Return to Schedule HERE

14.07 Outdoor Noise Propagation

Accurate noise modeling for petrochemical plants – impact of compressor Piping
Time: 7:20 am

Author: Arindam Ghosh

Abstract ID: 2130

Compressor piping is a dominant noise source in petrochemical plants with large centrifugal compressors. Acoustic insulation is used on compressor suction, discharge and recycle lines as a measure to mitigate noise radiating from compressor piping. This paper will demonstrate using case studies the importance of acoustic insulation on compressor piping as the primary and most cost effective noise control method for both community and in-plant noise. Case studies include the predicted and measured noise levels obtained during post startup noise surveys. This paper will also illustrate that to obtain good agreement with measured noise levels it is imperative to accurately model the piping sources following the actual piping layout and account for distance attenuation. A cost-benefit analysis of using complete compressor houses and/or acoustic blankets will be presented along with the efficacy of various types of acoustic insulation including elastomeric foam and aerogel based insulation systems. Different acoustic requirements for hot and cold insulation systems will also be presented.

You must be logged in to download paper. Click here to login

Ground Attenuation Factor Based on Measurements
Time: 7:00 am

Author: Dan Lin

Abstract ID: 2405

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

You must be logged in to download paper. Click here to login

A study on variations in excess attenuation due to ground surface and meteorological conditions based on a long-term outdoor sound propagation experiment
Time: 6:00 am

Author: Takatoshi Yokota

Abstract ID: 2679

From the winter of 2018, outdoor sound propagation experiments (maximum horizontal range: 300 m) have been repeatedly conducted three times a day on weekdays at a glider airfield in Hokkaido, Japan. The ground condition of the experimental field is grass-covered in summer and snow-covered in winter. In each experiment, impulse responses have been measured by time-stretched pulse method and excess attenuation has been obtained at receiving points. Meteorological data at the field has been also measured. Based on the data of excess attenuation collected under various meteorological conditions over a long period, variation in sound propagation characteristics due to the differences in ground surface condition and meteorological condition has been investigated. The numerical analysis based on the GFPE method has been also carried out with changing the parameter of meteorological condition and ground surface condition. By comparing the results with the experimental data, the prediction method of the variations in excess attenuation has been also investigated.

You must be logged in to download paper. Click here to login

A comparison of the ground excess attenuation model in Harmonoise with finite-difference time-domain solutions under grounds with mixed types
Time: 6:20 am

Author: Yusaku Koshiba

Abstract ID: 3165

Total noise exposure is calculated for the evaluation of health effects caused by environmental noise. For the calculation, computationally drawn noise maps are used. In the computation process, sound propagation over ground surface with mixed types should be calculated for better accuracy. One engineering model that allows such calculation is the ground excess attenuation model of the Harmonoise model. However, the applicability of the model to such complex grounds remains unclear. In this study, a 40m-length ground surface with a discontinuity in flow resistivity is defined. By moving the discontinuity position, sound propagation from a point source and a receiver at each end is calculated using the model and a numerical method. The numerical method is the finite-difference time-domain method with porous medium modeling that has been proven to be accurate. It is found from the numerical results that in higher frequencies the excess attenuations in terms of the discontinuity position have fluctuations. The fluctuations are found to correspond to the interference by diffraction path difference passing the discontinuity. In contrast, the model results exhibit smooth transition from an extremity of single flow resistivity surface to another. A simple model of such diffraction needs to be developed.

You must be logged in to download paper. Click here to login

Open source acoustic model development for natural & protected environments
Time: 7:40 am

Author: Adwait Ambaskar

Abstract ID: 2070

Natural quiet and the sounds of nature are important natural resources and experiencing them is an important aspect of outdoor recreation experiences. Anthropogenic sound can negatively impact these resources and diminish the benefits realized from outdoor recreation. On public lands where many types of recreation share trails and landscapes, the sounds produced by some types of recreation (e.g., motorized recreation) can negatively impact the experiences of others.  To effectively manage public resources including natural soundscapes and recreation opportunities, public land and recreation managers need an understanding of the effects of recreation-caused sounds like those associated with motorized recreation. Acoustic models for recreation and protected areas provide an essential tool to help in predicting sound levels generated by these anthropogenic sources and can aid in studying the extent of potential recreation conflicts, while providing a definite direction to mitigate such conflicts. An open source outdoor sound propagation model integrated with Geographic Information Systems (GIS) lays out a good foundation for mapping visitor experience affected by sound sources like gas compressors and motorized recreation sounds. The results thus produced present a preliminary version of an outdoor sound propagation tool, to assist parks and state forest services in making important management decisions to refine visitor experience.

You must be logged in to download paper. Click here to login

Landscape depressions can create silent zones in noise polluted parks
Time: 6:40 am

Author: Timothy Van Renterghem

Abstract ID: 2170

Excessive road traffic noise exposure in (sub)urban parks hinders its restorative function and will negatively impact the number of visitors. Especially in such green environments, noise abatements by natural means, well integrated in the landscape, are the most desired solutions. Although dense vegetation bordering the park or raised berms could come first in mind, local landscape depressions are typically underused. In this work, a case-study of a small suburban park, squeezed in between two major arterial roads, is analyzed. The spatially dependent road traffic noise exposure in the park is assessed in detail by mobile sound pressure level measurements. Local reductions of up to 6-7 dBA are found at landscape depressions of only a few meters deep. It can therefore be concluded that this is an efficient measure and should be added to the environmental noise control toolbox for noise polluted parks.

You must be logged in to download paper. Click here to login