Main Noise Research Articles

Numerical determination to loaded tooth contact performances in consideration of misalignment for the spiral bevel gears

In order to meet demands of low noise and strong strength from their transmission of spiral bevel gears, loaded tooth contact analysis (LTCA) technique has become an increasingly access to determining the loaded tooth contact performances directly affecting the above demands. Moreover, the misalignment always is a main noise factor in the actual manufacturing and can directly affect the loaded tooth contact performances. Distinguish with the conventional simulated loaded tooth contact analysis (SLTCA) based on finite element simulation software package, a numerical loaded tooth contact analysis (NLTCA) method in consideration of the misalignments is presented for the spiral bevel gears. First, an improved computation model is established to perform the tooth contact analysis (TCA) considering the misalignments. Moreover, the principal curvature of contact points is also determined as the input for the proposed numerical LTCA. In the consideration of influences of the different misalignment, the loaded tooth contact performance items such as loaded contact force, loaded contact pattern, elastic contact deformation and loaded transmission error are calculated, respectively. Finally, the numerical instance including the results from SLTCA is given to verify the proposed method.

Near-surface scattered waves enhancement with source-receiver interferometry

Near-surface scattered waves (NSWs) are the main noise in seismic data in areas with a complex near surface and can be divided into surface-to-surface scattered waves and body-to-surface scattered waves. We have developed a method for NSW enhancement that uses modified source-receiver interferometry. The method consists of two parts. First, deconvolutional intersource interferometry is used to cancel the common raypath of seismic waves from a near-surface scatterer to the common receiver and the receiver function. Second, convolutional interreceiver interferometry is used to compensate the common raypath of seismic waves from the common source to the near-surface scatterer and the source function. For an isotropic point scatterer near the earth’s surface in modified source-receiver interferometry, a body-to-surface scattered wave can be reconstructed by constructive interference not only among three body-to-surface scattered waves but also among a body-to-surface scattered wave and two surface-to-surface scattered waves; a surface-to-surface scattered wave can be reconstructed by constructive interference not only among three surface-to-surface scattered waves but also among a surface-to-surface scattered wave and two body-to-surface scattered waves. According to stationary phase analysis based on the superposition principle, we have developed a so-called dual-wheel driving configuration of modified source-receiver interferometry for enhancing NSWs in the data of conventional seismic exploration. The main advantages of the scheme are that (1) it can be used to enhance NSWs without the need for any a priori knowledge of topography and near-surface velocity, (2) it can be used to reconstruct NSWs from real sources to real receivers, including 3D near-surface side-scattered waves, and (3) it can be applied to conventional seismic data with finite-frequency bandwidth, spatially limited and sparse arrays, different source and receiver functions, and static correction. Numerically simulated data and field seismic data are used to demonstrate the feasibility and effectiveness of the scheme.

Noise Prediction and Control in a Cruise Ship

Based on the statistical energy analysis (SEA) method, the noise prediction of the cruise ship’s cabins was analyzed and the results show that the noise energy of the engine room (ER) is the highest in the whole cabins, and the energy propagates in the direction of the ship’s bow and stern with the ER centered. In order to reduce the noise of the ER, the main characteristics of the noise source were analyzed. The contribution rate of each noise source to the ER and the input power of the diesel engine structure-borne and air-borne noise to the ER were analyzed and calculated. The analysis shows that air-borne noise of diesel engine is the main noise source in the ER. Then the acoustic enclosures were applied to the diesel engine to control air-borne noise and the sound insulation effect of the acoustic enclosure under different working conditions was studied. The results shows that in the case of only considering the air-borne noise of the diesel engine, the sound pressure level(SPL) of the ER is reduced by about 36dB(A)∼62dB(A). In the case where all excitations are loaded, the SPL of the cabin is reduced by an average of about 10.8dB (A), which shows a better sound insulation effect.

The influence of large foundation arrangement on underwater radiated noise of underwater vehicle engine compartment

Mechanical vibration is the main noise source of underwater vehicle. The foundation of the main power is an important pathway of mechanical noise. Large size foundation of the power not only affects the vibration transmitted from the power to the hull structure, but also affects the vehicle shell radiation area and radiation efficiency, thus affecting the radiation noise of underwater vehicle. Based on the study of the influence of the large size foundation arrangement on the radiated noise of underwater vehicles, two new types of foundation arrangement were proposed. The foundation could meet the requirements on the acoustic performance, and could greatly reduce the radiation surface area of the shell and reduce the radiated Sound Pressure. To the power compartment general layout and support function, three foundation layout schemes such as continuous style, large span style and bulkhead support style in the typical excitation of power equipment were designed. Further way, far field underwater radiation noise of the compartment was numerically calculated. The results show that bulkhead support style can effectively reduce underwater acoustic radiation of the compartment shell on the premise of the meet the weight control and impedance characteristics.

Numerical study of potential application of active suction and blowing through blade tip perforation to reduction of helicopter rotor thickness noise

The article explains a new concept (called here ATNC – active thickness noise control) of the application of surface transpiration to the reduction of helicopter main rotor harmonic noise. The ATNC method is based on an introduction of four cavities covered by perforated plates (connected to pressure reservoirs) at the leading and trailing edges of the outer 20% of blade span. For an exemplary, two-bladed (NACA 0012 airfoil) model helicopter rotor of Purcell in low-lifting, hover conditions (tip Mach number MaT = 0.66 and collective θ = 1.5° ) the results of numerical simulations, based on the SPARC code (Spalart-Allmaras turbulence and Bohning-Doerffer transpiration models), prove that the acoustic pressure fluctuations are significantly reduced by ATNC in the near-field of blade tip. The peak amplitude is attenuated by more than 45%, with a reduction of the Overall Sound Pressure Level OASPL by 3.4 dB. It is shown also that the venting has not only a large impact on the acoustic radiation, but also on the aerodynamic performance of the rotor, expressed in terms of the torque penalty of 38%. The ATNC method proves to be a promising candidate as a mean of helicopter rotor thickness noise control, but not in the current arrangement.

Problem of the Community Noise Reduction for Aircraft with Open Rotor Engines

This paper considers the problem of community noise for an aircraft with contra-rotating open rotors. Main noise sources are described. Basic methods of noise reduction are considered. A noise reduction method by increasing the axial spacing between propellers is proposed from the test results.

Characterization and optimization of a tapered amplifier by its spectra through a long multi-pass rubidium absorption cell.

We present a method to characterize and optimize a tapered-amplifier laser system (TALS) by its spectral quality through a long multi-pass rubidium absorption cell. A thermal vapor cell is used to measure the non-resonant spectrum of TALS, including the broadband amplified spontaneous emission (ASE), which is its main spectral noise. This method gives a simple quantified measurement to optimize various working parameters of a TA, including current and temperature online. It can as well be used to compare various TA chips based on their usage time during our precision measurement experiments. The results of this method are compared and found in sync with traditional methods of Fabry-Perot cavity and beat measurements. Such characterization and optimization are important for noise control in atom interferometers, atomic clocks, and other atomic manipulations. It can very well be used for investigating nonlinearity and ASE inside amplifying chips and can be utilized in other applications of ASE using bioimaging.

An alternative close-proximity test to evaluate sound power level emitted by a rolling tyre

The noise emission of a rolling tyre is produced by different physical mechanisms generated during the tyre-road interaction, being the main noise source of a vehicle when driving at high speeds. Diverse measurement methods can be found in the literature to assess the rolling noise emission. In that sense, the close-proximity (CPX) method allows to evaluate tyre/road sound level with at least two microphones operating in the close field of the test tyre. This paper presents a new methodology, based on the CPX method, which allows assessing the sound power level of the rolling tyre by introducing some changes in the traditional close-proximity test. The methodology (named A-CPX) has been analytically and experimentally validated, and is finally used to obtain the total tyre/road sound power level emitted by the whole set of tyres of a vehicle.

A low phase noise super–harmonic coupling quadrature VCO using an additional double frequency oscillator

In this paper, using an additional oscillator that operates at twice the main output frequency, super–harmonic coupling is created between two LC cross–coupled oscillators. The additional oscillator output signals are injected into the two main oscillators in a special way, such that in addition to forcing those oscillators to work in quadrature mode, a tail current shaping technique is performed on them, through the same circuit path. As a result, the main oscillators output phase noise is reduced. The second harmonic signals with the help of two additional NMOS transistors shape the gate voltages and consequently the drain current of the tail transistors. The quadrature mode operation of the proposed circuit is mathematically proved and the intrinsic tail current shaping behavior of it is analyzed. The proposed QVCO is designed in a 0.18 μm CMOS technology with a supply voltage of 1.8 V and a total power consumption of 4.4 mW at 2 GHz center frequency with 5.5% tuning rage. Simulation results confirm the proposed quadrature mode operation. It also shows the phase noise of −128.1 dBc/Hz for the proposed QVCO at 1 MHz offset and 1.92 GHz carrier, which is 9.3 dB better than that of the conventional Parallel (P)–QVCO. The maximum phase error for 0.5% I and Q tank capacitor mismatch is 1.47°.

Searching for dark matter annihilation from individual halos: uncertainties, scatter and signal-to-noise ratios

Individual extragalactic dark matter halos, such as those associated with nearby galaxies and galaxy clusters, are promising targets for searches for gamma rays from dark matter annihilation. We review the predictions for the annihilation flux from individual halos, focusing on the effect of current uncertainties in the concentration-mass relation and the contribution from halo substructure, and also estimating the intrinsic halo-to-halo scatter expected. After careful consideration of recent simulation results, we conclude that the concentrations of the smallest halos, while well-determined at high redshift, are still uncertain by a factor of 4–6 when extrapolated to low redshift. This in turn produces up to two orders of magnitude uncertainty in the predicted annihilation flux for any halo mass above this scale. Substructure evolution, the small-scale cutoff to the power spectrum, cosmology, and baryonic effects all introduce smaller, though cumulative, uncertainties. We then consider intrinsic variations from halo to halo. These arise from variations in concentration and substructure, leading to a scatter of ∼2.5 in the predicted annihilation luminosity. Finally, we consider the problem of detecting gamma rays from annihilation, given the expected contributions from other sources. We estimate the signal-to-noise ratio for gamma-ray detection as a function of halo mass, assuming that the isotropic gamma-ray background and cosmic rays from star formation are the main noise sources in the detection. This calculation suggests that group-scale halos, individually or in stacks, may be a particularly interesting target for the next generation of annihilation searches.

Mixed Noise Removal Algorithm Combining Adaptive Directional Weighted Mean Filter and Improved Adaptive Anisotropic Diffusion Model

A mixed noise removal algorithm combining adaptive directional weighted mean filter and improved adaptive anisotropic diffusion model is proposed. Firstly, a noise classification method is introduced to divide all pixels into two types as the pixels corrupted by impulse noise and the pixels corrupted by Gaussian noise. Then an adaptive directional weighted mean filter is developed to remove impulse noise, which can adaptively select the optimal direction template from twelve direction templates and replace the gray level of each impulse noise corrupted pixel by the weighted mean gray level of pixels on the optimal direction template. Finally, an improved adaptive anisotropic diffusion model is developed to remove Gaussian noise in the initial denoised image, which can finely classify image features as smooth regions, edges, corners, and isolated noises by characteristic parameters and variance parameter and conduct adaptive diffusion for different image features by designing reasonable eigenvalues of diffusion tensor. A large number of experimental results show that the proposed algorithm outperforms many existing main mixed noise removal methods in terms of image denoising and detail preservation.

Complexity Study on the Unsteady Flow Field and Aerodynamic Noise of High-Speed Railways on Bridges

To study complexity distributions of unsteady flow field and aerodynamic noise of a high-speed railway on bridges, an aerodynamic noise model of a railway was obtained. Meanwhile, detailed structures such as 6 bogies, 3 air conditioning units, 1 pantograph fairing, and 1 pantograph were considered. Numerical simulation was conducted to flow fields around the high-speed railway running on the bridge under a crosswind-free environment, with running speed of 350 km/h. Hence, unsteady flow behavior characteristics of the complete high-speed railway were obtained. Numerical simulation was conducted to noises of the railway on the bridge in combination with detached eddy simulation and acoustic analogy theory. Meanwhile, the broadband noise model was used for the quantitative analysis on distribution characteristics of the dipole noise source and quadrupole noise source of the high-speed railway on the bridge. Studied results proved that aerodynamic noise of the railway was caused by eddy shedding and fluid separation. Main noise sources of the high-speed railway include areas such as pantographs, train head streamline, bogies, windshield, and an air conditioning unit. Maximum sound pressure level and average sound pressure level of the high-speed railway on the bridge were 2.7 dBA and 2.3 dBA, respectively, more than those of the high-speed railway on a flat ground. On the bridge, the maximum sound pressure level of the pantograph on the bridge was 3.1 dBA larger than that on the flat ground. In addition, incoming flows of the high-speed railway on the bridge had greater impacts on aerodynamic noises around the railway compared with those of wake flows. Meanwhile, in directions of incoming flows and wake flows, linear relationship was between the sound pressure levels of noise monitoring points which had different distances from the train head nose and the logarithm of the distances.

Overview of active and passive systems for the turboprop modern generation

Nowadays, one of the main marketing objectives of the new generation of turboprop aircrafts is the noise control to enhance the internal comfort. The propellers represent in fact the main noise source whose amplitude and frequencies depend on some design parameters such as its rotational angular speed, number of blades, power at shaft generating aircraft thrust and blades geometry. The higher energy levels are within the low-frequency region, corresponding in particular to the first blade passing frequency and its harmonics. The design goal is therefore to increase the passenger comfort level by controlling the propeller tonal noise and related vibrations. The present paper is aimed at discuss some relevant technological solutions to minimize the fuselage internal noise field at the passengers positions at each of the first three tones of the propeller load as well as due to other external aero-acoustic sources.

Investigation of the Acoustical Environment of the Elderly’s Living Place

A questionnaire survey was conducted in the residential quarters of Guangzhou, for which 582 elderly people over 60 years old were randomly recruited. The hearing impairment of the participants was evaluated using the Hearing Handicap Inventory for the Elderly (HHIE), The participants’ subjective responses to the acoustical environment of their living place and the impact of the living acoustical environment (LAE) on the participants were investigated. The results show that the participants with a low HHIE score and no hearing impairment evaluated their LAE more favourably, and they considered that the effect of the LAE on their daily life was weak. However, those with a high HHIE score and severe hearing impairment evaluated their LAE poorly, and considered its effect on their daily lives to be significant. For the elderly, the worse the hearing is, the higher their demand for a better LAE. Traffic, construction, residential quarters, and noise from next door or upstairs neighbours were the main noise sources in the elderly’s living places, and traffic noise, construction noise, and noise from next door and upstairs were the most influential sources. 28.9% of the respondents had trouble hearing what their family said in their living place. The elderly without hearing impairment considered that continuous noise was the main reason that they could not hear what their family said in their living place, while those with hearing impairment believed that their own hearing problem was a contributing factor.

Acoustic energy harvesting using piezoelectric generator for railway environmental noise

High-speed trains have a sustained high-noise level for long periods during operation. Although such high-noise levels are effective for acoustic energy harvesting, a practical design for an acoustic energy harvesting system from a high-speed train is lacking. In this study, the design of an energy harvesting system was implemented utilizing noise from a high-speed train during practical operation. We investigated the noise generated from a high-speed train and derived the characteristics of the main noise sources. The results confirmed that low-frequency noise of 50–200 Hz was generated in the passenger, cab, and between car sections. Results from this investigation were used to design a Helmholtz resonator for a target noise of 174 Hz based on a theoretical model. Moreover, numerical simulation was conducted using sound source speakers to investigate vibrations in the walls of the resonator. Finally, energy harvesting experiments were conducted using various types of piezoelectric elements such as rectangular and circular plates. Experimental results indicate that approximately 0.7 V was generated for an incident sound pressure level of 100 dB using a large rectangular plate. Such power level is sufficient to power a variety of low-power electric devices.

Study on vibration and noise characteristics of rounded-jointed silent chain system

Vibration and noise are the important factors to limit the transmission performance of the silent chain. In order to improve the vibration and noise characteristics of the silent chain system during the operation, the multi-platform jointed analysis method is applied to research the vibration and noise radiation of the rounded-jointed silent chain system. By building the three-dimensional model of rounded-jointed silent chain system, the vibration response analysis is performed to obtain the resonanceparameters and structural deficiencies of the rounded-jointed silent chain system. On the basis of the vibration response analysis of the silent chain system, the acoustic radiation analysis is performed to obtain the main noise occurrence frequency and the location of the noise source, and the results are consistent with the vibration response analysis. This study provides an important basis for reducing the vibration and noise of the silent chain system and improving the overall performance of the silent chain system.

Effects of Crosswind Flight on Rotor Harmonic Noise Radiation

To develop recommendations for procedures for helicopter source noise characterization, the effects of crosswinds on main rotor harmonic noise radiation are assessed using a semi-empirical model of the Bell 430 helicopter. Crosswinds are found to have a significant effect on blade-vortex interaction (BVI) noise radiation when the helicopter is trimmed with the fuselage oriented along the inertial flight path, resulting in a “slipped” flight condition. However, the magnitude of BVI noise remains unchanged when the pilot orients the fuselage along the aerodynamic velocity vector, “crabbing” for zero aerodynamic sideslip angle. The effects of wind gradients on BVI noise are also investigated and found to be smaller in the crosswind direction than in the headwind direction. The effects of crosswinds on lower harmonic noise sources at higher flight speeds are also assessed. In all cases, the directivity of radiated noise is somewhat changed by the crosswind. The model predictions agree well with a limited set of flight test data for the Bell 430 helicopter for cruise and approach flight conditions, both measured with and without crosswinds present. The results of this investigation would suggest that flight paths for future acoustic flight testing are best aligned across the prevailing wind direction to minimize the effects of winds on noise measurements when wind cannot otherwise be avoided.

ВОЛНОВОЙ ПАРАМЕТР КАК КРИТЕРИЙ В ОСНОВЕ МЕТОДА ИССЛЕДОВАНИЯ АКУСТИЧЕСКИХ ИСТОЧНИКОВ ПРИ СТАРТЕ РАКЕТ

The purpose of this work is to develop a method for determining the types of acoustic sources of radiation and their acoustic fields during the space rockets launch in the first seconds based on the wave parameter values. The main noise source during the space rocket launch is its propulsion system (PS). The cross-section of the nozzle is taken as the oscillation source. The theory of siren sound emission is based on the acoustic power calculation of a jet as a volume sound radiator or a radiator with a space velocity. In the model of a volumetric spherical radiator, the front of a spherical wave is a spherical surface, and the sound rays, according to the definition of the wave front, coincide with the radii of the sphere. As a result of the divergence of waves, the sound intensity decreases with distance from the source. The present work has a prospective character for clarifying the nature of the acoustic fields and for calculating the noise levels from the space rocket launch when designing the cosmodromes. In the requirements for the construction of such structures, the noise impact on the environment of infrasound radiation upon launching launch vehicles is identified. A method for determining the types of acoustic radiation sources during the space rocket launch and their acoustic fields has been developed. The method makes it possible to develop physical models of acoustic fields and apply known mathematical models to calculating their characteristics. The method is applicable for the study of acoustic emissions in the first seconds of the space rocket launch based on the determination of the wave parameter kR and allows us to provide valid data on the levels of sound pressure, intensity and acoustic power at specific points of airspace around the PS in the first seconds of the launch. The character of the acoustic wave radiation from a hole in a specific size gas flue has been studied. To calculate the acoustic characteristics, an algorithm and a program on Java programming language have been developed. Two models of acoustic field generation in the environment are described during the work of a rocket as a plane radiator and spherical waves, depending on the value of the wave parameter kR. A technique for calculating the noise of a remote control in the range for the first 1.5-4 seconds of the space rocket start time is developed

Experimental Analysis of Cyclical Dispersion in Compression-Ignited Versus Spark-Ignited Engines and Its Significance for Combustion Noise Numerical Modeling

As noise pollution remains one of the biggest hurdles posed by thermal engines, increasing efforts are made to alleviate the generation of combustion noise from the early design stage of the chamber. Since the complexity of both modern chamber geometries and the combustion process itself precludes robust analytic solutions, and since the resonant, highly three-dimensional pressure field is difficult to be measured experimentally, focus is put on the numerical modeling of the process. However, in order to optimize the resources devoted to this simulation, an informed decision must be made on which formulations are followed. In this work, the experimental cyclic dispersion of the in-cylinder pressure is analyzed in two typical compression-ignited (CI) and spark-ignited (SI) engines. Acoustic signatures and pressure rise rates (PRRs) are derived from these data, showing how while the preponderance of flame front propagation and dependency of previous cycle in SI engine noise usually calls for multicycle, more complex turbulence modeling such as large Eddy simulation (LES), simpler unsteady Reynolds-averaged Navier-Stokes (URANS) formulations can accurately characterize the more consistent pressure spectra of CI thermal engines, which feature sudden autoignition as the main noise source.

Analysis of operating noise characteristics and contribution for automotive seat backrest adjuster

Background/Objectives: This study involved basic research on operating noise in an automotive seat backrest adjuster through analysis of noise sources, noise source contributions, and seat pad noise reduction effects.Methods/Statistical analysis: The test product was a driver seat of 3300cc commercial sedan. First, basic data is obtained through analysis of driving mechanism of seat backrest adjuster. Based on this, vibration and noise characteristics were analyzed by operating test of backrest adjuster, and contribution analysis to noise sources was performed. Finally, by analyzing the effect of noise reduction on the seat pad, the effect of each noise source on the backrest operating noise was determined.Findings: First, it was confirmed that the low frequency fluctuation caused by the total noise is dependent on change in the load generated by eccentric rotation of the recliner gear. Therefore, it was found that the design of the recliner gear teeth was a decisive factor in controlling the motor load. Second, the 20th order (1,320Hz) of the DC geared motor was the main cause of operating noise, which was derived from friction noise of brush-commutator and torque ripple noise. This noise accounted for more than 55% of total operating noise. In addition, the 30th order amounted to approximately 18%. In other words, the harmonic components of the DC geared motor created most of the noise, and changing the brush material and reducing torque ripple is expected to significantly improve the overall operating noise. Lastly, as a result of the seat pad noise reduction effect, total power decreased by more than 11dB (A). In addition, it was confirmed that the 20th order cause of the main noise was reduced by about 45%p.Improvements/Applications: The noise contribution of the seat recliner adjuster derived from this study can be used as a basic data for noise reduction.