INVESTIGATION OF NATURAL FREQUENCIES OF COMPLEX WATER PIPELINES

The article deals with the problem of emergence of noise and vibration from pipelines of multi-storey residential buildings. The determination method of risk of increased noise and vibration using the modal analysis method in the ANSYS Workbench software packages is offered. The numerical modal analysis of straight pipeline sections with various geometrical parameters is carried out. Risk predictions of possible resonant modes are made. The maximum allowed span lengths between supports for sections of pipeline systems with a diameter of 15, 20, 25, 32, 40, 48, 60, 70, 102, 114, 140, 168, 180, 219 mm are offered.

ANALYSING ACOUSTIC PROPERTIES OF A SUBWAY TRACK

This paper describes laboratory measurement of acoustic properties of subway track samples, with the main focus on the change of the basic material of selected components of a rail fastening system. They were identical in shape, the only difference was in the material used. A suitable methodology based on measuring the acoustic response to mechanical shock was developed for laboratory measurements. The measured data was assessed with an appropriate mathematical apparatus based on signal analysis methods in the time and frequency domain. Based on the tests performed, the acoustic properties of the structures examined were deter

ACOUSTIC PERFORMANCES OF METAL SAMPLES MANUFACTURED BY ADDITIVE TECHNOLOGIES

Porous materials (PMs) have been widely used since the development of powder metallurgy. PM samples are obtained by various methods, while the structure varies from sample to sample. Deviation from a given structure leads to a deviation of the specified properties up to 30%, including acoustic. Selective laser melting (SLM), allows to obtain samples with a low structural deviation (up to 13%) in a wide porosity range P=0.3-0.7. An increase in the sound absorption coefficient and the expansion of the frequency range allows to use such samples in noise reduction units’ designs. Nine samples with different porosity and cell shape were obtained by the SLM method with the use of AlSi10Mg aluminum powder obtained by gas atomization and BB751P nickel powder obtained by plasma centrifugal spraying. The porosity of the samples (P) varied in the range (0.3–0.7), the diameter was D = 34.5 mm, and the height varied in the range of 15–45 mm. The acoustic characteristics comparison of traditional PMs with porous fused material (PFM) by the sound absorption index shows that PM, as a rule, are superior to PFM, while it is approximately equal to porous cast

FERROELECTRICS IN ACOUSTOELECTRONICS

Аcoustoelectronics is one of the areas of acoustics, associated with the use of mechanical resonance effects and the piezoelectric effect, as well as the effect based on the interaction of electric fields with waves of acoustic stresses in a piezoelectric material. The main materials used in acoustoelectronics are ferroelectrics, which are mainly complex oxide materials. This article discusses the possibility of increasing the purity and homogeneity of ferroelectric materials, as well as softening the regimes of their synthesis using the solution extraction-pyrolytic method. It is shown that the synthesis temperatures of BaTiO3, SrTiO3, and Pb(Zr)TiO3 ferroelectric films are reduced to 550-600°C, and the synthesis time is down to 5-10 minutes. The dielectric constant and Curie temperature values correspond to the maximum characteristics for these materials. Thus, using the extraction-pyrolytic method we obtained suitable for use in acoustoelectronic technology ferroelectric films.

THE EFFECTIVENNESS OF SOME PRACTICAL METHODS OF LOWERING THE BACKGROUND ACOUSTIC NOISE, PRODUCED BY THE ENGINE TEST BENCH TECHNOLOGICAL EQUIPMENT

When conducting acoustic researches and finishing works on combustion engines specialized technological equipment and tools mounted mainly in anechoic chambers are used. In order to ensure the high quality and objectivity of the research results of the sound fields produced by the research object it is crucial to achieve a sufficiently low parasitic background noise produced by technological equipment and tools of an engine test bench. The source of a high background noise re-emited to the anechoic chambers interior is structural vibrations of the solid objects of load carrying and flatsheet box-type structures of the bench. The article considers tested technical methods of improving vibroacoustics of load carrying and envelope structures of the engine test bench, which is in startup, commissioning and preliminary operation phase in the research center of a car manufacturer. Therewith there was a requirement to prevent any fundamental changes of the bench original basic construction, in order to minimize potential material and financial expenses for its reengineering process. Tested design solutions allow to reduce the level of parasitic noise disturbances, produced directly by the bench equipment in an anechoic chamber, up to 12 dBA.

COVID-19 AND SOUNDSCAPE CHANGES DUE TO THE LOCKDOWN. THE CASE OF LIMA, PERU

The COVID-19 pandemic has changed the way of life of the world’s population, and initially all non-essential commercial and industrial activities in all countries were suspended, as well as the temporary closure of major airports and educational activities. As never before, environmental sound levels were reduced as a result of the quarantine, as the authorities ordered people to remain confined in their homes in order to reduce and prevent the SARS-CoV-2 transmission. Cities became silent and in some cases birds and wildlife “took over” this situation. This change in the soundscape led to sounds that were previously masked, now being heard, i.e. HVAC and other noises. This article presents the case of Lima, Peru, in which the impact and annoyance produced by aircrafts overflights are analyzed (during 2020); as well as the healthy soundscape levels achieved ‘thanks’ to the commercial lockdown and leisure activities.

Acoustics of impacts as a factor of ensuring mutational and evolutionary transformations of the environment

Within the framework of the conceptual approach, taking into account the previously unknown, first identified by the authors features of the conditions of the internal energy equilibrium of material media (between their different physical nature energy states), the real contribution of acoustic disturbances experienced by media in the conditions of existence into ensuring of their and of the material world as a whole mutational and evolutionary transformations is taken into account and confirmed.

VIBRATIONS OF THE CLOSED FRAME STRUCTURES IN A STEADY-STATE CONDITION

The load-bearing frames of the technological machinery of various functional purposes, such as bridge and gantry cranes, locomotives, motor locomotives, etc., are energetically closed rod systems [1-10].

CALCULATIONS FOR EVALUATING THE ACOUSTIC EFFICIENCY OF MEASURES TO REDUCE PULSE NOISE IN INDUSTRIAL PREMISES

At modern manufacturing enterprises, machines and mechanisms that emit pulsed noise are widely used. Pulse noise has a more harmful effect on workers than time-constant, time fluctuating and intermittent noises. Pulse noise reduction is possible through the application of design changes in the pulse noise source and the development of organizational, technological, construction and acoustic measures. The choice of specific events is made on the basis of their acoustic efficiency assessment. For this purpose, it is necessary to have a method for calculating pulse noise that takes into account its space-time characteristics and their possible changes with structural changes of the source, as well as with changes in the space-planning and acoustic parameters of premises. In the article, to assess the acoustic efficiency of pulse noise, it is proposed to use a combined calculation method developed by the authors, taking into account the real mirror-diffuse nature of sound reflection from the room fences. On its basis, it is analyzed the possibilities of using various methods and means to reduce the impact of noise on the workers in rooms with pulsed sound sources.

TECHNIQUE FOR ESTIMATING THE EFFICIENCY OF NOISE PROTECTIVE ACOUSTIC SCREENS IN THE PRESENCE OF FLAT ANTI-DIFFRACTORS

To increase the efficiency of acoustic screens when protecting against acoustic noise, anti-diffractors are used to reduce the diffraction level on the upper edge of the screen. The aim of the work is to refine the mathematical model used to assess noise protection efficiency with the help of an acoustic screen with an installed one-sided flat-type anti-diffractor. The well-known techniques based on the principle of the amplitude dependence of the sound wave intensity from two sources are analyzed: a point-type noise source and a secondary cylindrical wave source - the screen edge, on which the sound wave is diffracted. Taking into account that the change in the distance between the anti-diffractor and the working point in the acoustic shadow zone is associated with a change in the diffraction angle, it is proposed to evaluate the acoustic screen effectiveness by comparing the initial sound wave propagation paths. An approach to a mathematical calculation model formation is proposed, in which the diffraction point located at the intersection of two components of the wave path to the operating point is considered to be the location of the sound wave secondary source in the area of the screen upper edge: from the noise source to the flat-type anti-diffractor installed on the upper edge of the screen, and from the anti-diffractor rear edge to the operating point. Relationships that make it possible to solve the problem of analytical assessment of noise-protective acoustic screens' effectiveness when installing anti-diffractors on their upper face in the form of flat hinged panels oriented towards the acoustic shadow are obtained.