Kotenko, S. G. “Reducing of noise levels from moving sources by acoustic shields with ultimate acoustic insulation”. Published as manuscript.
Candidate of Technical Sciences dissertation, specialty 05.09.08. Applied acoustics and acoustic engineering, the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute,” the Ministry of Education and Science of Ukraine, Kyiv, 2019.
The dissertation is dedicated to solution of the actual problem: determination of patterns of change in the effectiveness of acoustic shields from their design parameters and geometric location, searching for ways to increase their effectiveness. To do this, we have analyzed all currently available methods, compared them, and identified their drawbacks.
Since the technical requirements for the operation of shields require technical gaps, the task of finding the effectiveness of an acoustic shield with a gap at its basis has been set and solved in the paper for the first time; the problem of finding the acoustic field around the infinitely long acoustic shield with perforation has been set and solved for the first time; the model of the acoustic shield with the ultimate acoustic insulation in the form of a perforated acoustically-hard shield has been suggested for the first time; the computer modeling of the acoustic shield was improved with the help of the finite-element method for finding the levels of sound pressure of a moving sound source around the acoustic shield; a high quality evaluation of the effectiveness of acoustic shields with ultimate acoustic insulation in a wide range of frequencies and sizes of acoustic shields has been obtained.
The paper offers a new mathematical model of acoustic shield with ultimate acoustic insulation. To solve the problem, the method of partial areas was used. This made it possible to determine the acoustic field around the shield and estimate the decrease in the sound pressure by the shield.
The full-scale investigation and experimental studies were conducted that showed high accuracy of the correlation with the model.
A new method for calculating the acoustic insulation of shields was developed, using holes and gaps in the shield body. Numerous values and comparisons of using different sizes of gaps in the shield body have been presented in the paper, which allows editing the value of the soundproofing properties of the materials. As we know, the soundproofing properties affect the overall effectiveness of the shield. Also, the calculations and comparison of shields with different acoustic insulation have helped identify that the shield’s acoustic self-insulation of more than 38 dB is equal to an absolutely hard shield. This allows us to conclude that it is not necessary to invest extra money in highly insulating materials to increase the effectiveness of the shield. The effectiveness is rather influenced by geometric dimensions.
The paper also presents numerical calculations of the shield effectiveness, depending on their geometric dimensions. They make it clear that the higher the height, the greater the effectiveness of the shield. One can also see that three-meter-high shields have very low effectiveness. Therefore, the uselessness of using shields of such height on a flat terrain has been proven.
In the paper, the computer software for calculation of the effectiveness of acoustic shields has been improved. The improved version takes into account the gap and the acoustic self-insulation of the shield body.
The practical importance of the results obtained is in the use of acoustic shields with a hole in their basis, in the assessment of the acoustic properties of the shields with ultimate acoustic insulation, in the establishment of quantitative relationships between the geometric parameters of the acoustic shield and its effectiveness, and in taking them into account in the acoustic design of acoustic shields.
The results of the dissertation were used in calculation work during development of recommendations for design of acoustic shields in Ukraine. Also, recommendations for introduction of changes in state standards were developed.
Keywords: Doppler Effect, shield with a gap, ultimate acoustic insulation, acoustic shield effectiveness, sound pressure reduction, noise protection, noise maps.
