TECHNIQUE FOR ESTIMATING THE EFFICIENCY OF NOISE PROTECTIVE ACOUSTIC SCREENS IN THE PRESENCE OF FLAT ANTI-DIFFRACTORS

Akustika ◽  
2021 ◽  
pp. 22-28
Author(s):  
E.V. Fedoseeva ◽  
V.V. Bulkin ◽  
M.V. Kalinichenko
Keyword(s):  
Sound Wave ◽  
Noise Source ◽  
Acoustic Noise ◽  
Cylindrical Wave ◽  
Operating Point ◽  
Secondary Source ◽  
Amplitude Dependence ◽  
Wave Source ◽  
Acoustic Shadow ◽  
Flat Type

To increase the efficiency of acoustic screens when protecting against acoustic noise, anti-diffractors are used to reduce the diffraction level on the upper edge of the screen. The aim of the work is to refine the mathematical model used to assess noise protection efficiency with the help of an acoustic screen with an installed one-sided flat-type anti-diffractor. The well-known techniques based on the principle of the amplitude dependence of the sound wave intensity from two sources are analyzed: a point-type noise source and a secondary cylindrical wave source - the screen edge, on which the sound wave is diffracted. Taking into account that the change in the distance between the anti-diffractor and the working point in the acoustic shadow zone is associated with a change in the diffraction angle, it is proposed to evaluate the acoustic screen effectiveness by comparing the initial sound wave propagation paths. An approach to a mathematical calculation model formation is proposed, in which the diffraction point located at the intersection of two components of the wave path to the operating point is considered to be the location of the sound wave secondary source in the area of the screen upper edge: from the noise source to the flat-type anti-diffractor installed on the upper edge of the screen, and from the anti-diffractor rear edge to the operating point. Relationships that make it possible to solve the problem of analytical assessment of noise-protective acoustic screens' effectiveness when installing anti-diffractors on their upper face in the form of flat hinged panels oriented towards the acoustic shadow are obtained.

Acoustic Noise-Source Identification in Aircraft-Based Atmospheric Temperature Measurements

AIAA Journal ◽  
2002 ◽  
Vol 40 (7) ◽  
pp. 1382-1387 ◽  
Author(s):  
Ronald J. Hugo ◽  
Scott R. Nowlin ◽  
Ila L. Hahn ◽  
Frank D. Eaton ◽  
Kim A. McCrae
Keyword(s):  
Source Identification ◽  
Noise Source ◽  
Acoustic Noise ◽  
Atmospheric Temperature ◽  
Temperature Measurements ◽  
Noise Source Identification

scholarly journals Experimental investigation on the potential of the Feedback Fx-LMS Active Noise Control technology for use in industrial generator sets

2021 ◽  
Vol 312 ◽  
pp. 08007
Author(s):  
Marco Ciampolini ◽  
Lorenzo Bosi ◽  
Luca Romani ◽  
Andrea Toniutti ◽  
Matteo Giglioli ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Noise Control ◽  
Noise Source ◽  
Acoustic Noise ◽  
Active Noise Control ◽  
Lms Algorithm ◽  
Destructive Interference ◽  
Exhaust Pipe ◽  
Least Mean Square ◽  
Active Noise

Active Noise Control (ANC) has been considered a promising technology for the abatement of acoustic noise from the mid-20th century. Feedback and Feedforward ANC algorithms, based on the destructive interference principle applied to acoustic waves, have been developed for different applications, depending on the spectrum of the noise source. Feedback ANC algorithms make use of a single control microphone to measure an error signal which is then employed by an adaptive filter to estimate the noise source and generate an opposite-phase control signal. The Fx-LMS (Filtered-X Least Mean Square) algorithm is mostly adopted to update the filter. Feedback ANC systems have proven to be effective for the abatement of low-frequency quasi-steady noises; however, different challenges must be overcome to realize an effective and durable system for high-temperature application. This paper aims at experimentally assessing the feasibility of a Feedback Fx-LMS ANC system with off-line Secondary Path estimation to be used in mid-size diesel gensets for the reduction of the exhaust noise. Several solutions are proposed, including the mechanical design, the development of the Fx-LMS algorithm in the LabVIEW FPGA programming language, and the key features required to prevent parts from thermal damage and fouling. The developed prototype was implemented on a 50-kW diesel genset and tested in a semi-anechoic chamber. The noise abatement inside the exhaust pipe and at different measurement points around the machine was evaluated and discussed, showing good potential for improving the acoustic comfort of genset users.

Drive-by large-region acoustic noise-source mapping via sparse beamforming tomography

2016 ◽  
Vol 140 (4) ◽  
pp. 2530-2541 ◽  
Author(s):  
Cagdas Tuna ◽  
Shengkui Zhao ◽  
Thi Ngoc Tho Nguyen ◽  
Douglas L. Jones
Keyword(s):  
Noise Source ◽  
Acoustic Noise ◽  
Large Region ◽  
Sparse Beamforming

Structural and acoustic noise produced by turbulent flow over an elastic trailing edge

1993 ◽  
Vol 442 (1916) ◽  
pp. 533-554 ◽  
Keyword(s):  
Turbulent Flow ◽  
Elastic Plate ◽  
Acoustic Noise ◽  
Acoustic Radiation ◽  
Steel Plates ◽  
Control Surface ◽  
Secondary Source ◽  
Thin Elastic Plate ◽  
Mean Flow ◽  
Trailing Edge

An analysis is made of the sound and vibration produced by turbulent flow at low Mach number over the trailing edge of an elastic plate. The trailing edges of airfoils and other flow control surfaces are known to be important sources of high frequency sound. When the surface is compliant the turbulent edge-flow also excites structural modes of vibration. In conditions of heavy fluid loading, which typically occurs in underwater applications, the energy imparted to the structural motions can be large, and the subsequent scattering of ‘surface waves’ at mechanical discontinuities is frequently an important secondary source of sound. In this paper general formulae are developed for the structural and acoustic edge-noise when the control surface is modelled by a semi-infinite, thin elastic plate which can support bending waves. Numerical results are given for steel plates in air and in water. In the latter case it is shown that, when the frequency is smaller than the coincidence frequency the bending wave power exceeds the total sound power generated at the edge by 20–40 dB, independently of the mean flow velocity, so that sound generated by secondary scattering may then be the dominant source of acoustic radiation.

scholarly journals An Aero-acoustic Noise Distribution Prediction Methodology for Offshore Wind Farms

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 18 ◽  
Author(s):  
Jiufa Cao ◽  
Weijun Zhu ◽  
Xinbo Wu ◽  
Tongguang Wang ◽  
Haoran Xu
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Farm ◽  
Noise Source ◽  
Acoustic Noise ◽  
Turbine Blades ◽  
Wind Farms ◽  
Noise Generation ◽  
Human Beings ◽  
Wind Turbine Noise

Recently attention has been paid to wind farm noise due to its negative health impact, not only on human beings, but also to marine and terrestrial organisms. The current work proposes a numerical methodology to generate a numerical noise map for a given wind farm. Noise generation from single wind turbines as well as wind farms has its basis in the nature of aerodynamics, caused by the interactions between the incoming turbulent flow and the wind turbine blades. Hence, understanding the mechanisms of airfoil noise generation, demands access to sophisticated numerical tools. The processes of modeling wind farm noise include three steps: (1) The whole wind farm velocity distributions are modelled with an improved Jensen’s wake model; (2) The individual wind turbine’s noise is simulated by a semi-empirical wind turbine noise source model; (3) Propagations of noise from all wind turbines are carried out by solving the parabolic wave equation. In the paper, the wind farm wake effect from the Horns Rev wind farm is studied. Based on the resulted wind speed distributions in the wind farm, the wind turbine noise source and its propagation are simulated for the whole wind farm.

Mapping Heavy Vehicle Noise Source Heights for Highway Noise

2018 ◽  
Vol 2672 (24) ◽  
pp. 134-143 ◽  
Author(s):  
Carrie Janello ◽  
Paul R. Donavan
Keyword(s):  
North Carolina ◽  
Noise Source ◽  
Operating Conditions ◽  
Heavy Vehicle ◽  
Secondary Source ◽  
Noise Sources ◽  
Vehicle Noise ◽  
Heavy Trucks ◽  
Heavy Truck ◽  
Pavement Noise

The NCHRP Project 25-45 was initiated in 2013 to measure noise sources during heavy truck pass-bys using the acoustic beamforming method. Phase I testing included measurements from four relatively flat sites in Northern California, where heavy trucks traveled under moderate vehicle speeds. Sixteen additional sites in North Carolina were tested as part of Phase II. These sites had varying pavement grades, faster/slower posted speed limits, and varying operating conditions. The source mapping results from both phases were used to develop noise versus height profiles. The profiles were not significantly dependent on site and operating conditions. Average profiles were developed for each site to demonstrate that the predominant noise source was tire/pavement noise, with engine/powertrain being the secondary source; elevated sources occurred rarely and were equal to or greater than tire/pavement for only 0.5% of the total 1,289 trucks measured, while only 1.8% were within 5 dB(A) of the pavement source and 4.7% were within 10 dB(A).

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