Sound Pressure Amplitude Research Articles

Correlation analysis of oxy-fuel jet in cross-flow on thermoacoustic instability in a model gas turbine combustor

To reveal the correlation between sound pressure and heat release rate of unsteady flames under oxy-fuel jet in cross flow. Correlation analysis of oxy-fuel jet in cross-flow on thermoacoutic instability flames was studied experimentally in a model gas turbine combustor. Four factors were investigated—the flow rate, temperature, injector numbers and injector diameters. Results indicate that thermoacoustic instability can be suppressed if the flow rate, injector numbers and the diameters of the jet in cross-flow increase. The average sound pressure amplitude declines from 23.6 Pa to a value that below 10 Pa. While thermoacoustic instability can be retriggered as the temperature of the jet in cross-flow increase. The correlation coefficient between sound pressure and CH* chemiluminescence under different CO2/O2 or N2/O2 jet in cross flow was presented. Correlation coefficients decline from 0.56 to zero as the flow rate or temperature increase, but it finally increases to a positive value. Correlation coefficients declines from 0.56 to zero as the injector number or diameter increase, but it declines to a negative value eventually. The length of flame fronts and roots was shortened as the flow rate or oxygen ratio increase. The average flame length declines from 110 mm to 70 mm. Three different flame modes were observed: the elongated root dominated, the shortened root dominated and the reattached dominated flames. This article could be instructive to the suppression of thermoacoutic instability in gas turbines.

Developing a device measuring the middle ear reflex in rat ears: A preliminary study

Purpose The middle ear muscle (MEM) reflex is the contraction of the stapedius and tensor tympani muscles in the middle ear cavity in response to loud sound, and relies on a healthy population of auditory nerve fibers. Thus, the MEM reflex can be used as a diagnostic test to quantify auditory nerve survival. This study aims to develop a device to measure the MEM reflex in an animal model, with a long-term goal to develop a biomarker for auditory nerve degeneration. Methods A source device was constructed using a hearing aid speaker attached to a long and thin tube to create high impedance. A probe consists of a microphone placed near the tip of the tube and the sound source. Sound pressure that reflects the MEM reflex was measured in the probe ear of anesthetized rats while an elicitor stimulus was presented in an opposite ear. Results The probe to measure the MEM reflex was verified having a constant volume velocity sensitive to changes in sound pressure. Increases in amplitude of sound pressure were apparent when the stimulation signal was presented in the stimulating ear and the amplitude was decreased to baseline when the signal was turned off. After sacrifice of the animal, the reflex was absent. Conclusions Results showed the feasibility of the probe with high source impedance to measure the MEM reflex in animal ears. Absent reflex after animal sacrifice indicates that the MEM reflex measured using this probe was not an artifact or biological noise. Keywords: Middle ear muscle reflex; Impedance; Rat

Method of Separation of Incidental Acoustic Field on Cylindrical Shell by Vector Processing

A theoretical and experimental study on the separation method of the incident sound field based on a small-scale vector sensor is proposed in this study, with the aim of resolving the problem of separation and acquisition of an incident sound field under the interference of near-field sound scattering from a cylindrical shell in water. The method of identifying and separating sound waves obtained under plane wave conditions is extended to complex sound-field conditions. Simulation and experimental results show that the vector separation method can greatly reduce the sound pressure amplitude and the phase deviation of the incident sound field, which is affected by near-field scattering from the cylindrical surface. The separation accuracy is related to the deviation angle and the distance from the target surface. The maximum deviation of the pressure amplitude is less than 1 dB, and the phase deviation is less than 3°. This method can effectively suppress the near-field scattering of the cylindrical shell and improve the separation accuracy of the incident sound field. The research results have reference value for a range of practical engineering applications.

Dynamic behavior of acoustic cavitation bubble originated from heterogeneous nucleation

Acoustic cavitation bubbles are considered to be generated due to heterogeneous nucleation because a smaller amount of energy is required in this case compared with homogeneous nucleation. A typical example of such nucleation sites is tiny cracks filled with gas, commonly termed as “gas pocket.” Such microcracks can exist in abundance on the surface of reactor walls or sonotrodes used for the cavitation treatment. Eventually, the heterogeneously nucleated cavitation bubble is detached from the solid surface; however, the detachment mechanism has been unclear so far. Therefore, the present study numerically investigated the dynamic behavior of the cavitation bubble originated from the heterogeneous nucleation at wall cracks. During propagation of an ultrasound wave through a liquid, gas pockets in cracks oscillate sinusoidally when the sound pressure amplitude and crack radius are small. In this case, the bubble cannot detach from the surface. On the other hand, as the sound pressure amplitude, crack size, and/or contact angle become larger, the bubble begins to oscillate non-linearly that causes liquid jetting. The liquid jetting can cause the bubble detachment from the surface due to the interaction between the liquid jet and the bottom wall. Stronger liquid jetting makes many small detached bubbles.

Sound Pressure Interference and Phase Velocities in Shallow Water: Calculation and Experiment

A study was carried out on the interference structure of sound pressure amplitudes, longitudinal projections of phase gradients, and calculated phase velocities in a plane-parallel waveguide. It has been established that the phase velocity values of the sound pressure field and the effective phase velocities in the zones of interference maxima calculated by various methods are quite stable and agree well both with each other and the experimental data. It is shown that at the frequencies for which an array is located in zones of interference maxima, using an equivalent plane wave model and effective phase velocities instead of the sound speed in water reduces the bearing estimation error.

Study on the Effect of Mineral Particle Sizes on the Spectral Characteristics of Sound and Vibrations in Rock Drilling

This study aimed to investigate the relationships between particle sizes and spectral characteristics of the sound or vibration signals generated in rock drilling processes. Several drilling experiments were conducted on concrete specimens of different aggregate sizes. By using an indoor signal acquisition and analysis system, data from the sound waves and vibrations were collected, the characteristic signals were extracted, and the spectral characteristics of the sound and vibrations of different aggregate sizes were identified. An approach based on frequency band analysis was adopted. In this approach, the average amplitude of each frequency band was calculated after frequency segmentation. The overall distribution trend in the frequency domain is conveniently observed, and the trend line patterns reflect the effect of aggregate sizes. The time-domain features of sound and vibration, such as the amplitude of sound pressure and vibration, are important indexes that roughly reflect grain sizes. The general trend is that the larger the amplitudes of sound and vibration, the larger the grain size. The frequency domain features of sound and vibration, such as the distribution of energy at high and low frequencies, can also reflect grain sizes. The general trend is that the larger the high-frequency composition of sound and vibration, the smaller the aggregate size. These results are useful for revealing the influence mechanism of rock particle sizes on the vibration spectral characteristics in drilling processes. The study provides a possibility for developing a method to evaluate the information on rock structures collected from drilling vibration or sound signals for the fine exploration of geological surveys.

Evaluation of the sound field in ultrasonic atomization using a horn

Efficiency of ultrasonic atomization can be enhanced by using a horn, where the sound pressure amplitude increases. In the present paper, the effects of a horn on the atomization rate and the sound field have been evaluated by changing the tip diameter of the horn. As a result, by decreasing the horn tip diameter, the maximum sound pressure became higher, but it was revealed that the high sound pressure was limited to the interior of the horn and the very small region near the horn tip because of the diffraction of the sound wave.

Noise sources of an unconfined and a confined swirl burner

The sound sources of an unconfined and a confined swirl burner are investigated by a two-step approach. The Reynolds number based on the injector diameter downstream of the swirler is ReD = 8800 and the swirl number is S = 0.73. First, the conservation equations of a compressible fluid are solved to determine the flow field under reacting and non-reacting conditions. The solution determines the mean flow field and the source terms of the acoustic perturbation equations (APE). The contributions of the various sound sources are analyzed by solving the acoustic perturbation equations (APE) in a computational aeroacoustics (CAA) simulation for each of the source terms. For the unconfined swirl burner, the precessing vortex core (PVC) of the swirl flow is a dominant sound source in non-reacting flow, whereas in reacting flow the unsteady heat release dominates the sound field. This changes when the burner is confined. A self-excited instability occurs at the quarter-wave mode of the burner and further sources, i.e., the momentum source due to fluctuations of the pressure at the flame front and the energy source due to velocity fluctuations at the flame front, become important to accurately predict the sound pressure amplitude of the limit cycle.

Helmholtz Resonator in Laboratory Experiments

The acoustic resonance in four glass Helmholtz resonators with diameters of 70, 52, 40, and 32 mm was detected in the frequency range of 360 to 1700 Hz using the simple experimental setup presented in this paper. The measured amplitudes of acoustic pressure required correction since the sound pressure amplitude of the loudspeaker used was not constant over the whole frequency range. The plots of the corrected acoustic pressure amplitude against frequency (resonance curves) showed expected amplitude enhancement (resonance) around the declared resonance frequencies of the resonators used. Fitting the theoretical dependence for the displacement amplitude of forced oscillations as a function of frequency to the plots of the corrected acoustic pressure amplitude against frequency provided the values of natural frequencies and damping constants of the resonators. The presented setup can be included in laboratory experiments or in a modified version as a demonstration experiment in physics lectures for undergraduate students.

Optimization of Ultrasonic Acoustic Standing Wave Systems

Ultrasonic acoustic standing wave systems find use in many industrial applications, such as sonochemical reactions, atomization of liquids, ultrasonic cleaning, and spray dry. In most applications, highest possible sound pressure levels are needed to achieve optimum results. Until now, the atomization of liquids is limited to fluids with low viscosity, as systems generating sufficient sound pressure for atomizing fluids with higher viscosities are often not marketable due to their low throughput or high costs. For the production of polymer or metal powders or the dispensing of adhesives, highest sound pressures should be achieved with systems in suitable size, with good efficiency and at low cost but without contamination of sonotrodes and reflectors by the dispersed media. An alternative to the use of more powerful transducers is increasing the intensity of the acoustic standing wave field by optimizing the boundary conditions of the acoustic field. In most existing standing wave systems a part of the radiating sound waves does not contribute to the process, as the waves spread into the wrong direction or wipe themselves out due to interference. In order to obtain maximum sound pressure amplitudes in the standing wave field, all waves should be trapped between the sonotrode and the reflector. In addition, the resonance condition should be met for all radiated waves. These conditions can be fulfilled by optimizing the shapes of sonotrode and resonator as well as the distance between them. This contribution reports on a model, which is able to simulate the sound field between a transducer surface and a reflector. Using a linear finite-element model, the boundary conditions of the standing wave system are optimized. Sound pressure levels of the standing wave field are calculated for different shapes of reflectors and boundary conditions like the distance between the transducer and the reflector. The simulation results are validated by sound-field measurements via refracto-vibrometry and a microphone. Finally, optimization guidelines for the generation of high-intensity acoustic standing wave fields are shown and verified by measurements.

Study on the Characterization Method of Ultrasonic Cavitation Field based on the Numerical Simulation of the Amplitude of Sound Pressure

In order to meet the visualization requirements of the cavitation field distribution in the ultrasonic cavitation reactor, a method based on the numerical simulation of the amplitude of sound pressure is proposed. In order to verify that the amplitude of sound pressure plays a decisive role in cavitation effect, the dynamic equation of a single cavitation bubble is established, and the influence law of the amplitude of sound pressure on cavitation motion is analyzed in principle; then, the three-dimensional model of the self-built drum type ultrasonic cavitation reactor is built using the finite element software COMSOL Multiphysics, and the amplitude distribution of the sound pressure at the longitudinal section is obtained when the liquid height was 25 mm, 60 mm and 90 mm. Through the comparison of aluminum foil corrosion experiments, it shows that the numerical simulation method based on the amplitude of sound pressure can accurately characterize the distribution area of ultrasonic cavitation field, which overcomes the disadvantage of time-consuming and labor-consuming in the traditional measurement method of cavitation field distribution, and lays a foundation for the study of the distribution law of ultrasonic cavitation field.

Nonlinear propagation and anomalous absorption of ultrasound in liquid

Recent work has rendered possible the formulation for the nonlinear propagation of pressure waves in liquids by using the generalized Navier - Stokes equations and the modified equations of state, with the heat transfer and fluid viscidity taken into consideration. And the nonlinear approximation solution of the second order term is obtained. The conclusion concerns the acoustic pressure, phase speed, attenuation, and velocity distribution function. When the amplitude of driving acoustic pressure is higher than the cavitation threshold of the host liquid, the cavitation occurs. The cavitation bubbles will prevent the sound field from spreading in the liquid, and the acoustic energy accumulates near the cavitation zone. So when studying the transmission characteristics of acoustic wave in the liquid, the cavitation attenuation must be considered. Note that the particularity of cavitation bubble movement, cavitation bubble vibration and viscous force are simulated under the initial driving sound. Through the analysis, it is found that the transmission of sound is influenced by the viscosity of the fluid, heat transfer, driving sound pressure (amplitude, frequency, duration) and cavitation bubble in liquid. The physical mechanism is that the higher driving pressure causes the cavitation to turn stronger, the acoustic loss to be faster, the sound propagation distance to be smalletr and the vibration of bubbles to transfer energy from the fundamental wave to harmonics. As a result, the stronger absorption from the liquid causes abnormal phenomena, and the output sound is lower finally. It shows that the nonlinear radial motion of cavitation bubble is mainly responsible for the sound intensity attenuation.

Моделирование инфразвукового пистонфона

There are presented the results of numerical simulation of an applied acoustic problem – modeling of gas processes occurring in the measuring chamber of the infrasound pistonphone 3202 at different frequencies of piston oscillation (0.1 – 1000 Hz) and characterized by extremely small Mach numbers (9.1·10-7÷9.1·10-3). The simulation was performed using quasi-gas-dynamic (QGD) and quasi-hydrodynamic (QHD) equations of a viscous compressible heat-conducting gas with the use of a time-explicit difference scheme, all spatial derivatives was approximated by central differences. It is shown that QGD and QHD models can be used for a simulation of applied acoustics and, in particular, to the simulation of infrasonic pistonphone: the stability limits of the QGD and QHD algorithms in this problem were determined, the dependence of sound pressure on the tuning parameter α is investigated and it is shown that this dependence is quite small. The spectra of sound pressure at the control point calculated by QGD and QHD are given, their dependence on the tuning parameter α is shown, both models equally predict the value of the sound pressure amplitude at the fundamental frequency oscillations. At the end of the article, the sound pressure at the control point at the fundamental frequency oscillations obtained by using QGD and QHD is compared with the values calculated by using semi-empirical formula of sound pressure at closed volume for a case of small oscillations using the polytropic index obtained by Henry Gerber instead of the adiabatic coefficient.

Finite element numerical simulation analysis based on ultrasonic phased array

In this paper, the ultrasonic phased array technology is used to detect the defects in the welded seam test specimens. Using pulse echo method to detect a specimen with defects and establishing the corresponding numerical model. At the same time, the finite element is used to simulate the propagation of ultrasonic waves in the defective test specimens, and figures of the sound pressure amplitude are obtained. Compared with the theoretical values, the experimental values and the simulated values show good agreement, and the errors are only - 1.37% and 4.11%, respectively. The results show that the ultrasonic phased array with finite element simulation is effective.

Reception characteristics investigation and measurement of capacitive micromachined ultrasonic transducer

Purpose As a new type of ultrasonic transducer with significant advantages, capacitive micromachined ultrasonic transducer (CMUT) has good application prospect. The reception characteristic of the CMUT is one of the important factors determining the application effect. This paper aims to study the reception characteristics of CMUT. Design/methodology/approach In this paper, the state equation is deduced and the analysis model is established in SIMULINK environment based on the lumped parameter system model of the CMUT cell. Based on this analysis model, the influencing factors of CMUT reception characteristics are studied and investigated, and the time-domain and frequency-domain characteristics are investigated in detail. Findings The analysis results show that parameters directly affect the reception characteristics of the CMUT, such as direct current (DC) bias voltage, input sound pressure amplitude and frequency. At the same time, the measurement system is built and the reception characteristics are verified. Originality/value This paper provides an effective method for rapid analyzing the reception characteristics of CMUT. These results provide an important theoretical basis and reference for further optimization of CMUT structure design, and lay a good foundation for the practical application measurement.

The Peculiarities of Sound Propagation in Shallow Fresh Water for Different Depths of Sound Source

The experimental results of measurement of the scalar and vector characteristics of an acoustic field in shallow water with a carbon bottom are analyzed. Simultaneous recording of the sound pressure and three orthogonal components of particle velocity was carried out using a sound pressure receiver and a vector receiver. A towed transducer was the source of the tone signal; the noise signal from a passing ship was a source located near the water—air boundary. In the spatial decay of the sound field components, significant variations in the levels of sound pressure and particle velocity components were observed, regardless of the depth of the sound source. When the sound source was located in the depth of the water layer, the dependence of the spatial decrease in the acoustic field components is diverse, while when the noise signal source was located below the water—air interface, the decay character of the sound pressure amplitudes and of the vertical component of the particle velocity were the same throughout the measurement path.

Numerical Simulation of Acoustic Wave Generated by the AC Arc

For the calculation of near-field acoustic waves generated by a relatively long arc, the spatial distribution of arc power density should be taken into account. An electrosound combined simulation of the ac arc was conducted. First, the arc was numerically simulated based on the 2-D MHD model. It was found that the spatial distribution of electric power density in the arc was highly nonuniform with significantly higher power density in the region close to the electrodes. Then, the acoustic wave generated by the arc was numerically simulated with the sound sources, taking the obtained distribution of arc power density into account. It was found that dP/dt , the derivative of arc power, was an important parameter that determined the sound pressure. The waveform of sound pressure was exactly of the same shape as that of dP/dt and the amplitude of sound pressure was proportional to that of dP/dt . The acoustic wave obtained by the simulation agreed well with the experimentally measured one. The dependence of the wave pressure on the propagating distance was compared to that of the spherical wave based on a monopole sound source, which confirmed the necessity of the electrosound combined simulation.

A Wear Detection Parameter for the Wheel–Rail Contact Based on Emitted Noise

This article describes how a wheel–rail wear detection parameter based on noise was developed by running a rapid transit train instrumented with microphones in a depot with a small curve radius. This full-scale test made use of previous knowledge gained from lab-scale tests. The lab- and full-scale tests showed that noise could be used as an indicator of wear transition, when normal wear turns into severe or catastrophic wear. This transition was accompanied by a significant increase in sound pressure and a broader sound pressure amplitude spectrum; that is, a narrow initial amplitude distribution in the normal wear regime and a broader distribution in the severe wear regime. The measured noise from the inner/low and outer/high rails was analyzed in conjunction with the wear from the outer wheel and comparisons were made between cleaned (exposed to severe wear) and lubricated (no wear) rail. Based on those analyses, a wear detection parameter criterion was developed for this specific train. This wear parameter has been implemented in a real-time condition monitoring system so that warnings of the risk for severe wear could be sent to the maintenance department. Validation of the wear parameter and challenges linked to open system conditions are discussed in this article.

Influence of visibility of wind farms on noise annoyance – A laboratory experiment with audio-visual simulations

Noise annoyance reactions in the population due to wind farms are related to visual as well as noise-related impacts of the farms. Improved understanding of these effects may support the planning of better accepted wind farms. Recently, tools for visualization and auralization of wind farms have been developed that allow mutually studying audio-visual effects on annoyance. The objective of this study was to investigate the audio-visual effects of different wind turbine noise situations on short-term noise annoyance in a psychophysical laboratory experiment, considering serial position effects (simple order and differential carryover effects). A set of 24 audio-visual situations covering a range of acoustical characteristics (sound pressure level, periodic amplitude modulation) and visual settings (landscape with visible wind turbine, landscape only, grey background) was created. The factorial design of the experiment allowed separating audio-visual effects from serial position effects on noise annoyance. Both visual and acoustical characteristics were found to affect noise annoyance, besides the participants’ attitude towards wind farms. Sound pressure level and amplitude modulation increased annoyance, the presence of a visualized landscape decreased annoyance, and the visibility of a wind turbine increased annoyance. While simple order effects could be eliminated by counterbalancing, the initial visual setting strongly affected the annoyance ratings of the subsequent settings. Due to this differential carryover effect, visual effects could be assessed reliably only as long as the participants saw the initial visual setting. Therefore, the presentation order of audio-visual stimuli should be carefully considered in experimental studies and in participatory landscape planning.

MECHANISMS OF GENERATION AND SOURCES OF NOISE IN SUPERSONIC JETS

Interest in the development of models and methods focused on the mechanisms of noise generation in jet flows is due to strict noise requirements produced by various industrial devices, as well as the possibilities of using sound in engineering and technological processes. The tools of physical and computational modeling of gas dynamics and aero-acoustics problems are considered, and noise sources and mechanisms of noise generation in supersonic jet flows are discussed. The physical pattern of the flow in free supersonic under-expanded jets is discussed on the basis of experimental and numerical data, as well as the flow structure arising from the interaction of a supersonic under-expanded jet with a cylindrical cavity. The influence of the nozzle pressure ratio and cavity depth on the sound pressure level, amplitude and frequency characteristics of the flow parameters is studied.