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Mcaninch, Gerry L.

Publications and source records attributed to Mcaninch, Gerry L..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

On The Determination of Shadow Boundaries and Relevant Eigenrays For Sound Propagation In Stratified Moving Media

The eiconal and ray equations for a stratified moving medium are analyzed to determine which rays connect a source located at an altitude z = z(sub s) to an observer on the ground plane. The characteristics of all available rays are ascertained. Further, the rays which determine the shadow boundary are found. Thus, the shadow boundary may be easily calculated and any observers for which an eigenray does not exist eliminated from further consideration. Therefore, the analysis may be applied to save computer time in two ways. First, rays that do not reach the ground may be eliminated before they are traced, and observers for which no eigenray exists may be eliminated from consideration.

Mcaninch, Gerry L.↗
NASA NTRS1992

The Pekeris problem, and the interior of the pulsating sphere, first success of exact ray theory, and what rays?

This paper presents what is probably the first application of exact ray theory to provide nontrivial exact solutions of the Helmholtz equation. First, the Pekeris problem is considered. This is followed by consideration of the problem of the field maintained within a uniformly pulsating sphere. In the Pekeris problem, an iterative solution provides the exact solution on the second iteration. In the second problem, it is shown that the exact ray theory eliminates the focus of the geometric theory.

Mcaninch, Gerry L.↗
NASA NTRS1992

Atmospheric effects on sonic boom: A program review

The program goals were determined after consideration of the weaknesses in our understanding of atmospheric effects on sonic boom waveforms left in the wake of the cancellation of the U.S. SST in the 70's and the advancements in acoustics and atmospheric science since that time. For example, a considerable body of knowledge on molecular absorption has built up in the acoustics community over the last 15 years and this has not been incorporated into the sonic boom theory. Further, it was felt that the understanding of atmospheric turbulence had also advanced considerably during that time period. Therefore, key elements of the current program are the development of an improved atmospheric absorption model and an improved atmospheric turbulence model. The advances made in computer power over the last 15 years were also considered, and will be utilized to remove restrictions on the analytical model for turbulence effects on sonic boom waveforms. Although the majority of disturbing sonic booms will not occur at focuses or caustics, it was felt that this was an area that required further understanding, thus it will be looked into. Finally, in order to insure that the current effort, which is basically analytical in nature, retains a firm grasp on reality, a data base of sonic boom waveforms and associated weather data is being compiled, and a set of scale model experiments is being planned to guide the overall efforts.

Mcaninch, Gerry L.↗
NASA NTRS1987

Evaluation of a scale-model experiment to investigate long-range acoustic propagation

Tests were conducted to evaluate the feasibility of using a scale-model experiment situated in an anechoic facility to investigate long-range sound propagation over ground terrain. For a nominal scale factor of 100:1, attenuations along a linear array of six microphones colinear with a continuous-wave type of sound source were measured over a wavelength range from 10 to 160 for a nominal test frequency of 10 kHz. Most tests were made for a hard model surface (plywood), but limited tests were also made for a soft model surface (plywood with felt). For grazing-incidence propagation over the hard surface, measured and predicted attenuation trends were consistent for microphone locations out to between 40 and 80 wavelengths. Beyond 80 wavelengths, significant variability was observed that was caused by disturbances in the propagation medium. Also, there was evidence of extraneous propagation-path contributions to data irregularities at more remote microphones. Sensitivity studies for the hard-surface and microphone indicated a 2.5 dB change in the relative excess attenuation for a systematic error in source and microphone elevations on the order of 1 mm. For the soft-surface model, no comparable sensitivity was found.

Parrott, Tony L.↗
NASA NTRS1987

Effects of velocity profile on boundary-layer shielding

A simple uniform flow boundary-layer model is used to study the effects on the acoustic field at the aircraft fuselage of placing Large Eddy Break Up devices in the boundary layer. The introduction of velocity defects into the boundary layer is shown to enhance boundary-layer shielding. Furthermore, shielding improvements are found to occur by moving the velocity defect further from the wall, by increasing its extent within the boundary layer, and by decreasing the minimum velocity in the defect.

Mcaninch, Gerry L.↗