Noise Field Research Articles

Restoration of Well-Posedness of Infinite-Dimensional Singular ODE’s via Noise

In this paper we aim at generalizing the results of A. K. Zvonkin (That removes the drift, 22, 129, 41) and A. Y. Veretennikov (Theory Probab. Appl., 24, 354, 39) on the construction of unique strong solutions of stochastic differential equations with singular drift vector field and additive noise in the Euclidean space to the case of infinite-dimensional state spaces. The regularizing driving noise in our equation is chosen to be a locally non-Hölder continuous Hilbert space valued process of fractal nature, which does not allow for the use of classical construction techniques for strong solutions from PDE or semimartingale theory. Our approach, which does not resort to the Yamada-Watanabe principle for the verification of pathwise uniqueness of solutions, is based on Malliavin calculus.

Research on vibration fatigue damage identification of oil and gas pipeline under the condition of measured noise injection

The acoustic emission signals collected by oil and gas pipelines on offshore platforms are disturbed by noise, which makes it difficult to locate the pipeline damage. To solve this problem, in this study, the measured noise signal of the offshore platform pipeline was first obtained through vibration noise acoustic emission tests. The measured field noise of the offshore platform was injected into a lead break signal collected in the laboratory, and then the injected noise signal was identified by the damage identification method based on empirical mode decomposition (EMD) combined with a probabilistic neural network (PNN). Finally, the method of time difference localization was used for preliminary localization, and then a backpropagation (BP) neural network was used to correct the localization results. The results showed that the recognition method based on EMD combined with the PNN network achieved a 97% recognition accuracy in cases with large amounts of measured noise interference. The fatigue crack localization method based on the BP neural network time difference correction method was used to locate the acoustic emission fatigue crack in the test data, and the average localization error after correction was less than 2%.

Sensitivity of strong lensing observations to dark matter substructure: a case study with Euclid

ABSTRACTWe introduce a machine learning method for estimating the sensitivity of strong lens observations to dark matter subhaloes in the lens. Our training data include elliptical power-law lenses, Hubble Deep Field sources, external shear, and noise and PSF for the Euclid VIS instrument. We set the concentration of the subhaloes using a vmax–rmax relation. We then estimate the dark matter subhalo sensitivity in 16 000 simulated strong lens observations with depth and resolution resembling Euclid VIS images. We find that with a 3σ detection threshold, 2.35 per cent of pixels inside twice the Einstein radius are sensitive to subhaloes with a mass Mmax ≤ 1010 M⊙, 0.03 per cent are sensitive to Mmax ≤ 109 M⊙, and the limit of sensitivity is found to be Mmax = 108.8 ± 0.2 M⊙. Using our sensitivity maps and assuming CDM, we estimate that Euclid-like lenses will yield $1.43^{+0.14}_{-0.11}[f_\mathrm{sub}^{-1}]$ detectable subhaloes per lens in the entire sample, but this increases to $35.6^{+0.9}_{-0.9}[f_\mathrm{sub}^{-1}]$ per lens in the most sensitive lenses. Estimates are given in units of the inverse of the substructure mass fraction $f_\mathrm{sub}^{-1}$. Assuming fsub = 0.01, one in every 70 lenses in general should yield a detection, or one in every ∼ three lenses in the most sensitive sample. From 170 000 new strong lenses detected by Euclid, we expect ∼2500 new subhalo detections. We find that the expected number of detectable subhaloes in warm dark matter models only changes relative to cold dark matter for models which have already been ruled out, i.e. those with half-mode masses Mhm > 108 M⊙.

Evaluation of a low speed stage coupling with regard to structure-borne sound propagation in a wind turbine

Due to recent advances in the field of broadband aerodynamic noise, tonalities of wind turbines (WT) are increasingly coming into focus in the wind industry. In this case, the structure is excited inside the drivetrain and the structure-borne sound propagates through the machinery and ultimately to the surfaces of the WT, where it is radiated into the ambient air. Since any tonalities are a system characteristic, they should be considered at an early stage of product development. On the one hand, great efforts are being made to develop ever lower-toned drivetrains. On the other hand, tonalities can efficiently be neutralised by systematically decoupling the excitations in the drivetrain from the sound-emitting surfaces of the wind turbine. In addition to the well-studied behaviour regarding the decoupling of non-torque rotor loads from the drivetrain, in this paper the influence of a low speed stage (LSS) coupling on the structure-borne sound propagation inside of an integrated drivetrain is investigated. In a previous study at the Center for Wind Power Drives, it could be shown that in an integrated drivetrain, the transfer paths through the main shaft and subsequently the main bearing becomes the dominant transfer path. This is in contrast to classic bearing configurations where the torque arms of the gearbox are the dominant transfer paths of excitations from the gearbox, revealing an increased potential of LSS Couplings especially for integrated drivetrains. Detailed numerical investigations are performed in order to understand and quantify the usage of a LSS coupling for lowering sound power levels of a WT.

Evaluation of the Impedance Variability Effect of Acoustic Liner on Aircraft Engine Fan Noise in Calculation of Far Field Sound Modes Propagation

The influence of the impedance variability of the acoustic liner of an air intake on aircraft engine fan noise in the far field has been studied. The calculations were carried out in an axisymmetric statement for single modes based on the finite element solution to the Blokhintsev equation for the acoustic potential. The acoustic liner impedance was determined from a well-developed semiempirical model that takes into account the influence of a high sound pressure level (SPL) and grazing flow. A procedure has been developed for calculating the propagation of single sound modes through the air intake of an aircraft engine with a variable liner impedance depending on the flow velocity and SPL at a local point. The calculation procedure has been validated. Calculations were made for single mode propagation into the forward hemisphere for an air intake on the wall of which the following conditions were set: rigid wall, constant impedance (the impedance does not change along the liner) and variable impedance (the impedance changes along the liner depending on the changes in the velocity of the grazing flow and SPL). According to the calculation results, it was found that constant and variable impedances yield different SPL values in the far field; as well, taking into account the impedance variability changes not only the SPL values in the far field, but also the direction of the maximum mode radiation.

On the finiteness of the moments of the measure of level sets of random fields

General conditions on smooth real valued random fields are given that ensure the finiteness of the moments of the measure of their level sets. As a by product a new generalized Kac-Rice formula (KRF) for the expectation of the measure of these level sets is obtained when the second moment can be uniformly bounded. The conditions involve (i) the differentiability of the trajectories up to a certain order k, (ii) the finiteness of the moments of the k-th partial derivatives of the field up to another order, (iii) the boundedness of the joint density of the field and some of its derivatives. Particular attention is given to the shot noise processes and fields. Other applications include stationary Gaussian processes, Chi-square processes and regularized diffusion processes. AMS2000 Classifications: Primary 60G60. Secondary 60G15.

Experimental investigation on cylinder noise and its reductions by identifying aerodynamic sound sources in flow fields

Through anechoic wind tunnel tests, this study comprehensively investigates the noise and drag reductions on a circular cylinder with dimples. Dimples built on a surface pattern fabric cover the cylinder surface as one of the passive flow control methods. The force, noise, and flow field measurements are performed at diameter-based Reynolds numbers ranging from 3×104 to 1.3×105, covering the sub-critical, critical, and supercritical regimes. The force and noise measurement results show that dimple fabric simultaneously reduces noise and drag in the critical regime. The changes in flow structures were characterized by the Time-resolved Particle Image Velocimetry (TR-PIV) measurements. Based on the vortex sound theory, the flow analysis shows that the dominant sound sources are found to be concentrated near the cylinder surface, which is caused by the unsteady vortex motions near the separation locations during the process of vortex shedding. The cross-correlation between the synchronized TR-PIV and microphone measurements further supports the conclusions. Moreover, the cylinder noise reductions controlled by the dimples are directly associated with the reduced sound sources in the critical and supercritical regimes, corresponding to the reduced strength of the vortex shedding.

Numerical Simulation Analysis of Flow Noise Characteristics of Underwater Vehicle

Based on the standard large eddy simulation and k-epsilon model, the steady flow field and navigation flow noise of the underwater vehicle shell are simulated. In this paper, the underwater vehicle model is established by referring to classic SUBOFF model. The standard k-epsilon method is used to study the pressure distribution characteristic, velocity distribution characteristic, and velocity vector distribution characteristic on and around the shell of the underwater vehicle at different speeds. The results indicate that the pressure increases with the increase of the speed and in the bow of the shell is the largest. A large eddy simulation was used to analyze the noise characteristics of sailing flow at different speeds. The results show that the sound pressure level of navigation flow noise is higher in the low-frequency band, and will increase with the increase in speed.

Numerical Analysis of Flow Field and Aerodynamic Noise in Intake Structure

The CFD numerical simulation was used to simulate the flow field and sound field of the intake system, combined with the acoustic finite element method. Based on the Lighthill acoustic analogy and the Möhring acoustic analogy method, the internal sound source distribution of the intake system, the intensity of the nozzle noise and the acoustic directivity were analyzed. Improvement measures were proposed from the perspective of noise transmission, and the influence of different wall thicknesses on the wall stimulated radiation noise, as well as the effects of attaching sound absorbing materials and spraying damping materials on wall radiation noise were studied.

Roadway noise field measurements and modeling large sites in CadnaA

Modeling roadway automobile traffic noise in CadnaA prediction software offers the opportunity to extrapolate larger site information from a small sample of field measurements. This presentation will discuss two case studies where multiple short term field measurement locations were used to calibrate large site noise analyses. Using publicly available Average Annual Daily Traffic (AADT) counts from local municipalities as the basis for site calculations was attempted but found to not correlate well with field measurements. A review and discussion of the differences will be presented.

ANOMALOUS SEISMIC NOISES FROM THE DECEMBER 9, 2020 M<sub>W</sub> = 5.6 KUDARA EARTHQUAKE IN THE BAIKAL BASIN

Studies have been conducted on the variations of ambient noise recorded by broadband and short-period seismic stations in the area of South Baikal before and after the large December 9, 2020 Kudara earthquake with Mw = 5.6. 10 days before the earthquake, there was a gradual increase of oscillation amplitudes in the frequency range from 0.01 to 0.1 Hz, with an increasing background observed also during 4 days after the main shock (period from 01.12.2020 to 13.01.2021). The maximum amplitude increase is 19.5 against the background. During this time, there were recorded 48 aftershocks. The analysis of direction of particle motion in seismic waves over the reporting period showed an abrupt change in the orientation of oscillations, which is fully consistent with the azimuth for the main shock epicenter. The analysis of seismograms over the next period (from December 13) did not show similar effects in the ambient noise field. Apparently, the ambient noise field reflected the process of slow faulting before the earthquake and after the main shock with subsequent attenuation.

Effect of Tip Clearance Size on the Cavitation Flow and Noise Characteristics of the NACA0009 Hydrofoil

The noise characteristics of NACA0009 hydrofoil with tip clearance are discussed. Select SST k- ω Turbulence model and Schnerr Sauer cavitation model simulate tip leakage cavitation flow. The results show that the simulation results are in good agreement with the original records, and the tip clearance reduces the energy characteristics of the hydrofoil. With the expansion of tip clearance model, TLV and cavitation compressive strength gradually decrease. In addition, the study of far-field noise shows that the nonspecific curve of the total noise coefficient of far-field noise shows a disc shaped symmetric structure. Compared with the original hydrofoil, when the tip clearance is 20 mm, the far-field dipole noise value at 170 ° angle is reduced by 17.68%. Tip clearance reduces offline and far-field noise. Far field noise decreases with the increase of tip clearance model.

Free Vibration Characteristics of CFRP Laminate with One-Dimensional Periodic Structures.

This paper proposes an approach of stacking prepreg periodically for carbon fiber-reinforced polymer composites (CFRP) laminate. This paper will discuss the natural frequency, modal damping, and vibration characteristics of CFRP laminate with one-dimensional periodic structures. The damping ratio of CFRP laminate is calculated using the semi-analytical method which combines modal strain energy with the finite element method. The finite element method is used to calculate the natural frequency and bending stiffness which are verified with experiments. The numerical results of the damping ratio, natural frequency, and bending stiffness are in good agreement with the experiment results. Finally, the bending vibration characteristics of CFRP laminate with one-dimensional periodic structures and traditional CFRP laminate are investigated with experiments. The finding confirmed that the CFRP laminate with one-dimensional periodic structures exists band gaps. This study provides theoretical support for the promotion and application of CFRP laminate in the field of vibration and noise.

Analysis of unsteady flow field and near-field aerodynamic noise of scale high-speed trains in long tunnel

The hybrid LES/APE method is used to simulate the unsteady flow field and the near-field aerodynamic noise of a 1/25 scale eight-coach high-speed train in long tunnel, validated by time-averaged pressure coefficients and Power Spectral Density of surface pressure from the aerodynamic wind tunnel test of a same scale two-coach train model. Train induced wind with the maximum velocity of 28 m/s in the opposite direction of train operating is formed in tunnel. Blocking effect leads to larger turbulent pressure and streamwise increment of turbulent power level from 133.7 dB to 138.2 dB, which is from130.3 dB to 133.4 dB in open air. With APE solver, three cases including tunnel with fully reflective walls, tunnel with fully absorptive walls and open air, are conducted to compare the influence of blocking effect and acoustic reflection on sound pressure. Total sound pressure level on the train body in tunnel is overall stronger than that in open air. The difference of sound power level between tunnel and open air is mostly contributed by acoustic reflection: 84.7 % at Coach 1, 84.3 % at Coach 8 and 66.0 ∼ 77.5 % from Coach 2 to Coach 7. Five peak frequencies: 520 Hz, 800 Hz, 1440 Hz, 2600 Hz and 3880 Hz are found from the frequency spectra of sound pressure of the probes in bogie cavities and pantograph grooves, in tunnel with fully reflective walls. Sound pressure modes help to clarify the generation mechanisms of peak frequencies: 520 Hz and 800 Hz are caused by the tunnel cavity resonance; 1440 Hz is caused by the first-order vertical mode from the bottom of the pantograph groove to the top of tunnel walls; 2600 Hz is caused by the first-order vertical mode from the ground to the top of bogie cavity, but 3880 Hz is not generated by simple in-phase cavity resonance.

The noise-generating mechanism of rod-airfoil configuration and the effect of spanwise length on noise prediction

The wake-blade interaction in turbo-engines is the primary source of broadband noise. In this work, the noise mechanism of a benchmark rod-airfoil configuration is exhaustively analyzed using compressible Large Eddy Simulation (LES) and Ffowcs Williams-Hawkings (FW-H) methods. The baseline model with a spanwise length shortened by 7d (d is the rod diameter) is simulated under periodic boundary conditions, and the effect of spanwise lengths on noise prediction and correlation is investigated in combination with two other models (3d and 1d). In terms of the baseline model, the noise predicted by different FW-H surfaces is compared first, and the noise radiated from different chordwise and spanwise regions of the airfoil surface reveal the generating mechanism of the main dipolar noise and the effect of periodic boundary conditions on noise prediction, respectively. Additionally, the fluctuating surface pressure characterized at four frequency bands confirms that the wake-airfoil interaction dominates the leading-edge noise at low frequencies. The characteristic frequencies of the noise and transient velocity fields reveal that the primary broadband noise source is the interaction of large-scale vortices with the airfoil surface at the leading-edge region. Finally, the effect of spanwise length on noise prediction and correlation is studied for three models. The differences in the flow structures lead to different features of their coherence coefficients. The results presented in this work provide a comprehensive understanding of the noise-generating mechanism of wake-airfoil interaction in turbomachinery and the practical application of simplified models in the future numerical simulations.

Hydre: a noise radar to automatically track down excessively noisy vehicles in real traffic conditions

The developments made by Bruitparif since 2016 around sound source localization technologies applicable to the field of environmental noise resulted in the launch on the market of a patented combined acoustic and imaging sensor called "Medusa". An article of law was voted in France at the end of 2019 in order to enable the experimentation of noise radars in order to punish drivers causing significant noise nuisances by their behavior. The evaluation process includes track trials, roadsite tests and a final phase with fines. We will describe this national experimentation and the context in which it takes place. We will then detail the prototype called "Hydre" that we have developed for this purpose, and will present case results showing how it solves the major difficulties of the legal measurement of the pass-by noise of vehicles in real traffic conditions.

Passive Amplification and Noise Mitigation of Optical Signals Through Talbot Processing

Noise is one of the rare aspects of experimental work that crosses all boundaries. It is present from scientific fields like ultrafast optical signal detection to applied fields such as image processing, or even in our day-to-day lives when we are simply trying to have a conversation in a loud room. In all these cases, incoherent, stochastic noise tends to drown a signal we aim to detect, and various techniques may need to be employed to improve the clarity of the waveform, which is characterized by the signal-to-noise ratio (SNR). Yet, considering the ubiquity of noise in scientific and technology fields, it may be surprising how few methods there exists for denoising a signal. Active amplification techniques alone cannot be employed for weak, noisy signals, since the SNR is inevitably degraded due to fundamental laws of physics, while bandpass filtering schemes necessarily lead to an attenuation of the signal. In this article, we review recent advances on the concept of passive amplification techniques based on the Talbot effect to enhance the noise properties of signals through coherent energy redistribution. We demonstrate the basic framework starting from pulse repetition rate multiplication with the Talbot effect. We then extend this theory to show the principle behind passive amplification of periodic waveforms, and then how this idea can be extended to arbitrary (generally, aperiodic) signals. Methods for passive amplification of both the time-domain and the frequency-domain representations of the signal of interest are reviewed. While here we focus on the application of the technique for optical signals in the standard telecommunication band (near wavelengths of 1550 nm), the proposed denoising scheme relies on widely available wave manipulations, such that it may offer exciting opportunities for any kind of physical wave support, such as acoustics, plasmonics and other regimes of the electromagnetic spectrum, like microwaves or X-rays.

Wind turbine noise modeling including aeroacoustic sources and propagation effects: comparison against field measurements

The study of wind turbine noise and its impact is of growing importance with the increase in the demand for green and clean energy. As it is known that wind turbine noise can be a cause of annoyance in the vicinity of wind farms it is beneficial to predict with certain accuracy the generated noise in the design phase itself. A crucial step is the validation of prediction models against field measurements (in-situ). This article presents a wind turbine noise prediction model that combines Amiet's theory to calculate trailing edge noise and turbulence interaction noise in free field with a wide-angle parabolic equation valid in moving media to account for the long-range acoustic propagation effects. The model considers the wind turbine as an extended noise source and the rotation effects (such as the convective amplification and Doppler effect) are taken into account. The predicted noise levels are compared to those obtained from a measurement campaign where acoustic, meteorological and ground impedance data have been recorded simultaneously. First, the sound source model is validated close to the wind turbines for different wind speeds and directions. Then, noise predictions are compared to SPL measurements at various distances from the sound source, between 350 and 1300meters.

Deep Learning Methods for Improving Electromagnetic Telemetry Signal-to-Noise Ratio

Summary Electromagnetic (EM) telemetry is a cost-competitive method for communication between downhole tools and oilfield surface equipment. However, EM telemetry use is limited to wellsite deployments that result in favorable signal-to-noise ratio (SNR) levels. Increasingly, the EM attenuation brought by deeper wells, conductive service fluids, and conductive formation layers has made it more important to increase EM telemetry SNR. This study explored the ability of various deep learning (DL) methods to improve EM telemetry SNR with data sets composed of mixed synthetic downhole signals and real field noise. The DL models explored were previously proven to achieve state-of-the-art performance with seismic random noise attenuation and speech separation use cases. Furthermore, architectural adjustments that improved model performance with EM telemetry data were targeted. Then, the SNR improvement performance of different design changes was evaluated. Finally, the study targeted improvements that reduced the requirements for deployment hardware, including number of stakes, without sacrificing SNR improvement performance. Optimized models were found to successfully improve SNR in EM telemetry data, outperforming traditional bandpass filter methods and enabling the demodulation of mixtures that were otherwise too noisy to be demodulated.

Abnormal Signals Elimination in Hardness Evaluation Using Barkhausen Noise and Tangential Magnetic Field

Abnormal Signals Elimination in Hardness Evaluation Using Barkhausen Noise and Tangential Magnetic Field