scholarly journals Analysis of Sound Waves with Semi Perforated Pipe

2019 ◽  
Vol 2 (3) ◽  
pp. 704-710
Author(s):  
Burhan Tiryakioglu
Keyword(s):  
Boundary Condition ◽  
Fourier Transform ◽  
Wave Equation ◽  
Pipe Wall ◽  
Far Field ◽  
Sound Waves ◽  
Hopf Equation ◽  
Hopf Method ◽  
The Fourier Transform ◽  
Perforated Pipe

The paper presents analytical results of radiation phenomena at the far field and solution of the wave equation with adequate boundary condition imposed by the pipe wall. An infinite pipe with perforated part is considered. The solution is obtained by using the Fourier transform technique in conjunction with the Wiener-Hopf Method. Applying the Fourier transform technique, the boundary value problem is described by Wiener Hopf equation and then solved analytically.

scholarly journals Radiation analysis of sound waves from semi-infinite coated pipe

2018 ◽  
Vol 18 (1) ◽  
pp. 92-111 ◽  
Author(s):  
Burhan Tiryakioglu ◽  
Ahmet Demir
Keyword(s):  
Fourier Transform ◽  
Sound Waves ◽  
Algebraic Equations ◽  
Total Field ◽  
Hopf Equation ◽  
Waveguide Modes ◽  
Linear Algebraic Equations ◽  
Pipe Radius ◽  
Expansion Coefficients ◽  
The Fourier Transform

An analytical solution is presented for the problem of radiation of sound waves from a semi-infinite circular cylindrical coated pipe which is partially lined from inside. By stating the total field in duct region in terms of normal waveguide modes (Dini’s series) and using the Fourier transform technique elsewhere, we obtain a Wiener–Hopf equation whose solution involving three sets of infinitely many unknown expansion coefficients satisfying three systems of linear algebraic equations. This system is solved numerically and the influence of some parameters (pipe radius, impedances, extension, etc.) on the radiation phenomenon is displayed graphically.

A model supersonic buried-nozzle jet: instability and acoustic wave scattering and the far-field sound

2015 ◽  
Vol 778 ◽  
pp. 189-215 ◽  
Author(s):  
Arnab Samanta ◽  
Jonathan B. Freund
Keyword(s):  
Far Field ◽  
Sound Waves ◽  
Vortex Sheets ◽  
Instability Waves ◽  
Acoustic Wave Scattering ◽  
Instability Modes ◽  
Source Mechanisms ◽  
Upstream Direction ◽  
Field Radiation ◽  
Hopf Method

We consider sound source mechanisms involving the acoustic and instability modes of dual-stream isothermal supersonic jets with the inner nozzle buried within an outer shroud-like nozzle. A particular focus is scattering into radiating sound waves at the shroud lip. For such jets, several families of acoustically coupled instability waves exist, beyond the regular vortical Kelvin–Helmholtz mode, with different shapes and propagation characteristics, which can therefore affect the character of the radiated sound. In our model, the coaxial shear layers are vortex sheets while the incident acoustic disturbances are the propagating shroud modes. The Wiener–Hopf method is used to compute their scattering at the sharp shroud edge to obtain the far-field radiation. The resulting far-field directivity quantifies the acoustic efficiency of different mechanisms, which is particularly important in the upstream direction, where the results show that the scattered sound is more intense than that radiated directly by the shear-layer modes.

Scattering by a semi-infinite sandwich panel perforated on one side

1990 ◽  
Vol 431 (1883) ◽  
pp. 465-479 ◽  
Keyword(s):  
Approximate Solution ◽  
Cellular Structure ◽  
Sandwich Panel ◽  
Asymptotic Limit ◽  
Sound Waves ◽  
Elastic Plates ◽  
Major Difficulty ◽  
Hopf Equation ◽  
Hopf Method ◽  
Thin Elastic Plates

The scattering of sound waves by the edge of a sandwich panel which consists of two thin elastic plates containing a light interior cellular structure is analysed. The Wiener-Hopf method is used to examine the interaction effects of a semi-infinite panel clamped to a semi-infinite rigid screen. One major difficulty is that the presence of two different velocity potentials on either side of the plane y = 0, results in a matrix Wiener–Hopf equation. An approximate solution is given in the asymptotic limit of small values of a parameter ז , which accounts for the perforations.

scholarly journals Dynamic RCS Estimation according to Drone Movement Using the MoM and Far-Field Approximation

2021 ◽  
Vol 21 (4) ◽  
pp. 322-328
Author(s):  
Dong-Yeob Lee ◽  
Jae-In Lee ◽  
Dong-Wook Seo
Keyword(s):  
Fourier Transform ◽  
Cross Section ◽  
Method Of Moments ◽  
Iterative Process ◽  
Rotation Angle ◽  
Field Approximation ◽  
Far Field ◽  
Impedance Matrix ◽  
The Matrix ◽  
The Fourier Transform

Micro-Doppler signatures from the rotating propellers of a drone can be utilized to distinguish the drone from clutter or airborne organisms with similar radar cross section (RCS) levels, such as birds and bats. To obtain the micro-Doppler signatures of a drone, calculation or measurement of the electric field scattered from the rotating propellers is essential. In this paper, using the relative angle concept and far-field approximation, we propose a way to rapidly estimate the dynamic RCS of a drone with several propellers according to its movement. In addition, based on the fact that the shape of the propeller does not change even if it rotates, we construct an impedance matrix only once and apply the matrix to the method of moments instead of the iterative process of calculating the impedance matrix and inverse matrix for each rotation angle of the propeller. Finally, by using the Fourier transform of the results from the proposed method, the rotation frequencies of the propellers according to the movement of the drone can be obtained.

Zum kollektiven Anteil des Plasma-Mikrofeldes

1968 ◽  
Vol 23 (10) ◽  
pp. 1488-1498
Author(s):  
K. Hunger ◽  
R.W. Larenz
Keyword(s):  
Fourier Transform ◽  
Dipole Moment ◽  
Space Charge ◽  
Long Range ◽  
Field Distribution ◽  
Computer Experiments ◽  
Far Field ◽  
Nearest Neighbour ◽  
Charge Fluctuations ◽  
The Fourier Transform

The Holtsmark microfield evaluation is rediscussed. It is shown that in the usual computation of the Fourier transform a term is neglected which has the dimension of a dipole moment density. This term occurs only for long range forces (here Coulomb ones) and remains undetermined in the limit of an infinitely large system without interaction. Furthermore, it is sensitive to deviations from ergodicity. The true microfield distribution results as a Holtsmark distribution centered at the generally nonvanishing far field. As the distribution of the latter is Gaussian the complete distribution results as a convolution of the Holtsmark distribution with that of the far field. The parameter of the Gaussian far field distribution is computed for a non interacting plasma consisting of N charges, by taking into account explicitely the collective field of space charge fluctuations. The formulae arrived at with respect to the microfield as well as the micropotential suggest to perform numerical computer experiments (HUNGER, LARENZ and WILKE, to be published). For an interacting plasma, the far field is obtained qualitatively. It agrees with the microfield of HUNGER and LARENZ (1961). The far field dominates the Holtsmark nearest neighbour field at plasma conditions kT/e2n1/3 > 1.

scholarly journals The interaction of a contact discontinuity with sound waves according to the linearised Navier-Stokes equations

1970 ◽  
Vol 17 (1) ◽  
pp. 37-46
Author(s):  
W. M. Anderson
Keyword(s):  
Fourier Transform ◽  
Contact Surface ◽  
Stokes Equations ◽  
Asymptotic Series ◽  
Density Perturbation ◽  
Navier Stokes ◽  
Sound Waves ◽  
Navier Stokes Equations ◽  
Initial Discontinuity ◽  
The Fourier Transform

AbstractThe resolution of a small initial discontinuity in a gas is examined using the linearised Navier-Stokes equations. The smoothing of the resultant contact surface and sound waves due to dissipation results in small flows which interact. The problem is solved for arbitrary Prandtl number by using a Fourier transform in space and a Laplace transform in time. The Fourier transform is inverted exactly and the density perturbation is found as two asymptotic series valid for small dissipation near the contact surface and the sound waves respectively. The modifications to the structures of the contact surface and the sound waves are exhibited.

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