A complex of analytical models for predicting noise in an aircraft cabin

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A unified approach is proposed to solve vibration problems for stiffened plates, shells, and other arbitrary stiffened structures. The approach is applicable under the condition that independent solutions for the stiffened structure and the stiffening elements are known in the form of explicit expressions determining generalized displacements through generalized forces. The proposed universal equation is used to solve the problem of deterministic vibrations of a closed cylindrical shell with "smeared" stringers and irregular dis crete frames. The solution is used to estimate the effect of noise suppression achieved in the cabin of a pro peller airplane by stopping some of the frames positioned near the propeller.

Section: Introductionmentioning

confidence: 99%

Evaluation of the effect of stopping selected frames on noise in the cabin of a propeller airplane

Efimtsov

Lazarev

2015

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“…(1), we obtain (2) where P is Fourier transformation p, analysis of how the critical layer affects noise propaga tion in plane parallel flows can be found in [21]. At the edge of the boundary layer r = r b , the equality of the solution obtained in the boundary layer region and the constant flow region should be satisfied, as well the as equality of their first derivatives, i.e., (3) where P BL is the solution within the boundary layer such that P BL (r f ) = 1 and (r f ) = 0; γ m is a constant. System of equations (3) establishes a relationship between coefficients a m , b m , and γ m , which makes it possible to express the amplitude of the scattered wave b m and the amplitude of the sound field within the boundary layer γ m by means of the amplitude of the incident field a m :…”

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confidence: 99%

“…The influence of the boundary layer has been studied mainly in relation to simulation of acoustic loads on the fuselage surface, which are necessary for deter mining noise in an aircraft's cabin (the problem of noise simulation in an aircraft cabin has been eluci dated in [2][3][4]). So, in [5][6][7], the influence of the boundary layer was considered in the simplest case of plane waves and a two dimensional boundary layer on an infinite plane, and it was shown that the boundary layer can exert a significant effect on the acoustic load at the surface of a body.…”

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confidence: 99%

The effect of an aircraft’s boundary layer on propeller noise

Belyaev

2012

Today, it is greatly hoped that the effect of noise screening with airframe design elements (wing, fuse lage, empennage, etc.) can be used to reduce engine noise. It is expected that this will enable significant reduction in community noise in comparison to tradi tional design. To estimate the size of the screening effect, the simplest model of a point source near a hard surface is commonly used (see, e.g., [1]); the presence of the boundary layer at the surface is usually ignored.This work is devoted to studying how the boundary layer at an aircraft's fuselage affects engine noise. The influence of the boundary layer has been studied mainly in relation to simulation of acoustic loads on the fuselage surface, which are necessary for deter mining noise in an aircraft's cabin (the problem of noise simulation in an aircraft cabin has been eluci dated in [2][3][4]). So, in [5][6][7], the influence of the boundary layer was considered in the simplest case of plane waves and a two dimensional boundary layer on an infinite plane, and it was shown that the boundary layer can exert a significant effect on the acoustic load at the surface of a body. For the two dimensional problem, analytic solutions for noise propagation in an isothermal isentropic boundary layer for three velocity profiles were obtained-linear [8], exponen tial [9], and in the form of a hyperbolic tangent [10]-as well as in a nonisothermal boundary layer with a lin ear velocity profile [11]. A two dimensional problem for a realistic boundary layer velocity profile was numerically solved in [12], where it was found that the boundary layer effect can attain a value of 30 dB. The results of these studies revealed a qualitative agreement with the experimental data for acoustic loads on an aircraft fuselage. To improve the quantitative agree ment, solutions were proposed to a three dimensional problem for a monopole noise source [13] and a pro peller [14] near a round hard cylinder, as well as near a hard cylinder with a nonaxisymmetric cross section [15]. The results of three dimensional calculations agreed well with experimental data.The aim of this work is to determine the boundary layer effect not on acoustic loads at an aircraft's fuse lage, but on community aircraft noise. To the best of the author's knowledge, the only study dealing with this influence is [13], which considered a point mono pole as a noise source. The justification for replacing a distributed noise source with a point source as applied to problems of noise screening with a surface was stud ied in detail in [16] using a propeller as an example, and it was shown that such a replacement can lead to substantial errors, even if the propeller is simulated by several point sources instead of just one. The impor tance of taking into account source distribution in studying noise scattering by a hard surface was also demonstrated for turbulence jet noise in [17] and vor tex wake noise behind a bluff body in [18]. Therefore, it is of interest to study how the boundary layer at the fuselage affect...

“…A method of calculating noise in a cabin based on analytical models for calculating vibrations of a regu larly supported shell (a fragment of plane fuselage) was described in [1][2][3][4]. A model taking into account the discreteness of all ribs (both stringers and bulkheads) is the most interesting.…”

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confidence: 99%

“…A method for solving a limited shell taking into account all three components of dis placement of the shell and the corresponding relations was presented in [2,3]. We also gave the expressions [4] for a simplified problem of vibrations of infinite closed cylindrical shell taking into account only the normal component of displacement.…”

mentioning

confidence: 99%

Calculation of bulkhead vibrations in a supported shell simulating a plane fuselage

Efimtsov¹,

Lazarev²

2014

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Noise from external sources penetrates a plane cabin through the board construction in several ways. They include direct penetration through loose fiber layers and indirect penetration through the attach ment points of interior panels to transverse ribs (bulkheads). The analytical method of calculating vibrations of an orthogonally supported shell (developed by us earlier) makes it possible to correctly calculate bulkhead vibrations. As a result, noise penetration into the cabin through the attachment points of interior panels can be determined analytically. The first part of the solution to this problem is presented (i.e., the relations and examples of calculating bulkhead vibrations upon point excitation of the shell and excitation by pressure fluc tuations of the turbulent boundary layer are given).