• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Aug 2008

Volume 124, Issue 2, pp. 689-EL61

Return to All Sections
back to top
RSS Feeds

Modeling of wave dispersion along cylindrical structures using the spectral method

Florian Karpfinger, Boris Gurevich, and Andrey Bakulin

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 859-865 (2008); (7 pages) | Cited 4 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Algorithm and code are presented that solve dispersion equations for cylindrically layered media consisting of an arbitrary number of elastic and fluid layers. The algorithm is based on the spectral method which discretizes the underlying wave equations with the help of spectral differentiation matrices and solves the corresponding equations as a generalized eigenvalue problem. For a given frequency the eigenvalues correspond to the wave numbers of different modes. The advantage of this technique is that it is easy to implement, especially for cases where traditional root-finding methods are strongly limited or hard to realize, i.e., for attenuative, anisotropic, and poroelastic media. The application of the new approach is illustrated using models of an elastic cylinder and a fluid-filled tube. The dispersion curves so produced are in good agreement with analytical results, which confirms the accuracy of the method. Particle displacement profiles of the fundamental mode in a free solid cylinder are computed for a range of frequencies.
Show PACS
43.40.At Experimental and theoretical studies of vibrating systems
43.58.Ta Computers and computer programs in acoustics
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Hq Velocity and attenuation of acoustic waves

Guided wave propagation and mode differentiation in hollow cylinders with viscoelastic coatings

Jing Mu and Joseph L. Rose

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 866-874 (2008); (9 pages) | Cited 4 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Guided wave propagation theories have been widely explored for about one century. Earlier theories on single-layer elastic hollow cylinders have been very beneficial for practical nondestructive testing on piping and tubing systems. Guided wave flexural (nonaxisymmetric) modes in cylinders can be generated by a partial source loading or any nonaxisymmetric discontinuity. They are especially important for guided wave mode control and defect analysis. Previous investigations on guided wave propagation in multilayered hollow cylindrical structures mostly concentrate on the axisymmetric wave mode characteristics. In this paper, the problem of guided wave propagation in free hollow cylinders with viscoelastic coatings is solved by a semianalytical finite element (SAFE) method. Guided wave dispersion curves and attenuation characteristics for both axisymmetric and flexural modes are presented. Due to the fact that dispersion curve modes obtained from SAFE calculations are difficult to differentiate from each other, a mode sorting method is established to distinguish modes by their orthogonality. Theoretical proof of the orthogonality between guided wave modes in a viscoelastic coated hollow cylinder is provided. Wave structures are also calculated and discussed in view of wave mechanics in multilayered cylindrical structures containing viscoelastic materials.
Show PACS
43.40.At Experimental and theoretical studies of vibrating systems
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Bi Mathematical theory of wave propagation
43.20.Ks Standing waves, resonance, normal modes

Edge resonance in semi-infinite thick pipe: Numerical predictions and measurements

M. Ratassepp, A. Klauson, F. Chati, F. Léon, and G. Maze

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 875-885 (2008); (11 pages) | Cited 2 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This paper presents theoretical and experimental studies of axisymmetric longitudinal guided wave L(0,2) interaction with the free edge of the pipe. A numerical method based on normal mode superposition is applied to predict the edge resonance by an analysis of dispersion relations of separate modes. In parallel, the finite element analysis and experimental measurements prove the existence of edge resonance in the pipe in case of L(0,2) wave incidence. It is shown that the edge resonance is mainly caused by the first pair of complex modes. Additionally the behavior of edge resonance phenomenon as a function of the curvature of the pipe is studied. The displacement amplitudes measured at the edge demonstrate that the edge resonance is affected by the frequency and thickness to midradius ratio of the pipe, and it is losing its strength in thicker pipes, as the growing difference between the outer and inner radii destroys symmetry. The reflected energy amplitudes show that at the resonance frequencies the incident wave is strongly converted to L(0,1) and L(0,3) modes, depending also on the curvature parameter of the pipe.
Show PACS
43.40.Ey Vibrations of shells
43.20.Ks Standing waves, resonance, normal modes
43.40.At Experimental and theoretical studies of vibrating systems

Active damping control unit using a small scale proof mass electrodynamic actuator

Cristóbal González Díaz, Christoph Paulitsch, and Paolo Gardonio

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 886-897 (2008); (12 pages) | Cited 3 times

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This paper presents a study on the design and use of a small scale proof mass electrodynamic actuator, with a low mounting resonance frequency, for velocity feedback control on a thin rectangular panel. A stability-performance formula is derived, which can be effectively used to assess the down scaling effects on the stability and control performance of the feedback loop. The design and tests of a velocity feedback loop with a prototype small scale proof mass actuator are also presented. When a feedback control having a gain margin of about 6 dB is implemented, so that there is little control spillover effect around the fundamental resonance of the actuator, reductions of vibration between 5 dB and 10 dB in the frequency band between 80 Hz and 250 Hz have been measured at the control position.
Show PACS
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.50.Ki Active noise control
43.40.At Experimental and theoretical studies of vibrating systems

Smart panel with active damping units. Implementation of decentralized control

Cristóbal González Díaz, Christoph Paulitsch, and Paolo Gardonio

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 898-910 (2008); (13 pages)

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This paper contains the second part of a study on a smart panel with five decentralized velocity feedback control units using proof mass electrodynamic actuators [ González Díaz et al., J. Acoust. Soc. Am. 124, 886 (2008) ]. The implementation of five decentralized control loops is analyzed, both theoretically and experimentally. The stability properties of the five decentralized control units have been assessed with the generalized Nyquist criterion by plotting the loci of the eigenvalues of the fully populated matrix of frequency response functions between the five error signals and five input signals to the amplifiers driving the actuators. The control performance properties have been assessed in terms of the spatially averaged response of the panel measured with a scanning laser vibrometer and the total sound power radiated measured in an anechoic room. The two analyses have shown that reductions of up to 10 dB in both vibration response and sound radiation are measured at low audio frequencies, below about 250 Hz.
Show PACS
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.50.Ki Active noise control
43.40.At Experimental and theoretical studies of vibrating systems

Nondestructive characterization of musical pillars of Mahamandapam of Vitthala Temple at Hampi, India

Anish Kumar, T. Jayakumar, C. Babu Rao, Govind K. Sharma, K. V. Rajkumar, Baldev Raj, and P. Arundhati

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 911-917 (2008); (7 pages)

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This paper presents the first scientific investigation on the musical pillars of the Vitthala Temple at Hampi, India. The solid stone columns in these pillars produce audible sound, when struck with a finger. Systematic investigations on the acoustic characteristics of the musical pillars of mahamandapam (great stage) of the Vitthala Temple have been carried out. The 11 most popular pillars that produce sounds of specific musical instruments are considered for the investigations. The sound produced from these 11 most popular musical pillars was recorded systematically and different nondestructive testing techniques such as low frequency ultrasonic testing, impact echo testing, and in situ metallography were employed on the musical columns of these pillars. The peak frequencies in the amplitude spectrum of the sound produced from various columns in these pillars are correlated with the dimensional measurements and ultrasonic velocity determined using impact echo technique. The peak frequencies obtained experimentally have been found to have excellent correlation with the calculated flexural frequencies based on the dimensional measurements and ultrasonic velocities of the columns.
Show PACS
43.40.At Experimental and theoretical studies of vibrating systems
43.40.Cw Vibrations of strings, rods, and beams
43.75.Zz Analysis, synthesis, and processing of musical sounds

Defect detection and localization in orthotropic wood slabs by inversion of dynamic surface displacements

Anthony J. Romano, Joseph A. Bucaro, and Saikat Dey

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 918-925 (2008); (8 pages) | Cited 1 time

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The nondestructive evaluation inversion and generalized force-mapping techniques developed and demonstrated for isotropic thin plates by Bucaro et al. [(2004). “Detection and localization of inclusions in plates using inversion of point actuated surface displacements,” J. Acoust. Soc. Am. 115, 201–206 ] are extended to the case of orthotropic plates. The extended techniques are applied to a finite-element generated numerical database for point excited wooden slabs with and without an internal defect at 5 and 10 kHz. Operation of the original isotropic algorithms on the wood surface displacements is shown to fail in recovering the uniform elastic parameters or in detecting and locating the defect. The new algorithms based on the wave equation for a thin, orthotropic plate successfully convert the surface displacements on the uniform wooden slab to elastic parameter maps which serve to detect and localize the defect in the flawed plate. The results, particularly at the higher frequency, indicate that the onset of failure in the thin plate approximation impacts both the inversion and the generalized force-mapping accuracy. However, in this case use of the inversion algorithm to obtain modified wave equation coefficients followed by operation of the force-mapping algorithm with these new parameters inserted is shown to successfully mitigate this effect.
Show PACS
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.Dx Vibrations of membranes and plates
43.60.Pt Signal processing techniques for acoustic inverse problems
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close