Sound Distribution Research Articles

Sound source distribution of high-speed trains and reduction of aerodynamic bogie noise

When the Shinkansen train runs at a high speed more than 300 km/h, the contribution ratio of the aerodynamic noise generated from bogies to the total wayside noise is as large as 30%. This is because the aerodynamic noise is proportional to the 6th power of the train velocity. RTRI has designed and made a large new microphone array with a diameter of 3m easy to install in the wayside of the railway. By applying the latest deconvolution algorithm to improve the spatial resolution of sound sources, it was found that the most prominent noise sources distribute around the train nose, pantographs and bogies. Because Japanese environmental standards impose to evaluate the A-weighted maximum noise level at the point 25m apart from the nearest truck after applying time-weighting, S, the aerodynamic bogie noise needs to be reduced. For this reason, we conducted a wind tunnel test to develop countermeasures to reduce aerodynamic bogie noise. As a result, several measures are found to be effective.

Improving the intelligibility of underground station public address / voice alarm systems using horizontal line array

As London's extensive underground network passenger communication is highly dependent on its Public Address/ Voice Alarm system, attention to its efficacy is of great importance. In its current state, the system lacks 21st-century performance which could be implemented using modern technologies. Underground station currently struggle to achieve the minimal life safety intelligibility requirements established by the British standard and bringing an uncomfortable experience to millions of daily passengers. A reinterpretation of the line array / planar source concept in computer simulations has been used to raise the intelligibility beyond the minimal requirements by achieving a homogeneous sound distribution close to the public, with minimal room excitation. This approach minimises destructive reverberant interference and hence proves to improve intelligibility.

The Study of the Sound Waves Transmission along the Fluid Line through the TsN-2 Electric Pump

BACKGROUND: Noise at production site or at any other place where technical equipment operates is a huge issue. It has a strong negative effect on human nervous system, reduces average lifespan and causes a number of severe diseases. That is why reduction of noise, produced by pumps, is one of the current priorities of hydraulic engineering.
 AIMS: In this study, the experimental research of sound transmission through an operating pump and a non-operating pump was carried out. The aim of the research is to find out, whether the last stage of a multistage pump is the main source of hydrodynamic noise (HDN) in pressure line (or the first stage in suction line), or all stages somehow contribute to HDN.
 METHODS: The experiment was carried out on the TsN-2 two-stage impeller pump. In order to generate a sinusoidal signal, an imbedded generator, a vibration test rig and a power amplifier were used. Data acquisition for measurement of HDN and vibrations was performed with use of a conditioning amplifier, a hydrophone and an accelerometer. A 4-channel spectrum analyzer served as a device for processing the studied signal. In addition, a theoretical calculation, considering some physical assumptions, was carried out in order to obtain a more general and accurate concept.
 RESULTS: After completing the experiment, hydrodynamic noise levels and differences for three cases were obtained. These cases are for the switched-on pump, the switched-off pump and for the pump with the removed stage. The data obtained with hydrophones (hydrodynamic noise levels) was correlated with the data obtained with accelerometers (vibration levels). As the correlated data analysis result, the sound insolation distribution over the spectrum was obtained.
 CONCLUSIONS: According to the study results, it can be concluded that the absence of one of two stages ambiguously affected on the sound-insolation properties of the pump. Moreover, no firm conclusions can be drawn about the pump operation influence on the change in its sound-insolation properties.

Numerical Simulation of Flow-Induced Noise in Horizontal Axial Flow Pumps in Forward and Reverse Conditions

This paper investigates the influence of pressure pulsation and flow-induced noise using a two-way dual-purpose pump. The pressure pulsation signal is obtained from the Detached Eddy Simulation (DES) turbulent model calculation as the fan sound source, and the noise sound field distribution in the impeller is calculated. The numerical results show that the external characteristics and pressure pulsation obtained from the simulation correlate well with the experimental values. Under different working conditions, the pressure pulsation decreases with the increase in the flow rate; no evident dominant frequency occurs in the frequency spectrum at a low flow rate, and many spurious frequencies occur. The primary frequency in the runner chamber is the leaf frequency, and that in the nonblade area is the rotating frequency. The sound field distribution of the flow-induced noise has dipole characteristics, and its directivity distribution and sound pressure radiation level can reflect the pressure pulsation characteristics. It is primarily affected by the blade frequency, and the distribution with the flow rate is consistent with the pressure pulsation. Avoiding a low flow and operating in a reasonable flow area can effectively reduce pressure pulsation and flow-induced noise and ensure the stability of unit operation.

Experimental study on levitation control of particles and liquid droplets by vortex acoustic field enhanced by subwavelength pipe

The nonlinear propagation of acoustic waves in a medium generates acoustic radiation force. Using acoustic radiation force, particles and liquid droplets in gases can be levitated and manipulated. Acoustic levitation techniques can manipulate larger objects in the medium without contact, and therefore have been widely used in chemical analysis, droplet dynamics, and bioreactors. The acoustic levitation researches mainly focus on manipulating particles and droplets in an open environment, which provides flexibility in its use. However, this approach has limitations in terms of its efficiency in utilizing acoustic field energy. In this work we propose a concept of subwavelength pipe-enhanced acoustic tweezers, in which the acoustic field is used to manipulate expanded polystyrene particles (EPS) and droplets inside an acoustic pipe with an inner diameter smaller than the wavelength. In this work, we use four small transducers to excite a single low-order mode of a circular waveguide and its simplex state, and we also use the vortex sound field generated inside the waveguide to levitate and manipulate expanded polystyrene particle and droplet in the air. Compared with previous work in an open environment, we significantly enhance the acoustic radiation force by means of the acoustic resonance effect of the subwavelength duct, with both radial and axial suspension force magnitude increasing considerably. Similar concepts of subwavelength optical waveguides and resonant cavities and their effectiveness were already well known and widely used in the field of optics. In this work we first explain theoretically the basis for the design of subwavelength pipe-enhanced acoustic tweezer dimensions. Then, we point out in simulation that the pipe-enhanced acoustic tweezers, compared with the open environment acoustic tweezers, have strong sound field gradient distribution and acoustic radiation force distribution in the pipe. This conclusion is demonstrated experimentally. Finally, the manipulation of droplet and particle levitation and rotation in subwavelength-pipe-enhanced acoustic tweezers is systematically carried out. In this work we introduce the concept of subwavelength acoustic pipe for acoustic manipulation, which is expected to deepen the physical understanding of the interaction between acoustic fields and matter, and to develop new miniaturized acoustic manipulation devices for levitating particles and droplets.

Evaporation kinetics during containerless chemical synthesis of ZIF-8 in levitated droplets.

Zeolitic imidazolate framework-8 was synthesized in a containerless state via acoustic levitation. The cavitation effect of ultrasound affected the coordination connection of organic ligands in acoustically levitated droplets and they exhibited a conspicuous difference in the particle size distribution as compared with those under normal conditions. Herein, methanol was chosen as the solvent to investigate the influence of droplet evaporation on acoustic levitation synthesis. The kinetic parameters of droplet evaporation such as geometrical morphology transformation, concentration change and temperature evolution were measured for the levitation state. Surface evaporation resulted in the drastic deformation of the droplet during ZIF-8 synthesis and caused its vertical vibration and shape oscillation. The abrupt change of the levitation state aggravated the sound field effect on the containerless synthesis and caused a decrease of particle size distribution. A two-dimensional axis-symmetry model was used to visually simulate the sound field distribution during acoustic levitation synthesis based on the finite element method. The fabricated ZIF-8 was able to remove phthalic acid in wastewater through adsorption, and its kinetic features followed a pseudo second-order rate model.

Dynamics of supply chain distribution systems in the apparel industry

Expansion into new markets creates new opportunities and dynamics which could enhance a company’s growth prospects. It thus calls for scalable supply chain distribution systems in competitive marketplaces. The retail supply chain requires sustainable distribution systems to enhance cost efficiency. This study examined the influence of centralised, decentralised, or hybrid distribution systems on agile service delivery, productive human capacity and the supply chain process and technology. First, the study aimed to establish whether a centralised or decentralised supply chain distribution system supports expansion to the African marketplace. Secondly, this study assessed the challenges of inventory positioning and availability on the existing outbound and inbound product flow systems across the African continent. Thirdly, the study examined the interrelated strategic distribution centre performance level to develop the supply chain distribution value proposition model. A descriptive research design was employed using univariate and multivariate methods and data were gathered from 100 staff in an apparel company. The study found that a sound distribution centre requires efficient supply chain systems and a strong workforce. This calls for training and development of employees to improve the organisation’s productivity and efficiency. The managerial implications include the need to ensure that distribution centres support sustainable product availability.

Research on the Archaeoacoustic Simulation of Daxiong Main Halls in Chinese Buddhist Temples Through Comsol Tool

The acoustic analysis plays an irreplaceable role in obtaining information on Chinese Buddhist main halls tradition and relative practice that includes sound, deepening our comprehension of Chinese Buddhist architectural heritage. Various ceremonies and dojos constitute rich types of Buddhist main halls’ sound fields. In this paper, the indoor sound fields of four main halls in the Buddhist temples are researched and compared. This paper used Sketchup to build the models and simulate sound fields when conducting ceremonies and dojos using Comsol Multiphysics software. The four main halls are Chongshan temple main hall, Xiantong temple main hall, Shuxiang temple Manjusri hall and Bodhisattva Top main hall, which are located in separately four temples of Shanxi Wutai mountain in China. Targeting three acoustic parameters including the reverberation time(RT), the first ray arrival time(Re1first) and surface sound pressure level(SPL) distribution, we simulated the acoustic effect of the space occupancy, Buddha realm space and worship space, indicating that the acoustic wave diffusion rate was positively correlated with proportion of hall height to depth, while the first arrival time is exactly the opposite. The largest RT at 2000Hz(about 1.3s)in the shortest period for 500Hz voice was observed in the main hall of Pusa Peak, while T60 even reached 4s in Xiantong temple main hall. The acoustic wave transmission rate was positively correlated with proportion of hall’s height to depth, but the first ray arrival time was the opposite. The main hall of Pusa Peak had the shortest (0.0150s) first ray arrival time，the Shuxiang temple main hall had the longest time(0.0381s). In all the cases, appearing of the "sound shadow area" of the surface SPL distribution and the uneven sound energy distribution showed pillars in the middle space exerting significant impact on the acoustics of the Daxiong main hall.

Full waveform autofocus inversion based microwave induced transcranial thermoacoustic tomography with a human skull validated

Stroke is the third leading cause of mortality in many countries. Thermoacoustic imaging has the potential for stroke detection. However, some parameters in thermoacoustic imaging, such as speed of sound, are difficult to be obtained in advance, and a constant velocity value is assumed in the reconstructed algorithm. Thermoacoustic signals propagate through the soft brain tissue and the skull in actual stroke detection. This mismatch between the assumed and actual sound velocity will degrade the imaging quality. In this Letter, we propose a full waveform autofocus inversion method to reconstruct thermoacoustic images for stroke noninvasive and non-ionizing detection. Employing the difference between the simulation forward sensor signals and the measured signals, the approximate speed of sound distribution is updated continuously. The numerical simulation of a real human brain model and the experiment of a real human skull help us to validate the performance of the proposed method in clinical transcranial thermoacoustic detection.

Estimation of sound speed profiles based on remote sensing parameters using a scalable end-to-end tree boosting model

IntroductionIn underwater acoustic applications, the three-dimensional sound speed distribution has a significant impact on signal propagation. However, the traditional sound speed profile (SSP) measurement method requires a lot of manpower and time, and it is difficult to popularize. Satellite remote sensing can collect information on a large ocean surface area, from which the underwater information can be derived.MethodIn this paper, we propose a method for reconstructing the SSP based on an extensible end-to-end tree boosting (XGBoost) model. Combined with satellite remote sensing data and Argo profile data, it extracts the characteristic matrix of the SSP and analyzes the contribution rate of each order matrix to reduce the introduction of noise. The model inverts the SSP above 1000 m in the South China Sea by using the root mean square error (RMSE) as the precision evaluation index.ResultThe results showed that the XGBoost model could better reconstruct the SSP above 1000 m, with a RMSE of 1.75 m/s. Compared with the single empirical orthogonal function regression (sEOF-r) model of the linear regression method, the RMSE of the XGBoost model was reduced by 0.59 m/s.DiscussionFor this model, the RMSE of the inversion results was smaller, the robustness was better, and the regression performance was superior to that of the sEOF-r model at different depths. This study provided an efficient tree boosting model for SSP reconstruction, which could reliably and instantaneously monitor the 3D sound speed distribution.

Acoustic Feature Extraction Method of Rotating Machinery Based on the WPE-LCMV

Fault diagnosis plays an important role in the safe and stable operation of rotating machinery, which is conducive to industrial development and economic improvement. However, effective feature extraction of rotating machinery fault diagnosis is difficult in the complex sound field with characteristics of reverberation and multi-dimensional signals. Therefore, this paper proposes a novel acoustic feature extraction method of the rotating machinery based on the Weighted Prediction Error (WPE) integrating the Linear Constrained Minimum Variance (LCMV). The de-reverberation signal is obtained by inputting multi-channel signals into the WPE algorithm using an adaptive optimal parameters selection function with the sound field changes. Then, the incident angle going from the fault source to the center of the microphone array is calculated from the full-band sound field distribution, and the signal is de-noised and fused using the LCMV. Finally, the fault feature frequency is extracted from the fused signal envelope spectrum. The results of fault data analysis of the centrifugal pump test bench show that the Envelope Harmonic Noise Ratio (EHNR) is more than twice that of the original signal after the WPE-LCMV processing. Compared to the Recursive Least Squares and the Resonance Sparse Signal Decomposition (RLS-RSSD) and the parameter optimized Variational Mode Decomposition (VMD), the EHNR has a higher value for all types of faults after applying the WPE-LCMV processing. Furthermore, the proposed method can effectively extract the frequency of bearing faults.

Aplikasi Acoustic Shells untuk Mendukung Pertunjukan Musik Kamar di Stage Candra Metu ISI Denpasar

Purpose: This article intends to explain the results of using acoustic shells on Candra Metu performance stage at the Indonesian Institute of the Arts Denpasar in an effort to overcome the problem of musicians on stage without using additional PA System. It was intentional so that the quality of the sound’s character authenticity from the acoustic instrument does not change. The acoustical problem in the Candra Metu stage conduces: (1) inadequate sound distribution which were directed to musicians, (2) musicians are not be able to hear between others during the performance. Research Method: The research method used in writing this article is pre-experimental with One-groups pretest-posttest design, which is explained using qualitative-descriptive method with interdisciplinary approach. Results and discussion: The attempt to overcome sound distribution deficient in the Candra Metu stage by testing the acoustic shells as a performance support during chamber music performance. The acoustic shells’ setting and the arrangement of distance between musicians can affect the sound distribution, where the test result shows that by providing panel reflector could affect and increase the sound intensity on the stage. Implication: The application of acoustic shells on the stage can be helpful to increase sound distribution, whereas to obtain the advantage for musician such as clarity on stage, it is necessary to do acoustic simulation in order that the design of acoustic shells can be redeveloped.

Simulation and Analysis of Civil Aircraft Cabin Sound Field and STI based on Wave6

The cabin loudspeakers of civil aircraft are very important equipment of passenger address system, and the layout scheme of cabin loudspeaker is one of the important factors affecting the audio quality of passenger address system. In the preliminary design stage of passenger address system, the simulation of sound field and STI of cabin loudspeaker by simulation tools is an important means to study, predict, demonstrate and judge the quality of cabin sound field. In this paper, we adopt an equal straight section of a civil aircraft model which is a twin-aisle wide body with a typical three classes, and simulate and compare the sound field distribution and STI of the main areas of the cabin through Wave6 simulation tool based on two different loudspeakers layout schemes, so as to give the recommended layout scheme of the cabin loudspeakers.

Developing a modelling approach for sound propagation through turbulent boundary layer and applying to train pantograph

Sound propagation through turbulent boundary layer (TBL) is of great significance in transports where a TBL is attached to their external surfaces, for instance, air planes and high speed trains. Precise predictions of sound propagation through TBLs to their external surfaces can be extremely useful for their corresponding interior noise control. It is well known that a TBL is classified as an inhomogeneous flow medium and existing approaches are not capable to well predict its influence on sound propagation. Insight of sound propagation through TBLs is required but relevant research on this topic is limited in the literature. In this work, a modelling approach is developed to predict the influence of TBLs on sound propagation. In the proposed approach, the ray tracing method is employed to predict the evolution of sound waves when they are passing through a TBL, with which the equivalent phase speed of sound can be obtained and used to calculate the the Doppler factor so that the traditional methods can be extended to predict sound distribution in inhomogeneous flow media. The validation of this modelling approach is performed by using two cases. The first case is to predict the convective effect of sound propagation in a uniform mean flow and the predicted results are compared with analytical solutions. The second case is sound propagation through a TBL and the predictions obtained from this proposed approach are compared with numerical simulations obtained from the finite element (FE) method. In both cases, the convective effect obtained from this proposed approach is close to the analytical solution or the FE prediction. After that, the proposed approach is used to predict the sound propagation from a high speed train pantograph to the external surfaces of the train with considering the influence of the TBL. The corresponding results are verified by using FE simulations. This work shows that the proposed approach is effective and efficient, and also, it enhances the understanding of sound propagation in inhomogeneous flow media.

A study on non-destructive testing of geometrical parameters of self-piercing riveting joints using an acoustic microscope with a scanning focusing converter

ABSTRACT A non-destructive technique was proposed for geometrical parameters’ measurement of self-piercing riveting (SPR) joints based on ultrasonic C-scan image. Firstly, in order to enhance the detection precision, the characteristics of the ultrasonic echo signal at the edge of internal structure were analysed, and a theoretical formula on its sound intensity distribution was established. Then, an image segmentation process for the detection of SPR expansion diameter was suggested. Results showed that taking the greyscale value at the ‘inflection point’ from the C-scan image as the threshold of the segmentation, the non-destructive test results can get good correlation with the metallographic cross section, which provides a new method on the quality evaluation of SPR by using non-destructive test.

Research on the Sound Absorption Performance of Porous Asphalt Concrete with Different Air Voids Based on the Finite Element Models

This paper aims to investigate the effect of the void structure of porous asphalt concrete (PAC) on the sound absorption performance. The sound absorption coefficient (SAC) spectra of PAC with various voids were measured using the transfer function method and the air void structure was identified from Computed Tomography (CT) scanning images. The finite element model (FEM) of the void structure was established via CT cross-sectional images to research the noise reduction mechanism of PAC. At different frequencies, the sound pressure level distribution and SAC were calculated. The following are the main conclusions: (1) As the void content of PAC increases, the SAC spectrum curve becomes higher, more rightward and wider, while the peak values, their corresponding frequencies and mean values increase. (2) The SAC decreases with the average number of voids within each image and increases with the void equivalent diameter and fractal dimension; there exist linear relationships between these three parameters and the SAC. (3) The sound absorption capacity of the void with larger size and fractal dimension is higher than the smaller one and the voids connected to the upper and lower surfaces provide more noise reduction. (4) The FEMs of PAC can predict the SAC of PAC.

ACOUSTIC TOMOGRAPHY ALGORITHM FOR DETERMINING THE SPATIAL ISOTROPICITY OF THE HYDROACOUSTIC FIELD

One of the primary characteristics of the marine environment is the speed of sound, which very sensitively reflects its smallest changes. Moreover, this characteristic is integral, integral. It inseparably characterizes the state of the system, which is formed by a whole complex of influences and reactions to them. By separating the effects and reactions on the so-called temperature, salinity, pressure, known to us at this stage of the development of the physics, we supposedly simplify the system and its understanding, but in fact we get confused, giving one of the factors very great or very little importance (the possibilities of influence on system). Acoustic tomography is based, among other things, on the sound irradiation of the marine environment and the analysis of the received signal for the purpose of evaluating changes in its characteristics after passing through the water space. Changes in the characteristics of the acoustic signal can occur for annual reasons, one of which is spatial changes in the vertical distribution of sound speed. As a result of theoretical research in the direction of passive acoustic tomography, using the methods of modeling the refraction of acoustic waves, a new type of quantitative characteristics of the acoustic field was determined for the first time. The principle of determining the appropriate reference characteristic of the acoustic field is proposed, on the basis of which the basis for creating algorithms for restoring the vertical distribution of sound speed is developed. The algorithm for determining the reference characteristic, including, includes the calculation of acoustic energy losses, which is translated into the frequency domain to determine the positive extremum of the amplitude spectrum and the calculation of the reference characteristic of the regional acoustic field in the time domain. One of a number of algorithms for determining the spatial isotropy of the vertical sound speed distribution has been adapted. The implementation of the specified algorithm of passive acoustic tomography will provide ship sonar with input data for depth determination, which will increase the safety of navigation.

Overview of ocean ambient noise interferometry – Theory and simulation

Ambient noise interferometry is a passive acoustic technique for environment characterization. The technique uses coherent ambient sound to approximate the Green’s function between two sensors. It has previously been used in ocean acoustics to passively estimate water temperature, sound-speed structure, and mode shapes as well as for sensor localization. Since this technique utilizes the ambient noise field, whose characteristics are often unknown, understanding the effects of non-isotropic ambient sound is important for ambient noise interferometry. In this talk, an overview of the theoretical literature for noise interferometry will be presented with a specific emphasis on the effects of non-isotropic ocean noise source distributions. Additionally, simulations that explore the emergence of the Green’s function will be presented. Specifically, sound source distributions and environmental parameters such as sound speed profile will be explored. Lastly, the implications of these works on the possibilities and limitations of ambient noise interferometry will be discussed. [Work supported by the ONR.]

Optical Wave Microphone Measurement and Visualization of Pressure Waves Generated From a Surface Dielectric Barrier Discharge Element Driven by a High-Voltage Pulse Power Supply

In this study, pressure waves generated by applying a pulsed high voltage (HV) to a surface dielectric barrier discharge element were measured using optical wave microphone. The authors conducted experiments by changing parameters, such as the magnitude, polarity, and repetition rate of the applied pulsed voltage, and the distance between the laser of the optical wave microphone and the electrode of the surface discharge element. In the measurements at different distances between the laser and the electrode, the propagation of pressure waves was observed, and the propagation speed could be estimated. Measurements taken within 4 mm from the HV electrode suggested the influence of shock waves due to significant intensity and propagation speed above the speed of sound in air. Furthermore, the sound field of the surface discharge driven by the pulsed HV was measured by using the optical wave microphone computer tomography (CT) scan technique, and the two-dimensional sound field distribution was made.

Transformer Behavior Feature Identification and Analysis Technology Based on Acoustic Interference

At present, most of the researches are based on linear systems, whose convergence speed and steady-state error are irreconcilable, and in actual operation, nonlinear factors greatly reduce the control performance of linear systems. If the nonlinear problem in the system can be solved, the active noise reduction system can choose low-cost electroacoustic devices with nonlinear distortion, which can not only improve the noise reduction performance, but also has special significance for reducing the cost of the system. Therefore, the main purpose of this paper is to study the feature identification and analysis of transformers based on sound wave interference. This paper explores the propagation, absorption and radiation process of the vibration generated by the transformer core and winding in the surrounding space, and finally obtains the vibration and noise signals of the transformer body, as well as the air sound field distribution at a specific spatial Experiments show that, compared with before the noise reduction experiment, the mean value of the noise in each main frequency band is reduced by about 7dB after the noise reduction experiment.