Acoustics 1988: Laser-generated underwater sound

Pierce, Allan D.; Berthelot, Yves H.

doi:10.1121/1.397825

Cited by 40 publications

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“…Below the fundamental mode, the monopole radiation in the baffled plate case now becomes dipole radiation in the unbaffled plate case. By analogy with a sphere of radius a, where a monopole has σ = (ka) 2 and a dipole has σ = (ka) 4 /4 [73], the formula can be expressed as…”

Section: Results and Comparison With Baffled Platementioning

confidence: 99%

“…(5.2) is called the perforation constant [61] that includes the effect of friction between the air and the plate interface in the hole due to the viscosity. This end correction is proportional to an added mass in the proximity of a moving rigid piston [4,73]. This can be used assuming that the velocity in the hole is uniform.…”

Section: The Effect Of Fluid Viscosity and End Correctionmentioning

confidence: 99%

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Sound radiation from perforated plates

Putra

Thompson

2010

Journal of Sound and Vibration

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FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS INSTITUTE OF SOUND AND VIBRATION RESEARCH Doctor of Philosophy SOUND RADIATION FROM PERFORATED PLATES by Azma PutraPerforated plates are quite often used as a means of engineering noise control to reduce the sound radiated by structures. However, there appears to be a lack of representative models to determine the sound radiation from a perforated plate. The aim of this thesis is to develop such a model that can be used to give quantitative guidance corresponding to the design and effectiveness of this noise control measure.Following an assessment of various models for the radiation efficiency of an unbaffled plate, Laulagnet's model is implemented. Results are calculated and compared with those for baffled plates. From this, simple empirical formulae are developed and give a very good agreement with the analytical result. Laulagnet's model is then modified to include the effect of perforation in terms of a continuously distributed surface impedance to represent the holes. This produces a model for the sound radiation from a perforated unbaffled plate. It is found that the radiation efficiency reduces as the perforation ratio increases or as the hole size reduces. An approximate formula for the effect of perforation is proposed which shows a good agreement with the analytical calculation up to half the critical frequency. This could be used for an engineering application to predict the noise reduction due to perforation.The calculation for guided-guided boundary conditions shows that the radiation efficiency of an unbaffled plate is not sensitive to the edge conditions. It is also shown that perforation changes the plate bending stiffness and mass and hence increases the plate vibration.The situation is also considered in which a perforated unbaffled plate is located close to a reflecting rigid surface. This is established by modifying the Green's function in the perforated unbaffled model to include an imaginary source to represent the reflected sound. The result shows that the presence of the rigid surface reduces the radiation efficiency at low frequencies.The limitation of the assumption of a continuous acoustic impedance is investigated using a model of discrete sources. The perforated plate is discretised into elementary sources representing the plate and also the holes. It is found that the uniform surface impedance is only valid if the hole distance is less than an acoustic wavelength for a vibrating rectangular piston and less than half an acoustic wavelength for a rectangular plate in bending vibration. Otherwise, the array of holes is no longer effective to reduce the sound radiation.Experimental validation is conducted using a reciprocity technique. A good agreement is achieved between the measured results and the theoretical calculation for both the unbaffled perforated plate and the perforated plate near a rigid surface.

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Section: Results and Comparison With Baffled Platementioning

confidence: 99%

Section: The Effect Of Fluid Viscosity and End Correctionmentioning

confidence: 99%

Sound radiation from perforated plates

Putra

Thompson

2010

Journal of Sound and Vibration

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“…The idea that any disturbance governed by the linearized Navier-Stokes equations can be considered as a superposition of vorticity, entropy, and acoustic modes was expressed a long time ago (see, for example, [Pie89], pp. 519 and 524).…”

Section: Biorthogonal Eigenfunction Systemmentioning

confidence: 99%

“…(2.103)]. The classification of the modes follows from their properties outside the boundary layer (one can find discussion of the properties of vorticity, entropy and acoustic modes in [Pie89]). …”

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confidence: 99%

Theoretical and Computational Studies of Stability, Transition and Flow Control in High-Speed Flows

Tumin¹

2008

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Public Reporting burden for this collection of information is estimated to average I hour per response. including the time for reviewing instructions, searching existing data sources. gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services. Directorate for information Operations and Reports. 1215 AFOSR /t0P(f North Randolph Street AFRL-SR-AR-TR-08-0144Suite 325, Room 3112 Arlington, VA 2299 3-1768 I1. SUPPLEMENTARY NOTESThe views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other documentation. Approved for public release; distribution unlimited. ABSTRACT (Maximum 200 words)A comprehensive study of stability and receptivity of hypersonic boundary layers has been carried out. The main results of the project: 1. Mathematical method of the multimode decomposition for three-dimensional perturbations in compressible boundary layers has been developed. The method provides analysis of experimental and computational results for modes of discrete and continuous spectra. 2. Theory of boundary-layer receptivity was developed for roughness-induced perturbations in incompressible and compressible boundary layers. 3. The transient growth phenomenon in compressible boundary layers over flat plate, sphere, and sharp cone has been studied. The work was accompanied by development of solvers for these geometries. IntroductionThe potential of sustained hypersonic flight to revolutionize military and commercial activity is well recognized, and is reflected in recent initiatives such as the National Aerospace Initiative. High-speed vehicles will substantially impact military strategy by providing new defensive options such as a rapid on-demand global strike capability with much shorter response times than currently possible. Furthermore, the development of new technologies based on air-breathing propulsion can be leveraged to considerably reduce the cost of accessto-space, the benefits of which are both military as well as commercial. However, daunting technical challenges remain in realizing such vehicles. The harsh environment imposed by the envelope of such future missions is manifested in the severe anticipated thermo-mechanical loads and various propulsion-related requirements. Although the diversity of the physical phenomena encountered is broad, several key limiting issues have been identified as primary challenges, including both local and global constraints such as, for example, cowl lip loading and airframe balance. A scrutiny of the problems identified reveals the pervasive importance of several basic fluid dynamic phenomena. One of these, and possibly the least understood, is that of high-speed transition.The impact of hypersonic boundary lay...

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“…Thus, the semiempirical formulae proposed by Sutherland [15]: " ¼ In addition, an adiabatic relationship for a compressible fluid is used to related the absolute temperature and the pressure…”

Section: Vocal Tract Tracheamentioning

confidence: 99%

Numerical simulation of unsteady flow through the rigid glottis

Nomura

Funada

2006

Acoust. Sci. & Tech.

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The present study is intended as an investigation of speech dynamics, particularly the unsteady motion of glottal flow in the larynx. In order to focus on only fluid motion, the vocal cords are assumed to be non-vibrating rigid bodies, although the glottal sound source is described as the interaction between the flow and the vibrating vocal cords. The glottal flow based on the twodimensional rigid body model is simulated by solving basic equations in a compressible viscous fluid that is subject to appropriate initial and boundary conditions. The obtained results demonstrate that the initial glottal flow was a simple symmetric jet and that the flow became an unsteady complicated flow with vortices distributed in two-dimensional space. Furthermore, the structure of the complicated flow changed with time. These results indicate that simple assumptions, such as linearization of the fluid equations or one-dimensional models, are inappropriate for analysis of the speech production process.

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Acoustics 1988: Laser-generated underwater sound

Cited by 40 publications

References 0 publications

Sound radiation from perforated plates

Sound radiation from perforated plates

Theoretical and Computational Studies of Stability, Transition and Flow Control in High-Speed Flows

Numerical simulation of unsteady flow through the rigid glottis

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