Core Noise Research Articles

Quantification of core noise using coherent output method: experiment and result on turbofan demonstrator

New turbofan architectures have increasing bypass ratios which makes the core noise an more important source. An identification of its contribution in the total noise has been performed on a DGEN380 turbofan demonstrator using pressure measurement: The remote pressure probes with piezo-electric pressure sensors are installed at 14 locations in the nozzle. The far field noise was caught using 25 microphones array parallel to the engine axis. A coherent output power analysis based on multiple reference channels was applied to identify the active part of the combustion noise and in a reciprocal way the acoustic component in the duct propagated in the test room. The processing allows to calculate the far field contribution and directivity of the core noise. K-type thermocouples were implemented to quantify temperature fluctuations in the engine nozzle. The thermocouples were manufactured with two different wire diameters (from 25 to 80µm) which give different frequency responses. An in-situ compensation method was developed to correct the signal and increase the useful frequency range of the temperature measure. This allows to cover the whole core noise frequency range. This project has received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreement No. 886554.

Natural ventilation and acoustic privacy in settlement cores: a review of window technology and night-time economy planning policy

This study reviewed the potential of partially open windows to address the challenges of natural ventilation and night-time airborne noise within settlement cores. These areas, which often feature historic buildings, require sensitive interventions to balance the conservation of heritage with the need for liveable, sustainable cities. The 'night-time economy' (NTE) encompasses a diverse range of businesses, services, and events that operate beyond traditional daytime hours, such as restaurants, bars, nightclubs, entertainment venues, cultural events, and 24-hour services. Night-time noise disturbances can be detrimental to residents' health and well-being. A case study examined the solutions proposed by contemporary NTE planning policy to address night-time noise in settlement cores, particularly in instances where the expansion of NTE areas and extended trading hours are considered. No physical solution mitigation strategies for noise reduction were identified in the NTE policy, and only a management approach was proposed. This study examines the potential of innovative acoustically attenuated partially open windows as a strategic solution to airborne night-time noise pollution from a night-time economy. This solution may improve energy efficiency and sustainability in cities while allowing the night-time economy and residential areas to coexist more harmoniously.

A comprehensive analysis of thermal–hydraulic signatures in neutron noise of WWER-type reactors

The neutron noise phenomenon, occurring in all types of nuclear reactors, provides valuable insights into the dynamic behavior of these reactors. In this work, a well-justified approach for modeling neutron noise induced by thermal–hydraulic sources in a hexagonal reactor core is presented in detail. These sources encompass fluctuations in key features of the inlet coolant, including flow rate, temperature, and boric acid concentration. Our proposed approach touches on various aspects of the distribution of thermal–hydraulic parameters among coolant loops, accounting for both uniform and non-uniform distributions. The latter allows for the asymmetric and asynchronous distribution of their fluctuating component among the coolant loops. To manage such complexity, it becomes imperative to determine the contribution of each fuel assembly based on each coolant loop. To achieve this, CFD simulations are conducted for the downcomer and lower plenum of the reactor pressure vessel. These simulations provide essential data to establish the coolant mixing matrix, which accounts for non-uniform distributions. The obtained mixing matrix is subsequently integrated into our neutron noise simulator, DYNOSIM, ensuring the faithful reproduction of neutron noise. Our study comprehensively analyzes both uniform and non-uniform scenarios. The radial and axial distributions of neutron noise amplitude and phase are examined for these scenarios. Their qualitative verifications are conducted by prior works in this field. Furthermore, we compare one of the uniform scenarios with reference results obtained using a frequency domain simulator. Notably, our CFD simulation results closely match the experimental data. Our findings demonstrate the effectiveness and efficiency of this methodology in modeling and understanding neutron noise in hexagonal reactor cores.

Simulation and analysis of core barrel vibrational modes associated with neutron noise phenomena in WWER-type reactors

This survey focuses on an approach to address various vibrational modes of the core barrel in a hexagonal-structured reactor core. The core barrel vibration is considered one of the main mechanical vibrations in a high-power nuclear reactor, initiating core component malfunctions and safety issues. Here, a well-reasoned method is proposed to handle the triple vibrational modes of such core barrels, whether individually or in combination with fuel assembly vibrations. The modeling of core barrel vibrations involves modifying the lattice water width for boundary fuel assemblies and correlating it with external reactivity in the time-dependent calculation. The radial and axial distributions of neutron noise amplitude, phase, and spectrum are further analyzed for several scenarios using the designed neutron noise simulation tool, DYNOSIM. The outcomes support using the suggested methodology to simulate neutron noise in hexagonal cores due to different modes of core barrel vibration.

Research on a Time Difference Processing Method for RTD-Fluxgate Data Based on the Combination of the Mahalanobis Distance and Group Covariance.

During the measurement of magnetic fields, Residence Time Difference (RTD)-fluxgate sensors suffer from abnormal time difference jumps due to the random interference of magnetic core noise and environmental noise, which results in gross errors. This situation restricts the improvement of sensor accuracy and stability. In order to solve the above problems efficiently, a time difference gross error processing method based on the combination of the Mahalanobis distance (MD) and group covariance is presented in this paper, and the processing effects of different methods are compared and analyzed. The results of the simulation and experiment indicate that the proposed method is more advantageous in identifying the gross error in time difference. The signal-to-noise ratio for the time difference is improved by about 34 times, while the fluctuation of the Negative Magnetic Saturation Time (NMST) ΔTNMST is reduced by 95.402%, which significantly reduces the fluctuation of time difference and effectively improves the accuracy and stability of the sensor.

Modeling and simulation of neutron noise triggered by fuel assembly vibrations in 3D hexagonal geometry

Neutron noise is a natural phenomenon in nuclear reactors. Hence, its investigation plays a significant role in nuclear reactor physics and safety-related issues. While neutron noise could have various origins, the proposed work focuses on those induced by fuel assembly vibration in hexagonal cores. To this aim, a 3D neutron noise simulator has been developed based on the multi-point kinetics equations for a hexagonal geometry coupled with the expanded multi-nodal approach as a thermal-hydraulic model. Employing these models, the neutron noise was analyzed in the time domain to provide the advantage of modeling non-linearities. This simulator is capable of simultaneous simulation of vibrating fuel assemblies with various vibrational characteristics, in particular, mode. It features the capability of neutron noise modeling at both the nuclear data generation level and the level of the neutronic calculations. The validity of the model is demonstrated by a transient accident and a noise problem. The outcomes are compared to reference data, showing good agreement. Then, to further study noise responses, several scenarios encircling various vibrating fuel assemblies in different situations are simulated. These experiments prove the appropriate performance of the proposed simulator for modeling and analyzing neutron noise in hexagonal cores.

Study on flow-induced noise characteristics of multistage depressurization valve in the nuclear power plant

In this study, the flow-induced noise generated by the second-loop main feedwater regulating valve in a nuclear power plant is analyzed. Based on the Ffowcs Williams and Hawkings acoustic analog equation and internal flow characteristics, the noise level and characteristics under monopole, dipole, and quadrupole noise sources are numerically investigated. The results show that the cavitation noise under a monopole noise source, water hammer impact noise under a dipole noise source, and turbulence noise under a quadrupole noise source have a certain influence on the generation and propagation of valve core noise. The maximum noise level is located in the turbulence generation region after the hedge and is about 188 dB. The frequency characteristics of the turbulence noise are obtained through spectrum and octave analyses. The results show that the low and middle frequency bands are narrow, and the sound pressure level (SPL) gradually increases with increasing frequency. The wider the high frequency, the lower the SPL. The continuous broadband frequency characteristics are dominated by the middle and high frequencies. The study results provide some reference for investigating valve noise and designing active noise reduction.

Low-frequency duct noise control using coupled loudspeakers.

A duct noise control device is introduced based on a Herschel-Quincke (HQ) tube and electro-mechanical coupling. The device consists of the main duct segment and one set of connected loudspeakers, which functions as a side-by tube in a traditional HQ tube. The acoustic waves imposed on the upstream loudspeaker can be transmitted to the other loudspeaker via the connecting circuit immediately, which represents a fast track when compared with the wave transmission via the fluid medium in the main duct. It is the core noise attenuation mechanism in this silencer. The transfer matrix method is used to investigate the silencer performance. A periodic silencer array is also developed to broaden the bandwidth and increase the magnitude of noise attenuation. The results predicted by the plane wave theory fit well with the simulation using a three-dimensional finite element method. A simplified experiment was conducted to verify the silencing effect of the silencer and the accuracy of theoretical prediction method. Contrasting with a traditional reactive silencer, low-frequency noise attenuation can be achieved in a more compact and flexible way, which can be seen as an improvement in low frequency noise control.

An 8-Bit in Resistive Memory Computing Core With Regulated Passive Neuron and Bitline Weight Mapping

The rapid development of artificial intelligence (AI) and Internet of Things (IoT) increase the requirement for edge computing with low power and relatively high processing speed devices. The computing-in-memory (CIM) schemes based on emerging resistive nonvolatile memory (NVM) show great potential in reducing the power consumption for AI computing. However, the inconsistency of the NVM may significantly degenerate the performance of the neural network. In this article, we propose a low power resistive RAM (RRAM)-based CIM core to not only achieve high computing efficiency but also greatly enhance the robustness by bit line (BL) regulator and BL weight mapping algorithm. The simulation results show that the power consumption of our proposed 8-bit CIM core is only 12.6 mW ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$256\times 256$ </tex-math></inline-formula> at 8b). The spurious-free dynamic range (SFDR) and signal to noise and distortion ratio (SNDR) of the CIM core achieve 62.64 and 45.92 dB, respectively. The proposed BL weight mapping scheme improves the top-1 accuracy by 2.46% and 3.47% for AlexNet and VGG16 on ImageNet Large Scale Visual Recognition Competition 2012 (ILSVRC 2012) in 8-bit mode, respectively.

Research on power transformer vibration and noise under DC bias condition

In the process of Ultra high voltage direct current (UHVDC) transmission, the direct current (DC) bias of power transformer is easily induced, which makes the transformer exciting current distorted, the ferromagnetic material saturated and the magnetic leakage increased, and then leads to the increase of core vibration and noise. Aiming at this problem, taking a 240 MVA, 330 kV three-phase five-column power transformer as an example, the coupling of the electromagnetic field, structural force field and acoustic field is studied, and the influence of DC bias on vibration and noise of power transformer core is analyzed in this paper. According to the magnetic density and electric density of transformer core under different magnetic bias degree, the structural force field is solved, and the displacement and surface acceleration of core are obtained, which can be as the excitation of sound field to determine the noise distribution of transformer. In order to avoid the natural frequencies which easily cause resonance, the modal analysis is needed to obtain the natural frequencies and modal modes of the core. The transformer noise under no-load and DC bias conditions of the prototype is tested experimentally and compared with the theoretical calculation, the results prove the accuracy of the simulation calculation method in this paper.

Core noise and GW sensitivities of AMIGO

AMIGO–The Astrodynamical Middle-frequency Interferometric Gravitation-Wave (GW) Observatory is a first-generation mid-frequency GW mission bridging the sensitivity gap between the high-frequency GW detectors and low-frequency space GW detectors. In our previous works, we have obtained appropriate heliocentric orbit formations of nominal arm length 10,000[Formula: see text]km with their first-generation time-delay configurations satisfying frequency noise reduction requirement, and we have also worked out thrust-fuel friendly constant-arm heliocentric orbit formations. In this paper, we review and study noise requirements and present the corresponding GW sensitivities. From the design white position noises and acceleration noises, we obtain the GW sensitivities for the first-generation Michelson X TDI configuration of baseline AMIGO (b-AMIGO), AMIGO and enhanced AMIGO (e-AMIGO). In view of the current technology development, we study and indicate steps to implement the AMIGO mission concept.

Research on the Effect of Core Joints on Transformer Noise

In order to study the effect of different joint types on the core noise of transformer, this article proposes a method based on the equivalent magnetostriction properties of the core joints. First, the 2-D magnetic field simulation of the core model with joints is performed to obtain the flux density distribution, by which the equivalent magnetization and magnetostriction characteristics of the joint are calculated. Then, core joints are defined by a new material with equivalent properties to simulate the magnetic field of the 3-D core models, and the magnetic-force–acoustic coupling analysis is performed by the finite element method to calculate the noise of the models. Finally, the effectiveness of the calculation method is verified by noise test. The results show that the simulation is consistent with the test. This article provides a new method for improving the accuracy of transformer core noise prediction further.

Influence of viscosity on entropy noise generation through a nozzle

Entropy (temperature) fluctuations produced by turbulent flames generate noise when they are accelerated by the flow. This so-called entropy noise is an important contributor to core noise in modern aeroengines and several semi-analytical models exist in the literature for its prediction. All these models assume the flow to be inviscid. In the present paper, contribution of viscosity on entropy noise generation and scattering through a nozzle is investigated numerically with URANS simulations and analytically through the extension of the 2D inviscid model of Emmanuelli et al. (2020). Simulations indicate noise generation and scattering is slightly reduced in the medium-frequency range in the presence of viscosity with variations below 3 dB in comparison to reference inviscid data. This noise variation is qualitatively well reproduced by the low-order model. The major effect of viscosity on noise generation and propagation lies in the presence of boundary layers. Viscous entropy noise sources and viscous diffusion of acoustic perturbations have a negligible impact on noise. Discrepancies between simulations and analytical solutions are found to come from the radial evolution of the acoustic waves in thick boundary layers, not accounted for in the model, and which impact noise scattering.

Study on Sound Field Distribution Rule for Tank Structures of Large Oil-immersed Transformers

Large oil-immersed transformers are an important part of the transmission and distribution network in power systems. Power transformers are the main noise source of substations. Because of the uneven manufacturing process, aging equipment, long-term operation, and close distance from sensitive points, the problem of transformer noise pollution has become increasingly prominent. In this paper, the transmission and analysis model is established for transformer sound waves on the interface between insulating oil and tank body according to the sound wave propagation rule in complicated medium, and the simplified acoustic simulation model is constructed for large oil-immersed transformers by simulating the vibration noise of transformer core with monopole sound source, with which, the sound field distribution rule inside and outside the transformer tank structure is obtained, and finally, the influence factors for noise distribution are given. The results of the study provide control basis for reducing transformer noise.

MODELLING AND ANALYSIS OF FUEL ASSEMBLY VIBRATIONAL MODES IN PWRS USING SIMULATE-3K

Some of the KWU pre-KONVOI PWRs operating across Europe saw a systematic increase in the neutron noise levels over several cycles in the last decade, and subsequently, core internals’ movements, especially vibrations of fuel assemblies with specific designs were identified as one of the plausible causes. Therefore, it is important to develop computational methods that can allow to investigate and predict the reactor noise response to fuel assemblies vibrations. To this aim, the 3D nodal reactor dynamics code SIMULATE-3K is used at PSI with a special module called the ‘assembly vibration model’ that imitates time-dependent motions of fuel assemblies by dynamically modifying the water-gaps surrounding the laterally moving fuel assemblies. The varying water-gaps are represented by the variation in the corresponding two-group macroscopic cross sections generated using the lattice code CASMO-5 in 2D. The studies conducted so far to assess the methodology for full core noise simulations were based on assuming vibrations of a clamped-free cluster of fuel assemblies that are unsupported from both ends. However, as this represents a non-physical movement, further developments were made at PSI to allow simulating more realistic movements of fuel assemblies such as the cantilevered mode vibration. The updated methodology, along with evaluations of the simulated noise response to realistic vibration modes, is presented in this paper. Results show that, as expected, the radial and axial neutron noise behaviour follow the vibration pattern of the imposed time-dependent axial functions corresponding to the natural oscillation modes of the fuel assemblies, thereby providing confidence in the application of the developed methodology for numerical neutron noise analyses of the PWR cores.

Leveraging non-contrast head CT to improve the image quality of cerebral CT perfusion maps.

Purpose: The purpose of our work is to present a method that utilizes high-quality non-contrast CT (NCCT) images to reduce the noise of CT perfusion (CTP) baseline images to improve the visibility of infarct core in cerebral blood volume (CBV) maps. Methods: First, a theoretical analysis of the CTP imaging system was performed to demonstrate that for both deconvolution- and non-deconvolution-based CTP systems. The noise of CBV maps is profoundly influenced by the baseline image noise. Consequently, baseline noise reduction is extremely effective in improving the contrast-to-noise ratio (CNR) of ischemic lesions in CBV maps. Second, a method was proposed to fuse the freely available NCCT images with the original CTP baseline images. An optimal weighting scheme was derived such that the noise of the fused baseline image is minimized. Third, the impact of the proposed NCCT-baseline fusion method was investigated using five in vivo canine subjects with different infarct core sizes. NCCT and CTP scans were performed following a clinical stroke CT imaging protocol using a 64-slice MDCT. Two of the subjects also received a diffusion-weighted imaging scan using a 3T-MRI scanner to establish the reference diagnosis for the infarct core. Results: For all five canine subjects, the proposed method led to lower CBV noise and better conspicuity of the infarct core. Compared with a standard CTP postprocessing method, the proposed method reduced the CBV noise standard deviation by and increased the CNR of infarct core by ( ). Conclusions: By utilizing the high-quality NCCT images to reduce CTP baseline image noise, the quality of CBV maps and the conspicuity of ischemic infarct core can be effectively improved. The proposed method can be readily implemented with minimal interruption to the existing clinical workflow.

Magnetostrictive Characteristics of the Grain-Oriented Electrical Steel in an Epstein Frame Magnetized with a DC Biased Magnetic Field

The presence of direct current (dc) biased magnetic field enhances the vibration and noise in the transformer cores due to magnetostrictive effect in the grain-oriented electrical steel laminations. Based on an Epstein frame, an experimental setup was built to measure the in-plane magnetostriction, the principal magnetostriction was computed under a dc bias, and the influence of dc bias magnetic field on the magnetostrictive property of electrical steel sheet was investigated. A model based on a back propagation neural network (BPNN) method assisted with the Levenberg–Marquardt algorithm was proposed to describe the magnetostrictive behaviour in the presence of dc bias. Finally, the BPNN model was verified by comparing the measured magnetostriction and the computed one. This research is helpful to make an accurate estimation to deformation of iron core under a dc bias.

Modelling and analysis of fuel assembly vibrational modes in PWRs using SIMULATE-3K

Some of the KWU pre-KONVOI PWRs operating across Europe saw a systematic increase in the neutron noise levels over several cycles in the last decade, and subsequently, core internals’ movements, especially vibrations of fuel assemblies with specific designs were identified as one of the plausible causes. Therefore, it is important to develop computational methods that can allow to investigate and predict the reactor noise response to fuel assemblies vibrations. To this aim, the 3D nodal reactor dynamics code SIMULATE-3K is used at PSI with a special module called the ‘assembly vibration model’ that imitates time-dependent motions of fuel assemblies by dynamically modifying the water-gaps surrounding the laterally moving fuel assemblies. The varying water-gaps are represented by the variation in the corresponding two-group macroscopic cross sections generated using the lattice code CASMO-5 in 2D. The studies conducted so far to assess the methodology for full core noise simulations were based on assuming vibrations of a clamped-free cluster of fuel assemblies that are unsupported from both ends. However, as this represents a non-physical movement, further developments were made at PSI to allow simulating more realistic movements of fuel assemblies such as the cantilevered mode vibration. The updated methodology, along with evaluations of the simulated noise response to realistic vibration modes, is presented in this paper. Results show that, as expected, the radial and axial neutron noise behaviour follow the vibration pattern of the imposed time-dependent axial functions corresponding to the natural oscillation modes of the fuel assemblies, thereby providing confidence in the application of the developed methodology for numerical neutron noise analyses of the PWR cores.

Numerical Study of Entropy Wave Evolution within a HPT Stage

Component reciprocal interaction and aero-thermal coupling are critical aspects in modern turbomachinery design. Combustors and highpressure turbine (HPT) interaction is extremely critical due to the compact and lightweight system design. In this context, computational and experimental analyses are thus necessary to study the interaction of the high temperature gas coming from combustor systems and entering the turbine in order to avoid engine mis-operations and to lower the indirect core noise generation. This paper presents a numerical study of pulsating temperature distortion (entropy wave) evolution within a high pressure turbine stage. Four different clocking positions between the 11 temperature spots and the 22 stators have been studied. The numerical results, obtained by URANS computations (TRAF code) and by a dedicated post-processing based on Fourier coefficients, have been compared with experimental measurements coming from the Laboratorio di Fluidodinamica delle Macchine (LFM) of the Politecnico di Milano (Italy) where the HP stage rig is located. The excellent agreement between numerical results and experimental acquisitions confirms the accuracy of the numerical approach. Such results also suggest recommendations for the thermal design of the rows and are the main prerequisite for the study of the indirect core noise generation.

An intelligent paradigm for denoising motion artefacts in ECG preprocessing: smart filters

A well-recorded ECG contains complete information of various heart diseases. The detection of cardiac diseases encompasses ECG signal pre-processing, feature extraction and classification of the cardiac disease from the detected abnormality. A minute change in ECG due to noise signals changes the characteristics of ECG which results in a wrong diagnosis of the heart disease. The main focus of this paper is on developing and implementing a novel smart filter design for filtering the core noise signals that distort the original ECG. The core noise signals are identified as power line interference (PLI), baseline wander and electromyography (EMG). The comparison of the proposed filter design in terms of signal to noise ratio and power spectral density indicates that the proposed filter design has a good response characteristic for noise filtration. The eradication of these noise signals helps to achieve accurate identification of heart disease and makes the life of physicians easier.