Final report: Improvement of the computational methods of the Norwegian Defence Estates Agency for computing noise from the Norwegian defence training ranges

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This report summarizes efforts made to improve the ability of the Norwegian Defence Estates Agency (NODEA) to calculate noise and vibration levels from military activities. Accurate noise maps are essential for conforming to the strict noise emission limits set by the authorities. Failure to do so may ultimately stop or limit the military activity allowed at a training range. This work has been conducted as a joint 3 year effort with NODEA (FUTURA, FoU) as the client. The project group consisted of FFI, NGI (Norwegian Geotechnical Institute) and SINTEF ICT. During the project period 30 reports, 9 conference proceedings and 1 journal paper have been published. To estimate the noise level NODEA employs the linear noise propagation program Milstøy (MS), version 2.3.2. Input to MS is a source database for the sound pressure relatively close to the weapon, approximately 250 m for a 155 mm howitzer or 10 m for a ri e. The sound propagation is then calculated to produce noise maps for area planning work by the local authorities. In this project the purpose has been both to enhance the computational methods in MS, and to improve the source database. During this project we have developed a new research version of Milstøy, version MS 2.4.1 (named NMS). This report describes the new features implemented in NMS (new Milstøy) . NMS includes new emission data for several weapons, e.g. M109, CV90, 12.7 mm, AG3, C8 and MP7. This improved emission database will greatly improve the noise maps produced for these weapons. A method has been developed to calculate emission data for a weapon based on geometry, bullet properties and gun powder parameters. This should be helpful when experiments are too expensive or impossible to conduct. New computational kernels have been developed with special attention to calculate the prediction of low frequency sound, below 100 Hz. The method Nord2000Road is included in NMS. This new version has little in common with the old Nord2000 kernel from MS 2.3.2. A new low frequency model (LF-model) has been developed to deal with sound below 100 Hz. Motivated by this, the internal structure of NMS has been changed to allow for new types of ground classes. Each new ground class is described by a complex frequency dependent admittance function which varies with air temperature and angle of incidence. These have been computed using the software Multipor, taking into account the acousto-seismic interaction at the air-ground interface. The new types of ground classes also allow more realistic ground models which are needed for low frequency noise. Further improvements of the calculation of the ground effect have been investigated, and promising novel results have been obtained. These have, however, not been included since the work is not nalized. An empirical method for propagation of blast noise has been included based on a statistical analysis of measurement data from detonations at Finnskogen. This method also calculates the standard deviation of the prediction. The NORTRIAL database was developed to facilitate validation of the developed computational kernels. It includes measurements of detonations of C4 at Finnskogen in Norway in 1994 and 1996. NORTRIAL is written in Matlab, and is easy to use for validation purposes. It is freely available on request. The problem of insulating houses from low frequency noise and vibration has been considered. Unfortunately, no new methods with increased performance for insulating existing homes have been found. However, suggestions have been made about how to build new houses to reduce this problem. New methods for measuring indoor low frequency noise have also been suggested.
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