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Dec 1986

Volume 80, Issue S1, pp. S1-S128

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back to top Session G. Shock and Vibration I: Flow‐Induced Structural Vibration
Invited Papers
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A new model of wall pressure fluctuations (A)

James M. Witting

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S14-S14 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Recent work has led to a new spectral model for pressure fluctuations at a rigid plane wall bounding a turbulent boundary layer, based on an explicit representation of structures in the boundary layer near the wall—bursts and sweeps—that exchange momentum within the layer and support the shear stress there [J. M. Witting, Noise Control. Eng. J. 26, 28—43 (1986)]. The fluctuating wall pressure results from the contributions of a collection of independent bursts and sweeps. Each burst and sweep is modeled as a dipole flow that moves with the local mean flow, has a finite duration, and has the correct strength to mix the fluid through a Prandtl mixing length above and below its center. This paper describes some of the salient features and extensions of the model, emphasizing (1) the physical interpretation of the model structure and its three adjustable parameters, which are sufficient to yield predictions for all frequencies and wavelengths, (2) the ranges of frequencies and wavenumbers over which the model can be applied with confidence, based both on theory and past experiments, and (3) the applicability of the modeling approach to other situations.
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Boundary layer transition as a source of noise and vibration (A)

Gerald C. Lauchle and M. A. Josserand

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S14-S14 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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When laminar flow over a rigid or flexible surface becomes unstable, an intermittent flow state occurs. This intermittent flow regime, called the transition region, is where turbulent spots are created, and then grow as they convect downstream at a velocity typically equal to 0.7 times the free‐stream velocity. The spots eventually coalesce to form the beginning of the fully developed turbulent boundary layer. The statistics of the velocity or pressure fluctuations in the transition region are essentially stationary in time, but nonhomogeneous in the streamwise direction. Fundamentally, it has been argued that this region is capable of creating monopole sound radiation, e.g., Lauchle [J. Acoust. Soc. Am. 69, 665–671 (1981)] and Sornette and Lagier [Acustica 55, 255–267 (1984)]. Also, it has been suspected that a transitional boundary layer can induce wall vibrations. These issues have been under study for some time. We have completed a set of measurements on the. space‐time statistics of turbulent spots in a naturally occurring transition zone and from them developed an analytical model for the wavenumber‐frequency spectrum of the pressure fluctuations. Based on this model, it appears that the transition zone wall pressure is less intense than that of a fully developed turbulent layer by a factor equal approximately to the intermittency factor. This presentation will review the current research findings on wall pressure fluctuations and radiated sound caused by boundary layer transition. [Work supported by Applied Research Laboratory under NAVSEA contract.]
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Wave vector‐frequency spectra of nonhomogeneous fields (A)

Wayne A. Strawderman

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S15 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The utility of wave vector‐frequency spectral analysis for the description and interpretation of hydroacoustic and structural‐acoustic fields has been amply demonstrated over the past decade in both theoretical and experimental applications. In the majority of these applications, the statistics of the random fields of interest were assumed to be stationary and homogeneous. While many of the hydroacoustic and structural‐acoustic fields of practical interest can be considered stationary, few can be considered homogeneous. Structural‐acoustic fields are nonhomogeneous owing to the space‐varying nature (e.g., boundaries) of practical structures. In hydroacoustics, the natural growth of the turbulent boundary layer results in a nonhomogeneous pressure field at the boundary. This paper addresses the application of wave vector‐frequency analysis to the description and interpretation of nonhomogeneous, but stationary, fields. Whereas only one definition of the wave vector‐frequency spectrum exists for a homogeneous, stationary field, several alternative definitions of the wave vector‐frequency spectrum are possible for the nonhomogeneous, stationary field. The utility of these various spectral forms for the analysis and interpretation of nonhomogeneous, stationary fields is assessed.
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Analytical structural acoustics of submerged cylindrical shells (A)

A. Harari and B. E. Sandman

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S15 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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A detailed analytical model of ring‐stiffened cylindrical shell vibration is presented. The model is to accept excitation due to turbulent boundary layer pressure fluctuations. The mathematical model is capable of predicting the acoustical effects of a compliant decoupling layer attached to the external surface of the shell structure. Both the shell vibration levels and farfield acoustic pressures are predicted. A few focused example results are presented with and without acoustical decouplers.
Contributed Papers
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Wall pressure measurements and acoustics in turbulent pipe flow (A)

Mark A. Daniels and Gerald C. Lauchle

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S15 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Measurements of the turbulent boundary layer (TBL) wall pressure spectrum and acoustic field were conducted in the Boundary Layer Research Facility of the Applied Research Laboratory. This facility uses glycerine as the working fluid. Subminiature, piezoresistive pressure transducers were used for these measurements. The TBL wall pressure spectrum was obtained using a novel signal processing technique (transducer difference signals) that minimized both acoustic and vibration‐induced noise while maintaining the integrity of the measured TBL wall pressure spectrum. A measurement involving the coherence function between these transducer difference signals validated the measured TBL wall pressure spectra and all assumptions used in the development of the measurement technique. The measured nondimensionalized spectra of the TBL fluctuating wall pressure are compared to those measured in previous investigations. These comparisons have substantiated a maximum, normalized transducer diameter for the complete resolution of the high‐frequency spectral energy associated with the pressure fluctuations within the TBL. In this investigation, a transducer diameter of 2.1 viscous wall units is demonstrated. This is a factor of 9, smaller than ever before achieved. [Work supported by Applied Research Laboratory E/F Program under NAVSEA contract.]
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Fluid loading on vibrating plates in a uniform flow field via a wave‐vector/time domain method (A)

Dong‐Jye Li and Peter R. Stepanishen

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S15 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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A new approach is presented to evaluate the fluid loading on vibrating elastic plates with specified time‐dependent velocities in uniform flows. An in vacuo eigenfunction expansion with time‐dependent coefficients is used to describe the specified normal velocity of the plate. Acoustical fluid loading on the plate is expressed as an eigenfunction expansion in which each modal coefficient is expressed as a summation of convolution integrals involving fluid/modal impulse responses and the modal velocities coefficients. Wave‐vector/time domain methods are used to develop expressions for the fluid modal impulse responses. Numerical results are presented to illustrate the characteristics of the fluid/modal impulse responses and fluid loading for various plates and Math numbers. (Work supported by ONR.]
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Planar elastic vibrators in a uniform flow field with broadband mechanical excitations (A)

Dong‐Jye Li and Peter R. Stepanishen

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S15 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Flow‐induced forces on structures can significantly affect their dynamic response. A new method is presented to evaluate the dynamic response of planar elastic vibrators in uniform fluid flow fields to broadband mechanical excitations. The approach is based on the use of in vacuo eigenfunction expansion to solve the fluid‐loaded problem. The time‐dependent coefficients of the modal expansion for the velocity are shown to satisfy a set of coupled convolution integral equations which involve mode and Mach number‐dependent impulse responses. Pressures in the field are simply expressed as a summation of uncoupled convolution integrals. Numerical results are presented to illustrate the effects of Mach number on the transient response of a plate subjected to a broadband mechanical excitation. [Work supported by ONR.]
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Interaction between a laminar boundary layer and an elastic layer (A)

Mauro Pierucci and Pedro Morales

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S15-S16 (1986); (2 pages)

Online Publication Date: 13 Aug 2005

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A two‐dimensional viscous flow field is bounded on both sides by a purely elastic layer of finite thickness that supports both shear and longitudinal waves. The mean flow field is assumed to be a Poiseuille flow. The boundary layer equations are linearized to the Orr‐Sommerfeld equation and the interaction between the fluid and the elastic layer occurs through the continuity of velocity and stress at the fluid‐solid interface. The stability of the disturbances in the fluid and the elastic layer is analyzed. Kaplan [“The Stability of a Laminar Incompressible Boundary Layer in the Presence of Compliant Boundaries,” MIT Report No. ASRL‐TR‐116‐1 (1964)] analyzed the stability characteristics of the problem by solving for the eigenvalues of the problem. The numerical solution of the eigenfunctions of the Orr—Sommerfeld equation has always been a very difficult and tricky problem. Davey [“An Automatic Orthonormalization Method for Solving Stiff Boundary Valve Problems,” J. Comput. Phys. 51, 343–356 (1983)] has developed a technique which allows for quick solution for the eigenvalues and the eigenfunction of the problem at any Reynolds number. This technique has been applied to the problem at hand and it has given solutions in a quick and efficient manner. The results for the stability of the boundary layer disturbances are presented in the form of velocity profiles (eigenfunctions) within the fluid and the solid layer.
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Plumbing noise measurement and isolation (A)

Jerry P. Christoff

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S16-S16 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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Plumbing noise measurements on valves used for domestic lavatories, showers, tubs, and toilets have been measured utilizing the approach outlined in ISO Standard 3822. This technique evaluates the flow induced structural vibration transmitted into the piping system. The results clearly indicate that the principal source of noise is turbulence within the valve mechanism and not due to excessive velocities in the piping. Comparisons will be provided between American and European products. Several standard methods of isolating pipe wall vibration from building components are also evaluated.
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Hydroelastic analysis of multiple circular cylinders in an inviscid incompressible flow (A)

W. H. Lin

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S16-S16 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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This paper presents a theoretical analysis and numerical results of hydroelastic oscillations of a group of parallel, circular, elastic cylinders in an inviscid incompressible flow. On the assumption that the turbulent fluid loading is negligible, the principal excitations considered are the steady hydrodynamic force due to the existence of the cylinders in the smooth flow and the self‐excited hydrodynamic forces caused by the motion of the cylinders. These hydrodynamic forces are obtained by solving a Lapace's equation for a potential function with Neumann conditions on the cylinders and the finiteness condition at infinity. The cylinders are assumed to be slender‐beam rods with straight axes so that the hydrodynamic forces acting on the axes do not produce any twisting and the equations of motion of the cylinders' flexure can be approximated by slender‐beam theory. The hydroelastic equations describing the interaction between the fluid motion and the cylinders' motion are casted into a matrix form and solved by the method of matrix inversion with the aid of digit computers. The critical flow speeds are determined by solving a complex eigenvalue problem associated with the coefficient determinant of the matrix equation with the method of iteration. Numerical results show that the added mass coefficients and the hydroelastic coefficients are symmetrical, and that the critical flow speeds depend much on the number, configuration, and orientation of the cylinders. This work was performed during the author's tenure with Argonne National Laboratory, Argonne, IL 60439.
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Reducing the flow‐induced self‐noise of a sonar: A successful enhancement of experimental and numerical models (A)

Bernard Garnier and Jacqueline Larcher

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S16-S16 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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The noise created by an external turbulent boundary layer in the heavy fluid contained in a sonar dome strongly depends on the dynamic properties of this shell. This work was performed to define the best design of the shell for a given shape, a given flow velocity, and a given sonar frequency range to minimize the flow‐induced self‐noise blinding the sonar in passive listening operational situations. Prior steps of this work were presented to the 106th Meeting of ASA [J. Larcher, J. Acoust. Soc. Am. Suppl. 1 74, S48, S78 (1983)] but they only reported simulations results. Since that time, operational prototypes have been measured out at sea; the results observed on operative sonars corroborate the whole predictive tool, which efficiently imbricates simplistic theoretical models with experimental simulations of the hydrodynamic excitation on 1/4 scaled or 1/1 sonar dome prototypes.
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Flow‐induced noise and vibration of confined jets (A)

Kam W. Ng

J. Acoust. Soc. Am. Volume 80, Issue S1, pp. S16-S16 (1986); (1 page)

Online Publication Date: 13 Aug 2005

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An experimental program was conducted in the acoustical water tunnel to determine the flow‐induced noise and vibration on pipes due to various flow restrictors. Several flow restrictor configurations were tested for a range of flow velocities (up to 15 m/s). The flow configurations tested include: pipe flow, and flow restrictors with circular, coannular, rectangular cross‐sectional areas, as well as multiple circular and slot jets. Wall pressure fluctuation and acceleration measurements were made using miniature hydrophones, flush‐mounted on the inside wall of the pipe, and accelerometers mounted on the outside wall. Spectral and cross‐spectral densities of the wall pressure and acceleration signals were determined. Experimental results showed that the flow‐induced noise levels vary with the pipe axial location. The peak noise is located at the vicinity of the end of the jet potential core (six jet diameters downstream of the jet). Correlation of noise versus velocity showed a velocity to the 4.8th power relationship. Normalized noise spectra were obtained for the various flow configurations. The spectral shapes of the various flow configurations are quite similar, except that the coannular and slots jets show more high‐frequency noise. The pipe‐wall structural resonances were identified by correlating the various hydrophone signals. These resonance frequencies were consistent with the results obtained by impact testing. Furthermore, results from the correlation of hydrophone signals showed the existence of coherent structures, which probably control the generation of turbulence generated noise, near the exit of the jet.
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