scholarly journals Prediction of Acoustic Energy Radiated by Bubble Produced by Raindrops

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Qi Li ◽  
Shu Liu ◽  
Dajing Shang
Keyword(s):  
Ambient Noise ◽  
Sound Pressure ◽  
Noise Source ◽  
Tap Water ◽  
Acoustic Energy ◽  
Underwater Noise ◽  
Theoretical Derivation ◽  
Dipole Radiation ◽  
Sinusoidal Oscillator ◽  
Series Of Experiments

Underwater noise produced by rainfall is an important part of underwater ambient noise. The bubbles produced by raindrops are the main noise source of underwater noise. Generally, the sound pressure signal of individual bubbles is easily contaminated by tank reverberation, hydrodynamic flow, and laboratory electrical noise. In order to solve this problem, this study proposes a method for calculating the acoustic energy of the bubble produced by a raindrop when the latter falls onto a plane water surface. For this purpose, a series of experiments was conducted in a 15 m × 9 m × 6 m reverberation tank filled with tap water. The bubble produced by a raindrop behaves as a simple exponentially damped sinusoidal oscillator. Based on the dipole radiation pattern, a formula was derived to predict the sound energy of these bubbles. The damping coefficient of the bubble formed by raindrops is found to differ appreciably from the empirical value of the bubble formed by other mechanisms. The resonance frequency of the bubbles is found to decrease with time. It is due to the rapid increase in the distance between the bubble and the interface. Then, the formula is optimized by using these two improved variables. The experimental results agree well with the theoretical derivation.

scholarly journals Measurement of Underwater Acoustic Energy Radiated by Single Raindrops

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2687
Author(s):  
Shu Liu ◽  
Qi Li ◽  
Dajing Shang ◽  
Rui Tang ◽  
Qingming Zhang
Keyword(s):  
Ambient Noise ◽  
Sound Pressure ◽  
Tap Water ◽  
Acoustic Energy ◽  
Underwater Sound ◽  
Underwater Noise ◽  
Energy Characteristics ◽  
Sound Energy ◽  
Dipole Radiation ◽  
Series Of Experiments

Underwater noise produced by rainfall is an important component of underwater ambient noise. For example, the existence of rainfall noise causes strong disturbances to sonar performance. The underwater noise produced by a single raindrop is the basis of rainfall noise. Therefore, it is necessary to study the associated underwater noise when drops strike the water surface. Previous research focused primarily on the sound pressure and frequency spectrum of underwater noise from single raindrops, but the study on its sound energy is insufficient. The purpose of this paper is to propose a method for predicting the acoustic energy generated by raindrops of any diameter. Here, a formula was derived to calculate the underwater sound energy radiated by single raindrops based on a dipole radiation pattern. A series of experiments were conducted to measure the underwater sound energy in a 15 m × 9 m × 6 m reverberation tank filled with tap water. The analysis of the acoustic energy characteristics and conversion efficiency from kinetic to acoustic energy helped develop the model to predict the average underwater sound energy radiated by single raindrops. Using this model, the total underwater sound energy of all raindrops during a rainfall event can be predicted based on the drop size distribution.

Retrieval of amplitude and attenuation from ambient seismic noise: synthetic data and practical considerations

2020 ◽  
Vol 222 (1) ◽  
pp. 544-559
Author(s):  
Lianqing Zhou ◽  
Xiaodong Song ◽  
Richard L Weaver
Keyword(s):  
Numerical Simulation ◽  
Seismic Data ◽  
Seismic Noise ◽  
Ambient Noise ◽  
Linear Array ◽  
Noise Source ◽  
Synthetic Data ◽  
Real Data ◽  
Noise Correlation ◽  
Theoretical Derivation

SUMMARY Ambient noise correlation has been used extensively to retrieve traveltimes of surface waves. However, studies of retrieving amplitude information and attenuation from ambient noise are limited. In this study, we develop methods and strategies to extract Rayleigh wave amplitude and attenuation from ambient noise correlation, based on theoretical derivation, numerical simulation, and practical considerations of real seismic data. The synthetic data included a numerical simulation of a highly anisotropic noise source and Earth-like temporally varying strength. Results from synthetic data validate that amplitudes and attenuations can indeed be extracted from noise correlations for a linear array. A temporal flattening procedure is effective in speeding up convergence while preserving relative amplitudes. The traditional one-bit normalization and other types of temporal normalization that are applied to each individual station separately are problematic in recovering attenuation and should be avoided. In this study, we propose an ‘asynchronous’ temporal flattening procedure for real data that does not require all stations to have data at the same time. Furthermore, we present the detailed procedure for amplitude retrieval from ambient noise. Tests on real data suggest attenuations extracted from our noise-based methods are comparable with those from earthquakes. Our study shows an exciting promise of retrieving amplitude and attenuation information from ambient noise correlations and suggests practical considerations for applications to real data.

scholarly journals A System for Acoustic Field Measurement Employing Cartesian Robot

2016 ◽  
Vol 23 (3) ◽  
pp. 333-343 ◽  
Author(s):  
Maciej Szczodrak ◽  
Adam Kurowski ◽  
Józef Kotus ◽  
Andrzej Czyżewski ◽  
Bożena Kostek
Keyword(s):  
Acoustic Field ◽  
Energy Flow ◽  
Velocity Vector ◽  
Sound Pressure ◽  
Sound Field ◽  
Acoustic Energy ◽  
The Other ◽  
Object Shape ◽  
Movement Path ◽  
Optimum Path

AbstractA system setup for measurements of acoustic field, together with the results of 3D visualisations of acoustic energy flow are presented in the paper. Spatial sampling of the field is performed by a Cartesian robot. Automatization of the measurement process is achieved with the use of a specialized control system. The method is based on measuring the sound pressure (scalar) and particle velocity(vector) quantities. The aim of the system is to collect data with a high precision and repeatability. The system is employed for measurements of acoustic energy flow in the proximity of an artificial head in an anechoic chamber. In the measurement setup an algorithm for generation of the probe movement path is included. The algorithm finds the optimum path of the robot movement, taking into account a given 3D object shape present in the measurement space. The results are presented for two cases, first without any obstacle and the other - with an artificial head in the sound field.

Noise Reduction of Blade-Passing Frequency Components in a Centrifugal Blower

2004 ◽  
Author(s):  
Yutaka Ohta ◽  
Eisuke Outa
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Noise Source ◽  
Higher Order ◽  
Pressure Level ◽  
Source Distribution ◽  
Centrifugal Blower ◽  
Blade Passing Frequency ◽  
Active Cancellation ◽  
Frequency Components

A hybrid-type noise control method is applied to fundamental and higher-order blade-passing frequency components, abbreviated to BPF components, radiated from a centrifugal blower. An active cancellation of the BPF noise source is conducted based on a detailed investigation of the noise source distribution by using correlation analysis. The sound pressure level of 2nd- and/or 3rd-order BPF can be reduced by more than 15 decibels and discrete tones almost eliminate from the power spectra of blower-radiated noise. On the other hand, the sound pressure level of the fundamental BPF is difficult to reduce effectively by the active cancellation method because of the large amplitude of the noise source fluctuation. However, the fundamental BPF is largely influenced by the frequency-response characteristics of the noise transmission passage, and is passively reduced by appropriate adjusting of the inlet duct length. Simultaneous reduction of BPF noise, therefore, can be easily made possible by applying passive and active control methods on the fundamental and higher-order BPF noise, respectively. We also discuss the distribution pattern of BPF noise sources by numerical simulation of flow fields around the scroll cutoff.

A Method for Noise Source Levels Inversion with Underwater Ambient Noise Generated by Typhoon in Deep Ocean

2018 ◽  
Vol 26 (02) ◽  
pp. 1850007 ◽  
Author(s):  
Qiulong Yang ◽  
Kunde Yang ◽  
Shunli Duan
Keyword(s):  
Ambient Noise ◽  
Noise Source ◽  
Surface Wind ◽  
Deep Ocean ◽  
Noise Sources ◽  
Noise Field ◽  
Sea Surface Wind ◽  
Source Level ◽  
The Western Pacific ◽  
Good Agreement

Sea-surface wind agitation can be considered the dominant noise sources whose intensity relies on local wind speed during typhoon period. Noise source levels in previous researches may be unappreciated for all oceanic regions and should be corrected for modeling typhoon-generated ambient noise fields in deep ocean. This work describes the inversion of wind-driven noise source level based on a noise field model and experimental measurements, and the verification of the inverted noise source levels with experimental results during typhoon period. A method based on ray approach is presented for modeling underwater ambient noise fields generated by typhoons in deep ocean. Besides, acoustic field reciprocity is utilized to decrease the calculation amount in modeling ambient noise field. What is more, the depth dependence and the vertical directionality of noise field based on the modeling method and the Holland typhoon model are evaluated and analyzed in deep ocean. Furthermore, typhoons named “Soulik” in 2013 and “Nida” in 2016 passed by the receivers deployed in the western Pacific (WP) and the South China Sea (SCS). Variations in sound speed profile, bathymetry, and the related oceanic meteorological parameters are analyzed and taken into consideration for modeling noise field. Boundary constraint simulated annealing (SA) method is utilized to invert the three parameters of noise source levels and to minimize the objective function value. The prediction results with the inverted noise source levels exhibit good agreement with the measured experiment data and are compared with predicted results with other noise sources levels derived in previous researches.

Investigation of chlorine wall decay in an old, decommissioned metallic pipe using a pipe section reactor

2020 ◽  
Vol 20 (3) ◽  
pp. 953-962
Author(s):  
R. Tonev ◽  
G. Dimova
Keyword(s):  
Reaction Rate ◽  
Rate Coefficient ◽  
Tap Water ◽  
Decay Rates ◽  
Free Chlorine ◽  
Reaction Rate Coefficient ◽  
Pipe Section ◽  
Reaction Coefficient ◽  
Bulk Reaction ◽  
Series Of Experiments

Abstract The study investigates the kinetics of free chlorine depletion in tap water from the Sofia distribution network. The overall decay rates, the bulk reaction rate coefficient, the wall reaction rate coefficient and the influence of mass transfer have been determined in a laboratory pipe section reactor (PSR), testing an old decommissioned metallic pipe. In total, 23 series of experiments were performed under different initial free chlorine concentrations and different hydraulic conditions. The applicability of different chlorine decay mathematical models has been investigated. A new model was proposed, combining zero order bulk reactions and first order wall reactions, describing the laboratory results with Nash-Sutcliffe efficiency coefficients over 0.99. The obtained values for the wall reaction coefficient vary in the range 0.008–0.030 m/h, decreasing exponentially with increasing initial chlorine concentration.

Detection of Non-Metallic Cords Using Synthetic Aperture Acoustic Imaging

2012 ◽  
Author(s):  
John A. Judge ◽  
Joseph F. Vignola ◽  
Aldo A. J. Glean ◽  
Teresa J. Ryan ◽  
Chelsea E. Good ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Ground Surface ◽  
Acoustic Imaging ◽  
Acoustic Energy ◽  
Synthetic Aperture ◽  
Two Dimensional ◽  
Two Dimensional Image ◽  
Imaging Approach ◽  
Different Diameters ◽  
Made In

Synthetic aperture acoustic (SAA) imaging is a technique for remotely obtaining information about the location, geometry, and mechanical properties of objects based on the way they scatter incident acoustic energy. Results are presented for an experimental investigation of the use of SAA imaging to detect non-metallic cords of different sizes laid in various configurations on the ground surface in an outdoor urban environment. Interest in this application of SAA stems from the fact that non-metallic cords are not readily detectable with synthetic aperture radar (SAR) and that the SAA imaging approach represents a relatively inexpensive alternative or supplement to SAR. The measurement system is comprised of a mobile acoustic transceiver (a speaker and microphone) that broadcasts a burst chirp with a bandwidth of 2–15 kHz. The recorded signal is used to form a two-dimensional image of the distribution of acoustic scatterers within the scene. For this study, five different diameters (2–15mm) of nylon cord laid on the ground were imaged in different configurations. These measurements were made in the presence of urban ambient noise of varying levels. The goal of this study was to identify the effect of environmental noise and other parameters on detectability. The results demonstrate that non-metallic cords can be detected acoustically if the angle to the transceiver path is sufficiently small.

An analysis of low‐frequency wind‐generated ambient noise source levels in the ocean

1988 ◽  
Vol 83 (S1) ◽  
pp. S87-S87
Author(s):  
W. M. Carey ◽  
D. J. Kewley ◽  
D. G. Browning ◽  
W. A. Von Winkle
Keyword(s):  
Ambient Noise ◽  
Noise Source ◽  
Low Frequency
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