Acoustic Performance Study of Fiber-Optic Acoustic Sensors Based on Fabry–Pérot Etalons with Different Q Factors

The ideal development direction of the fiber-optic acoustic sensor (FOAS) is toward broadband, a high sensitivity and a large dynamic range. In order to further promote the acoustic detection potential of the Fabry–Pérot etalon (FPE)-based FOAS, it is of great significance to study the acoustic performance of the FOAS with the quality (Q) factor of FPE as the research objective. This is because the Q factor represents the storage capability and loss characteristic of the FPE. The three FOASs with different Q factors all achieve a broadband response from 20 Hz to 70 kHz with a flatness of ±2 dB, which is consistent with the theory that the frequency response of the FOAS is not affected by the Q factor. Moreover, the sensitivity of the FOAS is proportional to the Q factor. When the Q factor is 1.04×106, the sensitivity of the FOAS is as high as 526.8 mV/Pa. Meanwhile, the minimum detectable sound pressure of 347.33 μPa/Hz1/2 is achieved. Furthermore, with a Q factor of 0.27×106, the maximum detectable sound pressure and dynamic range are 152.32 dB and 107.2 dB, respectively, which is greatly improved compared with two other FOASs. Separately, the FOASs with different Q factors exhibit an excellent acoustic performance in weak sound detection and high sound pressure detection. Therefore, different acoustic detection requirements can be met by selecting the appropriate Q factor, which further broadens the application range and detection potential of FOASs.

Multistable autonomous motion of fruit on a smooth hotplate

Origin of scale coupling may be clarified by the understanding of multistability, or shifts between stable points via unstable equilibrium points due to a stimulus. When placed on a glasstop hotplate, cobs of corn underwent multistable autonomous oscillation, with unsteady viscous lubrication below and transitional plumes above, where the buoyancy to inertia force ratio is close to ≥ 1.0. Subsequently, viscous wall-frictional multistability occurred in six more types of smooth fruit with nominal symmetry. Autonomous motion observed are: cobs roll, pitch and yaw; but green chillies, blueberries, tropical berries, red grapes, oblong grapes and grape tomatoes roll and yaw. The cross products of the orthogonal angular momentum produce the observed motion. The prevalence of roll and yaw motion are the most common. Lubricant film thickness h$$\propto$$ ∝ U/(TF), for cob mass F, tangential velocity U and temperature T. In heavier cobs, the film thins, breaking frequently, changing stability. Lighter cobs have high h, favoring positive feedback and more spinning: more T rises, more viscosity of water drops, increasing U and h more, until cooling onsets. Infrequent popping of the tender corn kernel has the same mean sound pressure level as in hard popcorn. The plume vortex jets lock-in to the autonomous rolling cob oscillation. Away from any solid surface, the hot-cold side boundary produces plumes slanted at ± 45°. Surface fencing (13–26 μm high) appears to control motion drift.

Acoustic Slow-Wave Effect Metamaterial Muffler for Noise Control of HVDC Converter Station

Aiming at the noise control of the HVDC converter station, a one-dimensional two-port metamaterial muffler based on the acoustic slow-wave effect is designed and manufactured. The metamaterial muffler achieves a broadband quasi-perfect absorption of noise from 600 to 900 Hz while ensuring a certain ventilation capacity. In addition, the internal equivalent sound velocity curve and the sound pressure and velocity field of the muffler are used to reveal the mechanism of its broadband quasi-perfect sound absorption. The performance of the muffler was verified by theoretical, numerical, and experimental models. The work in this paper is of guiding significance for solving the noise problem in HVDC converter stations.

Environmental noise-induced cardiovascular responses during sleep

Study Objectives This study was designed to test the utility of cardiovascular responses as markers of potentially different environmental noise disruption effects of wind farm compared to traffic noise exposure during sleep. Methods Twenty participants underwent polysomnography. In random order, and at six sound pressure levels from 33 dBA to 48 dBA in 3 dB increments, three types of wind farm and two types of road traffic noise recordings of 20-sec duration were played during established N2 or deeper sleep, each separated by 20 seconds without noise. Each noise sequence also included a no-noise control. Electrocardiogram and finger pulse oximeter recorded pulse wave amplitude changes from the pre-noise onset baseline following each noise exposure and were assessed algorithmically to quantify the magnitude of heart rate and finger vasoconstriction responses to noise exposure. Results Higher sound pressure levels were more likely to induce drops in pulse wave amplitude. Sound pressure levels as low as 39 dBA evoked a pulse wave amplitude response (Odds ratio [95% confidence interval]; 1.52 [1.15, 2.02]). Wind farm noise with amplitude modulation was less likely to evoke a pulse wave amplitude response than the other noise types, but warrants cautious interpretation given low numbers of replications within each noise type. Conclusion These preliminary data support that drops in pulse wave amplitude are a particularly sensitive marker of noise-induced cardiovascular responses during. Larger trials are clearly warranted to further assess relationships between recurrent cardiovascular activation responses to environmental noise and potential long-term health effects.

Acoustic analysis of selected sacred buildings in Szczecin

The aim of this study was to assess acoustically selected sacred buildings located in Szczecin. The research part contains the research methodology and the results obtained. The research was carried out using two methods. The first one is the integrated impulse response method, where, using a bursting balloon, the time of sound pressure drop was measured at selected points of the object. In the interrupted noise method, the sound pressure drop was measured after the noise generated by the omnidirectional loudspeaker had ceased. Reverberation time was calculated for the results obtained, which is the main and basic parameter determining the interior acoustics. On the basis of the above-mentioned measurements, the reverberation indicators for the temples were also calculated. When analyzing the components of the reverberation indicator, it was noticed that poor acoustics in the sanctuary concerns speech, while interior acoustics is good for the reception of organ music. In the analyzed church, the reception of liturgical music is also better than the reception of speech, but the differences between these values are small.

Sound generation mechanism of compressible vortex reconnection

We study the sound generation mechanism of initially subsonic viscous vortex reconnection at vortex Reynolds number $Re~(\equiv \text {circulation}/\text {kinematic viscosity})=1500$ through decomposition of Lighthill's acoustic source term. The Laplacian of the kinetic energy, flexion product, enstrophy and deviation from the isentropic condition provide the dominant contributions to the acoustic source term. The overall (all time) extrema of the total source term and its dominant hydrodynamic components scale linearly with the reference Mach number $M_o$ ; the deviation from the isentropic condition shows a quadratic scaling. The significant sound arising from the flexion product occurs due to the coiling and uncoiling of the twisted vortex filaments wrapping around the bridges, when a rapid strain is induced on the filaments by the repulsion of the bridges. The spatial distributions of the various acoustic source terms reveal the importance of mutual cancellations among most of the terms; this also highlights the importance of symmetry breaking in the sound generation during reconnection. Compressibility acts to delay the start of the sequence of reconnection events, as long as shocklets, if formed, are sufficiently weak to not affect the reconnection. The delayed onset has direct ramifications for the sound generation by enhancing the velocity of the entrained jet between the vortices and increasing the spatial gradients of the acoustic source terms. Consistent with the near-field pressure, the overall maximum instantaneous sound pressure level in the far field has a quadratic dependence on $M_o$ . Thus, reconnection becomes an even more dominant sound-generating event at higher $M_o$ .

Road traffic noise assessment in a hospital area in Umuarama - Brazil

In hospital environments, high noise levels can result in damage to patients' treatments, delaying their rest and recovery. The sound pressure level (SPL) in hospital areas during the day must not exceed 50 dB and 45 dB (A) at night, according to NBR 10.151/2019. This research aimed to carry out environmental monitoring of equivalent sound pressure levels (LAeq) at fifteen points in the vicinity of three hospitals in the central region of the municipality of Umuarama-PR, during working days, at four different times, in the months of August, September and November 2018 and continued in March 2019. To this end, we sought to map the LAeq of the points, compare them with data from municipal and federal legislation and relate the LAeq to the volume of vehicular traffic. The collected SPL were higher than recommended by NBR 10.151 at all times and measurement points, during the week, and when considering the municipal regulations, only one point is in the equipment's accuracy limit. From the statistical analysis, a very strong correlation was observed between LAeq and the total volume of vehicles, and also a strong correlation between the descriptors L10 and L50 and the volume of vehicles. The Traffic Noise Index (TNI) was also calculated and the LAeq values ​​were compared with a subjective noise rating. The results show a scenario of noise pollution in the area and there is a need for the application of mitigating measures.

Numerical Analysis of Aeroacoustic Phenomena Generated by Truck Platoons

In recent years there has been dynamic progress in the development of fully autonomous trucks and their combination and coordination into sets of vehicles moving behind each other within short distances, i.e., platooning. Numerous reports from around the world present significant benefits of platooning for the environment due to reduced emissions, reduced fuel costs, and improved logistics in the transport industry. This paper presents original aerodynamic and aeroacoustic studies of identical truck column models. They are divided into four main stages. In the first, a truck model and three columns of identical trucks with different distances between the vehicles was made and tested using computational fluid dynamics (CFD). Two turbulence models were used in the study: k−ω shear stress transport (SST) and large eddy simulation (LES). The aim of the work was to determine the drag coefficients for each set of vehicles. The second stage of work included determination of sound field distributions generated by moving vehicles. Using the Ffowcs Williams–Hawkings (FW-H) analogy, the sound pressure levels were determined, followed by the sound pressure levels A. In order to verify the correctness of the work carried out, field tests were also performed and additional acoustic calculations were carried out using the NMPB-Routes-2008 and ISO 9613-2 models. Calculations were performed using SoundPlan software. The performed tests showed good quality of the built aerodynamic and aeroacoustic models. The results presented in this paper have a universal character and can be used to build intelligent transport systems (ITSs) and intelligent environmental management systems (IEMSs) for municipalities, counties, cities, and urban agglomerations by taking into account the platooning process.

STUDY OF THE COAGULATION OF AEROSOL PARTICLES IN THE SCRUBBER ULTRASOUND CHAMBER

В данной работе представлены результаты исследования процесса коагуляции частиц аэрозоля моноаммонийфосфата в модельной ультразвуковой (УЗ) камере скруббера. Изучено поведение аэрозольных частиц внутри камеры на расстоянии 100 мм и 400 мм от ультразвукового излучателя с частотой излучения 22 кГц. Представленные результаты показывают практически отсутствие коагуляции частиц при интенсивности звукового давления 140 dB и процесс активной коагуляции при интенсивности звукового давления 150 dB для выбранного образца. Начальная массовая концентрация фосфата аммония в камере составляла 1 г/м3. Измерения дисперсного состава аэрозоля внутри камеры показали, что более интенсивно коагуляция проходила в области 400 мм. Через 30 минут воздействия значение среднего объемно-поверхностного диаметра частиц аэрозоля в камере изменилось на 238,4 %. This paper presents the results of the study of the coagulation of the monoammonium phosphate aerosol particles in the model ultrasonic scrubber chamber. The behavior of aerosol particles inside the chamber is studied at the distance of 100 mm and 400 mm from the ultrasonic emitter with 22 kHz of the radiation frequency. The presented results show almost complete absence of particle coagulation at the sound pressure intensity of 140 DB and the active coagulation process at the intensity of 150 dB for the selected sample. The initial mass concentration of ammonium phosphate in the chamber was 1 g / m3. Measuring the dispersed composition of the aerosol showed that coagulation proceeds more intensively in the region of 400 mm. After 30 minutes of exposure the value of the average surfactant diameter of the aerosol particles in the chamber has changed by 238.4%.

Nonlinear modeling and prediction of forklift acoustic annoyance based on the improved neural networks

Aiming at the characteristics of high decibels and multiple samples for forklift noise, a subjective evaluation method of rank score comparison (RSC) based on annoyance is presented. After pre-evaluation, comprehensive evaluation and data tests on collected 50 noise samples, the annoyance grades of all noise samples were obtained, and seven psycho-acoustic parameters including linear sound pressure level (LSPL), A-weighted sound pressure level (ASPL), loudness, sharpness, roughness, impulsiveness and articulation index (AI) were determined by correlation calculation. Considering the nonlinear characteristics of human ear subjective perception, objective parameters, and annoyance were used as input and output variables correspondingly and then three nonlinear mathematical models of forklift acoustic annoyance were established using traditional artificial neural network (ANN), genetic-algorithm neural network (GANN), and particle-swarm-optimization neural network (PSONN). Moreover, the prediction accuracy of the three models was tested and compared by sample data. The results indicate that the average relative error (ARE) between the experimental and predicted values of acoustic annoyance based on PSONN model is 3.893%, which provides an effective technical support for further optimization and subjective evaluation.