ANALYSIS OF THE EFFICIENCY OF ACOUSTIC SCREENS OF DIFFERENT DESIGNS

Various sources of noise in cities and ways to combat them are considered. The effi ciency of two types of acoustic screens is analyzed: single-layer and two-and three-layer. The positive and negative characteristics of various designs of existing acoustic screens are listed. A fundamentally new design of the acoustic screen is described: the panels have a ridge profi le, they are located along the vertical axis of the frame with a step at which the panels above the located ridge cover the top of the lower ridge, the outer surfaces of the panels and their end parts are made of a material that has sound-refl ecting properties, and the inner surfaces of the panels are made of sound-absorbing material. Such an acoustic screen is devoid of the disadvantages inherent in acoustic screens of other structures and is more effi cient. The considered invention allows due to the use of the ridge shape of acoustic panels: prevent the refl ection of sound energy in the direction of noise sources (a small part will be directed upwards); provide almost complete absorption of sound energy as it passes through the channels formed by the ridge panels; provide the same effective protection against noise sources located on both sides of the screen; prevent the formation of snow and ice crust on sound-absorbing surfaces, which ensures the constant eff ectiveness of the screen in diff erent seasons of the year; reduce metal consumption, which will reduce the weight of the structure without reducing its effi ciency and reduce the cost of acoustic screens.

Sound power and sound energy measurements using an ellipsoidal measurement surface

To support purchasing low noise products, sound power and sound energy measurements of sufficient quality need to be routinely made by consumers on a global scale. Sound power measurements using ISO 3744, 3745, and 3746 are conducted in a free field using an acoustic far-field approximation of the intensity integrated over an enveloping measurement surface. Sound power and sound energy measurements generally use a hemispherical, parallelepiped, or cylindrical measurement surface. Those measurement surfaces have limitations and assume that the measurement points lie on the measurement surface often in preferred positions. An alternative approach is to choose microphone positions that optimally satisfy the assumptions of the measurement. The measurement surface should then be fit to the chosen microphone positions. Regression methodologies are available for fitting ellipsoids. The number of microphone positions can be as few as three to fit an ellipsoid. An ellipsoidal measurement surfaces can abut zero, one, two, or three orthogonal reflecting planes. Correction equations for the microphone locations and the angle errors for the microphone orientation and wave propagation direction are shown. This paper will present simulations of sound power, sound energy, and corrections for environmental reflections for ISO 3745 and other measurement surfaces.

Noise reduction of plenum window with add-in dual staggered sound scatterer arrays

In present study, a 1:4 scaled down model was used to explore the noise reduction across the plenum window with add-in dual staggered scatterer arrays (sonic-crystal). Reverberation time inside the model space was measured firstly to eliminate the effect of the possible reverberation variation on the sound transmission loss of the plenum window. Two sonic-crystal arrays, the two-by-two and two-by-three scatterer arrangements, were adopted for measurement. A total of four arrays was thus tested after the staggering. Computational simulation was conducted for the sound field inside the plenum chamber to study the noise reduction mechanism of the present window system. Results show that the noise reduction of the plenum window was improved by varying degrees due to the placement of the dual staggered sonic-crystal. The Installation of the dual staggered sonic-crystal increased the sound energy reflections out of the plenum window inlet and decreased the sound energy that passed through the plenum window cavity. At the same time, the resonances inside the window cavity also contributed to the sound transmission loss of the plenum window. The noise reduction across the plenum window was enhanced. The improvement was between ~2 to ~2.7 dBA.

Analysis of Underwater Acoustic Propagation under the Influence of Mesoscale Ocean Vortices

Mesoscale ocean vortices are common phenomenon and fairly distributed over the global oceans. In this study, mesoscale vortex in the South China Sea is identified by processing of AIPOcean data. The characteristic parameters of the identified vortex are extracted by using Okubo-Weiss (OW) method. The empirical sound velocity formula and interpolation method are used to obtain the spatial characteristics of temperature and sound velocity of the mesoscale vortex. After this, a theoretical model based on the Gaussian method is established to fit and simulate the vortex parameters. Using this model, the influence of mesoscale vortex strength, cold and warm vortex, vortex center position and sound source frequency on sound propagation are analyzed in COMSOL software. Finally, the actual parameters of the identified vortex are compared with the ideal Gaussian vortex model. It is found that different types of mesoscale vortices have different effects on the underwater sound propagation characteristics. Cold vortices, for example, cause the sound energy convergence zone to move toward the sound source, reducing the convergence zone’s span, whereas warm vortices cause the sound energy convergence zone to move away from the sound source, increasing the convergence zone’s span. Furthermore, the stronger the mesoscale vortices, the greater the impact on the sound field. Our COMSOL-based results are consistent with previous research, indicating that this model could be useful for studying underwater acoustic propagation in vortices.

Mobile sonouroflowmetry using voiding sound and volume

Uroflowmetry (UF) is a common clinic-based non-invasive test to diagnose Lower Urinary Tract Dysfunction (LUTD). Accurate home-based uroflowmetry methods are needed to conveniently conduct repeated uroflowmetries when patients are physiologically ready to urinate. To this end, we propose and evaluate a novel mobile sonouroflowmetry (SUF) method that estimates the urinary flow rate from a sound signal recorded using a mobile phone. By linearly mapping the total sound energy to the total voided volume, the sound energy curve is transformed to a flow rate curve allowing the estimation of the flow rate over time. An evaluation using data from 44 healthy young men showed high similarity between the UF and SUF flow rates with a mixed-effects model correlation coefficient of 0.993 and a mean root mean square error of 2.37 ml/s. Maximum flow rates were estimated with an average absolute error of 2.41 ml/s. Future work on mobile uroflowmetry can use these results as an initial benchmark for flow rate estimation accuracy.

Measurement of Underwater Acoustic Energy Radiated by Single Raindrops

Underwater noise produced by rainfall is an important component of underwater ambient noise. For example, the existence of rainfall noise causes strong disturbances to sonar performance. The underwater noise produced by a single raindrop is the basis of rainfall noise. Therefore, it is necessary to study the associated underwater noise when drops strike the water surface. Previous research focused primarily on the sound pressure and frequency spectrum of underwater noise from single raindrops, but the study on its sound energy is insufficient. The purpose of this paper is to propose a method for predicting the acoustic energy generated by raindrops of any diameter. Here, a formula was derived to calculate the underwater sound energy radiated by single raindrops based on a dipole radiation pattern. A series of experiments were conducted to measure the underwater sound energy in a 15 m × 9 m × 6 m reverberation tank filled with tap water. The analysis of the acoustic energy characteristics and conversion efficiency from kinetic to acoustic energy helped develop the model to predict the average underwater sound energy radiated by single raindrops. Using this model, the total underwater sound energy of all raindrops during a rainfall event can be predicted based on the drop size distribution.