Introduction
This Wind Turbine Noise Model is derived from the method
documented by the International Energy Agency: Expert Group Study on
Recommended Practices for Wind Turbine Testing and Evaluation, 4.
Acoustics Measurements of Noise Emission from Wind Turbines, 3.
Edition 1994. It is a simple model which assumes spherical spreading
from a point source either in free space (spherical) or over a
reflective plane (hemi-spherical). It can also take into account
atmospheric attenuation, using an attenuation rate entered by the
user. The source sound power and the absorption coefficient are both
assumed to be broad band. Source to receiver distances are
calculated by simple geometric means and the total received noise
from each turbine logarithmically added.
Users should note that the model does not take account of:
- Uneven topography
- Large obstructions in the propagation path, e.g. barriers etc
- Refraction of noise, e.g. due to atmospheric effects such as
temperature inversion
- Wind speed or direction effects
- Any change in the propagation with changing frequency
More sophisticated models, allowing some of these additional
factors to be taken into account, are available. Those wishing to
understand some of the other factors affecting propagation of sound
outdoors should consult:
- ETSU W/13/00385/REP: A critical appraisal of wind farm noise
propagation. Available from ETSU
- ISO 9613: Calculation of absorption of sound by the atmosphere
- Woods Practical Guide to Noise Control, Woods of Colchester
- Noise and Vibration Control, Edited by L. L. Beranek,
ISBN 07-004841-X
This work is no longer supported by the current
programme.
Instructions
To use the model please enter the grid references (Easting
& Northing) of the wind turbine and property locations to
1 meter resolution. Also enter the absolute height (H) of
these locations above sea level. Don't forget to check the boxes
(Inc) by the turbines and properties for those you wish to
include when calculating the noise level. Any entries that are left
blank or are not numbers will be assumed to be equal
to zero.
Enter Lw, the sound power level of the turbine
and the Source Height above ground level (usually the
hub height). Atmospheric absorption can be included, check the box
and enter the value (0.005dB/m is commonly used). The model will
calculate both spherical and hemi-spherical source types, either can
be selected using the option buttons.
That's it, press Calculate and the noise levels due to the
turbines at each property should be calculated and displayed in the
boxes on the right.
The model uses JavaScript and
therefore only works if your browser is JavaScript enabled. This
software has not been subjected to NPL's Quality Assurance
procedures. No warranty or guarantee applies to this software, and
therefore any users should satisfy themselves that it meets their
requirements.
The propogation of the noise is calculated using the following
formula:
Where:
- r is the distance from source to receiver
- a is the absorption due to the atmosphere (dB/m)
- The first equation is for Hemi-Spherical radiation and the
second for Spherical
In order to avoid problems in taking the Log10 of
zero, if the combined distance from any turbine to any property is
zero that combination will be ignored.
Any comments or suggestions about this model please contact Richard
Lord.
Last modified on: Wednesday, 18-Feb-2004 10:42:35
GMT |
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