scholarly journals On the Acoustical Implications of Vortex Shedding from an Exhaust Pipe

1981 ◽  
Vol 103 (4) ◽  
pp. 378-384 ◽  
Author(s):  
S. W. Rienstra
Keyword(s):  
Sound Speed ◽  
Ambient Medium ◽  
Jet Flow ◽  
Edge Condition ◽  
Exhaust Pipe ◽  
Ambient Flow ◽  
Reflected Wave ◽  
Radiated Sound ◽  
Subsonic Jet ◽  
Radiated Sound Power

Asymptotic approximations for small Strouhal number are derived for the solution of the problem of the interaction between an acoustic wave and a subsonic jet flow issuing from a semi-infinite pipe. Density and sound speed differences between the jet flow and the (slowly moving) ambient medium, and a general edge condition are included. The approximations relate to the field inside the jet flow, to the far field, to the reflection coefficient, end-impedance and end correction for the reflected wave inside the pipe, and to the transmitted and radiated sound power. Within the range of parameters considered, the effect of the density and sound speed differences and ambient flow is found to be appreciable, although the character of the solution is not changed. However, the choice of the edge condition does have important implications; specifically, the phase of the reflected wave is most sensitive to only slight deviations from the Kutta condition.

Measurements of subsonic jet noise and comparison with theory

1971 ◽  
Vol 46 (3) ◽  
pp. 477-500 ◽  
Author(s):  
P. A. Lush
Keyword(s):  
Critical Frequency ◽  
Jet Noise ◽  
Jet Flow ◽  
Critical Value ◽  
Emission Angle ◽  
Frequency Parameter ◽  
Air Jet ◽  
Radiated Sound ◽  
Jet Velocity ◽  
Subsonic Jet

Measurements of the noise field from a 25 mm diameter subsonic air jet are presented. These results are analysed in some detail by determining both the jet velocity dependence and the directivity of the intensity of the radiation in 1/3-octave bands at particular values of the frequency parameter, \[ (fD/V_J)(1-M_c\cos\theta). \] This procedure should ensure that a particular source in a geometrically similar position in the jet is always observed, whatever the jet velocity, diameter and emission angle.These results are compared with the predictions of Lighthil's (1952) theory of convected quadrupoles. It is shown that the theory predicts the variation of the intensity with jet velocity and emission angle provided that the observed frequency is below a certain critical value, which depends on jet diameter and emission angle and is independent of jet velocity. Above this critical frequency, the predicted variations overestimate the measurements and it appears that the convective amplification predicted by the theory is much reduced. The variation of this critical frequency is explained by assuming that substantial interaction occurs between the radiated sound and the jet flow when the wavelength of the sound becomes shorter than the sound path length in the jet flow.

A Study on Relevance between Distortion of Distributed Mode Loudspeaker and Characteristic of Sound Panel

2011 ◽  
Vol 291-294 ◽  
pp. 2105-2110
Author(s):  
Liang Jin Luo
Keyword(s):  
Vibration Frequency ◽  
Sandwich Panel ◽  
Flexural Vibration ◽  
Sound Power ◽  
Impedance Matrix ◽  
Cell Ratio ◽  
Radiated Sound ◽  
Sound Sensitivity ◽  
The Relationship ◽  
Radiated Sound Power

From flat-plate flexural vibration and radiated sound power discussed the inherent relationship between panel vibration frequency of distributed mode loudspeaker and geometric parameters, impedance matrix of soundboard and studied the relationship between soundboard structure of polyester foam sandwich panel and distortion of loudspeaker. Experimental results showed that distortion increases as the cell size and compress modulus, cell ratio, cell open ratio and thickness increases, but the sound sensitivity decreases as the compress modulus increases.

scholarly journals FE-BE computation of electromagnetic noise of a permanent-magnetic excited synchronous ma-chine considering dynamic rotor eccentricity

2018 ◽  
Vol 211 ◽  
pp. 18005
Author(s):  
Marcel Clappier ◽  
Lothar Gaul
Keyword(s):  
Sound Power ◽  
Fe Model ◽  
Electromagnetic Noise ◽  
Structural Dynamic ◽  
Magnetic Forces ◽  
Rotor Eccentricity ◽  
Resonance Frequencies ◽  
Radiated Sound ◽  
Run Up ◽  
Radiated Sound Power

Electromagnetic noise in Electrical Machines (EMs) occurs due to vibrations caused by magnetic forces acting onto rotor and stator surface. This is the dominant source for the considered permanent-magnetic excited synchronous machine in this paper. The radiated electromagnetic noise is sequentially calculated by a Finite Element (FE) and Boundary Element (BE) computation. An electromagnetic FE model is created to determine magnetic forces. Structure-borne sound and rotor dynamics are calculated using a structural dynamic FE model for the EM housing and the rotor. In order to predict resonance frequencies and amplitudes as reliable as possible, it is important to know the direction-dependent stiffness of the laminated rotor stacks and mechanical joints as well as their structural damping. Thereby, the properties of the laminated stack can be determined experimentally by a shear and dilatation test. Mechanical joint properties can be modelled by Thin-Layer Elements (TLEs) and the overall damping by the model of constant hysteretic damping. The radiated sound power is determined by a direct BE computation. The influence of dynamic rotor eccentricity on radiated sound power is examined for a run-up of the EM. All FE models are verified by data from experimental modal analysis.

Acoustic Radiation Simulation of Marine Sliding-Thrust Bearing Shell Based on SYSNOISE

2011 ◽  
Vol 291-294 ◽  
pp. 1961-1964
Author(s):  
Guang Liang Zhao
Keyword(s):  
Dynamic Analysis ◽  
Boundary Element ◽  
Thrust Bearing ◽  
Acoustic Radiation ◽  
Element Model ◽  
Sound Power ◽  
Supporting Structure ◽  
Radiated Sound ◽  
The Impact ◽  
Radiated Sound Power

This paper takes marine Kingsbury sliding thrust bearing as the research object and conducts the finite element dynamic analysis with the aid of ANSYS software. On this basis, the acoustic boundary element model of a sliding thrust bearing shell is established with the ANSYS dynamic analysis results as the boundary excitation conditions. Besides, the radiated sound power of the shell is calculated by indirect boundary element method in SYNOSISE software. The influence of different condition parameters on the radiated sound power of the shell is perceived through the analysis of several rotation-thrust conditions. As for the special structure of this kind of sliding-thrust bearing, this paper states the impact of the supporting structure performance parameters, the pad number and damp of shell on the shell radiated sound power. The optimized measure for the supporting structure and the plan concerning the pad number’s selection lays the theoretical basis for damping and noise-reducing research on marine sliding-thrust bearing and its rotor system.

Vibroacoustic Optimization of Mechanical Structures: A Controlled Random Search Approach

2012 ◽  
Vol 622-623 ◽  
pp. 158-161 ◽  
Author(s):  
Mostafa Ranjbar ◽  
Steffen Marburg
Keyword(s):  
Random Search ◽  
Power Level ◽  
Search Method ◽  
Frequency Range ◽  
Controlled Random Search ◽  
Sound Power Level ◽  
Specific Frequency ◽  
Radiated Sound ◽  
Search Approach ◽  
Radiated Sound Power

A combination of controlled random search method and geometry modification concept is used to minimize the root mean square level of structure borne sound for a model. The structure is a rectangular plate made of steel. A specific frequency range for this porpuse is considered. The results show that this approach could produce significant reduction in the value of radiated sound power level of the structure within a limited time.

Weak Radiator Design Using Dimples

2010 ◽  
Author(s):  
Wen Nan Cheng ◽  
Chih Chun Cheng ◽  
Gary H. Koopmann
Keyword(s):  
Vibration Mode ◽  
Design Method ◽  
Vibration Modes ◽  
The Finite Element Method ◽  
Key Issues ◽  
Beam Surface ◽  
Specific Frequency ◽  
Radiated Sound ◽  
Radiated Sound Power ◽  
Do So

A design method for achieving minimum sound radiation from a beam is presented. The strategy is to form a series of cylindrical dimples on the beam surface in order to make one or more vibration modes of this dimpled beam have the same shape as the weak modes. Consequently, the dimpled beam behaves as a weak radiator when one or more vibration modes are excited. Instead of minimizing the radiated sound power at a specific frequency or in a bandwidth, the objective is to maximize the modal assurance coefficient (MAC) which quantifies resemblance between the vibration mode of a dimpled beam and a weak mode. To perform this strategy, two key issues are addressed in this paper. The first is to determine the so-called weak mode of a beam. And the second is how to determine the required dimple size and the dimple location on this beam so that the dimpled beam may have vibration modes resembled to the weak modes. A methodology to do so based on the finite element method and the mode assurance criteria is proposed. Results show that the radiation efficiency of the dimpled beam after optimization using MAC as the objective is generally lower than the uniform beam. However, the effectiveness of this strategy depends on how close in shape between the vibration mode of the dimpled beam and the designated weak mode.

Passive and Active Control of the Radiated Sound Power from a Submarine Excited by Propeller Forces

2013 ◽  
Vol 57 (1) ◽  
pp. 59-71 ◽  
Author(s):  
Sascha Merz ◽  
Nicole Kessissoglou ◽  
Roger Kinns ◽  
Steffen Marburg
Keyword(s):  
Active Control ◽  
Sound Power ◽  
Radiated Sound ◽  
Radiated Sound Power
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