Intense sound levels produced by engineering equipment have become an acute issue. As most of engineering equipment require air supply, exhaust and good ventilation, it is not possible to control the noise by covering them with tight hoods. Louver with blades covered with acoustic materials and gaps that enable free circu- lation of air are used to this end. Three louver configurations were tested in the semi-anechoic chamber: bare metal louver blades, louver with blades covered with 20-mm-thick polystyrene foam slabs on both sides, and louver with blades covered with 15-mm-thick glass wool slab. According to the test results, louver with blades covered with glass wool slab demonstrated the best noise attenuation characteristics. The reduction of equiv- alent sound pressure level subject to blade inclination angle was from 10.8 to 12.5 dB. Sound pressure level reduction by louver with blades covered with poly- styrene foam slabs was weaker: the reduction of equivalent sound pressure level was from 5.4 to 8.4 dB. Louver with blades not covered with any acoustic material demonstrated the least noise attenuation result from 1.9 to 3.9 dB
Transport noise is a serious problem in cities and has a negative impact on both health and economics. In addition to the aforementioned unnoticed health effects, traffic noise has also been identified as one of the leading causes of sleep disorders, annoyance and negative cardiovascular effects. This research consists of three parts: part one involves onsite measurements of traffic noise in Trakai town; part two simulates traffic noise at different average vehicle speeds; part three assesses the number of people affected by traffic noise. The carried-out simulation has demonstrated that the noise level changes very slightly at different average vehicle speeds. It should be noticed that more noise is generated at average vehicle speed of 30 km/h rather than at 50 km/h. The assessment of the annoyance level has disclosed that an average vehicle speed of 30 km/h should cause the highest level of annoyance (highest – 26.8%).
Akustinės žaliuzės yra skirtos įrenginių, kuriems reikalingas vėdinimas bei oro įtraukimas-išmetimas, triukšmui slopinti. Iš įrenginių išeinantis oro srautas pereina per konstrukcijos plokštes, kurios sugeria iš įrenginių sklindantį triukšmą. Tačiau konstrukcijos plokštės pratekančiam orui sukelia aerodinaminį pasipriešinimą, dėl kurio gali atsirasti neigiamas efektas: susidaro per dideli slėgiai, oras negali laisvai judėti ir tai trukdo įrenginių veikimui. Todėl norint išspręsti šį uždavinį, buvo pasitelkta modeliavimo programa SimScale, kuria, naudojant tarptautinį kodą CFD, skirtą fluidų dinamikos modeliavimui, buvo sumodeliuotas aerodinaminis konstrukcijos pasipriešinimas, plokštes pakreipiant skirtingais kampais. Modeliavimo metu buvo nustatyta, kuriose vietose susidaro didžiausi slėgiai, taip pat kur atsiranda turbulentinis oro judėjimas. Modeliavimo metu buvo nustatyta, jog didinant konstrukcijos plokščių pasvirimo kampą, slėgis prie konstrukcijos padidėja nuo 45 Pa iki 9 kPa, oro greitis, praėjęs pro konstrukciją, pakinta nuo 13 m/s iki 70 m/s.
In this study, the insertion loss of devulcanized waste rubber baffles was evaluated. Acoustic baffles are suitable for reducing noise from the devices or machines by interfering with their emitting sound waves. Knowledge of the acoustic properties of the material used is of significant importance in ensuring the effectiveness of the acoustic properties of the baffle. Basic properties include airborne sound insulation, which is usually determined during laboratory testing. Baffle consists of sound absorbing and sound insulating materials. In this study, plasterboards were used as sound insulating material and devulcanized waste rubber as sound absorbing material. Devulcanization targets mostly the scission of sulphur crosslinks. Devulcanization techniques that have been explored in rubber recycling include thermos-chemical, microbiological, ultrasonic microwave thermos-chemical devulcanization in a supercritical carbon dioxide medium (scCO2). In this study, two types of rubber granules were devulcanized by grinding method and one other type was chemically devulcanized. Three types of rubber granules were mixed together in increasing 25 % proportion steps and glued with patented polyurethane glue. Total of 15 different composition devulcanized waste rubber granule boards were made. Rubber boards were attached together with the plasterboards. Insertion loss of the different composite baffles was measured in semi-anechoic chamber in a purposefully designed stand in 1/3rd-octave bands. The results showed that the insertion loss of the baffles depends mostly on the rubber granule board density. Increasing the density of the rubber board, insertion loss also increased. 5–6 dB insertion loss difference was measured between the most and the least dense rubber granule board baffles.
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