The SoundPLAN Expert System for Industry Noise

Transcription

1 The SoundPLAN Expert System for Industry Noise Differences in approach between the optimization of transportation noise and industry noise In contrast to transportation noise where noise barriers are the most common practice for noise control, industry noise is customarily controlled at the source rather than at the transmission path. Just as Wall Design is the critical module needed for evaluating and controlling transportation noise (SoundPLAN info #4), the Expert System for Industrial Noise is the critical module used to optimize industrial noise at the source level. Like Wall Design, the Expert System requires a precalculations of the noise off-line before processing the results for optimizing the noise control. To the left is a window from the Expert system showing the receiver's ranking and contributions. The receivers with the greatest excesses over the noise limits (the receiver with the most problems) are at the top. When a receiver in this list is highlighted, the contribution list is then ranked in

2 accordance to the contributions for the receiver. Sources near the top of the list will need attention. Only the major contributors to the receivers with the highest infringement are useful to lower the noise levels sufficiently for the entire area around the plant/industrial site. In the lower half of the screen you can select the controls and visualizations you prefer. Among the options is the possibility to define noise control measures (silencers, for example) with each measure having a difference level and a price. Spectral and single value differences are possible. Defining noise control You can enter multiple attenuations for each source. They can be defined as alternative noise control concepts or they can be used in addition. For example, a silencer can be used along with a different fan with more fan blades. This can be an addition, but if silencer A is to be evaluated against silencer B that has a different price and performance, then the options cannot be done as an addition but must be seen as alternatives. Data for the attenuation can come from the library if the attenuation is defined spectrally, or it can be entered locally if it is a single value. Other information available in the Expert System Graphics Top view projection 3D solid model Day histogram

3 at the receiver of the sources of the contributions of sources to the. receiver Spectrum of the noise level at the receiver of the sound power of the source of the contribution of a source to the. receiver Contribution sums (ranked source. contributions) Measures (graphic above) Attenuation measure range (ranking the. different measures) Attenuation/cost plot Using the automatic noise control With the initial single point calculation, SoundPLAN collects all the information about the propagation, the daily history of the sources and their contributions, the spectral information of the sources and the receivers, and each contribution. The first step of the optimization is entering the values for each of the sources, indicating how much the noise can be controlled and the costs of the noise control. Start the optimization from the main menu under Measures/Optimization. The program looks for each receiver with major contributions and compares the possible attenuation measure's price to performance. The program selects the cheapest solution that substantially lowers the noise levels. After the selection of the noise control measure, the list of receivers is again ranked to ensure the receiver with the highest infringement receives the most attention. The selection of noise control

4 measures continues until all receivers are below the defined noise limit. The example: A Wind Farm Methods to optimize and reduce the noise from a planned wind farm The aerial photograph to the left has receiver locations marked as yellow stars and wind turbines marked as purple dots. The wind turbines are planned in a grid with a higher spacing in the direction of the prevailing wind. The spacing is 5 x D in wind direction and 3 x D in the perpendicular direction. D is the diameter of the rotor. Defining the wind turbine 38 wind turbines are planned. They are entered as point sources at the position of the hub of the rotor (i.e. 90 meters above the terrain). For the planning scenario, the total sound power for a single turbine is set to 106 db(a). A total of 10 relevant noise sensitive receivers is scattered around the area with the wind turbines. One of the farm houses is located in the middle of the area for the wind turbines. The ambient conditions for all 10 receivers were measured to establish a base line without the wind turbines. In order to not exceed the noise limits at the receivers, the background noise level is taken into account. In the lower frame to the right of the table, the maximal contributions are listed for each of the receivers for day, evening and night. It becomes evident that the night time period is the most critical period, so the selection of noise control measures needs to occur for night time. To get all data needed for the evaluation in the Expert System, the program must save the data especially for the Expert System.

5 The documentation (single receivers) revealed that the noise limits are violated by up to 12.2 db at night time, by 2 infringements at evening time, and are OK during day time. Reducing wind turbine noise Modern windmills can reduce noise emission by decreasing the rotation speed. A typical reduction of 3dB or 6dB occurs with only a 5% or 10% reduction in efficiency. If this is not sufficient, the last possibility is the complete shutdown of one of the wind mills during a specific time period. This is less efficient than the reduction of rotation speed, since no electricity is produced. Because of this, the owners will react very sensibly to this topic as their objective is to get as much electrical power out of the wind farm as possible! With the SoundPLAN module Expert System for Industry, it is possible to find the best possible combination of noise reduction to electrical efficiency. The procedure to achieve this balance can be seen below. Optimizing with the Expert System When opening the calculated results from the wind turbines, the initial screen is the same as seen at the beginning of this article. The top two windows show the ranked receivers to the left and the ranked contributions for the highlighted receiver to the right. The diagram shows the quietest source contributions to the right and adds noisier and noisier contributions. It is easy to see noise control must start with the sources to the left. If the noisiest 3 wind turbines were disabled, the level would drop from 50 db to 45, but

6 the goal is to reduce the noise to 37 db. To control noise from the wind turbines, three alternative noise control measures are assigned to each wind mill. Reduction of 3dB with a loss of power output of 3% Reduction of 6dB with a loss of power output of 6% Switching off the wind turbine with a loss of 100% The noise control measures are defined in the "Attenuation Library" and then assigned to all sources. The optimization is started by clicking the menu item "Measures/Optimization." The program then evaluates and ranks the noise control measures and presents them in both a table and a diagram. As all options for all sources and all receivers are weighed against each other, you can imagine how much time could be spent doing this by hand. With the Expert System it is only a little bit of CPU time! If you have other considerations and want to modify the optimized solution, you can manually define the noise control options for each source as being on or off and have the program re evaluate using the changed objective. This is also very efficient in Expert System for Industry Noise. Results After optimizing the wind turbine setup to avoid infringements at the noise sensitive receivers at night, the optimization results are saved as an "attenuation"

7 file which can be added to any calculation. With just this addition and requesting a new file number for the new Grid Noise Map, the calculation of the wind mill scenario is run to produce the noise map for the noise situation at night. With SoundPLAN s ability to produce multiple drawings on the same sheet using the same geometry parameters and colors, etc., it is fast and easy to create the plot to the left where the top drawings show scenarios without and with noise control and the bottom row shows the difference map, a box with legends and the table with the individual receivers. The two regular noise maps share the same scale but a new scale was introduced for the difference map. Expert System for Industrial Noise This module not only fixes problems in the planned wind farm, but also focuses on noise control for industrial plants where multiple different sources must be controlled, each with a different noise control option. Having multiple options for each source and many noise sensitive receivers with different transmission paths, means it would be very time consuming to find the best solution for noise control if calculations were done without the Expert System which finds the best solutions for noise control automatically. The graphic to the left is an example of a power plant evaluated using the Expert System.

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