Active Resonators for Noise Absorption

2006 ◽  
Vol 128 (1) ◽  
pp. 115 ◽  
Author(s):  
Jing Yuan
Keyword(s):  
Noise Absorption

scholarly journals Case study of the mesospheric and lower thermospheric effects of solar X-ray flares: coupled ion-neutral modelling and comparison with EISCAT and riometer measurements

2008 ◽  
Vol 26 (8) ◽  
pp. 2311-2321 ◽  
Author(s):  
C.-F. Enell ◽  
P. T. Verronen ◽  
M. J. Beharrell ◽  
J. P. Vierinen ◽  
A. Kero ◽  
...  
Keyword(s):  
Solar Proton ◽  
Spectral Irradiance ◽  
Cluster Ions ◽  
Ion Chemistry ◽  
Density Profiles ◽  
X Ray ◽  
Noise Absorption ◽  
D Region ◽  
Electron Density Profiles ◽  
Cosmic Noise

Abstract. Two case studies of upper mesospheric and lower thermospheric (UMLT) high-latitude effects of solar X-ray flares are presented. Sodankylä Ion-neutral Chemistry Model (SIC) electron density profiles agree with D-region EISCAT and riometer observations, provided that the profiles of the most variable ionisable component, nitric oxide, are adjusted to compensate for NOx production during preceding geomagnetically active periods. For the M6-class flare of 27 April 2006, following a quiet period, the agreement with cosmic noise absorption observed by the Sodankylä riometers was within reasonable limits without adjustment of the [NO] profile. For the major (X17-class) event of 28 October 2003, following high auroral activity and solar proton events, the NO concentration had to be increased up to on the order of 108 cm−3 at the D-region minimum. Thus [NO] can in principle be measured by combining SIC with observations, if the solar spectral irradiance and particle precipitation are adequately known. As the two case events were short and modelled for high latitudes, the resulting neutral chemical changes are insignificant. However, changes in the model ion chemistry occur, including enhancements of water cluster ions.

scholarly journals Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects

2018 ◽  
Vol 8 (10) ◽  
pp. 1923
Author(s):  
Martin Dannemann ◽  
Michael Kucher ◽  
Eckart Kunze ◽  
Niels Modler ◽  
Karsten Knobloch ◽  
...  
Keyword(s):  
Polymer Films ◽  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Acoustic Energy ◽  
Acoustic Damping ◽  
Acoustic Performance ◽  
Acoustic Liners ◽  
Flexible Polymer ◽  
Noise Absorption ◽  
Aero Engines

In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise absorption for HR liners is presented. By replacing rigid cell walls in the liner’s honeycomb core structure by flexible polymer films, additional acoustic energy is dissipated. A manufacturing technology for square honeycomb cores with partially flexible walls is described. Samples with different flexible wall materials were fabricated and tested. The acoustic measurements show more broadband sound absorption compared to a reference liner with rigid walls due to acoustic-structural interaction. Manufacturing-related parameters are found to have a strong influence on the resulting vibration behaviour of the polymer films, and therefore on the acoustic performance. For future use, detailed investigations to ensure the liner segments compliance with technical, environmental, and life-cycle requirements are needed. However, the results of this study show the potential of this novel liner concept for noise reduction in future aero-engines.

scholarly journals IMPROVEMENT OF MUFFLER S DESIGN FOR REDUCTION OF THE LEVEL OF SOUND PRESSURE ON SMALL TRACTORS OPERATORS

2021 ◽  
Author(s):  
M. I. Podolsky ◽  
◽  
I. Y. Lilevman ◽  
O. Y. Lilevman ◽  
O. Y. Kedrovsky ◽  
...  
Keyword(s):  
Internal Combustion Engines ◽  
Gas Flow ◽  
Sound Pressure ◽  
Internal Combustion ◽  
Pressure Level ◽  
Combustion Engines ◽  
Sound Waves ◽  
Exhaust Gases ◽  
Noise Absorption ◽  
Made In

Noise background, as an important factor in the working conditions of agricultural operators, has a direct impact on human health and productivity. This topic is especially relevant for small tractors, which in most cases are not equipped with cabs. One of the main means of reducing the sound pressure on the operator are the mufflers of exhaust gases, which mainly have a labyrinth-absorbing type of action. The paper proposes a fundamental approach to the design of the muffler by the criterion of reflection and scattering of sound waves with the verification of efficiency by computer simulation. The purpose of research: - to improve the working conditions of operators of small tractors that are not equipped with cabs, by reducing the sound pressure level from internal combustion engines; - to improve the noise-absorbing properties of mufflers of exhaust gases of engines with observance of requirements to manufacturability of process of their manufacturing; - to develop a structural scheme of the exhaust gases muffler based on the results of preliminary modeling and analysis of the trajectory of the gas flow in the cavity of its working part. Methods. Determination of the sound pressure level of the engine of a small tractor by mathematical (computer) modeling of the behavior of the exhaust gas flow in the muffler cavity in different frequency ranges. Results. The article analyzes the main sources of noise during the operation of agricultural machinery with internal combustion engines (ICE). On the basis of literature sources and methods, their separate degree of influence on the complex picture of noise pollution of the working space of the operator of a small tractor is established. A comparative analysis of the efficiency of mufflers, created on the generally accepted principles and approaches to the design of such devices. According to the results of previous tests, shortcomings and limitations in the application of design concepts were identified, an additional analysis of external causes and factors was made, and adjustments were made to the method of creating muffler designs. An alternative design approach to the creation of internal combustion engine mufflers of small tractors is proposed and computer modeling of the processes of sound pressure distribution and sound waves in their cavity is performed. Conclusions. 1. A layout diagram of the design of the exhaust muffler, containing a resonator chamber and a shell module, which is made in the form of a three-stage ribbed diffuser of oscillations of the exhaust flow pulses with an additional surface layer of the vibration absorber. The parameters of the exhaust flow of exhaust gases of a typical diesel engine of a small tractor with a capacity of 24 hp are calculated. (pressure - 11652 Pa, acceleration – 90-105 m / s2, frequency - 1950-3300 Hz), which performed computer simulations of the process of gas movement in the muffler cavity of the proposed layout. Optimal design parameters were selected to ensure the maximum possible noise absorption with a body diameter of 150 mm and a length of 600 mm. The calculated sound pressure when working at the crankshaft speed (1700-2000) rpm does not exceed 72 dB. At the same time, the design of the muffler is made in compliance with the requirements for economic feasibility, manufacturability and in accordance with the capabilities of industrial production. A further direction of research is the manufacture of an experimental sample of the muffler and testing for the efficiency of its noise absorption in the conditions of operation of small tractors.

scholarly journals Pulsating aurora and cosmic noise absorption associated with growth-phase arcs

2018 ◽  
Vol 36 (1) ◽  
pp. 59-69 ◽  
Author(s):  
Derek McKay ◽  
Noora Partamies ◽  
Juha Vierinen
Keyword(s):  
Growth Phase ◽  
Optical Emission ◽  
Border Region ◽  
Emission Region ◽  
Expansion Phase ◽  
Phase Dynamics ◽  
Noise Absorption ◽  
Initial Stage ◽  
Cosmic Noise

Abstract. The initial stage of a magnetospheric substorm is the growth phase, which typically lasts 1–2 h. During the growth phase, an equatorward moving, east–west extended, optical auroral arc is observed. This is called a growth-phase arc. This work aims to characterize the optical emission and riometer absorption signatures associated with growth-phase arcs of isolated substorms. This is done using simultaneous all-sky camera and imaging riometer observations. The optical and riometric observations allow determination of the location of the precipitation within growth-phase arcs of low- (<10  keV) and high- (> 10 keV) energy electrons, respectively. The observations indicate that growth-phase arcs have the following characteristics: The peak of the cosmic noise absorption (CNA) arc is equatorward of the optical emission arc. This CNA is contained within the region of diffuse aurora on the equatorward side. Optical pulsating aurora are seen in the border region between the diffuse emission region on the equatorward side and the bright growth-phase arc on the poleward side. CNA is detected in the same region. There is no evidence of pulsations in the CNA. Once the equatorward drift starts, it proceeds at constant speed, with uniform separation between the growth-phase arc and CNA of 40±10 km. Optical pulsating aurora are known to be prominent in the post-onset phase of a substorm. The fact that pulsations are also seen in a fairly localized region during the growth phase shows that the substorm expansion-phase dynamics are not required to closely precede the pulsating aurora. Keywords. Ionosphere (auroral ionosphere)

scholarly journals Determination of the altitudinal peak of Cosmic Noise Absorption using a vertical parallax technique

2004 ◽  
Vol 31 (7) ◽  
pp. n/a-n/a ◽  
Author(s):  
M. B. Terkildsen ◽  
B. J. Fraser ◽  
H. Yamagishi
Keyword(s):  
Noise Absorption ◽  
Cosmic Noise

Noise Absorption of Automotive Seats

1998 ◽  
Author(s):  
Pusheng Chen ◽  
Gordon Ebbitt
Keyword(s):  
Noise Absorption
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