Phase Reversal Barriers for Better Noise Control at Low Frequencies: Laboratory Versus Field Measurements

Previous investigations have determined that the noise transmission into a finite cylindrical structure at low frequencies is dominated by the cavity resonances. Therefore, noise control at the first several cavity resonances for a Chamber Core cylinder can significantly reduce the noise level at low frequencies inside the cylinder. This work explores the feasibility of noise control for the Chamber Core cylinder using cylindrical Helmholtz resonators. The targeted frequencies are the first four cavity resonances. Detailed considerations of the resonant frequency calculation, resonator design, and experimental verification are presented. The effects on the noise reduction spectrum of two closely spaced resonators are experimentally studied. The optimal position of the resonators is also discussed. The noise control results indicate that the Helmholtz resonators can significantly attenuate the noise level at the targeted frequency bands.

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A Comparison of Standard Coherence Models for Inflow Turbulence With Estimates from Field Measurements

Journal of Solar Energy Engineering ◽

10.1115/1.1797978 ◽

2004 ◽

Vol 126 (4) ◽

pp. 1069-1082 ◽

Cited By ~ 28

Author(s):

Korn Saranyasoontorn ◽

Lance Manuel ◽

Paul S. Veers

Keyword(s):

Single Point ◽

Test List ◽

Structural Response ◽

Field Measurements ◽

Horizontal Wind ◽

International Electrotechnical Commission ◽

Horizontal Wind Speed ◽

Low Frequencies ◽

Inflow Turbulence ◽

Vertical Turbulence

The Long-term Inflow and Structural Test (LIST) program, managed by Sandia National Laboratories, Albuquerque, NM, is gathering inflow and structural response data on a modified version of the Micon 65/13 wind turbine at a site near Bushland, Texas. With the objective of establishing correlations between structural response and inflow, previous studies have employed regression and other dependency analyses to attempt to relate loads to various inflow parameters. With these inflow parameters that may be thought of as single-point-in-space statistics that ignore the spatial nature of the inflow, no significant correlation was identified between load levels and any single inflow parameter or even any set of such parameters, beyond the mean and standard deviation of the hub-height horizontal wind speed. Accordingly, here, we examine spatial statistics in the measured inflow of the LIST turbine by estimating the coherence for the three turbulence components (along-wind, across-wind, and vertical). We examine coherence spectra for both lateral and vertical separations and use the available ten-minute time series of the three components at several locations. The data obtained from spatial arrays on three main towers located upwind from the test turbine as well as on two additional towers on either side of the main towers consist of 291 ten-minute records. Details regarding estimation of the coherence functions from limited data are discussed. Comparisons with standard coherence models available in the literature and provided in the International Electrotechnical Commission (IEC) guidelines are also discussed. It is found that the Davenport exponential coherence model may not be appropriate especially for modeling the coherence of the vertical turbulence component since it fails to account for reductions in coherence at low frequencies and over large separations. Results also show that the Mann uniform shear turbulence model predicts coherence spectra for all turbulence components and for different lateral separations better than the isotropic von Ka´rma´n model. Finally, on studying the cross-coherence among pairs of turbulence components based on field data, it is found that the coherence observed between along-wind and vertical turbulence components is not predicted by the isotropic von Ka´rma´n model while the Mann model appears to overestimate this cross-coherence.

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Broad-band electric field measurements above thunderstorms by the IME-HF instrument prepared for the TARANIS mission

10.5194/egusphere-egu2020-15159 ◽

2020 ◽

Author(s):

Ondřej Santolík ◽

Ivana Kolmašová ◽

Radek Lán ◽

Luděk Uhlíř ◽

Jean-Louis Rauch ◽

...

Keyword(s):

Electric Fields ◽

Gamma Ray ◽

Broad Band ◽

Field Measurements ◽

Detection Algorithm ◽

X Rays ◽

Scientific Instruments ◽

Frequency Range ◽

Low Frequencies ◽

Blue Jets

<p>A broad-band analyzer of the IME-HF instrument (&#8220;Instrument de Mesure du champ Electrique Haute Frequence&#8221;) is prepared for the TARANIS (Tool for Analysis of RAdiation from lightNIng and Sprites) micro-satellite of the French space agency CNES. The spacecraft is based on the MYRIADE series platform. It will be launched on a Sun synchronous polar orbit at 700 km altitude. TARANIS will carry a complex payload of six scientific instruments to study radiation from lightning and optical phenomena (Transient Luminous Events) observed at altitudes between 20 and 100 km (blue jets, red sprites, halos, elves). The scientific instruments onboard TARANIS will detect electromagnetic radiation from very low frequencies up to 37 MHz, optical radiation, X rays (with an aim to study the Terrestrial "Gamma-ray" Flashes), and energetic electrons.</p><p>The IME-HF instrument will record waveform measurements of fluctuating electric fields in the frequency range from a few kHz up to 37 MHz, with the following scientific aims: (i) Identification of possible wave signatures associated with transient luminous phenomena during storms; (ii)&#160;&#160;&#160; Characterization of lightning flashes from their HF electromagnetic signatures; (iii) Identification of possible HF electromagnetic or/and electrostatic signatures of precipitated and accelerated particles; (iv) Determination of characteristic frequencies of the medium using natural waves properties; (v) Global mapping of the natural and artificial waves in the HF frequency range, with an emphasis on the transient events. The instrument will be also able to trigger and record interesting intervals of data using a flexible event detection algorithm.</p>

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Design and analysis of ultra-wideband antennas for transient field excitations

Advances in Radio Science ◽

10.5194/ars-14-25-2016 ◽

2016 ◽

Vol 14 ◽

pp. 25-29

Author(s):

Miroslav Kotzev ◽

Matthias Kreitlow ◽

Frank Gronwald

Keyword(s):

Field Measurements ◽

Ultra Wideband ◽

Transient Field ◽

Wideband Antennas ◽

Frequency Spectra ◽

Low Frequencies ◽

Full Wave ◽

Wide Range ◽

High Pulse ◽

Broadband Pulse

Abstract. This work addresses the design of two ultra-wideband antennas for the application of transient field measurements that are characterized by frequency spectra that typically range from a few MHz to several GHz. The motivation for their design is the excitation of high power transient pulses, such as double exponential or damped sinusoidal pulses, within highly resonant metallic enclosures. The antenna design is based on two independent numerical full-wave solvers and it is aimed to achieve a low return loss over a wide range of frequencies together with a high pulse fidelity. It turns out that antennas of the conical and discone type do achieve satisfactory broadband characteristics while limitations towards low frequencies persist. Also the concept of fidelity factor turns out as advantageous to determine whether the proposed antennas allow transmitting certain broadband pulse forms.

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A Study of Nonstationary Wind Effects on a Full-Scale Large Cooling Tower Using Empirical Mode Decomposition

Mathematical Problems in Engineering ◽

10.1155/2017/9083426 ◽

2017 ◽

Vol 2017 ◽

pp. 1-15 ◽

Cited By ~ 2

Author(s):

X. X. Cheng ◽

J. Dong ◽

Y. Peng ◽

L. Zhao ◽

Y. J. Ge

Keyword(s):

Empirical Mode Decomposition ◽

Cooling Tower ◽

Time History ◽

Field Measurements ◽

Wind Pressure ◽

Wind Effects ◽

Intrinsic Mode Functions ◽

Low Frequencies ◽

Mode Decomposition ◽

Pressure Time

Wind effects on structures obtained by field measurements are often found to be nonstationary, but related researches shared by the wind-engineering community are still limited. In this paper, empirical mode decomposition (EMD) is applied to the nonstationary wind pressure time-history samples measured on an actual 167-meter high large cooling tower. It is found that the residue and some intrinsic mode functions (IMFs) of low frequencies produced by EMD are responsible for the samples’ nonstationarity. Replacing the residue by the constant mean and subtracting the IMFs of low frequencies can help the nonstationary samples become stationary ones. A further step is taken to compare the loading characteristics extracted from the original nonstationary samples with those extracted from the processed stationary samples. Results indicate that nonstationarity effects on wind loads are notable in most cases. The passive wind tunnel simulation technique based on the assumption of stationarity is also examined, and it is found that the technique is basically conservative for use.

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On the Optimal Field Sensing in Near-Field Characterization

Sensors ◽

10.3390/s21134460 ◽

2021 ◽

Vol 21 (13) ◽

pp. 4460

Author(s):

Amedeo Capozzoli ◽

Claudio Curcio ◽

Angelo Liseno

Keyword(s):

Near Field ◽

Gaussian Quadrature ◽

Field Measurements ◽

Singular Value ◽

Low Frequencies ◽

Virtual Sensors ◽

Phase Measurements ◽

Singular Functions ◽

Virtual Field ◽

Value Decomposition

We deal with the problem of characterizing a source or scatterer from electromagnetic radiated or scattered field measurements. The problem refers to the amplitude and phase measurements which has applications also to interferometric approaches at optical frequencies. From low frequencies (microwaves) to high frequencies or optics, application examples are near-field/far-field transformations, object restoration from measurements within a pupil, near-field THz imaging, optical coherence tomography and ptychography. When analyzing the transmitting-sensing system, we can define “optimal virtual" sensors by using the Singular Value Decomposition (SVD) approach which has been, since long time, recognized as the “optimal” tool to manage linear algebraic problems. The problem however emerges of discretizing the relevant singular functions, thus defining the field sampling. To this end, we have recently developed an approach based on the Singular Value Optimization (SVO) technique. To make the “virtual” sensors physically realizable, in this paper, two approaches are considered: casting the “virtual” field sensors into arrays reaching the same performance of the “virtual” ones; operating a segmentation of the receiver. Concerning the array case, two ways are followed: synthesize the array by a generalized Gaussian quadrature discretizing the linear reception functionals and use elementary sensors according to SVO. We show that SVO is “optimal” in the sense that it leads to the use of elementary, non-uniformly located field sensors having the same performance of the “virtual” sensors and that generalized Gaussian quadrature has essentially the same performance.

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Development of acoustic metamaterials for efficient sound control noise mitigation

10.32469/10355/88138 ◽

2021 ◽

Author(s):

◽

Huy Nguyen

Keyword(s):

Fano Resonance ◽

High Performance ◽

Noise Control ◽

Single Layer ◽

Acoustic Metamaterials ◽

Noise Mitigation ◽

Short Channel ◽

Low Frequencies ◽

Helmholtz Resonators ◽

Unit Cells

Acoustic metamaterials have been studied intensively recently since they can expose unnatural-born properties, potentially breaking the capacity limits of conventional acoustic materials. Since these interesting properties are mostly observed around metamaterials' local resonances/anti-resonance, resonance-based acoustic metamaterials are most popular in developing metamaterials. Employing resonance-based unnatural born properties such as effective negative mass density, effective negative bulk modulus, and acoustic hyper-damping on designing noise control solutions can give excellent devices showing such high performance that conventional acoustic material cannot achieve. This dissertation is an effort to employ acoustic metamaterials in designing efficient noise control. First, membrane-type acoustic metamaterials (MAM) will be employed to design a lightweight acoustic panel with high sound transmission loss (STL) in broadband at low frequencies. Negative density at around the anti-resonance of MAM gives it high capability on blocking sound. A double MAM-layer structure is proposed to double the STL performance of unit cells theoretically. Therein, simulation by using COMSOL Multiphysics is the main tool to optimize the unit cell design, panel structure, and effect of panel frame's vibration. Fabrication of the optimal design and experiments are also conducted to verify the calculation and simulation predictions. In addition to the acoustic panel, MAM is used to design a highly efficient acoustic energy harvester working at low frequencies. A magnet coin is deployed close to a magnet coil attached to the mass of MAM. The maximum oscillation of the coil due to MAM's first local resonance will induce a strong electric current inside the coil. Hence, energy can be harvested by an external resistor representing loads of harvesting devices. A complete theoretical model of the harvester is also developed in order to optimize its performance. Multiphysics simulation is conducted to verify the theoretical predictions. Besides MAM, Helmholtz has been used to design a high-performance and broadband acoustic silencer. Specifically, five slit-type Helmholtz resonators, which possess a massive viscous area, are packed together to create a single-layer silencer. In turn, two single-layer silencers are combined to form a double-layer silencer, which in theory double performance on noise blocking of the single-layer silencer. Theoretical models of slit-type Helmholtz resonators and silencers are developed completely and well validated with simulation and experimental results. Finally, Fano resonance resulting from the coupling between resonant and non-resonant channels will be explored and employed to design an ultra-broadband acoustic barrier with high ventilation. The resonant channel is generally represented a space-coiling channel, and the non-resonant channel represents ventilation or a straight and short channel. First, the formation of coupling Fano resonance will be theoretically addressed. Subsequently, acoustic hyper-damping is proposed by integrating thin acoustic foams into velocity anti-nodes in the resonant channel. In the end, an ultra-broadband acoustic barrier with high ventilation and STL is designed by employing three rows of hyper-dampened unit cells. Fabrication and experiment also are conducted to verify the simulation prediction.

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On low frequencies emitted by air guns at very shallow depths — An experimental study

Geophysics ◽

10.1190/geo2018-0687.1 ◽

2019 ◽

Vol 84 (5) ◽

pp. P61-P71 ◽

Cited By ~ 1

Author(s):

Daniel Wehner ◽

Martin Landrø ◽

Lasse Amundsen

Keyword(s):

Large Volume ◽

Field Experiments ◽

Field Measurements ◽

Seismic Source ◽

Sea Surface ◽

Frequency Signal ◽

Low Frequencies ◽

Air Gun ◽

Seismic Acquisition ◽

Marine Seismic

In marine seismic acquisition, the enhancement of frequency amplitudes below 5 Hz is of special interest because it improves imaging of the subsurface. The frequency content of the air gun, the most commonly used marine seismic source, is mainly controlled by its depth and the volume. Although the depth dependency on frequencies greater than 5 Hz has been thoroughly investigated, for frequencies less than 5 Hz it is less understood. However, recent results suggest that sources fired very close to the sea surface might enhance these very low frequencies. Therefore, we conduct dedicated tank experiments to investigate the changes of the source signal for very shallow sources in more detail. A small-volume air gun is fired at different distances from the water-air interface, including depths for which the air bubble bursts directly into the surrounding air. The variations of the oscillating bubble and surface disturbances, which can cause changes of the reflected signal from the sea surface, are explored to determine whether an increased frequency signal below 5 Hz can be achieved from very shallow air guns. The results are compared with field measurements of a large-volume air gun fired close to the sea surface. The results reveal an increased signal for frequencies below 5 Hz of up to 10 and 20 dB for the tank and field experiments, respectively, for the source depth at which the air gun bubble bursts directly into the surrounding air. For large-volume air guns, an increased low-frequency signal might also be achieved for sources that are slightly deeper than this bursting depth. From these observations, new design considerations in the geometry of air-gun arrays in marine seismic acquisition are suggested.

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Low Frequency Noise Considerations for Combustion Turbine Projects

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/97-gt-140 ◽

1997 ◽

Author(s):

Lisa A. Beeson ◽

George A. Schott

Keyword(s):

Noise Control ◽

Low Frequency ◽

Frequency Noise ◽

Low Frequency Noise ◽

Pressure Pulsations ◽

Relative Difficulty ◽

Low Frequencies ◽

Sound Energy ◽

Frequency Sound ◽

Human Ear

Combustion turbine projects have become a popular choice for providing a clean and efficient source of electricity. However, since combustion turbines generally produce low frequency sound energy, special siting considerations should be evaluated to minimize the potential for impacts on sensitive receptors, such as residences, churches, hospitals, and schools. For successful siting of combustion turbine projects near sensitive receptors, it is necessary to incorporate noise control features into plant designs to reduce not only audible noise but also noise at frequencies which are even lower than the human ear can perceive. These extremely low frequencies can rattle walls and windows, causing pressure pulsations which may be perceived by some people, or vibration of small objects inside houses and other structures. Even “quiet” plants which include extensive noise control features may still result in perceptible low frequency noise due to the relative difficulty of attenuating low frequency sound energy. Noise attenuation options are discussed, including active, passive, and reactive technologies, along with the impacts associated with each type of design. Guidelines for siting combustion turbine power generation facilities near sensitive receptors are presented, to enable development of projects which not only meet applicable noise requirements, but also reduce the potential for community complaints.

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Multi-tonal low frequency noise control using Helmholtz resonators with complex cavity designs for aircraft cabin noise improvement

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-2569 ◽

2021 ◽

Vol 263 (2) ◽

pp. 3975-3986

Author(s):

Tenon Charly Kone ◽

Sebastian Ghinet ◽

Raymond Panneton ◽

Thomas Dupont ◽

Anant Grewal

Keyword(s):

Noise Control ◽

Transmission Loss ◽

Low Frequency ◽

Helmholtz Resonator ◽

Sound Insulation ◽

Frequency Noise ◽

Low Frequency Noise ◽

Low Frequencies ◽

Helmholtz Resonators ◽

Resonance Frequencies

The noise control at multiple tonal frequencies simultaneously, in the low frequency range, is a challenge for aerospace, ground transportation and building industries. In the past few decades, various low frequency noise control solutions based on acoustic metamaterial designs have been presented in the literature. These solutions showed promising performance and are considered a better alternative to conventional sound insulation materials. In the present investigation, it was noticed that subdividing the cavity of a Helmholtz resonator allowed the control of multi-tonal noise at several resonance frequencies simultaneously and a shift of the resonance peaks towards the low frequencies. This paper proposes concepts of Helmholtz resonators with subdivided cavities to improve the sound transmission loss (STL) performance and simultaneously control the noise at several tonal frequencies. HRs with cylindrical shaped cavities were embedded in a layer of porous material. The STL of the metamaterial noise insulation configuration was predicted using serial and parallel assemblies of transfer matrices (TMM) incorporating a thermo-viscous-acoustic approach to accurately account for the viscous and thermal losses of acoustic wave propagation within the metamaterial. The STL calculated using the proposed TMM approach were observed to be in excellent agreement with the finite element method (FEM) numerical results.

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