Error analysis and calibration for underwater sound intensity measuring system

Based on measuring the cross-spectrum density of sound pressure between two hydrophones, the facility for underwater sound intensity measurement is investigated and designed. According to the principle of two-hydrophone method for intensity measurement, the error analysis is carried out. Given the method of sound intensity measurement calibration for this underwater sound intensity measurement facility, the uncertainty of intensity measurement by this facility is evaluated. It is shown that the analysis and evaluation are agreeable to the experimental results.

Scanning paths for estimating sound power of noise sources by sound intensity scanning method

A mathematical model of deterndulng sound power by using the scanning method is developed. It is assumed that the scanning speed is constant and the noise source is stationary The accuracy of estimating sound power along some simple paths on the surfaces such as rectangle, disc and hemisphere is analyzed. It is argued that the accuracy of estimating sound power is strongly depended on a suitable selection of scan path. The accurate estdriation of sound power can be made by scanning along some simple paths.

SCATTERING OF SOUND FROM A PAIR OF FINITE CYLINDERS——A PRELIMINARY STUDY APPLICABLE TO SOUND INTENSITY TECHNIQUE

In this paper, it is studied that the scattering effect is caused by microphones itself, on both wave magnitude and phase. The experimental method was found difficult to do this. We will apply the Boundary Element Method(BEM) to the problem and explain the results obtained. The numerical method seems to be a powerful tool in this situation.

Rotational character of sound intensity and surface sound intensity

By using the concept of complex sound intensity, the rotational character of the active sound intensity which is the real component of the complex sound intensity is descussed in this paper. It is shown that it is the irrotational component of the active sound intensity that transfers sound energy in sound field. When sound power is measured with the two- microphone technique, the rotation of the active sound intensity has an effect on it. Because the irrotational component of the active sound intensity depends only on the surface sound intensity, measuring the surface sound intensity can avoid the effect of the rotation. Based on atuo- power spectra, formulas about the surface sound intensity are given in this paper, providing a theoretical basis for measuring the surface sound intensity.

Response characteristics of sonar receiver under intense sound pulse

For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interference are analyzed by simulations and experiments. An AGC simulation model based on the voltage control amplifier VCA810 prototype is proposed. Then static and dynamic simulations are realized with single frequency signal and linear frequency modulated （LFM） signal commonly used in the active sonar. Based on intense sound pulse （ISP） interference experiments, the real-time response characteristics of each module of the receiver are studied to verify the correctness of the model as well as the simulation results. Simulation and experiment results show that, under 252 dB/20 μs ISP interference, the specific sonar receiver will produce sustained cut top oscillation above 30 ms, which may affect the receiver and block the regular sonar signal.

Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number

Due to the high speed of underwater vehicles, cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle. The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region. The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented. Based on the sound attenuation coefficients with various vapor volume fractions, the attenuation of sound intensity is calculated under large cavitation number conditions. The result shows that the sound intensity attenuation is fairly small in a certain condition. Consequently, the intensity attenuation can be neglected in engineering.

Noise Control of a Domestic Refrigerator Using a Natural Material Based Composite

This paper studies the acoustics of a frost free three door domestic refrigerator.Then,as a case study,the radiated noise reduction in the refrigerator using a natural material base composite is presented.Composites manufactured out of Jute,which is a plant fiber abundantly and cheaply available in India and Bangladesh are used in the noise reduction in the refrigerator.Mostly in this work,composites made out of felts of jute were used as barriers for noise control of the refrigerator.Measured acoustical,thermal and physical properties of various jute composites are reported.Noise sources in the refrigerator were characterized using sound intensity method and sound pressure level measurements.It is found that the compressor and the evaporator fan are the predominant noise sources.The jute composite treatment done to the refrigerator shell around the evaporator fan reduced the refrigerator noise level by 5 dB and improved its measured sound quality metrics without affecting the cooling performance of the refrigerator.

Space-division multiple access for CDMA multiuser underwater acoustic communications

Time reversal mirror （TRM） can use the physical characteristics of the underwater acoustic （UWA） channel to focus on the desired user in multi-user UWA communication. The active average sound intensity （AASI） detector can estimate all azimuths of users with the same frequency band at the same time in order to achieve directional communication by vector combination. Space-division multiple access （SDMA） based on TRM combined with the AASI detector is proposed in this paper, which can make the capacity of the code division multiple access （CDMA） UWA system significantly increase. The simulation and lake test results show that the 7-user UWA multi-user system can achieve low bit error communication.

Protective effects of the cochlear efferent system on the outer hair cells against intense sound:evidences from DPOAEs

It has been revealed in recent years that contralateral acoustic stimulation can affect cochlear active mechanisms through activating medial olivocochlear system (MOC) of the cochlear efferent nerve fibers. The MOC is therefore postulated to exert protective effects on outer hair cells (OHCs) under intense sound condition. In this study the effects of 4 kHz intense tone exposure on distortion product otoacoustic emissions (DPOAEs) in guinea pigs with and without contralateral white noise stimulation were observed so that to investigate the protective effects of MOC on OHCs. The results showed that DPOAEs obviously deceased after the intense tone exposure in all animals, while both the amplitude reduction and the affected frequency range of DPOAEs were smaller in animals with simultaneously delivered contralateral white noise during the tone exposure than that in animals without colltralateral acoustic stimulation. The above results may suggest some protective nature of the contralateral sound stimulating effects which might be mediated through the activity of MOC. These perhaps can serve as the evidence that the protective mechanism against intense sound operates in the outer hair cells which are strongly innervated by MOC

The effect of noise exposure on sleep quality of urban residents:A comparative study in Shanghai,China

Noise exposure is becoming extremely common in urban area,but its specific impact on sleep remains controversial.Considering the limitations of previous researches,a field study which can conduct both horizontal and longitudinal analysis was designed.Urban participants were tested during two weeks in their homes,and the noise level of bedroom was artificially regulated by changing the status of window and door.During the 1050 test nights in 75 households,noise exposure was reflected from both instrument monitoring at night and perception questionnaire in the morning,and sleep quality was accessed from actigraphy and questionnaire.The analysis results showed that,92.3%of the bedroom acoustic environment did not meet the minimum requirements of Chinese standards,and 87.9%of subjects had ever experienced harmful noise during the test period.Furthermore,sleep quality was affected by noise exposure from the perspective of both physiological and psychological;the duration of rapid eye movement(REM)sleep was significantly(p<0.05)shortened with the increase of sound intensity,the duration of deep sleep shortened and subjective sleep quality worsened significantly(p<0.05)with the increase of acoustic sensation vote.In addition,females were more sensitive to noise exposure and their subjective sleep quality was more likely to be influenced by emotions.This study has important implications for acoustic environment design of bedrooms in cities,and suggested more attention should be paid to the anxiety caused by noise exposure.

Investigation of straightforward impedance eduction method on single-degree-of-freedom acoustic liners

In order to address the current aircraft noise problem, the knowledge of impedance of acoustic liners subjected to high-intensity sound and grazing flow is of crucial importance to the design of high-efficiency acoustic nacelles. To this end, the present study is twofold. Firstly, the StraightForward impedance eduction Method(SFM) is evaluated by the strategy that the impedance of a liner specimen is firstly experimentally educed on a flow duct using the SFM, and then its accuracy is checked by comparing the numerical prediction with the measured wall sound pressure of the flow duct. Secondly, the effects of grazing flow and high-intensity sound on the impedance behavior of two single-layer liners are investigated based on comparisons between educed impedance and predictions by three impedance models. The performance of the SFM is validated by showing that the educed impedance leads to excellent agreement between the simulation and the measured wall sound pressure for different grazing flow Mach numbers and Sound Pressure Levels(SPLs) and over a frequency range from 3000 Hz down to 500 Hz. The grazing flow effect generally has the tendency that the acoustic resistance exhibits a slight decrease before it increases linearly with an increase in Mach,predicted successfully by the sound-vortex interaction theoretical model and the Kooi semi-empirical impedance model. However, the Goodrich semi-empirical impedance model gives only a simple linear relation of acoustic resistance starting from Mach zero. Additionally, when the SPL increases from 110 to 140 d B in the present investigation, the acoustic resistance exhibits a significant increase at all frequencies in the absence of flow; however, the resistance decreases slightly under a grazing flow of Mach 0.117. It indicates that the SPL effect can be greatly inhibited when flow is present,and the grazing flow effect can be reduced partly as well at a relatively high SPL.

GIS model for identifying urban areas vulnerable to noise pollution： case study

The unprecedented expansion of the national car ownership over the last few years has been determined by economic growth and the need for the population and economic agents to reduce travel time in progressively expanding large urban centres. This has led to an increase in the level of road noise and a stronger impact on the quality of the environment. Noise pollution generated by means of transport represents one of the most important types of pollution with negative effects on a population＇s health in large urban areas. As a consequence, tolerable limits of sound intensity for the comfort of inhabitants have been determined worldwide and the generation of sound maps has been made compulsory in order to identify the vulnerable zones and to make recommendations how to decrease the negative impact on humans. In this context, the present study aims at presenting a GIS spatial analysis model-based methodology for identifying and mapping zones vulnerable to noise pollution. The developed GIS model is based on the analysis of all the components influencing sound propagation, represented as vector databases （points of sound intensity measurements, buildings, lands use, transport infrastructure）, raster databases （DEM）, and numerical databases （wind direction and speed, sound intensity）. Secondly, the hourly changes （for representative hours） were analysed to identify the hotspots characterised by major traffic flows specific to rush hours. The validated results of the model are represented by GIS databases and useful maps for the local public administration to use as a source of information and in the process of making decisions.

Theoretical Modeling and Analysis of Vibroacoustic Characteristics of an Acoustic Metamaterial Plate

Locally resonant metamaterial plates with subwavelength bandgaps can be exploited for the simultaneous control of structural vibrations and acoustic radiation.The present work theoretically investigates the vibroacoustic characteristics of a metamaterial plate with periodic lateral local resonance.The high accuracy of the presented method is evident from the consistency of the cross mobility of the metamaterial plate calculated with the finite element technique.The modal superposition approach and Rayleigh integral technique are adopted to formulate the mean square velocity and acoustic radiation power in terms of the structural deflection and sound pressure to capture the vibroacoustic coupling characteristics of the metamaterial plate and the surrounding environment.Large vibration suppression and sound reduction with high radiation efficiency can be observed within the frequency ranges of interest.The near-field sound intensity and far-field acoustic pressure distributions inside and outside the bandgaps are plotted and analyzed.The results from this work can be utilized to set design guidelines for metamaterial design to achieve prescribed vibroacoustic characteristics.