摘要:

The vibration of shallow spherical and ellipsoidal dishes with variable thickness along the gradient from the apex is studied. The dishes are point‐clamped at the apex or surface‐clamped over concentric central regions which are modeled as singly and doubly connected domains, respectively. This model simulates domes, tank covers, radar dishes, or the antennas of certain communication satellites which are clamped over a finite region at the apex. The Ritz method is used to develop an efficient numerical procedure incorporating the boundary support characteristics intrinsically. Comparison with finite element and experimental results shows good consistency. Sets of useful vibration frequencies with additional mode shapes are presented to illustrate the capability of the method.

ISSN:0001-4966    

DOI:10.1121/1.414548

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

In this study, the flexural vibration in a finite piezoelectric circular hollow cylinder belonging to crystal class 6mmis considered. Both the inner and outer curved surfaces and the end plane surfaces are free from traction and electric potential. Solutions for the mechanical displacements and the electric potential are derived in a series form. Boundary conditions on shear stress are satisfied exactly term by term in the series and the remaining boundary conditions are satisfied by an orthogonalization procedure. Numerical analysis is carried out for the piezoelectric ceramic PZT4. The natural frequencies are calculated for the circular modes one and two and presented graphically.

ISSN:0001-4966    

DOI:10.1121/1.414549

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A ray perturbation formulation for the calculation of rays and travel times in isotropic inhomogeneous media is presented. The ray perturbation theory employed is of first order for the ray deflection and of second order for the travel time. The initial slowness model is parametrized in terms of triangular cells; values are assigned initially to grid nodes and the slowness gradient is assumed to be constant between nodes. The assumption of a constant slowness gradient within a cell leads to a simplification of the ray perturbation equations and a straightforward analytic solution for ray segments in the cells. Imposing boundary conditions that require continuity at cell interfaces leads to a separate tridiagonal system of equations for each component of the ray‐path location vector, which produces an extremely efficient algorithm. The accuracy and speed of this scheme with a 2‐D synthetic crosswell experiment is evaluated. The computation times for the calculations described in this paper depend only on the number of nodes that influence each ray, not the total number of nodes parametrizing the model, so the method promises an even greater increase in speed for 3‐D applications.

ISSN:0001-4966    

DOI:10.1121/1.414550

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A transient solution is presented which models the fluid–solid interaction of a thin elastic prolate spheroidal shell loaded end‐on by a nonconservative acoustic shock wave. Solutions to the Lagrangian equations of motion are provided for the normal and tangential shell displacement fields, as well as for the incident, scattered, and radiated fluid pressure fields. The explicit analytic solutions converge uniformly and absolutely to the exact solution of the actual coupled differential equations over the entire temporal and spatial domains both in the structure and in the fluid. Numerical results for the free vibrations and for the transient fluid–solid interactions of a fluid‐loaded prolate spheroidal shell are presented. As in the case for the spherical geometry, the fluid loading is shown to down shift the frequencies and to introduce additional proliferant structural frequencies. Long time history plots of the shell displacements are presented for the submerged shock‐loaded low aspect ratio case. Insights into the qualitative and quantitative effects of the fluid on the structural response are revealed.DOE−MACSYMAwas used extensively to develop and verify the solutions.

ISSN:0001-4966    

DOI:10.1121/1.414551

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject antinoise into the duct to destructively interfere with the tonal sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the disturbance and the control sources is based on duct modal expansion. Attenuation of the radiated sound field is accomplished using a multiple‐channel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The model is used to evaluate the performance of the control system for single and multiple circumferential arrays of control sources. The model can be extended for use in design optimization. Sample results are presented to illustrate the predicted sound attenuations.

ISSN:0001-4966    

DOI:10.1121/1.414552

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The question of acoustics for both speech and music in the same space can be addressed by variable acoustics and/or ideal room acoustics for one use and electronic enhancement for the other. A large cathedral can have near‐ideal acoustics for liturgical music and satisfactory speech intelligibility by the use of conventional, historically proven architectural design, hard finish surfaces, and a carefully designed, installed, maintained, and operated sound amplification system. Holy Cross Cathedral, Boston, is one such situation. The sound system design, and evaluation of results using the Crown–Techron, L. G. Marshall early‐to‐late ratio (ELR) testing technique [J. Acoust. Soc. Am.96, 2251–2261 (1994)] are discussed.

ISSN:0001-4966    

DOI:10.1121/1.414553

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

In this paper, an identification approach is introduced for the parametric calibration of electroacoustic transducers. The method is based on the conventional substitution technique for hydrophone calibration and a parametric estimation technique for a linear system. The calibration is carried out in three main steps: (1) measurement of the combined transfer function of an electroacoustic transmitter–hydrophone system; (2) parametric estimation of the measured transfer functions with time delay, and calculation of the zero(s)/pole(s) of the system; (3) common polynomial extraction and reconstruction of the transducer’s characteristics. The calibration approach is illustrated with simulations as well as experiments. This new approach will allow the simultaneous calibration of transmitter and one or more hydrophones, and can be used to calibrate the relative amplitude characteristics as well as the phase characteristics of transducers.

ISSN:0001-4966    

DOI:10.1121/1.414554

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The maximum amplitude of a waveform corresponding to a particular harmonic spectrum depends on the phases of its harmonic components. A waveform with a low peak‐to‐rms ratio is desirable in situations requiring a maximum signal‐to‐noise ratio. This paper introduces a genetic algorithm‐based method for selecting the phases that produces better results than previously described methods. Results for four different amplitude spectra are given. For the case of a flat spectrum with up to 40 harmonics, the genetic algorithm finds peak factors (peak/√2 rms) ranging from 0.98 to 1.24.

ISSN:0001-4966    

DOI:10.1121/1.414555

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The theoretical scattering of acoustic wave pulses from irregular surfaces is studied by using time‐domain analysis. The purpose has been to examine the application of acoustic time‐domain reflectometry (ATDR) to the nondestructive testing of surface geometry characteristics. A finite‐difference time‐domain (FDTD) simulation method is used to obtain the reflected wave response from irregular surfaces to an incident short pulse by calculating the scattered field and determining the net pressure at an acoustic sensing transducer. Various configurations pertinent to nondestructive testing of irregular surfaces are considered and the relationships between the transducer output waveform and the surface features are investigated. A strong correlation between the pulse width of the reflected pulse and the surface roughness is established for important configurations of interest. Results are determined for a range of surface conditions extending from the Kirchhoff limit where single scattering approximation is accurate to cases where complex multiple scattering effects become important. Conditions for departure from the single scattering limit are identified from simulations.

ISSN:0001-4966    

DOI:10.1121/1.414556

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A new cochlear modeling technique has been developed in which the number of assumptions required in model formulation is significantly less than in previous modeling studies. The main new feature of the method is that it allows individual cellular and membrane components of the organ of Corti to be embedded within the model fluid in their true structural positions, with connections to neighboring elements reflecting anatomical geometry. The cochlea is divided into a three‐dimensional finite element (3‐D FE) network of nodes, connected by branches representing the local mechanical properties. The model system of simultaneous equations, obtained by applying continuity at each node, is solved iteratively using a variant of the conjugate gradient method. Here the formulation and implementation of the 3‐D FE method are described. Force generation by outer hair cells is included and results are presented which demonstrate the effect of tectorial membrane and Deiters’ cell mechanical properties on the effectiveness of the cochlear amplifier.

ISSN:0001-4966    

DOI:10.1121/1.414557

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP