摘要:

By using the pressure field as the basic unknown variable, two three‐dimensional acoustic finite element algorithms computer codes, viz., ACOU3.A and ACOU3.B, have been implemented. Code ACOU3.A is designed for the uniform‐grid space discretization such that the storage of the global pseudostiffness matrix is reduced to a single column vector of “27” elements, applicable to any inhomogeneous media. Likewise code ACOU3.B is designed for the irregular‐grid space descretization and possesses the same feature of a reduced global pseudostiffness matrix of ACOU3.A. By using ACOU3.A, three 30 × 30 × 30 elements models were investigated. including (i) a half‐space, (ii) a half‐space with a 10 × 7 × 5 elements inclusion. and (iii) a half‐space with a 10 × 2 × 5 elements inclusion, where the inclusion has the physical property different from the halfspace. In order to demonstrate the third dimension effects on wave propagation. the above posed three‐dimensional problem to the equivalent axial‐symmetric and two‐dimensional approximation models was reduced. By using a full three‐dimensional algorithm, the amplitude of the reflected waves carries the information of the third dimension thickness of the inclusion, which cannot be obtained by either the axial‐symmetric, or the two‐dimensional approximations.

ISSN:0001-4966    

DOI:10.1121/1.2023705

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The estimated residual error (or its bound) for numerical quadratures is usually expressed in terms of a derivative of some order of the integrand or some residual factor of the integrand after factoring out a countable number of zeros and singularities that occur along the integration path. The order of the derivative is a function of the number of sample points for evaluating the integrand. Regrettably, the magnitudes of these higher‐order derivatives are difficult enough to estimate for even analytic sound velocity profiles. In practice, observed sound velocity profiles, which are usually given in tabular form and include measurement errors, exacerbate our inability to assess the magnitudes of these higher‐order derivatives. An estimate of the residual error expressed in terms of a first derivative would be far more practical for both analytic and observed sound velocity profiles.

ISSN:0001-4966    

DOI:10.1121/1.2023706

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A common complaint among musicians is that they are almost never involved in the preliminary planning stage when a new concert hall is being built. The basic planning which determines the acoustical properties of the finished building is thus left to architects, acousticians, and engineers, who are usually nonmusicians. There are certain criteria which the musicians—who must, after all, live with the hall long after the architects and acousticians have departed—consider basic. There are building materials they prefer for acoustical reasons, and configurations they consider better than others. What are these considerations, and how subjective are they? Do they have any validity when measured against the scientific data of the experts? Is it possible for the scientific community to learn from the experiences of practicing musicians who play in the halls they design—and conversely, would the musicians profit by paying closer attention to the work of scientists and acousticians?

ISSN:0001-4966    

DOI:10.1121/1.2023708

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The radial response of a bubble in a liquid subject to an acoustic field has long been the object of considerable interest [see, for example, W. Lauterborn, J. Acoust. Soc. Am.59, 283–293 (1976); B. E. Noltingk and E. A. Neppiras, Proc. Phys. Soc. London Ser. B63, 674 (1950)]. However, the most often generated graph in these theoretical and numerical studies, the radius‐time (R‐T) curve, has never been experimentally observed until now. The first direct observation of the R‐T response of a single bubble will be presented. The measurements were made on a bubble “levitated” [M. Strasberg, J. Acoust. Soc. Am.33, 359 (1961)] near the antinode of an acoustic stationary wave by digitizing the output of a photodiode monitoring the intensity of laser light scattered by the bubble. Comparisons will be made with the results of some recent numerical models. [Research supported by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2023712

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Enhancement of the cavitational effect of iodine release from sodium iodide solution during repetitive 1‐MHz tone burst excitation of the solution of a rotating test tube has been reported. [V. Ciaravino, H. G. Flynn, and M. W. Miller, Ultrasound Med. Biol.7, 159–166 (1981)]. This enhancement was attributed to concurrent operation of two mechanisms: depletion of small nuclei from the cw mode size distribution generated during a tone burst, and survival from the previous tone burst of small nuclei lying in the same size range that is depleted in the cw mode. Twenty‐four hours after exposing C1300 neuroblatoma cells (N2A) in rotating tubes to 1‐MHz ultrasound tone bursts [1:1, durations from 6 to 600 ms; 3.4 W/cm2spatial peak, burst average intensity, and 5 min total treatment duration (on + off periods)] at 37°C, enhancement of protein synthesis compared to control cells was observed. Protein synthesis was measured by uptake of3H‐leucine. The similarity between results observed for cavitation‐stimulated iodine release and cellular protein synthesis is highly suggestive of cavitation as the cause for this biological effect. [Work supported by PHS.]

ISSN:0001-4966    

DOI:10.1121/1.2023715

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Previously it has been shown [M. J. Hinich and W. Rule, J. Acoust. Soc. Am.58, 1023–1029 (1975); W. S. Hodgkiss, IEEE J. Ocean. Eng.OE‐8, 120–130 (1983)] that deformations of towed arrays from a straight line shape can produce significant distortions in beam patterns and errors in bearing estimation if the beamforming assumes linearity. It has also been shown that a deformed array helps to remove left/right ambiguities in the beam patterns, provided the beamforming is done with the correct array configuration. In this work these two effects are studied for undamped and damped sinusoidally deformed arrays (as observed in practice) of one, two, and three half‐cycles with relatively small array amplitudes. By use of fixed arc length separations along the array, the phone (x, y) coordinates are determined numerically for each sinusoidal shape. The complex pressure fields are modeled for sources at various locations. Then beamforming is carried out (1) with the known array configuration, and (2) assuming that the array is linear. Degradations resulting from assuming linearity and the ability to remove left/right ambiguities are discussed in terms of reduced gain, angular resolution, and bearing errors.

ISSN:0001-4966    

DOI:10.1121/1.2023721

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A transmitting array that is designed to generate specified evanescent pressure fields near the array is described. The pressure fields are convective in nature, moving parallel to the plane of the array with a phase velocity that is slow, i.e., less than the speed of sound in water. A slow phase velocity corresponds to a spatial wavenumberkwhich is greater than the corresponding acoustic wavenumber in water. Such an array can be used to obtain the response of extended acoustic sensors to high‐wavenumber pressure components such as exist in turbulent flow fields. Two small prototype planar arrays have been designed and constructed. The first one utilizes the piezoelectric polymer (PVDF) as its active material while the other one utilizes a Neoprene‐lead titanate composite material. The positive electrodes on both arrays are segmented into independently driven areas by use of equally spaced stripes. Experimental results obtained for the prototype arrays are compared with computer model predictions. [Work partially supported by ONT.]

ISSN:0001-4966    

DOI:10.1121/1.2023727

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

As part of its research and development program for development of renewable energy sources, Southern California Edison has monitored the acoustic emission of several different horizontal and vertical axis wind turbine generators with power generation capacity ranging from 80–500 kW. Noise measurements included: frequency spectrum (infrasonic through audible range), directivity, nearfield and farfield, and short and long duration. This presentation will summarize the results of the tests and measurements of both vertical and horizontal axis wind turbines.

ISSN:0001-4966    

DOI:10.1121/1.2023731

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The profile of neural excitation pattern along the cochlea produced by a longitudinally oriented bipolar electrode pair was estimated by forward masking. Two types of masking patterns were observed. The first was produced by electrode pairs with low (behavorial) threshold currents, and displayed two peaks approximately located above the two electrodes of the bipolar pair. The second was produced by pairs with higher threshold, and displayed a single peak approximately midway between the two electrodes. These masking patterns are similar to the two types of current distribution patterns observed in a tank model consisting of a 22‐banded electrode array fixed into a normal saline filled tube of 5 mm diameter. It is possible that the bipolar pairs with lower threshold and double‐peaked masking patterns are situated closer to the residual auditory fibers and neurons. In another study, the masking patterns for two bipolar electrode pairs interleavely stimulated were found to follow approximately the maximum of the two masking patterns for the two electrode pairs activated in isolation.

ISSN:0001-4966    

DOI:10.1121/1.2023737

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Modeling studies on current distributions along the cochlea produced by an intracochlear electrode array were conducted in a tank model. The tank consisted of a 22‐banded electrode array fixed into a normal saline‐filled tube of 5 mm diameter. Bipolar electrical stimulation was used, and the potentials within the saline were measured to enable the calculation of the current distribution. Current distribution depended on the ratio of the radial distance from the electrode array at which the distribution was measured to the distance between the two electrode bands used for bipolar stimulation. For small ratios, the distribution displayed two peaks directly above the two bands; while for large ratios, the distribution displayed only one peak midway between the two bands. Also investigated was the interaction that occurs when more than one bipolar pair were stimulated simultaneously. The results showed that the resulting distribution also depended on the above defined ratio. These results obtained from the tank model were verified by computer simulation.

ISSN:0001-4966    

DOI:10.1121/1.2023742

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP