摘要:

A combined analytical and experimental study is presented to demonstrate that the four‐pole parameters of a truncated, thin conical shell, under axial excitations, may be accurately obtained by applying membrane shell theory. A general calculation procedure is described, and the numerical results are applied to determine the mechanical impedances of shell‐mass systems, and then compared with test data for three shell models with semivertex angles 0°, 15°, and 30° over a frequency range from 20 to 600 cps. The exce lent agreement indicates that the four‐pole parameters calculated through the present analysis are adequate for vibration analyses, if the input excitation frequency is appreciably lower than a theoretical singularity, on the frequency spectrum inherent to the membrane shell theory. If the excitation frequency is near or above this singularity, a more accurate bending shell theory must be used.

ISSN:0001-4966    

DOI:10.1121/1.1910881

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

In an earlier paper dealing with dispersion of waves in composite rods, it was noted that the dispersive properties of one rod were quite different from those of another with different properties. This observation prompted the speculation that the dispersive properties of a composite rod could be controlled through a choice of the geometric and material parameters of the rod. In this paper, we show how the dispersive properties can be controlled; that is, we show the influence of each of the parameters on the dispersive characteristics of a rod. Our previous study had led us to suppose that if we were sufficiently adroit, we could choose the rod parameters so that the resulting composite rod would be nondispersive. Our study here shows that this is impossible and that a rod will always be dispersive, at least if it has a traction‐free surface. We show that, with a very restricted, theoretical exception, the least dispersive composite rod is the degenerate one: the one‐material rod.

ISSN:0001-4966    

DOI:10.1121/1.1910882

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Transient analysis of the propagation of waves due to an electric‐potential pulse concentrated at a point on the boundary of a piezoelectric plate of crystal class 6mmis carried out. Normal stress is analyzed for an exponential pulse and a step pulse. Numerical results are obtained for a cadmium selenide crystal.

ISSN:0001-4966    

DOI:10.1121/1.1910883

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The sound radiated by the sudden release of a uniformly condensed sphere of fluid surrounded by an extended uncondensed fluid of different acoustical properties has a characteristic sawtooth pattern, a consequence of repeated reflections inside the sphere. The form of the pattern depends on the relative densities and speeds of sound in the two media.

ISSN:0001-4966    

DOI:10.1121/1.1910884

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

One limit to the precision of finding the direction of an underwater sound source with an electrically steered array is the phase error in each hydrophone output signal. A theoretical relation between the standard deviation of hydrophone phase error and the standard deviation of array direction‐finding error is derived in this paper. Supporting experimental evidence is presented from measurements on two multielement, scanning‐sonar‐type, circular arrays.

ISSN:0001-4966    

DOI:10.1121/1.1910885

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The wave theory of an underwater, spherical Luneberg lens is discussed in terms of a generalized wave equation, which differs from the ordinary wave equation in that it contains a term involving the gradient of the density of the lens. The special case where the density of the lens has a constant value (to a first approximation) is studied in detail. This case is of some importance since it corresponds to the compliant‐tubing lens built and tested by W. J. Toulis [J. Acoust. Soc. Am.35, 286–292 (1963)]. For this case, we determine the analytic solution of the wave equation when the lens is being irradiated by plane waves and then present the results of a numerical evaluation of that solution. In particular, we calculate the acoustic pressure field along the axis of the lens and the pressure receiving patterns. These results give us the gain and beamwidths for the range 1⩽k0a⩽30 (k0being the wavenumber in water,athe radius of the lens). Finally, the theory is compared with Toulis's experimental results, and the agreement is found to be quite good.

ISSN:0001-4966    

DOI:10.1121/1.1910886

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An experimental study has been made of the variability of acoustic transmission in the ocean at frequencies around 270 cps between a fixed bottomed source and fixed bottomed receivers. Transmitted signal level was observed at two distances: 2 and 700 NM (nautical miles), over periods ranging from 1 to 22 h. Simultaneous measurements were made at several hydrophones at each location to investigate correlation of fluctuations at various pair spacings. Two types of variation were noted. At the 2‐mile range, quasiperiodic variations in level occurred with a predominant frequency of 0.12 cps, similar to that of surface waves. These are believed to be due to multipath interference of signals reflected one or more times from the moving surface. At the 700‐NM range, such variations were also observed; in addition, large slower fluctuations were observed, with periods of a few minutes to several hours. These are believed to be due to changing multipath interferences among signals passing through moving or changing water masses of different refractive indices (e.g., internal waves). Cross‐correlation coefficients of either type of fluctuation were small: 0.1–0.2 at pairs of hydrophones with spacings of 25–1815 ft.

ISSN:0001-4966    

DOI:10.1121/1.1910887

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The vertical coherence of underwater sound in a convergence zone has been investigated by means of a vertical receiving array of six hydrophones spaced212 ftapart and hung at a depth of 3800 ft from a surface ship. A second ship towed a 1120‐Hz CW source outward in range from 28 to 43 miles. The outputs of the different hydrophones, when correlated together, yield correlation coefficients equal to nearly unity when in the convergence half‐zones at 30 and 38 miles, and show only a slow falloff with increasing separation. In between zones, where bottom‐reflected paths occur, the correlation coefficient was much smaller and was found to fall off faster with increasing separation. It may therefore be concluded that a vertical array located in the convergence zone of a distant source will experience a higher signal‐to‐noise ratio as a result of two effects: an increased signal level due to convergence, amounting to 10 dB in one experiment, and an increased array gain due to the greater coherence of the received sound.

ISSN:0001-4966    

DOI:10.1121/1.1910888

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A technique for rating floors for impact‐sound insulation by subjective comparisons of the sounds of transmitted footsteps is described. The subjective judgments were used as a criterion for checking objective ratings obtained with the standard ISO impact machine. A previous study was done in the laboratory on variations of a reinforced concrete‐slab floor. Further observations have now been made in typical buildings, with special attention to wood‐joist floors. For the whole study, the correlation between subjective and machine ratings is limited in range if the usual shape of reference contour, adopted for example by the U.S. Federal Housing Administration, is used. This contour makes the results, especially for hard‐surfaced concrete floors, dependent on high‐frequency noise that is characteristic of the machine rather than of actual footsteps. A better correlation is obtained by changing from the present FHA reference contour to one that reduces the emphasis on high frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1910889

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The paper describes the acoustical design and testing of a 3250‐seat multipurpose auditorium. Among the problems discussed here is the question of what reverberation time is optimal for a hall that uses a sound‐reinforcement system to augment the direct sound. The design and performance of a sound‐reinforcement system for the hall is also described. The hall has a volume of about 800 000 ft3and a midfrequency RT of 2.3 sec when empty and 1.7 sec when full. The bass ratio is approximately 1.3. The maximum variation of the sound level over the seating area is 4.5 dB. The noise level (onCweighting) in the fully occupied hall is 42±1 dB without air conditioning and 52±1 dB with air conditioning.

ISSN:0001-4966    

DOI:10.1121/1.1910890

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP