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Keywords = free-field acoustic characteristics

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28 pages, 15257 KiB  
Article
Influence of Free Surface on the Hydrodynamic and Acoustic Characteristics of a Highly Skewed Propeller
by Duo Yu, Youbin Yu and Suoxian Yang
J. Mar. Sci. Eng. 2024, 12(12), 2208; https://doi.org/10.3390/jmse12122208 - 2 Dec 2024
Viewed by 893
Abstract
The noise analysis of a large-scale aquaculture vessel reveals that during its navigation, the primary equipment noise, particularly from the propeller, exerts a notable influence on the aquaculture environment for large yellow croaker. The free surface greatly impacts the noise performance of propellers, [...] Read more.
The noise analysis of a large-scale aquaculture vessel reveals that during its navigation, the primary equipment noise, particularly from the propeller, exerts a notable influence on the aquaculture environment for large yellow croaker. The free surface greatly impacts the noise performance of propellers, which is a significant factor affecting the fish’s habitat. This study adopts the numerical simulation method to analyze the hydrodynamic and acoustic characteristics of the E1619 propeller operating near the free surface. The open-water performance and noise calculations of the propeller are verified through experiments, and the effects of different immersion depths and advance coefficients on the propeller are explored. The results demonstrate that the free surface significantly affects the thrust, torque, and noise of the propeller, especially at shallow immersion depths and low advance coefficients. Surface wave pattern causes the instability and breakup of tip vortices, causing increased thrust and torque fluctuations, reduced efficiency, and significant overall sound pressure levels in the entire flow field. As immersion depth and advance coefficients increase, the interaction between tip vortices and the free surface weakens, wake vortex instability decreases, and noise levels gradually reduce. These analyses and conclusions can guide the design of next-generation propellers for aquaculture vessels to optimize performance near the free surface. Full article
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19 pages, 7020 KiB  
Article
Facade Design and the Outdoor Acoustic Environment: A Case Study at Batna 1 University
by Sami Hamouta, Noureddine Zemmouri and Atef Ahriz
Buildings 2024, 14(11), 3339; https://doi.org/10.3390/buildings14113339 - 22 Oct 2024
Viewed by 1489
Abstract
The relationship between architectural design and outdoor acoustic environments remains underexplored, particularly in educational spaces where noise levels impact comfort and usability. This study investigates the impact of building facade height on the outdoor acoustic environment in university courtyards. Acoustic measurements were conducted [...] Read more.
The relationship between architectural design and outdoor acoustic environments remains underexplored, particularly in educational spaces where noise levels impact comfort and usability. This study investigates the impact of building facade height on the outdoor acoustic environment in university courtyards. Acoustic measurements were conducted in two courtyards at Batna 1 University, each surrounded by buildings with distinct facade heights. Key acoustic parameters, including reverberation time (RT), early decay time (EDT), rapid speech transmission index (RaSTI), Definition (D50), and sound pressure level (SPL) attenuation were evaluated at specified source-receiver distances. The results reveal a strong correlation between RT20 and distance at higher frequencies due to building facade reflections, while lower frequencies are more influenced by geometric configuration and material absorption properties. The results demonstrate that RT and EDT increase logarithmically or polynomially with distance, especially at higher frequencies (2000–4000 Hz), due to the decrease in direct sound energy and increase in reflected sound amplitude. Taller building facades lead to longer RT and EDT values compared to lower heights. D50 and RaSTI decrease polynomially with increasing source–receiver distance, with lower values observed in the courtyard with taller facades, indicating reduced speech clarity. The SPL attenuation is influenced by surrounding geometry, with the least reduction in the courtyard with lower facade heights, followed by the taller facade courtyard, contrasting with semi-free field conditions. These findings highlight the significant role of building facade height and architectural elements in shaping the acoustic characteristics of outdoor spaces, providing valuable insights for designing acoustically comfortable urban environments, particularly in educational settings. Full article
(This article belongs to the Section Building Energy, Physics, Environment, and Systems)
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15 pages, 3651 KiB  
Article
Experimental Analysis of Noise Characteristics on Different Types of Pavements inside and outside Highway Tunnels
by Wanyan Ren, Yi Zhang, Minmin Yuan and Jun Li
Coatings 2024, 14(9), 1213; https://doi.org/10.3390/coatings14091213 - 20 Sep 2024
Viewed by 1103
Abstract
Aiming to reduce noise pollution and optimize the acoustic quality in highway tunnels, the noise characteristics on different types of pavements were analyzed and compared in this research, based on the on-site noise measurement in two tunnels with the free fields as a [...] Read more.
Aiming to reduce noise pollution and optimize the acoustic quality in highway tunnels, the noise characteristics on different types of pavements were analyzed and compared in this research, based on the on-site noise measurement in two tunnels with the free fields as a control group. Specifically, the noise characteristics include two aspects: various noise and noise time attenuation performance. Various noise includes on-board sound intensity (OBSI) noise and cabin noise. The noise time attenuation performance uses the indicator of reverberation time. Three types of pavements were measured, including dense-graded asphalt concrete (DAC) and single-layered and double-layered porous asphalt (PA) pavement. The results showed that, for the same type of pavement, compared with the free fields, the difference in OBSI noise in tunnels was within a range of less than 1 dBA; the cabin noise increased by 3.4 dBA~6.6 dBA. The noise level in tunnels was greater than that outside tunnels, and the longer tunnel exhibited higher traffic noise and worse noise time attenuation performances. For the same tunnel, PA pavement could reduce the cabin noise by 3.8 dBA~6.7 dBA. PA pavement also exhibited shorter reverberation time. The application of PA pavement could effectively improve the acoustic quality in the tunnel. This research contributes to noise pollution abatement and the improvement of the comfort and safety of drivers in tunnels. Full article
(This article belongs to the Special Issue Novel Cleaner Materials for Pavements)
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21 pages, 7379 KiB  
Article
Noise Prediction Study of Traction Arc Tooth Cylindrical Gears for New Generation High-Speed Electric Multiple Units
by Zhaoping Tang, Zhenyan Chen, Jianping Sun, Menghui Lu and Hui Liu
Lubricants 2023, 11(9), 357; https://doi.org/10.3390/lubricants11090357 - 23 Aug 2023
Cited by 4 | Viewed by 1859
Abstract
As the speed of the new generation of high-speed electric multiple units (EMU) increases, the requirements for vibration and noise reduction in traction gear trains are becoming higher and higher. Although most researchers have focused on the vibration mechanics analysis of gears, the [...] Read more.
As the speed of the new generation of high-speed electric multiple units (EMU) increases, the requirements for vibration and noise reduction in traction gear trains are becoming higher and higher. Although most researchers have focused on the vibration mechanics analysis of gears, the actual noise has the most direct impact on passenger experience and safety. To address this problem, a new type of curved cylindrical gear is proposed to analyze the dynamic characteristics of the gear pair and predict its radiated noise based on the acoustic-vibration coupling theory using the finite element-boundary element method. Parametric modeling of the gear pair using CREO and assembly motion analysis were performed. ANSYS was used to analyze the stress distribution, inherent frequency, and inherent vibration pattern of the gear pair, and harmonic response analysis was performed using the modal superposition method to solve the displacement frequency response curve and vibration characteristics. ACTRAN was used to construct the free-field model, create acoustic excitation based on the acoustic-vibration coupling equation, set the field points, and predict radiated noise. The research results show that the noise is mainly concentrated in the tooth meshing area, and the root mean square RMS range of its sound pressure level value is 91–100 dB. Its dynamic characteristics and noise values are in line with the traction requirements of high-speed EMU, providing a new idea for improving the noise prediction of traction gears for new generation high-speed EMU, which in turn strongly support the noise control of high-speed EMU stock and thus improve the passenger experience and driving environment. Full article
(This article belongs to the Special Issue Advances in Gear Tribology)
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17 pages, 12047 KiB  
Article
Mixing Characteristics and Parameter Effects on the Mixing Efficiency of High-Viscosity Solid–Liquid Mixtures under High-Intensity Acoustic Vibration
by Xiaobin Zhan, Lei Yu, Yalong Jiang, Qiankun Jiang and Tielin Shi
Processes 2023, 11(8), 2367; https://doi.org/10.3390/pr11082367 - 6 Aug 2023
Cited by 3 | Viewed by 2898
Abstract
High-intensity acoustic vibration is a new technology for solving the problem of uniform dispersion of highly viscous materials. In this study, we investigate the mixing characteristics of high-viscosity solid–liquid phases under high-intensity acoustic vibration and explore the effect of vibration parameters on the [...] Read more.
High-intensity acoustic vibration is a new technology for solving the problem of uniform dispersion of highly viscous materials. In this study, we investigate the mixing characteristics of high-viscosity solid–liquid phases under high-intensity acoustic vibration and explore the effect of vibration parameters on the mixing efficiency. A numerical simulation model of solid–liquid–gas multiphase flow, employing the volume of fluid (VOF) and discrete phase model (DPM), was developed and subsequently validated through experimental verification. The results show that the movement and deformation of the gas–liquid surface over the entire field are critical for achieving rapid and uniform mixing of the solid–liquid phases under acoustic vibration. Increasing the amplitude or frequency of vibration can intensify the movement and deformation of the free surface of gas and liquid, improve the mixing efficiency, and shorten the mixing time. Under the condition of constant acceleration, the mixing efficiency of materials is higher at low frequency and high amplitude. Further, we define a relationship that predicts desirable mixing conditions as a function of amplitude and frequency. This serves as a valuable reference guide for evaluating the minimum requirements when selecting operating parameters. Full article
(This article belongs to the Special Issue Numerical Calculation and Experimental Measurement in Multiphase Flow)
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14 pages, 2834 KiB  
Article
Modeling the Impact of Phonon Scattering with Strain Effects on the Electrical Properties of MoS2 Field-Effect Transistors
by Huei Chaeng Chin, Afiq Hamzah, Nurul Ezaila Alias and Michael Loong Peng Tan
Micromachines 2023, 14(6), 1235; https://doi.org/10.3390/mi14061235 - 12 Jun 2023
Cited by 2 | Viewed by 2020
Abstract
Molybdenum disulfide (MoS2) has distinctive electronic and mechanical properties which make it a highly prospective material for use as a channel in upcoming nanoelectronic devices. An analytical modeling framework was used to investigate the I–V characteristics of field-effect transistors based on [...] Read more.
Molybdenum disulfide (MoS2) has distinctive electronic and mechanical properties which make it a highly prospective material for use as a channel in upcoming nanoelectronic devices. An analytical modeling framework was used to investigate the I–V characteristics of field-effect transistors based on MoS2. The study begins by developing a ballistic current equation using a circuit model with two contacts. The transmission probability, which considers both the acoustic and optical mean free path, is then derived. Next, the effect of phonon scattering on the device was examined by including transmission probabilities into the ballistic current equation. According to the findings, the presence of phonon scattering caused a decrease of 43.7% in the ballistic current of the device at room temperature when L = 10 nm. The influence of phonon scattering became more prominent as the temperature increased. In addition, this study also considers the impact of strain on the device. It is reported that applying compressive strain could increase the phonon scattering current by 13.3% at L = 10 nm at room temperature, as evaluated in terms of the electrons’ effective masses. However, the phonon scattering current decreased by 13.3% under the same condition due to the existence of tensile strain. Moreover, incorporating a high-k dielectric to mitigate the impact of scattering resulted in an even greater improvement in device performance. Specifically, at L = 6 nm, the ballistic current was surpassed by 58.4%. Furthermore, the study achieved SS = 68.2 mV/dec using Al2O3 and an on–off ratio of 7.75 × 104 using HfO2. Finally, the analytical results were validated with previous works, showing comparable agreement with the existing literature. Full article
(This article belongs to the Special Issue Recent Advances in Molecular/Nano Electronics)
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13 pages, 7447 KiB  
Article
Application of Vortex Identification Methods in Vertical Slit Fishways
by Chunying Shen, Ruiguo Yang, Mingming Wang, Shihua He and Shan Qing
Water 2023, 15(11), 2053; https://doi.org/10.3390/w15112053 - 29 May 2023
Cited by 5 | Viewed by 2104
Abstract
The reproduction and survival of fish are often negatively affected by the construction of dams and other hydroelectric projects, which cut off their migratory routes. Building effective fish passage facilities that allow fish to pass through dams smoothly alleviates the negative impact of [...] Read more.
The reproduction and survival of fish are often negatively affected by the construction of dams and other hydroelectric projects, which cut off their migratory routes. Building effective fish passage facilities that allow fish to pass through dams smoothly alleviates the negative impact of hydroelectric projects on the ecological environment, thus protecting the diversity of aquatic species and preventing the extinction of indigenous fish. Vertical slit fishways are highly effective, but turbulence inside the fishway pools directly affects fish passage. In this study, the large-eddy simulation framework is used to capture the vortex characteristics in the interior of vertical slit fishway pools, and the volume of fluid method is applied to simulate the free surface. The independence of the grid is assessed by the large-eddy simulation quality index, and the simulation results are compared with experimental acoustic Doppler velocimetry data. This work characterizes the vortex flow field inside the vertical slit fishway using the Q-criterion, Omega method, and Liutex vortex identification method. The results show that the vortex structure inside the fishway pool has obvious three-dimensional characteristics and vortex structure varies within the different fishway pool chambers. The analysis and comparison of the three different vortex identification methods show that the vortex structure captured by the Liutex method is more consistent with the actual motion pattern of the fishway water flow. Full article
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26 pages, 11088 KiB  
Article
Thermoacoustic Combustion Stability Analysis of a Bluff Body-Stabilized Burner Fueled by Methane–Air and Hydrogen–Air Mixtures
by Vito Ceglie, Michele Stefanizzi, Tommaso Capurso, Francesco Fornarelli and Sergio M. Camporeale
Energies 2023, 16(7), 3272; https://doi.org/10.3390/en16073272 - 6 Apr 2023
Cited by 3 | Viewed by 3104
Abstract
Hydrogen can play a key role in the gradual transition towards a full decarbonization of the combustion sector, e.g., in power generation. Despite the advantages related to the use of this carbon-free fuel, there are still several challenging technical issues that must be [...] Read more.
Hydrogen can play a key role in the gradual transition towards a full decarbonization of the combustion sector, e.g., in power generation. Despite the advantages related to the use of this carbon-free fuel, there are still several challenging technical issues that must be addressed such as the thermoacoustic instability triggered by hydrogen. Given that burners are usually designed to work with methane or other fossil fuels, it is important to investigate their thermoacoustic behavior when fueled by hydrogen. In this framework, the present work aims to propose a methodology which combines Computational Fluid Dynamics CFD (3D Reynolds-Averaged Navier-Stokes (RANS)) and Finite Element Method (FEM) approaches in order to investigate the fluid dynamic and the thermoacoustic behavior introduced by hydrogen in a burner (a lab-scale bluff body stabilized burner) designed to work with methane. The case of CH4-air mixture was used for the validation against experimental results and benchmark CFD data available in the literature. Numerical results obtained from CFD simulations, namely thermofluidodynamic properties and flame characteristics (i.e., time delay and heat release rate) are used to evaluate the effects of the fuel change on the Flame Response Function to the acoustic perturbation by means of a FEM approach. As results, in the H2-air mixture case, the time delay decreases and heat release rate increases with respect to the CH4-air mixture. A study on the Rayleigh index was carried out in order to analyze the influence of H2-air mixture on thermoacoustic instability of the burner. Finally, an analysis of both frequency and growth rate (GR) on the first four modes was carried out by comparing the two mixtures. In the H2-air case the modes are prone to become more unstable with respect to the same modes of the case fueled by CH4-air, due to the change in flame topology and variation of the heat release rate and time delay fields. Full article
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9 pages, 2409 KiB  
Article
Dynamical Structures of Multi-Solitons and Interaction of Solitons to the Higher-Order KdV-5 Equation
by Fahad Sameer Alshammari, Zillur Rahman, Harun-Or Roshid, Mohammad Safi Ullah, Abdullah Aldurayhim and M. Zulfikar Ali
Symmetry 2023, 15(3), 626; https://doi.org/10.3390/sym15030626 - 2 Mar 2023
Cited by 8 | Viewed by 1846
Abstract
In this study, we build multi-wave solutions of the KdV-5 model through Hirota’s bilinear method. Taking complex conjugate values of the free parameters, various colliding exact solutions in the form of rogue wave, symmetric bell soliton and rogue waves form; breather waves, the [...] Read more.
In this study, we build multi-wave solutions of the KdV-5 model through Hirota’s bilinear method. Taking complex conjugate values of the free parameters, various colliding exact solutions in the form of rogue wave, symmetric bell soliton and rogue waves form; breather waves, the interaction of a bell and rogue wave, and two colliding rogue wave solutions are constructed. To explore the characteristics of the breather waves, localized in any direction, the higher-order KdV-5 model, which describes the promulgation of weakly nonlinear elongated waves in a narrow channel, and ion-acoustic, and acoustic emission in harmonic crystals symmetrically is analyzed. With the appropriate parameters that affect and manage phase shifts, transmission routes, as well as energies of waves, a mixed solution relating to hyperbolic and sinusoidal expression are derived and illustrated by figures. All the single and multi-soliton appeared symmetric about an axis of the wave propagation. The analyzed outcomes are functional in achieving an understanding of the nonlinear situations in the mentioned fields. Full article
(This article belongs to the Section Physics)
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17 pages, 13733 KiB  
Article
Numerical Simulation of the Maneuvering Motion Wake of an Underwater Vehicle in Stratified Fluid
by Chang Shi, Xide Cheng, Zuyuan Liu, Kunyu Han, Penghui Liu and Long Jiang
J. Mar. Sci. Eng. 2022, 10(11), 1672; https://doi.org/10.3390/jmse10111672 - 6 Nov 2022
Cited by 7 | Viewed by 2605
Abstract
When a vehicle moves underwater, disturbance is generated and a wake remains that destroys the original free surface and produces a new wake. In order to study the mechanism and characteristics of the wave-making wake generated by the maneuvering motion of an underwater [...] Read more.
When a vehicle moves underwater, disturbance is generated and a wake remains that destroys the original free surface and produces a new wake. In order to study the mechanism and characteristics of the wave-making wake generated by the maneuvering motion of an underwater vehicle in density-stratified fluid, the k-ε model and the VOF method that is based on the RANS equation were used in this paper to analyze the SUBOFF model in stratified fluid at different drift angles. Numerical simulation of the maneuvering motion was carried out under these angles, and the corresponding changes in flow field caused by this motion were analyzed. The results from the comparison and analysis of the surface wave wakes under different drift angles in stratified fluid show that with the increasing drift angle, the motion wake of the vehicle still exhibits obvious Kelvin wave system characteristics. However, there are significant changes in hydrodynamic performance. The asymmetry of the surrounding flow field will increase with the increase in the drift angle. The pressure of the underwater vehicle is inversely proportional to the velocity of the surrounding flow field, and the amplitude of the peak and trough of the free surface wave is linearly related to the change in the drift angle. The numerical simulation can serve as a reference for the non-acoustic detection of the motion heading of an underwater vehicle and the motion trajectory of anti-reconnaissance underwater vehicles under actual sea conditions. Full article
(This article belongs to the Section Ocean Engineering)
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21 pages, 13037 KiB  
Article
Scattering and Directionality Effects of Noise Generation from Flapping Thrusters Used for Propulsion of Small Ocean Vehicles
by Kostas Belibassakis, John Prospathopoulos and Iro Malefaki
J. Mar. Sci. Eng. 2022, 10(8), 1129; https://doi.org/10.3390/jmse10081129 - 17 Aug 2022
Cited by 10 | Viewed by 1929
Abstract
Flapping-foil thrusters are systems that operate at a substantially lower frequency compared with marine propellers and are characterized by a much smaller power concentration. These biomimetic devices are able to operate very efficiently, offering desirable levels of thrust required for the propulsion of [...] Read more.
Flapping-foil thrusters are systems that operate at a substantially lower frequency compared with marine propellers and are characterized by a much smaller power concentration. These biomimetic devices are able to operate very efficiently, offering desirable levels of thrust required for the propulsion of small vessels or autonomous underwater vehicles (AUVs), and can be used for the standalone propulsion of small vessels or for augmenting ship propulsion in waves, alleviating the generation of noise and its adverse effects on sea life, particularly on marine mammals. In this work, we consider the generation of noise by flapping foils arranged in the neighborhood of the above vessels including the scattering effects by the hull, which, in addition to free-surface and seabed effects, significantly contribute to the modification of the characteristics of the acoustic field. A Boundary Element Method (BEM) is developed to treat the 3D scattering problem in the frequency domain forced by monopole and dipole source terms associated with the Ffowcs Williams and Hawkings (FW-H) equation. Numerical results are presented in selected cases illustrating that the hull geometry and acoustic properties, as well as the sea surface and seabed effects, are important for the determination of the directionality of the generated noise and significantly affect the propagation in the underwater ocean environment. Full article
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14 pages, 2137 KiB  
Article
Target Strength Measurements of Free-Swimming Sandeel Species, Ammodytes spp., in a Large Indoor Experimental Aquarium
by Yanhui Zhu, Kosuke Mizutani, Kenji Minami, Hokuto Shirakawa, Yohei Kawauchi, Huamei Shao, Makoto Tomiyasu, Yuka Iwahara, Tsutomu Tamura, Masahiro Ogawa, Kai Tatsuyama and Kazushi Miyashita
J. Mar. Sci. Eng. 2022, 10(7), 966; https://doi.org/10.3390/jmse10070966 - 14 Jul 2022
Cited by 2 | Viewed by 2698
Abstract
The sandeel species (Ammodytes spp.) occupy a critical ecological position in connecting lower trophic levels to higher ones. However, they are strongly affected by the marine environment and their catch rates are trending downward. In this study, the target strength (TS [...] Read more.
The sandeel species (Ammodytes spp.) occupy a critical ecological position in connecting lower trophic levels to higher ones. However, they are strongly affected by the marine environment and their catch rates are trending downward. In this study, the target strength (TS) of sandeel species was measured in free-swimming specimens using a split-beam quantitative echo sounder with 38 and 120 kHz frequencies in a physically controlled environment. Parameters a and b used in the estimated TSmean–fork length (FL: 13.5–21.5 cm) equation were 53.7 and −124.3 dB at 38 kHz, and 71.3 and −153.2 dB at 120 kHz, respectively. The TS of the sandeel species were not proportional to the square of the FL but increased relatively rapidly with increasing body size. In addition, the mean and standard deviation of the swimming angle for the sandeel species from the acoustic data at 120 kHz were −2.2° and 7.7°, respectively, and most were in the −30° to 30°, range. Furthermore, TS was stronger at 38 kHz than at 120 kHz for all FL classes. The use of such frequency characteristics could facilitate the discrimination of fish species in the field and the sustainable assessment of sandeel species stocks. Full article
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22 pages, 10401 KiB  
Article
A Denoising Method of Micro-Turbine Acoustic Pressure Signal Based on CEEMDAN and Improved Variable Step-Size NLMS Algorithm
by Jingqi Zhang, Yugang Chen, Ning Li, Jingyu Zhai, Qingkai Han and Zengxuan Hou
Machines 2022, 10(6), 444; https://doi.org/10.3390/machines10060444 - 4 Jun 2022
Cited by 4 | Viewed by 2126
Abstract
The acoustic pressure signal generated by blades is one of the key indicators for condition monitoring and fault diagnosis in the field of turbines. Generally, the working conditions of the turbine are harsh, resulting in a large amount of interference and noise in [...] Read more.
The acoustic pressure signal generated by blades is one of the key indicators for condition monitoring and fault diagnosis in the field of turbines. Generally, the working conditions of the turbine are harsh, resulting in a large amount of interference and noise in the measured acoustic pressure signal. Therefore, denoising the acoustic pressure signal is the basis of the subsequent research. In this paper, a denoising method of micro-turbine acoustic pressure signal based on the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) and Variable step-size Normalized Least Mean Square (VSS-NLMS) algorithms is proposed. Firstly, the CEEMDAN algorithm is used to decompose the original signal into multiple intrinsic mode functions (IMFs), based on the cross-correlation coefficient and continuous mean square error (CMSE) criterion; the obtained IMFs are divided into clear IMFs, noise-dominated IMFs, and noise IMFs. Finally, the improved VSS-NLMS algorithm is adopted to denoise the noise-dominated IMFs and combined with the clear IMF for reconstruction to obtain the final denoised signal. Adopting the above principles, the acoustic pressure signals generated by a micro-turbine with different rotation speeds and different states (normal turbine and fractured turbine) are denoised, respectively, and the results are compared with the axial flow fan test (ideal interference-free signal). The results show that the denoising method proposed in this paper has a good denoising effect, and the denoised signal is smooth and the important features are well preserved, which is conducive to the extraction of acoustic pressure signal characteristics. Full article
(This article belongs to the Section Turbomachinery)
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12 pages, 4912 KiB  
Technical Note
Coastal Acoustic Tomography of the Neko-Seto Channel with a Focus on the Generation of Nonlinear Tidal Currents—Revisiting the First Experiment
by Minmo Chen, Aruni Dinan Hanifa, Naokazu Taniguchi, Hidemi Mutsuda, Xiaohua Zhu, Zenan Zhu, Chuanzheng Zhang, Ju Lin and Arata Kaneko
Remote Sens. 2022, 14(7), 1699; https://doi.org/10.3390/rs14071699 - 31 Mar 2022
Cited by 6 | Viewed by 2500
Abstract
The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisited to elucidate the propagation and generation characteristics of the M2 and M4 tidal currents with a second CAT experiment, which was conducted from 3–6 April 2018 (local [...] Read more.
The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisited to elucidate the propagation and generation characteristics of the M2 and M4 tidal currents with a second CAT experiment, which was conducted from 3–6 April 2018 (local time). Two-dimensional flow fields of the M2 and M4 tidal currents and the residual current were reconstructed using a coast-fitting inversion model with the reciprocal travel-time data of five acoustic stations. The M2 tidal current is a progressive-type wave that propagates eastward at a speed of 0.7 ms−1, much slower than expected for free progressive tides in this region (19 ms−1). The M4 nonlinear current constructed an out-of-phase relationship between the western and eastern halves of the tomography domain, implying the generation of standing-type waves. Such nonlinear processes led to flood- and ebb-dominant tidal current asymmetries for the western and eastern halves of the model domain, respectively. The two-day mean residual currents constructed a northeastward current with a maximum speed of 0.3 ms−1 in the western half of the model domain and a clockwise rotation in the eastern half. The averaged inversion errors were 0.03 ms−1, significantly smaller than the amplitude of the aforementioned currents. Full article
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14 pages, 1278 KiB  
Article
Recovering the Free-Field Acoustic Characteristics of a Vibrating Structure from Bounded Noisy Underwater Environments
by Wei Lin and Sheng Li
Sensors 2021, 21(16), 5521; https://doi.org/10.3390/s21165521 - 17 Aug 2021
Cited by 1 | Viewed by 1981
Abstract
The vibrational behavior of an underwater structure in the free field is different from that in bounded noisy environments because the fluid–structure interaction is strong in the water and the vibration of the structure caused by disturbing fields (the reflections by boundaries and [...] Read more.
The vibrational behavior of an underwater structure in the free field is different from that in bounded noisy environments because the fluid–structure interaction is strong in the water and the vibration of the structure caused by disturbing fields (the reflections by boundaries and the fields radiated by sources of disturbances) cannot be ignored. The conventional free field recovery (FFR) technique can only be used to eliminate disturbing fields without considering the difference in the vibrational behavior of the structure in the free field and the complex environment. To recover the free-field acoustic characteristics of a structure from bounded noisy underwater environments, a method combining the boundary element method (BEM) with the vibro-acoustic coupling method is presented. First, the pressures on the measurement surface are obtained. Second, the outgoing sound field and the rigid body scattered sound field are calculated by BEM. Then, the vibro-acoustic coupling method is employed to calculate the elastically radiated scattered sound field. Finally, the sound field radiated by the structure in the free field is recovered by subtracting the rigid body scattered sound field and the elastically radiated scattered sound field from the outgoing sound field. The effectiveness of the proposed method is validated by simulation results. Full article
(This article belongs to the Special Issue Underwater Acoustics Modelling and Control)
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