scholarly journals Study of a Nonlinear Membrane Absorber Applied to 3D Acoustic Cavity for Low Frequency Broadband Noise Control

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1138 ◽  
Author(s):  
Jianwang Shao ◽  
Tao Zeng ◽  
Xian Wu
Keyword(s):  
Degrees Of Freedom ◽  
Noise Control ◽  
Normal Modes ◽  
Low Frequency ◽  
Harmonic Balance Method ◽  
Nonlinear Normal Modes ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Acoustic Cavity ◽  
Nonlinear Membrane

As a new approach to passive noise control in low frequency domain, the targeted energy transfer (TET) technique has been applied to the 3D fields of acoustics. The nonlinear membrane absorber based on the TET can reduce the low frequency noise inside the 3D acoustic cavity. The TET phenomenon inside the 3D acoustic cavity has firstly investigated by a two degrees-of-freedom (DOF) system, which is comprised by an acoustic mode and a nonlinear membrane without the pre-stress. In order to control the low frequency broadband noise inside 3D acoustic cavity and consider the influence of the pre-stress for the TET, a general model of the system with several acoustic modes of 3D acoustic cavity and one nonlinear membrane is built and studied in this paper. By using the harmonic balance method and the numerical method, the nonlinear normal modes and the forced responses are analyzed. Meanwhile, the influence of the pre-stress of the nonlinear membrane for the TET is investigated. The desired working zones of the nonlinear membrane absorber for the broadband noise are investigated. It can be helpful to design the nonlinear membrane according the dimension of 3D acoustic cavity to control the low frequency broadband noise.

Efficiency of an ANC system in the tractor cabin under controlled engine workload

2020 ◽  
Vol 68 (5) ◽  
pp. 339-357
Author(s):  
Roberto Fanigliulo ◽  
Lindoro Del Duca ◽  
Laura Fornaciari ◽  
Renato Grilli ◽  
Roberto Tomasome ◽  
...  
Keyword(s):  
Sound Pressure ◽  
Noise Control ◽  
Active Noise Control ◽  
Low Frequency ◽  
Engine Performance ◽  
Noise Spectrum ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Residual Noise ◽  
Agricultural Tractor

The noise at the driver seat of an agricultural tractor is produced mostly by the engine. Its characteristic broadband noise spectrum varies considerably with engine workload. The passive noise control techniques adopted in tractor cabins, based on the application of sound-absorbing and sound-proofing materials, are effective against medium-high frequencies noise components. The residual noise in sound-proof cabins is characterized by tonal emissions with low frequency components (< 500 Hz) but regarded as responsible for various disorders and diseases following long-term exposure. In addition to the "A" weighting filter adopted to evaluate occupational exposure to noise, other approaches are reported in the scientific literature considered more appropriate to evaluate low frequency noise (LFN), as well as studies testifying the effectiveness of active noise control (ANC) technologies in the low frequency range. In this article, the performance of an ANC system is evaluated in its ability to reduce noise levels inside the soundproof cabin of an agricultural tractor. To test this system, spectro-phonometric measurements of the equivalent linear sound pressure level were conducted under controlled and repeatable engine workloads, obtained by connecting the tractor to a dynamometric brake, while simultaneously acquiring the related engine performance curves. Altogether, three different couples of loudspeakers were tested. Frequency analysis in one-third octave band showed that the ANC system was mainly effective against LFN components (below 120 Hz) with peaks of reduction up to 20 dB. Then, on the basis of indications from previous studies, the data of linear sound pressure levels were processed applying the "A", "B", and "C" weighting filters, to show the different emphasis given to the effects of the system. Eventually, a point-by-point composition of the equivalent levels of sound pressure was drawn over the whole range of the engine, to highlight the conditions in which the ANC system was more effective.

scholarly journals Acoustic notch filtering earmuff utilizing Helmholtz resonator arrays

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0258842
Author(s):  
Fumiya Mizukoshi ◽  
Hidetoshi Takahashi
Keyword(s):  
Resonant Frequency ◽  
Noise Control ◽  
Active Noise Control ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Honeycomb Structure ◽  
Sound Insulation ◽  
Frequency Noise ◽  
Target Frequency ◽  
Notch Filtering

In recent years, noisy bustling environments have created situations in which earmuffs must soundproof only specific noise while transmitting significant sounds, such as voices, for work safety and efficiency. Two sound insulation technologies have been utilized: passive noise control (PNC) and active noise control (ANC). However, PNC is incapable of insulating selective frequencies of noise, and ANC is limited to low-frequency sounds. Thus, it has been difficult for traditional earmuffs to cancel out only high-frequency noise that people feel uncomfortable hearing. Here, we propose an acoustic notch filtering earmuff utilizing Helmholtz resonator (HR) arrays that provides a sound attenuation effect around the tuneable resonant frequency. A sheet-like sound insulating plate comprising HR arrays is realized in a honeycomb structure. Since the resonant frequency is determined by the geometry of the HR arrays, a highly audible sound region can be designed as the target frequency. In this research, the acoustic notch filtering performance of the proposed HR array plate is investigated in both simulations and experiments. Furthermore, the fabricated earmuffs using the novel HR array plates achieve a sound insulation performance exceeding 40 dB at the target frequency, which is sufficiently high compared to that of conventional earmuffs. The experimental results confirm that the proposed device is a useful approach for insulating frequency-selective sound.

Model Reduction of a Nonlinear Rotating Beam Through Nonlinear Normal Modes

1999 ◽  
Author(s):  
E. Pesheck ◽  
C. Pierre ◽  
S. W. Shaw
Keyword(s):  
Differential Equations ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Nonlinear Partial Differential Equations ◽  
Normal Modes ◽  
Nonlinear Normal Modes ◽  
Single Equation ◽  
Rotating Beam ◽  
Model Size ◽  
Nonlinear Normal

Abstract Equations of motion are developed for a rotating beam which is constrained to deform in the transverse (flapping) and axial directions. This process results in two coupled nonlinear partial differential equations which govern the attendant dynamics. These equations may be discretized through utilization of the classical normal modes of the nonrotating system in both the transverse and extensional directions. The resultant system may then be diagonalized to linear order and truncated to N nonlinear ordinary differential equations. Several methods are used to determine the model size necessary to ensure accuracy. Once the model size (N degrees of freedom) has been determined, nonlinear normal mode (NNM) theory is applied to reduce the system to a single equation, or a small set of equations, which accurately represent the dynamics of a mode, or set of modes, of interest. Results are presented which detail the convergence of the discretized model and compare its dynamics with those of the NNM-reduced model, as well as other reduced models. The results indicate a considerable improvement over other common reduction techniques, enabling the capture of many salient response features with the simulation of very few degrees of freedom.

Low-frequency noise control using layered granular aerogel and limp porous media

2021 ◽  
Vol 263 (4) ◽  
pp. 2724-2729
Author(s):  
Yutong Xue ◽  
Amrutha Dasyam ◽  
J. Stuart Bolton ◽  
Bhisham Sharma
Keyword(s):  
Noise Control ◽  
Glass Fibers ◽  
Low Frequency ◽  
Normal Incidence ◽  
Frequency Noise ◽  
Fibrous Materials ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Fibrous Media ◽  
Impedance Tube Method

The acoustic absorption of granular aerogel layers with a granule sizes in the range of 2 to 40 μm is dominated by narrow-banded, high absorption regions in the low-frequency range and by reduced absorption values at higher frequencies. In this paper, we investigate the possibility of developing new, low-frequency noise reduction materials by layering granular aerogels with traditional porous sound absorbing materials such as glass fibers. The acoustic behavior of the layered configurations is predicted using the arbitrary coefficient method, wherein the granular aerogel layers are modeled as an equivalent poro-elastic material while the fibrous media and membrane are modeled as limp media. The analytical predictions are verified using experimental measurements conducted using the normal incidence, two-microphone impedance tube method. Our results show that layered configurations including granular aerogels, fibrous materials, and limp membranes provide enhanced sound absorption properties that can be tuned for specific noise control applications over a broad frequency range.

scholarly journals SeMSA: a compact super absorber optimised for broadband, low-frequency noise attenuation

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Andrew McKay ◽  
Ian Davis ◽  
Jack Killeen ◽  
Gareth J. Bennett
Keyword(s):  
New Technology ◽  
Perforated Plate ◽  
Low Frequency ◽  
Broadband Noise ◽  
Frequency Noise ◽  
Noise Attenuation ◽  
Loss Mechanism ◽  
Small Form Factor ◽  
Broadband Sound ◽  
Sub Wavelength

Abstract The attenuation of low-frequency broadband noise in a light, small form-factor is an intractable challenge. In this paper, a new technology is presented which employs the highly efficient visco-thermal loss mechanism of a micro-perforated plate (MPP) and successfully lowers its frequency response by combining it with decorated membrane resonators (DMR). Absorption comes from the membranes but primarily from the MPP, as the motion of the two membranes causes a pressure differential across the MPP creating airflow through the perforations. This combination of DMR and MPP has led to the Segmented Membrane Sound Absorber (SeMSA) design, which is extremely effective at low-frequency broadband sound absorption and which can achieve this at deep sub-wavelength thicknesses. The technology is compared to other absorbers to be found in the literature and the SeMSA outperforms them all in either the 20–1000 Hz or 20–1200 Hz range for depths of up to 120 mm. This was verified through analytical, finite element and experimental analyses.

scholarly journals Plate-Type Acoustic Metamaterials: Experimental Evaluation of a Modular Large-Scale Design for Low-Frequency Noise Control

Acoustics ◽  
2019 ◽  
Vol 1 (2) ◽  
pp. 354-368 ◽  
Author(s):  
Linus Ang ◽  
Yong Koh ◽  
Heow Lee
Keyword(s):  
Large Scale ◽  
Noise Control ◽  
Traffic Noise ◽  
Low Frequency ◽  
Industrial Applications ◽  
Frequency Noise ◽  
Acoustic Metamaterials ◽  
Scale Design ◽  
Stress Uniformity ◽  
Plate Type

For industrial applications, the scalability of a finalised design is an important factor to consider. The scaling process of typical membrane-type acoustic metamaterials may pose manufacturing challenges such as stress uniformity of the membrane and spatial consistency of the platelet. These challenges could be addressed by plate-type acoustic metamaterials with an internal tonraum resonator. By adopting the concept of modularity in a large-scale design (or meta-panel), the acoustical performance of different specimen configurations could be scaled and modularly combined. This study justifies the viability of two meta-panel configurations for low-frequency (80–500 Hz) noise control. The meta-panels were shown to be superior to two commercially available noise barriers at 80–500 Hz. This superiority was substantiated when the sound transmission class (STC) and the outdoor-indoor transmission class (OITC) were compared. The meta-panels were also shown to provide an average noise reduction of 22.7–27.4 dB at 80–400 Hz when evaluated in different noise environments—traffic noise, aircraft flyby noise, and construction noise. Consequently, the meta-panel may be further developed and optimised to obtain a design that is lightweight and yet has good acoustical performance at below 500 Hz, which is the frequency content of most problematic noises.

Bifurcation of Nonlinear Normal Modes by Means of Synge’s Stability

2011 ◽  
Author(s):  
Young S. Lee ◽  
Heng Chen
Keyword(s):  
Harmonic Balance ◽  
Coupled Oscillators ◽  
Normal Modes ◽  
Harmonic Balance Method ◽  
Orbital Stability ◽  
Nonlinear Normal Modes ◽  
Energy Transfers ◽  
Wide Range ◽  
Energy Domain ◽  
Nonlinear Normal

We study bifurcation of fundamental nonlinear normal modes (FNNMs) in 2-degree-of-freedom coupled oscillators by utilizing geometric mechanics approach based on Synges concept, which dictates orbital stability rather than Lyapunovs classical asymptotic stability. Use of harmonic balance method provides reasonably accurate approximation for NNMs over wide range of energy; and Floquet theory incorporated into Synges stability analysis predicts the respective bifurcation points as well as their types. Constructing NNMs in the frequency-energy domain, we seek applications to study of efficient targeted energy transfers.

A review of current strategies and criteria for low‐frequency noise control from combustion turbines

1999 ◽  
Vol 105 (2) ◽  
pp. 1220-1220
Author(s):  
Robert A. Putnam ◽  
Roland Hetzel ◽  
Johannes van de Logt
Keyword(s):  
Noise Control ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise
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