摘要:

An experimental investigation has been carried out on the production of high‐intensity tones by axisymmetric ring cavities. Maximum sound production occurs during an acoustic resonance at Strouhal numbers, which depend only on the local flow velocity independent of cavity location. Values of sound pressure of about 115 dB at 1‐m distance can be generated by axisymmetric ring cavities on projectiles moving at a relatively low flight speed equal to 70 m/s. Frequencies in the audible range up to several kilohertz can be generated aeroacoustically. A simple analytical model has been developed to explain the experimental observations.

ISSN:0001-4966    

DOI:10.1121/1.395652

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Light diffraction and finite amplitude loss are used to measure the acoustic nonlinearity parameter for water, methanol, liquid nitrogen, and liquid helium‐II. In all cases, the finite amplitude loss technique yielded higher values than the light diffraction technique or thermodynamic estimates from published data.

ISSN:0001-4966    

DOI:10.1121/1.395653

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

An imploding cavity in a fluid‐filled borehole is potentially attractive as a powerful source of acoustic energy for borehole seismic experiments. It is reasonable to model the fluid pressure response due to the implosion as purely one‐dimensional. A simple analysis based on the assumption that the fluid behaves elastically, with a linear pressure/strain relation, predicts that the fluid pressure response becomes negative at depths less than that of the source. This is an untenable prediction since a fluid cavitates under negative pressure. It is more realistic to assume that the fluid behaves in a linear elastic fashion for negative strains (and positive pressures), and that the fluid pressure is zero for positive strains. This leads to a nonlinear, free‐boundary problem in acoustic wave propagation, which surprisingly has a closed‐form analytical solution. The analysis predicts the existence of several unexpected phenomena which could complicate the interpretation of data taken in borehole seismic experiments utilizing this type of source.

ISSN:0001-4966    

DOI:10.1121/1.395654

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Detailed calculations are made of the transmit–receive mode echo responses arising from solid targets of various size interrogated by short pulses of ultrasound propagating in a fluid medium. The theoretically predicted results are in good agreement with experimentally measured results obtained using transducers typical of those used in nondestructive evaluation. The effects of target size, field position, and material on both the amplitude and shape of the echo responses are investigated. The structure of the responses is explained in terms of the plane and edge waves radiated by the source. Implications for the use of ultrasonic pulse‐echo techniques to characterize real defects are considered.

ISSN:0001-4966    

DOI:10.1121/1.395655

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

An exact solution is given for the reflection of a plane wave normally incident on a rigid solid with periodically spaced semi‐infinite circular holes. Analytical considerations, verified by numerical calculations, show that the reflection coefficient is unity at the cutoff frequencies defined by the periodicity of the holes. This result is independent of the volume fraction of the holes. It implies that the porous solid acts like a rigid solid at these frequencies. The problem of plane‐wave incidence from the holes is also solved. A reflection coefficient of unity is obtained at the same frequencies, again implying a rigid effect. Below the first cutoff frequency, the reflection coefficient can be parametrized by a simple scalar frequency dependent quantity. This simple result can be interpreted in terms of a displaced pressure continuity condition.

ISSN:0001-4966    

DOI:10.1121/1.395656

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The sound field from a point source above an infinite plane with an impedance discontinuity is studied by considering the Helmholtz equation. With boundary conditions the Helmholtz equation is transformed into a singular integral equation and an exact solution formula is given. The formula is evaluated for the case when the source and the receiver are close to the boundary, many wavelengths from the discontinuity. The evaluation gives, among other things, information on the dependence of the surface wave structure on the impedances and—in the case of no surface waves—information on the farfield solution. If one of the impedances gives a surface wave in the case of a homogeneous boundary, then a surface wave appears also in the nonhomogeneous case and is modified depending on the other impedance. In the case of no surface waves, the rapid decay of the sound field in the homogeneous case does not appear in the nonhomogeneous case since the discontinuity acts as a weak source of slowly decaying waves. A number of experiments are suggested by the results. A new treatment of the special case of a homogeneous boundary is also given, with a new asymptotical expansion of the solution.

ISSN:0001-4966    

DOI:10.1121/1.395657

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A simplified model is developed for describing the free and forced oscillations of the quadrupole mode of a liquid drop freely suspended in a liquid host. The decay rate of the free oscillations and the phase‐frequency relation for the forced oscillations are derived and compared with previous theories. A parameter, interfacial viscosity, is included as an example to demonstrate the versatility of this simplified model. The application of this model in determining the interfacial tension between two liquids is discussed. The experimental technique and some results for different liquids are briefly reviewed.

ISSN:0001-4966    

DOI:10.1121/1.395658

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The monaural speech‐reception threshold of sentences in noise, here defined as the 50% correct‐syllables threshold, was measured for a female speaker with and without speechreading via a video monitor. The additional visual information resulted in a 4.6‐dB lower threshold for a group of 12 young subjects and in a 4.0‐dB lower threshold for a group of 18 elderly subjects compared to auditory presentation alone.

ISSN:0001-4966    

DOI:10.1121/1.395659

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Spontaneous otoacoustic emissions are recorded from frog ears at various body temperatures. Frequency spectra and amplitude distributions of emissions are determined. Both power and frequency of emission signals show a strong temperature dependence.

ISSN:0001-4966    

DOI:10.1121/1.395660

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.395849

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP