Extended Kirchhoff Integral Formulations for Sound Radiation from Vibrating Cylinders in Motion

1993 ◽  
Vol 115 (3) ◽  
pp. 324-331 ◽  
Author(s):  
S. F. Wu ◽  
Z. Wang
Keyword(s):  
Acoustic Pressure ◽  
Near Field ◽  
Translational Motion ◽  
Sound Radiation ◽  
Forward Direction ◽  
Numerical Results ◽  
Rectilinear Motion ◽  
Dimensionless Frequency ◽  
Translational Speed ◽  
Kirchhoff Integral

This paper presents numerical results of sound radiation from vibrating cylinders in rectilinear motion at constant subsonic speeds by using the extended Kirchhoff integral formulations recently derived by Wu and Akay (1992). In particular, the effects of the interaction between the turbulent stress field and the vibrating surface in motion are examined. Numerical results demonstrate that this interaction is significant in the near-field when the dimensionless frequency ka > 2 and the dimensionless source translational speed M > 0.1. If this interaction is completely neglected, the predicted acoustic pressure is underestimated by as much as 10 to 20 percent in the near field. The effects of this interaction, however, decrease in the far-field. The effects of surface translational motion on the resulting sound radiation are also examined. It is found that the surface translational motion has a significant effect on the resulting sound generation in both near- and far-fields. The amplitude of the acoustic pressure is approximately doubled in the forward direction when ka > 2 and M > 0.2, which corresponds to at least a 5 dB increase in the SPL value.

RADIATED ACOUSTIC PRESSURE FROM A MOVING, NONUNIFORMLY VIBRATING CYLINDER WITH TWO SPHERICAL ENDCAPS

1994 ◽  
Vol 02 (01) ◽  
pp. 71-82 ◽  
Author(s):  
ZHAOXI WANG ◽  
SEAN F. WU
Keyword(s):  
Near Field ◽  
Translational Motion ◽  
Normal Component ◽  
Forward Direction ◽  
Numerical Results ◽  
Surface Velocity ◽  
Reverse Direction ◽  
Far Field ◽  
Field Source ◽  
Sound Diffraction

This paper presents numerical results of radiated acoustic pressures from a moving, nonuniformly vibrating cylinder with two spherical endcaps, based on an extended Kirchhoff integral formulation. Specifically, we consider cases in which the normal component of the surface velocity is nonzero on a portion of the surface, and zero elsewhere. Numerical results demonstrate that the radiation patterns depend critically on the frequency and source dimensions. For a noncompact source, the strongest radiation may not necessarily stem from a vibrating surface, but rather from a nonvibrating surface due to the effect of sound diffraction. The more noncompact the source is, the larger the number of side lobes in the near field and the more concentrated these side lobes will be. In the far field, however, the side lobes become smeared and less distinguishable. In other words, the effect of sound diffraction is greatly reduced in the far field. Source translational motion induces sound radiation in the perpendicular direction and enhances the radiated acoustic field in general. Enhancement in the forward direction is much greater than in the reverse direction.

Simulation of Vehicle Pass-by Noise Radiation

1999 ◽  
Vol 121 (2) ◽  
pp. 197-203 ◽  
Author(s):  
S. F. Wu ◽  
Z. Zhou
Keyword(s):  
Acoustic Pressure ◽  
Numerical Solutions ◽  
Normal Component ◽  
Sound Radiation ◽  
Forward Direction ◽  
Numerical Results ◽  
Surface Velocity ◽  
Pressure Fields ◽  
Vibration Responses ◽  
Element Method

This paper presents an extended Kirchhoff integral formulation for predicting sound radiation from an arbitrarily shaped vibrating structure moving along an infinite baffle. In deriving this formulation, the effect of sound reflection from the baffle is taken into account by using the image source theory. Moreover, the effect of source convection motion and that of motion-induced fluid-structure interaction at the interface on the resulting acoustic pressure field are considered. The formulation thus derived is used to calculate sound radiation from a simplified vehicle model cruising along a solid ground at constant speeds. Since analytical and benchmark numerical solutions for an arbitrarily shaped vibrating object in motion are not available, validations of numerical results are made with respect to those of a point source. Next, sound radiation from a full-size vehicle is simulated. For simplicity, the vehicle is assumed to be made of a shell-type structure and excited by harmonic forces acting on its four tires. Vibration responses subject to these excitations are calculated using finite element method (FEM) with HyperMesh® version 2.0 as pre- and post-processors. Once the normal component of the surface velocity is specified, the radiated acoustic pressure fields are determined using boundary element method (BEM). Numerical results show that the effect of source convection motion enhances sound radiation in the forward direction, but reduces that in the rearward direction. Changes in the resulting sound pressure fields become obvious when the Mach number exceeds 0.1, or equivalently, when a vehicle cruises at 70 mph or higher.

Visualization of Sound Radiation From a Bowling Ball

1999 ◽  
Author(s):  
Kesho Leach ◽  
Sean F. Wu
Keyword(s):  
Acoustic Pressure ◽  
Near Field ◽  
Sound Radiation ◽  
Measured Data ◽  
Planar Surface ◽  
Accuracy Of Measurements ◽  
Helmholtz Equation Least Squares ◽  
Ball Surface ◽  
Frequency Regime ◽  
Vibration Shaker

Abstract This paper presents results of an investigation on visualization of sound radiation from a bowling ball via the Helmholtz Equation Least Squares (HELS) method [Wang and Wu, 1997; Wu and Wang, 1998; Wu and Yu, 1998]. In conducting the tests, the bowling ball was excited by a vibration shaker using a random signal. The radiated acoustic pressures were measured over both conformal and planer surfaces at certain distances away from the source. The measured data were taken as the input to a computer model based on the HELS formulation. The reconstructed acoustic pressures on the surface and in the field were compared with the measured data at the same locations. Also shown are comparisons of the reconstructed and measured acoustic pressure spectra at various locations on the bowling ball surface. Results demonstrate that the accuracy of reconstruction based on measurements over a conformal surface is much higher than that over a planar surface. This is because a planar surface often extends beyond the near-field region, thus making the accuracy of measurements inconsistent. Nevertheless, satisfactory visualization of acoustic pressure distribution over the entire bowling ball surface can still be obtained, at least in the low-to-mid frequency regime, based on the measurements over a finite, planar surface on one side of the source. Such a capability is unique to the HELS method. However, the efficiency of numerical computations of the HELS method is expected to deteriorate at high frequencies, a difficulty inherent in all expansion theories.

Influence of Internal Structures of High Modal Density on Shell’s Radiation

1997 ◽  
Author(s):  
Lionel Oddo ◽  
Bernard Laulagnet ◽  
Jean-louis Guyader
Keyword(s):  
Cylindrical Shell ◽  
Sound Radiation ◽  
Numerical Results ◽  
Structural Damping ◽  
Radiation Spectra ◽  
Modal Density ◽  
Internal Structures ◽  
High Modal Density

Abstract The aim of this paper is to study the sound radiation by a cylindrical shell internally coupled with mechanical structures of high modal density. The model is based on a mobility technique. The numerical results show a smoothing of the cylinder’s velocity and radiation spectra associated with an increase of the apparent damping. The use of the S.E.A. method allows us to calculate an additional structural damping of the shell, equivalent to the effect of the internal structures.

Vertical seismic profile migration using the Kirchhoff integral

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 786-799 ◽  
Author(s):  
P. B. Dillon
Keyword(s):  
Wave Equation ◽  
Wave Field ◽  
Near Field ◽  
Synthetic Data ◽  
Real Data ◽  
Seismic Profile ◽  
Processing Strategies ◽  
Receiver Array ◽  
Vsp Data ◽  
Kirchhoff Integral

Wave‐equation migration can form an accurate image of the subsurface from suitable VSP data. The image’s extent and resolution are determined by the receiver array dimensions and the source location(s). Experiments with synthetic and real data show that the region of reliable image extent is defined by the specular “zone of illumination.” Migration is achieved through wave‐field extrapolation, subject to an imaging procedure. Wave‐field extrapolation is based upon the scalar wave equation and, for VSP data, is conveniently handled by the Kirchhoff integral. The migration of VSP data calls for imaging very close to the borehole, as well as imaging in the far field. This dual requirement is met by retaining the near‐field term of the integral. The complete integral solution is readily controlled by various weighting devices and processing strategies, whose worth is demonstrated on real and synthetic data.

Analysis of sound radiation from the coupling effect of vibrating noise and moving-vehicle noise on bridges

2005 ◽  
Vol 32 (5) ◽  
pp. 881-898 ◽  
Author(s):  
Yong-Seon Lee ◽  
Sang-Hyo Kim ◽  
Won-Suk Jang
Keyword(s):  
Dynamic Response ◽  
Noise Level ◽  
Acoustic Pressure ◽  
Sound Radiation ◽  
Element Model ◽  
Frequency Noise ◽  
Vehicle Noise ◽  
The Road ◽  
Vehicle Weight ◽  
Vibration Noise

An acoustic finite element model of a bridge is developed to evaluate the noise generated by the traffic-induced vibration of the bridge. The dynamic response of a multi-girder bridge, modeled by a three-dimensional (3-D) frame element model, is analyzed with a 3-axle (8 degrees of freedom (DOF)) truck model and a 5-axle (13 DOF) tractor-trailer. The flat plate element is used to analyze the acoustic pressure due to the fluid–structure interactions between the vibrating surface and contiguous acoustic fluid medium. The radiation fields of noise with a specified distribution of vibrating velocity and pressure on the structural surface are also computed using the Kirchhoff–Helmholtz integral. Among the diverse parameters affecting the dynamic response of a bridge, vehicle velocity, vehicle weight, and spatial distribution of the road surface roughness are found to be the main factors that increase the level of vibration noise. In an attempt to illustrate the influence of the structural vibration noise of a bridge to total noise level around the bridge, the random function is used to generate the vehicle noise source including the engine noise and the rolling noise between the road and tire. The results show that the low-frequency noise produced by the vibrating bridge members amplifies the high-frequency vehicle noise by 4–7 dB. In addition, the amplification rate of noise increases with traveling speed and vehicle weight. Key words: acoustic pressure on surface, sound radiation, noise level, Kirchhoff–Helmholtz integrals, dynamic response, vehicle noise model, sound pressure level.

Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources

2001 ◽  
Vol 124 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Kean Chen ◽  
Gary H. Koopmann
Keyword(s):  
Active Control ◽  
Near Field ◽  
Low Frequency ◽  
Sound Radiation ◽  
Sound Field ◽  
Sound Power ◽  
Frequency Range ◽  
Sound Sources ◽  
Frequency Sound ◽  
Secondary Sources

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.

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