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

NUMERICAL SIMULATION OF THE LIGHT AIRCRAFT PROPELLER NOISE UNDER STATIC CONDITION

The problem of simulation the noise generated during the operation of the propeller is considered. Calculation methods are described and numerical simulation of the noise of a light aircraft propeller by the acoustic-vortex method is performed. The results of numerical modeling of the tonal components of the propeller noise when operating under static conditions are compared with experimental data and calculation results based on a semiempirical model.

THEORETICAL STUDIES OF THE VELOCITIES OF THE VIBRATIONS OF DRILL BITS WOODWORKING DRILLING MACHINES

On woodworking machines of the drilling group, drill bits of the following diameters (mm) are used at rotation speeds: SvP2 and SvA-2-ø 50 mm, n = 3000 rpm 4500 rpm; Sv8, Sv12-ø 10-16 mm, n = 2800 rpm; SGVP-ø up to 35 mm, n = 2800 rpm. Acoustic models are described in detail in [1] as can be seen from the analytical dependences of sound pressure levels to calculate the noise spectra, it is necessary to determine the oscillation velocities of the drill bit at their natural frequencies.

THEORETICAL STUDY OF THE NOISE EMISSION OF THE FLEXIBLE CONNECTION OF THE ABRASIVE BELT-GRINDING WOODWORKING MACHINES

This paper presents the results of theoretical studies of the drive belting and grinding belts` acoustic characteristics as elements of flexible connections, that fundamentally distinguishes them from bobbin sanding and cylinder-grinding woodworking machines. It also has the significant differences in comparison with other sources in terms of stiffness and tension forces. The choice of the noise source models is justified by the characteristic features of the kinematics of the machine tools and the grinding technological process. The arrangement of the machines` acoustic system of chosen group suggests that the main sources of energy radiation are: grinding belts and belt drives of the work pieces and grinding units, ground work pieces, electric motors. It is compared the expected noise levels with sanitary standards for determining the excess and the sources that generate them. These data are the main information for the acoustic calculation and design of the noise reduction systems of the above sources at the design stage in such woodworking equipment, and it also determines the acoustic efficiency of the noise protection systems and consider to design these systems in accordance with the implementation of the sanitary noise standards at the machine operator workplaces.

ON DESIGNING IMPEDANCE TUBE WITH GRAZING FLOW

The article considers the general issues arising in designing the experimental setup “Impedance tube with grazing flow”, the main structural units of the setup, and their purpose. It is given the basic requirements to be provided by the setup when testing samples of acoustic liners used in an aircraft engine. The choosing of the design parameters of the setup is based on the analysis of the known analytical solutions of the acoustics and gas dynamics, and on the numerical simulation of the grazing flow in the impedance tube.

SOUND PROPAGATION THROUGH STRUCTURAL COMPONENTS UNDER CONDITIONS OF NON-RIGID CONTACT AT THE BOUNDARIES BETWEEN THEM

The report considers the problem statement, derivation and solution of the dispersion equation for sound propagation in a layered inhomogeneous medium with oriented fracturing, simulated by the presence of boundary conditions in the "linear slip" approximation. Numerical solutions are obtained and analyzed for the frequency range and values of the parameters of contact breaking, which is relevant in the problems of ultrasonic measurements

SANITARY PROTECTION ZONES BY NOISE FACTOR FROM GAS DISTRIBUTION POINTS

The power equipment of thermal power plants is a source of noise to the surrounding area. One of the sources of noise for the surrounding area are gas distribution points (GDP) of thermal power plants (TPP) and district thermal power plants (RTS). Noise from gas distribution points may exceed sanitary standards at the border of the sanitary protection zone. The article shows that the radiated noise from gas distribution points depends on the power of the thermal power plant (natural gas consumption) and the type of valves. Three types of valves used in gas distribution points are considered. Formulas are obtained for calculating the width of the sanitary protection zone for gas distribution points for thermal stations, depending on the consumption of natural gas (electric power of the thermal power plant) and the type of valve. It is shown that, depending on the valve used, the noise level at the border of the sanitary protection zone can either meet sanitary standards or exceed them. This allows at the design stage to select the required type of valve or to determine mitigation measures from hydraulic fracturing.

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.