A New Type of Muffler Based on Microperforated Tubes

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
S. Allam ◽  
M. Åbom
Keyword(s):  
Acoustic Impedance ◽  
Noise Control ◽  
Wave Impedance ◽  
Sound Waves ◽  
Submillimeter Range ◽  
Perforated Plates ◽  
Characteristic Wave ◽  
Standard Temperature ◽  
New Type ◽  
Temperature And Pressure

Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (∼400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e.g., for use in automotive exhaust or ventilation systems, is investigated.

ESEM - A multipurpose surface Electron Microscope

1986 ◽  
Vol 44 ◽  
pp. 632-633 ◽  
Author(s):  
G.D. Danilatos
Keyword(s):  
Electron Microscope ◽  
Room Temperature ◽  
Environmental Scanning ◽  
Gas Composition ◽  
Saturated Water Vapor ◽  
Surface Electron ◽  
Current State ◽  
Saturated Water ◽  
New Type ◽  
Temperature And Pressure

Over recent years a new type of electron microscope - the environmental scanning electron microscope (ESEM) - has been developed for the examination of specimen surfaces in the presence of gases. A detailed series of reports on the system has appeared elsewhere. A review summary of the current state and potential of the system is presented here.The gas composition, temperature and pressure can be varied in the specimen chamber of the ESEM. With air, the pressure can be up to one atmosphere (about 1000 mbar). Environments with fully saturated water vapor only at room temperature (20-30 mbar) can be easily maintained whilst liquid water or other solutions, together with uncoated specimens, can be imaged routinely during various applications.

Characteristic Wave Impedance of Ti-Mo System Composites and FGM

2005 ◽  
pp. 1537-1540
Author(s):  
Chuan Bin Wang ◽  
Qiang Shen ◽  
Guoqiang Luo ◽  
Lian Meng Zhang
Keyword(s):  
Wave Impedance ◽  
Characteristic Wave

scholarly journals HIGH SPEED PHOTOMICROGRAPHY OF LIVING CELLS SUBJECTED TO SUPERSONIC VIBRATIONS

1931 ◽  
Vol 15 (2) ◽  
pp. 147-153 ◽  
Author(s):  
E. Newton Harvey ◽  
Alfred L. Loomis
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Living Cells ◽  
Air Bubbles ◽  
Sound Waves ◽  
Camera System ◽  
Fluid Movement ◽  
High Frequency Sound ◽  
Frequency Sound ◽  
New Type

A new type of camera system is described capable of taking 1200 pictures a second through a microscope objective. Photographs showing the destruction of Arbacia eggs by high frequency sound waves indicate that the disintegration occurs in less than 1/1200 second. Eggs drawn out into spindle or tadpole shapes suggest that rapid movements of the fluid tearing the eggs may be responsible for the disintegration. Although no cavitated air bubbles show in the photographs, other experiments make it likely that the rapid fluid movement is the result of submicroscopic cavitation.

scholarly journals Investigating the Effect of Solid Boundaries on the Gas Molecular Mean-Free-Path

2009 ◽  
Author(s):  
Erik J. Arlemark ◽  
Jason M. Reese
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Free Path ◽  
Mean Free Path ◽  
Gas Flows ◽  
Standard Temperature ◽  
Binary Collisions ◽  
The Mean ◽  
Temperature And Pressure ◽  
Definition Of

A key parameter for micro-gas-flows, the mean free path, is investigated in this paper. The mean free path is used in various models for predicting micro gas flows, both in the governing equations and their boundary conditions. The conventional definition of the mean free path is based on the assumption that only binary collisions occur and is commonly described using the macroscopic quantities density, viscosity and temperature. In this paper we compare the prediction by this definition of the mean free paths for helium, neon and argon gases under standard temperature and pressure conditions, with the mean free paths achieved by measurements of individual molecules using the numerical simulation technique of molecular dynamics. Our simulation using molecular dynamics consists of a cube with six periodic boundary conditions, allowing us to simulate an unconfined gas “package”. Although, the size of this package is important, since its impact on computational cost is considerable, it is also important to have enough simulated molecules to average data from. We find that the molecular dynamics method using 20520 simulated molecules yields results that are within 1% accuracy from the conventional definition of the mean free paths for neon and argon and within 2.5% for helium. We can also conclude that the normal approximation of only considering binary collisions is seemingly adequate for these gases under standard temperature and pressure conditions. We introduce a single planar wall and two parallel planar walls to the simulated gas of neon and record the mean free paths at various distances to the walls. It is found that the mean free paths affected by molecular collisions with the walls corresponds well with theoretical models up to Knudsen numbers of 0.2.

A Markov‐Gauss algorithm for blocking well logs

Geophysics ◽  
1988 ◽  
Vol 53 (8) ◽  
pp. 1118-1121 ◽  
Author(s):  
Paul N. Chouinard ◽  
Ken V. Paulson
Keyword(s):  
Electrical Resistivity ◽  
Markov Chain ◽  
Acoustic Impedance ◽  
High Probability ◽  
Rock Type ◽  
Well Logs ◽  
Physical Parameters ◽  
New Type

A characteristic common among petrophysical sections is “blockiness,” which results from the high probability that a given rock and the rocks above and below it are all of the same type. Furthermore, if a new rock type is encountered, the next rock’s type is dependent upon this new type and not on a previous type. This suggests that a Markov chain would be an appropriate basis for modeling such physical parameters as acoustic impedance, electrical resistivity, etc.

scholarly journals Silencer With Tunable Resonators for Active Noise Control

2012 ◽  
Author(s):  
Olivier Cherrier ◽  
V. Pommier-Budinger
Keyword(s):  
Noise Control ◽  
Active Noise Control ◽  
Electromechanical System ◽  
Perforated Plates ◽  
Acoustic Resonators ◽  
Active Noise ◽  
Tunable Resonators ◽  
Resonance Frequencies

The article deals with active noise control and presents a silencer made of tunable acoustic resonators to reduce variable tonal noises. The silencer is composed of baffles with acoustic resonators made of two superposed and identically perforated plates associated with cavities. One of the plates is mobile and its displacement is controlled by an electromechanical system, allowing changing the internal shapes of the holes of the perforated layers. Consequently the impedance of the resonators and their resonance frequencies can be controlled. These tunable resonators can be used for noise control of variable tonal noises such as those generated by fans for example. The advantages of the proposed system are the simplicity of the actuation and the compactness of the system.

Sign in / Sign up

Export Citation Format

Share Document