A time-domain implementation of surface acoustic impedance condition with and without flow

1996 ◽  
Author(s):  
Yusuf Ozyoruk ◽  
Lyle Long
Keyword(s):  
Time Domain ◽  
Acoustic Impedance ◽  
Impedance Condition

scholarly journals A New Implementation of the Extended Helmholtz Resonator Acoustic Liner Impedance Model in Time Domain CAA

2016 ◽  
Vol 24 (01) ◽  
pp. 1550015 ◽  
Author(s):  
L. Pascal ◽  
E. Piot ◽  
G. Casalis
Keyword(s):  
Time Domain ◽  
Helmholtz Resonator ◽  
Aircraft Engine ◽  
Original Method ◽  
Computational Domain ◽  
Impedance Model ◽  
Wide Range ◽  
Impedance Condition ◽  
Condition Modeling ◽  
Standard Liner

The application of wall acoustic lining is a major factor in the reduction of aircraft engine noise. The extended Helmholtz Resonator (EHR) impedance model is widely used since it is representative of the behavior of realistic liners over a wide range of frequencies. Its application in time domain CAA methods by means of [Formula: see text]-transform has been the subject of several papers. In contrast to standard liner modeling in time domain CAA, which consists in imposing a boundary condition modeling both the cavities and the perforated sheet of the liner, an alternative approach involves adding the cavities to the computational domain and imposing a condition between these cavities and the duct domain to model the resistive sheet. However, the original method may not be used for broadband acoustics since it implements an impedance condition with frequency independent resistance. This paper describes an extension of this method to implement the EHR impedance model in a time domain CAA method.

A Time-Domain Implementation of Surface Acoustic Impedance Condition with and Without Flow

1997 ◽  
Vol 05 (03) ◽  
pp. 277-296 ◽  
Author(s):  
Yusuf Özyörük ◽  
Lyle N. Long
Keyword(s):  
Signal Processing ◽  
Time Domain ◽  
Domain Model ◽  
Infinite Impulse Response ◽  
Two Dimensional ◽  
Response Type ◽  
Recursive Filter ◽  
Processing Theory ◽  
Impedance Condition ◽  
Z Domain

The impedance condition in computational aeroacoustic applications is required in order to model acoustically treated walls. The application of this condition in time-domain methods, however, is extremely difficult because of the convolutions involved. In this paper, a time-domain method is developed which overcomes the computational difficulties associated with these convolutions. This method builds on the z-transform from control and signal processing theory and the z-domain model of the impedance. The idea of using the z-domain operations originates from the computational electromagnetics community. When the impedance is expressed in the z-domain with a rational function, the inverse z-transform of the impedance condition results in only infinite impulse response type, digital, recursive filter operations. These operations, unlike convolutions, require only limited past-time knowledge of the acoustic pressures and velocities on the surface. Examples of one- and two-dimensional problems with and without flow indicate that the method promises success in aeroacoustic applications.

The frequency and the time‐domain responses of a buried axial conductor

Geophysics ◽  
1980 ◽  
Vol 45 (5) ◽  
pp. 941-951 ◽  
Author(s):  
Koji Tsubota ◽  
James R. Wait
Keyword(s):  
Magnetic Dipole ◽  
Time Domain ◽  
Dipole Source ◽  
Earth Model ◽  
Layered Earth ◽  
Vertical Magnetic Dipole ◽  
Lateral Inhomogeneity ◽  
Impedance Condition ◽  
The Time Domain ◽  
Lower Medium

Our objective is to analyze the frequency and the time‐domain responses of a two‐dimensional lateral inhomogeneity such as an axial conductor which is buried in a stratified earth. Such inhomogeneities in the earth’s structure give complex transients that cannot be interpreted using just a uniformly layered earth model. To proceed, we determine the fields of a thin axial conductor carrying a filamental current situated in the lower medium of a two‐layered earth. This infinitely long axial conductor is characterized by a specific axial impedance. The impedance condition can be used to determine the total field response when the source is a magnetic dipole. Some results are presented that show the waveform at the induced current in a buried axial conductor excited by an impulsive current in a vertical magnetic dipole source located on the earth’s surface. A feature of the waveform is the reversal of the polarity that would not occur in the absence of the buried cable.

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