Machinery Noise Research Articles

Effects of Noise and Vibration Changes from Agricultural Machinery on Brain Stress Using EEG Measurement

In this study, the agricultural work stress induced by the noise and vibration of some agricultural machinery was analyzed through electroencephalogram (EEG) measurements. The values of spectral edge frequency (SEF) 95%, relative gamma power (RGP), and EEG-based working index (EWI), utilized as stress indicators, were derived by analyzing the EEG data collected. The EEG analysis revealed that agricultural work stress manifested when participants engaged in agricultural tasks following a period of rest. Additionally, the right prefrontal cortex was identified where the values of SEF95% and RGP increased concurrently with the rise in noise (61.42–88.39 dBA) and vibration (0.332–1.598 m/s2). This study’s results are expected to be utilized as foundational data to determine the agricultural work stress felt by farmers during work through EEG analysis in response to changes in noise and vibration.

Developing and testing systems for the attenuation of ships' machinery noise

With ships operating in areas including important marine biodiversity, it is crucial to understand the sources and characteristics of underwater noise and develop effective measures to mitigate underwater noise's impact on the environment. The underwater noise signature from a ship is usually dominated by machinery noise and propulsion engines at low speeds. Given the importance of onboard electrical power, diesel generators might continuously function (i.e., even when a ship is docked) and generate low-frequency underwater noise. Université de Sherbrooke (Sherbrooke, Canada) and Innovation Maritime (Rimouski, Canada) lead a collaborative work focusing on the means and methods for attenuating machinery noise. Two main research axes are considered. The first concerns the setup and validation of a small-scale platform that can be used to test noise reduction methods in a controlled water basin environment. The second research axis investigates passive, tunable, and possibly multi-resonant vibroacoustic solutions to attenuate machinery noise. These solutions mostly come as 3D-printed folded quarter-wave resonators following spiral or cantilever resonators. Acoustic resonators can also be embedded into a layer of sound-absorbing material to improve soundproofing properties at specific frequencies. The applications and scope of this work are finally put into perspective.

A procedure for estimating mitigation effect of air injection on ship underwater radiated noise

Increasing evidence exists that underwater radiated noise (URN) from ships has a negative impact on marine ecosystems. This has led to numerous initiatives aimed at monitoring and mitigating ambient sound levels generated by shipping. Within the European Union, noise abatement is being addressed by a wide range of stakeholders, with activities focused on developing procedures and thresholds for evaluating noise impact as well as knowledge on the effectiveness of a range of mitigation measures. In the SATURN project, MARIN is studying air injection systems for mitigation of both propeller cavitation and machinery noise; the so-called "Prairie" and "Masker" systems. Model-scale tests have been performed in order to quantify performance in terms of sound level reductions for a range of test conditions. In this paper we elaborate a procedure for applying the processed measurement data to ship-scale URN predictions for assessing mitigation potential during the early design stage. Data reduction of the model test results is explained, leading to a model for estimating the mitigation effect and power requirement of the two systems. We subsequently apply the model to a number of test cases, covering both measured and calculated source levels. Limitations of the approach will also be discussed.

Assessment of the effectiveness of ship machinery noise reduction measures using a test platform in a water basin

Underwater radiated noise (URN) from commercial shipping is partly responsible for increased ocean ambient noise levels in the last decades. To preserve marine wildlife, there is a need to reduce it. Machinery noise is the dominant URN source at lower speeds. Mitigation technologies exist to reduce it, but a lack of quantitative data regarding their effectiveness results in limited practical ship applications since the cost-to-benefit ratio is imprecise. A small ship-like structure (test platform) representative of a ship section is designed and constructed to conduct measurements in a controlled environment and at a lower cost than actual on-ship testing. The platform is deployed in a water basin whose acoustic response is first characterized by reverberation measurements. Vibroacoustic sources simulate structure-borne and airborne noise, while hydrophones and sensors measure the response in the water basin and of the platform. Measurements with and without standard mitigation technologies installed in the platform are conducted to quantify the insertion loss. Up to 37 and 20 dB URN reductions are obtained with elastic mounts and mineral wool, respectively. The results obtained with the platform and the developed methodology can support and guide the implementation of mitigation measures in current and future ship constructions.

Porous acoustic metamaterial for simultaneous control of high and low frequency machinery noise: Case study of a water pump.

An acoustic metamaterial (AMM) consisting of a porous material (melamine foam) layer above a symmetrical labyrinthine metamaterial, incorporating a micro-hole and micro-slit cover plate, is proposed to simultaneously mitigate low and high frequency noise from industrial machineries. Theoretical model of sound absorption by this AMM is developed and validated numerically and experimentally. Sensitivity analysis indicates that increasing the length of the labyrinthine pathway and cover plate thickness and decreasing the slit width, slit length, and hole diameter shifts the peak sound absorption to lower frequencies. This material is successfully applied as a sound absorptive enclosure of a 0.5 hp water pump to reduce its sound pressure levels across widely separated frequencies of 1414-2245 Hz (high frequency) and 176-222 Hz (low frequency). This study offers guidelines to noise control engineers for controlling low and high frequency noise in industrial machineries.

(Digital Presentation) Mechanically Driven Electromagnetic Energy Harvesting for Power System Sensing Applications

Introduction Energy harvesting is a process of producing energy or usable power from the environment. Among potential ambient energy harvesting sources, electromagnetic (EM) field offers the great promise for emerging power system applications. This is because EM energies are widely available around the current-carrying wires (busbars) that connect various power devices and equipment. Most previous works on EM energy harvesting were built upon AC transmission lines [1-5], whereas modern power systems are typically driven by renewable DC energy sources. In this work, a mechanically-driven, DC-based EM energy harvesting system is designed and implemented as a lab-scale prototype to ultimately power sensing devices in the power system. Key Results: The schematic diagram and the photograph image of the EM induction experimental setup are shown in Figures 1a) and 1b), respectively. The energy harvester consists of a high permeability (μ ~ 2300) ferrite toroidal coil (cross sectional area 760 mm2) that is placed below a DC conducting (copper) slab at a distance of 1 cm. According to the Faraday’s law of induction (Equation 1), the open circuit voltage is proportional to the time rate of change of the magnetic flux (dφ/dt). This work is sharply distinguished from other works because the time variant nature originates from the physical vibration without using the AC power source. As seen in the figure, the toroidal coil is directly attached to a vibrator, thus experiencing a light-to-moderate amount of vibration. Here, the copper slab emulates the busbar in the power system, and the vibrator represents a practical scenario where the energy harvester is exposed to mechanical, machinery, and other noise sources.Figure 2 plots the open circuit voltage (VOC) as a function of the number of coil turns (N) for the experimental setup shown in Fig. 1. VOC was measured using a multimeter between two terminals of the coil for the maximum current of 3 A applied to the copper slab. As expected, a linear trend of VOC vs. N was observed with the VOC value as high as 51.4 mV for the case of 2,500 turns. Importantly, VOC is scalable to the value that is sufficiently high to drive most modern sensing devices because VOC is proportional to current (I). It is common that more than 100 A flows in the busbar of the power system, which escalates VOC to more than 1.7 V. The idea of increasing VOC by increasing current is confirmed in Figure 3; we repeated the experiments by lowering the current value in the copper slab, and obtained the linear trend line. Thus, both results shown in Figures 2 and 3 indicate a strong correlation of our energy harvester prototype with the EM theory. The maximum VOC value we obtained (51.4 mV) is separately shown in Figure 4 as a photograph image of the multimeter reading.In Table 1, we estimated the VOC values that can be readily achievable in the power system that affords the busbar current of 300 A and/or the 10,000 coil turns. For example, as compared with a previous work [3] with VOC of 1.4 V for 30 A (AC), this work features VOC of about 2 V with the 30 A DC power source. Significance: This work demonstrates the possibility of newly developing an mechano-electromagnetic energy harvester for modern power systems. Taking full advantage of EM energies and vibration present in the power system, the proposed DC-sourced energy harvesting scheme can greatly facilitate development and adoption of various sensing/monitoring/diagnosis device technologies. This is because these devices will not require separate batteries or power sources; they will be easily powered using the electromagnetic energy and mechanical vibration.

Boosted Fourier nonlinear filter and boosted even mirror Fourier nonlinear filter for active control of machinery noises

To overcome the limitations of the Fourier nonlinear filter and even mirror Fourier nonlinear filter-based adaptive algorithms for active noise control, this paper introduces boosted Fourier nonlinear filter and boosted even mirror Fourier nonlinear filter algorithms. Weight updating equations for the proposed algorithms are derived. Their performance is compared with Fourier nonlinear filter and even mirror Fourier nonlinear filter. Experimentally recorded bandsawand compressor noises are utilized for the analysis. The analysis is carried out for (a) linear primary and linear secondary paths, and (b) nonlinear primary path and linear secondary path. Visual inspection of residual noises after control and dB values of residual noises are utilized to understand the performance of the developed algorithms.

Evaluation of the performance of technologies for reducing ships' machinery noise using a small-scale ship-like structure in a Water Basin

Ocean ambient levels have increased in the last decades, especially in the low-frequency domain (under 500 Hz). This increase is partly due to underwater radiated noise (URN) from commercial ships. Excessive URN harms marine life and is, therefore, considered a pollution that needs to be reduced. At low speeds, machinery is the primary noise source on ships. Mitigation technologies exist to limit machinery’s contribution to URN. While implementing these technologies is costly, a lack of quantitative data regarding their exact performances usually results in limited concrete ship applications since the cost-to-benefit ratio is imprecise. This study aims to quantify better the performance of standard noise mitigation technologies using a small-scale ship-like structure in a water basin. The basin’s acoustic field is first characterized with and without the structure. The structure is then equipped with different mitigation technologies. A loudspeaker and a vibration shaker are fed with pink noise or measured signals on actual machinery. Hydrophones, microphones, accelerometers, and force sensors measure the response in the basin and on the structure. The performance of each tested technology is evaluated and ranked in terms of URN reduction. The relative contributions of airborne and structure-borne transmission paths on URN are also examined.

Use of metamaterials to reduce underwater noise generated by ship machinery

Reducing underwater noise pollution from ship machinery is a significant challenge. Ship machinery usually operates at fixed speeds and emits tonal noise with large amplitudes at low frequencies. Conventional soundproofing materials are inadequate for absorbing tonal noise and require large thicknesses at low frequencies. Quarter-wavelength resonators effectively absorb sound at their fundamental frequency and odd harmonics. Still, the applicability of this solution is nevertheless limited by its length requirement, which becomes cumbersome at low frequencies and, thus, large wavelengths. This study explores different structured metamaterial designs based on labyrinth, coiled quarter-wavelength resonators, and hybrid configurations combining glass wool and coiled resonators. Analytical, numerical calculations, and experimental tests are carried out under normal plane wave incidence (using an impedance tube) and a diffuse acoustic field (in a small reverberant cabin). In particular, a numerical optimization based on a periodic unit cell model is used to optimize the hybrid configuration and analyze its behavior under variable plane wave incidence angles. Preliminary tests conducted in a water basin using a small, straightforward aluminum box equipped with some proposed designs indicate reductions in underwater noise levels. The proposed solutions offer limited-cost and compact solutions for mitigating machinery noise and, potentially, the preservation of marine ecosystems.

Superior damping capacity of a C-containing FCC medium-entropy alloy

Construction machinery noise not only affects its service life, but also brings hazards to people's physical and mental health. Achieving a high and stable internal friction characteristic to eliminate noise and mechanical vibrations is always the desired goal in the design of damping alloys. In the study, we present a C-containing Fe-Mn-Cr-Ni medium entropy alloy that exhibits a superior damping capacity with an internal friction peak value of 0.083. The Finkelstein-Rosin relaxation peak appears at 550 K in the internal friction spectrum, which is attributed to the reorientation of C-C pairs and C substitutional atom pairs under stress, with the diffusion activation energy are 155.172 kJ·mol−1 and 166.711 kJ·mol−1, respectively. The relaxation of Finkelstein-Rosin peak enhances the damping capacity of the alloy, which provides an effective method for regulating the damping properties of medium entropy alloys.

Sealing strip acoustic performance evaluation using WF-VMD based signal enhancement method

The sealing strip is an essential component that rubs against the sunroof supporting rod when the sunroof is opening or closing. The acoustic performance of the sealing strip, such as sound pressure level (SPL) and psychoacoustic annoyance (PA), is important for automobile comfort. However, no automated equipment is available for evaluating the acoustic performance of the sealing strip. Moreover, the weak sealing strip acoustic signal, under the strong noise of the running vehicle or machinery, is difficult to obtain, making it hard to be accurately evaluated. In this paper, a sealing strip acoustic performance detector is developed to simulate the frictional state between the sealing strip and the supporting rod, and a weak sealing strip acoustic signal enhancement method based on Wiener filtering (WF) and variational mode decomposition (VMD) is proposed. The machinery noise’s spectrum is obtained through multitaper spectrum estimation and wavelet thresholding. The sealing strip acoustic signal’s spectrum is estimated by subtracting the machinery noise’s spectrum from the spectrum of the noisy signal. Therefore, an accurate prior signal-to-noise ratio (SNR) estimation required in WF can be obtained, and distortion in the estimated sealing strip acoustic signal is reduced. The estimated acoustic signal is further decomposed into multiple intrinsic mode functions (IMF), based on which an optimized estimated signal is finally constructed, thus realizing the enhancement of weak sealing strip acoustic signal. The effectiveness and applicability of the proposed method are validated by experiments conducted with different sealing strips and compression levels. The average correlation coefficient between the optimized estimated signal and the actual sealing strip acoustic signal is 94.2 %. Three sealing strips’ acoustic performances under various compression levels and friction speeds are accurately evaluated using SPL and PA.

Subjective evaluation on vibratory feeling to noises containing a low-frequency tonal component

Machinery noises sometimes contain low-frequency tonal components and cause an increase in noise annoyance due to the tones. It is also known that the oppressive or vibratory feeling is a unique sensation to low-frequency sounds below 100 Hz, which may also account for the increase in noise annoyance. In this study, auditory experiments were conducted to investigate the relationship between the intensity and frequency of the tonal components and the vibratory feeling. The test stimuli were broadband noises that simulated environmental noises with one additional tonal component. The frequency and the tonal audibility were varied in the range of 31.5 to 400 Hz, and 0, 3, 6, 9, and 12 dB, respectively. As a result, the energy of the component below 100 Hz was found to be strongly correlated with the vibratory feeling. Furthermore, the relationship between sound pressure level and the vibratory feeling was examined using LSL weighting characteristics, which have been proposed for the evaluation of vibration and oppression sensation caused by low-frequency sound.

Review on Current Applications of Metamaterial in Hong Kong Noise Control and its Potential Application in Construction Sites

During the past few years, construction works for infrastructure and housing developments in Hong Kong have been brisk with economic growth. There are nearly two construction sites in every square kilometer of our limited urban/built-up land. Hence, noise from construction works is one of the major concerns to our community. Striking a balance between ever-tightening construction programme and quieter living environments is crucial to support our sustainable development. Typical construction noise control pinned on using noise barriers for meeting both noise standards and rising public expectations. However, conventional material of noise barriers cannot effectively address and reduce construction machinery noise with a characteristic spectrum under various engineering constraints, e.g. loading, space, construction time and cost, etc. Recently, an emerging technology, acoustic metamaterials, takes a new approach that allows optimization of noise reduction targeting the characteristic spectrum within the said constraints. This paper will briefly introduce the principle of acoustic metamaterial and its current applications in noise control industries. Perspective applications of acoustic metamaterial for construction noise control and the potential benefits will also be discussed.

Modelling of noise due to impulsive excitation using nonlinear time series analysis

Early acoustic machine design phases should target safety and comfort requirements, minimising the risk of hearing damage and noise exposure and ensuring a pleasant machine sound. Therefore, physical mechanisms of sound generation, propagation and radiation need to be modelled. Today, nonlinear physical relations in vibroacoustic models such as contact problems are mostly linearised. The aim of this paper is to increase the prediction quality of vibroacoustic models so that physical mechanisms behind sound generation due to complex physical, nonlinear phenomena can be better understood. The focus is on sound generation due to impulsive excitation, which is a significant sound generation mechanism in machinery, e.g. considering gears, forming processes (e.g. punching), or road loads of vehicles. We describe a model setup to simulate impulsive excitation on a laboratory scale, where structural vibrations can be analysed. Physical correlations including nonlinear correlations could be identified using nonlinear time series analysis. Recurrence plots will be used to identify features such as phase space contraction, e.g. to identify damping. These features form the basis to deepen the physical understanding of machinery noise, to contribute to enhanced acoustic machine designs and to enhance data-driven modelling using sparse regression in future research.

Cavitation flow and noise reduction design of bionic hydrofoil based on orthogonal optimization

Hydrofoils hold considerable academic and practical significance in the realms of marine science, energy generation, and water-based engineering. They offer enhanced speed, efficiency, stability, and maneuverability. Bionic structures have emerged as potent tools for reducing energy losses and noise in hydraulic machinery, making bionic hydrofoils a hotbed of research activity. While prominent scholars have historically directed their bionic investigations toward airfoils, operating in compressible flow fields, recent research has shifted its focus to hydrofoils. The hydrofoil's operating environment is characterized by water instead of air, featuring incompressible flow, relatively low Reynolds and Mach numbers, and notably, cavitating flow. This study presents the bionic optimization design of a wavy leading edge for the hydrofoil, employing orthogonal experimental theory. The authors establish rankings for structural parameters of bionic hydrofoils and identify optimal parameter combinations, offering an optimization strategy for selecting bionic configurations. Subsequently, the authors conduct a numerical investigation into cavitating flow, integrating the FW–H (Ffowcs Williams and Hawkings) equation for the analysis of cavitation-induced noise. Notably, this research delves into the underlying mechanisms responsible for the efficacy of bionic structures in enhancing hydrodynamic performance, particularly in the reduction of cavitation-induced noise within cavitating flow, an area scarcely explored in formal publications. The results reveal that the amplitude of the wavy leading edge exerts the most significant influence on the lift-to-drag ratio, as well as the far-field sound pressure level, followed closely by the wavelength. When compared with a baseline hydrofoil, the optimized bionic hydrofoil demonstrates a substantial 45% reduction in maximum cavity volume and a noteworthy 1.3 dB reduction in far-field noise sound pressure level. These findings underscore the capacity of the optimized bionic hydrofoil to effectively suppress cavitation and its associated noise. The established optimization strategy, focused on cavitation suppression and noise reduction, lays a robust foundation for subsequent studies involving complex working conditions.

Weighted block ℓ1 norm induced 2D off-grid compressive beamforming for acoustic source localization: Methodology and applications

Identifying acoustic sources with high spatial resolution and precision is significant for machinery noise control. Off-grid compressive beamforming is an effective method for creating acoustic maps with a high spatial resolution. In this study, a two-dimensional off-grid compressive beamforming method via weighted block ℓ1 norm regularization (WBS-OCSBF) is proposed. The weighted ℓ1 norm offers a more uniform sparsity penalty compared to the ℓ1 norm. This method can enhance the performance of off-grid compressive beamforming. Additionally, it is easily implemented on mature linear programming solvers and converges with only a few iterations. Numerical simulations are conducted to analyze the effects of several major parameters on the performance of the proposed method. The simulation results demonstrate the superiority of the proposed method over some traditional methods. The proposed method is then validated using a loudspeaker noises localization experiment. A gearbox transmission system and a transformer are used as two specific objects to explore the industrial application value. The proposed method can effectively localize the gear meshing noise and transformer discharge faults with a high spatial resolution.

Modernization of the instrumentation requirements to support ISO noise test standards

ISO TC43/SC1/WG28 develops the basic machinery noise test standards for products and equipment. This includes the determination of sound power levels in the ISO 3740 series and the measurement of operator/bystander sound pressure levels in the ISO 11200 series. The instrumentation requirements for these standards have historically been based on a reference the sound level meter standard, IEC 61672, supplemented by another to IEC 61260 for fractional octave filters. Both IEC standards are fundamentally based on the concept of the measurement system being a packaged sound level meter. Many modern implementations of these standards no longer use a sound level meter. Many now use multi-channel, computerized instrumentation systems and custom software. These systems provide measurement equivalence to the IEC sound level measurement standards. However, they don’t fully comply with all of the requirements in these IEC standards. Many acoustic testing programs have chosen to ignore these non-complianceissues, have implemented systems that are more efficient, lower measurement uncertainty and provide measurement equivalence to IEC 61672 and IEC 61260. As industry has already decided to implement these systems, there is a need to develop modernized instrumentation requirements to support the basic sound power and sound pressure level measurement standards using current technology.

Design and correlation analysis of quasi-zero stiffness passive vibration isolation air spring

Vibration isolation systems are widely used in high-end automobile manufacturing, precision instrument processing, building and bridge seismic resistance, ship machinery noise reduction and other engineering fields, with good development prospects. At present, the existing vibration isolation systems on the market are mainly divided into active and passive vibration isolation systems. Passive vibration isolation does not require external energy input. Its structure is simple and the control scheme is easy to implement. However, passive vibration isolation performs well in high frequency vibration but not in low frequency. As a new nonlinear low-frequency vibration isolation technology, the quasi-zero stiffness vibration isolation system has changed the traditional concept of linear system vibration isolation. In addition, compared with traditional spring, air spring as a new type of elastic vibration isolation mechanism has many excellent performances, such as high fatigue resistance and high stiffness. Therefore, this paper uses air spring to design a passive vibration isolation quasi-zero stiffness air spring structure with good vibration isolation effect, simple structure and low cost in both low-frequency and high-frequency vibration.

On how natural and urban soundscapes alter brain activity during cognitive performance

Listening to natural or urban soundscapes has previously been shown to differentially modulate performance in a subsequent cognitive task. The present study inquired the effect of listening to urban (traffic and machinery noise) vs. natural (birds, water and wind) soundscapes on cognitive performance, mood, stress reactivity and the consequences for brain activity during a cognitive task assessed before and after soundscape exposure. In a randomized experiment, 30 participants were exposed to three conditions on three separate testing days: urban, natural and no soundscape. Before and after the functional MRI session participants performed a dual n-back, a backward digit span task and filled out mood, stress reactivity and aesthetic preference questionnaires. The natural soundscapes did lead to better cognitive performance however, the effect did not reach significance. Exposure to the natural soundscapes resulted in a significant decrease of negative affect and participants rated them as significantly more aesthetic. On the brain level, listening to the urban soundscape was associated with an increase in superior temporal gyrus (STG) activity during the subsequent dual n-back task. However, this result was statistically not corrected and remains exploratory in nature. This result could potentially hint at information processing becoming less efficient in early primary sensory area as a result of exposure to the urban soundscape. Correlations between affect/cognition and task related brain activity revealed clusters in the attention-network.

Localization of cyclostationary acoustic sources via cyclostationary beamforming and its high spatial resolution implementation

The localization of cyclostationary sound sources is important for rotating machinery noise source identification and fault diagnosis. Cyclostationary sound sources are a special class of nonstationary sound sources, which exhibit periodic changes in statistics. Most of the conventional sound source identification methods are based on the stationary sound source assumption, which do not consider the cyclostationarity of the radiated sound field by rotating machinery. Thus, they are hard to localize the acoustic sources with different cyclic frequencies. In this paper, a novel technique of localizing the cyclostationary acoustic sources with different cyclic frequencies is proposed. First, the cyclostationary conventional beamforming (CSCBF) method is deviated. In CSCBF, the cyclic-cross-spectral matrix (CCSM) is defined considering all the cross cyclic spectral correlation (CSC) between different microphones in the array. The left steering vector and right steering vector are constructed to focus the CCSM on each scanning grid point at a given combination of cyclic frequency and spectral frequency. Then, the high resolution cyclostationary beamforming (HR-CSBF) is further developed to improve the spatial resolution of CSCBF. In HR-CSBF, two linear equations according to the property of CSC is established as the acoustic inverse problems. With the sparse distribution of the cyclostationary sources in the space as the prior knowledge, the iterated Bayesian focusing (IBF) is utilized to obtain a robust and sparse solution in HR-CSBF. Numerical simulations and experiments are conducted to validate the proposed methods. To explore the potential applications of the proposed methods, the localization of high pressure pump (HPP) and rolling bearing with outer-race failure are also used to evaluate the effectiveness of the proposed methods. It turns out that both CSCBF and HR-CSBF can localize the cyclostationary sources with different cyclic frequencies. Compared with CSCBF, HR-CSBF can achieve a higher spatial resolution in the obtained acoustic map.