Noise Radiation Research Articles

On the modeling of thin moving sound sources using a cutFEM approach

While for vibro-acoustic analysis it is often assumed that the source is stationary, in many situations it is moving. Thus, to accurately determine the acoustic response of these systems, a time-varying system has to be solved. This leads to additional challenges, such as how to deal with the varying geometrical configuration and choosing an appropriate time-stepper. Recently, it was shown that cut finite elements (cutFEM) might be a viable solution, since this approach uses a stationary background mesh and cuts the elements wherever the moving source is located, thus omitting remeshing and mesh morphing steps. In this contribution, the approach is extended to also include the possibility to model thin sources (plates/shells), which are a common cause for noise radiation in structures. This is a non-trivial extension, since an immersed thin source leads to a discontinuity in the pressure response among the cut and a local doubling of the elements to capture the pressure on both sides of the cut. This paper describes how to perform numerical integration on the cut elements, how to apply stabilization, and shows a stable time-integration scheme to calculate the solution. It concludes by showing an example of a moving line source.

Modulation of wake evolution, separation, and radiated noise by a cylinder with porous media cladding

In this paper, the effects of porous media parameters on circular cylinder wake flow and radiation noise are investigated using large eddy simulations and Ffowcs Williams–Hawkings acoustic analogy. We performed three-dimensional numerical simulations for flow around the cylinder coated with a porous layer of different pores per inch in a subcritical flow regime (ReD=4.7×104) to explore the control mechanism of porous media on wake and radiation noise. The results show that the application of porous media significantly alters the separation pattern behind the cylinder and stabilizes the shear layer detached from the cylinder. The existence of porous layers leads to the transformation of chaotic and irregular vortex structures into more orderly vortices. Moreover, this study also reveals that the cylinder coated with high pore density can provide the desired noise reduction. The analysis of vortex sound theory indicates that porous media reduces the interaction area and magnitude of the positive and negative Lamb vector divergences, which is beneficial for drag reduction and noise attenuation. In addition, the comparison of sound pressure contours shows that the application of porous media does not change the radiation mode of noise, but the porous media with high pore density helps to decrease the generation of noise and intensity of the sound source.

Research on Feature Extraction of Underwater Acoustic Target Radiation Noise Based on Machine Learning Algorithm

Underwater acoustic target recognition is a very important technology in the field of underwater acoustics, with great economic and military value. Feature extraction technology for underwater acoustic target radiation noise signals is the key to achieving acoustic target recognition. This study aims at the feature extraction task of acoustic targets and extracts 10 types of 252-dimensional feature vectors from three domains: time domain, frequency domain, and auditory domain. Through 7 machine learning algorithms for classification and recognition experiments, the experimental results show that the recognition performance of the ensemble classifier is much better than that of a single classifier. For different types of features, this study combines three ensemble learning algorithms and feature selection algorithms to select the original 252-dimensional features. The feature selection experiment shows that the wrapper feature selection algorithm has the best effect, and the feature vector dimension can be reduced to 40 dimensions. The recognition accuracy rate is not less than 92.8%, which provides feature extraction guidance for acoustic target recognition based on feature extraction.

Optimizing Radiation Dose Using Ctdi Value Analysis and Image Quality in the Thorax Low Dose CT Scan (LDCT) Technique with Reduced Dose Variations Using Idose Software

Radiation exposure to patients with higher cumulative effective doses on thorax CT scanning is very detrimental for cancer patients undergoing follow-up and raises the level of concern about the harmful effects of radiation doses received by patients. Reducing the tube voltage will reduce the radiation dose and image quality. To maintain good image quality, the iDose strength level is set. iDose is able to reduce radiation dose and improve image quality by maintaining low noise. Analyze the optimization of radiation dose and image quality in the thorax Low Dose CT Scan (LDCT) examination protocol with tube voltage settings and variations in the use of iDose software. This type of research is True-Experimental research with a Posttest-Only Control Design. The object used is a water phantom with tube voltage settings of 80 kVp, 100 kVp and 120 kVp and the use of iDoe 3 -5. Assessment includes radiation dose, noise, SNR and NPS. After getting optimal results from setting the tube voltage and iDose strength level, these results were applied to a Thorax CT Scan examination in patients, and a subjective assessment of image quality was carried out. Reducing the tube voltage (kVp) from 120 kV to 80 kV was able to reduce the radiation dose by 69.8%, and reducing the tube voltage from 120 kV to 100 kV in the Thorax CT Scan protocol was able to reduce the radiation dose by 34.2 %. There is an influence of setting the tube voltage and setting the iDose strength level on the radiation dose and image quality of the Low Dose CT Scan of the Thorax. Setting tube voltage and high iDose strength levels can improve image quality in CT scans, characterized by decreasing noise and NPS values and increasing SNR values. Tube voltage settings and iDose level settings affect the radiation dose and image quality. The use of a tube voltage of 80 kVp and strength level iDose 5 is able to provide optimal radiation dose and image quality on Thorax Low Dose CT Scan.

A theoretical study on altering the frequency of high-order modes using a time-varying wall property

Noise radiation by aero-engines features high circumferential modes and high frequencies. It is rather difficult to suppress such high-order modes near their cut-on frequencies. Delicate designs are needed. When the engine operation conditions change, a design good for one set of parameters may not be optimal for another. This study explores a new path: an electromagnetic diaphragm with a MOSFET-controlled shunt circuit can be used to convert the wave frequency to any value at will by creating a digitally pre-defined time-varying material property. When properly organized, the incident sound energy is dispersed to several frequencies, some of which are below the cutoff frequency. In this way, it is showed that part of the energy of high-order modes can be reduced. This method creatively utilizes electroacoustic coupling to alter frequencies and control the propagation of high-order modes. Additionally, the time-variation is made on a passive basis in the sense that it requires no sensor input and no energy input to the actuator, thus ensuring stability and potential application in engineering.

An investigation of shock cell-related noise in an installed, full-scale tactical jet engine using acoustical holography

Shock cells in imperfectly expanded supersonic jet flows have been found to contribute to the noise radiated by these jets. Acoustic phenomena such as screech and broadband shock-associated noise have been linked to the shock cell structure in jets. Acoustical holography has been used to study various jet noise source and radiation characteristics. Holography-based reconstructions near the acoustic source in an installed, full-scale tactical jet engine have yielded features indicative of the known shock cell structure in the jet. This paper presents these results and investigates the characteristics of these features, including their distribution and relative amplitudes.

Comparing acoustical measurements from Falcon 9 launches

The Falcon 9 rocket has successfully launched nearly 300 orbital missions, providing the opportunity to study noise radiation and propagation variability. Acoustical measurements of several Falcon 9 launches have been made on and near Vandenberg Space Force Base, ranging 0.5 to 14 km from the launch pad. This paper’s purpose is to compare collocated measurements from different Falcon 9 launches to begin to understand data variability as a function of launch and environmental conditions. One far-field location, at a distance of 8.4 km, has been measured across all launches, whereas several other locations spanned subsets of launches. This comparative analysis includes time-varying levels, spectra, and waveform statistics such as the pressure derivative skewness. Time periods of particular interest are liftoff, peak noise, and late into the launch when the vehicle is significantly downrange. [Work supported in part by the NSF REU program and by USACE.]

An investigation of drone propeller noise generation in a turbulent wake

Unmanned aerial vehicles (UAVs) are becoming popular as they can be used in a range of applications including surveillance, delivery, agriculture, aerial photography, and search and rescue. This paper presents an experimental study to characterise the effect of turbulent inflow disturbance on the noise generated by a drone propeller using a low-noise, open-jet anechoic wind tunnel facility at UNSW. Advanced precision composites (APC) two-bladed, 12-inch rotors were tested at rotational speeds between 4000 and 8000 RPM at a freestream velocity of 15 m/s. The inflow disturbance upstream of the propeller is the wake of a NACA0012 profile wing to which the propeller is mounted. Hot-wire anemometry has been used to characterise the wake of the strut. The turbulence intensity, mean velocity, and turbulence length scale is calculated to characterise the turbulence ingested by the propeller. Acoustic measurements have been taken with multiple microphones to study the sound directivity and noise radiation of the propeller. A load cell is used to measure the torque and thrust produced by the propeller. This experimental program aims to characterise the wake profile ingested by the propeller and examine the associated noise generation.

Fast estimation of distance between two hydrophones using ocean ambient noise in multi-ship scenarios

Accurately estimating the bearing of a target with two hydrophones requires knowing the precise distance between them. However, in practice, it is difficult to measure this distance accurately due to the influence of current. To solve this problem, we propose a method for extracting the time-domain Green’s function between two points in multi-ship scenarios and for extracting the time-domain waveform arrival structure between two hydrophones in real-time based on long samples of ship radiation noise cross-correlation. Using the cross-correlation function of the radiated noise from any ship located in the end-fire direction of the two hydrophones, we can estimate the distance between the hydrophones in real-time. To verify the accuracy of our estimation, we compare the result of azimuth estimation with the actual azimuth based on the azimuth estimation of a cooperative sound source in the maritime environment. Our experimental results show that the proposed method correctly estimates the distance between two hydrophones that cannot be directly measured and estimates the position of a cooperative sound source 4 km away with an average deviation of less than 1.2°.

Mechanism of noise reduction caused by thickening top plate for high-speed railway box-girder bridge

For the high-speed railway concrete box-girder bridge, thickening the top plate can effectively reduce the structural noise radiation caused by moving trains. However, the noise reduction mechanism for thickening top plate has not been investigated. This mechanism is systematically studied in this paper by employing a train-track-bridge spatially coupled dynamics model and an acoustics boundary element model of the box-girder bridge. The results demonstrate that the top plate is the dominant noise source for the concrete box-girder bridge. Thickening top plate can significantly reduce the noise radiation capacity of the box-girder bridge, mainly through three mechanisms: (1) reducing the local modal shapes and vibrations of top plate, (2) decreasing the acoustic radiation efficiency, and (3) redistributing the train-induced vibration in the bridge. Furthermore, these three aspects collectively determine the total amount and spatial distribution of the noise radiation from the box-girder bridge due to moving trains. It is crucial to comprehensively these three aspects for the low-noise design of box-girder bridge.

Experimental and Simulation Research on the Vibration Characteristics of the Traction Motor of Medium and Low Speed Maglev Train under Electromagnetic Excitation

In a medium and low speed maglev train, the linear induction motor (LIM) is employed as the traction motor, during operation its vibration characteristics correlate with the dynamic performance and noise radiation characteristics of the train. This paper conducted tests and established a three-dimensional simulation model of the LIM in a medium and low speed maglev train, to study the motor vibration characteristics by comparative analysis between test and simulation. The analysis results showed that the electromagnetic excitation sources of the train appear in the high-frequency band, with the main characteristic frequencies of 497.33 Hz, 994.33 Hz, 1989.00 Hz, and 3977.67 Hz. The structural modal analysis and vibration harmonic response analysis of the motor showed that the 3rd, 8th, and 18th modal frequencies of the motor structure approximate the frequencies of the electromagnetic excitation sources. As a result, the motor generates resonance at 497.33 Hz and 994.33 Hz under that excitation. The validity of the simulation was confirmed by the corresponding tests. From the perspective of theory, experiment, and simulation, this research can contribute to the optimization of traction systems in the future design of medium and low speed maglev trains.

Research on dynamic characteristics and radiation noise of a helicopter main reducer based on finite element and boundary element method

Research on dynamic characteristics and radiation noise of a helicopter main reducer based on finite element and boundary element method

Simulation of Isolated and Installed Jet Noise at Mach = 0.9: Influence of Numerical Mesh and Physical Insights

AbstractThe noise radiated by an isothermal, single-stream jet with a Mach number M = 0.9 and diameter-based Reynolds number ReD = 106 is investigated numerically without and with the presence of a flat plate. Noise sources are predicted with Zonal Detached Eddy Simulations yielding Wall Modelled LES in attached boundary layers (so called ZDES mode 3) together with turbulence tripping inside the nozzle to recover an initially turbulent flow, while radiated pressure is extrapolated with integral methods. Numerical methodology, namely grid and statistical convergence of the signals, is assessed for the isolated jet. Noise levels are accurately simulated at least up to St = 8 and integrated pressure levels collapse within 1 dB with the experiments. In the presence of the plate, a noise radiation methodology based on both Ffowcs Williams Hawkings and Kirchhoff integral methods is proposed to reconstruct the pressure signals at microphone locations with a reduced numerical cost. The simulation compares very favorably with the experimental data, azimuthal noise variations induced by the plate are correctly captured and noise levels collapse within 1 dB. It is concluded the numerical methodology is mature enough for application in an industrial context.

Infrared HOT Photodetectors: Status and Outlook.

At the current stage of long-wavelength infrared (LWIR) detector technology development, the only commercially available detectors that operate at room temperature are thermal detectors. However, the efficiency of thermal detectors is modest: they exhibit a slow response time and are not very useful for multispectral detection. On the other hand, in order to reach better performance (higher detectivity, better response speed, and multispectral response), infrared (IR) photon detectors are used, requiring cryogenic cooling. This is a major obstacle to the wider use of IR technology. For this reason, significant efforts have been taken to increase the operating temperature, such as size, weight and power consumption (SWaP) reductions, resulting in lower IR system costs. Currently, efforts are aimed at developing photon-based infrared detectors, with performance being limited by background radiation noise. These requirements are formalized in the Law 19 standard for P-i-N HgCdTe photodiodes. In addition to typical semiconductor materials such as HgCdTe and type-II AIIIBV superlattices, new generations of materials (two-dimensional (2D) materials and colloidal quantum dots (CQDs)) distinguished by the physical properties required for infrared detection are being considered for future high-operating-temperature (HOT) IR devices. Based on the dark current density, responsivity and detectivity considerations, an attempt is made to determine the development of a next-gen IR photodetector in the near future.

Analysis of Vibration and Acoustic Radiation Characteristics of Reinforced Laminated Cylindrical Shell Structure

This paper investigates the acoustic radiation characteristics of reinforced laminated cylindrical shell structures in the medium-low frequency range (1~1000 Hz) of aircrafts, submarines, and deepwater thrusters by combining simulation analysis and experimental testing. The research focuses on reinforced laminated plates, where experimental setup is established to measure structural modal parameters and structural acoustic power, and a finite element model is developed to verify the reliability of the finite element modeling method through comparison with experimental and simulation results. Simultaneously, a finite element model of the reinforced laminated cylindrical shell structure is established, and finite element simulation analysis is conducted to investigate the effects of different reinforcement methods, reinforcement quantities, reinforcement lengths, and reinforcement thicknesses on the acoustic radiation characteristics of the structure. The results indicate that in the frequency range of 1~1000 Hz, ribbed reinforcement exhibits better performance in reducing structural noise radiation compared to longitudinal reinforcement. With the increase in reinforcement quantity and thickness, the structural acoustic radiation decreases. Meanwhile, with the increase in reinforcement length, the overall sound power level of the structure shows a trend of first increasing and then decreasing.

Exploring Soil Spatial Variability with GIS, Remote Sensing, and Geostatistical Approach

This article provides a thorough overview of a wide range of advanced statistical methods that have found extensive and resilient applications in the intricate field of spatial modeling for variables in a geographical information system (GIS) platform. The noteworthy triumph of these approaches can be due to a convergence of speed, dependability, precision, and an inherent eco-consciousness that coexist to reshape the scenario of environmental data analysis. The utilization of these models has outshined conventional methods in the present terrain of scientific investigation and environmental analysis, becoming an authentication of innovative research and decision-making procedures. These approaches demonstrate commendable data utilization efficiency by effectively accepting reduced sample sizes. This not only saves resources but also aligns with the ethical imperative of minimizing environmental effects wherever possible. Furthermore, the combination of these statistical techniques with GIS has paved the way that greatly expands their utility. This tool helps to discover deep spatial linkages, extrapolate trends, and findings into actionable insights that are relatable across all disciplines. These approaches encompass not only predictive modeling but also the realms of error assessment and efficiency evaluation. In conclusion, the adoption of these statistical methods is quite useful in facilitating sound decision-making environmental studies. Some of the domains include soil properties, air quality parameters, vegetation distribution, land cover and land use, water quality parameters, temperature and climate variables, natural hazards, urban infrastructure planning, ecological habitats, noise pollution levels, and radiation and exposure assessment. As the trajectory of scientific growth unfolds, these techniques will serve in directing researchers, practitioners, and policymakers to a future where empirical accuracy and environmental consciousness meet synergistically.

Recent Advances in Vibro-Acoustics and Noise Control Of Aerospace Composite Structures

Composite structures are widely used in a variety of industrial applications due to their excellent mechanical properties, such as high stiffness-to-weight ratio, etc. The same characteristics that impart excellent mechanical efficiency, however, also result in efficient transmission and radiation of acoustic noise, posing serious vibro-acoustical problems for a variety of engineering systems in which composite structures are used. The composite structures are efficient radiators of noise mainly due to excitation and propagation of supersonic bending and/or shear waves in the structures. Composite skin-stringer structures mostly support supersonic flexural or bending waves propagating in the laminated structure whereas noise radiation by sandwich structures is dominated by supersonic shear waves in the core. Noise control of composite structures presents a significant technical challenge as the main advantages afforded by these structures, such as low weight and high strength, must not be compromised by added treatments. Recently, research has also been conducted to improve attenuation of vibration and noise radiation from such structure using nano-technology. This paper presents state-of-the-art review of the vibro-acoustics and noise control technology for aerospace composite structures.

Experimental Study on Wind Turbine Airfoil Trailing Edge Noise Reduction Using Wavy Leading Edges

Aerodynamic noise produced by the rotating blade is an important hindrance for the rapid development of modern wind turbines. Among the various noise sources, the airfoil trailing edge noise contributes a lot to the wind turbine noise. The control of wind turbine airfoil trailing edge self-noise by bio-inspired sinusoidal wavy leading edges is experimentally studied in a semi-anechoic chamber. The noise radiated by the baseline NACA 0012 airfoil and various wavy airfoils is measured using a planar microphone array consisting of fifty-two microphones. The noise source identifications are achieved by using the CLEAN-SC method. The effects of velocity and angle of attack on noise radiation of the baseline airfoil are analyzed in detail. The noise control law of the wavy amplitude and wavelength on airfoil trailing edge noise is explored. Based on the acoustic beamforming results, the noise control effects of the wavy leading edges are intuitively demonstrated. In general, the wavy leading edge with a larger amplitude and smaller wavelength has a better effect on the airfoil trailing edge noise reduction. The maximum sound pressure level reduction can be up to 33.9 dB. The results of this study are expected to provide important information for wind turbine aerodynamic noise control.

Robust Monocular Visual Inertial Odometry in γ Radioactive Environments using Edge-based Point Features

Abstract In the γ radioactive environment, high-energy photons induce degradation of the image sensor, which effects feature detection and tracking in the Visual Inertial Odometry (VIO) algorithm and deteriorates its localization performance. To address this issue, in this work, we propose a monocular VIO method using edge-based point features. To mitigate the effects of radiation noise, firstly, in the image preprocessing module, the median filter is used for real-time image denoising. Secondly, in the data association module, both Shi-Tomasi and edge-based point features are detected. The edge-based point feature is the endpoint or corner point in the salient edge map, which is more robust to radiation noise. Then, the bi-directional motion parallaxes and the RANdom SAmple Consensus (RANSAC) method are exploited to reject outliers. Finally, the point features measurements and Inertial Measurement Unit (IMU) pre-integration measurements are added into a tightly-coupled sliding window optimization VIO framework for localization estimation. The proposed method is verified by synthetic and real γ radioactive environment datasets. The experimental results show that the proposed method achieves more accurate and robust localization than the state-of-the-art VIO approaches in the γ radioactive environments.

On-field noise measurements and acoustic characterisation of multi-rotor small unmanned aerial systems

The noise signature of small Unmanned Aerial Systems (sUAS) is highly influenced by specific operating and weather conditions. Accurate noise assessment of sUAS operations requires field noise measurements that capture all the complexity of sound emission and propagation during realistic flight situations. This paper presents a measurement and analysis framework for the acoustic characterisation of sUAS through the calculation of conventional noise metrics (LAmax and LAE), frequency and directivity features. Using a multi-channel measurement approach, and back-propagating the sound from ground microphone to source, the presented framework allows the calculation of acoustic hemispheres for a selection of acoustic metrics. Important findings are that (i) the framework is robust for a variety of multi-rotor sUAS varying in size and configuration; (ii) broadband noise and tonal noise are the dominant noise sources during flyover for larger sUAS and smaller sUAS respectively; (iii) the maximum noise radiation of the sUAS tested is found in the rear arc of polar directivity; and (iv) angles of maximum radiation of amplitude modulated noise have been found for most sUAS tested at Θ angles±30∘. This work is intended to be relevant in establishing common protocols regarding sUAS acoustic certification between environmental policymakers, stakeholders, and industry.