Characteristics Of Sound Field Research Articles

A Review of the Flow-Induced Noise Study for Centrifugal Pumps

Flow-induced noise is a significant concern for the design and operation of centrifugal pumps. The negative impacts of flow-induced noise on operating stability, human health and the environment have been shown in many cases. This paper presents a comprehensive review of the flow-induced noise study for centrifugal pumps to synthesize the current study status. First, the generation mechanism and propagation route of flow-induced noise are discussed. Then, three kinds of study methodologies, including the theoretical study of hydrodynamic noise, numerical simulation and experimental measurement study, are summarized. Subsequently, the application of the three study methodologies to the analysis of the distribution characteristics of flow-induced noise is analyzed from aspects of the noise source identification and comparison, the frequency response analysis, the directivity characteristics of sound field and the noise changing characteristics under various operating conditions. After that, the analysis of the noise optimization design of centrifugal pumps is summarized. Finally, based on previous study results, this paper puts forward the unsolved problems and implications for future study. In conclusion, the information collected in this review paper could guide further study of the flow-induced noise of centrifugal pumps.

Research on Racetrack Coil EMAT FE Model and Sound Field Characteristics

Research on Racetrack Coil EMAT FE Model and Sound Field Characteristics

Size Effect Study on High Frequency Transducers for Sensitivity Enhancement

In a high frequency ultrasonic imaging system, high signal-noise-ratio (SNR) is highly demanded to acquire high quality images. Transducer sensitivity enhancement is essential to increase the SNR. In this work, size effect of transducers with working frequency 12MHz and 20MHz is systematically studied to find its relationship with sensitivity. FEM (Finite Element Method) models are built to analyze the impedance and sound field characteristics for different size transducers. Pulse-echo measurement experiments are carried out to compare the performance variation induced by the size effect. Simulation results suggest that working frequency is mainly determined by the piezoelectric slice thickness, the values of admittance are dependent on the area value of transducers and the optimum width is 1.5mm-1.7mm for 12MHz transducer and 1.1mm-1.3mm for 20MHz transducer. The admittance measurement results and pulse-echo results confirm the simulation conclusion and certify that 12MHz transducer with 1.5mm width and 3.0mm length, 20MHz transducer with 1.2mm width and 3.0mm length have the highest sensitivities. Their echo peak-peak values can reach 1.248V and 1.332V, respectively. These results indicate that sensitivity can be enhanced by optimizing transducer size. Methods utilized in this work are of great significance in a broader range of transducer design cases such as IVUS system and array transducers.

Self-focusing Linear Array Sound Field Characteristics and Testing

Self-focusing Linear Array Sound Field Characteristics and Testing

Experimental analysis of sound field in the tire cavity arising from the acoustic cavity resonance

The acoustic cavity resonance noise inside the tire-wheel assembly is known to contribute to audible noise in the passenger compartment of vehicles, but it is difficult to attenuate the effect of tire cavity resonance noise. The purpose of this paper is to experiment and analyze the sound field in the tire cavity of a revolving tire through a customized sound pressure sensor fixed on the inner surface of the tire, and to obtain the distribution and frequency characteristics of sound field. Furthermore, the paper concerns the effects of the inflation pressure, the running velocity, and the load on the sound pressure distributions and its frequency characteristics, and the influence of these parameters are analyzed. The research is helpful to understand and attenuate the tire acoustic cavity resonance.

Prediction of sound fields after propagation through sound barriers by CNN and DCNN algorithms

Sound fields are affected by the size of the space and the surrounding environments. The ray tracing method analyze the sound propagation through geometric constraints. For prediction of sound fields in a real-time to investigate the influence of surrounding environments, an effective calculation method is required. During the prediction, it is necessary to calculate the sound field distribution according to the layout of equipment or sound reflecting devices to minimize noise in working spaces. This procedure is required for an optimal arrangement of barriers according to noise sources. To improve this repetitive work, it is devised to develop a machine learning model that predicts the change in the sound field according to the position of sound barrier through CNN and DCNN algorithms. Training data were generated by using a commercial tool. The proposed approach recognizes the characteristics of sound fields at spaces after acoustic barriers.

Modulation of sound waves for flow past a rotary oscillating cylinder in a non-synchronous region

Modulation of sound waves for the laminar flow past a rotary oscillating circular cylinder has been studied for a free-stream Reynolds number Re = 150 and Mach number M = 0.2. Modulation of sound waves has been observed if the combination of applied rotary oscillation frequency and amplitude belongs to the nonsynchronous region where the hydrodynamic and acoustic quantities vary with the vortex shedding frequency as well as the applied forcing frequency. Two-dimensional direct numerical simulations (DNS) are carried out on a highly refined grid using high resolution physical dispersion relation preserving schemes for a nondimensional forcing frequency-ratio range 0.1 ≤ fr ≤ 2.0 at a nondimensional surface speed A1 = 0.1. Both the synchronous and the nonsynchronous zones are identified based on the time-varying fluctuations in the lift and the drag coefficients. In the nonsynchronous zone, modulation phenomena of the lift and the drag coefficients are explained by plotting the stream-function contours over multiple vortex shedding cycles. The modulation periods associated with the fluctuating lift and the drag coefficients are different for some cases. This particular observation is in contrast with the observation expressed in the previous studies investigating similar problems. Disturbance pressure fields obtained from the present DNS data are used to analyze the characteristics of radiated sound fields, especially in the nonsynchronous zone. Information related to aerodynamic sound sources has been obtained using approximated Lighthill’s stress tensor, and it is shown that the aerodynamic sound sources also display the modulation phenomenon similar to that observed in the vortex shedding process. Sound fields related to the nonsynchronous zone also exhibit the modulation phenomenon and are governed by the shedding frequency, the forcing frequency, and their linear combinations. Radiated sound field characteristics are further related to the time-varying fluctuations of the lift and the drag coefficients using Curle’s acoustic analogy. Modulated sound waves observed along the upstream and the transverse directions have similar time variation as that of the drag and the lift coefficients, respectively. The phenomenon of beat formation has been observed for the ranges 0.9 ≤ fr ≤ 0.99 and 1.2 ≤ fr ≤ 1.4. Although the observed modulation of sound waves varies significantly with the forcing frequency-ratio, the net radiated sound power has almost remained constant in the nonbeating, nonsynchronous zone. Furthermore, it is confirmed that the dominant sound modes obtained during the proper orthogonal decomposition of disturbance pressure fields in the nonsynchronous zone are related to the shedding frequency-ratio, the forcing frequency-ratio, and their linear combinations.

From Local Structure to Overall Performance: An Overview on the Design of an Acoustic Coating.

Based on the requirements of underwater acoustic stealth, the classification and research background of acoustic coatings are introduced herein. The research significance of acoustic coatings is expounded from the perspective of both the military and civilian use. A brief overview of the conventional design process of acoustic coatings is presented, which describes the substrates used in different countries. Aimed at the local design of acoustic coatings, research progress on passive and semi-active/active sound absorption structure is summarized. Focused on the passive acoustic coatings; acoustic cavity design and optimization, acoustic performance of acoustic coatings with rigid inclusions or scatterers, and acoustic coatings with a hybrid structure are discussed. Moreover, an overview of the overall design of acoustic coatings based on the sound field characteristics of the submarine is also presented. Finally, the shortcomings of the research are discussed, breakthroughs in acoustic coating design research are forecast, and the key technical issues to be solved are highlighted.

Optimization of Secondary Sources Configuration in Two-Dimensional Space Based on Sound Field Decomposition and Sparsity-Inducing Regularization

During the design of transducers configuration for an active noise control system, current optimization methods need to predetermine the error sensors configuration, which significantly increases the workload of later optimization of the secondary sources configuration. In this study, a new method free from specific error sensors configuration information is presented that higher order microphones are used to capture the sound field so as to formulate the cost function in wave domain. In addition, according to sparsity characteristics of the primary sound field, sparsity-inducing regularization is introduced to optimize the secondary sources configuration, including the number and positions, by calculating a sparse approximate solution to underdetermined equations. Effects of the number of candidate secondary sources are discussed, and the comparison with the uniform configuration and the optimized configuration using the genetic algorithm is performed. Results show that the proposed method can optimize the secondary sources configuration effectively independent of the error sensors configuration information. The noise reduction of the proposed method is close to that by the genetic algorithm, while other evaluation metrics for the system are much better, which would benefit the stability of active noise control system.

Propagation characteristics of underwater plasma pulse sound source

The signal propagation characteristics of underwater plasma pulsed sound source have important guiding significance for the research and application of underwater directional radiation technology. In this thesis, the model propagation method is used to analyze the signal propagation law of underwater plasma pulse source with different depths. Firstly, the propagation model of underwater plasma sound source is established. Secondly, the distribution characteristics of underwater sound field at different depths are simulated. The research results show that the simulation results can express the underwater sound field characteristics at different depths, which proves the effectiveness of the simulation model, and lays a foundation for further research on underwater pulse directional radiation technology and improving the underwater application of pulse sound source.

The effect of structural-acoustic coupling on the sound field in a trapezoidal enclosure

The sound field characteristics in a trapezoidal enclosure surrounded by a flexible wall, which is adjacent to the tilted one, are investigated and compared with the case of a rectangular enclosure. The acoustic modes of trapezoidal enclosure are obtained by the coupling of the modes of rectangular enclosure that bounds it. The coupling system model is then built between trapezoidal enclosure modes and flexible wall modes using modal coupling theory. Based on the coupled system model, the effect of flexible wall modal density on the resonance frequencies and the decay times of coupled system are analyzed. Compared with the case of rectangular enclosure, the variation of the resonance frequency and the decay time of enclosure-controlled system mode is determined by its mode indices and tilted wall location when the panel modal density is changed. When the modal indices of trapezoidal sound field in the two directions unparallel to the tilted wall are equal to zero simultaneously, the effect of inclination angle on the resonance frequencies and decay times of these coupled system modes can be neglected. Otherwise, the coupling system modes behaviors are changed with the elevation angle. In addition, the coupling selection between the modes of trapezoidal enclosure and flexible wall is discussed in detail.

Spatial Wiener filter to reduce spatial aliasing with spherical microphone arrays.

Three dimensional acoustic soundfields can be represented by a set of spherical harmonic coefficients that are extracted from pressure signals recorded by a spherical microphone array. The extraction method used and truncation order chosen introduce errors of spatial aliasing in the coefficients and truncation error in a reconstructed signal. A spatial Wiener filter (SWF) extraction method is proposed in this paper, using second order statistics of typical soundfield characteristics (signal power, estimated source locations, and internal microphone noise) and accounts for the presence of coefficients beyond the truncation order to reduce spatial aliasing in the extracted coefficients. The SWF can also distinguish between "wanted" and "unwanted" sources, reducing the contributions of unwanted sources to the extracted coefficients. The SWF is compared against the state of the art methods; regularized inverse (or generalized inverse), and orthonormal extraction methods, which are explored under a similar framework to the SWF. The authors compare these methods and show the benefit of the SWF for plane waves, with varying assumptions about the source characteristics. The SWF can also extract coefficients beyond the traditional truncation limit of a given array, unlike other methods.

Study on acoustic and flow induced noise characteristics of L-shaped duct with a shallow cavity

An aerodynamic sound generated by a flow inside a duct is one of the noise pro- blems. Flows in ducts with uneven surfaces such as grooves or cavities can be seen in various industrial devices and industrial products such as air-conditioning equipment in various plants or piping products. In this article, we have performed experiments and simulations to clarify acoustic and flow-induced sound characteris- tics of L-shaped duct with a shallow cavity installed. The experiments and simula- tions were performed under several inflow velocity conditions. The results show that the characteristics of the flow-induced sound in the duct are strongly affected by the acoustic characteristics of the duct interior sound field and the location of the shallow cavity. Especially, it was found that the acoustic characteristics were af- fected by the location of the shallow cavity in the frequency range between 1000 Hz and 1700 Hz.

Vertical correlations of sound field at large depths in deep water

The research on the vertical correlation characteristics of sound field in deep water has important implications for enhancing the vertical array gain and improving the ability to detect the underwater target. Based on a deep-water experiment conducted in the South China Sea, the vertical coherence of sound fields in the direct zone, shadow zone and convergence zone are analyzed with the sound signals received by a vertical line array that covers the maximal depth to 1,866 m. The numerical analysis based on the ray theory is carried out to provide corresponding theoretical explanations to the variations of the vertical correlation characteristics at different ranges and depths. The vertical correlation coefficients in the direct zone are higher than 0.707 for the whole depth and drop very little with the increase of the vertical depth. It is because the main contributions come from direct arrival ray and sea surface reflection ray. The pulse structure is relatively simple, and the time delays of the two rays increase with the space between two receivers increasing. In the shadow zone, sound energy mainly comes from bottom reflection. Therefore, the vertical correlation coefficients are relatively low. Multi-path arrival is observed obviously. Vertical correlation coefficients drop quickly with depth increasing. With range increasing, the time delays of the multi-path pulses decrease. The vertical correlation coefficients at the same depth will increase a little with range increasing. Near the first convergence zone, vertical correlations oscillate periodically with the increase of vertical separation, and share the same distribution pattern with the sound energy along the vertical direction, which is caused by the periodical oscillation of two groups of the refracted rays from water volume. The refracted rays have the same amplitude, therefore, the time delays of the two group of rays increase with receiver depth increasing, and the phase of sound filed fluctuates in <inline-formula><tex-math id="M1">\begin{document}$The research on the vertical correlation characteristics of sound field in deep water has important implications for enhancing the vertical array gain and improving the ability to detect the underwater target. Based on a deep-water experiment conducted in the South China Sea, the vertical coherence of sound fields in the direct zone, shadow zone and convergence zone are analyzed with the sound signals received by a vertical line array that covers the maximal depth to 1,866 m. The numerical analysis based on the ray theory is carried out to provide corresponding theoretical explanations to the variations of the vertical correlation characteristics at different ranges and depths. The vertical correlation coefficients in the direct zone are higher than 0.707 for the whole depth and drop very little with the increase of the vertical depth. It is because the main contributions come from direct arrival ray and sea surface reflection ray. The pulse structure is relatively simple, and the time delays of the two rays increase with the space between two receivers increasing. In the shadow zone, sound energy mainly comes from bottom reflection. Therefore, the vertical correlation coefficients are relatively low. Multi-path arrival is observed obviously. Vertical correlation coefficients drop quickly with depth increasing. With range increasing, the time delays of the multi-path pulses decrease. The vertical correlation coefficients at the same depth will increase a little with range increasing. Near the first convergence zone, vertical correlations oscillate periodically with the increase of vertical separation, and share the same distribution pattern with the sound energy along the vertical direction, which is caused by the periodical oscillation of two groups of the refracted rays from water volume. The refracted rays have the same amplitude, therefore, the time delays of the two group of rays increase with receiver depth increasing, and the phase of sound filed fluctuates in <inline-formula><tex-math id="M1">\begin{document}$\left[ {0,2} {\text{π}}\right]$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.png"/></alternatives></inline-formula>periodically. The periodicity causes the sound intensity and the vertical correlation coefficients to have the same oscillation structures. If the rays have the same phases, the main contribution comes from refraction rays, the structure of the pulses is relatively simple and causes vertical correlation to be higher. Otherwise, the main contribution comes from bottom reflected rays, the structure of the pulses is complex, and vertical correlation drops down. <b><i>Corresponding Author: Li Zheng-lin</i></b> $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20190134_M1.png"/></alternatives></inline-formula>periodically. The periodicity causes the sound intensity and the vertical correlation coefficients to have the same oscillation structures. If the rays have the same phases, the main contribution comes from refraction rays, the structure of the pulses is relatively simple and causes vertical correlation to be higher. Otherwise, the main contribution comes from bottom reflected rays, the structure of the pulses is complex, and vertical correlation drops down.

Acoustic environment research of railway station in China

One characteristic of railway stations in China is that the entrance hall, ticket office, integrated waiting hall and auxiliary space are all concentrated in a large span of space, forming a unified whole space. However, the multi-function fusion in such a large space results in a series of acoustic problems, such as long reverberation time, high environmental noise and poor language articulation. Therefore, it is necessary to study the acoustic environment of railway stations in China. In this study, the sound field characteristics of the typical railway station are studied to reveal its law of sound propagation. Next, subjective evaluation and objective experiments are carried out to study the acoustic environment and comfort in the waiting hall. Finally, based on the comparative analysis of various influential factors, such as sound source and sound field, this paper advances some suggestions for the acoustical design of high-speed railway stations.

Numerical simulation on the impact of the bionic structure on aerodynamic noises of sidewindow regions in vehicles

The paper adopted a bionic hemispherical convex structure in the A pillar-rear view mirror regions according to actual requirements. Furthermore, impacts of the bionic structure on aerodynamic characteristics and noises in the region were studied. Friction resistance of airflows was greatly reduced, fluctuations and pulsation pressures of flow fields were also reduced, and characteristics of flow fields and sound fields were improved. The computational results were finally verified by the experimental test. Firstly, the aerodynamic lift force coefficient and drag force coefficient of the bionic model were computed, and they were obviously lower than those of the original model. The adhesive force between tires and ground during vehicle running was increased, and the danger degree of “waving” of high-speed vehicle running was weakened. In this way, stability of vehicle running could be improved. Secondly, flow fields of the bionic model were computed. Compared with the original model, an obvious vortex was behind the original model, while no vortexes were behind the bionic model. Therefore, convex structures of the bionic model had obvious impacts on flow fields behind the rear view mirror. Airflow separation situations were obvious improved at wheels, windshield and rear side windows of the bionic model. Due to blocking of convex structures of the A pillar and rear view mirror in the bionic model, airflows was hindered and obvious dragging phenomena were formed. Therefore, flow fields in the side window regions could be improved greatly. In addition, the flow field scope under the rear view mirror in the bionic model was also decreased. Ringed vortex structures appeared behind the rear view mirror in the bionic model. The ringed vortex structures were closely interlaced and then extended together backwards. Vortexes behind the rear view mirror in the original model were chaotic, where most of them were attached on the surface of side windows. In the original model, turbulent flows with certain strength were on the right upper corner of the side window region. In the bionic model, no turbulent flows were in the same regions. This result indicated that through using the bionic convex structures, airflows flowing through side windows could be combed and could move backwards towards upper and lower edges of the side windows. It could be predicted that pulsation pressures on the side window surface would surely decrease. Therefore, aerodynamic noises caused by pulsation pressures in side window regions would also be improved correspondingly. Especially in regions behind A pillar-rear view mirrors, the maximum noise reduction amplitude reached about 20 dB.

An Exploratory Analysis of Sound Field Characteristics using the Impulse Response in a Car Cabin

Sound environments in cars are becoming quieter and receiving attention because of the prevalence of low-noise engines such as hybrid and electric engines and the manifestation of automated driving. Although the car cabin has potential as a listening space, its acoustic quality has not been examined in detail. The present study investigated sound field characteristics in the car cabin using acoustic parameters obtained by impulse response analysis. In particular, effects of the passenger position, open windows and the use of an air conditioner on acoustic parameters were investigated. The passenger position affected the sound strength at low frequencies. Rear seats, except for the rear central seat, had lower interaural correlation than the front seats, suggesting that rear seats have more diffused sound fields. The opening of windows and use of air conditioners attenuated the ratio of early- and late-arriving energy at high frequencies, suggesting a loss of clarity for music.

Method for the measurement of the underwater transient sound characteristics in a reverberation tank

A method to evaluate the sound power of transient sound sources in reverberation tanks is proposed and tested. The method is based on the steady state sound field characteristics in closed space, which are analyzed by normal-wave theory. To eliminate the interference caused by the boundary of the sound field, the volume integral of the spatial mean-square pressure in local space is measured and the sound power density of the non-anechoic is then obtained. Using the relationship between the sound field in the enclosed space and that of the free field, the sound power of the sound source can be obtained using the measured spatial mean-square pressure. The sound power of an impulsive sound generated by a spherical sound source is measured in a reverberation tank and the results are compared with the sound power measured in anechoic pool to verify the accuracy of the proposed method. The proposed method can be used to measure the radiated sound power of different types of transient sound sources in reverberation tanks.

Integrating remote microphone signals with hearing-aid processing

Remote microphones (RM) are used with hearing aids to provide speech signals free from noise and room reverberation. However, because the RM signal bypasses the acoustics of the head and pinna, it can provide an unnatural signal that is lateralized at the center of the head rather than localized at the talker. A structural binaural model is combined with synthesized early room reflections to provide the missing externalization cues. The effectiveness of this simulation has been demonstrated over headphones using linear amplification to compensate for the hearing loss. In a hearing aid, however, the RM processed signal is combined with the acoustic inputs at the hearing-aid microphones, and the processed hearing-aid output is combined with the reverberated speech that is transmitted through the vent or open fitting. The hearing-aid processing implemented in the experiments described in this presentation includes both linear amplification and wide dynamic-range compression. The externalization, spatial soundfield characteristics, and sound quality provided by the entire signal-processing system are evaluated for normal-hearing and hearing-impaired listeners.

Research on the well at the top edge of noise barrier

Wells mounted on the top edge of barrier could improve the noise reduction effect of the barrier. In order to research the characteristics of the well, the 2D boundary element method (BEM) was adopted, the insertion loss (IL) of different type of barriers were calculated, the effect of well was analysed. Results showed that, almost 1.5 dBA of the IL is aroused by the reflect sound of the well. So, it is important to improve the sound field inside the well to improve the noise reduction effect of the barrier. The sound field inside the well depends on the sound diffraction effect, therefore, the characteristics of sound field diffracted by a single edge was analysed by the geometrical theory of diffraction (GTD) method. Then the effect of well width on the noise reduction effect was discussed according to the sound diffraction loss. To verify the discussion conclusions, the noise reduction effect of barrier with different width of well was simulated and compared. In addition, experiments were also carried out in a semi-anechoic chamber using full-scale models. Both the experimental and simulation results show that, to play a better role of the well, the well width should be greater than 1/3 of the well depth.