Calculation Of Noise Research Articles

Impact of buildings, forests and cliffs on aircraft noise mapping: Case study

Current best practice aircraft noise calculations primarily focus on strategic noise mapping to assess compliance with legal noise limits. To date, the effects of shielding by buildings or reflections from buildings, forests or cliffs have not been considered in noise mapping, despite their potential impact on results, particularly in mountainous and/or densely built urban areas. In this study, the effects of shielding by buildings and reflections from buildings, forests and cliffs on aircraft noise results were assessed. Calculations were performed with the sonAIR simulation tool for a residential area close to the runway of a military airfield in a mountain valley in Switzerland. The calculations revealed that shielding and reflections may locally strongly affect the results. While this may yield valuable insights for special investigations, calculations without accounting for these effects are still recommended for large-scale noise mapping, to obtain a better overview of the noise exposure and legal compliance.

Linewidth Measurement of a Narrow-Linewidth Laser: Principles, Methods, and Systems.

Narrow-linewidth lasers mainly depend on the development of advanced laser linewidth measurement methods for related technological progress as key devices in satellite laser communications, precision measurements, ultra-high-speed optical communications, and other fields. This manuscript provides a theoretical analysis of linewidth characterization methods based on the beat frequency power spectrum and laser phase noise calculations, and elaborates on existing research of measurement technologies. In addition, to address the technical challenges of complex measurement systems that commonly rely on long optical fibers and significant phase noise jitter in the existing research, a short-delay self-heterodyne method based on coherent envelope spectrum demodulation was discussed in depth to reduce the phase jitter caused by 1/f noise. We assessed the performance parameters and testing conditions of different lasers, as well as the corresponding linewidth characterization methods, and analyzed the measurement accuracy and error sources of various methods.

Calculation of the Worst-Case Voltage Noise for a Power Distribution Network Based on Ramp Current

Calculation of the Worst-Case Voltage Noise for a Power Distribution Network Based on Ramp Current

Integrated design optimization of ducted lift fan for lift enhancement and noise reduction based on nested NFFD control body

In order to enhance the aerodynamic performance and reduce the aerodynamic noise of the coaxial dual-rotor ducted fan, this paper proposes a stepwise optimization strategy based on nested NFFD (Nurbs-Based Free-Form Deformations) control body parameterization. This strategy takes into account the optimization of aerodynamic performance, which involves significant deformations, and noise reduction, which requires fine deformations. By doing so, it effectively addresses the issue of drastically increased computational complexity and time consumption associated with conventional multi-objective optimization methods. By designing the aerodynamic shape of the blades, along with aerodynamic performance parameter calculation and aerodynamic noise calculation modules, it is possible to achieve lift enhancement and noise reduction for the ducted fan. The numerical simulation results demonstrate that the flow field over the optimized blade surface is improved significantly. The lift has increased from 3.45N to 3.54N, resulting in a 2.6% enhancement. Additionally, the noise level has decreased from 72.33dB to 69.52dB, achieving a noise reduction of 2.81dB.

Magnetic noise modeling and calculation of Fe-based nanocrystalline in the SERF magnetometer considering temperature effects

The Fe-based nanocrystalline has been widely used in the innermost magnetic shielding of the spin-exchange relaxation-free (SERF) magnetometer due to its high permeability and low magnetic noise, which are significant factors limiting the sensitivity and accuracy of the measurements. However, the operating temperature of the inner shielding layer is around 80°C, and temperature has a significant impact on the magnetic noise of Fe-based nanocrystalline. To precisely analyze the magnetic noise of the Fe-based nanocrystalline in the SERF magnetometer, we first numerically simulate the 1K107 Fe-based nanocrystalline magnetic shielding barrel using the finite element method (FEM). Then, a variable-temperature dynamic Jiles-Atherton (VTDJA) model is proposed. The losses of 1K107 under various temperature are separated. The magnetic noise of 1K107 is computed using the Fluctuation-Dissipation theory. Finally, the magnetic noises of 1K107 at 25℃ and 80℃ are measured by setting up an experimental test system. Results show that the simulated deviation of the magnetic noise at 80°C and 25°C is 32 %, and the actual measured deviation is 48 %. The errors between simulated and measured magnetic noises at 25°C and 80°C are 5.29 % and 6.54 %, respectively. This study provides a novel method for the performance optimization of the SERF magnetometer.

Analysis and measurement of magnetic noise in multilayer magnetic shielding system combined with mu-metal and ferrite for atomic sensors

The multilayer magnetic shielding system is widely used in atomic sensors. However, for miniaturized atomic sensors with volume limitations, such as spin-exchange relaxation-free (SERF) gyroscopes, the remaining environmental magnetic interference and mu-metal magnetic noise will affect the sensitivity of atomic sensors. In this study, we establish a comprehensive magnetic noise calculation model for the magnetic shielding system of a SERF gyroscope, which considers the influence of the environmental magnetic noise on the magnetic shielding and the coupling effect between different layers. For suppressing magnetic noise of the magnetic shielding system, the property of different ferrites was measured and compared, then the particle swarm optimization is applied to design the magnetic shielding structure. Finally, the experimental device is established for measuring performances of the magnetic shielding system per and post optimization. By comparison, radial and axial magnetic noise post optimization are decreased by 37% and 22%, respectively.

A mathematical‐boundary‐recognition domain‐decomposition Lattice Boltzmann method combined with large eddy simulation applied to airfoil aeroacoustics simulation

AbstractBeing a direct computational aeroacoustics method, Lattice Boltzmann method (LBM) has great potential and broad application perspective in the field of numerical simulation of aerodynamic noise due to its low dispersion and low dissipation. A series of numerical algorithms and the related improvements based on the standard LBM method are proposed and developed in this paper to adapt to the airfoil noise calculation with complex grid at middle‐high Reynolds number. First, a new mathematical‐boundary‐recognition algorithm based on Green's formula is proposed to deal with complex curved geometric models, which is validated by three‐element airfoil 30P30N benchmark. Then, in order to reduce grid redundancy and improve computing efficiency, the grid refinement technique of domain decomposition model (DDM) is adopted and also improved, which is verified by calculating the flow and sound fields around 2D and 3D cylinders at Reynolds number equal to 90,000. Finally, three different LES turbulence models are combined with the standard MRT‐LBM method, where different finite difference schemes are used to solve Reynolds stress tensor which is different from the traditional one. Through the direct acoustic numerical simulation of NACA0012 airfoil at Reynolds number equal to 200,000, the effects of Smagorinsky models and Wall‐adapting local eddy‐viscosity (WALE) model on aerodynamic noise prediction are compared and analyzed. Overall, the proposed methodology is shown to be appropriate for predicting the aerodynamic noise at low Mach number and can successfully simulate the generation and propagation of far field acoustics.

An aero-structure-acoustics evaluation framework of wind turbine blade cross-section based on Gradient Boosting regression tree

Under the rapid development of wind turbines, the rotor size has substantially increased in recent years. To meet the key design criteria, finding a trade-off between aerodynamic, structure and noise (ASN) impact becomes a challenging problem. The blade cross-section is the basic element of the blade, its outer contour is the airfoil profile that produces aerodynamic loads as well as noise, and the inner part is the supporting composite material that provides enough stiffness to balance the loads. Modifying local blade sections can adjust the rotors’ overall performance. However, in the work of blade-combined ASN optimization, the iterative process using traditional numerical simulation methods becomes extremely heavy. In this study, a sustainable database is created based on a large number of calculations of aerodynamic, structural and noise attributes at various cross-sections. Then a platform named AFML (Airfoil machine learning) for simultaneously predicting the comprehensive performance of the cross-section is constructed by using the integrated Gradient Boosting Regression Tree algorithm. Results show that the prediction accuracy of AFML is acceptable even for unseen inflow conditions. By calling the pre-trained AFML, ASN data of the cross-section can be immediately obtained, and the blade shape and inner structure can be updated quickly.

Machine Learning Aided Low-Order Predictions of Fan Stage Broadband Interaction Noise

A fast method for predicting turbofan fan-stage broadband interaction noise is being developed. The downstream propagating acoustic power in the bypass duct due to the response of the fan exit guide vane (FEGV) to fan wake turbulence is computed based on two-dimensional flat-plate cascade analysis and Green’s method. This study focused on using machine learning to define the fan wake parameters used as inputs to the FEGV response and noise calculation. Machine-learning algorithms are being trained using computational fluid dynamics results. This paper describes the accuracy of machine learning given the available rotor wake data. Further, the effect of errors in the learned input data on the acoustic prediction was studied. Based on this study, the method shows great promise.

Hybrid NVH modeling approach: High quality of NVH results enables psychoacoustic analysis of numerical computations

In the field of acoustics, the human perception of sound is often more important than the overall sound pressure level. The human perception is highly individual and is linked to how the user's expectations of the sound and the actual perceived sound match. Thus, generalization is difficult. However, psychoacoustic parameters that are developed and validated by means of jury tests are an established tool in the field of experimental measurements to quantify the human perception for specific acoustic phenomena like tonality, roughness, and loudness. Since the precision of numerical simulations results is continuously improving, these psychoacoustics parameters can be applied as well to the results of numerical simulation. In this Paper, the advantages of this approach are shown using the example of a numerical model of an e-bike. E-bikes have become increasingly popular in recent years, used for commuting, transporting loads or, in the case of e-mountain bikes, just for fun. As already mentioned, the acceptance of a sound is strongly linked to the expectations of the user. Since the electric drive unit of an e-bike is added to an acoustically known system, the user expects the sound to be quiet rather than dominant. Different e-bike analyses are presented using numerical and experimental methods. The numerical model used in this project predicts the sound generated by the electrical drive unit and radiated by the frame. For the calculation of airborne noise the distribution of velocities on the surface of the frame is used as an input, which is taken from a previous simulation of structure-borne noise. The model to simulate the structure-borne noise consists of a detailed representation of the carbon frame and simplified representations of different components such as battery, fork etc. With the help of the numerical model, different combinations of frame and electrical drive can be analyzed and compared by psychoacoustic parameters. The validity of the approach is shown by means of data from experimental measurements.

Patterns of the noise level change at different speeds for mixed traffic flows

The study describes the problems of determining the normative levels of traffic noise on city main streets. The main statements and preliminary laws that are taken into account when determining the acoustic characteristics of the urban environment in the current building regulations are considered. It was established that the main factor that determines the acoustic load on city streets is the type of covering. The dynamics of the level of traffic noise of mixed flows, taking into account different types of coverage at different speed regimes, are also determined. The obtained results partially differ from the calculated values, and therefore are relevant for the development of modern norms and rules for the calculation of traffic noise on city highways.

Fast simulation of neutron noise using the Transient Fission Matrix approach and validation on the CROCUS reactor

This article presents the development of a neutron noise calculation technique with a reduced calculation time based on the TFM (Transient Fission Matrix) approach. The latter contains different information such as the system transfer function (fission and absorption probability density functions and corresponding neutron multiplicity) of prompt and delayed neutrons, and the corresponding propagation time. This information is used to reconstruct neutron showers based on precursor decays up to the shower disappearance by absorption, leakage or delayed neutron precursor creation. Then pseudo-detectors such as fission chamber count rate histograms are reconstructed from these neutron showers and the αprompt is calculated from the cross-correlation function. A very good agreement has been obtained on the uranium-fueled light water reactor CROCUS between the model developed and the reference value.

Aerodynamic noise from a high-speed train bogie with complex geometry under a leading car

Among the various aerodynamic noise sources associated with high-speed trains, the bogie regions, and particularly the leading bogie, contribute most to the overall noise. To control this noise, insight into the noise generation mechanisms is imperative but relevant studies are limited due to the difficulties of simulating the flow in regions with complex geometry. An investigation is presented of the aerodynamic noise from a bogie under the leading car of a high-speed train using Delayed Detached Eddy Simulation method. A hybrid grid system is utilized to simulate the flow field, which provides input for the far-field noise calculations based on the Ffowcs Williams and Hawkings equation. Analysis shows that the outer bogie components experience large pressure fluctuations as they are immersed in the shear layer detached from upstream, which is therefore identified as playing a critical role in the noise generation. The resulting noise spectra are broadband and dominated by low frequencies. Compared with the bogie, the bogie cavity and train nose emit 5 dB greater sound power for the current geometry. This study improves understanding of the mechanisms behind the generation of aerodynamic noise in train bogies and lays the foundations for future studies of train bogie noise reduction.

Orthotropic Material Parameters Identification Method of Stator Core and Windings in Electric Motors

The accurate equivalent orthotropic material parameters (OMPs) of stator core and windings are the basis of modal analysis in electric motors and the key to precisely predicting electromagnetic vibration and noise. A CNN (convolutional neural network)-MPGA (multi-population genetic algorithm) based OMPs identification method of stator core and windings for electric motors is proposed in this study. Firstly, the surrogate models between the material parameters and eigenmode frequencies are trained with CNN for stator core and windings. Then, MPGA is utilized to identify the equivalent OMPs of stator core and windings combined with tested eigenmode frequencies. Finally, two different classes of electric machines are selected to verify the method. The CNN-MPGA based method in this study can quickly and accurately identify OMPs of stator core and windings. It is significant for the calculation and suppression of electromagnetic noise for electric motors.

Study on noise calculation method considering gear and flap conditions during aircraft landing

Looking at recent aircraft noise by component, engine noise has become quieter, while aerodynamic noise such as airframe noise, gear, and flap noise has become relatively louder. Gradually, it has become necessary to take aerodynamic noise into account appropriately. Therefore, using the regression calculation results of aircraft noise by J-FRAIN, we examined to modify performance data and Noise-Power-Distance (NPD)data, which represent component changes consistent with the AERC model, an existing aircraft noise model in Japan. For performance data, gear and flap parameters were added to the already used altitude, speed, and thrust. For NPD data, correction NPD data were prepared for the gear and flap changes using the J-FRAIN calculation results. Using these data, noise calculations were performed considering gear and flap status during aircraft landing. In addition, aircraft landing noise was measured under a flight path of about 30 km around Narita Airport in Japan to confirm the validity of the noise calculation results. Some measured aircraft gear and flap status were obtained and the results of the matched noise calculations were compared with the measured noise.

Study on the design values of windows for high-rise residential buildings on street level based on Odeon simulation calculations

With the development of road traffic, the surrounding residents are inevitably disturbed by the increasing noise. Long-term exposure to noise can affect the daily lives of residents. Installing sound-insulating windows is a reliable way to reduce indoor noise, so it is vital to choose the right one. However, the weighted sound insulation measured in the laboratory cannot be used directly in predictive calculations of indoor noise. This study uses Odeon to simulate the outdoor and indoor sound fields. The simulated data is analyzed based on the formulae in the Beijing Local Standards. The results show a correction of -1.3 to 0.6 dBA for window design values in indoor rough decoration condition and -0.6 to 1.3 dBA in indoor fine decoration condition. This study provides a useful method and reference for environmental assessment work.

Open-source software to calculate industrial, railway, and road traffic noise

Dutch noise legislation provides instructions and formulas to calculate noise exposure levels on a similar level to Cnossos or ISO 9613-2. The instructions are implemented in commercially available software packages. Each implementation includes a pathfinder and a sound propagation/attenuation module. Whilst the attenuation is described in detail in the legislation, the pathfinder is not and its design is left to the software company. Currently there are only proprietary, closed-source implementations available. That is going to change. Based on a previously closed-source solution, we are working towards an open-source, national implementation to calculate noise levels based on 3D model input. We implemented the updated Dutch calculation method and improved the pathfinder. For example, this now includes sloped barriers. Only the calculation core is part of this project: the development of a graphical user interface is not planned, but can be provided by others. Also, other implementations of the Dutch noise calculation directive can still co-exist next to our open-source solution, since the legislation only specifies the instructions and has no requisite for a specific implementation. In this paper we will discuss the open-source implementation, the impact on noise modelling in the Netherlands and its potential applications outside of the Netherlands.

How to ensure reliable noise calculations with Cnossos-EU

The paper will discuss how to use the Cnossos-EU model in a consistent way across different users and software tools. This is based on a study related to implementation of Cnossos-EU in Norway. In the study a noise mapping task was given to two independent consultancy firms with long experience in the field. For some areas, the results show large differences between the two, up to 10 dB and more, even when the same method and same software tool was used. Comparisons revealed that different understanding of input data, different parameter settings in the calculation, and different company practices could explain the differences in the results. The study revealed a clear need for guidelines to ensure common assessment of noise mapping tasks. The paper will describe user guidelines to overcome this kind of problem in context of Cnossos-EU calculations. The guidelines are aimed for the Norwegian consultant industry.

Magnetic noise analysis for small magnetically shielded room in different environmental magnetic fields

The compact high-performance magnetically shielded room (MSR) provides near-zero magnetic field environment for low-cost magnetoencephalography (MEG) measurements. Predicting the level of magnetic noise in the MSR under different magnetic field holds significant importance for the deployment of MEG systems. In this paper, the magnetic noise of MSR in different operational conditions is studied. The magnetic noise in MSR is modeled as residual environmental noise, material one, and additional one. A quantitative model for magnetic noise calculation is established, leading to the definition of the Weak Shielding Factor (WSF), which establishes a relationship between the environment magnetic noise and MSR one. Verification experiments are conducted using a compact MSR, a magnetically shielded box, and a cylindrical magnetically shielded bucket. The average magnetic noise error between calculated and measured values in 1–100 Hz range for the three shielding structures are 8.29%, 12.33%, and 7.50%, respectively, which shows the effectiveness of the proposed method.

Parametric Doppler correction for wayside array acoustic signal via short-time reconstruction

The trackside acoustic detection system (TADS) plays a vital role in vehicle bearings condition monitoring. However, the inevitable Doppler distortion embedded in collected data will bring considerable difficulties to defect inspection and diagnosis in the system. The distortion elimination approaches mainly achieve spectrum recovery based on time-domain interpolation resampling (TIR) in a data-driven way. These will be further limited by the requirement to signal to noise ratio (SNR) or calculation speed. Considering the principle of wayside acoustic physical model and the benefits of array acoustic in practice, this study proposes an adaptive parametric Doppler correction (PDC) scheme based on short-time reconstruction (STR), including perception modeling, inverse perception optimization and Doppler correction. Firstly, mathematical modeling with multiple perception operators, including acoustic amplitude modulation operator, frequency modulation operator and array time delay operator, a wayside acoustic physical model based on array sensing is established. Secondly, through the corresponding inverse multiple perception operators, a transition signal with frequency-domain energy concentrated is obtained for the optimal moving parameters searching. Thirdly, within short-time sequence segments of the sound source, the real-time position recovery is realized via the proposed STR with formulaic propagation delay compensation. Theoretically, it can be seen that the proposed PDC scheme can simultaneously recover the amplitude, frequency distribution and phase of the Doppler signal, which can be applicable to all wayside acoustic diagnosis scenarios. With the correction analysis of simulation and experimental array defect signals, it can be confirmed that the proposed STR-based PDC scheme is effective for Doppler signal recovery in high fidelity, and has great potential to the real-time diagnosis of TADS.