| Abstract [eng] |
General characteristic of the dissertation Problem of the work. With a rapid development of industrialisation and urbanisation, the environmental pollution has greatly increased. Upon automating the manufacturing industry and agriculture, with traffic flows in towns and residential areas increasing and household equipment becoming more modern, the number of acoustic discomfort zones is rapidly growing. People are exposed to noise not only at workplaces abut also on the streets and at home. As maintained by doctors, noise reduces immunity of the organism and, as a source of chronic stress, has an adverse effect on the central nervous system and causes various health disorders. Even a relatively low noise of 60–70 dB causes a headache, dizziness, squeak in the ears, insomnia, and worsens memory, attention and orientation. A noisy environment reduces working efficiency, reaction speed, movement coordination and increases nervous strain and a risk of traumas. The noise dispersed by stationary sources may be reduced by replacing components with less sounding ones, applying rubber, plastic or other materials on the surface of installations. If it is impossible to reduce noise in the place of its generation, hoods are fitted out, premises are insulated and noise suppressing systems are used (noise reducing barriers, volumetric noise absorbers, wall insulation with noise-proof materials). The dispersion of traffic-generated noise is reduced by noise suppression walls, green plantations and buildings shields. Other effective measures include vehicle speed limitations, replacement of a road paving surface, traffic limitation and regulation. When analysing the possibility of implementing noise reduction measures and methods, a digital modelling of noise dispersion, evaluating the topographic and meteorological conditions as well as traffic characteristics in the locality, is very important. Topicality of the problem. Noise is generated by various technological processes. Noise level limits are exceeded not only at workplaces or in enterprise territories but also on the outside, i.e. in the residential area. Thus, the occupational safety conditions at workplaces are violated, quiet rest is disturbed and human health is undermined in the residential area. It is essential to limit the dispersion of the noise from mobile and stationary sources by absorbing or insulating it with the help of noise suppression walls. Various materials of the new generation, whose acoustic properties are not researched to the full extent, are used for their structures. This is particularly important when replacing large-dimensioned and solid materials with light structures that are easier to assemble and more suitable aesthetically. This work used the target experimental base and equipment necessary for the laboratory research on acoustic properties of such materials and structures made of them. Object of the work. Mobile and stationary sources of noise and a noise suppression chamber. Aims of the work 1. To evaluate the dispersion of noise from stationary and mobile sources in the environment and provide for effective techniques and measures to reduce it by using a noise suppression chamber for research into acoustic properties of materials. 2. To estimate the efficiency of the noise reduction measures through modelling noise dispersion in the environment. Tasks of the work 1. To design and fit out a noise suppression chamber and use it for research into the noise absorption and insulation properties of different materials. 2. To determine the levels and dispersion of noise from different mobile and stationary sources of noise. 3. To determine the longitudinal sound wave attenuation coefficient μ for individual building materials. 4. Through laboratory experiments in the noise suppression chamber, to estimate the reduction of a noise level in building structures and determine the airborne sound attenuation index DLR for them. 5. To envisage measures for reducing the noise generated by railroad and motor traffic as well as in industrial enterprise territories. 6. To estimate the efficiency of the measures reducing noise from mobile and stationary sources with the software “CadnaA”. Methodology of research. The measuring method of the partitions, blocking sound dispersion in the air under laboratory conditions, is presented according to ISO. Comparison of the results obtained through chamber research was investigated in different materials. The noise measuring method was preferred to find noise levels generated by railroad and motor traffic. Dispersion of the noise caused by the sources was estimated with the noise dispersion modelling software “CadnaA”. Scientific novelty. Novelty of the work is research on acoustic qualities of the construction materials recommended for noise absorption and insulation was done in a special noise suppression chamber. The noise reduction efficiency of such materials and building structures made of them was evaluated theoretically and through modelling with the software “CadnaA”. Dispersion of the noise caused by mobile and stationary sources and the efficiency of the existing noise reduction measures were researched by natural experiments, whereas the acoustic properties of building materials were estimated by the coefficients μ and DLR. Practical value. This work deals with the dispersion of the noise caused by mobile and stationary sources of noise and the ways of its reduction. It evaluates the current situation and searches for the ways of how to reduce noise dispersion to the residential area. The noise reduction measures, selected on the basis of the obtained findings and calculations, can be applied in practice. The results of the natural and chamber experiments and noise reduction measures can be applied for various stationary and mobile sources of noise. Defended propositions 1. The standardised difference in sound level (DnT,W), i. e. the index given in ISO 140-3, can be measured with the accuracy of ±3 dB in a 1 m2 specimen in the noise suppression chamber. 2. On the basis of the parameters evaluated in the noise suppression chamber, the acoustic properties of homogeneous building materials can be compared by the longitudinal sound wave attenuation coefficient μ, whereas those of building structures – by the airborne sound attenuation index DLR.. 3. Noise reduction efficiency can be achieved by the walls of thin-walled material structures. Approbation of the scientific work. On the basis of the work results, 2 articles were published in reviewed publications included in the list of ISI Web of Science journals, 2 articles – in reviewed publications being on the ISI Master List, 3 articles – in reviewed publications on the list of ISI Proceedings, and 5 articles – in other scientific publications. The scope of the scientific work. The scientific work consist of the general characteristic of the disertation, 5 chapters, conclusions and recomendations, list of literature, list of publications. The total scope of the disertation 154 pages, 79 pictures, 17 tables and 33 formulas. General conclusions 1. A noise suppression chamber was designed and fitted out wherein acoustic qualities of different individual materials and their compositions were researched and compared. The results of the noise insulation and difference in sound level indexes determined in the noise suppression chamber, at the error mean no bigger than 3 dB, were equal to the results of natural experiments performed with similar specimens. 2. On the basis of the acoustic parameters of materials recorded in the noise suppression chamber, the longitudinal noise attenuation coefficient μ, evaluating noise suppression in a material thickness measuring unit, was determined. Gypsum cardboard and wood chipboard are distinguished by good acoustic qualities, whose obtained values of the coefficient μ, depending on frequency, are 540–710 m–1. 3. Noise reduction efficiency of the structures used in the work was described by the airborne sound attenuation index (DLR). The performed analysis of the tested specimens of building material structures showed that high values of the index DLR (32–33 dB) was obtained when 10 mm thick wood chipboard is used as one component of the structure and such structures belong to the highest group of the airborne sound attenuation group. 4. The equivalent noise level, created by the stationary industrial source, was reduced by 18 dBA whit 8 m high barrier. Complex implementation of noise reduction measures (application of noise-absorbing materials on façade walls and increasing the noise suppression wall's height to 10 meters by the bulk fertiliser terminal) would reduce the equivalent noise level another 7–8 dBA. 5. After constructing a noise suppression wall from the materials from one of the structures, the noise level in the residential area was reduced to the required level of 55 dBA if the wall’s height was increased up to 14 meters. 6. It was determined by the experiments in natural conditions that noise levels at the same distance behind the noise suppression wall of Perspex and behind that of the cellular concrete expanded clay block structure are the same in the limits of errors and reach 62–63 dBA. Therefore, it can be concluded that efficient noise reduction can be achieved with the help of light structures. Recommendations 1. The noise insulating properties of various individual building materials or their compositions can be researched in the noise suppression chamber. The advantage of this chamber lies in the fact that only a 1 m2 element of the specimen is necessary for research, thus specimen assembling and research costs are reduced compared with the research conducted when an entire partition has to be installed. 2. The proposal is to reduce low-frequency dispersion by using a perforated tin structure with a rock wool and steel sheet filler. After performing the experiments in laboratory c. |
