NASA Scientific and Technical Aerospace Reports

International Acoustics Experiment (ASIAEX). From 2 to 5 June, operations from the Melville were coordinated with those
of the Chinese research vessels Shi Yan 2 and Shi Yan 3 in order to conduct studies in wide-band propagation and reverberation
using explosive charges deployed from both Chinese vessels. The ASIAEX ECS 2001 experiment produced a remarkable set
of measurements on acoustic propagation and scattering in an Asian littoral sea, along with environmental measurements
required for its interpretation.
DTIC
China; Seas; Sound Waves; Wave Propagation
20040073714 Duke Univ., Durham, NC
Passive Differential Matched-Field Depth Estimation of Moving Acoustic Sources
Kraut, Shawn; Krolik, Jeffrey; Mar. 14, 2001; 18 pp.; In English; Original contains color illustrations
Report No.(s): AD-A422624; No Copyright; Avail: CASI; A03, Hardcopy
Workshop presentation of passive differential matched-field depth estimation of moving acoustic sources. The objective
of Passive Moving Target Depth Estimation (MTDE) is to discriminate submerged versus surface targets by exploiting
changes in the spatial wavefront at the array due to multipath propagation from a moving source.
DTIC
Depth; Depth Measurement; Sound Generators
20040073743 Naval Research Lab., Stennis Space Center, MS
Dynamic Ambient Noise Model (DANM) Evaluation Using Port Everglades Data
Pflug, Lisa A.; Thompson, Charles; Hall, Tracy; Apr. 5, 2004; 41 pp.; In English; Original contains color illustrations
Contract(s)/Grant(s): Proj-71-7076-A3
Report No.(s): AD-A422664; NRL/FR/7185--04-10064; No Copyright; Avail: CASI; A03, Hardcopy
Measured omnidirectional noise at a shallow water site near Port Everglades and radar tracks for local ships were used
to evaluate a new ambient noise model, the Dynamic Ambient Noise Model (DANM), developed for use on board Navy
systems. For four consecutive days of data, the daily means of the modeled noise levels were higher than the data. The most
likely cause of mismatch was two factors associated with the ship sources. The first was the relative assignments of ship
classes to the radar track vessels for input to the model. The vessels were assigned classes by speed with no means to
discriminate between large vessels traveling at low speeds and recreational vessels that do not contribute significantly to the
noise field. The second factor was the source level model within DANM, which is implemented with no speed dependence.
A dependence was introduced into the model through the ships class assignments, but would be more properly implemented
within the model itself, and may be necessary for accurate predictions near a port. The lack of speed-dependent source levels
and the source level curves themselves may be the causes of the frequency dependence seen in the model/measurement
mismatch. Model predictions with all radar vessels assigned to the minimum source level resulted in lower but better model/
measurement agreement. This spread of about 10 dB in daily means with different source level assignments confirms that
source level assignments for dynamic shipping are critical to accurate model predictions. There was frequency dependence to
the mismatch, with the model matching better at higher frequencies. Shear propagation is unaccounted for in the propagation
models used by DANM and is a likely source of error for this environment at the lower frequencies.
DTIC
Ambience; Dynamic Models; Everglades (Fl); Noise (Sound); Ships
20040074216 NASA Langley Research Center, Hampton, VA, USA
Aeroacoustic Analysis of a Simplified Landing Gear
Lockard, David P.; Khorrami, Mehdi, R.; Li, Fei; [2004]; 12 pp.; In English; 10th AIAA/CEAS Aeroacoustics Conference,
10-13 May 2004, Manchester, UK
Contract(s)/Grant(s): 23-781-10-10
Report No.(s): AIAA Paper 2004-2887; No Copyright; Avail: CASI; A03, Hardcopy
A hybrid approach is used to investigate the noise generated by a simplified landing gear without small scale parts such
as hydraulic lines and fasteners. The Ffowcs Williams and Hawkings equation is used to predict the noise at far-field observer
locations from flow data provided by an unsteady computational fluid dynamics calculation. A simulation with 13 million grid
points has been completed, and comparisons are made between calculations with different turbulence models. Results indicate
that the turbulence model has a profound effect on the levels and character of the unsteadiness. Flow data on solid surfaces
and a set of permeable surfaces surrounding the gear have been collected. Noise predictions using the porous surfaces appear
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