Source Of Acoustic Energy Research Articles

Identification of noise sources of forge hammers during production: An application of residual spectrum techniques to transients

Three gravity-drop, four-piece forge hammers are analyzed to determine the principal structural sources of impulsive noise radiation during production forging. A three-input single-output model is used to describe the hammer system, based on “input” signals taken from one column, the anvil and the ram accelerations, and one “output” signal taken from the sound pressure at the operator's position. The frequency response functions between the elemental vibrations and the sound pressure signal are determined from these signals by residual spectrum techniques. For the three hammers studied, the analysis shows that the ram is a major source of acoustic energy radiated to the oeprator's position, while the columns and anvil radiate between 1 and 4 dB less energy. The three-input model is then used to estimate the effect of acoustic shrouds on the sound energy radiation. The results indicate that it may be necessary to treat all the structural elements before significant reductions can be achieved, due mainly to the high degree of interaction between the components. The residual spectrum derived from this model indicates that the three input model may not be totally adequate for all production hammers; it may be necessary to develop higher-input models, with use of data from more transducers located to sense a higher number of contributing vibration modes. However, in this study the three-input model accounted for 73–82% of the sound energy density at the operator's position.

Vortex Shedding as a Source of Acoustic Energy in Segmented Solid Rockets

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Ocean basin reverberation at very low frequencies

At low frequencies (<20 Hz), energy propagates very efficiently in the ocean. Acoustic energy can scatter off basin walls, islands, and sea mounts and propagate to a receiver as reverberation. For underwater explosions, large sources of acoustic energy, ocean basin reverberation can be especially significant. It may, for example, be useful in determining bottom and propagation parameters. Several models for the encounter of the acoustic energy with the basin wall have been suggested. These range from a simple scattering representation to more detailed multiple scattering or multiple reflection models. These models will be discussed, as well as reverberation data from several CHASE shots. Quantities focused on will be the reverberation level versus time and frequency dependence. The contribution of basin reverberation to low-frequency background noise will be discussed. [Work supported by DNA.]

Aerodynamic noise: Acoustic model sources versus acoustic energy sources

There has been considerable controversy surrounding the interpretation of the various theories of aerodynamic noise generation—those of dilatational (monopole) and of momentum flux (quadrupole), to which the vortex theory (dipole) may be added. The central issue has been the fundamental nature of the aerodynamic sound source. It is pointed out that these three theories are all of the nature of “acoustic models”, and their source terms should not be expected to have a simple one-to-one relation to the real physical sources, by which one is presumed to mean the action in those regions of the real flow in which kinetic flow energy is “transduced” to acoustic energy. One of the situations illustrated is that of the different acoustic models for aeolian tones, In which none of the three very different representations has a simple translation to the real flow. For example, the argument that fixed surfaces cannot be the origin of dipole sound relates to the real flow, but not to the acoustic model where the boundary conditions are different.

Some considerations in choosing an explosive source and processing filter for the measurement of transmission loss

Explosives are often used as a source of acoustic energy in transmission measurements in the ocean because of the broad-band spectra of underwater explosions and the wide range of levels that can be generated. At the same time, this broad-band spectrum can complicate a transmission loss measurement because the spectral character of the shock wave and subsequent bubble pulses of the shot can be very similar to the spectral character of the loss which is due to the multipath structure of the propagation. This complication can be avoided by the proper choice of the detonation depth and the charge weight. When these choices have been made, the properties of the analyzing filter of the data processing system must then be selected; this must be done with regard for the nature of that portion of the multipath structure to be resolved as well as the nature of the charge spectrum. This paper discusses the principles involved in making these choices and gives illustrations of both short- and long-range measurements.

The Principles Involved in Choosing an Explosive Source and Processing Filter for the Measurement of Transmission LOSS

Explosives are often used as a source of acoustic energy in transmission measurements in the ocean because of the broad-band spectra of underwater explosions and the wide range of levels that can be generated. At the same time, this broad-band spectrum can complicate a transmission loss measurement because the spectral character of the shock wave and subsequent bubble pulses of the shot can be very similar to the spectral character of the loss that is due to the multipath structure of the propagation. This complication can be avoided by the proper choice of the detonation depth and the charge weight. When these choices have been made, the properties of the analyzing filter of the data processing system must then be selected; this must be done with regard for the nature of that portion of the multipath structure to be resolved as well as the nature of the charge spectrum. This paper discusses the principles involved in making these choices and gives illustrations of both short- and long-range measurements.

Refraction Shooting with Expendable Sonobuoys: GEOLOGICAL NOTES

The use of expendable radio sonobuoys and a nonexplosive (air gun) sound source for shallow water refraction studies has shown that the sonobuoys can produce excellent refraction and wide-angle reflection data, and that measurements can be made during normal reflection profiling operations utilizing the same source of acoustic energy. The data are recorded in a manner that permits immediate analysis, thus better enabling the investigator to guide and evaluate a survey while it is in progress.