摘要:

A new bond graph model for conduction heat transfer is developed, and applied to thermal energy balance in the piezoelectric thickness vibrator. In formulation of the heat conduction model, the mechanical and electrical effects are included. Hence, it can be directly applied to the temperature-dependent thickness vibrator. For the purpose of evaluation of the new method, one-dimensional heat conduction excluding other variable effects is compared with the results of the analytic solutions in simple cases. The simulation illustrates the validity and the accuracy of the model. Although the model is applied to the one-dimensional case only, the method can be easily used for general heat conduction problems.

ISSN:0001-4966    

DOI:10.1121/1.419254

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This article develops a model of the piezoelectric ceramic vibrator which includes thermal energy exchange on an equal footing with the electrical and mechanical energy. By use of an isentropically linear model for the material and the bond graph models for a piezoelectric thickness vibrator and heat conduction previously developed by the authors, a thermodynamically complete model is developed. For a simple case, the predicted results from the developed model are compared with the results from experiments. Predictions are found to compare very favorably with these measurements.

ISSN:0001-4966    

DOI:10.1121/1.418167

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Matched-field processing (MFP) is a generalized procedure of array processing used in ocean acoustics to localize sources. It is based on comparing data with solutions to the wave equation using an assortment of linear and nonlinear methods. The applicability of MFP techniques to localize sources of vibration in structures is explored through simulations, starting with the relatively simple problem of localizing a point force on a simply supported laterally vibrating beam. The Bartlett, minimum variance (as well as the eigenvector versions of these two), and a matched modal processor are used. In all cases localization was achieved. Additional complications such as spring constraints were added in order to determine whether the MFP methods can still localize sources of vibrations without full detailed modeling of additional structural complexity. An application to nondestructive testing is also presented.

ISSN:0001-4966    

DOI:10.1121/1.418168

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Analytical estimates are made for mean and mean-square transient responses of a single degree of freedom master oscillator attached to an undampedNdegree of freedom random substructure. The ensemble averaged response is found to be, asymptotically for a large number of substructural degrees of freedom, in accord with the predictions of the Pierce–Sparrow–Russell theory. In particular the mean response of the master oscillator manifests an apparent damping. Corrections to this behavior are also predicted, but are found to lie well below the root-mean-square level of the fluctuations. The corrections are therefore, for practical purposes, unimportant. The ensemble average of the square of the response is also investigated and found to take a value at later times that is in accord with simple equipartition arguments advanced in an earlier paper. The power spectral density of the late time behavior is shown to be proportional to the square of the power spectrum of the early time response, and thus to be a narrower-band process than that of the early time behavior. Numerical simulations are presented which agree with the analytical predictions at moderate times, but also show an enhanced backscatter that develops over longer time scales.

ISSN:0001-4966    

DOI:10.1121/1.418169

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A new system was developed for the reciprocity calibration of acoustic emission transducers in Rayleigh-wave and longitudinal-wave sound fields. In order to reduce interference from spurious waves due to reflections and mode conversions, a large cylindrical block of forged steel was prepared for the transfer medium, and direct and spurious waves were discriminated between on the basis of their arrival times. Frequency characteristics of velocity sensitivity to both the Rayleigh wave and longitudinal wave were determined in the range of 50 kHz–1 MHz by means of electrical measurements without the use of mechanical sound sources or reference transducers.

ISSN:0001-4966    

DOI:10.1121/1.418170

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Structural damage from sonic booms is one of the potential environmental impacts of supersonic flight. This paper illustrates how structural acoustic techniques may be used to assess the potential for such damage in the absence of actual flyovers. Procedures are described whereby transfer functions relating structural response to sonic boom signature may be obtained with a stationary acoustic source and appropriate data processing. Further, by invoking structural acoustic reciprocity, these transfer functions may also be acquired by measuring the radiated sound from a structure that is mechanically driven. The approach is based on the fundamental assumption of linearity, both with regard to the (acoustic) propagation of the boom in the vicinity of the structure and to the structure’s response. Practical issues revolve around acoustic far field, source strength, and directivity requirements. The technique was evaluated on a specially fabricated test structure at Edwards AFB, CA. Blank shots from a cannon served as the acoustic source and taps from an instrumented hammer generated the mechanical drive. Simulated response functions were constructed. Results of comparisons with corresponding measurements recorded during dedicated supersonic flyovers with F-15 aircraft are presented for a number of sensor placements. Using the prediction of peak structural response as a metric, it was found that the direct and reciprocal simulation techniques produced ensemble-averaged mean percent errors of −4% and −26%, respectively. The corresponding standard deviations of these errors were 18% and 16%. Also, it was concluded that these uncertainties are consistent with that connected to the representation of the sonic boom itself.

ISSN:0001-4966    

DOI:10.1121/1.418128

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A boundary integral method for solving the exterior acoustic radiation problem of axisymmetric bodies with arbitrary boundary conditions is developed. The new formulation derives from the method proposed by Burton and Miller [Proc. R. Soc. London Ser. A323, 201–210 (1971)], which uses a linear combination of the Helmholtz integral equation and its normal derivative to ensure the uniqueness of the numerical solution at all frequencies. It is shown that the use of tangential operators enables one to easily compute the hypersingular integral without much extra effort. By taking advantage of the properties of axisymmetric geometry, and using the expansion of the boundary conditions and the surface distribution functions in Fourier series with respect to the angle of revolution, the surface integral is reduced to a line integral along the generator of the body, and Fourier integrals of the Green’s function and its derivatives over the circumferential angle. The Fourier integrals with singular kernels are evaluated using recurrence formulas in terms of the complete elliptic integrals. A new approach is then proposed to evaluate the Burton and Miller formulation at a corner by using the left-hand and right-hand limits of normal derivatives. Doing so, isoparametric elements throughout the surface of the body are able to be used. In order to demonstrate the validity and accuracy of the method, numerical results with quadratic isoparametric curvilinear elements are presented for radiation problems of a pulsating sphere, an oscillating sphere, and a finite cylinder with various boundary conditions.

ISSN:0001-4966    

DOI:10.1121/1.418174

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The transmission of harmonic vibratory power from a vibrating rigid body into a thin supporting cylindrical shell through multiple passive and active isolators is investigated theoretically. The model allows for the transmission of vertical and horizontal harmonic forces and moments about all three coordinate axes. Results show that over a frequency range from 0 to 200 Hz, the real power transmission into the supporting shell can be reduced substantially by employing in parallel with existing passive isolators, active isolators adjusted to provide appropriate control force amplitudes and phases.

ISSN:0001-4966    

DOI:10.1121/1.418171

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Local attenuation of sound pressure, which creates a zone of quiet, seems to be the only option if primary and secondary sources are well separated. Two major indexes of local control, the size of the quiet zone and the total sound power output, are mainly determined by the arrangement of primary sources, secondary sources, and error sensors. It has been found that the size of the quiet zone created by the control system with multiple secondary sources and error sensors is not simply the summation of quiet zones created by each individual control source. The interactions of the control sources, which are determined by the configuration of the system, play a very important role in the system performance. In this paper, a typical control arrangement with multiple secondary sources and multiple error sensors equally spaced in two parallel lines is examined. Results from computer simulation and experiments in an anechoic chamber show that there exists a range of optimal spacing for the secondary sources and error sensors. The control system will create the largest quiet zone and suffer the least increase of total sound power output in the optimal configuration.

ISSN:0001-4966    

DOI:10.1121/1.418172

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

This paper presents time-domain analysis and synthesis of active low-frequency noise control systems in rigid-walled ducts. In contrast to frequency-domain analysis, time-domain modeling provides a direct physical insight of the noise cancellation mechanism, where noise signals are assumed to be arbitrary real functions of time instead of harmonics. The time-domain analysis is based on a state-space model which is derived from the governing wave equation using combined numerical (finite difference) and analytical techniques. Optimal feedback control laws are synthesized for a variety of active noise control systems with different sensor and source arrangements. The responses of closed-loop systems are simulated, and the results are compatible with those of transfer function synthesis. In addition, the active control systems so designed have the potential of providing global, broadband, and optimal noise reductions without running into the annoying feedback problems in most feedforward control systems.

ISSN:0001-4966    

DOI:10.1121/1.418104

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP