Borehole waves are strongly affected by adjacent porous zones or by fractures intersecting the borehole. A theoretical description for both porous and fracture zones is possible based on the introduction of an effective borehole fluid bulk modulus, characterizing the wave attenuation via borehole wall impedance. This impedance can be calculated for both porous and fracture zones adjacent to the...

A time-domain computational approach is applied to investigate the behavior of perforated tube silencers at high sound levels. The one-dimensional computational technique employs a lumped parameter model for the perforate flows. The lumped parameter perforate model is based on time-invariant approximations for the equivalent length l(eq) and resistance R, consistent with the use of a nonlinear ...

Complement to standard E2611-09 of the American Society for Testing and Materials [Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method (American Society for Testing and Materials, New York, 2009)] is proposed in order to measure normal incidence sound transmission loss of materials in a modified impedance tube u...

1. ABSTRACT The characteristic impedance and other derivative acoustic properties of a material can be derived from impedance tube data using the specific impedance measured from samples with two different thicknesses. In practice, samples are chosen so that their respective thicknesses differ by a factor of 2. This simplifies the solution of the equations relating the properties of the two sam...

To minimize the flow-dependent effects caused by an endotracheal tube during impedance measurements, we recorded pressure inside the tube at its distal end. We used a commercial endotracheal tube with a lumen built into its wall with the opening located near the outlet of the tube. We characterized the effect of the tube by means of an effective transfer function (H). We measured H from 0.25-32...

Modeling a porous layer mounted on a vibrating structure using acoustic impedance is investigated in this paper. It is shown that the use of surface impedance usually measured with the impedance tube method can provide an inaccurate estimation of the acoustic pressure radiated by the covered structure. The paper focuses on the derivation of an impedance, denoted the “transfer impedance,” which ...

Porous metallic material and its compound sound absorbing structures are very popular for the practical applications in harsh environment such as high temperature, humidity, and high sound pressure levels. There are all kinds of mathematic models available to predict the sound absorption properties of porous metal in literatures elsewhere. In this work, Cellular Automata is applied to model the...

The next generation of linac-based free electron lasers will use very short bunches with a large peak current. For such beams, the impedance caused by submicron imperfections in the vacuum beam tube may generate an additional energy spread within the bunch. A review of two mechanisms of the roughness impedance is given with the emphasis on the importance of the high-aspect ratio property of the...