Mechanical Noise Research Articles

Density-based clustering with differential privacy

In recent years, differentially private clustering has received increasing attention. However, most existing differentially private clustering algorithms cannot achieve better results when handling non-convex datasets. To enhance knowledge extraction from data while protecting users' sensitive information, we propose a density-based clustering algorithm with differential privacy. Specifically, we incorporate differential privacy mechanisms into the density-based clustering paradigm to enhance the effectiveness of differentially private clustering on non-convex datasets. Firstly, to avoid privacy leakage, we employ the Laplace mechanism for inject noise into the density during the density estimation stage. Then, we design a privacy budget allocation scheme in the cluster expansion stage to make it harder for attackers to access private information. Theoretical analysis demonstrates that our algorithm satisfies ϵ-differential privacy. Experimental outcomes in synthetic and real-world datasets show that our introduced algorithm can obtain high-quality clustering results when dealing with non-convex datasets. In the approximation experiments, it is evident that our algorithm outperforms others in terms of approximation.

Experiment research on the characteristics and mechanism of noise caused by a car door sealing cavity at wind excitation

Due to the various geometric shapes of cavities within car door sealing systems, the resulting cavity noise induced by wind excitation exhibits complex characteristics, leading to unclear noise mechanisms. To address this, a study was conducted to examine the acoustic properties of door sealing cavities located in the B-pillar, C-pillar, and backdoor of an SUV within a full-scale aeroacoustic wind tunnel. The main objective was to explore the relationship between cavity noise and interior noise. The results showed that peak components in the sound pressure level spectrum of the cavities significantly contribute to interior noise, particularly for cavities located close to the car’s interior. To gain further insight, the geometric characteristics of the cavities were extracted and transformed into equivalent regular cavities. These equivalent cavities were subsequently tested for their noise performance in a small-scale aeroacoustic wind tunnel, and the occurrence mechanisms were thoroughly investigated. The results demonstrated that the noise spectra of different cavities, whether they had sealing strips or leakage gaps, exhibited typical multipeak characteristics, with some cases even leading to whistling (e.g. backdoor cavity). The reason for the whistling was a resonance when the self-sustained oscillation frequencies of the cavities coincided with or approached the Helmholtz resonance frequencies or modal frequencies of the cavities. Interestingly, the self-sustained oscillation frequency and cavity modal resonance still persisted even when the two frequencies were somewhat separated, albeit with peaks of lower magnitude in the sound pressure spectrum (e.g. in the sealed cavities of the B-pillar and C-pillar).

Multifunctional sensors for surface synchronized monitoring of Pressure/Biopotential signals and motion recognition

Surface biopotential dry electrodes are an important part of long-term healthcare health monitoring systems. During long-term dynamic monitoring, pressure fluctuations between the skin/electrode can affect the acquisition of ECG signals and reduce the stability of the system. In this study, by printing an interactive circuit on the back of the Fructus xanthii-inspired barb structure (FXbs) Ag/AgCl-TPU dry electrodes, the micro-nanocone PANI/PMMA flexible conductive film is encapsulated on the back of the FXbs dry electrode, and a multifunctional sensor and monitoring clothing are constructed, which can synchronously collect pressure signals and ECG signals, and can monitor human movements. In the simulation instrument and human skin surface, the influence of pressure fluctuation on the quality of ECG signal acquisition under different pressure, speed, and motion states is explored. In the simulation instrument, when the change rate of piezoresistive reaches the maximum value of 51.41 %, the fluctuation range of ECG is the smallest, which is 0.99 mV. On the surface of human skin, the change rate of piezoresistive and the fluctuation range of ECG in the turning state reach the maximum, which is 5.02 % and 5.99 mV, respectively. It can provide a reference to study the influence of pressure fluctuation on ECG signals on the surface of human skin, and at the same time, it can provide an experimental method and basis for the study of the dynamic noise mechanism at the electrode/electrolyte interface.

Design of Locally Resonant Acoustic Metamaterials with Specified Band Gaps Using Multi-Material Topology Optimization.

Locally Resonant Acoustic Metamaterials (LRAMs) have significant application potential because they can form subwavelength band gaps. However, most current research does not involve obtaining LRAMs with specified band gaps, even though such LRAMs are significant for practical applications. To address this, we propose a parameterized level-set-based topology optimization method that can use multiple materials to design LRAMs that meet specified frequency constraints. In this method, a simplified band-gap calculation approach based on the homogenization framework is introduced, establishing a restricted subsystem and an unrestricted subsystem to determine band gaps without relying on the Brillouin zone. These subsystems are specifically tailored to model the phenomena involved in band gaps in LRAMs, facilitating the opening of band gaps during optimization. In the multi-material representation model used in this method, each material, except for the matrix material, is depicted using a similar combinatorial formulation of level-set functions. This model reduces direct conversion between materials other than the matrix material, thereby enhancing the band-gap optimization of LRAMs. Two problems are investigated to test the method's ability to use multiple materials to solve band-gap optimization problems with specified frequency constraints. The first involves maximizing the band-gap width while ensuring it encompasses a specified frequency range, and the second focuses on obtaining light LRAMs with a specified band gap. LRAMs with specified band gaps obtained in three-material or four-material numerical examples demonstrate the effectiveness of the proposed method. The method shows great promise for designing metamaterials to attenuate specified frequency spectra as required, such as mechanical vibrations or environmental noise.

A multifunctional heterogeneous structure inspired by shell brick-mud structure: Balancing noise reduction and mechanical performance

Electric armoured vehicles, which are crucial for strategic operations, must possess superior mechanical properties and noise reduction to maintain normal functionality. However, achieving high energy absorption and noise reduction performance simultaneously is challenging with a single uniform material or structure. This study introduces heterogeneous structures with metal lattice skeletons filled with polymer materials. The skeleton, known as the bionic mantis shrimp structure (BMS), is filled with polyurethane and epoxy. Impedance tube experiments revealed that the sound absorption coefficients of Heterostructure-polyurethane foam (HS-PU) and Heterostructure-epoxy (HS-EP) are significantly higher than BMS. HS-PU achieved an average sound insulation of 33.6 dB, marking a 739 % improvement over BMS. Compression tests show that polymer filling can inhibit the destructive collapse of BMS and enhance its mechanical performance. HS-EP exhibits specific strength and specific energy absorption values of 57 MPa/(g·cm−3) and 30.75 J/g, respectively, representing an increase of 67.6 % and 315 % compared to BMS. Additionally, as the volume fraction of BMS increased in the heterogeneous structure, the elastic modulus and compressive strength increase while the specific energy absorption decreased. This research suggest that the design of metal/polymer heterogeneous structures offers a promising approach for developing high-strength and noise-reducing protective structures.

Utilization of recycled coral sand and aluminum scraps in foam concrete: Preparation, insulation of environmental noise and heat, and pore structure

The utilization of industrial and marine wastes in building materials can significantly mitigate resource consumption and environmental hazards. In this study, the waste aluminum scraps and coral sand were utilized as foaming agent and fillers for foam concrete (FC) to address application challenges associated with industrial and marine wastes. Simultaneously, their impact on the mechanical property, heat and noise insulation properties, as well as pore structure of FC were investigated. The response surface methodology was used to optimize the mix design of FC. Heat and noise insulation characteristics of FC were tested by a visible infrared thermometer and a self-manufactured soundproof device, while the pore characteristic was analyzed by digital image processing technique. Additionally, the effect of foaming agents and coral sand on the internal pore structure of FC was studied by means of microscopic analysis(FTIR, XRD, SEM). The results show that foam content significantly influenced the performance of FC. As the foam content reached 15%, the compressive strength was the worst (ranging from 1.26 to 1.59MPa). Additionally, foam and coral sand inhibited the expansion of sulfoaluminate cement. At 15% foam content and 30% coral sand content, the thermal conductivity decreased to 0.082 W/(m·℃), representing a reduction of 52.5% compared to the control group. Regarding noise reduction performance, a foam content of 10% yields optimal results. The heat and noise insulation properties were both improved due to the enhanced porous structure of coral sand. However, excessive admixtures, such as 50 % content of coral sand, could weaken the strength by destroying the fine pore structure. Microscopic analysis further revealed that foaming agents could affect the hydration of cement with little impact on macro performance. Moreover, they also enhanced the toughness of bubbles and changed the surface structure of pore walls to ensure the integrity of the pore structure of FC.

Device and Noise Performances of AlGaN/GaN High Electron Mobility Transistors with Various GaN Channel Layers Grown on AlN Buffer Layer

AlGaN/GaN high electron mobility transistors (HEMTs) with different GaN channel layers grown on AlN buffer layer are fabricated and investigated in order to optimize the device performances and to study the noise properties. To investigate the strain effect of the GaN channel layer grown on the AlN buffer layer, the positive shift of Raman peak is observed as the GaN channel becomes thinner. The threshold voltages (Vth) of the fabricated devices shift to positive direction according to the decreased GaN channel layer due to the decreased 2‐dimensional electron gas (2DEG) and deteriorated crystal quality of GaN channel layer. All devices demonstrated 1/f noise properties and the dominance of the carrier number fluctuations (CNF) noise mechanism. The largest trap density (Nt) value in the narrowest GaN channel device is because of the degraded crystal quality and the enhanced strain effect of the GaN channel layer. However, the lowest noise levels at the drain current (Id) > 10−6 A for the device with the GaN channel thickness of 30 nm grown on AlN buffer layer are observed to be due to the fully depleted GaN channel layer although its poor crystal quality.

DESIGN AND EVALUATION OF PIEZOELECTRIC-BASED PASSIVE DAMPING FOR HIGH FREQUENCY NOISE SUPPRESSION

This study focuses on developing a piezoelectric-based passive damper to mitigate high- frequency brake noise. The research investigates different designs of piezoelectric transducer elements to convert mechanical energy into electrical energy using a mass sliding belt test system that simulates real disc brake noise mechanisms. Integration of these electrical elements into the existing mass-sliding belt system is investigated. Five distinct piezoelectric transducer designs (Design-1, Design-2, Design-3, Design-4 and Design-5), each with unique technical specifications, boundary conditions, and scaling, are developed to suppress high frequency noise from friction-induced vibrations. To facilitate effective selection, a scoring method is employed, identifying Design-5 with a cylindrical model as the most efficient transducer design. Evaluation criteria include energy generation, compressive strength, operating temperature, weight, ergonomic usability, cost, and safety. Analyses are performed to assess potential stress-induced damage to the piezoelectric material resulting from the selected design. This study aims to contribute a novel perspective to noise reduction techniques and successfully demonstrates the integration of a piezoelectric transducer and an RLC circuit into a functional system.

Noise mechanism clarification in external-modulation Brillouin optical correlation-domain reflectometry with double-sideband modulator

Brillouin optical correlation-domain reflectometry (BOCDR) allows for relatively high spatial resolution and random accessibility with single-end light injection into the sensing fiber. Typically, BOCDR relies on directly modulating the laser diode’s driving current, which facilitates sinusoidal frequency modulation for distributed sensing but also introduces unintended power modulation that can degrade performance. To address these power variations, external-modulation BOCDR using a double-sideband modulator has been developed. However, this method generates substantial noise, overpowering the Brillouin signal and impeding accurate strain and temperature measurements. This study clarifies the previously unexplained noise mechanisms and suggests system design optimizations to mitigate their impact.

Acoustic cues of keyboard mechanics enable auditory localization of upright piano tones.

Piano tone localization at the performer's listening point is a multisensory process involving audition, vision, and upper limb proprioception. The consequent representation of the auditory scene, especially in experienced pianists, is likely also influenced by their memory about the instrument keyboard. Disambiguating such components is not obvious, and first requires an analysis of the acoustic tone localization process to assess the role of auditory feedback in forming this scene. This analysis is complicated by the acoustic behavior of the piano, which does not guarantee the activation of the auditory precedence effect during a tone attack, nor can it provide robust interaural differences during the subsequent free evolution of the sound. In a tone localization task using a Disklavier upright piano (which can be operated remotely and configured to have its hammers hit a damper instead of producing a tone), twenty-three expert musicians, including pianists, successfully recognized the angular position of seven evenly distributed notes across the keyboard. The experiment involved listening to either full piano tones or just the key mechanical noise, with no additional feedback from other senses. This result suggests that the key mechanical noise alone activated the localization process without support from vision and/or limb proprioception. Since the same noise is present in the onset of the full tones, the key mechanics of our piano created a touch precursor in such tones that may be responsible of their correct angular localization by means of the auditory precedence effect. However, the significance of pitch cues arriving at a listener after the touch precursor was not measured when full tones were presented. As these cues characterize a note and, hence, the corresponding key position comprehensively, an open question remains regarding the contribution of pianists' spatial memory of the instrument keyboard to tone localization.

Alignment Prediction of Air Spring Vibration Isolation System for Marine Shafting Based on Genetic Algorithm-Back Propagation Neural Network.

Shafting alignment plays an important role in the marine propulsion system, which affects the safety and stability of ship operation. Air spring vibration isolation systems (ASVISs) for marine shafting can not only reduce mechanical noise but also help control alignment state by actively adjusting air spring pressures. Alignment prediction is the first and a key step in the alignment control of ASVISs. However, in large-scale ASVISs, due to factors such as strong interference and raft deformation, alignment prediction faces problems such as alignment measurement sensors failure and difficulty in establishing a mathematical model. To address this problem, a data model for predicting alignment state is developed based on a back propagation (BP) neural network, fully taking advantage of its self-learning and self-adaption abilities. The proposed model exploits the collected data in the ASVIS instead of the alignment measurement data to calculate the alignment state, providing another alignment prediction approach. Then, in order to solve the local optimum issue of BP neural network, we introduce the genetic algorithm (GA) to optimize the weights and thresholds of the BP neural network, and an improved GA-BP model is designed. The GA-BP model can leverage the advantages of the global search capability of GA as well as the BP neural network's fast convergence in local search. Finally, we conduct experiments on a real ASVIS and evaluate the prediction models using different criteria. The experimental results show that the proposed prediction model with the GA-BP neural network can accurately predict the alignment state, with a mean-square error (MSE) of 0.0114. And compared to the BP neural network, the GA-BP neural network reduces the MSE by approximately 74%.

Deep learning-based acoustic emission data clustering for crack evaluation of welded joints in field bridges

To advance the intelligent operation and maintenance of bridges, a deep learning-based acoustic emission (AE) data clustering framework was developed for evaluating fatigue cracks in welded joints under conditions of operational noise interference and complex damage mechanisms. Specifically, a convolutional autoencoder (CAE) model was implemented to extract damage-sensitive features from AE wavelet images. Additionally, a physics-guided single-and-cross-case strategy using Gaussian mixture models (GMMs) was presented to diagnose overlapping microscopic noise and damage mechanisms across different cases with various crack lengths. Field tests demonstrated the efficiency of the proposed framework to distinguish AE data induced by noise, crack propagation, surface fretting, and impact, enabling accurate identification of no-damage, minor-damage, and serious-damage cases according to their characteristic mechanisms. Future work will incorporate long-term monitoring data from additional cases to further refine the damage quantification and enhance the overall robustness.

Noise Analysis and Structural Optimization of Automobile Scroll Compressor Air Valve

The air conditioning compressor is a critical component in automobile heating, ventilation and air conditioning systems. However, compressor noise has long been a problem for automobile manufacturers. In recent years, the development and application of automobile air conditioning scroll compressors has increased significantly due to their low mechanical vibration and noise. However, their limitations in terms of airflow pulse and noise cannot be ignored, especially in low speed and high load conditions where the noise generated has a negative impact on driving and passenger experience. Noise and airflow pulses are important considerations that cannot be ignored. This study innovatively modifies the end cap structure of the scroll compressor, using the principles of expansion muffler and insertion tube structure, with the aim of improving the acoustic quality of the scroll compressor. The results show that the novel valve construction can significantly reduce the sound pressure level of the scroll compressor noise to a maximum of 75.20 dBA. The results of this study provide a theoretical basis and practical technical applications for future research and development in the automobile industry.

Characteristics of the flow around finite wall-mounted square cylinders and the mechanism of tonal noise

Motivated by the need to reduce the noise from train pantographs, numerical simulations are carried out for the flow over finite wall-mounted square cylinders with different aspect ratios at a Reynolds number of 1.5×104. Five aspect ratios (height-to-width ratios) are taken into account, namely, 1.4, 4.3, 7.1, 10, and 12.9. The effect of the aspect ratio on the aerodynamic coefficients, the near-wall flow topologies, and the pressure distributions are studied in detail to give insight into the noise generation mechanisms. The pressure rate of change dp/dt on the cylinder surfaces is adopted to evaluate the dipole noise source. It turns out that distributions of dp/dt are closely related to flow evolutions near the free ends and the wall-mounting junctions of cylinders with different aspect ratios. High levels of dp/dt are found close to lateral trailing edges of the cylinder, while the strength grows quickly as the aspect ratio is increased. The far-field noise emitted from these cylinders is predicted using the Ffowcs Williams–Hawkings acoustic analogy and validated with wind tunnel measurements available in the literature. For receivers located in the cross-flow direction, a single acoustic tone near a Strouhal number of 0.1 is observed for cylinders with aspect ratios not greater than seven, while an additional tone at a higher Strouhal number occurs as the aspect ratio is further increased. The underlying mechanism of the tonal noise emitted to the far field is also investigated by combining the noise source localization and dynamic mode decompositions.

Different Fractional Charges from Auto- and Cross-Correlation Noise in Quantum Hall States without Upstream Modes.

Fractional charges of anyons can be extracted from shot noise in two ways. One can use either the autocorrelation noise of the current in one drain or the cross-correlation noise between two drains on the two sides of the device. The former approach typically overestimates the charge. This may happen due to upstream edge modes. We propose a mechanism for the excess autocorrelation noise without upstream modes. It applies to systems with multiple copropagating edge modes and assumes that the noise is measured at a low but nonzero frequency.

Influence of structural parameters of distributor disk on flow pulsation in axial piston pumps

Firstly, a virtual prototype of axial piston pump AMESim is used to observe the effects of outlet pressure, swashplate inclination, bulk modulus (compressibility), density, dynamic viscosity, air viscosity, air content, dead space volume, leakage of mating clearance of the moving parts, plunger cylinder clearance, eccentricity, contact length of the copper bushing of the high-pressure piston pump, and the over-flow area of the flow distributing disk on the swashplate torque, the pressure in the plunger chamber, the pulsation in the flow rate, and the backing-up. To explore the influence of fluid noise, mechanical noise and air noise. After comparison, the overflow area of the disk, which has the greatest influence on the noise, is selected as the research object, in which the structural parameters of the disk are the most important influencing factors. Finally, it is found that too large or too small overflow area will aggravate the fluid noise and mechanical noise of the piston pump. Therefore, the optimized design of the structure of piston pump flow distribution plate is of great significance to reduce the vibration and noise of the hydraulic system. This study catches the optimization method of axial piston pump flow distribution shock, which can provide a reference for the design and optimization of axial piston pumps.

Analysis Of The Edge Effect On Bird And Primate Distribution In The Ecological Corridor Habitat Of Mount Halimun Salak National Park (TNGHS)

This study aims to analyze the threat of edge effects on endemic animal populations due to the presence of causeways in the TNGHS corridor habitat. Indicators of the occurrence of edge effects are characterized by the further distance of wildlife populations from sources of disturbance such as noise, light, and frequency of human activity mechanisms. Belt transect research method for population study and distribution of Javan Gibbon and Surili. Intensive Point Account (IPA) to measure the diversity index of bird species and Javan eagles. Encounter Rate is used for animal distribution studies. Results On the observation transect made along 3 km, the population density of Javan Gibbons was obtained 0.114 ind/ha, Surili 0.024 indv/ha, and Monkey 0.028 indv/ha. Bird species diversity index in 3 habitat patches each Purasari H'= 2.78 with 38 species; Garehong with 27 species, and Corridor H'= 3,087 with 27 species. The similarity of species is that there are only 7 species of birds found in the 3 habitats of the patch. As a result of primate population density and burng species similarity, it can be concluded that the cross-corridor access road area has experienced an edge effect and tends to be a bottle-neck area for the distribution of animals, especially primates.

Acoustic resolvent analysis of turbulent jets

Abstract We perform a resolvent analysis of a compressible turbulent jet, where the optimisation domain of the response modes is located in the acoustic field, excluding the hydrodynamic region, in order to promote acoustically efficient modes. We examine the properties of the acoustic resolvent and assess its potential for jet-noise modelling, focusing on the subsonic regime. Resolvent forcing modes, consistent with previous studies, are found to contain supersonic waves associated with Mach wave radiation in the response modes. This differs from the standard resolvent in which hydrodynamic instabilities dominate. We compare resolvent modes with SPOD modes educed from LES data. Acoustic resolvent response modes generally have better alignment with acoustic SPOD modes than standard resolvent response modes. For the optimal mode, the angle of the acoustic beam is close to that found in SPOD modes for moderate frequencies. However, there is no significant separation between the singular values of the leading and sub-optimal modes. Some suboptimal modes are furthermore shown to contain irrelevant structure for jet noise. Thus, even though it contains essential acoustic features absent from the standard resolvent approach, the SVD of the acoustic resolvent alone is insufficient to educe a low-rank model for jet noise. But because it identifies the prevailing mechanisms of jet noise, it provides valuable guidelines in the search of a forcing model (Karban et al. in J Fluid Mech 965:18, 2023). Graphical abstract

Retention of Improved Plantar Sensation in Patients with Type II Diabetes Mellitus and Sensory Peripheral Neuropathy after One Month of Vibrating Insole Therapy: A Pilot Study.

Sensory peripheral neuropathy is a common complication of diabetes mellitus and the biggest risk factor for diabetic foot ulcers. There is currently no available treatment that can reverse sensory loss in the diabetic population. The application of mechanical noise has been shown to improve vibration perception threshold or plantar sensation (through stochastic resonance) in the short term, but the therapeutic use, and longer-term effects have not been explored. In this study, vibrating insoles were therapeutically used by 22 participants, for 30 min per day, on a daily basis, for a month by persons with diabetic sensory peripheral neuropathy. The therapeutic application of vibrating insoles in this cohort significantly improved VPT by an average of 8.5 V (p = 0.001) post-intervention and 8.2 V (p < 0.001) post-washout. This statistically and clinically relevant improvement can play a role in protection against diabetic foot ulcers and the delay of subsequent lower-extremity amputation.

Effects of an Owl Airfoil on the Aeroacoustics of a Small Wind Turbine

Aerodynamic noise emitted by small wind turbines is a concern due to their proximity to urban environments. Broadband airfoil self-noise has been found to be the major source, and several studies have discussed techniques to reduce airfoil leading-edge and trailing-edge noises. Reduction mechanisms inspired by owl wings and their airfoil sections were found to be most effective. However, their effect/s on the tip vortex noise remain underexplored. Therefore, this paper investigates the effects of implementing an owl airfoil design on the tip vortex noise generated by the National Renewable Energy Laboratory (NREL) Phase VI wind turbine to gain an understanding of the relationship, if any, between airfoil design and the tip vortex noise mechanism. Numerical prediction of aeroacoustics is employed using the Ansys Fluent Broadband Noise Sources function for airfoil self-noise radiation. Detailed comparisons and evaluations of the generated acoustic power levels (APLs) for two distinguished inlet velocities were made with no loss in torque. Although the owl airfoil design increased the maximum generated APL by the baseline model from 105 dB to 110 dB at the lower inlet velocity, it significantly reduced the surface area generating the noise, and reduced the maximum APL generated by the baseline model by 4 dB as the inlet velocity increased. The ability of the owl airfoil to mitigate the velocity effects along the span of the blade was found to be its main noise reduction mechanism.