground increase when 80 meter wind
speed increases
• Wind shear variation is highest at night and at low wind speeds
• Background sound will contaminate measurements of wind turbine
sound
- Wind alone can have a significant effect
- By definition, 90% of the turbine-on measurements have
background levels that are higher than the L90
• When measuring over five or 10 minutes, the wind speed exceeded
90 percent of the time is likely to be at a lower integer wind speed
than the mean wind speed
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More specific conclusions from the report
• Since L90 and wind speed are correlated, this means that the L90 is
also likely to occur at a lower wind speed relative to the mean.
Adjustments can be made to account for this.
• The 10th percentile wind speed is a function of the mean and
standard deviation of the measured wind speed over a period
• Considerations of sound metrics
- Using L90 of Lafmax (1-sec) for both background and turbine-on
measurements
- Improving predictability by establishing a turbine-only sound
limit based on background measurements during preconstruction
- Incorporating some type of statistical analysis to improve
confidence in compliance measurement
- Adjust turbine-on sound metric (if different from background
metric) to account for higher background sound.
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General conclusions
Overall, real-world systems are dynamic. Methods developed should take into
account likelihood that
• Conditions change during the measurement
• Conditions change over time
• Measurements including everything that produces sound in the
environment
• Methods to measure and model sound will have biases
• Methods to measure and model sound will have variability
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Kenneth Kaliski, P.E., INCE Bd. Cert.
Senior Director
Contacts
Contact
www.rsginc.com
[email protected]
802-295-4999