Noise Generation and Propagation Within Corrugated Pipes

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Differential Equation ◽  
Theoretical Model ◽  
Acoustic Wave ◽  
Standing Wave ◽  
Fatigue Damage ◽  
Acoustic Resonance ◽  
Noise Generation ◽  
Flow Conditions ◽  
Noise Levels ◽  
Acoustic Standing Wave

Corrugated pipes have the advantage of being flexible but the disadvantage of generating unacceptable levels of noise. The noise generated within these pipes is due to oscillation of vortices formed within the corrugations. The noise can induce vibration and unacceptable fatigue damage. Consequently, it is desirable to have a method for predicting the flow conditions that facilitate noise and the noise levels that are generated. This paper develops a theoretical model for the noise generation by considering the interaction of an acoustic wave with the vortices. The key issue that emerges is the delay or phase angle between vortex production in the corrugations and an acoustic standing wave. For the usual conditions, where there are many corrugations in a wavelength, it is possible to form a differential equation for the build-up and saturation of an acoustic resonance. The relative few parameters within this differential equation provide a good basis for modeling the occurrence and level of noise produced. It is anticipated that some experimental input will always be needed for particular corrugation geometries.

Acoustic Resonance in Aeroengine Intake Ducts

2004 ◽  
Vol 126 (3) ◽  
pp. 432-441 ◽  
Author(s):  
A. J. Cooper ◽  
A. B. Parry ◽  
N. Peake
Keyword(s):  
Theoretical Model ◽  
Analytical Methods ◽  
Swirling Flow ◽  
Acoustic Resonance ◽  
Rotating Stall ◽  
Flow Conditions ◽  
Resonance Phenomena ◽  
Axial Variation ◽  
Acoustic Lining

A theoretical model is used to investigate the effect of geometry, flow conditions and acoustic lining on the occurrence of acoustic resonance within aeroengine ducts. Semi-analytical methods are used to demonstrate that two types of acoustic resonance can be excited. The first is an intake resonance arising due to axial variation of the intake shape and the presence of swirling flow downstream of the rotor. The second occurs as a result of mode trapping between the rotor and stator. Such resonance phenomena may be relevant to the destabilization of the fan and the onset of flutter and rotating stall.

scholarly journals Analysis of the effects of acoustic levitation to simulate the microgravity environment on the development of early zebrafish embryos

RSC Advances ◽  
2020 ◽  
Vol 10 (72) ◽  
pp. 44593-44600
Author(s):  
Li Li ◽  
Ning Gu ◽  
Huijuan Dong ◽  
Bingsheng Li ◽  
Kenneth T. V. G.
Keyword(s):  
Wave Field ◽  
Standing Wave ◽  
Development Stage ◽  
Microgravity Environment ◽  
Acoustic Levitation ◽  
Zebrafish Embryos ◽  
Acoustic Standing Wave ◽  
Standing Wave Field

Influence of acoustic standing wave field creating acoustic levitation, on each development stage of early zebrafish embryos has been studied.

Effect of the Separation Distance on the Aeroacoustic Source of Multiple Shallow Cavities

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Ayman A. Shaaban ◽  
Samir Ziada
Keyword(s):  
Standing Wave ◽  
Separation Distance ◽  
Destructive Interference ◽  
Acoustic Standing Wave ◽  
Separation Ratio ◽  
Sound Levels ◽  
Standing Wave Method ◽  
Image Velocimetry ◽  
Strong Source ◽  
Shallow Cavities

Flow over ducted shallow cavities can excite fluid resonant oscillations. A common industrial application is the flow in corrugated pipes that can be modeled as a series of consecutive shallow cavities. In the current study, the effect of the separation distance on the aeroacoustic source of multiple shallow cavities is investigated. The standing wave method (SWM) is used to measure the source, where multiple microphones reconstruct the acoustic standing wave upstream and downstream of the cavities. The effect of the ratio between the separation distance to cavity length is investigated for a practical range from 0.5 to 1.375 for two- and three-cavity configurations. At low and intermediate sound levels, constructive hydrodynamic interference, resulting in a strong source, is observed for the extremum spacing ratios of 0.5 and 1.375. However, at high excitation levels, 10% and higher, the source, slightly but consistently, decreases upon increasing the separation ratio. These trends persist for both the double- and triple-cavity configurations. On the other hand, the separation distance of destructive interference is found to depend on the number of cavities of the tested configuration. Particle image velocimetry (PIV) measurements of the constructive interference cases show strong synchronized vorticity shedding in all cavities. Each cavity contribution to the total aeroacoustic source is then examined by means of Howe's analogy, and the percentage contribution of each cavity is found to depend on the excitation level.

The curve of knowledge transfer: a theoretical model

2019 ◽  
Vol 25 (1) ◽  
pp. 10-26 ◽  
Author(s):  
Pasquale De Luca ◽  
Mirian Cano Rubio
Keyword(s):  
Differential Equation ◽  
Ordinary Differential Equation ◽  
Theoretical Model ◽  
Knowledge Transfer ◽  
Transfer Process ◽  
Content Type ◽  
Positive Effects ◽  
Variation Rate ◽  
Effectiveness And Efficiency ◽  
Amount Of Knowledge

Purpose The knowledge transfer plays a key role in the firm’s capability to develop and to maintain a strategic competitive advantage over time. The capability of the firm to develop an efficient and effective process of knowledge transfer increases the internal skills and then the capability to compete in the business with positive effects on the performance. In order to maximize the effectiveness and efficiency of the knowledge transfer process it must be consider two main variables: the amount of knowledge to be transferred and the speed of the process. In this contest, the purpose of this paper is to developed a theoretical model, defined the knowledge transfer curve, able to evaluate the knowledge transfer process on the basis of its speed. Design/methodology/approach The curve of the knowledge transfer is based on the methodology of the learning curve. The curve of the knowledge transfer process can be evaluated on the basis of two main variables: the first is the content of knowledge to be transferred. It refers to the quality and quantity of the information to be transferred within the firm; and the second is the speed of the knowledge transfer process. It refers to the time in which the knowledge transfer can be realized. The function of the knowledge transfer is defined using ordinary differential equation. Findings There is an inverse relationship between time t and the variation rate r. The higher the variable r, the faster the knowledge transfer toward the level K. Therefore, the variable r measures the efficiency and effectiveness of the knowledge transfer process. On the basis of these considerations, manager must evaluate their policies about the knowledge transfer on the basis of their effects on the variable r: only the policy that increases its value can be considered effective for the knowledge transfer process. Originality/value The originality resides in the development of a theoretical model that is able to capture and measure the effectiveness and efficiency of the knowledge transfer. It is possible to define a curve of knowledge transfer on the basis of these two variables: content of the knowledge to be transferred and the time of the transfer process, by using an ordinary differential equation.

Vibrations and Waterborne Noise on Fishery Vessels

1988 ◽  
Vol 32 (02) ◽  
pp. 112-133
Author(s):  
W. Ojak
Keyword(s):  
United Nations ◽  
Noise Generation ◽  
Noise Levels ◽  
Structural Vibrations ◽  
Mechanical Vibrations ◽  
Noise Propagation ◽  
Research Institutes ◽  
Fishery Research ◽  
Elastically Supported ◽  
Agricultural Organization

The Food and Agricultural Organization of the United Nations granted a fellowship to the author to study, at several European ship research institutes, the problem of noise generation and propagation on fishery vessels. He later took part in the design of the fishery research vessel Prof. Siedlecki, which included the implementation of a series of antivibration and antinoise precautions. This paper compares vibration and noise levels on two fishery research vessels—the conventional RV G.O.Sars and RV Prof. Siedlecki. The paper is divided into two parts. In the first part, mechanical vibrations of the elastically supported propeller are dealt with and conditions for minimum vibration response are determined. In the second part, structural vibrations in the ships and noise propagation from the ships to the water are described. The paper concludes with data on structural vibrations and waterborne noise propagation. This paper, and the paper published in the June 1984 issue of JOURNAL OF SHIP RESEARCH [1],2 completes the author's approach to propeller vibrations.

scholarly journals Analysis and Application of Screens for Acoustic Impedance in a Speaker Box with a Passive Radiator to Decrease Standing-Wave Influence

2020 ◽  
Vol 10 (3) ◽  
pp. 866
Author(s):  
Yuan-Wu Jiang ◽  
Dan-Ping Xu ◽  
Zhi-Xiong Jiang ◽  
Jun-Hyung Kim ◽  
Ki-Hong Park ◽  
...  
Keyword(s):  
Standing Wave ◽  
Acoustic Resonance ◽  
Experimental Result ◽  
Parameter Method ◽  
Analysis Tool ◽  
Analysis Method ◽  
The Finite Element Method ◽  
Lumped Parameter ◽  
Acoustic Domain ◽  
Lumped Parameter Method

Micro speakers are playing an increasingly important role with the development of multimedia devices. This study applies the lumped-parameter method, which uses an equivalent circuit to model the electromagnetic and mechanical domains. The acoustic domain is modeled using the finite element method. Based on the analysis tool, the use of a screen is analyzed, and the screen is designed to depress the acoustic resonance in the sound-pressure-level curve and improve the performance. The samples are fabricated, and the experiment verifies the analysis method. The experimental result shows that the peak and dip due to the standing wave are cancelled, and the frequency response is smooth when the screen is used.

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