摘要 :
This study explores the physical interpretations of the instantaneous intensity, active intensity, and reactive intensity vectors in terms of energy transfer and wave properties in the nearfield of a general monochromatic sound fi...
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This study explores the physical interpretations of the instantaneous intensity, active intensity, and reactive intensity vectors in terms of energy transfer and wave properties in the nearfield of a general monochromatic sound field. The time dependent energy transfer is described by the instantaneous intensity, which contains contributions by the active intensity and the reactive intensity. The time independent intensity vectors are directly related to wave from properties. The active intensity vector is shown to be perpendicular to the resultant wave fronts and the reactive intensity is shown to point in the direction of decreasing pressure amplitude. Time dependent instantaneous intensity flux lines are drawn to show that in general the energy does not propagate with the resultant wave fronts. The speed of wave front propagation and the complex specific acoustic impedance are calculated from the nearfield measurements fo the time independent intensity vectors and energy densities. Five measured examples are presented which show that the location of energy sources, resonators, diffraction, and interference effects are clearly determined from analyses of the active intensity, reactive intensity, and potential energy, kinetic energy, phase speed, and complex specific acoustic impedance. Keywords: Acoustic intensity; Acoustic variables measurement; Acoustic waves; Acoustic wave effects; Acoustic wave intensity; Acoustic wave velocity; Nearfield acoustics. (JHD)
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The transmission of impulsive acoustic signals into a homogeneous soil medium was investigated. Measurements performed using a piezoelectric driver and a hydrophone as the acoustic sources demonstrate that both types of transmitte...
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The transmission of impulsive acoustic signals into a homogeneous soil medium was investigated. Measurements performed using a piezoelectric driver and a hydrophone as the acoustic sources demonstrate that both types of transmitters (positioned at the air soil interface) are capable of producing acoustic waves in soil. The relative strength of the acoustic signals produced by each source was found to be approximately equal. The angular distribution of acoustic energy transmitted into the soil was found to be omnidirectional. Accelerometers buried within a 1.2 m deep soil box were used to measure the attenuation of acoustic signals as a function of frequency. The attenuation was observed to increase with increasing frequency from a value of approximately 8 dB/ft at 1 kHz to 35 dB/ft at 8 kHz. Measurements of the wave motion at the air soil interface induced by a surface mounted transmitter show that large amplitude surface waves are produced by both types of transmitters. The amplitudes of the observed surface waves were large in comparison to the estimated amplitude of signals produced by subsurface scattering of acoustic waves. A longitudinal wave receiver designed to reduce the amplitude of surface waves in favor of acoustic waves scattered from subsurface targets was successfully tested.
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The purpose of the Resonance Meeting was to cover a broad range of uses of acoustic resonances to determine physical properties of matter. The meeting grew out of prior meetings in 1994 and 1995 that were devoted entirely to Reson...
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The purpose of the Resonance Meeting was to cover a broad range of uses of acoustic resonances to determine physical properties of matter. The meeting grew out of prior meetings in 1994 and 1995 that were devoted entirely to Resonant Ultrasound Spectroscopy (RUS). The international list of participants included cutting edge users of RUS and other resonance techniques, as well as researchers and graduate students who wanted to learn about and use these techniques. Universities from the United States and Japan, national laboratories and private research organizations were represented. The Resonance Meeting proved to stimulate extended discussions outside the scheduled sessions. The proceedings of the Resonance Meeting consist of two volumes. Volume 1 contains a verbatim transcript of each presentation. Volume 2 contains accompanying transparencies for each transcript. Anyone interested in obtaining more information on a particular presentation may contact the author(s). Volume 1 contains a complete list of participants and addresses.
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An invited paper co-authored with Jack Sheehan entitled 'Ocean Acoustic Field Matching: Normal Mode Filtering and Non-Gaussian Sources,' was published in the July 1993 issue of the IEEE Journal of Oceanic Engineering. This paper p...
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An invited paper co-authored with Jack Sheehan entitled 'Ocean Acoustic Field Matching: Normal Mode Filtering and Non-Gaussian Sources,' was published in the July 1993 issue of the IEEE Journal of Oceanic Engineering. This paper provides a theoretical foundation for the experimental findings that the acoustic field radiated from a large submerged object is a non-Gaussian random process. We develop a link between normal mode filtering and statistical field matching which is new and potentially important for underwater sound analysis. The results can be applied to other forms of acoustic radiation.
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This project has involved a broad investigation of the propagation characteristics of acoustic waves in inhomogeneous anisotropic media, with special emphasis on focusing and beam steering and an evaluation of potential device app...
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This project has involved a broad investigation of the propagation characteristics of acoustic waves in inhomogeneous anisotropic media, with special emphasis on focusing and beam steering and an evaluation of potential device applications of the phenomena. Attention was directed particularly at the possibilities for realizing electronically-controlled focusing and scanning of acoustic beams, functions of interest in applications such as acoustic spectrometry and acoustic imaging.
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The long-term goals are: 1) to take advantage of the ever-changing ocean environment's effects in order to provide a more complete understanding of long-range acoustic pulse propagation, 2) understanding the extent of fundamental ...
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The long-term goals are: 1) to take advantage of the ever-changing ocean environment's effects in order to provide a more complete understanding of long-range acoustic pulse propagation, 2) understanding the extent of fundamental limitations on ray-based acoustic tomography; of particular interest is the breakdown range of semiclassical methods, and 3) to address important basic physics issues that arise in the ocean problem, but within a more general context.
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摘要 :
This study explores the physical interpretations of the instantaneous intensity, active intensity, and reactive intensity vectors in terms of energy transfer and wave properties in the nearfield of a general monochromatic sound fi...
展开
This study explores the physical interpretations of the instantaneous intensity, active intensity, and reactive intensity vectors in terms of energy transfer and wave properties in the nearfield of a general monochromatic sound field. The time dependent energy transfer is described by the instantaneous intensity, which contains contributions by the active intensity and the reactive intensity. The time independent intensity vectors are directly related to wave from properties. The active intensity vector is shown to be perpendicular to the resultant wave fronts and the reactive intensity is shown to point in the direction of decreasing pressure amplitude. Time dependent instantaneous intensity flux lines are drawn to show that in general the energy does not propagate with the resultant wave fronts. The speed of wave front propagation and the complex specific acoustic impedance are calculated from the nearfield measurements fo the time independent intensity vectors and energy densities. Five measured examples are presented which show that the location of energy sources, resonators, diffraction, and interference effects are clearly determined from analyses of the active intensity, reactive intensity, and potential energy, kinetic energy, phase speed, and complex specific acoustic impedance. Keywords: Acoustic intensity; Acoustic variables measurement; Acoustic waves; Acoustic wave effects; Acoustic wave intensity; Acoustic wave velocity; Nearfield acoustics. (JHD)
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