Numerical Mode Matching Approach for Acoustic Attenuation Predictions of Double-Chamber Perforated Tube Dissipative Silencers with Mean Flow

2014 ◽  
Vol 22 (02) ◽  
pp. 1450004 ◽  
Author(s):  
Z. Fang ◽  
Z. L. Ji
Keyword(s):  
High Frequency ◽  
Present Method ◽  
Transmission Loss ◽  
Mode Matching ◽  
Acoustic Behavior ◽  
Frequency Range ◽  
Mean Flow ◽  
High Frequencies ◽  
Perforated Tube ◽  
Double Chamber

The transfer matrix method (TMM) based on numerical mode matching (NMM) approach is developed to investigate the acoustic behavior of double-chamber perforated tube dissipative silencer with mean flow. The present method is verified by comparing the transmission loss (TL) predictions and experimental data. Then the effects of mean flow, perforated tube offset and lengths of perforations are studied computationally. As the Mach number increases, the TL of dissipative silencer is lowered at most frequencies. The perforated tube offset may change the acoustic behavior in the mid-high frequency range. Increasing the total length of perforations increases TL at the mid-high frequencies.

Fluctuating boundary layer on a magnetized plate

1967 ◽  
Vol 63 (2) ◽  
pp. 513-525 ◽  
Author(s):  
Sahib Singh Chawla
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Surface Current ◽  
Frequency Range ◽  
Mean Flow ◽  
Wave Type ◽  
High Frequencies ◽  
Phase Lead ◽  
The Mean ◽  
The Magnetic Field

The laminar boundary layer on a magnetized plate, when the magnetic field oscillates in magnitude about a constant non-zero mean, is analysed. For low-frequency fluctuations the solution is obtained by a series expansion in terms of a frequency parameter, while for high frequencies the flow pattern is of the ‘skin-wave’ type unaffected by the mean flow. In the low-frequency range, the phase lead and the amplitude of the skin-friction oscillations increase at first and then decrease to their respective ‘skin-wave’ values. On the other hand the phase angle of the surface current decreases from 90° to 45° and its amplitude increases with frequency.

ACOUSTIC ATTENUATION CHARACTERISTICS OF STRAIGHT-THROUGH PERFORATED TUBE SILENCERS AND RESONATORS

2008 ◽  
Vol 16 (03) ◽  
pp. 361-379 ◽  
Author(s):  
Z. L. JI
Keyword(s):  
Performance Prediction ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Geometrical Parameters ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
One Dimensional ◽  
The One ◽  
Attenuation Characteristics ◽  
Perforated Tube

The one-dimensional analytical solutions are derived and three-dimensional substructure boundary element approaches are developed to predict and analyze the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators without mean flow, as well as to examine the effect of nonplanar waves in the silencers and resonators on the acoustic attenuation performance. Comparisons of transmission loss predictions with the experimental results for prototype straight-through perforated tube silencers demonstrated that the three-dimensional approach is needed for accurate acoustic attenuation performance prediction at higher frequencies, while the simple one-dimensional theory is sufficient at lower frequencies. The BEM is then used to investigate the effects of geometrical parameters on the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators in detail.

scholarly journals Acoustic Behavior of Halobacterium salinarum Gas Vesicles in the High-Frequency Range: Experiments and Modeling

2017 ◽  
Vol 43 (5) ◽  
pp. 1016-1030 ◽  
Author(s):  
Emmanuel Cherin ◽  
Johan M. Melis ◽  
Raymond W. Bourdeau ◽  
Melissa Yin ◽  
Dennis M. Kochmann ◽  
...  
Keyword(s):  
High Frequency ◽  
Halobacterium Salinarum ◽  
Acoustic Behavior ◽  
High Frequency Range ◽  
Gas Vesicles ◽  
Frequency Range

Mechanical Response of the Lungs at High Frequencies

1978 ◽  
Vol 100 (2) ◽  
pp. 57-66 ◽  
Author(s):  
J. J. Fredberg ◽  
A. Hoenig
Keyword(s):  
Efficient Method ◽  
High Frequency ◽  
Input Impedance ◽  
Mechanical Response ◽  
Airway Wall ◽  
Frequency Range ◽  
Resonant Frequencies ◽  
High Frequencies ◽  
Branching Networks ◽  
Adult Humans

We put forward an efficient method for computing the input impedance of complex asymmetrically branching duct networks, and apply this method to simulation of the dynamic response of the lungs of normal adult humans in the frequency range extending to 10,000 Hz. The results indicate that the response of comparable symmetric and asymmetric branching networks differ at high frequency (> 2 kHz in air), and that the airway wall response is an important factor in determining system damping and resonant frequencies.

scholarly journals Influence of perforation and sound-absorbing material filling on acoustic attenuation performance of three-pass perforated mufflers

2018 ◽  
Vol 10 (1) ◽  
pp. 168781401774801 ◽  
Author(s):  
Hongpu Huang ◽  
Zhenlin Ji ◽  
Zhuoliang Li
Keyword(s):  
Finite Element Method ◽  
Transmission Loss ◽  
The Finite Element Method ◽  
Frequency Range ◽  
Acoustic Attenuation ◽  
Pressure Drops ◽  
Outlet Tube ◽  
Middle Chamber ◽  
Absorbing Material ◽  
Perforated Tube

The finite element method is employed to calculate the transmission loss of three-pass perforated reactive and hybrid mufflers. The effects of perforated tubes and bulkheads on the transmission loss of three-pass reactive mufflers are investigated numerically. Two types of hybrid mufflers are considered, and the effects of sound-absorbing material filling and packed outlet tube on the acoustic attenuation performance of mufflers are analyzed. The perforations of the tubes and bulkheads and sound-absorbing material filling are demonstrated to have significant influence on the acoustic attenuation behaviors of the mufflers. The perforation of the tubes and bulkheads may shift the resonance from the low- to middle-frequency range. The sound-absorbing material filling in the middle chamber improves the acoustic attenuation performance at middle to higher frequencies and provides a relatively flat and broadband acoustic attenuation. It is found that the solid inlet or outlet tube replacing the perforated tube and sound-absorbing material filling in the middle chamber increases the pressure drops, while the rest configurations change the pressure drops slightly.

Flow Induced Aerodynamic Noise Analysis of Perforated Tube Mufflers

2012 ◽  
Vol 29 (2) ◽  
pp. 225-231 ◽  
Author(s):  
C.-N. Wang ◽  
C.-C. Tse ◽  
S.-C. Chen
Keyword(s):  
Transmission Loss ◽  
Noise Analysis ◽  
Helmholtz Resonator ◽  
Aerodynamic Noise ◽  
Mean Flow ◽  
Flow Effect ◽  
Flow Induced Noise ◽  
The Mean ◽  
Cfd Method ◽  
Perforated Tube

AbstractDespite the analysis of muffler performance for many years, most works focus mainly on reducing inlet sound and fail to consider the flow effect. Most of their results correlate well with the experimental measurements. Subsequent works have considered the mean flow effect. Owing to Doppler's effect, transmission loss curve of the muffler will shift in its corresponding frequency. However, the correlation is worse than the experimental results since the flow induced noise does not include in the analysis. This work elucidates how flow induced noise affects muffler performance by analyzing a uniform flow that passes through perforated mufflers. The flow field is calculated with the CFD method, followed by evaluation of the aerodynamic noise based on the simulation results. Additionally, the procedure is simplified by computing and comparing only the total sound power induced by the flow in the muffler interior. Two muffler types, Helmholtz resonator and plug perforated tube muffler, are analyzed and discussed.

A Numerical Analysis for Perforated Muffler Components with Mean Flow

1999 ◽  
Vol 121 (2) ◽  
pp. 231-236 ◽  
Author(s):  
Chao-Nan Wang
Keyword(s):  
Wave Propagation ◽  
Performance Prediction ◽  
Present Method ◽  
Mean Flow ◽  
Acoustic Performance ◽  
Higher Order Modes ◽  
Element Approach ◽  
The Mean ◽  
Perforated Tube ◽  
Plane Wave Propagation

A boundary element approach for analyzing the perforated muffler components with mean flow is developed. Most of the research on perforated mufflers is based on the assumption of plane wave propagation. In the present method, the effects of mean flow, including the convection effect in governing equation and the change of acoustic impedance of perforated tube, are considered and the influences of higher order modes are also included. The acoustic performance prediction is performed on the perforated intruding tube mufflers and also on the plug muffler with and without mean flow. Comparisons of the influences of various porosity, the mean flow velocities, the tube thickness and the hole diameters are investigated. However, the results need to be verified by further experimental measurement.

Extended High-Frequency Thresholds in Older Adults

1997 ◽  
Vol 40 (1) ◽  
pp. 208-214 ◽  
Author(s):  
Lois J. Matthews ◽  
Fu-Shing Lee ◽  
John H. Mills ◽  
Judy R. Dubno
Keyword(s):  
High Frequency ◽  
Age Groups ◽  
Test Session ◽  
Normal Hearing ◽  
Gender Effects ◽  
Frequency Range ◽  
Age And Gender ◽  
High Frequencies ◽  
And Gender ◽  
Test Retest Reliability

Most measures of auditory sensitivity at extended high frequencies (frequencies greater than 8 kHz) have been obtained from listeners with normal hearing less than 40 years of age. The purpose of this study was (a) to measure thresholds at frequencies above 8 kHz in older listeners who, as a group, have elevated thresholds at lower frequencies, and (b) to assess test-retest reliability, age and gender effects, and the influence of thresholds below 8 kHz. Extended high-frequency (EHF) thresholds were measured for 162 older listeners (60–79 years) using a commercially available high-frequency audiometer, with a frequency range of 8 to 18 kHz and an intensity range of 0 to 110 dB SPL. Thresholds were measured once at the beginning of a 1- to 2-hour test session and then remeasured at the end of the test session. EHF thresholds of older listeners with normal hearing at conventional audiometric frequencies were substantially higher than the thresholds reported for younger listeners with normal hearing by Dreschler and van der Hulst (1987). EHF thresholds of older listeners with hearing loss at conventional audiometric frequencies were further elevated as compared to older listeners with normal hearing. Differences in EHF thresholds between females and males were either not present or were reduced when gender differences in conventional audiometric thresholds were taken into account. No significant differences were seen in thresholds at 8 kHz and higher between the 60- to 69- and 70- to 79-year-old age groups. Results also indicated that thresholds above 8 kHz can be measured in older listeners within a clinically acceptable ±10 dB test-retest range.

scholarly journals Acoustic Attenuation Performance of Two-Pass Perforated Hybrid Mufflers with Mean Flow

2021 ◽  
Vol 26 (4) ◽  
pp. 306-315
Author(s):  
Yiliang Fan ◽  
Zhenlin Ji
Keyword(s):  
Analytical Approach ◽  
Transmission Loss ◽  
Glass Wool ◽  
Frequency Range ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
Fiber Glass ◽  
One Dimensional ◽  
The One ◽  
The Right

The one-dimensional (1-D) analytical approach is developed to predict and analyze the acoustic attenuation performance of two-pass perforated hybrid mufflers in the presence of mean flow. The expressions of complex acoustic wavenumber and impedance of long fiber glass wool are presented by using the impedance tube measurement and curve fitting. The 1-D approaches as well as the fitting expressions are validated by comparing the predicted and measured transmission loss of two-pass perforated hybrid mufflers with a different Mach number. Results illustrate that the 1-D predictions agree well with measurements below the plane wave cut-off frequency and deviate in higher frequency range. The influences of geometric parameters including the lengths of extended tubes, perforations on the right bulkhead and the outlet tube, and mean flow on the acoustic attenuation behavior of the hybrid mufflers are examined.

Inorganic-Organic Hybrid Polymers as Photo-Patternable Dielectrics for Multilayer Microwave Circuits

2002 ◽  
Vol 726 ◽  
Author(s):  
L. Fröhlich ◽  
R. Houbertz ◽  
S. Jacob ◽  
M. Popall ◽  
R. Mueller-Fiedler ◽  
...  
Keyword(s):  
Material Properties ◽  
High Frequency ◽  
Low Cost ◽  
Microwave Circuits ◽  
Cross Linking ◽  
Frequency Range ◽  
Hybrid Polymers ◽  
High Frequencies ◽  
Film Coatings ◽  
Organic Hybrid

AbstractInorganic-organic hybrid polymers (ORMOCE®s) combine very good optical and dielectricproperties in the frequency range up to 1 MHz (εr = 3.1 and tanδ = 0.004, both at 1 MHz). Thisis particularly promising for electro-optical (e/o) applications. Multi-layer microwave circuits forhigh frequency applications up to 100 GHz demand extraordinary material properties such as alow permittivity εr < 3 and a dielectric loss tanδ of about 10-3. For low-cost processing, direct UVpatterning would be particularly advantageous. Additionally, the material should be thermallystable at least up to temperatures around 300°C.We have developed a series of novel ORMOCE® materials for high frequency applications.Using these ORMOCE®s, thick film coatings (up to 150 m) can be produced and directlypatterned by UV lithography with sufficiently high resolution. The synthesis has been carried outusing styrene-substituted organosilanes and silanediols as precursors reacted by simplified solgel-processing in combination with organic cross-linking of polymerizable organic functions.The materials have been characterized at high frequencies up to 40 GHz, exhibiting verypromising dielectric properties of εr = 2.5 and tanδ = 0.0035.

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