The Noise-Producing Characteristics of Highly Loaded, Valveless, Pulse Combustors

1988 ◽  
Vol 110 (2) ◽  
pp. 238-245 ◽  
Author(s):  
J. A. C. Kentfield
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Noise Suppression ◽  
Analytical Data ◽  
Velocity Profiles ◽  
Noise Generation ◽  
Noise Levels ◽  
Transient Velocity ◽  
Inherent Problem ◽  
Frequency Pulse

An inherent problem of pulsating combustors is noise generation and the difficulty of predicting noise levels. Analytical data are presented which illustrate the transient velocity profiles prevailing at the open ends of the inlets and tailpipes of valveless pulse combustors. A comparison is made of measured sound pressure level spectra at these locations with corresponding predicted transient velocity profiles. It is shown that there is a correlation of the main characteristics of the noise spectra and velocity profiles. Consideration is also given to the problems of muffling valveless pulse combustors and the potential, from the noise suppression viewpoint, of twin-coupled units and relatively high frequency pulse combustors featuring multiple inlet passages. An indication is also given of how it may be possible to operate clusters, or arrays, of pulse combustors firing sequentially.

Prediction and analysis of sound field in long enclosures with a modal-based method

2021 ◽  
Vol 69 (6) ◽  
pp. 518-529
Author(s):  
Changyong Jiang ◽  
Xiang Liu ◽  
Stephany Y. Xu ◽  
Shangyu Zhang
Keyword(s):  
Porous Material ◽  
Point Source ◽  
Sound Pressure Level ◽  
High Frequency ◽  
Sound Pressure ◽  
Prediction Method ◽  
Sound Field ◽  
Pressure Level ◽  
Noise Levels ◽  
Level Reduction

In this paper, the efficacy of porous ceiling treatment to reduce noise levels inside a typical tunnel is examined with a validated modal-based prediction method. It is found that, for a point source, the effect of increasing porous ceiling thickness on sound pressure level (SPL) attenuation along the tunnel is limited. A porous ceiling with thickness of 0.3 m is comparable with an infinite porous ceiling in middle and high frequency ranges. For a line source, the effect of ceiling thickness on SPL reduc- tion in this typical tunnel is limited. Sound pressure level reduction of 4 dBA is real- ized with 0.3 m porous ceiling, which is the same as infinite ceiling and only 1 dBA smaller than the theoretically optimized value. These results suggest that, in the event only ceiling treatment is considered, 0.3 m porous material is sufficient for noise re- duction in this typical tunnel.

Noise Control on Diesel Tugs

1973 ◽  
Vol 10 (04) ◽  
pp. 321-333
Author(s):  
Thomas R. Dyer ◽  
Bertel Lundgaard
Keyword(s):  
Noise Level ◽  
Noise Suppression ◽  
Noise Control ◽  
Noise Generation ◽  
Noise Levels ◽  
Paper Briefly ◽  
Acoustic Treatment

The paper briefly gives basic acoustic definitions and explains the fundamental concepts used in noise control. The mechanics of noise generation and the various methods used in noise suppression are explained. The silencing program employed on two sister tugs, Edith Lovejoy and Anne Carlander, is described in detail. The acoustic treatment of the tugs is not identical and the resulting noise level differences are discussed. Alternative acoustic approaches are described and evaluated. The paper is illustrated with graphs and tables of noise levels, and shows typical vessel arrangements and acoustic treatment details. A short bibliography is included.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

scholarly journals The Effect of High Frequency Pulse on the Discharge Probability in Micro EDM

2017 ◽  
Vol 281 ◽  
pp. 012031
Author(s):  
Y Liu ◽  
Y Qu ◽  
W Zhang ◽  
F Ma ◽  
Z Sha ◽  
...  
Keyword(s):  
High Frequency ◽  
Micro Edm ◽  
Frequency Pulse

scholarly journals Transfer of diclofenac sodium across excised guinea pig skin on high-frequency pulse iontophoresis. I. Equivalent circuit model.

1990 ◽  
Vol 38 (4) ◽  
pp. 1019-1021 ◽  
Author(s):  
Tamotsu KOIZUMI ◽  
Masawa KAKEMI ◽  
Kazunori KATAYAMA ◽  
Hirohiko INADA ◽  
Kazuyoshi SUDEJI ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Equivalent Circuit ◽  
High Frequency ◽  
Diclofenac Sodium ◽  
Equivalent Circuit Model ◽  
Circuit Model ◽  
Pig Skin ◽  
Frequency Pulse

scholarly journals Power MOSFET Linearizer of a High-Voltage Power Amplifier for High-Frequency Pulse-Echo Instrumentation

Sensors ◽  
2017 ◽  
Vol 17 (4) ◽  
pp. 764 ◽  
Author(s):  
Hojong Choi ◽  
Park Woo ◽  
Jung-Yeol Yeom ◽  
Changhan Yoon
Keyword(s):  
Power Amplifier ◽  
High Voltage ◽  
High Frequency ◽  
Power Mosfet ◽  
Pulse Echo ◽  
Frequency Pulse

The Effect of HFPD Thermally Sprayed WC-Co Coatings on the Fatigue Behavior and Deformation of Al 2024-T4

2000 ◽  
Author(s):  
A. Ibrahim ◽  
C.C. Berndt
Keyword(s):  
High Frequency ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cycle Fatigue ◽  
Pulse Detonation ◽  
Deformation Behaviors ◽  
Life Distributions ◽  
Thermally Sprayed ◽  
Al 2024 ◽  
Frequency Pulse

Abstract The effect of high frequency pulse detonation (HFPD) and HVOF thermally sprayed WC-Co coatings on the high cycle fatigue (HCF) behavior of 2024-T4 aluminum was investigated. The fatigue life distributions of specimens in the polished and coated conditions are presented as a function of the probability of failure. The monotonic and cyclic deformation behaviors of the as-received and as-coated specimens were investigated. The conclusions show that, (i) the HFPD sprayed specimens exhibited slightly higher fatigue lives compared to the uncoated specimens, (ii) the HVOF sprayed specimens exhibited significantly higher fatigue lives compared to the uncoated specimens, and (iii) the as-coated specimen was cyclically stable.

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